Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Limited information is available on the apple preferences of the South African consumer market, which is characterised by diverse consumers from different age and ethnic groups with different food preferences. White, coloured and black consumers from different age groups were selected from the Stellenbosch area, Western Cape, South Africa. Consumer preference analysis for apple eating quality and appearance, and descriptive sensory analysis (DSA) were performed on nine commercial apple cultivars. Analysis of variance (ANOVA) conducted on mean preference scores for each age and ethnic group showed that preference generally differed between these groups. However, Ward’s statistical clustering that was applied to the same data set showed that the sociodemographic composition of consumer groups with similar apple preferences is not homogenous. Three consumer clusters were identified with similar preferences for apple eating quality (E1-3) and appearance (A1-3): E1 liked firmness and therefore tolerated sour taste and disliked mealiness. Although E1 liked sweet fruit, they indicated lower preference for sweet fruit compared to E2 and E3. E2 liked sour taste and apple flavour more compared to the other clusters while E3 disliked sour taste and had the highest preference for sweetness. Although coloured and black consumers generally disliked sour taste and E3 constituted a larger proportion of these consumers, the coloured and black consumers who liked or tolerated sour taste constituted approximately 41% of the total consumer population in the Western Cape. White and younger (<26 years) consumers were mostly in cluster E1 liking firm fruit. Peel colour preferred by the appearance preference clusters were: Green and pink bi-colour (A1), green/yellow and red-striped (A2); and red peel colour (A3). Consumers preferred the appearance of cultivars that associated with the eating quality attributes that they liked. When consumers’ preference for the eating quality of five cultivars were analysed during presentation with different levels of visual pictorial information (no, correct and incorrect photograph), mismatches between expected and actual eating quality preference resulted in lower preference scores. Apple breeding is time-consuming and expensive. Comprehensive knowledge of fruit quality parameters that drive consumer preference is required to streamline the breeding process. Eating quality and appearance attributes of four apple breeding families were subjected to instrumental and individual assessment by a trained assessor and DSA by a trained panel. Instrumental measurements could not predict the sensory attributes analysed by the individual assessor. Sensory textural attributes, apple flavour and sweet taste as quantified by DSA and instrumental measurement of titratable acidity (TA) and total soluble solids (TSS)/TA, but not TSS, could predict consumer preference. The assessor responsible for individual assessment could not predict the preference of the total consumer group. A quantitative genetic analysis of the data was carried out to quantify within- and between-family variation using ANOVA, variance components and heritability estimates. Variation between families was shown for attributes relating to colour and acidity, but not for sweet taste, TSS and apple flavour. Strong genetic control that was generally shown for colour attributes predicts a rapid selection response. Most attributes were inherited quantitatively, but TA showed complicated inheritance mechanisms. / AFRIKAANSE OPSOMMING: Min inligting is beskikbaar oor die appelvoorkeure van die diverse Suid-Afrikaanse verbruikersmark wat bestaan uit verbruikers van verskillende ouderdomme en etnisiteite met verskillende voedselvoorkeure. Wit, bruin en swart verbruikers van verskillende ouderdomsgroepe is geselekteer in Stellenbosch in die Wes-Kaap, Suid-Afrika. Verbruikersvoorkeuranalise vir die eetkwaliteit en voorkoms van appels en beskrywende sensoriese analise (BSA) is uitgevoer op nege kommersiële appelkultivars. Analise van variansie (ANOVA), uitgevoer op gemiddelde voorkeurdata per ouderdom en etniese groep, het getoon dat die voorkeure van hierdie verskillende groepe oor die algemeen verskil het. Volgens Ward statistiese groepering op dieselfde datastel was die sosiodemografiese samestelling van verbruikersgroepe met soortgelyke voorkeure egter nie homogeen nie. Drie verbruikersgroepe is geïdentifiseer met soortgelyke voorkeure vir appel eetkwaliteit (E1-3) en voorkoms (V1-3). E1 het ‘n voorkeur vir fermheid, ‘n afkeur vir melerigheid en verdra suurheid. Alhoewel E1 van soet vrugte gehou het, het hulle ‘n laer voorkeur vir soetheid as E2 en E3. E2 het ‘n voorkeur vir suurheid en appelgeur terwyl E3 ‘n afkeur vir suur smaak en die hoogste voorkeur vir soetheid getoon het. Alhoewel swart en bruin verbruikers meestal ‘n renons in suur smaak getoon het en meer van hierdie verbruikers tot E3 behoort, maak swart en bruin verbruikers wat suur smaak aanvaar ongeveer 41% van die totale verbruikersgroep in die Wes-Kaap uit. Wit en jonger (<26 jaar) verbruikers was meestal in E1 en het ‘n voorkeur vir fermheid getoon. Vrugkleurvoorkeure was vir groen en pienk (tweekleurig) (V1), groen/geel en rooi gestreep (V2) en rooi (V3). Verbruikers het ‘n voorkeur gehad vir die voorkoms van kultivars waarvan hulle die eetkwaliteit verkies het. Die effek van gevestigde kleur en smaak assosiasies is getoets deur verbruikers te versoek om die eetkwaliteit van vyf kultivars te evalueer tydens aanbieding daarvan met drie vlakke van visuele inligting, naamlik geen, korrekte en verkeerde foto. Verwarring tussen verwagte en werklike eetkwaliteit het gelei tot ‘n laer voorkeur. Teling van appels is tydrowend en duur. Uitgebreide kennis van die vrugkwaliteit parameters wat verbruikersvoorkeur dryf, is noodsaaklik vir effektiewe teling. Eienskappe wat verband hou met die eetkwaliteit en voorkoms van saailinge is in vier appelfamilies geanaliseer. Die eienskappe is geassesseer deur middel van instrumentele en individuele evaluasie deur ‘n opgeleide assessor asook deur BSA deur ‘n opgeleide paneel. Instrumentele analise kon nie die vlakke van sensoriese eienskappe voorspel soos waargeneem deur die individuele assessor nie. BSA van sensoriese tekstuureienskappe, appelgeur en soetheid, en instrumentele meting van titreerbare suur (TS) en totale oplosbare vastestowwe (TOV)/TS, maar nie TOV nie, kon verbruikersvoorkeur voorspel. Die assessor wat individuele evaluasies uitgevoer het, kon nie die voorkeur van ‘n groot verbruikersgroep akkuraat voorspel nie. Kwantitatiewe genetiese analise van die data is uitgevoer en binne- en tussen-familie variasie is gekwantifiseer deur middel van ANOVA, variansie komponente en oorerflikheidsskattings. Variasie tussen families is gevind vir kleureienskappe en suurheid, maar nie vir soet smaak, TOV en appelgeur nie. Resultate het getoon dat kleureienskappe meestal aan sterk genetiese beheer onderworpe is en dit dui op vinnige vordering met seleksie vir vrugkleur. Vrugeienskappe is meestal kwantitatief oorgeërf. Oorerwing van TS blyk ingewikkeld te wees.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Modified atmosphere packaging (MAP) is a dynamic process of altering gaseous composition inside a package. It relies on the interaction between the respiration rate (RR) of the produce, and the transfer of gases through the packaging material. These two processes are dependent on numerous factors such as storage temperature, film thickness and surface area, produce weight as well as free headspace within the pack. Therefore, in order to achieve the desired modified atmosphere in a given package, it is important to understand the three basic disciplines of MAP, namely produce physiology, polymer engineering, and converting technology. In this study the effects of storage conditions and duration on physiological responses i.e. respiration (RR) and transpiration rate (TR) of two pomegranate cultivars ‘Acco’ and ‘Herskawitz’, were investigated and mathematical models were developed to predict these physiological responses at given time and storage conditions. The result of this study showed that RR of whole pomegranate fruit was significantly higher than that of fresh arils, and that temperature had a significant impact on the RR of both whole fruit and fresh arils. The influence of time, and the interaction between temperature and time also had significant influences on RR of fresh pomegranate arils. These findings highlight the significance of maintaining optimal cold-storage condition for packaged arils or whole fruit along the supply chain. In addition, mathematical models based on the Arrhenius-type equation and the power function equation coupled with Arrhenius-type equation accurately predicted the effect of temperature and the influence of time and temperature on the RR of fresh pomegranate arils for both cultivars. Furthermore, the results of experimental and model prediction studies showed that both relative humidity (RH) and storage temperature had significant effects on TR. RH was the variable with the greatest influence on TR, and it was observed that arils were best kept at 5°C and 96% RH to maintain quality for 8 days. The applicability of the transpiration model developed was validated based on prediction of TR of pomegranate arils under different combinations of storage conditions. The model adequately predicted TR and provides a useful tool towards understanding the rate of water loss in fresh pomegranate arils as affected by storage conditions and duration. The effect of passive-MAP engineering design parameters as a function of produce weight contained, storage temperature and duration on fresh pomegranate arils was investigated. The result showed that produce weight of aril content, temperature and the interaction between temperature and time had slight but insignificant effects on measured physicochemical quality attributes. However, headspace gas concentration was significantly influenced by produce weight and storage temperature. Oxygen (O2) composition decline below 2% after day 3 and 5 at 15 and 10 ºC, respectively, while samples at 5 °C did not reach below 2% throughout the study. On the other hand, CO2 levels increased significantly during storage for all packaging conditions. This study showed the importance of a systematic approach to the design of optimal MAP systems. At lowest storage temperature the inability to achieve desired modified atmosphere (MA) required for optimal storage of arils despite the increase in produce weight, suggests that the use of active gas modification (gas flushing with recommended atmosphere) would be necessary. However, the present results show that at higher temperature macro/micro perforations would be required on the polymeric films used in the present study in order to avoid critical levels of O2 and CO2. The influence of passive MAP, storage temperature and duration on volatile composition and evolution of packaged pomegranate arils was investigated. The results showed that changes in aroma compounds were dependent on cultivar differences, storage condition and duration. Using GC-MS analysis of pomegranate juice HS-SPME extracts, a total of 18 and 17 volatiles were detected for ‘Herskerwitz’ and ‘Acco’, respectively. Furthermore, flavour life (7 days) was shorter than the postharvest life (10 days) for both cultivars. There was a decrease in volatile composition during the storage period (aldehydes < alcohols < esters) while the concentration (%) and composition of ethyl esters increased with storage time. These results highlight the need for a more precise definition of flavour shelf life for MApackaged pomegranate arils and other packaged fresh produce. The importance of maintaining optimal cold storage condition, selection of appropriate packaging materials and a systematic approach to the design and application of MAP systems has also been shown. / AFRIKAANSE OPSOMMING: Gemodifiseerde atmosfeer-verpakking (GAV) is ’n dinamiese proses waartydens die gassamestelling binne-in ’n verpakking gewysig word. Dit berus op die wisselwerking tussen die respirasietempo (RT) van die produkte en die oordrag van gasse deur die verpakkingsmateriaal. Hierdie twee prosesse is van verskeie faktore soos bergingstemperatuur, dikte van die film en oppervlakte, gewig van die produkte asook vry boruimte binne-in die pakkie afhanklik. Om dus die gewenste gemodifiseerde atmosfeer in ’n gegewe verpakking te verkry, is dit belangrik om die drie fundamentele dissiplines van GAV te begryp, naamlik produkfisiologie, polimeerontwerp, en omsettingstegnologie. In hierdie studie is die gevolge van bergingstoestande en -duur op fisiologiese reaksie, met ander woorde, respirasie- (RT) en transpirasietempo (TT) van twee geselekteerde granaatkultivars ‘Acco’ en ‘Herskawitz’, ondersoek en wiskundige modelle is ontwikkel om ons in staat te stel om hierdie fisiologiese reaksies by gegewe tyd- en bergingstoestande te voorspel. Die resultaat van hierdie studie het aangetoon dat die respirasietempo (RT) van heel granaatvrugte aansienlik hoër was as die RT van vars arils, en temperatuur het beduidende uitwerking op RT van beide heel vrugte en vars arils gehad. Die invloed van tyd, en die wisselwerking tussen temperatuur en tyd het ook ’n beduidende invloed op die RT van vars granaatarils gehad. Hierdie bevinding beklemtoon die belang van die handhawing van optimale koelbewaringstoestande vir verpakte arils of heel vrugte met die aanvoerketting langs. Daarbenewens wiskundige modelle wat gebaseer op die Arrhenius-tipe vergelyking en die magsfunksie-vergelyking gepaard met Arrhenius-tipe vergelyking, die uitwerking van temperatuur en die invloed van tyd en temperatuur op die RT van vars granaatarils vir beide kultivars onderskeidelik voldoende en akkuraat voorspel. Afgesien die resultate van eksperimentele en modelvoorspellings die studies aangetoon dat beide relatiewe humiditeit (RH) en bergingstemperatuur ’n beduidende uitwerking op TT het. RH was die veranderlike met die grootste invloed op TT, en it was waargeneem dat dit die beste was om arils teen 5°C en 96% RH te bewaar (8 dae). Die toepaslikheid van die transpirasiemodel wat ontwikkel is, is bevestig op grond van voorspelling van TT van granaatarils onder verskillende kombinasies van bergingstoestande. Die model het TT voldoende voorspel en sou ’n bruikbare instrument wees ten einde die waterverliestempo in vars granaatarils en ander vars produkte, soos deur bergingstoestande en duur beïnvloed, te begryp. Die uitwerking van passiewe-GAV ontwerpparameters as ’n funksie van gewig van die produkte, bergingstemperatuur en duur op vars granaatarils is ondersoek. Dit het aan die lig gebring dat gewig van die produkte, temperatuur en die wisselwerking tussen temperatuur en tyd ’n geringe maar onbeduidende uitwerking op gemete fisikochemiese gehalteeienskappe gehad het. Die gaskonsentrasie in die boruimte is betekenisvol beïnvloed deur gewig van die produkte en bergingstemperatuur. Die O2-samestelling het tot benede 2% gedaal na 3 en 5 dae by 15 en 10 ºC, onderskeidelik, terwyl monsters by 5 °C deur die studie heen nooit laer as 2% was nie. Aan die ander kant, CO2-vlakke het gedurende berging betekenisvol verhoog wat betref alle verpakkingstoestande. Hierdie studie het die belangrikheid van ’n sistematiese benadering by die ontwerp van ’n optimale GAV-stelsel aangetoon. By die laagste bergingstemperatuur dui die onvermoë om die gewenste gemodifiseerde atmosfeer (GA) wat vir optimale berging van arils benodig word, te verkry – ondanks die toename in die gewig van die produkte – daarop dat die gebruik van aktiewe gasmodifisering (gasspoeling met aanbevole atmosfeer) nodig sou wees. Egter die huidige uitslae aangetoon dat by hoër temperatuur, sou makro/mikroperforasies op die polimeerfilms wat gebruik word in die onderhawige studie egter nodig wees ten einde kritiese vlakke van O2 en CO2 te verhoed. Die invloed van passiewe GAV, bergingstemperatuur en duur op onstabiele samestelling en evolusie van verpakte granaatarils is ondersoek. Die resultate aangetoon dat veranderinge in aromaverbindings afhanklik was van kultivarverskille, bergingstoestande en duur. Met behulp van GC-MS-analise van granaatsap HS-SPME-ekstrakte, het ons ’n totaal van 18 en 17 vlugtige stowwe vir ‘Herskawitz’ en ‘Acco’, onderskeidelik bespeur. Verder het ons waargeneem dat die smaakleeftyd (7 dae) korter was as die na-oesleeftyd (10 dae) vir beide kultivar. Daar was ’n afname in vlugtige samestelling (aldehiede < alkohole < esters) terwyl die konsentrasie (%) en samestelling van etielesters het met bergingstyd verhoog. Hierdie resultate het die aandag gevestig op die behoefte aan ’n meer presiese definisie van geur-raklewe vir GA-verpakte granaatarils en ander verpakte vars produkte. Die belang van die handhawing van die optimale koelbewaringstoestand, seleksie van geskikte verpakkingsmateriaal en ’n sistematiese benadering tot die ontwerp van ’n optimale GAVstelsel, is ook beskryf.

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Selection of raw materials for a consistent and high quality end product has been a challenge for brewers globally. Various different factors may influence quality and although a great number of methods for malt analysis exist today for the prediction of end product quality, some still do not accurately represent malt performance in beer. This research focussed on determining parameters in malts to predict two of the major beer quality determining factors namely, foam- and flavour stability. Specific biochemical markers in barley malt such as lipid transfer protein 1 (LTP1) lipoxygenase-1 (LOX-1), anti-radical/oxidant potential (AROP), free amino nitrogen and intact protein were determined and used in beer quality prediction from malt character. These biochemical quality predictions were then correlated with the end product beer quality as assessed in sensory analysis trials on micro-brewed beers. Being such a multi-faceted factor in beer, LTP1 have already become an attractive field of study. LTP1 is primarily associated with stable beer foam, as a foam protein in its own right, and acting as a lipid scavenger. This protein is also theorised to play a role in the stability of beer flavour by possibly acting as anti-oxidant. Lastly LTP1 is known to have anti-yeast activity, which could negatively impact fermentation. In this study LTP1 and its lipid bound isoform LTP1b were successfully purified in an economical and easy five step protocol. Both isoforms showed temperature stability at temperatures >90°C and prefer more neutral and basic pH environments. Although the reported antioxidant activity was not observed, both purified LTP1 and LTP1b inhibited lipoxygenase-1 (LOX-1) activity, which is responsible for the enzymatic breakdown of linoleic acid to form 2(E)-nonenal. This is a novel finding that links LTP1 also to flavour stability. LTP1 exhibited anti-yeast activity whereas LTP1b lost most if not all the activity. However, since most of the LTP1 is converted to LTP1b and glycosylated isoforms during the brewing process fermentation will not be greatly influenced, while foam and flavour stability could still be promoted by the presence of LTP1b. Flavour deterioration of the final packaged product is partially due to the enzymatic production of 2(E)-nonenal by LOX-1 and the presence of free oxygen radical species, limited anti-radical/oxidant potential (AROP) and LTP1. The development of two 96-well micro-assays based on the ferrous oxidation-xylenol orange (FOX) assay for the determination of LOX-1 and AROP was successfully accomplished and compared well with established assays. The LOXFOX and AROP-FOX assays were specifically developed for the on-site, high throughput comparative determination of LOX-1 and AROP in malt and other brewery samples. The AROP-FOX and LOX-FOX micro-assays and a number of established assays were used to categorise malts in different predicted quality groups, various biochemical markers were measured which included LOX activity, LTP1 content, FAN values, intact protein concentration and AROP. An excellent trend (R2=0.93) was found between FAN/LOX and LTP1/LOX which also correlated with the novel observation that LOX-1 activity is inhibited by LTP1 at various concentrations. These trends could assist brewers in optimal blending for not only high quality end products but also fermentation predictions. To determine whether these biochemical markers selected for screening in barley malt are predictive of shelf life potential of the end product, sensory trials were performed. Three barley malt cultivars were selected for LOX, AROP, LTP1, protein and FAN content and used in micro-brewery trials at 0 and 3 months and evaluated using sensory analysis. Good correlation was found between the biochemical predictors and sensory trial for the best quality malt and beer. These parameters were therefore highly relevant for predicting shelf life potential, although additional research is required to elucidate the effect of LTP1 and LOX-1 on each other during the brewing process, since it seems that high LOX-1 concentrations could be leading to LTP1 decreases. With this study it is proposed that if more detailed protein or FAN characterisation is used together with the screening of LOX-1, LTP1 and AROP, an more accurate shelf life prediction, based on malt analysis, is possible and with the help of these parameters brewers can simply blend malts accordingly. / AFRIKAANSE OPSOMMING: Die keuse van roumateriaal om 'n konstante eindproduk van goeie kwaliteit te lewer, was nog altyd 'n uitdaging vir brouers wêreldwyd aangesien verskeie faktore 'n invloed het op die kwaliteit van die produk. Alhoewel daar tans verskeie metodes vir moutanalise bestaan wat die eindproduk–kwaliteit voorspel, is daar min wat werklik die eindproduk kwaliteit soos voorspel deur moutanalise verteenwoordig. Hierdie navorsing fokus op die bepaling van mout-eienskappe om twee van die belangrikste bierkwaliteitvereistes, naamlik skuim- en geurstabiliteit te voorspel. Spesifieke biochemiese eienskappe in garsmout soos lipiedtransportproteien-1 (LTP1), lipoksigenase-1 (LOX-1), antioksidant-antiradikaal potensiaal (AROP), vry aminostikstof (FAN) is geïdentifiseer en gebruik in voorspelling van bierkwaliteit vanaf moutkarakter. Hierdie biochemiese kwaliteit voorspellings is dan gekorreleer met die eindproduk soos ge-evalueer d.m.v sensoriese analise op mikro-gebroude bier. Omdat LTP1 soveel fasette in bier beïnvloed, het dit reeds 'n aanloklike studiefokus geword. LTP1 word hoofsaaklik geassosieer met stabiele skuimkwaliteit in bier en tree op as 'n lipiedmop (“lipid scavenger”). Die proteien speel teoreties ook 'n rol in die stabiliteit van bier geur deur moontlik as 'n anti-oksidant op te tree. Laastens is LTP1 bekend vir sy antigis aktiwiteit wat moontlik 'n negatiewe uitwerking op fermentasies het. Gedurende hierdie navorsing is LTP1 en sy lipiedbinding isoform LTP1b suksesvol gesuiwer met 'n ekonomies en eenvoudige 5-stap protokol. Beide isoforme het stabiliteit by temperature >90°C en meer neutrale en basiese pH omgewings getoon. Alhoewel die voorheen gerapporteerde anti-oksidant aktiwiteit vir LTP1 nie bevestig kon word nie, is daar wel gevind dat beide LTP1 en LTP1b, LOX-1, wat verantwoordelik is vir die ensimatiese afbraak van linoleensuur na 2(E)-nonenal, se aktiwiteit inhibeer. Dit is 'n unieke bevinding wat LTP1 ook koppel aan geurstabiliteit. LTP1 het antigis aktiwiteit getoon, maar LTP1b het die meeste, indien nie alle antigis-aktiwiteit verloor. Omdat die meeste van die LTP1's omgeskakel word na LTP1b's en geglikosileerde isoforme tydens die brouproses, sal fermentasie nie beduidend beinvloed word nie, maar die skuim- en geurstabiliteit sal steeds bevorder word deur die blote teenwoordigheid van die LTP1b. Geurverval van die finale verpakte produk is gedeeltelik a.g.v die ensimatiese produksie van 2(E)-nonenal deur LOX-1 en die teenwoordigheid van vry suurstofradikaal spesies, beperkte AROP en LTP1. Die ontwikkeling van twee 96-putjie mikroessaïs, gebasseer op die yster oksidasie-xilenol oranje (FOX) essai vir die bepaling van LOX-1 en AROP, was suksesvol en het goed vergelyk met reeds gevestigde essaïs. Die LOX-FOX en AROP-FOX mikroessaïs is spesifiek ontwikkel vir die residente, hoë deurvloei vergelykende bepaling van LOX-1 en AROP in mout en ander brouery-monsters. Die AROP-FOX en LOX-FOX mikroessaïs en 'n paar gevestigde essaïs is gebruik om moute te kategoriseer in die verskillende voorspelde kwaliteitsgroepe. Die biochemiese merkers wat gemeet is het die volgende ingesluit: LOX aktiwiteit, LTP1 inhoud, FAN waardes, proteïen konsentrasie en AROP. 'n Merkwaardige korrelasie (R2=0.93) is gevind tussen FAN/LOX en LTP1/LOX wat ook ooreenstem met die waarneming dat LOX-1 aktiwiteit onderdruk word deur LTP1 by verskeie konsentrasies. Hierdie korrelasies kan brouers help met optimale versnitting van moute vir, nie net die hoogste kwaliteit eindproduk nie, maar ook vir fermentasie voorspellings. Om te bepaal of hierdie geselekteerde biochemiese merkers in mout die potensieële raklewe van die eindproduk verteenwoordig, is sensoriese evaluerings uitgevoer. Drie gars-mout kultivars is geselekteer o.g.v LOX-, AROP-, LTP1-, proteïen- en FAN-inhoud en gebruik in mikro-brouery proewe en op 0 en 3 maande en is ge-evalueer deur sensoriese analise. Goeie korrelasie is gevind tussen die biochemiese voorspellers en sensoriese evaluering vir die beste kwaliteit mout en bier. Hierdie maatstawwe is daarom uiters relevant vir voorspelling van die potensiele rakleeftyd, alhoewel addisionele navorsing nodig is om die effek van LTP1 en LOX-1 op mekaar gedurende die brouproses te bepaal. Dit blyk dat 'n hoë LOX-1 konsentrasies kan lei tot 'n afname in LTP1. Met hierdie studie word dit voorstel dat, as meer gedetaileerde proteien of FAN karakterisering saam met LOX-1, LTP1, en AROP analise uitgevoer word, 'n meer akkurate raklewe voorspelling moontlik is en met behulp van hierdie parameters kan brouers moute dienooreenkomstig versnit.

Thesis (MSc Food Sc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The increased consumption of fresh produce has been shown to be related to increases in foodborne disease outbreaks and these have in many cases been ascribed directly to carry-over of pathogens from contaminated irrigation water. In South Africa, rivers are the main source of irrigation water but many have been found to be unsuitable for irrigation of fresh produce because of the unacceptably high levels of faecal contamination. The main aim of this study was to do a baseline evaluation of the microbiological quality of the Plankenburg and Eerste Rivers and to determine which bacterial contaminants are present. Two sampling sites were selected for the Plankenburg (Plank-1 and -3) and one for the Eerste River (Eerste-1). The microbiological analysis included aerobic colony count (ACC), aerobic and anaerobic sporeformers, Staphylococcus, Salmonella, Listeria, enterococci, coliforms, faecal coliforms and E. coli using standard methods. The faecal contamination levels for both rivers exceeded the DWAF and WHO guidelines of <1 000 E. coli per 100 mL water for irrigation of fresh produce intended to be consumed raw. The Plankenburg River sites always had higher coliform contamination levels (1 200 - 13 000 000 MPN per 100 mL water) than the Eerste River site (230 - 79 000 MPN per 100 mL water). There was also a high incidence of index organisms including Salmonella, Staphylococcus, Listeria and endosporeformers. The isolation of intestinal enterococci suggested the presence of potential pathogens that can cause disease outbreaks. The baseline data also showed large variations in microbial loads over the 15 month study with the faecal coliform counts ranging for Plank-1 from 1 200 to 7 000 000 MPN.100mL-1, Plank-3 from 10 to 460 000 MPN.100mL-1 and Eerste-1 from 28 to 79 000 MPN.100mL-1. The water temperatures at all three sites ranged from 12.1° to 21.7°C with COD values in most cases below 100 mg.L-1. As the baseline study showed large variations in microbial loads over the 15 month study period an assessment using the Colilert-18 system of the weekly, daily and hourly variations, for 6 weeks over a period of 4 months was conducted at site Plank-2. This site was specifically used as it is an irrigation source point for nearby fresh produce farmers and is about 2 km further downstream from an informal settlement. The weekly variation trend for total coliforms (TC) showed a decrease over the entire sampling period with the highest count of 3 200 000 MPN.100 mL-1 during the warmer period. The E.coli (Ec) counts showed a similar trend with the highest count of 440 000 MPN.100 mL-1 also in March. The daily variation trends were the same for both the TC and Ec and counts found to increase from Monday to Thursday followed by a decrease to Sunday. The highest counts were on Thursday with average TC and Ec counts of 1 900 000 and 160 000 MPN.100 mL-1, respectively. The hourly variation trends were similar for both TC and Ec with counts increasing from 06h00 to 12h00 followed by a decrease to 18h00. The increases in TC and Ec counts found during the weekly, daily and hourly variation trend studies clearly suggests that the 15 month sampling that was done once a month on Mondays at 08h00 could be considered an underestimation of the contamination levels of the Plankenburg and Eerste Rivers. The overall weekly variation trend for the water temperature showed a decrease over the sampling period while the daily and hourly variation trends showed an increase from 06h00 to 18h00. The overall weekly trend for pH differed from that of the temperature with an increase over the sampling period. The analysis of covariance showed no correlation (p < 0.05) between the physico-chemical (temperature and pH) and the microbial variables (TC and Ec). Therefore it was concluded that temperature and pH had no direct impact on either the total coliform or E. coli counts. Both the Plankenburg and Eerste Rivers were found to be unsuitable for the irrigation of fresh produce intended to be consumed raw due to the high levels of faecal contamination that exceeded DWAF and WHO guidelines. Irrigation with such water could pose a health risk because of presence of potential pathogens that could be carried-over to fresh produce. / AFRIKAANSE OPSOMMING: Die toenemende gebruik van vars produkte hou direk verband met die toename in voedseloordraagbare siektes. Alte dikwels kan dit toegeskryf word aan die teenwoordigheid van patogene in besproeiingswater. In Suid Afrika is riviere die hoofbron van besproeiingswater maar dit is al gevind dat meeste ongeskik is vir gebruik as besproeïngsbron as gevolg van die onaanvaarbare hoe vlakke van fekale besmetting. Die hoofdoel van hierdie studie was om ‘n basislyn evaluasie van die mikrobiologiese kwaliteit van die Plankenburg en Eerste Riviere te doen en ook vas te stel watter bakteriese kontaminante teenwoordig is. Twee bemonsteringpunte is geselekteer vir die Plankenburg (Plank- 1 en -3) en een vir die Eerste Rivier (Eerste-1). Mikrobiologiese analises met standaard metodes het die volgende ingesluit: aërobe kolonie telings (AKT), aërobe en anaërobe spoorevormers, Staphylococcus, Salmonella, Listeria, enterococci, koliforms, fekale koliforms en E. coli met gebruik van standaard metode. Die fekale besmettingsvlakke vir beide riviere het die DWAF en WHO leistreep van <1 000 E. coli per 100 mL water vir besproeiing van vars produkte wat rou geëet kan word oorskry. Die Plankenburg Rivier bemonsteringspunte het in alle gevalle ‘n hoër kolivorm besmettingsvlak (1 200 - 13 000 000 MPN per 100 mL water) as die Eerste Rivier punt (230 - 79 000 MPN per 100 mL water) gehad. Daar was ook ‘n hoër voorkoms van indeksorganismes insluitend Salmonella, Staphylococcus, Listeria en endosporevormers. Die voorkoms van ingewand enterococci was ‘n addisionele aanduiding van die voorkoms van patogene wat ernstige gesondheidsrisikos vir die verbruiker kan inhou. Die basislyn data het groot variasies in die mikrobe vlakke oor die 15 maand van studie getoon. Die faecal koliforms vir Plank- 1 het gewissel van 1 200 tot 7 000 000 MPN.100mL-1, vir Plank-3 van 10 tot 460 000 MPN.100mL-1 en vir Eerste-1 van 28 tot 79 000 MPN.100mL-1. Die water temperature het gewissel van 12.1° tot 21.7°C met die CSB waardes in meeste gevalle minder as 100 mg.L-1. Aangesien daar sulke groot variasies in mikrobe ladings oor die 15 maande tydperk voorgekom het, is die Colilert-18 sisteem gebruik om die weeklikse, daaglikse en uurlikse variasies vas te stel vir 6 weke oor ‘n periode van 4 maande by die Plank-2 bemonsteringspunt. Daar is spesifiek op die bemonsteringspunt gefokus omdat dit as ‘n besproeiingsbron gebruik word deur groente produsente. Dit is ook gelee ongeveer 2 km stroomaf van ‘n informele nedersetting. Die weeklikse variasies in totaal koliforms (TC) het ‘n afname oor die hele bemonsteringsperiode getoon, met die hoogstes telling van 3 200 000 MPN.100 mL-1 gedurende die warmer tydperk. Die E.coli (Ec) tellings het ‘n soortgelyke neiging getoon, met die hoogste telling van 440 000 MPN.100 mL-1 ook in Maart. Die daaglikse neigings was dieselfde vir beide die TC en Ec en die tellings het vermeerder van Maandag tot Donderdag, met ‘n afname tot Sondag. Die hoogste telling was op Donderdag met gemiddelde TC and Ec tellings van 1 900 000 and 160 000 MPN.100 mL-1, respektiewelik. Die uurlikse variasie profiel was soortgelyk vir beide TC and Ec met tellings wat vermeerder het van 06h00 tot 12h00 gevolg deur ‘n afname tot 18h00. Die toename in TC en Ec getalle soos vasgestel gedurende die weeklikse, daaglikse en uurlikse variasie het duidelik getoon dat die bemonsterings wat een maal per maand op Maandae om 08h00 gedurende die 15 maande tydperk uitgevoer is, tot ‘n erg onderskatting van die besmettings vlakke in die Plankenburg en Eerste Riviere gelei het. Die algehele weeklikse variasies vir die water temperatuur het ‘n verlaging oor die bemonsteringstydperk getoon terwyl die daaglikse en uurlikse variasie neigings ‘n verhoging van 06h00 tot 18h00 getoon het. Die weeklikse neigings vir pH het van die van die temperatuur verskil. Die analises van kovariante het geen korrelasie (p < 0.05) tussen die fisiese-chemiese (temperature en pH) parameters en die mikrobe veranderlikes (TC en Ec) getoon nie. Dus is daar afgelei dat temperatuur en pH geen direkte impak op die totale kolivorm of E. coli tellings gehad nie. Die data van die studie het duidelik getoon dat water van beide die Plankenburg en Eerste Riviere nie geskik is vir gebruik vir besproeiing van vars produkte wat rou geëet gaan word nie. In beide gevalle het die fekale besmettingsvlakke die DWAF en WHO leistreep oorskry. Besproeiing met sulke water hou ‘n gesondheidsgevaar in as gevolg van die teenwoordigheid van potensiële patogene wat oorgedra kan word na vars produkte.

Thesis (MSc Food Sc) (Food Science)--Stellenbosch University, 2008. / The change in aspalathin, iso-orientin, orientin and total polyphenol (TP) content of a commercially produced fermented rooibos (FR) extract was monitored throughout production. Particular attention was paid to the effect of spray-drying on FR and unfermented rooibos (UR) extracts. The quality of commercial, South African rooibos iced teas made with FR extract was also investigated with respect to the aforementioned parameters. Subsequently, the effect of heating and storage on the phenolic composition and colour of experimental iced teas containing respectively FR, UR and nano emulsified unfermented rooibos (NEUR) extracts was investigated. The combined effect of pH (pH 3-7) and storage (5, 30 and 40ºC), as well as high (660 mg/L, 0-7 days at 30ºC; UR only) and low (0.5 mg/L) concentrations of H2O2, was determined on reconstituted FR, UR and NEUR extracts. Finally, eight rooibos iced teas (four variants; unflavoured and lemon-flavoured) were analysed for plant-like, hay-like, rooibos and lemon flavour, as well as astringency, using descriptive sensory analysis. The degree of consumer preference of the flavoured variants was determined using the nine point hedonic scale. In all cases, changes in individual flavonoid content were quantified using HPLC. The TP content of the iced teas and commercial extracts was determined using the Folin-Ciocalteu assay. Browning of the iced teas and reconstituted extracts was monitored spectrophotometrically (420 nm). Aspalathin, iso-orientin and orientin were found to be present after all stages of the FR extract production process. Spray-drying, specifically, also did not reduce the content of these flavonoids, or the TP content, in FR and UR extracts. Despite the relatively good retention during the heating and storage of experimental rooibos iced teas, these flavonoids were either absent or present at extremely low levels in commercial iced teas. The latter suggested that either extremely low quantities of extract, no extract at all or extracts of poor quality, were used for the production of the analysed iced teas. Increased degradation was generally observed for sterilisation treatments compared to pasteurisation whilst losses during storage increased with time. The presence of citric acid, due to its pH-lowering effect, and ascorbic acid, due to its antioxidant activity, was integral to the retention of aspalathin, iso-orientin and orientin during heating, but less so during storage. The UR iced teas generally performed better than their FR counterparts, however, NEUR iced teas exhibited the greatest retention of the aforementioned flavonoids. Heating and storage resulted in browning of most iced teas, whilst the TP content increased slightly or remained unchanged. Phenolic retention in FR and UR extracts decreased with increasing pH and temperature, with concomitant browning. However, between pH 5 and 7, the stability of aspalathin was superior in the NEUR extract formulation. The latter also greatly resisted absorbance changes at pH 3 and 4, despite a loss of aspalathin. The phenolic content of UR extract was immediately reduced by high a concentration of H2O2, however, no significant (P≥0.05) changes in absorbance were detected, suggesting the formation of intermediate, colourless oxidation products. Formulations containing ascorbic acid experienced the greatest reductions. This was attributed to the iron reducing ability of this compound, as reduced iron accelerates the rate of the Fenton reaction. At low levels of H2O2, only the FR extract exhibited a loss of phenolic compounds. The level of iron in this extract was the highest. Despite having the greatest aspalathin and total flavonoid content, lemon flavoured unfermented rooibos iced tea (UF/LEMON) was disliked by consumers. Preference was directed away from the plant-like characteristic of this tea and towards rooibos flavour, characteristic of fermented rooibos iced tea. Iced tea comprising both FR and NEUR extract produced a product that 77% of consumers rated positively. Its slight hay-like flavour did not significantly (P≥0.05) reduce the liking of this product compared to fermented rooibos iced tea.

Thesis (MScVoedselwet)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Milk has been identified as having the potential of being a carrier of human pathogens, and it is thus essential to eliminate or reduce the likelihood of milk borne contamination. This problem of milk contamination is generally solved by the process of pasteurisation which is achieved by heating the "raw" material for a sufficient period of time to destroy any pathogenic and spoilage bacteria which may be present at a temperature of below 100°C. Presently, there are two basic methods of pasteurisation in use in the dairy industry, the LTLT and the HTST methods, where the applied heat treatment is considered sufficient to ensure public safety and adequate keeping quality. In addition to these, there is another method, the "pot" pasteurisation, to be found in Southern Africa that was designed to eliminate potential pathogenic and spoilage bacteria present in raw milk. As far as it is known no thermal studies have been done on the "pot" pasteurisation method. The objectives of this study were to determine the impact of different milk pasteurisation temperature and time combinations on the survival of selected microbes. The accuracy of the "pot" pasteurisation method and how it differs from the other pasteurisation methods was also determined using the same selected microbes. The six selected microbes were thermally inactivated by using the LTLT, HTST and the "pot" pasteurisation methods at low and high inoculum levels of 104 and 106 cfu.ml-1. The thermal death curves were constructed for each selected species. The selected microbes included the strains Bacillus cereus (S4), Chryseobacterium meningosepticum (S5), Pseudomonas putida (S6), Acinetobacter baumannii (C3), Escherichia coli (58) and Candida lipolytica (G1). Survivors were enumerated after heating for 0, 5, 10, 15, 20, 25, 30, 35 and 40 min for both the LTLT and HTST pasteurisation methods and after heating for 0, 10, 20 and 30 min for the "pot" pasteurisation method. The results from this study showed that with the exception of the B. cereus strain, the other selected microbes at both high and low concentration levels did not survive the LTLT or the HTST pasteurisation methods. It was found that for all the organisms used in this study, there was a rapid initial death rate just before the required pasteurisation temperatures of 63°, 72° and 90°C were reached, during the "come-up" period. In contrast, the results from the "pot" pasteuriser showed that theB. cereus (S4), Chr. meningosepticum (S5), P. putida (S6), A. baumannii (C3) and E. coli (58) strains survived the pasteurisation conditions applied. From these results it was thus concluded that the "pot" pasteuriser under the conditions evaluated in this study, did not pasteurise effectively. Therefore, it is recommended that the manufacturer improves the heating quality of the "pot" pasteuriser. As it was found that only the B. cereus (S4) strain survived all the different pasteurisation methods, future research needs to be done to determine at which temperature this heat resistant bacterial strain will be destroyed. This is very important because there is a need to destroy all the spoilage microorganisms that can lead to the deterioration of food products. / AFRIKAANSE OPSOMMING: Melk is 'n potensiële draer van mikrobes wat patogenies is vir die mens. Dit is dus essensiëel om die besmetting van melk te verlaag of te elimineer. Die probleem van melkbesmetting word opgelos deur die proses van pasteurisasie. Die proses word toegepas deur verhitting van die rou material vir 'n voldoende periode om patogeniese en bederf organismes te vernietig. Temperature onder 100°C word gebruik. In die suiwelbedryf word twee basiese metodes gebruik: die LTLT (lae temperatuur, lang tyd) metode en die HTKT (hoë temperatuur, kort tyd) metode. Albei hittebehandelings is voldoende om publieke veiligheid en 'n genoegsame rakleeftyd te verseker. 'n Derde metode, "pot" pasteurisasie, word in Suidelike Afrika gebruik. Die metode is ontwikkel om potensiële patogene en bederf organismes in rou melk te elimineer. Die probleem is dat daar geen navorsing op die temperatuur eienskappe van die “pot" metode gedoen is nie. Die doelwitte van hierdie navorsing was om die effek van verskillende temperatuur:tyd kombinasies op die oorlewing van sekere mikrobes te bepaal. Die akkuraatheid van die "pot" metode en die manier hoe dit van ander metodes verskil, is ook in ag geneem. Die navorsing is ten alle tye gebaseer op die geselekteerde mikroorganismes. Die ses geselekteerde spesies van mikrobes is vernietig deur middel van die LTLT, HTKT en "pot" pasteurisasie metodes. Die mikrobes is geïnaktiveer teen lae en hoë inokulums van 104 en 106 kve.ml-1. Terminale dodings kurwes is opgestel vir elke geselekteerde spesie. Die mikrobes van belang is Bacillus cereus (S4), Chryseobacterium meningosepticum (S5), Pseudomonas putida (S6), Acinetobacter baumannii (C3), Escherichia coli (58) en Candida lipolytica (G1). Die oorlewende mikroorganismes is na hitte behandelings van 0, 5, 10, 15, 20, 25, 30, 35 en 40 minute vir beide die LTLT en die HTKT pasteurisasie metodes en na hitte behandelings van 0, 10, 20, en 30 minute vir die "pot" pasteurisasie metode getel. Die resultate van die navorsing dui aan dat, behalwe vir B. cereus, die geselekteerde mikrobes teen beide lae en hoë konsentrasies nie die LTLT en die HTKT metodes oorleef het nie. Daar is gevind dat, vir al die organismes, vinnige aanvanklike dodingstempos teenwoordig was net voor die noodsaaklike pasteurisasie temperatuur van 63°, 72° en 90°C bereik is, gedurende die "come-up" periode. Inteenstelling hiermee het die resultate van die "pot" metode bewys dat B.cereus (S4), Chr. meningosepticum (S5), P. putida (S6), A. baumannii (C3) en E. coli (58) stamme die pasteurisasie toestande oorleef het. Uit die resultate is ’n gevolgtrekking gemaak dat die "pot" pasteurisasie metode nie effektief was nie. Daar word dus aanbeveel dat die vervaardiger die verhittings-kwaliteit van die "pot" pasteurisasie apparaat verbeter. Aangesien net die B. cereus (S4) stam al drie pasteurisasie metodes oorleef het, moet toekomstige navorsing gedoen word om die vernietigings temperatuur van dié hittebestande stam te bepaal. Die navorsing is van belang weens die behoeftes om alle bederf mikroorganismes wat tot die agteruitgang van voedsel produkte kan lei, te vernietig.

Thesis (MScVoedselwet)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Red meat has a limited shelf-life at refrigerated temperatures, where spoilage is mainly due to the proliferation of bacteria, yeast and moulds, acquired during the dressing process. In addition, almost a fifth of food-borne disease outbreaks, caused by microorganisms such as Escherichia coli 0157:H7, Listeria monocytogenes and Staphylococcus aureus are associated with red meat. To improve the microbiological quality of red meat, systems such as HACCP, GHP and GMP are currently practiced; however, these practices are not able to extend the shelf-life of these products. At present suitable food-grade preservatives are recommended, but the use of some of these preservatives is increasingly being questioned with regard to their impact on human health. Additionally, food service customers demand high quality products that have a relatively long shelf-life, but still prefer the appearance of minimally processed food. All these factors challenge the food manufacturing industry to consider more natural means of preservation. Antimicrobial metabolites of food grade bacteria, especially lactic acid bacteria, are attracting increasing attention as food preservatives. Bacteriocins are antimicrobial peptides (3 to 10 kDa) with variable activity spectra, mode of action, molecular weight, genetic origin and biochemical properties that are bacteriostatic or bactericidal to bacteria closely related and bacteria confined within the same ecological niche. Micro-organisms were isolated from beef, lamb and pork, obtained from four commercial retailers. The number of viable cells three days after the sell-by date at 4ºC ranged from 80 cfu.g-1 to 1.4 × 108 cfu.g-1. Fifty-three percent were Gram-negative bacteria, 35% Gram-positive and 12% yeast. The microbial population of the meat was greatly influenced by the origin, i.e. the retailer. Bacteriocins produced by Enterococcus faecalis BFE 1071, Lactobacillus curvatus DF 38, Lb. plantarum 423, Lb. casei LHS, Lb. salivarius 241 and Pediococcus pentosaceus ATCC 43201 were screened for activity against bacteria isolated from the different meat samples. Sixteen to 21% of the isolates, identified as members of Klebsiella, Shigella, Staphylococcus, Lactobacillus, Lactococcus, Leuconostoc, Enterococcus, Pediococcus, Streptococcus and Bacillus were sensitive to the bacteriocins. Curvacin DF 38, plantaricin 423 and caseicin LHS (2.35 to 3.4 kDa) had the broadest activity range and inhibited species of Lactobacillus, Pediococcus, Enterococcus, Listeria, Bacillus, Clostridium and Propionibacterium. The bacteriocins remained stable at 121ºC for 20 min, in buffers with a pH ranging from 2 to 10 and in NaCl concentrations of between 0.1 and 10% (m/v). Like most peptides, they were sensitive to proteolytic enzymes. Curvacin DF 38 is sensitive to amylase, suggesting that the bacteriocin might be glycosylated. To assess the efficiency of curvacin DF 38, plantaricin 423 and caseicin LHS as meat preservatives, they were partially purified by ammonium sulphate precipitation and separation in a Sep Pak C18 cartridge. The shelf-life of pork may be extended by up to two days. Meat samples treated with bacteriocins were darker than the control (untreated) sample. Descriptive sensory evaluation by a seven-member panel indicated that there were significant differences (P ≤ 0.05) regarding the aroma, sustained juiciness, first bite and metallic taste attributes of the control and the 4 day-treated samples. The control and 2 day-treated samples and the 2 day- and 4 day treated samples did not differ significantly regarding these attributes. There were no significant differences regarding the initial juiciness, residue and pork flavour attributes. Concluded from the results obtained in this study, bacteriocins produced by Lb. curvatus DF 38, Lb. plantarum 423 and Lb. casei LHS effectively extended the shelf-life of pork loins by up to 2 d at refrigerated temperatures with no drastic changes on sensory characteristics. In edition, the stability of these bacteriocins broadens their application as preservatives in many foods. / AFRIKAANSE OPSOMMING: Die rakleeftyd van rooivleis by yskastemperature is beperk, waar bederf hoofsaaklik deur die vermenigvuldiging van bakterieë, giste en swamme veroorsaak word. Die meeste van hierdie kontaminante is afkomstig van die slagtingsproses. Byna ’n vyfde van alle uitbrake van voedselvergiftigings wat deur organismes soos Escherichia coli 0157:H7, Listeria monocytogenes en Staphylococcus aureus veroorsaak word, word met rooivleis geassosieër. Die praktyke HACCP, GMP en GHP word tans toegepas om die mikrobiologies kwaliteit van vleis te handhaaf, maar is egter nie voldoende om die rakleeftyd van rooivleis the verleng nie. Die preserveermiddels wat huidiglik aanbeveel word vir dié doel, word toenemend bevraagteken aangaande die invloed daarvan op die menslike gesondheid. Hierby is daar ’n aanvraag na hoë kwaliteit, ongeprosesseerde produkte met ’n verlengde rakleeftyd. Gevolglik word die voedsel vervaardigings industries aangemoedig om meer natuurlike vorms van preservering the oorweeg. Die aandag word tans op die anti-mikrobiese metaboliete van voedselgraad microbes, veral melksuurbakterieë, gevestig. Bakteriosiene is anti-mikrobiese peptiede (3 tot 10 kDa) met verskeie aktiwiteitsspektra, werkswyse, molekulêre massa, genetiese oorsprong en biochemiese eienskappe. Bakteriosiene is meestal bakterie-dodend of - staties teen taksonomies naby geleë organismes en organismes vanuit dieselfde ekologiese nis. Mikroörganismes is geïsoleer vanuit bees-, skaap- en varkvleis, verkry vanaf vier supermarkte. Die aantal lewensvatbare selle per gram (cfu.g-1) het drie dae na die “verkoop”-datum by 4ºC vanaf 80 cfu.g-1 tot 1.4 × 108 cfu.g-1 gevarieër. Drie en vyftig persent van die isolate is as Gram-negatief, 35% as Gram-positief en 12% as giste geïdentifiseer. Die sensitiwiteit van hierdie isolate teen bakteriosiene wat deur Enterococcus faecalis BFE 1071, Lactobacillus curvatus DF 38, Lb. plantarum 423, Lb. casei LHS, Lb. salivarius 241 en Pediococcus pentosaceus ATCC 43201 geproduseer is, is vervolgens getoets. Tussen 16% en 21% van die isolate was sensitief teen die bacteriosiene en is onder andere as Klebsiella, Shigella, Staphylococcus, Lactobacillus, Lactococcus, Leuconostoc, Enterococcus, Pediococcus, Streptococcus en Bacillus geïdentifiseer. Die bakteriosiene met die wydste aktiwiteitsspektrum, naamlik, curvacin DF 38, plantaricin 423 en caseicin LHS is verder ondersoek. Hierdie antimikrobiese peptiede (2.35 tot 3.4 kDa) toon aktiwiteit teen spesies van Lactobacillus, Pediococcus, Enterococcus, Listeria, Bacillus, Clostridium and Propionibacterium. Die bakteriosiene is stabiel by 121ºC vir 20 min, in buffers met ‘n pH-reeks van tussen 2 en 10 en soutkonsentrasies vanaf 0.1% tot 10%. Soos die geval by meeste peptiede is hierdie bakteriosiene sensitief vir proteolitiese ensieme. Curvacin DF 38 is ook sensitief vir amylase, wat daarop dui dat hierdie bakteriosien moontlik geglikosileer is. Die effektiwiteit van curvacin DF 38, plantaricin 423 en caseicin LHS as preserveermiddel in voedselsisteme is getoets deur dit te suiwer (ammonium sulfaat presipitasie en Sep Pak C18 kolom) en op vark lendestukke aan te wend. Mikrobiese analise het bewys dat die rakleeftyd van vark met sowat 2 dae verleng kan word. Volgens die vleiskleurevaluering was die bakteriosien behandelde vark donkerder as die kontrole. Die aroma-, sappigheid-, tekstuur- en metaalgeur-eienskappe van die kontrole en die 4-dag behandelde monster het volgens ‘n opgeleide sensoriese paneel betekenisvol verskil (P ≤ 0.05). Die kontrole en die 2-dag behandelde en die 2-dag behandelde en die 4-dag behandelde monsters het nie betekenisvol verskil nie. Daar was geen betekenisvolle verskil aangaande die aanvanklike sappigheid-, residu- en varkgeur-eienskappe nie. Hierdie sensoriese eienskappe is belangrik ten opsigte van die verbruiker se aanvaarding van die produk. Vervolgens kan uit hierdie resultate afgelei word dat die bakteriosiene wat deur Lb. curvatus DF 38, Lb. plantarum 423 en Lb. casei LHS geproduseer word voldoende is om die rakleeftyd van vark lendestuk by 4ºC met 2 dae te verleng met min of geen effek op die sensoriese persepsie van die vleis. Hierdie bakteriosiene is ook stabiel onder verskeie kondisies wat die toepassing as preserveermiddel aansienlik verbreed.

Thesis (Msc Food Sc (Food Science))--University of Stellenbosch, 2009. / The use of near infrared (NIR) hyperspectral imaging and hyperspectral image analysis for distinguishing between whole maize kernels of varying degrees of hardness and fungal infected and non-infected kernels have been investigated. Near infrared hyperspectral images of whole maize kernels of varying degrees of hardness were acquired using a Spectral Dimensions MatrixNIR camera with a spectral range of 960-1662 nm as well as a sisuChema SWIR (short wave infrared) hyperspectral pushbroom imaging system with a spectral range of 1000-2498 nm. Exploratory principal component analysis (PCA) on absorbance images was used to remove background, bad pixels and shading. On the cleaned images, PCA could be used effectively to find histological classes including glassy (hard) and floury (soft) endosperm. PCA illustrated a distinct difference between floury and glassy endosperm along principal component (PC) three. Interpreting the PC loading line plots important absorbance peaks responsible for the variation were 1215, 1395 and 1450 nm, associated with starch and moisture for both MatrixNIR images (12 and 24 kernels). The loading line plots for the sisuChema (24 kernels) illustrated peaks of importance at the aforementioned wavelengths as well as 1695, 1900 and 1940 nm, also associated with starch and moisture. Partial least squares-discriminant analysis (PLS-DA) was applied as a means to predict whether the different endosperm types observed, were glassy or floury. For the MatrixNIR image (12 kernels), the PLS-DA model exhibited a classification rate of up to 99% for the discrimination of both floury and glassy endosperm. The PLS-DA model for the second MatrixNIR image (24 kernels) yielded a classification rate of 82% for the discrimination of glassy and 73% for floury endosperm. The sisuChema image (24 kernels) yielded a classification rate of 95% for the discrimination of floury and 92% for glassy endosperm. The fungal infected and sound whole maize kernels were imaged using the same instruments. Background, bad pixels and shading were removed by applying PCA on absorbance images. On the cleaned images, PCA could be used effectively to find the infected regions, pedicle as well as non-infected regions. A distinct difference between infected and sound kernels was illustrated along PC1. Interpreting the PC loading line plots showed important absorbance peaks responsible for the variation and predominantly associated with starch and moisture: 1215, 1450, 1480, 1690, 1940 and 2136 nm for both MatrixNIR images (15 and 21 kernels). The MatrixNIR image (15 kernels) exhibited a PLS-DA classification rate of up to 96.1% for the discrimination of infected kernels and the sisuChema had a classification rate of 99% for the same region of interest. The The iv sisuChema image (21-kernels) had a classification rate for infected kernels of 97.6% without pre-processing, 97.7% with multiplicative scatter correction (MSC) and 97.4% with standard normal variate (SNV). Near infrared hyperspectral imaging is a promising technique, capable of distinguishing between maize kernels of varying hardness and between fungal infected and sound kernels. While there are still limitations with hardware and software, these results provide the platform which would greatly assist with the determination of maize kernel hardness in breeding programmes without having to destroy the kernel. Further, NIR hyperspectral imaging could serve as an objective, rapid tool for identification of fungal infected kernels.

Thesis (Msc Food Sc (Food Science))--University of Stellenbosch, 2006. / Consumers demand beef products of consistent and satisfactory tenderness, acceptable meat colour, the necessary nutritional value, as well as being microbiologically safe. However, inconsistency in meat quality, and particularly tenderness, is a problem that has continuously plagued the meat industry Firstly, an investigation was undertaken to determine the muscle variation, particularly in the tenderness of South African beef muscles. Beef muscles were removed from the right-side of beef carcasses and the physical, chemical and sensory characteristics determined 72 h post-mortem. As the beef muscles differed significantly (P≤0.05) in these attributes, the need for increased attention to enhanced processing and meat ageing is accentuated. Therefore, two further investigations were executed, including an enhancement study and a shelf-life study. The enhancement study determined the time effect of a blend of sodium and potassium salts, various phosphates and lactates on the physical quality, chemical composition and sensory quality of South African beef muscles. The corresponding muscles were removed from the left-side of the same beef carcasses and infused 3 d postmortem. The changes in beef quality over 19 d and the initial proximate and mineral composition were determined. The infused beef increased in tenderness, while maintaining an acceptable red colour. The infused muscles had higher moisture and ash contents, and lower lipid and protein contents. The mineral content of the treated muscles increased due to the minerals contained in the infusion blend. For the sensory analysis, beef muscles were stored under vacuum for 24 h (4°C) until the physical data had been collected. Thereafter, the muscles were stored at −18°C until the descriptive sensory analysis could be performed. The infusion of beef muscles successfully enhanced the sensory attributes, resulting in significantly (P≤0.05) more juicy and tender beef. When used in a consumer preference test, the infused samples illustrated a significantly (P≤0.05) higher degree of liking. In the shelf-life study the effect of the blend on the physical attributes, proximate composition and microbial growth of South African beef muscle was determined. One muscle from the left-side of beef carcasses was infused 4 d post-mortem. The purge loss, colour changes and the microbial growth on the muscle steaks over 10 d (overwrap storage) was determined. The infused muscle showed greater colour loss (lower a*, b* and chroma values) during the 10-d period. Physical analysis (purge loss) indicated a significant difference (P≤0.05), with the treated sample losing 2.78% more purge. The infusion extended the microbiological shelf-life of beef by 1 d. Improvement of beef quality and its consistency is essential for the survival of the beef industry. The infusion of beef muscles has the potential to improve the current status of low meat consumption and inconsistent tenderness of fresh beef in South Africa. Despite decreased colour stability in the infused steaks, negatively affecting the purchasing decision of the consumer, the blend could still be applied successfully in the South African meat industry to extend the shelf-life of fresh beef and improve meat quality attributes, providing the consumer with a more acceptable beef product.

Thesis (MSc Food Sc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Listeria monocytogenes is a foodborne pathogen that has been isolated from a variety of food sources. It is the cause of the food-borne disease, listeriosis that shows symptoms such as meningitis, encephalitis and abortion. Different strains of L. monocytogenes exist and not all are thought to be pathogenic to humans. The aim of this study was to evaluate and compare conventional methods, culturing on selective (Oxford agar) and chromogenic (RAPID’L.mono agar) media, as well as speciesspecific and multiplex polymerase chain reaction (PCR) methods for the detection and identification of 94 L. monocytogenes isolates from various areas in an avocado processing facility, as well as the final product. To achieve a better understanding of the genetic diversity of the confirmed L. monocytogenes strains isolated from the avocado facility, two subtyping techniques, PCR-restriction fragment length polymorphism (PCR-RFLP) and pulsed-field gel electrophoresis (PFGE), were employed. All of the isolates were identified as Listeria species on both Oxford and RAPID’L.mono agar. On the RAPID’L.mono agar, 76 of the 94 isolates produced colonies typical of L. monocytogenes, with the remaining 18 showing colonies typical of L. innocua (n=13) and L. ivanovii (n=5). The species-specific PCR successfully amplified a 730 base pairs region of the hly gene of 80 of the 94 isolates. For the same 80 isolates the multiplex PCR successfully amplified 800, 517 and 238 base pair (bp) fragments of the inlA, inlC and inlJ genes, respectively. The remaining 14 isolates included the 13 isolates identified as L. innocua, as well as an isolate identified as L. monocytogenes on RAPID’L.mono. The results obtained on the Oxford agar showed a 100 % positive correlation when compared to the PCR results in identifying Listeria species, while the RAPID’L.mono had a 4 % false negative result in identifying L. monocytogenes compared to the PCR results. Sixty-four of the confirmed L. monocytogenes isolates were subtyped using PCRRFLP and PFGE. For the PCR-RFLP analysis, a 733 bp fragment of the inlA gene was successfully amplified for all of the isolates, followed by digestion with the restriction enzymes, AluI and Tsp509I. AluI produced three different banding patterns and Tsp509I produced two different banding patterns. Subtyping of the isolates using PFGE was carried out by macrorestriction of the genomic DNA with ApaI and AscI. The restriction fragments were resolved by PFGE and the fingerprints were classified into four clusters. In the combined analyses, cluster I contained forty-eight isolates (n=48), cluster II 1 isolate (n=1), cluster III fifteen isolates (n=15) and cluster IV 1 isolate (n=1). The PCR-RFLP results had a 98 % correlation with the PFGE results. The results of this study indicated inconsistencies between the results obtained by conventional and molecular detection methods for the identification of L. monocytogenes. Species-specific and multiplex PCR, however, proved useful to accurately detect and identify L. monocytogenes in a shorter period of time and could replace the use of conventional agar during identification. Both PCR-RFLP and PFGE proved useful in the subtyping of L. monocytogenes isolates with the PCR-RFLP being less expensive and results obtainable in a shorter period of time. / AFRIKAANSE OPSOMMING: Listeria monocytogenes is ‘n patogeen afkomstig van voedsel wat uit ‘n verskeidenheid voedselbronne geisoleer kan word. Dit is die oorsaak van die voedsel afkomstigde siekte, listeriosis met simptome soos harsingvliesontsteking, ensefalitis en aborsie. ‘n Verskeidenheid L. monocytogenes stamme bestaan, maar nie almal word as patogenies beskou nie. Die doel van hierdie studie was om konvensionele metodes, naamlik mikrobiologiese kweking op selektiewe (Oxford agar) en chromatografiese (RAPID’L.mono agar) media, sowel as spesies-spesifieke en multipleks polimerase ketting reaksie (PKR) metodes te evalueer en vergelyk vir die deteksie en identifikasie van 94 L. monocytogenes isolate geisoleer vanuit verskeie areas in ‘n avokado prosesseringsfasiliteit sowel as die finale produk. Om ‘n beter begrip van die genetiese diversiteit van die isolate wat as L. monocytogenes bevestig is te verkry, is twee subtiperingstegnieke, PKR-restriksiefragmentlengte polimorfisme (PKR-RFLP) en pulsveld jel-elektroforese (PVJE) toegepas. Beide Oxford en RAPID’L.mono agar het al die isolate as Listeria spesies geidentifiseer. Op die RAPID’L.mono agar het 76 van die 94 isolate kolonies tipies van L. monocytogenes gevorm, 13 kolonies was tipies van L. innocua (n=13) en vyf kolonies tipies van L. ivanovii (n=5). Die spesies-spesifieke PKR het ‘n 730 basis paar (bp) streek van die hly geen suksesvol geamplifiseer vir 80 van die 94 isolate. Die multipleks PKR het 800, 517 en 238 bp fragmente van die inlA, inlC and inlJ gene onderskeidelik, vir dieselfde 80 isolate suksesvol geamplifiseer. Die oorblywende 14 isolate het die 13 isolate wat as L. innocua geïdentifiseer is en die een isolaat wat as L. monocytogenes op RAPID’L.mono geïdentifiseer is ingesluit. Resultate verkry met die Oxford agar het 100 % ooreengestem met die PKR resultate vir die identifikasie van Listeria spesies. Die RAPID’L.mono het ‘n 4 % vals negatiewe resultaat gelewer in vergelyking met die PKR resultate. Vier-en-sestig van die bevestigde L. monocytogenes isolate is gesubtipeer deur PKR-RFLP en PVJE. Tydens die PKR-RFLP analise is ‘n 733 bp fragment van die inlA geen suksesvol geamplifiseer, gevolg deur vertering met die restriksie-ensieme, AluI and Tsp509I. AluI het drie verskillende bandpatrone opgelewer en Tsp509I twee verskillende bandpatrone. Subtipering deur PVJE is uitgevoer deur makro-restriksie van die genomiese DNA met ApaI en AscI. Die restriksie fragmente is geskei deur PVJE en die vingerafdrukke is in vier groepe geklassifiseer. Groep I het 48 isolate (n=48), groep II 1 isolaat (n=1), groep III 15 isolate (n=15) en groep IV 1 isolaat (n=1) gehad tydens die gekombineerde analise. Die PKR-RFLP resultate het 98 % ooreengestem met die van die PVJE. Die resultate van hierdie studie het teenstrydighede tussen die resultate van konvensionele en molekulêre deteksie metodes opgelewer vir die identifikasie van L. monocytogenes. Die spesies-spesifieke en multipleks PKR het egter beide goed te pas gekom vir die akkurate deteksie en identifikasie van L. monocytogenes en kan heel moontlik die gebruik van konvensionele agar tydens identifikasie vervang. Beide PKRRFLP en PVJE was nuttig vir die subtipering van L. monocytogenes isolate. PKR-RFLP is egter ‘n goedkoper tegniek en die resultate is in ‘n korter tydsperiode beskikbaar.