Thesis (MSc Food Sc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Please refer to fulltext for abstract. / AFRIKAANSE OPSOMMING: Sien asb volteks vir opsomming

Thesis(MSc Food Sc )--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Consumers are becoming more health conscious. Furthermore, time is a scarce human resource and therefore convenience is an important consideration when food choices are being made. A South African food company identified this trend and decided to develop a product that capitalised on these demands of health and convenience. The decision was made to develop a low-fat, low-cholesterol, low-saturated fatty acid, low-trans fatty acid, high-fibre wheat product with an intermediate glycemic index (GI). The market in Stellenbosch was scouted to determine whether a similar product already existed. Six products that made nutrient-, health- or any other claims were identified. Not one of the identified products, however, conformed to meet the requirements of the Department of Health for the product characteristics that were set. Therefore, the decision was made to continue the development of the low-fat, low-cholesterol, low-saturated fatty acid, low-trans fatty acid, high-fibre wheat product with an intermediate glycemic index (GI). To qualify as a low-fat product, the product had to contain less than 3 % fat. The ingredients were chosen with their fat content in mind. Fruit pulp is widely used in the preparation of baked low-fat products and was also used in this study to eliminate the use of butter, margarine and oil, but also to achieve the additional product criteria that was set by the food company, namely a chewy texture and a fruity flavour. Ingredients like soya flour, oatmeal, oats and wheat bran were chosen to increase the fibre content of the product, because all of these products have a fibre content of 10 g or more per 100 g. Two products were developed during 23 experiments. Except for the high fibre claim, both products met the criteria that were set before the development started, namely a low-fat, low-cholesterol, low-saturated fatty acid, low-trans fatty acid, high-fibre content and a calculated intermediate glycemic index (GI). One of the two concept products that were developed were chosen by an experienced panel to serve as basic product for an empirical study on the effect of different fibre levels on the glycemic index. Five different fibre levels were formulated by manipulating the amounts of wheat bran and oatmeal. The basic formula contained 6,25 % fibre and the other fibre levels were identified as: 4,39; 5,31; 7,45 en 8,17 %. The fibre levels were equal-distant. The prediction was made that the GI-value of the product will decrease as the fibre levels increase and the theoretical calculations confirmed this prediction. The real GI-values that were determined by blood glucose testings, however, showed an increase in GI-value up to the 6,25 % fibre level, followed by a.decrease in GI-value to the 8,17 % fibre level. It became apparent that more than just fibre played a role in the GI-values of the products. It is proposed that the results explained by fibre behaviour, starch gelatinisation and starch hydrolysis. Hundred households in Stell enbosch tested the developed product. Two fieldworkers identified 25 consumers in four retail stores in Stellenbosch and gave them the product and the questionnaire, which they had to complete at home after tasting the product. The questionnaires were then collected from the respondents' houses. A recognised measurement instrument, which is used by the South African food industry to determine the acceptability of a newly developed product, was used for assesing the results. The results showed that the orange flavour of the product led to a low overall acceptability of the developed product and that the other product concept (that was developed during the recipe development phase and not chosen by the panel) should be considered for testing its market potential. Another facet of the questionnaire determined the effect of buying practices, health consciousness and consumer knowledge on the consumer acceptability of the low-fat, high-fibre wheat product with an intermediate-GI-value. No correlation between these factors and consumer acceptability of the low-fat, high-fibre wheat product with an intermediate-GI-value were found. / AFRIKAANSE OPSOMMING: Die verbruiker word al meer gesondheidsbewus: Terselfdertyd is tyd 'n skaars menslike hulpbron, en word gerief gevolglik 'n belangrike oorweging tydens voedselkeuses. 'n Suid-Afrikaanse voedselmaatskappy het hierdie neigings geidentifiseer en besluit om 'n produk te ontwikkel wat aan hierdie vereistes van gesondheid en gerief voldoen. Daar is besluit om 'n lae vet-, lae cholesterol-, lae versadigdevetsuur-, lae transvetsuur-, hoe veselgraanproduk met 'n intermediere glukemiese indeks (GI) te ontwikkel. Die Stellenbosse mark is verken om vas te stel of daar reeds soortgelyke produkte op die mark was. Ses produkte wat nutrientinhoud-, gesondheid- of ander aansprake maak, is geidentifiseer. Geeneen van die produkte het egter aan die Departement van Gesondheid se konsepregulasies betreffende die etikettering van voedingsmiddels vir bogenoemde produkeienskappe voldoen nie. Gevolglik is besluit om met die ontwikkeling van die lae vet-, lae cholesterol-, lae versadigdevetsuur-, lae transvetsuur-, hoe veselgraanproduk met 'n intermediere GI voort te gaan. Om as 'n laevetproduk te kon kwalifiseer, moes die produk minder as 3 % vet bevat. Die bestanddele moes dus met inagneming van hul vetinhoud gekies word. Vrugtepulp word algemeen gebruik in die bereiding van gebakte laevetprodukte en is ook in hierdie studie gebruik om die gebruik van botter, margarien of olie te vermy, maar ook om aan die addisionele produkkriteria wat deur die maatskappy gespesifiseer is, naamlik 'n sagte tekstuur en vrugtige geur, te voldoen. Bestanddele soos soja-, hawermeel, hawer- en koringsemels is gekies om die veselinhoud van die produk te verhoog, aangesien hierdie bestanddele meer as 10 g vesel per 100 g bevat. Twee produkte is deur middel van 23 eksperimente ontwikkel. Met die uitsondering van die hoeveselinhoudaanspraak, het beide produkte aan die vereistes wat gestel is, naamlik 'n laevet-, laecholesterol-, laeversadigdevetsuur-, laetransvetsuur- en 'n hoeveselinhoud en 'n beraamde intermediere GI, voldoen. Een van die konsepprodukte is deur 'n ervare paneel gekies vir die empiriese studie waar die effek van verskillende veselvlakke op die GI bepaal is. 'n Standaard formule is aangepas om vyf verskillende veselvlakke te verkry deur die koringsemel- en hawermeelhoeveelhede te manipuleer. Die basisformule het 6,25 % vesel bevat en twee veselvlakke is daarbo en -onder as ge·identifiseer: 4,39; 5,31; 7,45 en 8,17 %, dit wil sê, veselvlakke met dieselfde grootte verskille. Daar is voorspel dat die GI-waarde van die produkte sou daal met 'n toename in die veselinhoud van die produk en die teoretiese berekeninge van die GI-waarde het hierdie voorspelling gestaaf. Die werklike GI-waardes wat met behulp van bloedglukoseresponse bepaal is, het egter 'n toename in GI-waarde tot by die 6,25 % veselvlak, gevolg deur 'n afname tot by die 8,17 % veselvlak aangedui. Dit het duidelik geword dat meer as slegs die veselinhoud 'n rol gespeel het by die GI-waarde van die produk. Die resultate is gevolglik aan die hand van die veselgedrag, styselgelatinisasie en styselhidrolise verklaar. Die verbruikersaanvaarbaarheid van die ontwikkelde laevet-, hoeveselproduk is by 100 huishoudings in Stellenbosch getoets. Twee veldwerkers het die verbruikers in vier kleinhandelaars in Stellenbosch genader en produkte met 'n gepaardgaande vraelys aan hulle oorhandig. Die produkte is tuis qeevalueer en die vraelyste is weer ingesamel. Ook vervat in die vraelys was 'n erkende meetinstrument wat deur die Suid-Afrikaanse voedselindustrie gebruik word vir die bepaling van verbruikersaanvaarbaarheid van 'n nuutontwikkelde produk. Uit die resultate het dit geblyk dat die lemoengeur van die produk gelei het tot die lae verbruikersaanvaarbaarheid van die ontwikkelde produk, en dat die ander produkkonsep (wat tydens die resepontwikkelingsfase ontwikkel is, en nie deur die ervare paneel gekies is nie) vir bemarkingspotensiaal getoets hoort te word. Die data wat uit die vraelyste ingesamel is, is ook gebruik om die effek van aankooppraktyke, gesondheidsbewustheid en verbruikerskennis op die verbruikersaanvaarbaarheid van die laevet-, hoeveselgraanproduk met 'n interrnediere-Gl-waarde te bepaal. Daar is geen verwantskap tussen hierdie faktore en die verbruikersaanvaarbaarheid van die laevet-, hoëveselgraanproduk met 'n intermedlere-Gl-waarde, gevind nie.

Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Developing countries such as South Africa are in dire need of nutritionally adequate dairy food and beverage sources that are ambient stable due to minimal access to refrigeration. One such product is Kefir, a naturally fermented milk beverage that originated in Caucasian China many centuries ago. The microorganisms responsible for fermentation of the milk are held together in a carbohydrate matrix in the form of small grains. These grains are then removed from the beverage prior to consumption, and added to fresh milk for new fermentations. This beverage holds great potential for large scale development due to the self-propagating nature of the grains, the lack of sophisticated equipment and knowledge necessary for production, and the appealing sensory characteristics of this beverage. This study was therefore performed as an initial investigation to determine the optimum fermentation conditions for large-scale grain production and optimal sensory appeal. Kefir grain production was found to be proportional to incubation temperature in the range studied (18°, 22°, 25° and 30°C), with maximum grain biomass increases of 500% for the Kefir incubated at 30°C over the 10 d trial. During fermentation of Kefir grains in milk, lactic acid and other metabolites are produced. Lactic acid results in coagulation of the milk, necessary to provide the characteristic texture and flavour of Kefir, as well as exerting a preservative effect. Lactic acid production was found to be strongly proportional to both incubation temperature and inoculum concentration. The samples containing 2% (w/v) Kefir grain inoculum concentration that were incubated at 25°C for 24 h were found to have optimum lactic acid levels for good quality Kefir (pH of 4.4 - 4.6 and TA of 1.0 - 1.15%). The other metabolites produced during Kefir fermentation are responsible for the specific flavour of Kefir, and include acetaldehyde, diacetyl, ethanol, acetone and 2-butanone. These compounds were studied using headspace gas chromatography over the fermentation period, which yielded good resolution and separation of all these compounds, however, only acetaldehyde, ethanol and acetone were found to be major metabolites in this study, These analytical results were then further compared to sensory results for key identified attributes, as obtained from a trained sensory panel, to enable recommendations for optimum fermentation conditions to be made. The studied attributes included sourness, sweetness, butteriness, creaminess, yoghurt flavour, cowiness, effervescence, yeastiness, smoothness and overall acceptability. It was apparent from this study that correlations between analytical and sensory data could be drawn, and that panellists were particularly accurate in detecting the attribute sourness resulting from the accumulated lactic acid in the Kefir. Overall acceptability also seemed to be intricately linked to the attribute creaminess, hence the regular literature references to full-cream Kefir as optimum for best sensory appeal. From this study, it was evident that Kefir with optimal sensory appeal is obtained with incubation for 18 h at moderate temperatures (22° or 25°C) and grain inoculum concentrations (0.8% w/v). / AFRIKAANSE OPSOMMING: In ontwikkelende lande soos Suid-Afrika, bestaan daar 'n groot behoefte aan voedsame suiwelprodukte wat stabiel is by kamer temperatuur aangesien 'n groot deel van die bevolking beperkte toegang tot verkoelingsfasiliteite het. Een so 'n produk is Kefir, 'n natuurlike gefermenteerde suiwelproduk wat sy oorsprong eeue gelede in China gehad het. Die mikroorganismes wat verantwoordelik is vir die fermentasie, is saamgebind in 'n koolhidraat matriks in die vorm van klein korrels. Hierdie korrels word verwyder uit die drankie voordat dit gedrink word, en word dan weer by vars melk bygevoeg vir 'n verdere fermentasie. Hierdie gefermenteerde produk het baie potensiaal vir massa-produksie, omdat die korrels natuurlik vermeerder, geen gesofistikeerde toerusting of kennis nodig is nie, en die finale produk hoogs aanvaarbare sensoriese eienskappe het. Die doel van die studie was om 'n inleidende ondersoek uit te voer om die optimum fermentasie toestande vir massakweking van korrels en die mees aanvaarbare sensoriese eienskappe te bepaal. Uit hierdie studie is gevind dat Kefirkorrel vermeerdering proporsioneel is tot die verhoging in inkubasie temperatuur in die gebied 18°, 22°, 25° en 30°C, met maksimum biomassa toenames van tot 500% vir Kefir wat vir 10 dae by 30°C geïnkubeer was. Gedurende fermentasie van Kefirkorrels in melk, word melksuur en ander metaboliete gevorm. Melksuur lei tot die verlaging van die pH van die melk, en veroorsaak stolling, wat noodsaaklik is vir die kenmerkende tekstuur en geur van Kefir, maar dien ook as 'n preserveermiddel. Daar is ook gevind dat melksuur produksie 'n direkte verband het met die inkubasie temperatuur en inokulum konsentrasie. Die monsters met Kefirkorrel inokulum konsentrasie van 2% (miv) wat vir 24 h by 25°C geïnkubeer is, het die optimale melksuur konsentrasies vir goeie kwaliteit Kefir bevat (pH van 4.4 - 4.6 en TA van 1.0 - 1.15%). Ander metaboliete wat belangrike geurkomponente van Kefir is, is asetaldehied, diasetiel, etanol, asetoon en 2-butanoon. Hierdie metaboliete is bepaal en geëvalueer met bodamp gaschromatografiese tegnieke gedurende die fermentasie, wat 'n goeie resolusie en skeiding gelewer het. In hierdie studie is slegs asetaldehied, etanol en asetoon as hoof Kefir metaboliete gevind. Die analitiese data is verder vergelyk met die sensoriese data van die hoof sensoriese komponente, soos bepaal deur 'n opgeleide sensoriese paneel, om die mees gunstigde fermentasie parameters te bepaal. Die geëvalueerde eienskappe was suurheid, soetheid, botterigheid, romerigheid, joghurt geur, koeismaak, gas inhoud, gisagtigheid, gladheid en algehele aanvaarbaarheid. Uit hierdie data is gevind dat daar wel 'n sterk korrelasie bestaan tussen die analitiese en sensoriese resultate, en dat paneellede in staat was om die suurheid, as gevolg van die gevormde melksuur, te bepaal. Algehele aanvaarbaarheid is definitief gekoppel aan romerigheid, daarom word volroommelk Kefir verkies bo die wat met afgeroomde melk berei is. Die data uit hierdie studie het ook getoon dat Kefir met optimale sensoriese eienskappe verkry is na 'n inkubasietyd van 18 h by "matige temperature" (22° of 25°C) en 'n Kefirkorrel inokulum van 0.8% (mIv).

Thesis (MSc Food Sc )--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Dried fruit is a well-known food product that has been produced for many years. The product characteristics have remained constant throughout this time with a moisture content of ca. 18 - 26% (mlm). However, in recent times there has been a definite trend towards a fmal dried fruit product in the intermediate moisture range with a moisture content of ca. 36%. The high water activity (aw) of the product (ca. 0.85) makes the product susceptible to microbiological spoilage and the product therefore requires a subsequent pasteurisation step to ensure a safe product. A further consequence of the increased moisture content, higher aw and the temperature of the pasteurisation step, is the increased rate of non-enzymatic browning reactions. Currently the shelf life is only 15 weeks while a minimum shelf life of 30 weeks is required to enable product export. Moisture sorption isotherms may be used to depict the relationship between moisture content and aw. Moisture sorption isotherms were thus determined for Royal type apricots and nectarines at 25° and 40°C. Samples, equilibrated at relative humidities in the range of 11-97%, were obtained using saturated salt solutions and a static gravimetric method. Isotherms were found to be of type I, typical of dried fruit. Six mathematical models namely; BET, GAB, Iglesias and Chirife, Halsey, Henderson, and Chung and Pfost, were fitted to experimental data. The GAB model predicted the aw of both apricots and nectarines the best at 25° and 40°C with the Henderson equation second best in all instances. The binding energy, as a function of moisture content, was calculated to determine energy requirements for drying. At low moisture contents « 20%) an increase of energy was required for drying. Discolouration of macerated dried Royal type apricots and nectarines during accelerated storage as affected by moisture (32, 36, and 40%, mlm) and sulphur dioxide (S02) content (2500, 3000 and 3300 mg.kg" for apricots; 1800, 2200 and 2600 mg.kg" for nectarines) was investigated. The macerated samples were stored at 30°, 40°, 50° and 60°C. Colour was quantified in terms of the L* value of the CIELab system (used throughout the study). Moisture and S02 contents affected both the initial fruit colour and the rate of discolouration. The highest L* values, i.e. lightest fruit colour, were obtained for fruit at 40% moisture content and the highest S02 levels. Increasing storage temperature accelerated the loss of moisture and S02. The influence of a 10°C increase in storage temperature on the rate of browning and thus shelf life was described in terms of the QIO value. QIO and aw values of apricots ranged from 1.96 - 2.47 and 0.833 - 0.890, respectively, while QIO values of 1.50 - 4.61 and aw values ofO.844 to 0.890 were obtained for nectarines. Discolouration of dried nectarine halves during accelerated storage at 40°C as affected by rehydration method, moisture content, packaging atmosphere and pasteurisation method, was investigated. The fruit halves were rehydrated using three different methods to obtain moisture contents of 36 and 40%, respectively. Dry heat and steam pasteurisation techniques were used to render a microbiologically safe product. Commercial packaging material was used and the atmosphere was modified with CO2 to lower the O2 concentration in the headspace. A two-step rehydration at 45°C, steam pasteurisation at 90°C for 150 minutes and packaging under a high CO2 atmosphere rendered a product with the best colour retention under accelerated storage conditions of 40°C for eight weeks. To confirm the results obtained with accelerated storage at temperatures that the product would normally be retailed at, shelf life tests were also performed at 5° and 25°C. Discolouration of whole dried Royal type apricot and nectarine halves as affected by rehydration method, moisture content, packaging atmosphere and pasteurisation method was investigated. The methodology for rehydrating, pasteurising and packaging the high moisture dried fruit developed in this study was compared against the standard method used by the industry. The new processing method increased shelf life. Samples were stored for a period of 30 weeks and were tested every five weeks to determine CO2 concentration in headspace, colour retention and S02 concentration of the fruit. Both apricots and nectarines achieved a shelf life of 30 weeks at both storage temperatures and an extrapolated shelf life of 89 weeks at 5°C, but only 32 weeks at 25°C. / AFRIKAANSE OPSOMMING: Droë vrugte is 'n welbekende voedselproduk en word reeds vir baie jare vervaardig. Die produkeienskappe het konstant gebly gedurende hierdie tydperk met 'n produkvoginhoud van ca. 18 - 26% (mlm). Daar is egter 'n tendens die afgelope tyd na 'n finale produk in die intermediêre voggebied met 'n voginhoud van ca. 36% en 'n water aktiwiteit (aw) van ca. 0.85. Hierdie verandering in voginhoud en aw maak die produk vatbaar vir mikrobiologiese bederf, en gevolglik word pasteurisasie benodig om dit te preserveer. 'n Verdere gevolg van die verhoogde voginhoud en aw en die hoë temperature van pasteurisasie, is die verhoogde tempo van nieensiematiese verbruiningsreaksies. Huidig is die produk se rakleeftyd 15 weke terwyl 'n minimum van 30 weke benodig word om hierdie produk suksesvol uit te voer. Vogsorpsie-isoterme kan gebruik word om die verwantskap tussen voginhoud en aw uit te beeld. Vogsorpsie-isoterme van Royal tipe applekose en nektariens is gevolglik bepaal by 25° en 40°C. Monsters, geëkwilibreer by relatiewe humiditeite van 11 - 97%, is verkry deur gebruik te maak van versadigde soutoplossings en 'n statiese gravimetriese metode. Tipe I isoterme, wat tipies van droëvrugte is, is verkry. Ses wiskundige modelle naamlik; BET, GAB, Iglesias en Chirife, Halsey, Henderson, en Chung en Pfost, is gepas op die data. Die GAB model het die aw van beide appelkose en nektariens by 25° en 40°C die beste voorspel en die Henderson model die tweede beste in al die gevalle. Die bindingsenergie as 'n funksie van voginhoud is bereken om die energie vereistes van droging te bepaal. By lae voginhoude (<20%) is 'n skerp styging in benodigde energie waargeneem. Die verkleuring van gemaalde gedroogde Royal tipe appelkose en nektariens gedurende versnelde opberging en die invloed van voginhoud (32, 36, en 40%, mlm) en swaweldioksied (S02) konsentrasie (2500, 3000 en 3300 mg.kg' vir appelkose; 1800, 2200 en 2600 mg.kg" vir nektariens) is ondersoek. Die gemaalde monsters is gestoor by 30°, 40°, 50° en 60°C. Kleur is gekwantifiseer in terme van L* waardes van die CIELab sisteem (ook gebruik vir daaropvolgende ondersoeke). Vog en S02 het albei die aanvanklike kleur asook die tempo van verbruining beïnvloed. Die hoogste L* waardes, d.i. die ligste kleur, is verkry vir die monsters met 40% voginhoud en die hoogte S02 vlakke. Verhoogde temperature tydens opberging het aanleiding gegee tot verhoogde verliese van vog en S02. Die invloed van 'n 10°C verhoging in opbergingstemperatuur op die tempo van verbruining en dus rakleeftyd, word beskryf in terme van QIO waardes. QIO en aw waardes van die appelkose het gestrek van 1.96 - 2.47 en 0.833 - 0.890, onderskeidelik, terwyl QIO waardes van 1.50 - 4.61 en aw waardes van 0.844 tot 0.890 verkry is vir die nektariens. Verkleuring van gedroogde nektarien halwes gedurende versnelde opberging by 40°C en die invloed van rehidrasie metode, voginhoud, verpakkingsatmosfeer en pasteurisasiemetode is ondersoek. Die vrughalwes is gerehidreer deur middel van drie metodes om die voginhoud te verhoog tot 36 en 40%, onderskeidelik. Droë hitte en stoompasteurisasie metodes is gebruik om 'n mikrobiologiese veilige produk daar te stel. Kommersiële verpakkingsmateriaal is gebruik en die CO2 konsentrasie van die atmosfeer in die verpakking is verhoog om die invloed daarvan te bepaal. 'n Twee-stap-rehidrasie by 45°C, stoompasteurisasie by 90°C vir 150 minute en 'n hoë C02 atmofeer het aanleiding gegee tot die monster met die beste kleurbehoud tydens versnelde opberging by 40°C vir agt weke. Om die resultate, verkry met die versnelde rakleeftyd studie, te bevestig by temperature waarby die produk normaalweg blootgestel sal word tydens kleinhandel, is 'n rakleeftyd studie uitgevoer by 5° en 25°C. Verkleuring van heel gedroogde Royal tipe appelkoos en nektarien halwes, die invloed van rehidrasie metode, voginhoud, verpakkingsatmosfeer en pasteurisasiemetode is ondersoek. Die metodiek vir die rehidrasie, pasteurisasie en verpakking van hoë vog droëvrugte ontwikkel in hierdie studie, is getoets teen die standaardmetode wat deur die industrie gebruik word. Die nuwe prosesseringsmetode het aanleiding gegee tot 'n langer rakleeftyd. Monsters is opgeberg vir 'n tydperk van 30 weke om die rakleeftyd te bepaal. Die CO2 konsentrasie in die pakkie, kleurbehoud en S02 konsentrasie van die vrugte is elke vyf weke getoets. Beide appelkose en nektariens het 'n rakleeftyd van 30 weke by albei opbergingstemperature behaal, terwyl 'n ekstra-gepoleerde rakleeftyd van 89 weke by 5°C en 32 weke by 25°C behaal is.

Thesis (MSc Food Sc )--Stellenbsosch University, 2003. / ENGLISH ABSTRACT: Kepi is a fermented milk beverage that originated in Eastern Europe. Traditional Kepi is a lightly acidic, carbonated beverage, with a slight yeasty taste. The starter used to produce this beverage is an irregularly shaped, yellowish-white grain-like structure similar in appearance to a cauliflower floret. The characteristic flavour of Kepi is produced by a complex spectrum of microbial species that include species of yeasts, lactic acid bacteria, acetic acid bacteria and mycelial fungi. At the end of the fermentation process the grainy starter can be recovered and re-used, since the microbes can easily be recovered as a solid matrix. The microbes comprising Kepi grains have only been identified using classical identification techniques such as selective growth media, morphological, physiological and biochemical characteristics. In this study, polymerase chain reaction (PCR)-based denaturing gradient gel electrophoresis (DGGE) analysis was used to typify and identify the complex microbial consortium present in the Kepi grains. A part of the 168 ribosomal RNA (rRNA) gene from the microbial population in mass-cultured, traditionally cultured and Irish Kepi grains were amplified using 'Eubacterial' specific primers and a part of the 268 rRNA gene was amplified using yeast specific primers. The PCR fragments were resolved by DGGE, resulting in unique fingerprints for the Eubacteria and yeasts present in the different Kepi grain types. The traditionally cultured Kepi grains were found to incorporate the most Eubacteria and yeast species, while the mass-cultured Kepi grains contained the lowest number of Eubacteria and yeast species. The different Eubacteria and yeast species were identified by cloning the PCR products and sequencing the cloned inserts. The obtained DNA sequences were compared to sequences available on the NCBI website. 8ix lactobacilli were identified: Lb. crispatus (KC-4); three Lb. species (KC-36, KC-38 and KC-43); and two unculturable lactobacilli (KC-2 and KC-3). The yeasts were identified as Saccharomyces cerevisiae (KC-y18) and Candida lambica (KC-y1). Unidentified isolates from kefiran strings that could not be identified using traditional methods were also identified by cloning the PCR products and sequencing the cloned inserts. The four isolates were identified as Lb. kefiri (KGI-A), Lb. parakefiri (KGIB), Lb. gallina rum (KGI-D) and an unculturable Lactobacillus (KGI-5). The phylogenetic relationship between the identified lactobacilli and the lactobacilli commonly found in Kepi grains was determined. The identified lactobacilli were grouped together in a clade with a bootstrap support value of 84%. The clade also contained representatives of Lb. delbrueckii subsp. lactis, Lb. acidophilus, Lb. gallinarum, Lb. helveticus, Lb. crispatus, Lb. species and unculturable lactobacilli. The bands in the peR-based DGGE fingerprints of the Eubacteria and the yeasts were identified, and a DGGE marker was subsequently constructed for the rapid identification of the Eubacteria present in mass-cultured Kepi grains. The data obtained in this study clearly showed that Kepi grains that are cultured differently, as well as Kepi grains from different origins have unique peRbased DGGE banding patterns for both the Eubacteria and yeasts present in the grains. The complex microbial consortium comprising Kepi grains could be typified and identified using PeR-based DGGE, DNA cloning and sequencing. The identification of the members of the microbial consortium is of importance for the future commercialisation of the mass-cultured Kepi grains. / AFRIKAANSE OPSOMMING: Kepi is 'n gefermenteerde melkdrankie wat sy oorsprong het in Oos Europa. Tradisionele Kepi is 'n effens suur, gekarboneerde drankie wat effens na gis smaak. Die beginkultuur wat gebruik word om dié drankie te maak is 'n oneweredige, geel-wit korrelagtige struktuur wat baie lyk soos 'n blomkoolkoppie. Die karakteristieke smaak van Kepi word geproduseer deur 'n komplekse spektrum mikrobiese spesies wat giste, melksuur- en asynsuurbakterieë en ~. misillêre fungi insluit. Aan die einde van die fermentasieproses kan die korrelagtige beginkultuur herwin word en weer gebruik word, aangesien die mikrobes maklik herwin kan word as 'n soliede matriks. Die mikrobes waaruit Kepikorrels bestaan, is nog slegs met behulp van klassieke identifikasiemetodes soos selektiewe groeimedia, morfologiese, fisiologiese and biochemiese eienskappe geïdentifiseer. In hierdie studie is polimerase kettingreaksie (PKR)-gebaseerde denaturerende gradiënt jelelektroforese (DGGE) analise gebruik om die komplekse mikrobiologiese konsortium in die Kepikorrels te tipeer en te identifiseer. 'n Gedeelte van die 16S ribosomale RNS (rRNS) geen van die mikrobiologiese populasie in massagekweekte, tradisioneel gekweekte en Ierse Kepikorrels is geamplifiseer met 'Eubakferiële' spesifieke peilers en In gedeelte van die 26S rRNS geen is geamplifiseer met gis spesifieke peilers. Die PKR fragmente is onderskei deur DGGE, wat unieke vingerafdrukke vir die Eubakteriële- en gisspesies in die verskillende Kepikorrel tipes gelewer het. Die tradisioneel gekweekte Kepikorrels het die meeste Eubakteriële- en gisspesies geïnkorporeer, terwyl die Ierse Kepikorrels die minste Eubakteriële- en gisspesies geïnkorporeer het. Die verskillende Eubakteriële- en gisspesies is geïdentifiseer deur klonering van die PKR produkte en deur die gekloneerde insetsels se volgordes te bepaal. Die ONS volgordes is dan vergelyk met volgordes wat op die NCSI webwerf beskikbaar is. Ses lactobacilli is geïdentifiseer: Lb. ctispetus (KC-4); drie Lb. spesies (KC-36, KC-38 en KC-43); en twee onkultiveerbare lactobacilli (KC-2 en KC-3). Die giste is geïdentifiseer as Saccharomyces cerevisiae (KC-y18) en Candida lambica (KC-y1). Ongeïdentifiseerde isolate van kefiranstringe is ook geïdentifiseer deur klonering van die PKR produkte en deur die gekloneerde insetsels se volgorde te bepaal. Dié vier isolate is geïdentifiseer as Lb. kefiri (KGIA), Lb. parakefiri (KGI-B), Lb. gallina rum (KGI-D) en 'n onkultiveerbare Lactobacillus (KGI-5). Die filogenetiese verwantskap is bepaal tussen die geïdentifiseerde lactobacilli en lactobacilli wat geredelik in Kepikorrels gevind word. Die geïdentifiseerde lactobacilli was saam in 'n groep gegroepeer met 'n bootstrap waarde van 84%. Die groep het ook verteenwoordigers van Lb. delbrueckii subsp. lactis, Lb. acidophilus, Lb. gallina rum, Lb. helveticus, Lb. crispatus, Lb. species en 'n onkultiveerbare laktobacilli ingesluit. Die bande in die PKR-gebaseerde DGGE vingerafdrukke van die Eubakterieë en die giste is geïdentifiseer, en 'n DGGE merker is gemaak vir die vinnige identifikasie van die Eubakterieë wat in die massagekweekte Kepikorrels teenwoordig is. Die data wat in die studie verkry, is wys duidelik dat Kepikorrels wat op verskillende maniere gekweek is, en wat verskillende oorspronge het, unieke PKR-gebaseerde DGGE bandpatrone het vir beide die Eubakterieë en giste wat in die korrels teenwoordig is. Die komplekse mikrobiologiese konsortium waaruit Kepikorrels bestaan kon getipeer en geïdentifiseer word deur PKR-gebaseerde DGGE, klonering van DNS en volgordebepaling. Die identifikasie van lede van die mikrobiologiese konsortium is belangrik vir die toekomstige kommersialisasie van die massagekweekte Kepikorrels.

Thesis (MSc Food Sc )--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Please refer to fulltext for abstract / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

Thesis (MSc Food Sc (Food Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The aim of this study was to investigate the impact of an extensive (free-range) and intensive (feedlot) production system on the consumer’s intrinsic preference cues (physical attributes, chemical composition, fatty acid profile, aroma, flavour, initial juiciness, sustained juiciness, first bite, residue, instrumental tenderness) for three muscles (Biceps femoris, Longissimus dorsi, Semimembranosus) of Dohne Merino lambs (8 months). Secondly to investigate the effect of natural exercise (grazing, extensive production systems) or restrictive movement (intensive production systems), on the muscle fiber type composition of the same lamb muscles and the subsequent effect on the meat quality characteristics. Intensively raised lambs produced carcasses with a significantly higher dressing percentage, thicker subcutaneous fat layer (13th rib and 3rd/4th lumbar vertebra) and a greater fat ratio (carcass composition). Meat of intensively raised lambs had a higher (p < 0.050) Homo-glinolenic (C20:3n6), Eicosapentaenoic (C20:5n3), Docosapentaenoic acid (C22:5n3) content and n3:n6 ratio. Extensively reared lambs had a higher (p < 0.050) slaughter weight, cold carcass weight and the meat of these lambs had a higher myoglobin content. Results of this study indicate that intensively reared lambs produced meat with more favourable sensory characteristics compared to the extensive production system as well as a significant increase in sensory tenderness for Biceps femoris muscle. Overall the Biceps femoris muscle was the muscle that was primarily affected by the treatment (production systems). The Biceps femoris from intensively raised lambs contained significantly more intramuscular fat and type IIB muscle fibers whereas the Bicpes femoris of the lambs from the extensive production system contained more (p < 0.050) insoluble collagen and type I muscle fibers. During texture profile analysis (instrumental tenderness test) the Longissimus dorsi and Semimembranosus of extensively raised lambs required a higher (p < 0.050) compression force during the first cycle of compression, indicating that these muscles are tougher. The results of this study provided valuable insight into the impact of production systems on lamb meat quality and that the application of intensive production systems will increase the sensory characteristics of the selected muscles from Dohne Merino lambs, especially the tenderness of the Biceps femoris, which has a high retail value. On the other hand health conscious consumers will prefer extensively produced meat due to the favourable n3:n6 ratio, intramuscular fat content and the presences of less visible fat (subcutaneous). / AFRIKAANSE OPSOMMING: Hierdie studie was tweedoelig en is uitgevoer op die Biceps femoris, Longissimus dorsi en Semimembranosus spiere van Dohne Merino lammers (8 maande oud). Die eerste doel van die studie was om te bepaal wat die effek van ‘n ekstensiewe (weiding) en intensiewe produksie sisteem sal wees op vleis verbruikers se algemene kwaliteit voorkeure (fisiese eienskappe, chemiese samestelling, vetsuur profile, aroma, smaak, sappigheid, taaiheid,). Tweedens om te bepaal tot watse mate natuurlike oefening, verkry deur weiding asook beperkte beweging as gevolg van voerkraal omstandighede, die spier vesel tipe samestelling sal verander en die direkte impak van die samestelling op kwaliteit eienskappe van vleis. Lammers van die intensiewe produksie sisteem het ‘n betekenisvolle verhoging in uitslagpersentasie, onderhuidse vet dikte (13de rib en 3de/4de lende werwel) en vet ratio (karkas samestelling) getoon. Die vleis van die lammers het meer (p < 0.050) C20:3n6, C20:5n3 en C22:5n3 vetsure bevat asook ‘n hoër n3:n6 ratio gehad. Lammers van die ekstensiewe produksie sisteem het ‘n betekenisvolle hoër slag en koue karkas gewig gehad. Die vleis van die lammers het meer (p < 0.050) mioglobien bevat as intensiewe lammers. Resultate van die studie dui aan dat die vleis van lammer van die intensiewe produksie sisteem meer gunstige sensories karakteristiek produseer in vergelyking met lammers van die ekstensiewe produksie sisteem, asook ‘n betekenisvolle verhoging in sensoriese sagtheid van die Biceps femoris spier. Die Biceps femoris was die spier in die studie wat die meeste geaffekteer was deur die behandeling (produksie sisteme). Die Biceps femoris spier van intensiewe lammers het meer intramuskulêre vet en tipe IIB spier vesels bevat teenoor die Biceps femoris van ekstensiewe lammers wat meer onoplosbare kollageen en tipe I spier vesels bevat het. Gedurende die tekstuur profiel analise (instrumentele sagtheid toets) het die Longissimus dorsi en Semimembranosus van ekstensiewe lammers a hoër kompressie krag vereis, wat aandui dat die spiere taaier is as die ooreenstemmende spiere van intensiewe lammers. Die resultate van die studie voorsien ons met waardevolle insig in die inpak van verskeie produksie sisteme op die kwaliteit van lams vleis. Die afleiding kan gemaak word dat die implementering van intensiewe produksie sisteem die sensoriese kwaliteit van die spiere van Dohne Merino lammers verbeter, veral die sagtheid van die Biceps femoris spier, wat ‘n hoë kommersiële waarde het. Laastens, gesondheidsbewus verbruikers sal verkies om vleis te koop van ekstensiewe lammers weens die gunstige n3:n6 ratio, spier vetinhoud en die minder sigbare vet (onderhuidse vet) op die vleis.

Thesis (MSc Food Sc (Food Science))--University of Stellenbosch, 2011. / Includes bibliography. / ENGLISH ABSTRACT: Alicyclobacillus species are thermo-acidophilic bacteria that produce highly resistant endospores able to survive the processing temperatures of fruit concentrate manufacturing, including evaporation and conventional pasteurisation (86 ° - 96 °C for ± 2 min). Alicyclobacillus endospores retain their viability in juice concentrates which, under favourable conditions, could germinate and multiply to numbers high enough to cause spoilage and product deterioration through the production of chemical taint compounds. This thesis reports on the distribution of Alicyclobacillus in the fruit concentrate processing environment and the effect of current manufacturing practices on the accumulation of Alicyclobacillus in fruit concentrates. These practices include the recirculation (recycling) of flume water as a means of water conservation, as well as continuous process running times when facilities operate at full capacity. This thesis also reports on the effect of fruit variety and skin type on the occurrence of Alicyclobacillus in fruit concentrates. Alicyclobacillus was monitored at nine processing stages of fruit concentrate manufacturing during the functioning of either a recirculating or a one-pass (not recirculated) flume water system. Significantly higher Alicyclobacillus levels were recovered in fruit mash, single strength juice, concentrate and the final pasteurised product (± 30 °Brix) during the functioning of a re circulating flume system, compared to when a one-pass flume system was functional (P < 0.05). Irrespective of the flume system, high Alicyclobacillus levels were recovered from the concentrate and condensate water (a by-product of juice concentration) from the evaporator, which makes this a point of concern during concentrate manufacturing. Manufacturing practices such as the recirculation of flume water and the recovery of condensate water for fruit washing purposes pose a potential risk of Alicyclobacillus contamination and accumulation in fruit concentrates and the processing environment. The effect of continuous process running times on Alicyclobacillus was monitored in a facility that was operating at full capacity. Sampling occurred every 12 h at four processing stages, during a processing tempo of 1.8 - 2.0 t h-1 for 108 h. Vegetative cells increased significantly (P < 0.05) in single strength juice and condensate water after 84 h of processing, with 3.15 and 3.85 log10 cfu mL-1 recovered, respectively. Similar accumulation patterns of vegetative cells were observed in concentrate and the final pasteurised product. Endospores in single strength juice, concentrate and the final product were also the highest after 84 h of processing with 1.32, 1.59 and 1.64 log10 cfu mL-1, respectively. When fruit concentrate manufacturing facilities process at full capacity, a restriction in the continuous process running time to under 84 h in between CIP procedures, along with good manufacturing practices, can minimise Alicyclobacillus accumulation in fruit concentrates. The effect of fruit skin type, specifically hairy-skinned stone fruits (peach and apricot) and smooth-skinned pome fruits (apple and pear) on the occurrence of Alicyclobacillus in concentrates were examined. Apple concentrate samples had the highest occurrence (average %) of vegetative Alicyclobacillus cells (50%), followed by apricot (40%), peach (15%) and pear (10%) concentrates. The occurrence of Alicyclobacillus endospores in fruit concentrate samples were also the highest in apple (50%), followed by pear (25%), apricot (20%), and peach (10%) concentrates. The occurrence of Alicyclobacillus vegetative cells and endospores did not differ significantly (P > 0.05) between concentrates from hairy-skin and smooth-skin fruit varieties. Thus it was concluded that fruit washing steps prior to processing was more critical for the control of Alicyclobacillus than the type of fruit skin being processed. / AFRIKAANSE OPSOMMING: Alicyclobacillus spesies is termo-asidofiliese bakterieë wat hoogs bestande endospore produseer met die vermoë om prosesseringstemperature, insluitend verdamping en konvensionele pasteurisasie temperature (86 ° - 96 °C vir ± 2 min), tydens die vervaardiging van vrugtekonsentraat te oorleef. Alicyclobacillus endospore behou hul lewensvatbaarheid in vrugtekonsentrate en kan in gunstige toestande ontkiem en vermeerder tot getalle wat wansmake in produkte kan veroorsaak weens die produksie van chemiese verbindings. Hierdie tesis doen verslag oor die verspreiding van Alicyclobacillus in die vrugtekosentraat prosesseringsomgewing en oor die effek van huidige produksie praktyke op die akkumulasie van Alicyclobacillus in vrugtekonsentrate. Die praktyke sluit in, die hersirkulering van leigeut (transport) water as ‘n wyse van waterbesparing, asook aaneenlopende prosesseringstye wanneer vrugtekosentraat fabrieke teen ‘n volle kapasiteit prosesseer. Daar word ook verslag gedoen oor die effek van verskillende vrug variëteite en vel tipes op die voorkoms van Alicyclobacillus in vrugtekonsentrate. Alicyclobacillus was gemonitor by nege verskillende stadiums van ‘n vrugtekosentraat prosesseringsfabriek tydens die funksionering van óf 'n hersirkulerende óf ‘n deurlopende (nie-hersirkulerende) leigeut waterstelsel. Alicyclobacillus vlakke was beduidend hoër in gemaalde vrugte, enkelsterkte sap, konsentraat en die finale gepasteuriseerde produk (± 30 °Brix), gedurende die funksionering van 'n hersirkulerende leigeutstelsel, in vergelyking met die funksionering van ‘n deurlopende leigeutstelsel (P < 0.05 ). Ongeag van die leigeutstelsel, is hoë vlakke Alicyclobacillus gevind in konsentraat en kondensaat water ('n by-produk van die sap konsentrasie porses) vanuit die verdamper, en maak dit dus ‘n punt van belang tydens die vervaardiging van vrugtekonsentraat. Daar is gevind dat vervaardigingspraktyke soos die hersirkulasie van leigeut water en die herwinnig van kondensaat water moontlike risiko’s inhou vir die besoedeling en akkumulasie van Alicyclobacillus in vrugtekosentrate en die prosesseringsomgewing. Die effek van aaneenlopende prosesseringstye op Alicyclobacillus was gemonitor in 'n vrugtekosentraat prosesseringsfabriek wat teen volle kapasiteit prosesseer. Steekproefneming het elke 12 h by vier prosesseringsstadiums geskied, tydens 'n prosesseringstempo van 1.8 - 2.0 t h-1 vir 108 h. Vegetatiewe selle het beduidend toegeneem (P < 0.05) in die enkelsterkte sap en kondensaat water na 84 uur van prosessering, met 3.15 en 3.85 log10 kve mL-1, onderskeidelik verhaal. Soortgelyke akkumulasiepatrone vir vegetatiewe selle was waargeneem in konsentraat en die finale gepasteuriseerde produk. Endospore in enkelsterkte sap, konsentaat en die finale produk was ook die hoogste na 84 uur van prosessering, met 1.32, 1.59 en 1.64 log10 kve mL-1, onderskeidelik. Wanneer vrugtekonsentraat fabrieke teen volle kapasiteit prosesseseer, kan 'n beperking in aaneenlopende prosesseringstye tot onder 84 h tussen CIP prosedures, gepaard met goeie vervaardigingspraktyke, die akkumulasie van Alicyclobacillus in vrugte konsentate verminder. Die effek van verskillende vrug variëteite se vel tipes, spesifiek harige-vel steenvrugte (perske en appelkoos) en gladde-vel kernvrugte (appel en peer) op die voorkoms van Alicyclobacillus in vrugtekonsentrate was ondersoek. Appel konsentaat monsters het die hoogste voorkoms van vegetatiewe Alicyclobacillus selle gehad (gemiddelde %), met (50%), gevolg deur appelkoos (40%), perske (15%) en peer (10%) konsentraat. Die voorkoms van Alicyclobacillus endospore in vrugte konsentraat monsters was weer die hoogste in appel (50%), gevolg deur peer (25%), appelkoos (20%), en perske (10%) konsentraat. Die voorkoms van Alicyclobacillus vegetatiewe selle en endospore het nie betekenisvol tussen konsentrate van harige-vel en gladdevel vrug variëteite verskil nie (P > 0.05). Die gevolgtrekking was dat vrugte wasstappe, voor die prosessering van vrugtekonsentraat, van meer belang is vir die beheer van Alicyclobacillus as die vel tipe van die vrug variëteit wat geprosesseer word.

Thesis (MSc Food Sc)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Alicyclobacilli are endospore-forming, thermophilic, acidophilic bacteria (TAB) that survive the pasteurisation process and spoil acidic fruit juices through the production of the taint compound guaiacol. Guaiacol causes an undesirable odour with an unpleasant smoky, medicinal or phenolic-like taste. This thesis reports on the precursors, vanillin and vanillic acid metabolised to guaiacol by Alicyclobacillus spp. in fruit juice, the pathway of guaiacol production and the spoilage potential of contaminated fruit juices supplemented with these precursors. A high performance liquid chromatography method with UV-diode array detection (HPLC-DAD) was developed for the simultaneous detection and quantification of guaiacol and its precursors. Alicyclobacillus acidoterrestris FB2 was incubated at 45 °C for 7 d in Bacillus acidoterrestris (BAT) broth supplemented with ferulic acid, vanillin or vanillic acid. The cell concentrations were determined every 24 h and the concentration of the precursors and the production of guaiacol was determined using HPLC-DAD. The guaiacol production was also determined using the peroxidase enzyme colourimetric assay (PECA). Alicyclobacillus acidoterrestris produced guaiacol from vanillin and vanillic acid, confirming both vanillin and vanillic acid as precursors for guaiacol production by A. acidoterrestris FB2. Furthermore, a metabolic pathway directly from vanillin to guaiacol was identified in this study. However, guaiacol was not produced by A. acidoterrestris FB2 in the samples supplemented with ferulic acid and it is, therefore, not considered a direct precursor for guaiacol production by A. acidoterrestris. The spoilage potential of apple juice supplemented with either 10 mg L-1 or 100 mg L-1 vanillin or vanillic acid by A. acidoterrestris FB2 (106 cfu mL-1) was also evaluated. The production of guaiacol increased with the increase in vanillin or vanillic acid concentrations (in BAT broth and apple juice) indicating that the concentration of vanillin and vanillic acid present in fruit juice will influence the spoilage potential of the juice. Guaiacol concentrations in apple juice well above the best estimated threshold value of guaiacol for taste (0.24 – 2.00 μg L-1) and odour (0.50 - 2.32 μg L-1) was produced by A. acidoterrestris FB2 in the apple juice supplemented with 10 mg L-1 vanillin or vanillic acid. This indicates that fruit juice with a vanillin or vanillic acid concentration as low as 10 mg L-1 has the potential to spoil if the juice is contaminated with A. acidoterrestris. The concentrations of vanillin and vanillic acid in different fruit juices can be used to indicate if a specific fruit juice is susceptible to guaiacol spoilage by Alicyclobacillus spp. In the development of juice products and different blends of fruit juices, special care must be taken not to concentrate the amount of vanillin and vanillic acid present in the fruit juices. / AFRIKAANSE OPSOMMING: Alicyclobacilli is endospoor-vormende, termofiliese, asidofiliese bacterie (TAB) wat die pasteurisasie proses oorleef en suur vrugtesappe bederf met die produksie van ‘n taint komponent guaiakol. Guaiakol veroorsaak ‘n ongewensde reuk en onaangename rookagtige, medisinale of fenoliese smaak. Hierdie tesis doen verslag oor die voorloper komponente, vanillien en vanilliensuur in vrugtesappe wat gemetaboliseer word na guaiakol deur Alicyclobacillus spesies, die padweg van guaiakol produksie en die bederfbaarheid van gekontamineerde vrugtesap aangevul met hierdie voorloper komponente. ‘n Hoëprestasie vloeistof chromatografie metode met UV-deteksie (skanderend) (HPVC) is ontwikkel vir die gesamentlike deteksie en kwantifisering van guaiakol en die voorloper komponente. Alicyclobacillus acidoterrestris FB2 is geïnkubeer by 45 °C vir 7 d in Bacillus acidoterrestris (BAT) medium aangevul met feruliensuur, vanillien of vanilliensuur. Die sel konsentrasies is elke 24 h bepaal en die aangevulde komponente en die geproduseerde guaiakol is bepaal deur van HPVC gebruik te maak. Die guaiakol konsentrasies is ook bepaal deur van die peroksidase ensiem kolorimetriese bepaling (PEKB) gebruik te maak. Alicyclobacillus acidoterrestris het guaiakol geproduseer vanaf vanillien en vanilliensuur, dus is beide vanillien en vanilliensuur bevestig as voorlopers van guaiakol produksie deur A. acidoterrestris FB2. A padweg direk van vanillien na guaiakol is in hierdie studie geïdentifiseer. Guaiakol is nie geproduseer deur A. acidoterrestris FB2 in the monsters wat met feruliensuur aangevul is nie en feruliensuur is dus nie ‘n direkte voorloper van guaiakol produksie deur A. acidoterrestris. Die bederf potensiaal van appelsap aangevul met 10 mg L-1 of 100 mg L-1 vanillien of vanilliensuur deur A. acidoterrestris (106 kve mL-1) is ook geëvalueer. Die produksie van guaiakol het toegeneem met die toename in vanillien of vanilliensuur konsentrasies (in beide BAT en appelsap) wat aandui dat die konsentrasie vanillien en vanilliensuur teenwoordig in vrugtesap die bederfbaarheid van die sap sal beïvloed. Guaiakol konsentrasies in appelsap hoog bo die drumpel waardes van guaiacol vir smaak (0.24 – 2.00 μg L-1) en reuk (0.50 - 2.32 μg L-1) is geproduseer deur A. acidoterrestris FB2 in die appelsap monsters aangevul met 10 mg L-1 vanillien of vanilliensuur. Hierdie verskynsel dui aan dat vrugtesap met ‘n vanillien of vanilliensuur konsentrasies van so laag as 10 mg L-1 die potensiaal het om te bederf indien die sap gekontamineer is met A. acidoterrestris. Die konsentrasies van vanillien en vanilliensuur in verskillende vrugtesappe kan gebruik word om aan te dui of ‘n spesifieke vrugtesap ‘n hoë risiko het vir guaiakol bederf deur Alicyclobacillus spesies. Tydens die ontwikkeling van vrugtesap produkte en verskillende mengsels van vrugtesappe moet seker gemaak word dat die hoeveelhede vanillien en vanilliensuur in die sappe nie gekonsentreer word nie.

Thesis (MSc Food Sc)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The relationship between malt fermentability and rheological variables, measured by means of the Rapid Visco Analyser (RVA) and application of multivariate data analysis, was investigated. The RVA Kilned Malt method was optimised to achieve maximum rheological discrimination between malt samples, differing in fermentability. Five concentrations and two particle sizes were used to investigate each malt sample. Data were analysed by two different data analysis techniques, namely principal component analysis (PCA) and analysis of variance (ANOVA). Rheological variables for peak-height, -width, -area and time occurrence, were able to discriminate between high (Metcalfe, Flagship), intermediate (SSG 585, PUMA) and low malt fermentability (SSG 506, SSG 564). Variation in particle size showed insignificant (P>0.05) fermentability discrimination. The malt to water ratio of 1:1.5 provided the best discrimination in fermentability. PCA applied to the entire dataset was the superior data analysis technique. Partial least squares (PLS) regression and Soft Independent Modeling of Class Analogy (SIMCA) were applied to predict malt fermentability. Recorded RVA data was regressed with both apparent attenuation limit (AAL) and free amino nitrogen (FAN), independently. Developed PLS calibration models were validated by test set and segmented crossvalidation for AAL and FAN, respectively. The SIMCA classification model developed was based on different malt fermentability classes, each PCA validated independently by test set validation. A strong correlation between RVA analysis and AAL was obtained (r=0.92), while FAN delivered a weak correlation (r=0.59). Regarding the SIMCA model; the proportion of test set samples correctly classified in terms of malt fermentability was 83%. South African malt blends were predicted to have low malt fermentability. Simulated blends were predicted to have high fermentability when using a minimum of 80% Metcalfe blended with SSG 506. Blends containing higher percentages of the low malt fermentability cultivar (SSG 506) were predicted to have an overall intermediate fermentability. Different experimental conditions were investigated during RVA analysis (i.e. instrument model; time/temperature profile, enzyme activity and heating/cooling rate). Rheological measurement using different RVA models gave similar PCA results, indicating adequate sensitivity of the older instrument for discrimination purposes. Matching the time/temperature profile used in the commercial brewery mashing process was rejected due to increased analysis time and rheological noise while reducing fermentability discrimination. Inactivating malt enzymes prior to RVA analysis provided useful sample information, such as the large starch granule’s mean diameter, extract and starch content, by measuring peak height and iv time to peak. The amount of starch damage inflicted on a malt sample increased after repeated centrifugal milling, but was unaffected by the sieve size used. Multivariate data analysis is a suitable statistical technique applied to rheological data and provided more relevant information than traditional univariate techniques. The RVA can be considered an ideal instrument within a grain laboratory as it allowed the investigation of different operating conditions. It is beneficial to use an inexpensive, routine method of analysis to measure various interacting factors. RVA rheological measurement demonstrated to be a decisive monitor of malt fermentability and is highly recommended to be incorporated within the barley breeding, malting and brewing industries. / AFRIKAANSE OPSOMMING: Die verwantskap tussen mout fermenteerbaarheid en reologie-veranderlikes, gemeet met die “Rapid Visco Analyser” (RVA) en toepassing van meerveranderlike data analise is ondersoek. Die RVA “Kilned Malt” metode is geoptimeer om maksimum reologiese diskriminasie, tussen gars kultivars van verskillende fermenteerbaarheid, te lewer. Vyf konsentrasies en twee partikel groottes is gebruik in die ondersoek vir elke mout monster. Data is deur beide hoof komponent analise (HKA) en variansie-analise (ANOVA) ondersoek om die verskillende data analise metodes met mekaar te vergelyk. Reologiese veranderlikes vir piek-hoogte, - wydte, -area en -vormingstyd, kon diskrimineer tussen hoë (Metcalfe, Flagship), intermediêre (SSG 585, PUMA) en lae (SSG 506, SSG 564) mout fermenteerbaarheid. Variasie in partikel grootte kon nie beduidende diskriminasie in fermenteerbaarheid aantoon nie. Die mout-totwater konsentrasie van 1:1.5 het die beste diskriminasie in fermenteerbaarheid gelewer. Die toepassing van HKA op die hele datastel was die beter analitiese tegniek. Parsiële kleinste kwadrate (PKK) regressie en Sagte Onafhanklike Modellering van Klas Analogie (SIMCA) is toegepas om mout fermenteerbaarheid te voorspel. Regressie tussen RVA data en skynbare attenuasie limiet (AAL), sowel as vrye amino stikstof (FAN) inhoud, is afsonderlik uitgevoer. Die geldigheid van regressie modelle is deur middel van toets stel en gesegmenteerde kruis-validasie vir AAL en FAN onderskeidelik uitgevoer. SIMCA klassifikasie modelle is gebaseer op verskillende mout fermenteerbaarheids-klasse, waarvan elke HKA klas individueel geldig is. RVA analise het ‘n sterk korrelasie met AAL (r=0.92), maar ‘n swak korrelasie met FAN (r=0.59) getoon. Die SIMCA model het 83% van toets stel monsters as korrek geklassifiseer in terme van mout fermenteerbaarheid. Suid Afrikaanse mout mengsels is voorspel as swak fermenteerbaar. Nagebootste mengsels is voorspel as hoogs fermenteerbaar wanneer minimum 80% Metcalfe met SSG 506 vermeng word. Sodra ‘n hoër persentasie van die swakker fermenteerbaarheids-kultivar (SSG 506) bygevoeg is, word intermediêre fermenteerbaarheid voorspel. Tydens RVA analise is verskillende eksperimentele toestande ondersoek (byvoorbeeld instrument model; tyd/temperatuur profiel; ensiem aktiwiteit en verhittings/verkoelings tempo). Die gebruik van verskillende RVA modelle het soortgelyke HKA resultate gelewer. Dus bevat die ouer instrument aanvaarbare sensitiwiteit vir diskriminasie doeleindes. Nabootsing van die tyd/temperatuur profiel in die kommersiële brouproses is verwerp, aangesien analise tyd en reologiese geraas toegeneem het, terwyl fermenteerbaarheidsdiskriminasie verminder het. Inaktivering van mout ensieme voor RVA analise lewer nuttige monster inligting; deur veranderlikes soos piek-hoogte en piek-tyd te meet, kan die groot stysel korrel se gemiddelde deursnit, ekstrakwaarde en stysel inhoud verkry word. Herhaalde sentrifugale maling van ‘n mout monster lei tot beskadiging van stysel, maar dit word nie deur sif grootte beïnvloed nie. Die toepassing van meerveranderlike data analise op reologiese data is waardevol en lewer meer relevante inligting in vergelyking met tradisionele eenveranderlike data analise. Die RVA is ‘n ideale instrument vir gebruik in ‘n graan laboratorium aangesien dit verskillende operatiewe kondisies kan ondersoek. Die gebruik van ‘n enkele, goedkoop, roetine analitiese metode is voordelig en het die potensiaal om ‘n magdom interaktiewe faktore te meet. RVA reologiese meting demonstreer die vermoë as ‘n deurslaggewende tegniek vir die bepaling van mout fermenteerbaarheid, gevolglik word toepassing sterk aanbeveel binne die gars teëlings-, vermoutings- en brouers-industrieë.