Thesis (MSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Kepi is a refreshing, fermented dairy beverage that has been consumed for centuries and is traditionally made by incubating Kepi grains in milk. The Kepi grain is a complex starter culture consisting of a variety of lactic acid bacteria and yeasts. The successful marketing of the grains requires the effective preservation of the microbes present in the grains as well as an appropriate packaging that will retain the acidification activity of the preserved grains over an extended period of time. The aim of this study was to evaluate different preservation techniques and packaging materials in terms of their respective abilities to retain grain viability and activity over an extended storage period. Four different preservation techniques (freezing at -18°C, refrigeration at 4°C, air-drying and Iyophilisation) and three packaging materials including a low density polyethylene film (LOPE), an oriented polyester film (OPET) and a metallised oriented polyester film (MOPET), were evaluated. Activity tests were used to evaluate the impact of the preservation techniques in terms of the retainment of the acidification activity of the preserved grains, and the storage potential of the preserved and packaged grains. The activity tests included changes in pH, %TA, lactic acid production and lactose and volatile compound content over an 18 h fermentation period. In addition, the microbial viability of the packaged Iyophilised grains after two months of storage, was also investigated. Frozen and refrigerated grains showed the best retainment of the acidification activity over a 10-month storage period. Air-drying and Iyophilisation showed a good retention of the activity up to three months of storage, but the application of these techniques both resulted in a retarded initial acidification activity. After 10 months of storage, the air-dried and Iyophilised grains showed only a low acidification activity. No volatile compounds could be detected during the course of the fermentation period, due to the relative short fermentation period of 18 h. Overall, the best retainment of the fermentation activity was given by the LOPE and the OPET packaging films. However, the storage period had a considerable influence on the retention of the activity of the packaged Iyophilised grains. The viability study of the Iyophilised packaged Kepi grains after two months of storage showed leuconostocs and lactobacilli to be the prevalent microbes in the grains. Low microbial counts were obtained from the lactococciselecting medium for all three of the differently packaged Kepi grains, whereas no growth was observed on the media that selected for the propionibacteria and yeasts. The OPET packaging film provided the best preservation of the microbial composition. It was, therefore, concluded that all four preservation techniques would be suitable for the preservation of Kepi grains and the subsequent storage at room temperature for three months. However, for storage periods of 10 months or longer the use of freezing and refrigeration are recommended as most suitable preservation techniques. All three of the packaging materials proved to be suitable for the packaging and storage of the Iyophilised Kepi grains for periods of up to one month. However, for storage periods of two months or longer, the use of the OPET film for the packaging and retainment of the acidification activity of the Iyophilised grains, can be recommended. / AFRIKAANSE OPSOMMING: Kepi is 'n eeu-oue verfrissende, gefermenteerde suiweldrankie wat tradisioneel vervaardig word deur Kepikorrels in melk te inkubeer. Hierdie Kepikorrels bestaan uit 'n komplekse samestelling van hoofsaaklik melksuurbakteriee en giste. Die effektiewe preservering en verpakking van die korrels is belangrike voorvereistes vir die suksesvolle bemarking daarvan. Dis belangrik dat die preserverinq en die verpakking van die korrels 'n positiewe bydrae sal lewer tot die behoud van die fermentasie-aktiwiteit van die mikrobes in die korrels oar 'n verlengde opbergingsperiode. Die doel van hierdie studie was om die opbergingspotensiaal van verskillend gepreserveerde en -verpakte Kepikorrels te evalueer in terme van die behoud van die lewensvatbaarheid en fermentasie-aktiwiteit van die samestellende mikrobes. Vier verskillende preserveringstegnieke (bevriesing by -18°C, verkoeling by 4°C, lugdroging en vriesdroging) en drie verskillende tipes verpakkingsmateriale, nl. 'n "low density polyethylene film" (LOPE), 'n "oriented polyester film" (OPET) en 'n "metallised oriented polyester film" (MOPET) was qeevalueer. Aktiwiteitstoetsing was gebruik om die impak van die verskillende preserveringstegnieke en die verpakkingsmateriale op die behoud van die fermentasie-aktiwiteit van die Kepikorrels te ondersoek. Die verskillende aktiwitieitstoetse wat gedoen is, het die meting van die verandering in pH, %TA, melksuur- en laktosekonsentrasie oor 'n fermentasieperiode van 18 h ingesluit. Tesame met die aktiwitietstoetsing IS die lewensvatbaarheid van die gevriesdroogde, verpakte Kepikorrels na twee maande van opberging ook ondersoek. Die bevrore en verkoelde Kepikorrels het die beste behoud van aktiwitiet na 'n 10-maande opbergingsperiode getoon. Die gelugdroogde en gevriesdroogde korrels het 'n goeie behoud van aktiwiteit getoon vir 'n opbergingstydperk van tot drie maande, maar beide die lugdroging- en vriesdrogingstegnieke het 'n aanvanklik vertraagde fermentasie-aktiwitieit getoon. Na 'n : opbergingsperiode van 10 maande het beide die gelugdroogde en gevriesdroogde korrels egter 'n lae fermentasie-aktiwiteit getoon. As gevolg van 'n relatiewe kort fermentasieperiode van 18 h kon geen vlugtige komponente in die Kepimonsters gevind word nie. Die LDPE- en OPET-verpakkingsmateriale het die beste behoud van die fermentasie-aktiwiteit van die gevriesdroogde korrels getoon. Die opbergingsperiode het egter 'n aansienlike impak op die aktiwitietsbehoud van die korrels gehad. Die lewensvatbaarheidstudie het aangetoon dat Leuconostoc- en Lactobacillus-spesies die oorheersende mikrobes in die verpakte, gevriesdroogde Kepikorrels na 'n opbergingsperiode van twee maande was. Lae mikrobiese tellings vir al drie van die verpakkingsmateriale was gevind op die Lactococcusselekterende medium, en geen mikrobegroei kon op die giste- en propionibakteriee-selekteringsmedium waargeneem word nie. Die beste behoud van die mikrobiese samestelling in die verpakte, gevriesdroogde Kepikorrels was gevind vir die OPET-verpakkingsmateriaal. Die gevolgtrekking kan gemaak word dat al vier die preserveringstegnieke geskik is vir die preservering van die Kepikorrels en die daaropvolgende opberging van drie maande by kamertemperatuur. Vir opbergingsperiodes van 10 maande en langer word die gebruik van bevriesing en verkoeling aanbeveel as die mees geskikte preserveringstegnieke. AI drie verpakkingsmateriale kan gebruik word vir die verpakking en opberging van gevriesdroogde Kepikorrels vir 'n tydperk van een maand. Indien 'n opbergingsperiode van twee maande of langer verlang word, word die OPET-verpakkingsmateriaal aanbeveel vir die suksesvolle behoud van die fermentasie-aktiwiteit van die Kepikorrels.

Thesis (MScFoodSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: The preservation of various fresh fish products is achieved by either smoking, salting, canning, freezing or fermenting a highly perishable raw product. Since many of these facilities are not readily available, the use of fermentation as a means of preserving the product has been extensively practiced. However, the fermentation of fish is a time consuming practise and only by accelerating the process would it be possible to ensure the production of a more cost effective and readily available safe end-product. The quality of the fermented fish product is partially determined by the fermentation conditions and the metabolic activity of the microbes present. The rapid identification of the microbes present during the fermentation would enable the selection of possible starters to ensure an accelerated production of high quality fermented fish products. This study was thus undertaken to develop identification fingerprints for bacteria isolated from fermented fish products. A 1300 bp fragment of the 16S rRNA genes of each of the bacteria previously isolated was successfully amplified using the PCR technique. The isolates included strains of the genera Bacillus, Staphylococcus, Sphingomonas, Kocuria, Brevibacillus, Cryseomonas, Vibrio, Stenotrophomonas and Agrobacterium. The data obtained can, therefore, be used in the identification of these microbes isolated from other similar fermented fish products. The fingerprints could also be used to assist in determining the dominant microbial populations responsible for the characteristic qualitative changes occurring in the fish product during fermentation. The microbial composition of a fermenting fish product partially determines the quality of the end-product, therefore, the use of selected bacterial starters could result in the accelerated production of a microbial safe fermented fish product. A further objective of this study was to accelerate the production of a fermented fish product by inoculating macerated trout with either selected lactic acid bacteria (LAB) or with selected bacteria with high proteolytic activity over a 30 day fermentation period. The LAB included a combination of Lactobacillus plantarum, Lactococcus diacetylactis and Pediococcus cerevisiae strains, whereas the bacteria with high proteolytic activity included strains of Kocuria varians, Bacillus subtilis, two strains of B. amyloliquefaciens and a combination of these bacterial species. The quality of the fermented product was determined using changes in product pH, titratable acidity (%TA) and free amino nitrogen (FAN) formation as efficiency parameters. The data obtained during the fermentation of the macerated trout showed that the selected starters did not have a significant effect on the pH decrease in the product over a 30 day fermentation period. The LAB strains did not have a significant effect on the %TA of the fermenting fish product, yet the presence of these bacteria appeared to limit the FAN production in the product. The bacteria with high proteolytic activity resulted in slightly enhanced %TA values and a higher FAN content in the fermented product. It was also determined that the LAB and Kocuria varians, in contrast to the Bacillus spp. inoculums, did not survive the fermentation conditions well, possibly due to the low pH environment. The presence of the starter bacteria in the fermenting fish mixture at the end of the fermentation was also successfully determined with the use of the PCR-RFLP technique. The fermented fish product, obtained at the end of the fermentation period, had a good aroma and compared favourably to similar commercially available fermented fish products. The use of different microbial starters could in future enable the production of a diverse range of high quality products, which could be produced and marketed locally. / AFRIKAANSE OPSOMMING: Die preservering van ‘n verskeidenheid vars vis produkte word bereik deur die hoogs bederfbare produk te rook, te sout, te blik, te vries of te fermenteer. Aangesien baie van hierdie fasiliteite nie geredelik beskikbaar is nie, is die gebruik van fermentasie as ‘n preserverings metode al ekstensief beoefen. Die fermentasie van vis is egter 'n tydsame proses en slegs deur die versnelling van die proses sal dit moontlik wees om die produksie van ‘n meer koste effektiewe en geredelike beskikbare veilige eindproduk te verseker. Die kwaliteit van die gefermenteerde vis produk word gedeeltelik bepaal deur die fermentasie kondisies en die metaboliese aktiwiteit van die mikrobes teenwoordig. Die vinnige identifikasie van die mikrobes teenwoordig gedurende die fermentasie sal die seleksie van moontlike suursels om die versnelde produksie van hoë kwaliteit gefermenteerde vis produkte moontlik maak. Hierdie studie is dus onderneem om identifikasie vingerafdrukke vir bakteriee wat gei'soleer is van gefermenteerde vis produkte moontlik te maak. ‘n 1300 bp fragment van die 16S rRNA gene van elkeen van die bakteriee wat voorheen gei'soleer is, is suksesvol geamplifiseer deur die PCR tegniek. Die isolate sluit in stamme van die genera Bacillus, Staphylococcus, Sphingomonas, Kocuria, Brevibacillus, Cryseomonas, Vibrio, Stenotrophomonas en Agrobacterium. Die data kan dus gebruik word in die identifikasie van hierdie mikrobes as dit gei'soleer word van ander gefermenteerde vis produkte. Die vingerafdrukke kan ook gebruik word om die dominante mikrobiese populasies wat verantwoordelik is vir die kenmerklike kwalitatiewe veranderinge wat plaasvind in die vis produk gedurende die fermentasie, te identifiseer. Die mikrobiese samestelling van ‘n fermenterende vis produk bepaal gedeeltelik die kwaliteit van die eindproduk, daarom kan die gebruik van geselekteerde bakteriese suursels die versnelde produksie van ‘n mikrobies veilige gefermenteerde vis produk teweeg bring. ‘n Verdere doel van hierdie studie was om die produksie van ‘n gefermenteerde vis produk te versnel deur fyngemaakte forel met of geselekteerde melksuurbakteriee of met geselekteerde bakteriee met hoë proteolitiese aktiwiteit te inokuleer oor ‘n 30 dag fermentasie periode. Die melksuurbakteriee het ingesluit ‘n kombinasie van Lactobacillus plantarum, Lactococcus diacetylactis en Pediococcus cerevisiae, terwyl die bakterieë met hoë proteolitiese aktiwiteit stamme van Kocuria varians, Bacillus subtilis, twee stamme van Bacillus amyloliquefaciens en ‘n kombinasie van hierdie bakteriese stamme ingesluit het. Die kwaliteit van die gefermenteerde produk is bepaal deur die veranderinge in die pH, titreerbare suur (%TS) en vrye amino stikstof (VAS) vorming van die produk as effektiwiteits parameters te gebruik. Die data wat verkry is gedurende die fermentasie van die fyngemaakte forel het gedui daarop dat die geselekteerde suursels nie ‘n merkwaardige effek op die afname in pH in die produk oor ‘n 30 dag fermentasie periode het nie. Die melksuurbakteriee het nie ‘n merkwaardige effek op die %TS van die gefermenteerde vis produk gehad nie, terwyl dit geblyk het dat die teenwoordigheid van hierdie bakterieë die produksie van VAS in die produk belemmer het. Die bakteriee met hoe proteolitiese aktiwiteit het ‘n effense verhoogde %TS en ‘n hoër VAS inhoud in die gefermenteerde produk veroorsaak. Dit is ook bepaal dat die melksuurbakteriee en Kocuria varians, in teenstelling met die Bacillus spp. inokulums, nie die fermentasie kondisies goed oorleef het nie, moontlik as gevolg van die lae pH omgewing. Die teenwoordigheid van die suursel bakteriee in die fermenterende vis mengsel aan die einde van die fermentasie is ook suksesvol bepaal met die PKR-RFLP tegniek. Die gefermenteerde vis produk, verkry aan die einde van die fermentasie periode, het ‘n goeie aroma gehad en het goed vergelyk met soortgelyke kommersieel beskikbare gefermenteerde vis produkte. Die gebruik van verskillende mikrobiese suursels kan in die toekoms die produksie van ‘n diverse reeks hoë kwaliteit produkte wat plaaslik geproduseer en bemark kan word moontlik maak.

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: The South African avocado fruit industry is export driven and the successful storage of fruits for extended periods is, therefore, essential. It was recorded that 7.7 million cartons were exported during the 1995 season. The shipping of the avocados takes approximately 15 days and the fruits are being stored at low temperatures to minimise the possibility of fruits softening. Unfortunately low temperature storage results in chilling injury. A possible method to increase avocado resistance to chilling injury is to administer a heat shock treatment. In this way the fruits are protected from chilling injury by inducing the formation of so-called heat-shock proteins which render the cell membranes more resistant to chilling injury. The objective of this study was to evaluate different heat shock treatment protocols as a method of preventing or minimising chilling injury and to extend the shelf-life of avocado fruits while exporting at the lowest possible temperature. Examining the effect of different temperatures and exposure times on the quality of the different avocado cultivars pursued this. The exterior chilling injury on each fruit was quantified and the firmness and internal quality parameters evaluated. A total of 32 Experimental Studies were conducted. The results showed that the Hot Water Heat shock Treatment (HWHST) worked effectively for the South African 'Fuerte' cultivar between 40° and 42°C for exposure times of between 20 and 30 min. The 'Edranol' cultivar also showed promising results between 40° and 42°C for exposure time of between 8 and 22 min. The HWHST was not effective on the South African 'Hass' cultivar. The 'Ryan' cultivar with its thick skin made this cultivar less susceptible to chilling injury and therefore HWHST would be unnecessary. The 'Pinkerton' cultivar had a lot of factors that influenced the results. Therefore, more research needed to be done on the 'Pinkerton' cultivar, before any conclusions could be obtained from this cultivar, although it showed potential. Hot air treatment worked fairly well, but unfortunately the long exposure time needed made this treatment unpractical. Throughout the whole study the importance of maturity surfaced as a major role in all the aspects of post harvest quality. / AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse avokado vrugtebedryf is hoofsaaklik gerig op die uitvoermark en daarom is dit belangrik dat die vrugte vir 'n bepaalde tyd suksesvolopgeberg kan word. Die sensus opname gedurende die 1995 seisoen het getoon dat 7.7 miljoen bokse avokados uitgevoer is. Die avokados word vir ongeveer 15 dae per boot vervoer, wat kan lei tot vrugte wat sag word. Om dit te verhoed, word die vrugte by lae temperature opgeberg. Ongelukkig veroorsaak lae opbergingstemperature koueskade. 'n Moontlike metode om avokados te beskerm teen lae temperature en koueskade te verminder, is om 'n hitteskok behandeling toe te pas. Op hierdie manier word die vrugte beskerm teen koueskade deur die vorming van sogenaamde hitteskok proteïene wat die selwande meer bestand maak teen koueskade. Die doel van hierdie studie was om die verskillende hitteskok behandelings protokols te evalueer as 'n metode van beskerming of vermindering van koueskade en om sodoende die rakleeftyd van avocados te verleng as die vrugte by lae temperature uitgevoer word. Eksperimente is uitgevoer om die effek van verskillende temperature en blootstellingstye op die kwaliteit van die verskillende avokado kultivars te bepaal. Die koueskade op die oppervlakte van elke vrug is bepaal en die fermheid en interne kwaliteit parameters is geëvalueer. In totaal is daar altesaam 32 Eksperimentele Studies gedoen. Die resultate het gewys dat die Warm Water Hitteskok Behandeling (WWHB) effektief was op die Suid-Afrikaanse 'Fuerte' kultivar by temperature tussen 40° en 42°C en by blootstellingstye van tussen 20 en 30 min. Belowende resultate is ook met die 'Edranol' kultivar by temperature tussen 40° en 42°C met blootstellingtye van tussen 8 en 22 min behaal. Die WWHB was oneffektief vir die Suid-Afrikaanse 'Hass' kultivar. Die 'Ryan' kultivar se dik skil het hierdie kultivar minder vatbaar gemaak vir koueskade en daarom was 'n WWHB onnodig gewees. By die 'Pinkerton' kultivar kon daar nog nie 'n gevolgtrekking gemaak word nie, aangesien daar nog baie faktore is wat ondersoek moet word, alhoewel die kultivar baie potentiaal getoon het. Warm lug behandeling het potensiaal gehad, maar die lang blootstellingstye het hierdie behandeling onprakties gemaak. Gedurende die hele studie is daar klem gelê op die rypheisgraad van die vrugte wat na vore gekom het as 'n belangrike faktor wat 'n hoofrol speel in al die aspekte van die na-oes kwaliteit.

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.