The optimisation of accelerated yogurt production

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Date
2010-11
Authors
Smith, Esti-Andrine
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Publisher
University of the Free State
Abstract
English: Yogurt is one of the most popular of the dairy product range and a reduction in price would increase its popularity. If ways to accelerate the fermentation process could be found, making it possible to produce larger quantities with existing infrastructure, the affect would be reduced unit costs. This in turn should lead to a reduced shelf price. It was therefore decided to undertake a study into identifying a way or ways to accelerate the process without affecting the quality of the final product. Initially two main problems with the current yogurt fermentation process were identififJd. Firstly, the variation in the composition of fresh milk influences the repeatability of independent yogurt fermentations. This problem was eliminated by substituting fresh milk with milk powder. : Secondly, the need arose to standardise the starter culture's inoculation load and grpwth stage. In order to do this, a suitable growth medium which enables spectrophotometrical growth rtJonitoring was developed. This medium is referred to as milk serum in this study. The standardisatipn of the preinoculum load enabled repeatability and resulted in a 17 % decrease in fermentation tire. Thus, any variation observed in fermentation time can be attributed to the specific suppleme~t or condition evaluated. The development of the milk serum was an important breakthrough because it enabled 'the evaluation of the impact of several supplements and physical conditions on the yogurt fermentation! process. Various supplements were evaluated. They included a wide array of vitamins, minerals, sugars and amino acids. It was found that only a small number were capable of decreasing the fermentation time, and in those instances the final product was unsuitable for human consumption. This is an indication that the starter bacteria do not have a deficiency for any of those supplements when milk was used as growth medium. It could therefore be concluded that milk is an ideal and complete growth medium for the starter organisms. After the evaluation of supplements had been completed, the effect of different conditions on the fermentation process was investigated. This included proteolytic treatment, eleatrical current application, pressure applications, de-aeration and different incubation temperatures. The treatment of milk with a commercial proteolytic enzyme prior to fermentation increased the pH at which the yogurt coagulated marginally and also resulted in a sweeter product. Milk pre-treated with an electrical current did not significantly affect the free calcium content, which indicates that the structure of the casein micelle was still intact. Various pressure treatments of yogurt milk did not significantly influence the yogurt fermentation time. It did however influence the yogurt setting pH. As the pressure treatments increased, the setting pH subsequently also increased, which resulted in a sweeter yogurt. I The de-aeration of milk did not significantly influence the yogurt fermentation time or the setting pH. I Pasteurisation of milk resulted in the decrease of yogurt fermentation time in ~omparison to unpasteurised milk. During studies done on various incubation temperatures, the optimal growth temperatures of the respective starter bacteria was clearly noticeable/visible. The individual yogurt batches obtained by incubations at 39 °C, 42 °C and 45 •c exhibited properties unique to each of the two starter bacteria. At the optimal growth temperature of L. bulgaricus, 45 °C, the yogurt exhibited hig,her lactic acid content (pH reduction), whereas the yogurt produced at 39 °C, the optimum growth terpperature of S. thermophilus, had increased slime production. It was evident during incubation temperature studies that the incubation temperature during yogurt manufacture influences the rate lof lactic acid production, as well as the rheological properties of the final product. The results obtained in this study indicate that further research, whether it be to decrease yogurt fermentation time or to improve the product, would be of great value.
Afrikaans: Jogurt is 'n baie gewilde suiwelproduk en 'n prysverlaging sal die gewildheid verder laat toeneem. Dit kan geskied deur maniere te vind om die fermentasieproses le versnel en sodoende dit vir jogurt vervaardigers moontlik te maak om groter hoeveelhede te produseer sonder enige infrastruktuur uitbreidings. Die voordeel kan dan deurwerk tot 'n verlaagde verbruikersprys. Daar is gevolglik besluit om 'n studie te onderneem om te bepaal of daar maniere gevind kan word om die proses te versnel maar steeds hoe kwaliteitsvlakke te handhaaf. Aanvanklik is twee hoof probleme met die huidige jogurtfermentasieproses geidentifiseer. Eerstens, die variasie in varsmelksamestelling bernvloed die herhaalbaarheid van onafhanklike fermentasies. Hierdie probleem is geillimineer deur vars melk te vervang met melkpoeier. Tweedens het die behoefte ontstaan om die suurselkultuur se inokulasielading en groeifase te standaardiseer. 'n Gepaste groeimedium waarin groei spektrofotometries gemonitor kan word, moes egter eers ontwikkel word. Die medium word in hierdie studie beskryf as melkserum. Die standaardisering van die pre-inokulumlading het herhaalbaarheid bewerkstellig en het gelei tot 'n 17 % verbetering in fermentasietyd. Enige variasie in fermentasietyd sal dus toegeskryif word aan die spesifieke aanvulling of kondisie wat geevalueer is. Die ontwikkeling van die melkserum was 'n belangrike deurbraak, omdat dit die evaluering van die impak van verskillende aanvullings en fisiese kondisies op die jogurtfermentasieproses moontlik gemaak het. Verskillende aanvullings is geevalueer. Dit sluit in 'n wye reeks vitamiene, minerale, suikers en aminosure. Daar is gevind dat net 'n klein hoeveelheid van bogenoemde aanvullings die fermentasietyd verkort het maar in daardie gevalle was die finale produk nie geskik vir menslike gebruik nie. Hierdie is 'n bewys dat die suurselkultuur nie 'n tekort aan enige van die getoetste aanvullings het wanneer melk as groeimedium gebruik word nie. Daar kan dus aanvaar!word dat melk 'n ideale en volmaakte groeimedium vir die suurselorganismes is. Nadat die evaluering van die aanvullings voltooi is, is die effek van verskillende kopdisies op die fermentasieproses getoets. Dit het proteolitiese behandeling, elektriese stroom blootstelling, druktoepassings, ontlugting en verskillende inkubasietemperature ingesluit. Die behandeling van melk voor fermentasie met 'n kommersiele proteolitiese ensiem, he! die stallings pH van die jogurt effens verhoog en het tot 'n soeter produk gelei. Melk wat vooraf behandel is met 'n elektriese stroom se kalsiuminhoud is nie betekenisvol bernvloed nie, wat aandui dat die struktuur van die kasernmisel onbeskadig is. Verskeie drukbehandelings op melk voor fermentasie het nie die jogurtfermentasietyd betekenisvol beinvloed nie. Die pH waarby die jogurt gestol het, is egter beinvloed. Soos die drukbehandelings verhoog het, het die pH waarby die jogurt gestol het ook verhoog, wat tot 'n soeter produk gelei het. Die ontlugting van melk het geen betekenisvolle invloed op jogurtfermentasietyd of pH van stalling gehad nie. Die gebruik van gepasteuriseerde melk het gelei tot korter fermentasietyd in vergelyking met ongepasteuriseerde melk. Gedurende studies op verskeie inkubasietemperature was die optimale groeitemperature van die onderskeie suurselbakterie duidelik sigbaar. Die onderskeie jogurt lopies wat geploduseer is by onderskeidelik 39°C, 42 °C en 45 °C het die unieke eienskappe van die twee onderskeie suurselbakterie vertoon. By die optimale groeitemperatuur van L. bulgaricus, naamlik 45 °C, het die jogurt verhoogde vlakke van melksuurproduksie gehad. Dit was in teenstelling met die jogurt wat geproduseer is by 'n fermentasietemperatuur van 39°C, die optimale groei tempratuur van S. thermophilus, wat verhoogde slym produksie getoon het. Dit was duidelik tydens inkubasietemperatuurstudies dat die inkubasietemperatuur tydens jogurtfermentasie die tempo van melksuurproduksie, asook die reologiese eienskappe van die final produk, beinvloed. Die resultate van hierdie studie dui aan dat verdere navorsing van groat waarde sal 1ees, hetsy vir versnelde fermentasie of 'n verbeterde produk as einddoel.
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Keywords
Fermentation, Growth medium, pH, Physical conditions, Process optimisation, Serum, Supplements, Yogurt, Yogurt industry, Dissertation (M.Sc. (Microbial, Biochemical and Food Biotechnology))--University of the Free State, 2010
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