Lab-scale optimisation of Kefir beverage production from mass-cultured and freeze-dried kefir grains

Latsky, Anneline (2004-12)

Thesis (MSc Food Sc)--Stellenbosch University, 2004.

Thesis

ENGLISH ABSTRACT: Kefir is a fermented dairy beverage resulting from the fermentation of milk with reusable Kefir grains. The grains consist of a complex combination of lactic acid bacteria and yeasts in a symbiotic relationship, embedded in a polysaccharide matrix called kefiran. Various problems are experienced during the commercialisation of the ready-made Kefir beverage and, therefore, it is more advantageous to market the grains, enabling the consumer to produce the beverage at home. Kefir grains could be mass-cultured and then preserved by Iyohilisation for successful long-term storage and easy distribution, during commercialisation. The microbial balance of the Kefir grains changes during both mass-culturing and freeze-drying, which will have an influence on the sensory properties of the Kefir beverage produced. The aim of this study was the optimisation of the production of Kefir from mass-cultured grains and from freezedried mass-cultured grains respectively. The sensory characteristics of the fermented beverages produced from these mass-cultured and preserved grains were determined. Mass-cultured Kefir grains were activated and Kefir produced using nine methods with different activation times and temperatures, different grain:milk ratios (36, 72 and 108 g grains.l⁻¹) and with different heat-treated milks (pasteurised, double pasteerised and UHT). The best Kefir beverage was produced by activation of the grains at 22°C for two successive 24 h incubation periods, followed by Kefir production at 22°C for 18 h and a maturation period at 18°C for 6 h. The milk was replaced before every incubation period, excluding the maturation period, and the fermentation vessel was swirled five times at the start of fermentation and after 18 h. This method resulted in a sour beverage with a thick consistency and the characteristic effervescence and flavour of Kefir. The optimal grain:milk ratio was identified as 36 g grains.l⁻¹ and the best heat-treated milks for the production of Kefir beverage were UHT and double pasteurised milk. Mass-cultured Kefir grains were freeze-dried for 1, 2, 3 and 6 d and the moisture loss determined. Freeze-dried grains were rehydrated for 1, 2, 6, 12 and 18 h to determine the optimal rehydration time. A sensory analysis was performed to compare the properties of Kefir produced from mass-cultured grains (Me), freeze-dried mass-cultured grains that were rehydrated and activated (FDRA) and activated mass-cultured grains that were freeze-dried and rehydrated (AFDR). The chemical compositions of mass-cultured grains (MC), mass-cultured, freezedried grains (MCFD), mass-cultured, freeze-dried grains that were rehydrated and activated (FDRA) and activated mass-cultured grains that were freeze-dried and rehydrated (AFDR), were also investigated. The optimum time to freeze-dry grains was 2 d and to rehydrate freeze-dried gtains was 1 h. The sensory analysis indicated that Kefir beverages prepared from FDRA and AFDR grains did not differ significantly and were less fermented than Kefir produced from MC grains. It was concluded that Kefir with excellent sensory characteristics can be produced from mass-cultured grains. Freeze-drying is a better method to preserve Kefir grains than freezing due to mass loss during freezing and easier distribution and storage of freeze-dried grains. The supplementation of freeze-dried grains with additional lactic acid bacteria and yeast isolates should be investigated.

AFRIKAANSE OPSOMMING: Kefir is 'n gefermenteerde suiwelproduk wat geproduseer word deur die fermentasie van melk met herbruikbare Kefirkorrels. Die korrels bestaan uit 'n komplekse kombinasie van melksuurbakterië en giste en is ingebed in 'n polisakkaried matriks genaamd kefiran. Verskeie probleme word ondervind met die kommersialisering van die klaar voorbereide Kefirdrankie en dit is meer voordelig om die korrels te bemark. Dit sal die verbruiker daartoe in staat stel om self Kefir tuis te produseer. Kefirkorrels kan in massa gekweek word en dan gevriesdroog word om langtermyn storing en verspreiding te vergemaklik tydens kommersialisering. Die spesifieke mikrobiese balans van die Kefirkorrels word tydens massakweking en vriesdroging versteur. Dus sal hierdie twee prosesse 'n invloed hê op die sensoriese eienskappe van die Kefir drankie geproduseer. Die doel van hierdie studie was die optimisering van die produksie van Kefir vanaf massagekweekte korrels en gevriesdroogde massagekweekte korrels. Die sensoriese karakteristieke van die Kefir geproduseer met hierdie korrels is ondersoek. Massagekweekte Kefirkorrels is geaktifeer en Kefir is geproduseer met nege verskillende metodes met variasies in die tyd en temperatuur kombinasies, verskillende korrel:melk verhoudings (36, 72 en 108g korrels.l⁻¹) en verskillende hittebehandelde melke (gepasteuriseerd, dubbel gepasteuriseer en UHT). Die beste Kefirdrankie is geproduseer deur die aktivering van die korrels by 22°C vir twee 24 h inkubasieperiodes, gevolg deur Kefir produksie by 22°C vir 18 uur en 'n verouderingsperiode by 18°C vir 6 h. Die melk was voor elke inkubasieperiode vervang, uitsluitende die verouderingsperiode. Die fermentasie houer is vyf maal gedraai aan die begin van fermentasie en na 12 h. Hierdie metode het gelei tot 'n drankie wat suur was met 'n dik konsistensie en die karakteristieke vonkeling en geur van Kefir. Die optimale korrel:melk ratio is geidentifiseer as 36 9 korrels.l⁻¹ en die verkieslike hittebehandelde melke is dubbel gepasteuriseerde en UHT melk. Massagekweekte Kefirkorrels was vir 1, 2, 3 en 6 dae gévriesdroog en die massaverlies is bepaal. Gevriesdroog korrels is gerehidreer vir 1, 2, 6, 12 en 18 h om die optimale rehidrasietyd te bepaal. 'n Sensoriese analise is uitgevoer om die eienskappe te vergelyk van Kefir geproduseer van massagekweekte korrels (MC), gevriesdroogde massagekweekte korrels wat gerehidreer en geaktiveer is (FDRA) en geaktiveerde massagekweekte korrels wat gevriesdroog en gerehidreed is (AFDR). Die chemiese samestelling van massagekweekte korrels (MC), massagekweekte, gevriesdroogde korrels (MCFD), massagekweekte, gevriesdroogde korrels wat gerehidreer en geaktiveer is (FDRA) en geaktiveerde massagekweekte korrels wat gevriesdroog en gerehidreer is (AFDR), is bepaal. Die optimum tydperk vir vriesdroging van korrels was 2 d en vir rehidrasie van gevriesdroogde korrels was 1 h. Die sensoriese analise het aangedui dat Kefir wat van FDRA en AFDR korrels geproduseer is, nie betekenisvol van mekaar verskil het nie, maar minder gefennenteerd was as Kefir wat van Me korrels geproduseer is. Die gevolgtrekking is gemaak dat 'n Kefirdrankie met uitstekende eienskappe geproduseer kan word met massagekweekte korrels. Vriesdroging is 'n beter metode as bevriesing om Kefirkorrels te preserveer a.g.v die ver1iesvan massa tydens bevriesing en die vergemakliking van vervoer en verspreiding van gevriesdroogde korrels. Die aanvulling van gevriesdroogde korrels met addisionele melksuurbakterieêen giste moet nog ondersoek word.

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