| Summary: | 博士 === 國立臺灣大學 === 畜產學研究所 === 88 === Kefir is kind of ethanol-fermented milk, made by kefir grains, which is considered as an aid in the therapy of gastro-intestinal disease. This study collected three groups of kefir grains from different regions in Taiwan, and investigated the effect of quality change during the period of fermentation and storage of three cultures, the influence of storage condition on activity of kefir grains, and the condition that could increase the production of kefiran. All this results could be used as the reference and basis of commercialization of kefir and kefiran.
In test I, three groups of kefir grains, which were collected from Xien-zhu, I-lan and Taipei regions in Taiwan, were labeled as T1, T2 and T3, respectively. The distributions of these three groups of kefir microbes in kefir grains were totally different under scanning electron micrographs. The incubation temperature had more influence on increasing the mass of kefir grains compared to the adding ratio of kefir grains; higher mass gain of kefir grains could be gotten under incubation temperature range from 21 to 27℃. In the sensory evaluation scores of kefirs, the acceptability of T3 in three groups of kefir of Taiwan is the highest.
In test II, the quality change of kefir during the fermentation of whole or skim milk at 21℃ in a period of 8 days was investigated. The consistence of curd of whole milk fermented for 3 days had better structure under scanning electron micrographs. Lactic acid bacteria and yeast could increase in number from 106 to 1012 CFU/ml and 104 to 109 CFU/ml, respectively. The production of kefiran had tremendous increase after 30 hours. During 60 days storage period, the viscosity of kefirs made by whole milk were significantly higher than that of kefirs made by skim milk, when the product was defined as kefir with pH 4.7. Lactic acid bacteria only had few increases in early storage period; however yeast appeared increasing state during whole storage period. The largest amount of kefir is reached after 20-30 days, and the amount of kefirs made by whole milk is significantly higher than that of kefirs made by skim milk.
In test III, the influence of the refrigeration, freeze and lyophilization on kefir starters were compared. Kefir grains, which refrigerated in skim milk, had higher activity and rapidly loss activity when storage times longer than 3 weeks. Early storage phase had more impact on lactic acid bacteria; however, later storage phases on yeast. Kefir grains with reduced activity greatly after starters freeze-dried, but the activity of lactic acid bacteria remained stable without any decreased during storage period of 8 months.
Test IV investigated the influence of incubation condition on the growth of microbial starters and production of kefiran. Whey media was a good base for growth of microbes; addition of glucose, lactose, sucrose and yeast extract could increase growth of microbes. Prolongation of incubation time, increased nitrogen content, addition 50 g/l of glucose and sucrose, and addition of yeast extract above 30 g/l could significantly increase the production of kefiran.
From the result shown above, we could get products of high acceptability and commercialization of kefir by adding 5% (w/v) starters of T3 in whole milk and fermenting for 36 to 72 hours. The commercialization of kefir grains could be achieved by manufacturing kefir grains in large amount under 21 to 27℃, and the refrigerating time no longer than 3 weeks. Adding C, N-source and yeast extract could increase the production of kefiran.
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