| Summary: | 碩士 === 國立臺灣大學 === 動物科學技術學研究所 === 96 === Kefir is a beverage produced by lactic-alcoholic fermentation of milk using kefir grains. However, kefir grains have a complex microbiological composition that makes it difficult to obtain an optimal and constant starter culture necessary for the production of a quality kefir beverage. Thus, the purpose of this study was to create a mimic kefir grain using encapsulated pure cultures to produce a milk beverage with characteristics similar to those of traditional kefir.
In this study, yeast (Klu. marxianus Y1, S. turicensis Y2, P. fermentans Y3) and LAB (Lb. kefiranofaciens H1, Lb. kefiri H2, Leu. mesenteroides H3, Lc. Lactis H4) were entrapped in microcapsules with three different groups. The encapsulated ratio of the strains was based on the distribution of kefir grains. After microencapsulation, both microencapsulated starter and kefir grain were incubated with milk at 20ºC, sieved and transferred to fresh pasteurized milk every 24 h. This procedure was repeated at 28 times. The sensory, microbial and chemical characteristics of microcapsule kefir and traditional kefir were determined. Results indicated that there were similar performance between microcapsule and traditional kefirs in microbial and chemical characteristics during the consecutive cultivations. Among different microcapsule groups, Group B, entrapped all strains of lactic acid bacteria and yeast, respectively in one microcapsule, had better organoleptic property with easy manufacturing processing. Consequently, this group was chosen for the following study.
Since kefir quality depends on microflora property, the scanning electronic microscopy and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) were also used to observe kefir starters in group B and grains. The SEM showed that the short-chain lactobacilli and lactococci were occupied on the surface and the long-chain lactobacilli were in the inner of LAB microcapsules. For yeast, high density of yeast cells was entrapped on crack of the surface and the interior of the microcapsules with surrounded by the short-chain lactobacilli. The distribution of the species of LAB and yeasts in kefirs from grains and microcapsules showed that Leu. mesenteroides and K. marxianus were the predominating microflora in both kefirs. There was no difference among cultivations.
In conclusion, kefir produced by microencapsulated starter, the basic microbiological, physicochemical and sensory characteristics of traditional kefir were reproduced with less acidity, which might increase the acceptability for kefir drink. This alternative procedure eliminating the problems arising from the use of kefir grains make possible the production of a standard product in the dairy industry.
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