Production and quality analysis of Tibetan kefir milk slice

Abstract: In order to produce a new type of tablet dairy food, Tibetan kefir was chosen as the research object to conduct the investigation. Tibetan kefir was cultured in fresh milk at 28 in an amount of 15 (g/mL) for backup, and the fresh milk is replaced every 24 h. An orthogonal experiment was conducted to optimize the formula of Tibetan kefir milk tablet based on 12 trained sensory evaluations' score. The optimal ratio was 10% skimmed Tibetan kefir lyophilized powder (Tibetan kefir was cultured at skimmed milk at 28℃ for 24 h, filtering out the Tibetan kefir, pouring the fermented liquid into several Petri dishes, which did not exceed the 2/3 height of the Petri dish. Petri dish are frozen at -60℃ for 3-4 h, then vacuum freeze drying them at 20 Pa vacuum degree for 24 h until the temperature of clapboard and the sample are the same, crush them for backup), 40% whole milk power, 14% sugar, 2.5% magnesium stearate, 2.5% sodium carboxymethyl cellulose (CMC-Na) and 31% skimmed milk powder. Based on the data detected by an electronic nose, the figures of linear discrimination analysis (LDA) were drawn and the flavor differences between skimmed and whole Tibetan kefir milk slice were shown objectively. It showed that the electronic nose can be used to differentiate and evaluate the whole milk Tibetan kefir milk tablet and the skimmed Tibetan kefir milk tablet, but cannot evaluate the different kind of skimmed Tibetan kefir tablet, which provides a reference for detection of the Tibetan kefir by electronic nose directly in the future. Using GB 4789.35 - 2010 as the method to count the number of the three kind of lactic acid bacteria in Tibetan kefir milk tablet, the sorting of the three kind of lactic acid bacteria's quantity in the optimal sensory Tibetan kefir milk tablet is Lactobacillus > Bifidobacterium > Streptococcus thermophilus. The total number of initial lactic acid bacteria in Tibetan kefir is 9.26 on the numerical, after 120 d preservation at 4℃, then the total number of lactic acid bacteria in Tibetan kefir decreased to 7.41 on the numerical, which is satisfied to the market requirement. It does not need a special storage environment, and the appropriate cryopreservation can guarantee the strain energy for a long period. In addition, the structure and the distribution of strains of Tibetan kefir and skimmed Tibet kefir milk tablet were compared by SEM. Bacillus accounted for the vast majority of the Tibetan kefir strains, the Bacillus in the Tibetan kefir tablet showed aggregation morphology. Considering the cost and quality, we believed that the Tibetan kefir milk tablet should have strong production feasibility and wide applications in food market.