| As yoghurt, a probiotic drink rich in lactic acid bacteria has drawn more and more attention and love, the production and sales of yoghurt has increased year by year. However, waste yoghurt come from the process of production and marketing, which forms about2.0%of the total yield. Investigations show that as long as the packaging is intact, the yoghurt would be uncontaminated and with no safety problem. And the nutritional and probiotic value can also be retained, so the waste yoghurt from manufacturing enterprise is potential to be used as feed additive. However, due to its high water content and requirements of the cold chain in transportation and storage, there are severe limits to produce feed additive out of waste yoghurt. This situation restricts the recycle of waste yoghurt and also forces most companies to pay third-party processing institutions for treating it as general waste, or directly discharge them into municipal sewer network, both of which cause great waste of resources. Therefore, it is a common problem for yoghurt industries.In this paper, we studied the method to recover the Lactic acid bacteria and nutrients in waste yoghurt. The main research in this paper included as follow:1) production process of yoghurt-sodium alginate/chitosan microcapsules by extrusion technology using sodium alginate and chitosan as wall material,2) investigation of the protective effect of the microencapsules on the survival rate of Lactic acid bacteria lactobacillus,3) optimization of microencapsulation process,4) characteristics analysis of the microcapsules,5) drying processes of microencapsulation, and6) shelf life determination of the microcapsules.The characteristics of the microcapsules were determinated by simulating the environment of gastrointestinal tract. Results show that Lactic acid bacteria are slowly released in the stimulated gastric juice, but much more quickly with a comparative larger amount in the stimulated intestinal juice. The quantity of alive bacteria in microcapsules was more than10’cfu/g. The microcapsules were subglobose with1-2mm in diameter and the water content of microcapsules was about1%. Based on the results of the Lactic acid bacteria survival rate, the optimum process of microencapsulation was drawn that the yoghurt-sodium alginate volume ratio of1:2, sodium alginate concentration (W/V) of2%, chitosan concentration (W/V) of1%, and the liquid pH value of6. The protective function of glycerol and maltodextrin on Lactic acid bacteria in freeze-drying was insidious. The possible explanation was that proteins in yoghurt could be natural protective agent and they have been matched up in the best condition. Compared with freeze-drying, vacuum drying not only kept a higher livability of Lactic acid bacteria, but also enjoyed a lower cost. Results of accelerated shelf life testing showed that vacuum packaging or normal packaging didn’t affect the residual rate of alive lactic acid bacteria and the encapsulation played the most important roles in storage. Shelf life test showed that microcapsules maintain quality for84days when stored at20℃. Storage at low temperature was the key of the shelf life, for the residual quantity of lactic acid bacteria in microcapsules stored at0-10℃declined slowly and the shelf life was more than one year. By the economic calculation of waste yoghurt recycling on industrial production, the results showed that the economic feasibility is good, and the study on the recycling of waste yoghurt in this paper is feasible. |
PDF Full Text Request