Studies On Processing Technology Of The Long Shelf-Life Yoghurt

Yoghurt is famous for its valuable nutritional and medical functions. Recently, the production of dairy especially all kinds of yoghurts develop rapidly in China. However, the short shelf-life of yoghurts markedly restricts the development of dairy industry. Meanwhile, most factories in our country still can not predominate the cold chain which is the key process to maintain the quality of yoghurts. Therefore, it's significant to enhance the yoghurts edible security, reduce the transportation costs of cold chain and develop long shelf-life yoghurt.The goal of this research was to prolong the shelf life of yoghurt by the following five methods: adding hydrocolloids, changing ratio of bacterias, post-sterilizing, adding combination antiseptics and adding Nisin-producing bacteria.The product investigation on different brands of yoghurts in the market showed that most of the popular yoghurts qualities were better than before. But there still existed some flaws such as syneresis, non-exquisition of organization condition, serious postacidification, bad taste and lack of fragrance etc..Based on screening of many kinds of hydrocolloids, the flaxseedgum, the guar gum, the denatured starch were chosen as the combination. The optimum proportion among them was 3:2:20. The product costs per ton were decreased by $103.5～128.5. This brought great economical benefits to enterprises. The shelf life was prolonged to 27d at 4℃by adding the combination hydrocolloids.The optimum condition for post-sterilization was the temperature was 64℃and the time was 20s. The storing experiment showed: the shelf life of yoghurts by post stetilizated was prolonged to 20d at 25℃, whose acidity, viscosity, chromaticity, and flavor were similar to ordinary yoghurt's.Through changing different ratio of bacterias, it was found that the taste was suitable when St:Lb=50:1. To some extent, it also can postpone the postacidification and prolong the shelf life to 26d at 4℃. The optimum combination antiseptic proportion in yoghurt was: Nisin 400IU/mL and Delvocid 0.02g/Kg. The combination of two substances can not only prevent the postacidification, but also inhibit the mold and yeasts. The yoghurt shelf life was prolonged to 30d at 4℃or 13d at 25℃.A mutant strain with high yield of Nisin, which was hereditarily stable, was obtained by the astronautics mutagenesis breeding technology. The research indicated the optimum proportion among St, Lb and Ll was 1:1:4. It can make the organization condition exquisite, non-whey separated, the growth of Bacilli inhibited and the shelf life prolonged to 26d at 4℃.