| Fermented milk (including fermented milk drink) products have attracted more and more consumers for good nutritional value and unique health benefits. Conventional fermented milk products with the require of refrigeration sales and short shelf life are always of high prime cost, so it is significant to develop long-shelf-life bacteria fermented milk products which are no need of cold chain storage and have broad market demand. At present, the key problems to be solved in the field of fermented dairy products at room temperature are How to improve the taste and flavor of fermented dairy products and how to increase the number of product shelf-life lactic acid bacteria. This paper mainly focused on the effect of heat stress on fermentation and functional characteristics of Lactobacillus rhamnose grx19, and optimized the craft of mass-producing live bacteria type normal temperature fermented milk and fermented milk drink. Furthermore, through pilot production, analysis of the quality of room temperature fermented milk and fermented milk drink products, laying the foundation for the further development of high quality fermented milk (drink). The main results are as following:1. Analysis of the effect of heat stress on fermentation characteristics of L. rhamnosus grxl9. After heat stress. the lag phase of L. rhamnosus grx19 increased by 8h, logarithmic growth period in 10th to 15th hour had been shortened by 3h. and the living bacteria number in stable period is higher than control group. The effect of heat stress on the hardness of L. rhamnosus grx19 fermented milk is not remarkable (P< 0.05). Meanwhile,the cohesiveness and adhesiveness of fermented milk increased by 33.3% and 26.8% respectively. During the storage in 4 ℃/28d, the acidity increased by the speed of 1.32 °T//d,29% lower than the control group; Viable bacteria counts of heat stress L. rhamnosus grx19 fermentation milk is 6.0×108CFU/mL at the end of the fermentation, then increased first and then decreased during storage, finally became stable, remained at 1.3×108 CFU/mL at 28 day. During the storage in 25 ℃/28d, the acidity increased by the speed of 5.26 °T/d,14.7% lower than the control group; Viable bacteria counts of heat stress L. rhamnosus grxl9 fermentation milk began to fall after a period of stability, and finally remained at 1.3×107 CFU/mL at 28th day.2. Analysis of the influence of heat stress on artificial digestive tolerance and antioxidant capacity of L. rhamnosus grx19. Heat stress makes the survival rate of L. rhamnosus grx19 0.89% higher in pH2.0 and 6.64% in pH3.0 in artificial intestinal juice for 3 hours; heat shock activation after generation makes the survival rate of L. rhamnosus grx19 9.03% higher in pH2.0 and 26.53% in pH3.0 in artificial intestinal juice for 3 hours respectively. The survival rate of L. rhamnosus grx19 in artificial intestinal juice for 3 hours had become 13.68% higher through the heat stress; the survival rate of L. rhamnosus grx19 in artificial intestinal juice for 1.5 hours and 3 hours had become separately 17.35% and 21.008%higher through activation after the heat stress.Heat stress increased L. rhamnosus grx19 tolerance in 0.3 g/100mL and 0.5 g/100mL concentrations of bile salts (P< 0.05), but tolerance decreasd (P< 0.05) after heat shock activation of one generation. Heat stress decreased L. rhamnosus grx19·OH removal rate (P< 0.05), but increased DPPH clearance rate (P< 0.05).3. The optimization of L. rhamnosus grx19 (room temperature fermented milk beverage) producing craft. Comprehensively compared in fermentation characteristic and sense organ with other different combinations,the best combinations of fermented milk (drink) were:L.rhamnosus grx19:S. thermophilus 90-57:S. thermophilus 937-1=1:1:1. The best stabilizer formula for fermented milk:pectin 0.20%, modified starch 0.10%, sodium alginate 0.20%. Fermented milk prepared water holding capacity of up to 76.28%. Fermented milk beverage best stabilizer formula is:the compound emulsifier (single lipid gump:sucrose ester= 1:1) 0.10%, pectin 0.25%, modified starch 0.10%, sodium alginate 0.15%. chelating agent (0.04%), sodium tripolyphosphate,. The preparation of fermented milk beverage stability coefficient was up to 0.95. Fermented milk through the second heat treatment(72 ℃/15 s), stored in common temperature,after 2 days living bacterium number rose to more than 1.0×106, and became above 1.0×108 4 weeks later, at the same time the acidification became weak and the stability decreased. Similarly, fermented milk drink through the second heat treatment(72 ×/15 s), stored in common temperature,after 2 days living bacterium number rose to more than 1.0×106, and became above 1.0×107 4 weeks later, at the same time the acidification became weak and the stability decreased.4. The pilot production and product quality analysis of L. rhamnosus grx19 (room temperature fermented milk beverage).(1) Added 6% sucrose and 0.4% compound stabilizer in skim milk with 11.5%, dissolved even after the filtration of homogeneous (20MPa,60 ℃), the 90-95 ℃ /15min heat treatment of the cooling to 37 ℃, inoculation of 3% starter. Heat stress on L.rhamnosus grx19, fermented in constant temperature of 37 ℃ till the acidity became 70°T, immediately cool demulsificated, and aseptic filled, then stored at room temperature after heat treatments of 72 ℃/15s twice. According to the optimization process of the pilot production of fermented milk, shelf-life at room temperature reached a minimum of 15d.(2) 11.5% skim milk dissolved after the filtration of homogeneous (20MPa.60 ℃). the 90-95 ℃/15min heat treatment of the cooling to 37 ℃, inoculation of 3% starter, fermented in the constant temperature of 37℃ till the acidity became 110 °T; then with containing 9% sucrose and 0.4% compound stabilizer syrup mixing, homogenizing (20MPa,60 ℃) after aseptic filling, and then stored at room temperature after the heat treatment of 72℃/15s twice. According to the optimization of the process in trial production of fermented milk beverage quality, the production is with lactic acid bacteria beverage color, uniform organization, delicate taste and can be stored at room temperature for 15d without remarkable changes. |
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