Thermal Protection Mechanism Of Milk-derived Components For Lactobacillus Bulgaticus During Spray Drying Based On Single Droplet Drying

The industry prefer spray drying technology for mass production of probiotics,due to simple equipment, low cost,be easy to ship and store. In the process of spray drying,mixing with high-temperature air would lead to cell death. To improve survival rates, researchers focus on the optimization of process parameters, cell density cultivation and protectants formula. But it's difficult to study the drying process, inactivation mechanisms, protective mechanism of protectants since drying process of probiotics is not visible in spray-drying. In this paper, single droplet drying was used to simulate spray-drying and it's able to see the drying process of probiotics in the single droplet drying. Besides, the optimal technological parameters were obtained by the single droplet drying. In this paper Lactobacillus bulgaricus was chosen as the strain and skimmed milk powder, lactose, whey protein were chosen as protectants. Moreover probiotics in vitro digestion was investigated and we compared and analysed the acidresistant ability and the bile salt-resistant ability of the Lactobacillus bulgaricus. The main results are as follows:1. By observing the morphology changes in drying and dissolving process of three protectants, the following conclusions could obtained: firstly lactose couldn't form outer shell in the drying process in stead of crystallization so that the temperature of droplet was lower than the other two. Secondly skim milk and whey protein could form outer shell significantly so water evaporation was blocked and the temperature were higher. In addition, as the protectant concentration was higher, the shell appeared ealier and moisture content of the dried particles was higher due to the thicker shell. But the shell of whey protein was more clear and soft due to the complex composition in skim milk. Thirdly when skim milk was drying, the protein —a composition of skim milk move faster towards surface and the lactose move slower. And it was caused by the hydration of protein. So if we could break the hydration and put off forming outer shell, it will be beneficial to probiotics survival.2. In this paper we investigated the drying kinetic parameters of Lactobacillus bulgaricus by single droplet drying- temperature, weight, survival rate. And the resultsare as follows: firstly the temperature of droplet has a close connection with the outer shell forming as described above. Secondly the results of survival rate indicated 10% skim milk and 20% whey protein have the best protective effect against the strain. Thirdly from the results of lactose, it was obtained that the rate of moisture evaporation would also lead to cell death in a large number. Forth at 90? of hot air, the content of water in whey protein is relatively low and the rate of survival is relatively high so that it could be the optimum parameters in spray-drying.3. In this paper 10% skim milk and 20% whey protein were chosen as protectants respectively in spray-drying and the rate of survival in the dried powder were measured. The results are as follows: firstly the viable cell added protectants are one order of magnitude higher than the probiotics alone indicating that 10% skim milk and 20% whey protein have the protective effect on the probiotics. Secondly in spray-drying as the inlet temperature was higher and the flow rate of sample was slow, the survival rate of probiotics in dried powder was higher. Thirdly as the inlet air temperature was 140 ? and the flow rate of 15ml/min, the rate of survival was the highest 23.12%.4. Probiotics in vitro digestion were carried out and the results are as following : firstly the simulated gastric fluid which ph was 2 had no bad effect on the Lactobacillus bulgaricus while that ph was 3 and ph was 4 would had so bad effect on probiotics that cell died in a large number. Secondly skim milk and lactose have better influence on probiotics than whey protein caused by hydrolysis in simulated gastric juice. Comparatively in simulated intestinal juice the 3 protectants had similar effects on probiotics. Thirdly the Lactobacillus bulgaricus could survive in the low concentration of bile salts. But the probiotics would be harmed in the high concentration of bile salts leading to large number of deaths.