Control of spoilage microorganisms in soybean milk by nipagin complex esters, nisin, sodium dehydroacetate and heat treatment

![CDATA[Soybean milk is a kind of highly perishable Asian traditional soy product, and this study was envisaged to extend its shelf-life through the application of hurdle technology. Twelve strains of bacteria were isolated from samples of spoilage soybean milk and were identified as Klebsiella oxytoca (S 5,S 7,S 8). Serratia marcescens (S 9,S 10,S 14, S 15, S 17), Klebsiella ozena (S 16, S 18), and Serratia plymuthica (S 21, S 25, S 28). To control these spoilage microorganisms, eight commonly used food preservatives were tested by Oxford Cup inhibition method. Results showed that sodium dehydroacetate, nipagin complex esters and nisin significantly inhibited the growth of the isolated strains with their MIC (minimum inhibition concentration) values ranging from 0.004% to 0.05%. Levels of heat treatment duration, together with concentrations of sodium dehydroacetate, nipagin complex esters, and nisin were employed as hurdle factors. The optimum conditions for improvement of the sshelf-life were gained from orthogonal tests as follows: heat treatment at 100C for 10 minutes, and nisin 0.004%, nipagin complex esters 0.008%, dehydroactetate 0.002%. The fresh soybean milk applied with the optimum formula could be maintained under upper limit of the microbial count (100 CFU/mL, DB44/425-2007 China) for more than 6 days at 25C and 11 days at 4C. Here in our study, hurdle technology approach significantly improved the shelf-life of soybean milk.]]