Development Of Rice Yoghurt Using Polymerized Whey Protein As Major Thickening Agent

Rice, one of the world’s most important crops, contains hypoallergenic starch and high-quality vegetable protein and posses many physiological effects. However, so far rice is mainly consumed as staple in the form of steak rice, and products with high-added value and convenient for carrying are scarce on market. Therefore, this study aims to develop a rice-based yogurt(RBY) using polymerized whey protein as major thickening agent. The RBY with high sensory and textural properties was produced by soaking, beating, gelatinization, fermentation processes. The study design and results were as follows:(1) In order to get the stable rice milk, the soaking process of rice, gelatinization process, emulsifier types and level were optimized. Absorption rate of rice reached the highest value with 23~24% when the soaking conditions were set as: soaking time of 3 hours, the rice-water ratio of 1:3, the soaking temperature of 25 ± 2o C; The highest gelatinization degree(87.65 ± 2.45%) was reached when the rice-water ratio was 1:12, gelatinization temperature 80 o C and gelatinization time 10 min; Lecithin with a level of 0.05% was selected as the best stabilizer for the stability ability time up to 5 days with better mobility.(2) To determine the RBY formula, the starter culture and inoculation, the additive amounts of inulin, sugar and protein were selected. The fermentation process was determined by the optimization of fermentation time and fermentation temperature. Through a single factor design, a Chris Hassen starter culture ABY-3containing a cocktail of Streptococcus thermophilus, Lactobacillus bulgaricus,Lactobacillus acidophilus and Bifidobacterium was chosen as the starter culture with an inoculation amount of 0.010%; The rest of major ingredients included 1% of inulin,1% of rice protein, 7% of sugar.(3) To determine the stabilizers for the rice yogurt, different proportions of polymerized whey protein and three kinds of stabilizer(xanthan gum, carrageenanand pectin) were experimented. The combination of 0.4% of PWP and 0.03% of xanthan gum was used as the thickening agent of the RBY. RBY with PWP and xanthan gum showed high water holding capacity(94.88 ± 0.55%) and no spontaneous liquid separated out.(4) The final product was analyzed for physical and chemical properties. The results showed that RBY with p H value of 4.24 ± 0.05 contained 2.00% protein and1.06% fat. The hardness and viscosity values of the RBY were 99.40 ± 6.20 g,viscosity 1573.20 ± 155.45 m Pa·S, respectively. The population of probiotic of the RBY reached 106 CFU / m L. RBY got an overall evaluation score of 4.33 ± 0.39(5-score scale). The microstructure analysis showed that structure of RBY with polymerized whey protein was dense with small pores.(5) Shelf life test indicated that population of probiotic remained stable with 106 CFU / m L during 8 weeks storage. p H of the RBY varied in the range of 4.0 to 4.5and viscosity 740 ~ 1600 m Pa·S. There were no yeasts and mould detected during the storage time.A new rice-based yogurt with good sensory and textural properties using polymerized whey protein as major thickening agent was successfully developed in this study. The development of the new product would not only make full use of the nutritional value of rice and rice protein and increase the variety of rice related products, but also offer a healthy choice for consumers with lactose intolerance or allergic to cow’s milk.