Factors Influencing The Qualities Change Of Soy Milk Powder During Storage

With the increase of storage time, the soybean milk powder will gradually lose itssolubility and palatability. The main reasons for those quality instabilities of the powders arevariations of storage conditions, changes of their own components and the effects of the metalions. Based on previous studies, soy milk powder was prepared by wet process and thenspray-dried. The effects of storage conditions and stabilizers on the reconstitution propertiesof the products were studied by two-factor experiments at environmental variations, includingtime, temperature, and relative humidity. In addition, the protein oxidation of soy milk powderand the impact of water activity have been particularly studied to analyze the storageinstability and the quality deterioration of soy milk powders.The results show that, at4℃, relative humidity of25%is the best storage conditions forsoybean milk powder. The influence of relative humidity on the reconstitution quality isgreater than the storage time, and effect of the temperature is less relatively. Under thedifferent temperatures and relative humidity, wettability and dispersibility of the productsdecreased significantly (P<0.05). With the extension of storage time, DSI also reduced (P<0.1). In addition, DSI at-20℃and35℃was lower than that at4℃and20℃.The effects of stabilizers were studied and most suitable amounts added were found: guargum0.15%, carrageenan0.04%, xanthan gum0.02%, and xanthan gum is the best singlestabilizing agent. With the increase of agents, the fat precipitation rate presented decrease atearlier stage and later showed an increase trend, DSI showed upward trend firstly, thendownward. The maximum particle size is29.12um, without significant quality differencecompared with that of the absence of stabilizers. During storage, soy milk powder particlesize and the percentage ratio were significantly increased after adding the stabilizer, and therate of increase is also greater. This proved that the stabilizer can only improve the quality ofsoybean milk powder, but will exacerbate the adhesion between particles during storage,resulting in soybean milk powder particle diameter enlarged and stability decreased. It is shown that the relative humidity and storage time are the most important factorinfluencing the oxidation of protein, while temperature is of negligible importance, especiallyon the PDI. With prolonged storage time, PDI (P<0.1) and the free sulfhydryl group content(P<0.01) decreased significantly at different temperatures and relative humidity conditions,but the carbonyl group content (P<0.01) increased significantly. This further confirmed thatwetting and dispersing time were prolonged, solubility and DSI were declined due to theoxidation of soy protein.Ferro Fontan and GAB model were used to fit moisture absorption isotherms andeffective moisture diffusion coefficient of soy milk powder, it was found that under thedifferent relative humidity, moisture absorption isotherms of soy milk powder present thesame trend, and the higher the relative humidity, the greater the adsorption of water. Whileeffective moisture diffusion coefficient decreased with the increase of water content, and theexperiment values are lower than the theoretical values, ranging from4.92×10-11to1.47×10-11,which is similar to the results of other researches.