Preparation Of Acid Soluble Soybean Protein And Its Application In Acidic Drinks

Soybean protein, which contains affluent essential amino acids of coordinate proportion, is an important source of high quality protein. As an important food and industrial raw materials, soybean protein is widely used in meat industry, but its application in the field of beverage is limited due to its limited solubility. Acidic beverage includes carbonated drinks, fruit juice, milk drinks, tea drinks, functional drinks and acidic solid beverage, takes over more than60%drinks market, if a new kind of product of a high solubility in acidic conditions was developed, the application of soybean protein in food industry will be broaden. Because the isoelectric point of soybean protein was between pH4.4and4.6, when the pH of the acidic beverages varies from3.0to4.5, the solubility of soy protein is quite low. In this paper, solubility of soybean protein in acidic environment is improved by means of phytase treatment and ultrafiltration, and acidic protease is also used to improve the taste of acid soluble soybean protein, so that it could be used in acidic drinks.Firstly, the effect of phytase treatment on the acid solubility of soybean protein is studied. It is concluded that when the solid content of the curd slurry is10%, the best phytase adding amount is30U/g, the ideal condition for the enzymatic reaction is pH3.0,40℃,45min. After enzymatic treatment, acid solubility and transmittance of SPI reach45.79%and68.5%, increased by30.65%and29.4%respectively. Combination of phytase and acid protease treatment hasn’t made the acid solubility of soy protein improve, when the adding amount of acid protease was0.6%, acid solubility and light transmittance are minimum; when the addition of acid protease was0.8%, soybean protein acidic drinks taste the best.Secondly, the effects of acidifying condition and physical modification on the acid solubility of soybean protein are studied. It is concluded that, any rise of curd broken temperature and acidifying temperature will lead to decrease of acid solubility of soybean protein. When the curd broken temperature was10℃, the acid solubility of soybean protein was55.70%, and when the curd broken temperature reached50℃, the acid solubility of soybean protein was only18.58%; when the acid regulating temperature was10℃, the acid solubility of soybean protein was50.01%, and when the acid regulating temperature was50℃, the acid solubility of soybean protein decreased to38.98%. After homogenization, neither acid solubility nor light transmittance of soybean protein was developed significantly. The acid solubility of soy protein reached61.70%, increased by14.20%after heated to100℃, and reached more than90%after UHT or micro waving, developed by43.22%and43.57%respectively. Furthermore, transparency of the samples heated by microwaving is the highest, reaching more than90%, while the transparency of the samples after UHT is only44.5%. Protein prepared by the enzymatic method cannot be directly applied to orange juice, and when it was added to transparent acidic beverage, although precipitation rate was very low, the beverage was opaque.Finally, a method of making acid soluble soybean protein by ultrafiltration was developed. Concentration of calcium chloride in extracting soybean protein and the role of ionic strength in concentration was studied. Results showed that, extracting the soybean protein from defatted soybean meal with0.15mol/L calcium chloride solution, followed by ultrafiltration with a molecular weight cut-off of10000Dalton membrane, and purified by adding2.5times of water to make the protein coagulate, the acid-solubility of the final product could reach94.50%, and the light transmittance could reach91.5%. Protein prepared by the ultrafiltration method couldn’t be directly applied to orange juice, but when it was added to transparent acidic beverage, the precipitation rate was very low, and the beverage was almost completely transparent.