Study On The Effect Of Ultrasonic Treatments On Structure And Functional Properties Of SPI

Soy protein is a high quality protein material. Both the nutritional value and economic costs have significant advantages, it has been widely used in the food industry. However, the functional properties of soy protein are not very good, there are certain limitations in applications. More and more studies focus on soy protein to improve the functional properties. Ultrasonic technology is one of the physical treatments that considered to be a safe approach with little impact of nutrients. The experiment used soy protein isolate as research object and used ultrasound technology to process soy protein in order to study the effects of ultrasound treatment on structure and functional properties of soy protein isolate.And the modified soy protein isolate was applied in low-fat mayonnaise. The main findings are as follows:1At400W-800W ultrasonic power, the soy protein isolate solution (30mg/mL) was treated30min-90min respectively. Then the fluorescence spectroscopy, UV absorption spectroscopy, SDS-PAGE electrophoresis and sulfhydryl content of soy protein isolate were measured to research the effects of ultrasonic treatments on the structure of soy protein isolate. The results showed that after different conditions A1(800W,30min), B1(600W,30min), B3(600W,90min), C2(400W,60min) treatments, fluorescence spectroscopy maximum absorption wavelength had blue shift, which indicated that the protein had certain aggregation. Ultrasonic power from400W to800W, fluorescence intensity was significantly reduced in different time conditions (P<0.05). In the vicinity of260-280nm UV absorbance occurred significantly improved (P<0.05), thereinto A3(800W,90min) UV absorbance was the maximum. At90min, from400W to800W UV absorbance value increased with ultrasonic power increasing. At400W ultrasonic treatment, UV absorbance values were increased and the changes between different processing time were small. SDS-PAGE electrophoresis profiles of B2(600W,60min), B3(600W,90min), C2(400W,60min),11S B subunit reduced. Ultrasonic treatments had greater impact on the11S subunit component. The total sulfhydryl content and reactive sulfhydryl content were significantly reduced. After the reactive sulfhydryl content decreased, the reactive sulfhydryl content firstly increased and then decreased with time. At30min and90min, the total sulfhydryl content was the maximum in400W (P<0.05).2At400W～800W ultrasonic power, the soy protein isolate solution (30mg/mL) was treated30min-90min respectively. Then the functional properties of soy protein isolate was studied. The results showed that ultrasonic treatment can significantly increase the solubility of soy protein (P<0.05). At different concentrations of NaCl solution, there was a big difference. In0M NaCl and0.1M NaCl solution, at400W and600W, the solubility of soy protein firstly increased and then decreased with time. In the800W power conditions, the solubility first reduced and then increased. In0.6M NaCl solution, the solubility was increasing with time. When ultrasonic power was400W, the emulsification was high and first increasing then reducing with time, but the emulsion stability reduced significantly with time (P<0.05). Gel strength of soy protein increased significantly and it first reduced and then increased with time from400W to800W after sonication (T<0.05). The gel elasticity were significantly increased (P<0.05). Turbidity were increased at different pH values, especially near the isoelectric point, the thermal aggregation was more obvious. Water holding capacity of soy protein decreased, but oil retention significantly increased (P<0.05).3At400W-800W ultrasonic power, the soy protein isolate solution (30mg/mL) was treated30min-90min respectively. The weak gel was applied in low-fat mayonnaise, its composition analysis, energy value, texture analysis and sensory evaluation were made. The results showed that the SPI was used as fat substitute in low-fat mayonnaise, the moisture, protein content was significantly improved, at the same time the energy value significantly reduced (.P<0.05). The sensory scores of LfC3(400W,90min) low-fat mayonnaise are not significant with the traditional high-fat mayonnaise (P>0.05), therefore, soy protein isolate with400W,90min ultrasonic treatment can be used as a functional ingredient applied in low-fat mayonnaise and can plays a role in reducing the fat content of mayonnaise and meeting the sensory demand to mayonnaise.