高黏度热聚合乳清分离蛋白-三聚磷酸钠的研制及其性质

Preparation and characters of whey protein isolate-sodium tripolyphosphate aggregates by heating

为了探究三聚磷酸钠(sodium tripolyphosphate,STPP)及热改性条件对乳清分离蛋白(whey protein isolate,WPI)聚合物性质的影响,该研究通过单因素和Box-Behnken优化试验进行工艺优化;利用荧光分光光度计、旋转流变仪、激光粒度分析仪和电子扫描显微镜对乳清分离蛋白聚合物性质进行研究。结果表明:在质量分数为10%WPI、0.09%STPP、90℃和p H值8.40条件下,热聚合反应42 min,WPI-STPP热聚合物黏度高达5 083 m Pa·s。对WPI-STPP热聚合物性质分析发现:与空白、WPI热聚合体相比,WPI-STPP热聚合物的持水性显著提高(P<0.05);表面疏水性有显著增加(P<0.05)。WPI-STPP热聚合物粒径((292.09±2.17)μm)显著增大(P<0.05),且表现出较高的弹性模量。WPI-STPP热聚合物具有较大片状微观结构且呈不规则性,这有利于黏度的增大。研究结果为改性乳清蛋白及其在酸奶方面的应用提供理论依据与技术参考。

This study was aimed to prepare the whey protein isolate（WPI） – sodium tripolyphosphate（STPP） aggregates using heating at higher pH value and evaluate their characteristics. The results of single-factor experiment showed that the increase of viscosity of polymers was different from the increasing of WPI concentration, temperature, p H value, STPP content and aggregation time. The models were obtained by using a Box-Behnken optimization experiment design with the 4 factors（temperature, p H value, STPP content and aggregation time） based on the results of single-factor experiments. The results of Box-Behnken optimization experiment showed that the order of the effect of the 4 factors on viscosity was as follows： temperature STPP content p H value aggregation time. The optimized condition determined was that 10%（w/w） WPI, 0.09%（w/w） STPP at 90°C for 42 min with p H value of 8.40, and the actual viscosity was 5083 mP a·s. The prepared WPI-STPP thermal aggregates were the thick sample with a semi flow state, and the regression model was fitted well. Determination of properties and structural analysis of WPI, WPI-STPP thermal aggregates and WPI aggregates showed the water holding capacity, surface hydrophobicity and rheological characteristics of WPI-STPP thermal aggregates were improved compared with WPI and WPI aggregates. For WPI aggregates, water holding capacity increased from 4.83 to 5.20 g per gram protein（P〈0.05）. However, the solubility of WPI-STPP thermal aggregates decreased from 88.5% to 34.50%, which was lower than that of WPI. Heat treatment and STPP significantly affected the surface hydrophobicity of the soluble aggregates. WPI-STPP thermal aggregates could form good cold-induced gels, which could widen its application in foods of gel type. When STPP was added, the average particle size of whey protein thermally polymerized increased from 31.39±1.81 μm for WPI to 292.09±2.17 μm for WPI-STPP thermal aggregates. The difference between strong and weak soluble gels could be assessed by the oscillatory dynamic experiments using parallel-plate geometries. Rotational rheometer showed that the rheological characteristics of WPI-STPP thermal aggregates were improved. The rheological characteristics were determined from storage and loss moduli as the functions of time and frequency. WPI-STPP thermal aggregates had higher storage modulus values. The results showed that the increasing of particles played a significant role in the water holding capacity and rheological properties of these dispersions. The microscopic structure analysis of WPI-STPP thermal aggregates showed that they denatured fully, and the larger irregular fractal aggregates of WPI-STPP thermal aggregates could be most useful to increase the viscosity. Transmission electron microscopy showed that heat-induced WPI-Na Cl soluble gels had a dense structure and a higher number of cross-links. The utilization of WPI-STPP thermal aggregates is very attractive due to the low-complexity processing conditions needed, lower production cost and higher nutritive value. The production cost of yogurt is less than yogurt with pectin according to the optimal technological condition of the experiment. The application of this technology proposed in this paper will bring great economic benefits for the yogurt processing industry.