超声处理对牦牛乳酶促凝胶流变特性的影响研究

为探究超声牦牛乳的酶促凝胶流变特性,并进一步分析超声后牦牛乳的蛋白疏水性和脂肪球粒径如何影响凝胶网络的形成,本研究以牦牛乳为原料,进行超声处理(时间5 min和10 min,功率300、400和500 W)后,编号为US1(300 W,5 min)、US2(300 W,10 min)、US3(400 W,5 min)、US4(400 W,10 min)、US5(500 W,5 min)和US6(500 W,10 min),以未处理的牦牛乳作为对照(CK),通过小振幅振荡时间扫描获取凝胶形成的流变信息。结果表明,超声处理后牦牛乳的脂肪含量、蛋白质含量以及pH值无显著变化(P>0.05),而均质效率和乳液稳定性显著提高(P<0.05);超声处理能够增加凝胶的储能模量,使得牦牛乳酶促凝胶的弹性增加。US5和US6的储能模量增幅最多(分别为6 824和7 189 Pa),但凝胶时间长。与CK相比,超声牦牛乳US1、US2、US3和US4的凝胶时间分别缩短了1.78、3.72、5.75和4.74 min;超声处理在改变乳蛋白表面疏水性的同时减小了脂肪球尺寸。与CK相比,US3最大荧光强度显著增加了51.22%(P<0.05),脂肪球粒径分布范围为0.300~4.002 μm,集中在1.974 μm处。US4最大荧光强度显著降低了5.31%(P<0.05),脂肪球粒径呈双峰分布,范围为0.131~4.502 μm。综上所述,经过不同时间和不同功率的超声处理后,US1~US6乳蛋白表面疏水性和脂肪球尺寸受到影响的程度不同,使得凝胶网络体系存在差异,从而表现出不同的凝胶特性。本研究为超声技术在牦牛乳凝胶类制品加工中的应用提供了理论基础。

Effect of Ultrasonic Treatment on Rheological Properties of Enzymatic Gel of Yak Milk

The rheological properties of enzymatic treated ultrasonic yak milk were studied to understand how the protein hydrophobicity and the particle size of fat ball affect the formation of gel network of ultrasonic-treated yak milk. Yak milk was treated with ultrasonic treatment (5 min and 10 min, power of 300, 400 and 500 W), numbered as US1 (300 W, 5 min ), US2 (300 W, 10 min ), US3 (400 W, 5 min ), US4 (400 W, 10 min ), US5 (500 W, 5 min ) and US6 (500 W, 10 min ), and untreated yak milk was used as control. The rheological information of gel formation was obtained through time scanning of small amplitude oscillation. There is no significant change in the fat content, protein content and pH of yak milk before and after ultrasonic treatment (P>0.05), but the homogenization efficiency and emulsion stability of yak milk were significantly improved (P<0.05). Ultrasonic treatment increased the storage modulus of gel and the elasticity of the yak milk enzymatic gel. The storage modulus of US5 and US6 increased the most (6824 Pa and 7189 Pa, respectively), but the gel time was long. Compared with yak milk CK, ultrasonic yak milk US1, US2, US3 and US4 shortened the gel time of emulsion by 1.78, 3.72, 5.75 and 4.74 min, respectively. The surface hydrophobicity of milk protein was changed and the size of fat globules reduced after ultrasound treatment. Compared with control, the maximum fluorescence intensity of US3 was significantly increased by 51.22% (P<0.05), and the fat globule size distribution ranged from 0.300 to 4.002 μm, concentrated at 1.974 μm. The maximum fluorescence intensity of US4 was significantly reduced by 5.31% (P<0.05), and the size of fat globules showed a bimodal distribution, ranging from 0.131 to 4.502 μm. In summary, after ultrasonic treatment with different time and power for US1~US6, the hydrophobicity of milk protein surface and the size of fat balls were varied, which changed the gel network systems with different gel properties.