低温贮藏时间对黄浆水酸奶稳定性的影响

Effect of low temperature storage time on stability of tofu whey yogurt

【目的】探索搅拌型黄浆水酸奶的稳定性随贮藏时间延长而变差的主要原因,为提高黄浆水酸奶的稳定性提供参考。【方法】以普通酸奶、大豆多糖酸奶为参照,以还原糖、粗多糖、pH、滴定酸度、持水力、表面疏水性、δ-电位、粒径、硬度和黏性以及微观结构为指标,将黄浆水酸奶于4℃下贮藏1,3,5,7,9 d后,取样分析其理化指标、凝乳结构及其间相互作用的变化,探究黄浆水酸奶的失稳机理。【结果】4℃低温贮藏过程中,黄浆水酸奶、大豆多糖酸奶和普通酸奶分别在贮藏的第5,7和9天出现乳清析出和油脂上浮现象。随贮藏时间延长,3种酸奶的还原糖含量总体均呈缓慢增加趋势,且在第7天开始大豆多糖酸奶及黄浆水酸奶中的还原糖增加幅度均显著高于普通酸奶,而3种酸奶中的粗多糖含量总体均始终呈减少趋势且无差异。低温贮藏1 d时,大豆多糖酸奶和黄浆水酸奶的pH均显著低于普通酸奶(P<0.05),随贮藏时间延长,3种酸奶的pH均总体呈下降趋势,至第9天时均稳定在4.3左右。黄浆水酸奶滴定酸度贮藏1 d就达100°T以上,显著高于大豆多糖酸奶,且均显著高于普通酸奶;3种酸奶的滴定酸度均随贮藏时间延长而持续上升,但普通酸奶和大豆多糖酸奶的滴定酸度值均未超过100°T,且均显著低于黄浆水酸奶(P<0.05)。低温贮藏过程中,普通酸奶和黄浆水酸奶持水力均呈先增加后降低趋势,分别在第5天和第3天达到峰值,大豆多糖酸奶的持水力整体呈升高趋势,且第7天起显著高于其余2种酸奶(P<0.05)。大豆多糖酸奶和黄浆水酸奶的疏水性在贮藏7 d后仍能保持在300以上,且均显著高于普通酸奶(P<0.05)。大豆多糖酸奶的δ-电位绝对值始终维持在6.8 mV以上,而另外2种酸奶在贮藏3~5 d后迅速下降到5 mV左右。在贮藏过程中,所有酸奶的粒径均呈增长趋势,但黄浆水酸奶和大豆多糖酸奶的粒径均维持在1μm以下,显著低于普通酸奶(1.4~2.0μm)(P<0.05)。低温贮藏1 d时,大豆多糖酸奶的硬度显著高于另外2种酸奶;随贮藏时间延长,普通酸奶的硬度持续增加,而大豆多糖酸奶和黄浆水酸奶的硬度随贮藏时间总体呈波动下降趋势,均于第9天达到最低。随贮藏时间延长,普通酸奶的黏性持续上升,黄浆水酸奶和大豆多糖酸奶的黏性呈波动下降,并分别在第7和9天呈显著下降趋势。【结论】影响黄浆水酸奶稳定性的关键因素是其黏性的显著降低,其次是静电作用和疏水作用的变化。

【Objective】The main reason for stability decrease of stirred tofu whey yogurt with the extension of storage time was explored to provide reference for improving the stability of tofu whey yogurt.【Method】Taking ordinary yogurt and soybean polysaccharides yogurt as references and using reducing sugar,crude polysaccharide,pH,titrated acidity,water holding capacity,surface hydrophobicity,δ-potential,particle size,hardness,viscosity and microstructure as indicators,tofu whey yogurt was stored at 4℃for 1,3,5,7 and 9 days,respectively.The physical and chemical indicators,curd structure and the interactions among them were analyzed to explore the instability mechanism of tofu whey yogurt.【Result】During low temperature storage at 4℃,tofu whey yogurt,soybean polysaccharides yogurt and ordinary yogurt showed whey separation and oil floating phenomenon in days 5,7 and 9,respectively.With the prolongation of storage time,their reducing sugar contents yogurt showed a slowly increasing trend,and the increases in soybean polysaccharide yogurt and tofu whey yogurt were significantly higher than that in ordinary yogurt since day 7,while their crude polysaccharide contents showed a decreasing trend without difference.After 1 day of low temperature storage,pH of soybean polysaccharide yogurt and tofu whey yogurt was significantly lower than that of ordinary yogurt(P<0.05).As storage time prolonged,their pH showed an overall downward trend,and became stable at 4.3 on day 9.After 1 day of storage,titrated acidity of tofu whey yogurt exceeded 100°T,which was significantly higher than that of soybean polysaccharide yogurt,and both of them were significantly higher than that of ordinary yogurt.The titrated acidity increased along with storage time,but the titrated acidity values of ordinary yogurt and soybean polysaccharide yogurt did not exceed 100°T and were significantly lower than that of tofu whey yogurt(P<0.05).During low temperature storage,water holding capacity of ordinary yogurt and tofu whey yogurt increased first and then decreased with peak values on day 5 and 3,respectively.The water holding capacity of soybean polysaccharide yogurt showed an overall increasing trend,which was always higher than those of the other two from day 7(P<0.05).The hydrophobicity of soybean polysaccharide yogurt and tofu whey yogurt remained above 300 after 7 days of storage,and it was significantly higher than that of ordinary yogurt(P<0.05).Theδ-potential value of soybean polysaccharide yogurt remained above 6.8 mV all the time,while that of the other two rapidly dropped to 5 mV after 3-5 days.During storage,grain size of all yogurt types increased,but those of tofu whey yogurt and soybean polysaccharide yogurt remained below 1μm,significantly lower than that of ordinary yogurt(1.4-2.0μm)(P<0.05).When stored at low temperature for 1 day,hardness of soybean polysaccharide yogurt was significantly higher than that of others.The hardness of common yogurt continued to increase along with storage time,while that of soybean polysaccharide yoghurt and tofu whey yogurt fluctuated and decreased,reaching the lowest on day 9.The viscosity of ordinary yogurt continued to increase with the extension of storage time,while that of tofu whey and soybean polysaccharide yogurt fluctuated and decreased significantly on day 7 and day 9,respectively.【Conclusion】The key factor affecting stability of tofu whey yogurt was the significant reduction of viscosity,followed by the changes of electrostatic and hydrophobic action.