琼脂是来源于江蓠等海洋红藻中的以半乳糖为主要成分的一种高分子功能性多糖,但琼脂在水中的溶解性较差,限制了其广泛应用。实验在比较不同改性手段对提高琼脂溶解性的基础上,筛选出合适的改性方法,进一步利用单因素试验和Box-Behnken中心组合设计的响应面分析法对琼脂改性工艺进行优化,并考察所制备的羟丙基琼脂作为稳定剂在饮用型酸奶中的应用情况。得到最优制备工艺条件为:反应温度为40 ℃,氢氧化钠用量为琼脂质量的6.0%,乙醇体积分数为60%。在此条件下,羟丙基琼脂的溶解温度为(81±1) ℃,凝胶强度为(408±20) g/cm2,白度为(54.13±0.4)%,经反复验证,工艺合理可行。酸奶发酵后添加羟丙基琼脂做稳定剂,酸奶持水力达到98.25%,保质期内肉眼观察无乳清析出。该实验的研究结果可为开发工艺简单的高品质改性速溶琼脂提供理论依据。
Agar is a functional polysaccharide derived from marine red algae such as Gracilaria, with galactose as the main component. However, the poor solubility of agar in water limits its wide application. In the present study, based on the comparison of different modification methods, hydroxypropylation was screened out to improve the solubility of agar, and single-factor tests and Box-Behnken central combination design response surface analysis were further used to optimize the modification process. In addition, the application of the prepared hydroxypropyl agar as a stabilizer in drinking yogurt was investigated. The results of the optimal process conditions were as follows: The reaction temperature was 40 ℃ and the amount of sodium hydroxide was 6.0% with the ethanol concentration of 60%. Under these conditions, the dissolution temperature of hydroxypropyl agar was (81±1) ℃, the gel strength was (408±20) g/cm2, and the whiteness was (54.13±0.4)%. After verification, the process was proved to be reasonable and feasible. With 0.08% hydroxypropyl agar was added into the fermented yogurt, the water-holding capacity of the yogurt reached 98.20%, and no whey precipitation was observed by naked eye observation during the 21-day shelf life. The present study could provide a theoretical basis for the development of a simple and high-quality modification process of agar.
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