利用Turbiscan多重光散射技术研究常温液体奶酪的稳定性

常温液体奶酪是一种能够在室温下贮藏3~6个月的奶酪产品。液体奶酪在经高温处理后体系中的微生物数量达到商业无菌水平，但由于液体奶酪是一种水包油的不稳定乳液体系，在常温贮藏过程中，由于分散相颗粒的迁移和粒径大小变化导致乳液体系容易出现聚集、絮凝、浮油及沉淀等失稳现象，从而影响产品品质，缩短产品货架期，准确判断液体奶酪的稳定性对优化其加工条件具有重要意义。传统液态乳制品的稳定性评价主要是通过加速实验后肉眼观察分层、沉淀等情况，以及动态光散射等手段，尚缺乏快速可靠以及量化的评价标准。Turbiscan多重光技术在测试流体的稳定性时，无需对样品进行前处理，可实时检测样品的背向散射光和透射光的强度，计算出体系内部颗粒的迁移速率、沉淀层的厚度、体系的不稳定指数等参数，因此是评价流体稳定性的有效手段。研究利用Turbiscan多重光散射技术评价乳化盐、乳化剂、稳定剂和甜味剂的添加量对常温液体奶酪稳定性影响，同时以TSI值和感官得分为响应值，采用响应面法中的Box-Behnken试验设计模型优化常温液体奶酪的最佳配方工艺条件，并分析了导致常温液体奶酪不稳定的主要因素。研究发现：当乳化盐添加量为0.20%，0.40%，0.60%和0.80%时，24 h后的不稳定性指数从0.4增加到12.6；当乳化剂添加量为0.80%，1.0%时，24 h后的不稳定性指数从0.95增加到3.9；当稳定剂添加量为0.7%，0.9%时，24 h后的不稳定性指数从0.9增加到1.3，而甜味剂对体系整体稳定性的影响差异不显著。各因素对常温液体奶酪的不稳定性指数和感官得分影响顺序为乳化盐添加量（A）＞乳化剂添加量（B）＞稳定剂添加量（C）。乳化盐添加量0.60%、乳化剂添加量0.60%、稳定剂添加量0.70%、甜味剂添加量5.5%时，产品品质最佳且稳定性最高，在此优化条件下，样品在37 ℃，24 h内的整体不稳定指数值为0.80，样品顶端、底端的背散射光强变化值分别为0.66和0.78，感官评分为89分。研究表明通过调整乳化盐、乳化剂和稳定剂的用量能够很好地解决常温液体奶酪分层的问题，提高常温液体奶酪的稳定性。

The Stability of Room Temperature Liquid Cheese Based on Turbiscan Multiple Light Scattering Technique

Liquid cheese stored at room temperature, which can remain stable at room temperature for 3~6 months, is a kind of processed cheese. After high-temperature treatment, the number of microorganisms in the liquid cheese system reaches the commercial aseptic level because the liquid cheese is an unstable emulsion system with oil in water. During the storage at room temperature, due to the migration of dispersed phase particles and the change of particle size, the emulsion system is prone to instability, such as aggregation, flocculation, oil slick and precipitation. It affects the product’s quality and shortens the product’s shelf life. Therefore, it is important to accurately judge the stability of liquid cheese to optimize its processing conditions. However, the stability evaluation of traditional liquid dairy products is mainly through accelerating the visual observation of stratification and precipitation, dynamic light scattering, and the lack of fast, reliable and quantitative evaluation standards. When testing fluid stability, Turbiscan multiple light technologies does not need to pretreatment the sample. It can detect the intensity of backscattered light and transmitted light in real-time, calculate the migration rate of particles inside the system, the thickness of the precipitation layer, and the instability index of the system, so it is an effective method to evaluate the stability of the fluid. The parameters such as the migration rate of particles in the system, the thickness of the precipitation layer and the instability index of the system are calculated, so it is an effective means to evaluate the stability of the fluid. Turbiscan multiple light scattering technique was used to evaluate the effect of emulsified salt, emulsifier, stabilizer and sweetener on the stability of room temperature liquid cheese. At the same time, according to the response value of TSI and sensory score, the optimum formulation conditions of room temperature liquid cheese were optimized by the Box-Behnken experimental design model of response surface method, and the main factors leading to the instability of room temperature liquid cheese were analyzed. It was found that when the amount of emulsified salt was 0.20%, 0.40%, 0.60%, 0.80%, the instability index increased from 0.4 to 12.6 after 24 hours; when the amount of emulsifier was 0.80%, 1.0%, the instability index increased from 0.95 to 3.9 after 24 hours. When the amount of stabilizer was 0.7% and 0.9%, the instability index increased from 0.9 to 1.3 after 24 hours, but the effect of sweetener on the overall stability of the system was insignificant. The influence order of various factors on the instability index and sensory score of room temperature liquid cheese is emulsified salt (A) > emulsifier (B) > stabilizer (C). When emulsified salt was added to 0.60%, emulsifier was 0.60%, stabilizer was 0.70%, and sweetener was 5.5%, the product quality was the best and the stability was the highest. Under the optimized conditions, the overall instability index of the sample at 37 ℃ for 24 hours was 0.80, the variation of backscattered light intensity at the top and bottom of the sample was 0.66 and 0.78 respectively, and the sensory score was 89.The results show that the problem of delamination of room temperature liquid cheese can be well solved, and the stability of room temperature liquid cheese can be improved by adjusting the emulsified salt, emulsifier and stabilizer.