The stability of the physicochemical characteristics of yoghurts during refrigerated storage is important for industry and the consumer. In this study we produced plain yoghurts with the addition of health-promoting whey protein concentrate (WPC), using two different starter cultures based on Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. Physicochemical changes (acidity, nutritional value, water activity, water-holding capacity, texture, and colour, including whitening and yellowing indices) as well as sensory changes occurring during 28-day refrigerated storage were determined. Starter cultures were found to significantly (p ≤ 0.05 and p ≤ 0.01) influence the water-holding capacity, firmness, consistency, cohesive strength and colour parameters of the curd. Use of whey protein concentrate affected both the physicochemical and sensory quality of the yoghurts. The additive had a significant effect on potential acidity, inhibiting the increase in lactic acid in the yoghurts during storage, and also reduced syneresis. However, it decreased the lightness of curd and negatively affected its sensory characteristics, primarily flavour. Moreover, nearly all parameters changed significantly with the passage of storage time (in most cases negatively). The exceptions were total protein and fat content. The changes, however, were not severe and remained at a level acceptable to tasters. Addition of 1% or 2% whey protein to yoghurt may be a good solution that can be routinely applied in the dairy industry to offer consumers a new functional product. A comprehensive assessment of the physicochemical and sensory changes occurring during refrigerated storage of yoghurts manufactured with the addition of WPC and using different cultures is crucial for modelling such a product.

中文翻译：

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添加了乳清蛋白的酸奶的理化参数与发酵菌菌株和贮藏时间的关系。

酸奶在冷藏过程中的理化特性的稳定性对工业和消费者而言非常重要。在这项研究中，我们使用基于嗜热链球菌和德氏乳杆菌亚种的两种不同的发酵剂培养物，添加了健康促进的乳清蛋白浓缩物（WPC），制成了普通酸奶。保加利亚。确定在28天的冷藏储存期间发生的物理化学变化（酸度，营养价值，水分活度，持水量，质地和颜色，包括增白和泛黄指数）以及感官变化。起始培养物发现显著（p ≤0.05和p≤0.01）影响凝乳的保水能力，硬度，稠度，内聚强度和颜色参数。浓缩乳清蛋白的使用会影响酸奶的物理化学和感官质量。添加剂对潜在的酸度有显着影响，可抑制酸奶中乳酸在储存过程中的增加，并降低脱水收缩。但是，它降低了凝乳的亮度，并负面影响了其感官特性，主要是风味。此外，几乎所有参数都随着存储时间的流逝而发生显着变化（在大多数情况下为负数）。总蛋白质和脂肪含量除外。然而，变化并不严重，并保持在品尝者可接受的水平。在酸奶中添加1％或2％的乳清蛋白可能是一个很好的解决方案，可以在乳品行业常规应用，为消费者提供一种新的功能性产品。全面评估添加WPC并使用不同培养物制成的酸奶的冷藏储存期间发生的物理化学和感官变化，对于建模此类产品至关重要。