Abstract Water retention is an important quality attribute for yogurt. Classically, stirred yogurt water retention is investigated using induced syneresis measurement (centrifugation), which does not characterize spontaneous syneresis. Low-frequency nuclear magnetic resonance (1H-LF-NMR) is a non-destructive technique to detect spontaneous syneresis. Experimental yogurt from pasteurized skim milk, and commercial stirred yogurts were analyzed with 1H-LF-NMR. After Laplace's transformation of the signal, hydrogen atoms pools were differentiated according to their mobility. Each hydrogen pool stood for a type of water mobility in the matrices characterized by a relaxation time (T2(i)), and a signal intensity (I2(i)). Yogurt water retention was assessed by induced syneresis and their structure was characterized using microscopy. Low frequency 1H-NMR detected four different water mobility groups in the matrices. Among these, there was a signal from bulk water, and another attributed to the separated serum (spontaneous syneresis). In experimental yogurts, spontaneous syneresis was visible, resulting in induced syneresis higher than 50%. Moreover, induced syneresis and spontaneous syneresis detected by 1H-LF-NMR were similar. In commercial yogurts, bulk water mobility reduced with increasing protein content and protein network density. Induced syneresis and bulk-water mobility correlated only in yogurts without gelatin. In the presence of gelatin, the network was more open, probably favoring bulk water mobility. This study shows that 1H-LF-NMR associated with microscopy image analysis efficiently assesses and describes yogurts water retention and spontaneous syneresis.

中文翻译：

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使用低频核磁共振氢和图像分析表征搅拌酸性乳凝胶中的脱水现象

摘要 保水性是酸奶的重要品质属性。传统上，使用诱导脱水收缩测量（离心）来研究搅拌酸奶的保水率，其不表征自发脱水收缩。低频核磁共振 (1H-LF-NMR) 是一种检测自发脱水收缩的无损技术。用 1H-LF-NMR 分析来自巴氏杀菌脱脂牛奶的实验酸奶和商业搅拌酸奶。在拉普拉斯对信号进行变换后，氢原子池根据其迁移率进行了区分。每个氢池代表矩阵中的一种水迁移率，其特征在于弛豫时间 (T2(i)) 和信号强度 (I2(i))。通过诱导脱水收缩来评估酸奶的保水性，并使用显微镜表征其结构。低频 1H-NMR 在基质中检测到四种不同的水迁移率基团。其中，有一个来自散装水的信号，另一个归因于分离的血清（自发脱水收缩）。在实验酸奶中，可以看到自发脱水收缩，导致脱水收缩率高于 50%。此外，通过 1 H-LF-NMR 检测到的诱导脱水收缩和自发脱水收缩是相似的。在商业酸奶中，随着蛋白质含量和蛋白质网络密度的增加，水的流动性降低。仅在不含明胶的酸奶中诱导脱水收缩和大量水流动性相关。在存在明胶的情况下，网络更加开放，可能有利于大量水的流动。这项研究表明，与显微镜图像分析相关的 1H-LF-NMR 可以有效地评估和描述酸奶的保水性和自发脱水收缩。