Influence of milk with a high somatic cell count on the physical characteristics and yogurt fermentation process

Abstract The aim of this study was to evaluate the fermentation characteristics and yogurts made from milk with high or low milk somatic cell count (CCS) and added or not with milk solids. Raw milk was collected at six days and subjected to various electronic analyzes of protein, fat, lactose, total solids, CCS and total bacterial count (CBT). The profile of the fermentation was monitored by pH and acidity, expressed as lactic acid. Yoghurts were analyzed for pH, acidity expressed as lactic acid and syneresis of final product at different storage times. The experiment was conducted in a randomized block design, with six replicates and split plots with treatments in installments (CCS levels x added or not added milk solids) and fermentation times and storage periods for yogurts subplots. Data were subjected to analysis of variance (ANOVA), regression or Pearson Correlation analysis, according to the tests. The results showed that CCS levels had effects on some milk parameters (p<0,05). However, no effects were observed on the fermentation profile and characteristics of yoghurt during storage, according to the CCS levels or adding milk solids.摘要 本研究旨在评估不同乳体细胞数（milk somatic cell count, CCS）、添加或不添加乳固体的牛乳的发酵特性及其制备的酸奶品质。实验共收集6批次生鲜牛乳，对其蛋白质、脂肪、乳糖、总固体含量、乳体细胞数及总细菌数（total bacterial count, CBT）开展多项电子检测分析。通过pH值与以乳酸计的酸度监测发酵过程的特性变化。针对不同贮藏时长的成品酸奶，分别测定其pH值、以乳酸计的酸度以及乳清析出量。本实验采用随机区组设计，设置6次重复，采用裂区处理结构：主区处理为乳体细胞数水平×是否添加乳固体，裂区处理为酸奶的发酵时长与贮藏周期。根据检验类型的不同，对实验数据分别开展方差分析（analysis of variance, ANOVA）、回归分析或皮尔逊相关分析。结果显示，乳体细胞数水平对部分牛乳参数存在显著影响（p<0.05）。但无论乳体细胞数水平或是否添加乳固体，均未对发酵过程特性以及贮藏期内的酸奶品质产生显著影响。