Department of Agricultural and Environmental Sciences (DiSAAT), University of Bari Aldo Moro, Via G. Amendola, 70126 Bari, Italy.
Department of Agricultural and Environmental Sciences (DiSAAT), University of Bari Aldo Moro, Via G. Amendola, 70126 Bari, Italy.
J Dairy Sci. 2019 Dec;102(12):10867-10876. doi: 10.3168/jds.2019-16615. Epub 2019 Sep 25.
Donkey milk is characterized by low contents of total solids, fat, and caseins, especially κ-casein, which results in formation of a very weak gel upon renneting. The objective of this study was to evaluate the effect of fortification of donkey milk with microbial transglutaminase (MTGase) for cheesemaking in relation to different enzyme addition protocols (patterns, PAT). Four independent trials were performed using MTGase (5.0 U/g of milk protein) according to the following experimental patterns: control (no MTGase addition); MTGase addition (40°C) 15 min before starter inoculation (PAT1); addition of MTGase to milk simultaneously with starter culture (40°C) (PAT2); and MTGase addition simultaneously with rennet (42°C) in acidified milk (pH 6.3) (PAT3). Evolution of pH during acidification, cheesemaking parameters, and proximal composition and color of cheese at 24 h were recorded. The protein fractions of cheese and whey were investigated by urea-PAGE and sodium dodecyl sulfate-PAGE. Addition of MTGase had no significant effect on moisture, protein, fat, or cheese yield. The addition of MTGase with rennet (PAT3) improved curd firmness compared with the control. Among the different patterns of MTGase addition, PAT3 reduced gel formation time, time between rennet addition and cheese molding, and weight loss of cheese at 24 h. The PAT3 treatment also resulted in the lowest lightness and highest yellowness color values of the cheese. Sodium dodecyl sulfate-PAGE of cheeses revealed that MTGase modified the protein pattern in the high-molecular-weight zone (range 37-75 kDa) compared with the control. Of the MTGase protocols, PAT3 showed better casein retention in cheese, as confirmed by the lanes of α- and β-caseins in the electropherogram of the whey, which was subtler for this protocol. In conclusion, MTGase may be used in cheese production from donkey milk to improve curd firmness; MTGase should be added simultaneously with the rennet.
驴乳的特点是总固形物、脂肪和酪蛋白含量低，尤其是κ-酪蛋白，这导致其在凝乳酶作用下形成非常弱的凝胶。本研究的目的是评估通过添加微生物谷氨酰胺转氨酶（MTGase）来强化驴乳进行干酪制作的效果，同时考虑不同的酶添加方案（方案，PAT）。使用 MTGase（5.0 U/g 乳蛋白）进行了四项独立试验，根据以下实验方案进行：对照（不添加 MTGase）；MTGase 添加（40°C）在接种 starter 前 15 分钟（PAT1）；MTGase 添加到同时含有 starter 培养物的牛奶中（40°C）（PAT2）；以及在酸化的牛奶（pH 6.3）中同时添加 MTGase 和凝乳酶（42°C）（PAT3）。记录酸化过程中 pH 的变化、干酪制作参数、以及 24 小时时奶酪的近侧成分和颜色。通过尿素-PAGE 和十二烷基硫酸钠-PAGE 研究奶酪和乳清中的蛋白质级分。添加 MTGase 对水分、蛋白质、脂肪或奶酪产率没有显著影响。与对照相比，添加 MTGase 与凝乳酶（PAT3）可提高凝乳的硬度。在 MTGase 添加的不同方案中，PAT3 可缩短凝胶形成时间、凝乳酶添加与奶酪成型之间的时间以及 24 小时时奶酪的失重。PAT3 处理还导致奶酪的亮度值最低，黄度值最高。SDS-PAGE 分析奶酪发现，与对照相比，MTGase 改变了高分子量区（37-75 kDa 范围）的蛋白质模式。在所有 MTGase 方案中，PAT3 显示出更好的酪蛋白保留在奶酪中，乳清电泳图中 α-和 β-酪蛋白的条带证实了这一点，而该方案的条带则更细微。综上所述，MTGase 可用于强化驴乳生产干酪，以提高凝乳硬度；MTGase 应与凝乳酶同时添加。
