集锦

烹饪增强了凝乳的去油性、熔化性，从而加快了挤压速度。

烹饪导致豆腐蛋白基质开裂，纤维结构减少。

挤压过程导致钙蛋白桥的增加。

挤压温度对熟凝乳的SME影响小于未熟凝乳。 

摘要 

人造酪蛋白凝胶，通常被称为奶酪凝乳，传统上在拉伸前通过浸入水中进行预热，这会影响奶酪的功能特性。这项工作旨在了解在实验室双螺杆、共旋转挤出机中的温度预热（烹饪）对80和90℃奶酪凝乳挤压过程以及对挤出物的组成、微观结构和功能特性的影响。烹饪显著提高了凝乳的熔化性和涂油性，更快挤压、更高的出口温度和更低的比机械能。结合共焦激光扫描显微镜和X射线显微断层扫描，在不同长度尺度上的显微镜观察表明，烹饪导致蛋白质基质中广泛的脂肪聚结和裂缝，导致挤出物具有较少的纤维结构、较低的弹性和抗张强度。挤出过程导致挤出物中钙桥的显著增加，这可能取代弱的水-蛋白质相互作用，并增加流动性更强的水部分的松弛时间（T2.2）。与未煮熟的凝乳相比，熟凝乳中的挤出温度对比机械能的影响较小，这可能是由于熟凝乳的挤出过程中更广泛的涂油所致。与微观观察结果一致，80 °C与90°C不同 温度，特别是脂肪含量分别为23.8–24.8%和29.5%（w/w）、脂肪球大小和分布，影响纤维形成。通常在90℃下挤出 具有更高的弹性和拉伸强度，这与良好拉长的脂肪结构域有关。这项研究提供了有关凝乳挤压过程的知识，催生了改进奶酪加工和设计定制奶酪产品的新想法。 

烹饪：挤压，干酪，凝乳结构

图2：在80°C下挤出的生豆腐、在80°C下挤出的熟豆腐、在90°C下挤压的生豆腐和在90°C下挤压的熟豆腐的横截面图和纤维形成图像。

Structural, rheological and functional properties of extruded mozzarella cheese influenced by the properties of the renneted casein gels

Highlights

Cooking enhanced curd oiling-off, meltability, and consequently faster extrusion.

Cooking resulted in cracks in curd protein matrix and a less fibrous structure.

Extrusion process induced an increase of calcium-protein bridges.

Temperature of extrusion had less effect on SME of cooked than uncooked curds.

Abstract

Renneted casein gels, often named cheese curds, are traditionally pre-heated by immersion in water before stretching, which influences cheese functional properties. This work aims to understａnd the effect of pre-heating (cooking) on extrusion process of cheese curds at 80 and 90 °C in a lab twin-screw, co-rotating extruder, and consequences for composition, microstructure and functional properties of the extrudates. The cooking significantly enhanced curd meltability and oiling-off, resulting in faster extrusion, higher exit temperature and lower specific mechanical energy. Microscopic observations at different length scales, combining confocal laser scanning microscopy and X-ray micro-tomography, showed that cooking caused extensive fat coalescence and cracks in protein matrix, resulting in extrudates with less fibrous structure, lower elasticity and tensile strength. The extrusion process induced significantly increased of calcium bridges in extrudates, which may replace weak water-protein interactions and increase relaxation time of the more water fraction (T2.2). The specific mechanical energy was less influenced by the extrusion temperature in cooked than uncooked curds, likely due to a more extensive oiling-off during extrusion of the cooked curd. In agreement with the microscopic observations, extrudates obtained at 80 °C differ from 90 °C specially regarding fat content respectively 23.8–24.8% and 29.5% (w/w) and fat globule size and distribution, influencing fiber formation. In general curds extruded at 90 °C had higher elasticity and tensile strength, which was related to the well-elongated fat domains. This study provided knowledge about extrusion process of curds generating new ideas to improve cheese processing and design customized cheese products.

Keywords Cooking Extrusion Cheese curd Structure 

Figure 2. Images from cros-sectional view and fiber formation of uncooked curd extruded at 80°C, cooked curd extruded at 80°C, uncooked curd extruded at 90°C and cooked curd extruded at 90°C.