Abstract
Rennet coagulation of goat milk heated to 65 °C/30 min (Gc), 80 °C/5 min (G8) and 90 °C/5 min (G9) was studied. A rheometer equipped with a vane geometry tool was used to measure milk coagulation parameters and viscoelastic properties of rennet gels. Yield parameters: curd yield, laboratory curd yield and curd yield efficiency were measured and calculated. Scanning electron microscopy of rennet gels was conducted. Storage moduli (G’) of gels at the moment of cutting were 19.9 ± 1.71 Pa (Gc), 11.9 ± 1.96 Pa (G8) and 7.3 ± 1.46 Pa (G9). Aggregation rate and curd firmness decreased with the increase of milk heating temperature, while coagulation time did not change significantly. High heat treatment of goat milk had a significant effect on both laboratory curd yield and curd yield. However, laboratory curd yield (27.7 ± 1.84%) of the G9 treatment was unreasonably high compared to curd yield (15.4 ± 0.60%). The microstructure of G9 was notably different compared to Gc and G8, with a denser and more compact microstructure, smaller paracasein micelles and void spaces in a form of cracks indicating weaker cross links. The findings of this study might serve as the bases for the development of different cheese types produced from high-heat-treated goat milk.
Highlights
Rennet coagulation is a fundamental part of the cheese making process, affecting both the quality and yield of cheese [1]
While in Gc and G8, the protein matrix was composed from large regular spheres of paracasein micelles, large void spaces and thick protein cross links, the G9 matrix was characterized by a dense, It could be concluded that heat treatment of goat milk prior to rennet coagulation affects compact microstructure, with smaller paracasein micelles and void spaces in a form of cracks, indicating significantly rennet coagulation, curd yield and gel microstructure
The higher the heat treatment, the slower the coagulation and the lesser the elastic nature of gels, but the final gels were less prone to rearrangement
Summary
Rennet coagulation is a fundamental part of the cheese making process, affecting both the quality and yield of cheese [1]. Factors affecting rennet coagulation of cow milk have been studied continually for decades and continue to be of interest [2,3]. Rheological measurements are a good tool for investigating rennet coagulation and the performances of different milk types. The viscoelastic nature of rennet gels is determined by rheological parameters such as storage modulus (G’) and loss modulus (G”) [3]. These parameters are often used to calculate milk coagulation properties (MCP) described by the following parameters: coagulation time (CT), aggregation rate (AR) and curd firmness (CF) [4,6].
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