Rheology and Microstructures of Rennet Gels from Differently Heated Goat Milk

Abstract

Rennet coagulation of goat milk heated to 65 degrees C/30 min (Gc), 80 degrees C/5 min (G8) and 90 degrees 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.