Rheology and Microstructures of Rennet Gels from Differently Heated Goat Milk

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.

Rheological Properties of Goat Milk Coagulation as Affected by Rennet Concentration, pH and Temperature

“…Often low protein content, especially αs1-casein in goat milk, contributes to lower firmness of rennet coagulated gel compared to cow milk, and also to lower production yield due to higher losses during curd processing [8]. Furthermore, high heat treatment of goat milk has a different effect on milk components, primarily proteins [14] and the coagulation process [15]. Despite the foregoing, goat milk products are usually produced based on technological procedures which apply to cow milk [16].…”

High Heat Treatment of Goat Cheese Milk. The Effect on Sensory Profile, Consumer Acceptance and Microstructure of Cheese

“…The microstructure of rennet gel (45 min after the addition of rennet) from milk heated to 80 °C/5 min showed higher level of similarity to gel from commonly pasteurized milk (65 °C/30 min) than to gel from milk heated to 90 °C/5 min [ 10 ]. After cheese production, a number of processes occur simultaneously, caused by fermentation/acidification.…”

“…The samples for SEM analysis (approximately5 mm × 5 mm × 15 mm) were cut from the interior of cheese blocks of C, E1 and E2 cheese variants after 3, 10 and 40 days of ripening. Samples were defatted and fixed as in the study of Miloradovic et al [ 10 ] critical point dried with liquid carbon dioxide, using a K850 Critical Point Drier (Quorum Technologies, Laughton, UK). Dried fractured rennet gel samples were attached to stubs and sputter coated with gold (50 nm) for 100 s at 30 mA (Sputter Coater BAL-TEC SCD 005, Scotia, New York, NY, USA).…”

“…Hence, high heating regimes have been successfully applied for goat rennet cheese yield enhancement [ 9 ]. Such a simple method leading to higher profitability is particularly significant since almost all goat cheese production is done at small scale [ 10 ].…”

Changes in Native Whey Protein Content, Gel Formation, and Endogenous Enzyme Activities Induced by Flow-Through Heat Treatments of Goat and Sheep Milk

“…The heat stability and heatinduced changes in the mineral balance of goat or sheep milk have been reported [9,[13][14][15][16][17]. The rennet clotting behavior of small ruminants' milk under various heating conditions has been assessed [13,[18][19][20]. There are also publications for the effect of heat treatments on the activity of endogenous enzymes that are indices for heat load such as alkaline phosphatase [21][22][23][24][25] and lactoperoxidase [23,26,27].…”