Factors Influencing the Stability of Goat Milk Proteins
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Abstract:
This study examined the effects of various factors on protein stability in the colostrum and mature milk of Laoshan dairy goats. The centrifugal sedimentation rate of goat milk proteins was analyzed under various conditions, including a range of temperatures and pH values, citric acid, calcium ion, sucrose, and ultra-high pressure, to evaluate the stability of the milk proteins. The results showed that colostrum was the most sensitive to heat during the first 1~3 days. On the first day, milk samples became extremely thick when heated up to 65 ℃ for 15 min, and both first-day and second-day milk samples caked and solidified when heated up to 70 ℃ for 15 min. The third-day milk samples caked and solidified when heated up to 85 ℃ for 15 min, and milk at 4~7 days did not cake or solidify when heated at 95 ℃. Therefore, as the lactation period was extended, the thermal stability of goat milk increased gradually. The goat milk had the highest stability at pH 6.9. When less than 1.0 mg/100 mL sucrose was added, the stability of the emulsion containing milk proteins was reduced, and when greater than 1.0 mg/100 mL was added, the milk stability increased with an increasing sucrose concentration, and the stability of milk casein micelles increased. The stability of goat milk protein decreased with increases in the citric acid and calcium ion concentrations. There was little effect of ultra-high-pressure processing at 300 MPa on the protein precipitation rate. At 500 MPa, the sedimentation rate significantly increased, reaching a maximal value of 7.35% after treatment for 15 min. Treatment with greater than 500 MPa caused a significant reduction in protein stability.
