Grazing season and forage type influence goat milk composition and rennet coagulation properties

Two different types of pasture (cultivated and rangeland) and 2 different hay qualities (high and low quality) were examined for their effects on goat milk composition and rennet coagulation properties. Furthermore, the effect of dietary treatments in both the early and late grazing season was studied. As lactation stage is known to influence milk composition, the goats in the early and late grazing season were in the same lactation stage at the start of the experiment. The milk composition was influenced both by dietary treatment and season. Milk from goats on pasture was superior to those on hay by containing a higher content of protein and casein, and the goats on cultivated pasture had the highest milk yield. Casein composition was significantly influenced by forage treatment. Goats grazing on cultivated pasture had higher contents of αs1-casein and also of κ-casein compared with the other treatments, whereas goats grazing on rangeland had the highest content of β-casein. Factors such as milk yield, casein micelle size, αs2-casein, and calcium content were reduced in late compared with early season. More favorable rennet coagulation properties were achieved in milk from the early grazing season, with shorter firming time and higher curd firmness compared with milk from the late grazing season, but the firming time and curd firmness were not prominently influenced by forage treatment. The content of αs2-casein and calcium in the milk affected the firming time and the curd firmness positively. The influence of season and forage treatment on especially milk yield, casein content, and rennet coagulation properties is of economic importance for both the dairy industry and goat milk farmers

Degradation of β-casomorphin-7 through in vitro gastrointestinal and jejunal brush border membrane digestion.

This work aimed to study the opioid peptide β-casomorphin-7 (BCM7) degradation or stability during digestion using human gastrointestinal (GI) juices and porcine jejunal brush border membrane (BBM) peptidases. Synthetic BCM7 was subjected to in vitro digestion by GI fluids obtained from human volunteers for 180 min, and to downstream degradation with porcine BBM vesicles. The BCM7 was sampled at 4 time points over 24 h after BBM addition. The digests were profiled by HPLC-electrospray ionization mass spectrometry (ESI/MS) to monitor BCM7 during GI digestion, and intact BCM7 through BBM digestion was quantified by reverse-phase (RP)-HPLC. We found that BCM7 was partly digested with human GI enzymes, as 3 proteolytic fragments in addition to f(60–66) YPFPGPI were detected: f(62–66) FPGPI, f(60–65) YPFPGP and f(61–66) PFPGPI. The RP-HPLC analysis revealed that 42% of the initial peptide was degraded after only 2 h of BBM digestion, and as much as 79% was degraded after 4-h digestion with supplementation of BBM. In conclusion, this study showed that most of BCM7 was degraded during GI and BBM digestion, although a small amount (5%) was still detected after 24-h digestion. It remains to be studied whether the small amount of intact BCM7 detected after in vitro digestion is transported via active transceptors in the human intestinal epithelial cells and enters blood circulation