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

The harmonized INFOGEST in vitro digestion method: From knowledge to action

Within the active field of in vitro digestion in food research, the COST Action INFOGEST aimed to harmonize in vitro protocols simulating human digestion on the basis of physiologically inferred conditions. A harmonized static in vitro digestion (IVD) method was recently published as a primary output from this network. To validate this protocol, inter-laboratory trials were conducted within the INFOGEST network. A first study was performed using skim milk powder (SMP) as a model food and served to compare the different in-house digestion protocols used among the INFOGEST members. In a second inter-laboratory study applying the harmonized protocol, the degree of consistency in protein hydrolysis was investigated. Analysis of the hydrolyzed proteins, after the gastric and intestinal phases, showed that caseins were mainly hydrolyzed during the gastric phase, whereas β-lactoglobulin was, as previously shown, resistant to pepsin. Moreover, generation of free amino acids occurred mainly during the intestinal phase.The study also showed that a few critical steps were responsible for the remaining inter-laboratory variability. The largest deviations arose from the determination of pepsin activity. Therefore, this step was further clarified, harmonized, and implemented in a third inter-laboratory study.The present work gives an overview of all three inter-laboratory studies, showing that the IVD INFOGEST method has led to an increased consistency that enables a better comparability of in vitro digestion studies in the future

Formation of biogenic amines and vitamin K contents in the Norwegian autochthonous cheese Gamalost during ripening

International audienceGamalost, a Norwegian mould (Mucor mucedo) ripened autochthonous cheese, is a potential functional food due to a high content of peptides that might reduce hypertension, however it has a high content of free amino acids which may be precursors for biogenic amines. This study aimed to investigate if Gamalost might have further health benefits or risks by determination of the formation of vitamin K and biogenic amines. The development of biogenic amines and vitamin K was analysed during ripening. Putrescine was the only biogenic amine detected by liquid chromatography in ripened Gamalost, in the range from 11 to 25 mg.kg−1. The presence of very low concentrations of biogenic amines may suggest that Gamalost is devoid of hazards posed on health. The menaquinones (vitamin K2) detected in Gamalost by high-performance liquid chromatography were MK-4 to MK-10 and among them, MK-9 was found in the significantly highest concentration (46 μg.100 g−1). The menaquinone content of Gamalost was attributed to the activities of the starter lactic acid bacteria used for fermentation during manufacture. Gamalost contained a significantly higher menaquinone content than Norvegia, a Norwegian cheese

Angiotensin I-converting enzyme inhibitory and antioxidant properties of rapeseed hydrolysates

v2012o

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

A comparison of effects of pH on the thermal stability and conformation of caprine and bovine lactoferrin

Thermal stability and structural changes in caprine lactoferrin (cLF) and bovine lactoferrin (bLF) at pH 2.0-8.0 were measured using thermal denaturation temperature (Tm) analysis, fluorescence spectroscopy and circular dichroism (CD). Thermal stability analysis indicated a Tm of 70°C for bLF and 67°C for cLF at pH 7.0. From pH 7.0 to 3.0, a gradual reduction in the Tm of both bLF and cLF was observed and reached a value of 39°C and 30°C, respectively. At pH 2.0-3.0, a partly unfolded structure of bLF and cLF was observed with a relatively low content of α-helix structure (3% and 7%, respectively), but still rich in β-structure (54% and 57%, respectively). A higher exposure of hydrophobic surfaces at low pH for bLF compared with cLF was proved by fluorescence studies. In conclusion, the structure of cLF was more affected by pH and showed lower temperature stability than bLF

Comparison of the digestion of caseins and whey proteins in equine, bovine, caprine and human milks by human gastrointestinal enzymes

The aim of this study was to compare the digestion of milk proteins from different species using an in vitro gastrointestinal model. Raw and heated milks from bovine, caprine, human and equine species were digested by human digestive enzymes. Digestion was performed in two 30-min sequential steps by digestive juices from the stomach (pH 2.5/37 °C) and from the duodenum (pH 8.0/37 °C). The degradation patterns of the milk proteins were visualized by SDS-PAGE and quantified using the ImageQuant program. Caseins in the equine milk were rapidly digested by the gastric juice in contrast to the caseins from the other species. During the subsequent digestion by the duodenal juice most of the caseins from all species were degraded within 5 min, and within 30 min only traces of caseins were detected. The mean casein micellar size varied between species in the range of 146.0–311.5 nm (equine > caprine > bovine > human). The α-lactalbumin from all species appeared to be very resistant to both gastric and duodenal digestions. A similar trend was shown for β-lactoglobulin from bovine and caprine milks, of which ~ 60% intact protein remained, while only 25% remained intact in equine milk after total digestion. Equine milk contained a high amount of lysozyme, of which 60% remained intact in the present study. In heated milks from all species, only α-lactalbumin degradation increased approximately 12–20% in comparison to the raw milk. This study shows that equine milk with fast digestible proteins could be considered as a replacement for bovine milk in the diet of people with special needs, such as infants and the elderly