Abstract
Little is known about the extent of variation and activity of naturally occurring milk glycosidases and their potential to degrade milk glycans. A multi-omics approach was used to investigate the relationship between glycosidases and important bioactive compounds such as free oligosaccharides and O-linked glycans in bovine milk. Using 4-methylumbelliferone (4-MU) assays activities of eight indigenous glycosidases were determined, and by mass spectrometry and 1H NMR spectroscopy various substrates and metabolite products were quantified in a subset of milk samples from eight native North European cattle breeds. The results showed a clear variation in glycosidase activities among the native breeds. Interestingly, negative correlations between some glycosidases including β-galactosidase, N-acetyl-β-d-glucosaminidase, certain oligosaccharide isomers as well as O-linked glycans of κ-casein were revealed. Further, a positive correlation was found for free fucose content and α-fucosidase activity (r = 0.37, p-value < 0.001) indicating cleavage of fucosylated glycans in milk at room temperature. The results obtained suggest that milk glycosidases might partially degrade valuable glycans, which would result in lower recovery of glycans and thus represent a loss for the dairy ingredients industry if these activities are pronounced.
Highlights
Since domestication, cattle have been selectively bred to improve different production traits such as meat quality or milk yield [1]
The present study investigated variations in glycosidase activities and naturally occurring OS, O-linked glycans of κ-CN and monosaccharides, as well as the potential associations between glycan substrates (OS and O-linked glycans) and metabolite products, in milk from native cattle breeds, based on the same sample set as Sunds et al [10]
An intriguing finding was the high activities of most glycosidases in milk from Norwegian Telemark cattle, which displayed significantly higher activities compared to the overall mean for both N-acetylβ-glucosaminidase, β-glucuronidase, α-fucosidase, β-galactosidase, α-glucosidase and β-glucosidase (p-values being
Summary
Cattle have been selectively bred to improve different production traits such as meat quality or milk yield [1]. Cattle breeds that were originally native to specific farming regions have been replaced by high-yielding breeds, e.g., Holstein-Friesians, which are high in milk yield [1,2,3]. The breeds, present great phenotypic diversity reflected in different coat colours, sizes of horns and milk compositional traits. This diversity can be attributed to adaptations to distinct environments and management systems, genetic drift and isolation in local geographic areas. They are, a unique genetic resource due to their diverse gene pool and phenotypic characteristics [2,4]
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