Effect of Processing on Cow’s Milk Protein Microstructure and Peptide Profile After In Vitro Gastrointestinal Digestion

Cow’s milk is an important part of the human diet, primarily due to its high nutritional content, particularly proteins and fats. The processing of milk enhances its safety while modifying its composition and structure, influencing bioactive peptide release, which impacts protein quality, digestion, and allergenicity. Recently, filtered milk, which undergoes pasteurisation and microfiltration, has become available in UK supermarkets, offering a longer shelf life than pasteurised milk. This study aimed to evaluate the effects of microfiltration on the protein structure of cow’s milk, compared with pasteurisation, including analysis of the peptide profile released after in vitro gastrointestinal digestion of commercially available semi-skimmed filtered and pasteurised cow’s milk. Dynamic light scattering analysis revealed that the Z-average particle size of filtered milk was significantly (p < 0.05) larger than that of pasteurised milk across all brands. Additionally, filtered milk exhibited a significantly (p < 0.05) lower free thiol concentration compared with pasteurised milk, indicating structural modifications in proteins. Confocal laser scanning microscopy (CLSM) further highlighted heterogeneities in the distribution of fat and protein, with filtered milk samples showing increased interaction between fat globules and proteins. After gastrointestinal digestion, the numbers of peptides released from filtered milk exceeded those of peptides released from pasteurised milk by an average of 5%. These results provide new insights into the potential impact of microfiltration on the microstructure of milk. Further investigations using advanced analytical techniques are needed to assess the implications of these changes on protein bioavailability and human health.