NMR comparison of in vitro digestion of Parmigiano Reggiano cheese aged 15 and 30 months

Abstract

The content of essential amino acids is an important aspect for determining the nutritional value of food proteins, but their digestibility is also a key property, deeply affected by food processing. The production of Parmigiano Reggiano cheese is closely related to the nutritional quality of the final product; in particular the high digestibility of its proteins is claimed to be proportional to cheese aging. Two different kinds of Parmigiano Reggiano, young (aged 15 months) and old (aged 30 months), were separately digested using an in vitro system that simulates digestive processes in the mouth, stomach and small intestine. Samples were collected at different stages of digestion and the process of protein hydrolysis was explored and compared by low-field (LF) and high-resolution (HR) NMR, together with other biochemical methods. HR-NMR allowed to simultaneously observe the quantity of free amino acids, peptides and proteins, also giving for these latter qualitative information about their dimension. LF-NMR, instead, gave the possibility to observe digestion with no treatments whatsoever, thus representing a technique suitable for on-line measurements. The results pointed out that cheeses with different aging times, although starting from distinct initial compositions, conclude digestion in a similar way, in terms of free amino acids and small organic compounds, but evolve with different kinetics of hydrolysis and peptide formation, discriminating the young from the old cheese.