Abstract
While the harmonized INFOGEST model provides a physiologically relevant platform for simulated digestion, it needs to be combined with adequate analytical methods to enable quantification and comparison of protein digestibility in different food matrices. We have shown that size exclusion chromatography (SEC) can be used to estimate the proportion of small peptides potentially available for uptake. Combined with determination of total dissolved protein, the % of small peptides per total protein was calculated as a physiologically relevant estimate of protein digestibility (DSEC). Values for DSEC differed for casein (87.6%), chicken mince (72.6%), heated pea protein concentrate (67.8%), bread (63%), beef entrecote (57.7%) and pea protein concentrate (57.8%). In contrast to existing methods (TCA soluble protein, free NH2-groups), the proposed SEC based method gives separate insight into the two fundamental processes during protein digestion (solubilization and break-down), while maintaining the ability to rank digestibility of very different food proteins.
Highlights
Dietary protein quality comprises two aspects, i.e., amino acid composition and availability
While Protein efficiency ratio (PER) is based on a rat growth assay, protein di gestibility corrected amino acid score (PDCAAS) and digestible indis pensable amino acid score (DIAAS) use amino acid scoring patterns in combination with protein digestibility based on true fecal nitrogen digestibility (PDCAAS) or true ileal digestibility of individual amino acids (DIAAS)
In this study we have further explored the use of size exclusion chromatography (SEC) for characterization and quantification of peptides released during in vitro digestion com bined with determination of soluble nitrogen
Summary
Dietary protein quality comprises two aspects, i.e., amino acid composition and availability. TCA pre cipitation is based on size and has been shown to correlate best with hydrophobicity of peptides (Yvon, Chabanet, & Pelissier, 1989) In all these cases, digestibility is defined as the proportion of soluble pro tein (measured as nitrogen or sum of amino acids) compared to total protein, with no or very little consideration to the significant amount oligopeptides in the digests. Digestibility is given either as the number of free NH2 groups per g protein or as the degree of hydrolysis, which is the number of hydrolyzed peptide bonds divided by the total number of peptide bonds in the sample (htot) All these quantitative methods are relatively simple to perform and can be used to compare complex foods, but the measured digestibility (in %) does not necessarily reflect the protein portion available for absorption. Results were compared with TCA precipitation and the TNBS approach with the aim to evaluate and select a simple, quantitative method which enables the direct comparison of protein digestibility in different food products
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