Partial replacement of animal protein sources with plant proteins is highly relevant for the food industry, but potential effects on protein digestibility need to be established. In this study, the in vitro protein digestibility (IVPD) of four protein sources and their mixtures (50:50 w/w ratio) was investigated using a transient pepsin hydrolysis (1 h) followed by pancreatin (1 h). The protein sources consisted of napin-rich rapeseed (Brassica napus L.) protein concentrates (RPCs; RP1, RP2) prepared in pilot scale and major bovine whey proteins (WPs; α-LA, alpha-lactalbumin; β-LG, beta-lactoglobulin). IVPD of individual protein sources was higher for WPs compared to RPCs. The RP2/β-LG mixture resulted in an unexpected high IVPD equivalent to β-LG protein alone. Protein mixtures containing RP1 showed a new IVPD response type due to the negative influence of a high trypsin inhibitor activity (TIA) level. Improved IVPD of RP1 alone and in protein mixtures was obtained by lowering the TIA level using dithiothreitol (DTT). These results showed that napin-rich protein products prepared by appropriate processing can be combined with specific WPs in mixtures to improve the IVPD.
Summary
Pressed cake from rapeseed (Brassica napus L.) is a promising plant protein source not yet utilised for human consumption due to the presence of antinutrients such as glucosinolates. Protein solubility is a crucial parameter influencing the functionality and thereby the applicability of proteins as food ingredients. A novel cruciferin‐rich rapeseed protein product was produced by an aqueous processing method in pilot plant scale. Intact glucosinolates were conserved by this procedure and largely removed from the protein products. Protein solubility in this product was examined when dispersed in 50 mm phosphate buffer, pH 8.0 with varying NaCl concentration (0–500 mm). Unexpectedly, a salting‐out effect was observed of the globulin proteins, as 15.9 ± 0.6% protein was in solution at 500 mm added NaCl, whereas 21.5 ± 1.1% was solubilised without added NaCl; whether the observed effects originates from lipid and fibre constituents in the product remains to be resolved.
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