Heating Reduces Proso Millet Protein Digestibility via Formation of Hydrophobic Aggregates

Abstract

Proso millet protein has reported structural similarities with sorghum. In order to explore the potential of this crop as an alternative protein source for people with gluten sensitivity, in vitro protein digestibility was analyzed. Dehulled proso millet flour was subjected to various processing techniques (dry heating and wet heating). Regardless of the processing technique there was a significant decline in digestibility of protein in proso millet flour when compared with unprocessed flour (from 79.7 ± 0.8% to 42.0 ± 1.2%). Reduced digestibility persisted even when cooking with reducing agents. Heating in the presence of urea (8 M) and guanidine-HCl (4.5 M) prevented the reduction in observed digestibility (urea cooked 77.4 ± 0.8%; guanidine HCl cooked 84.3 ± 0.9%), suggesting formation of hydrophobic aggregates during heating in water. This was supported by an increase in surface hydrophobicity upon cooking. Thus, the proso millet protein, termed panicin, forms hydrophobic aggregates that are resistant to digestion when subjected to heat.

Potential anti-inflammatory and lipase inhibitory peptides generated by in vitro gastrointestinal hydrolysis of heat treated millet grains

“…The heating process had an influence on the number of protein patterns in all protein fractions. The strongest effect was observed for protein fractions obtained after the treatment at 100°C, which is associated with the process of protein denaturation (Gulati et. al, 2017).…”

In vitro digestibility of proteins from historical and modern wheat cultivars

“…Gastrointestinal protein digestion was measured as described by Gulati et al, 11 with slight modifications. Dried, ground bread (120 mg) was suspended in 4 mL of simulated gastric fluid (SGF; 0.5 mol L -1 NaCl adjusted to pH 2.5 with HCl) and incubated at 37°C for 10 min.…”

“…Three milliliters of pancreatin (P-7545, Sigma-Aldrich) in SIF (2 mg mL -1 ) containing 2 μL mL -1 amyloglucosidase (3260 U mL −1 ; E-AMGDF, Megazyme, Bray, Ireland) was added to flour mixture and incubated for 4 h. Intestinal digestion was stopped by plunging the tubes into a boiling water bath for 5 min and then was immediately cooled. The digested samples were centrifuged and the supernatants were analyzed for primary amine groups with 2,4,6-trinitrobenzenesufonic acid (TNBS) using leucine as the standard as described in Gulati et al 11 Enzyme blanks, that is tubes containing enzymes and buffers without flour, were maintained and analyzed to correct for primary amines generated by the enzymes alone and subtracted from the sample results. Digestion for each sample was performed in duplicate and primary amines in each digested sample were further analyzed in duplicate.…”

Effect of domestic cooking on rice protein digestibility

“…In some Asian countries, pre‐cooking processes, such as washing and soaking, are performed to remove remaining dust, hull, and bran on the rice kernel surface and improved cooking quality (Yu, Turner, Fitzgerald, Stokes, & Witt, ). However, cooking, especially heat‐moisture treatment, can reduce protein digestibility of many cereals, such as rice (Kubota et al., ), wheat (Wu, Taylor, Nebl, Ng, & Bennett, ), sorghum (Vu, Bean, Hsieh, & Shi, ), and millet (Gulati et al., ). Factors affecting cereals protein digestibility can be categorized into exogenous and endogenous factors.…”