Abstract
Rice bran is an underutilized side-stream from white rice production, rich in protein and dietary fibre. The aim of the work was to study dry fractionation as a novel approach to enrich protein from non-heated, supercritical carbon dioxide–extracted milled rice bran. One-step air classification allowed protein enrichment from an original 18.5% up to 25.7% in the fine fraction. Alternatively, air classification of the non-milled raw material resulted in a fine fraction (19.7% protein) that was according to microscopy analysis free of pericarp structures, and a coarse fraction containing protein-rich aleurone and germ particles and pericarp structures. Further milling and air classification of the coarse fraction resulted in higher protein enrichment (to 27.4%). All the fine fractions produced by dry fractionation were also enriched in soluble dietary fibre whereas starch content was decreased. Additionally, the fine fractions showed improved protein solubility and colloidal stability and, thus, elevated applicability in food products as compared to the non-fractionated raw material.
Highlights
Increasing the use of plant-based proteins and foods in human nutrition is recommended from food security and sustainability perspectives (Aiking 2011)
In the whole rice kernel, a pericarp layer was observed as the outermost structure with a cuticle and an aleurone layer composed of cells containing protein underneath (Fig. 2a)
A fresh, non-heat stabilising, and defatted rice bran was used as a raw material in dry fractionation trials, since defatting is a prerequisite for milling which is needed in efficient dry fractionation (Schutyser et al 2015; Sibakov et al 2011)
Summary
Increasing the use of plant-based proteins and foods in human nutrition is recommended from food security and sustainability perspectives (Aiking 2011). This has raised an interest to valorise protein-rich ingredients from the by-products of the current agro-food industry. Rice bran, accounting for around 10% of the rice grain, is an underutilized side-stream from the white rice production process. Commercial milling of brown rice usually results in a by-product containing outer grain layers, germ, and some endosperm fractions, which are together called as rice bran. Due to the relatively high protein content of 13–19% (Juliano and Bechtel 1985) and dietary fibre (DF) content of 20–30% (AbdulHamid and Luan 2000; Juliano 1985; Saunders 1990), rice
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