Physicochemical, antioxidant properties and in vitro digestibility of wheat–purple rice flour mixtures

Abstract

SummaryThe physicochemical characteristics, antioxidant properties and in vitro digestibility of high-antioxidant content flours made from different combinations of Thai purple rice flour and refined wheat flour from 25%, 50% to 75% (w/w) were investigated and these were compared with whole flour from purple rice and refined wheat flour. The increase in substitution levels of purple rice flour affected all the functional properties of flours, at the same time the levels of dietary fibre, protein digestibility and antioxidant compositions were also changed. The purple rice flour exerted a particularly strong effect on starch digestibility as the purple rice increased to 50% in the mixture. Moreover, purple rice flour showed lower amounts of rapidly digested starch (RDS), whereas slowly digested starch (SDS) of whole flour from purple rice and 75% substitution purple rice flour was found to be the highest for all samples. The in vitro starch digestibility of all samples also showed a positive correlation between dietary fibre and antioxidant compounds. Overall, the addition of purple rice flour improved the final nutritional properties, notably a lower predicted glycaemic index, and a higher antioxidant potential, which are two important nutritional properties for human health.

Biscuits: A Substitution of Wheat Flour with Purple Rice Flour

“…Dietary fiber in the bran and germ of cereal grains has been added to biscuit formulations that originally contained almost no dietary fiber in the original recipe [33,47,48]. Substitution of purple rice flour for wheat flour will not only increase the dietary fiber and bioactive contents, but it is also a cheaper raw material [49].…”

“…In Thailand, red, purple and black rice is widely grown in different locations [56], which results in many different pigmentation phenotypes being observed throughout the country [57]. Many of the pigmented rice cultivars are reported to contain higher levels of antioxidants than white rice [15,36,49,58]. This can be classified depending on anthocyanin and proanthocyanidin compounds in the aleurone layer of rice grain [59].…”

“…Purple rice (var. Sanpatong) is widely grown in Northern Thailand and is becoming a popular crop because of its improved taste compared to white rice [15,49,62]. However, the price of purple rice is five times higher than normal white rice due to its lower productivity.…”

“…The bran layer of this rice has a high level of antioxidant compounds, mainly phenolic acids, flavonoids, anthocyanins and oryzanols [60,[64][65][66]. Purple rice has been shown to have significantly more anthocyanin contents than pigmented corn, wheat and barley [15,49,56,60]. The study of the anthocyanin profile by spectroscopy assay showed that extracted purple rice has four active components; cyanidin-3-O-glucoside (C3G), peonidin-3-O-glucoside, cyanidin-3,5-diglucoside, and cyanidin-3-glucoside [56,58].…”

A preparation of β-glucans and anthocyanins (LoGiCarb™) lowers the in vitro digestibility and in vivo glycemic index of white rice

“…There have been well-conducted studies on the efficacy of certain plant extracts that can lower the digestibility of starches. [2][3][4][5] Anthocyanins have been shown to have an effect on multiple pathways of starch digestion, including inhibition of amylase and glucosidase, 6,7 increasing the proportions of slowly digestible starch (SDS) and resistant starch (RS) and decreasing the proportion of rapidly digestible starch 2,3,5 and altering the starch matrix.…”