Variation of Phenolics, Tocols, Antioxidant Activities, and Soluble Sugar Compositions in Red and Black Rice (Oryza sativa L.) During Boiling

Abstract

Cereal Chem. 94(5):811-819This study systematically examined hydrothermal effects of antioxidant substances, such as total phenolic (TPC), flavonoid (TFC), and proanthocyanidin (TPAC) contents, cyanidin-3-O-glucoside (C3G), peonidin-3-O-glucoside (P3G), a-, g-, and d-tocopherols, and a-, g-, and d-tocotrienols, as well as antioxidant activities, color parameters, and soluble sugar compositions in red and black rice. It showed that color differences (DE) of black rice were higher than those of red rice caused by boiling. The processed red and black rice exhibited significantly (P < 0.05) lower TPC, TFC, TPAC, C3G, P3G, and antioxidant activities compared with the raw rice except bound TPC and bound antioxidant activity. Interestingly, soluble free pcoumaric and ferulic acids had higher contents in cooked red rice, and soluble free protocatechuic, vanillic, and sinapic acids had higher contents in cooked black rice. Boiling caused significant decreases of soluble conjugated phenolic acids and significant increases of insoluble bound phenolic acids in both red and black rice. Increases of total free tocol, glucose, and fructose contents were observed in most red and black rice. To increase the contents of some soluble free and insoluble bound phenolic acids, free vitamin E, and monosaccharides in red and black rice, boiled rice might be a good choice.

Vitamins in Cereals: A Critical Review of Content, Health Effects, Processing Losses, Bioaccessibility, Fortification, and Biofortification Strategies for Their Improvement

“…Taken together, parboiling, storage, and recooking as well as extrusion cooking can cause a loss of up to 90% of the total tocol content of rice ( 120 , 128 ). The loss of vitamin E after boiling is low, instead, an increase in the content has been reported in some cases, which is due to improved extraction after boiling ( 121 , 122 ) ( Table 6 ).…”

Effect of processing methods and storage on the bioactive compounds of black rice (Oryza sativa L.): a review

“…However, there was a notable rise in the amount of γ-tocotrienol, α-tocotrienol, γ-tocopherol, and total tocols. 118 When the cooking time is the same, the contents of total phenolic content, total flavonoid, condensed tannin, monomeric anthocyanin, cyanidin-3-glucoside, and peonidin-3-glucoside, as well as the antioxidant activities of black rice cooked by an electric hot plate cooker, are higher than those cooked by an automatic house-hold rice cooker. 119 The main reasons for the differences in polyphenol changes in black rice caused by different cooking methods are different cooking pressures and temperatures.…”

The Impact of Cereal Grain Composition on the Health and Disease Outcomes

“…Folic acid losses were lower after boiling and frying compared to microwave and pressure cooking ( 129 , 130 ) while vitamin B12 losses after boiling are moderate ( 131 ). Among methods that could cause vitamin C loss, pressure cooking appears to induce the maximum loss ( 132 , 133 ). Interestingly, a study carried out on two varieties of rice showed that boiling increases antioxidant activities and the glycaemic index but does not impact on the phenolic content ( 134 ).…”