Health Benefits and Phenolic Profiles of Pigmented Rice

Title: Phenolic Compounds and Potential Health Benefits of Pigmented Rice

Journal: IntechOpen – Recent Advances in Rice Research

Published: 2020

Background

Pigmented rice varieties such as black, red, and purple rice are rich in bioactive compounds, especially phenolic acids, anthocyanins, and proanthocyanidins. These compounds contribute to the rice's antioxidant, anti-inflammatory, antidiabetic, and anticancer properties. As consumer interest in functional foods rises, pigmented rice has gained attention for its potential health benefits. This chapter discusses the advanced analytical methods used to isolate and study these compounds, emphasizing the health-promoting roles of phenolic constituents in pigmented rice.

Materials & Methods

Extraction Techniques:

Conventional: Manual solvent extraction using various acidified methanol mixtures, acetone/water. Phenolics (soluble-free, conjugated, insoluble-bound) were extracted with 80% methanol, ethyl acetate, NaOH. Solid phase extraction (SPE) was used to purify polyphenols in pigmented rice.

Non-conventional:

Microwave-Assisted Extraction (MAE): Conditions (e.g., 70°C, 300 W, 10 min) effectively extracted anthocyanins.
Ultrasound-Assisted Extraction (UAE): Used 80% methanol, optimized at 45°C, 25 min for phenolic compounds.

Identification & Quantification:

Techniques: HPLC, LC-ESI-MS/MS, UPLC-ESI-QqQ-MS/MS.
Conditions: UPLC with HSS T3 column, mobile phase: 0.1% formic acid (A) & 0.1% formic acid in acetonitrile (B), 12 min run time.
Ion Modes: Positive mode for caffeic, ferulic acids, catechin, anthocyanins; negative for p-coumaric acid, quercetin.
Quantification: Based on external standards using MRM transitions.

Results

Phenolic Compounds Detected:

Vanillic, p-coumaric, protocatechuic, caffeic, ferulic acids (ferulic acid was major).
Flavonoids: Quercetin, catechin.
Anthocyanins: Cyanidin-3-O-glucoside predominant, especially in black rice. Malvidin-3-O-glucoside not detected.
Proanthocyanidins: Found only in red and black rice; concentration varied widely by genotype (15.57–1417.12 mg/kg).

MS/MS Fragmentation Data:

Ferulic acid: m/z 195 → 136.
Cyanidin-3-O-glucoside: m/z 449 → 287.
Pelargonidin-3-glucoside: m/z 433 → 271.
Peonidin derivative: m/z 463 → 301.

Quantitative Highlights:

Cyanidin-3-O-glucoside content higher in black rice than red.
Sri Lankan red rice bran: 11.95–24.70 mg/g proanthocyanidins; brown rice: 1.07–2.27 mg/g.

Chromatogram of cyanidin 3-O-glucoside (Wongsa et al., 2020)

(a) MS/MS spectrum of cyanidin 3-O-glucoside. (b) MS/MS spectrum of pelargonidin-3-O-glucoside. (c) MS/MS spectrum of peonidin 3-O-glucoside (Wongsa et al., 2020)

Reference

Wongsa, Prinya. "Phenolic compounds and potential health benefits of pigmented rice." Recent advances in rice research. IntechOpen, 2020. https://doi.org/10.5772/intechopen.93876

* For Research Use Only. Not for use in diagnostic procedures.

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