Polyphenol Bioavailability and Plasma Antiradical Capacity in Healthy Subjects after Acute Intake of Pigmented Rice: A Crossover Randomized Controlled Clinical Trial

Abstract

Health-promoting effects of plant foods have been emphasized in the last few decades and ascribed to the bioactive phytochemicals present therein-in particular, phenylpropanoids. The latter have been investigated for a number of preclinical biological activities, including their antioxidant power. Due to the paucity of human studies, in this randomized intervention trial, we investigated whether the acute intake of pigmented rice could increase the plasma bioactive levels and antiradical power in twenty healthy subjects. A crossover randomized controlled clinical trial was conducted on 19 volunteers. Artemide and Venere black rice cultivars were tested, while brown rice Carnaroli was used as a control. Each patient received randomly one serving (100 g) of rice on three different experimental days, separated by a 7-day washout period. After baseline blood withdrawal, time-course changes of plasma polyphenols, flavonoids and radical-scavenging capacity were determined at 30, 60, 120 and 180 min post rice intake. Compared to Carnaroli rice, the two black rice cultivars significantly increased the plasma levels of polyphenols and flavonoids at 60 and 120 min and, correspondingly, the plasma antiradical power at 60 min after consumption. Pigmented rice consumption can contribute to diet-related health benefits in humans.

Keywords: anthocyanins; antioxidant activity; black rice cultivars; cereals; flavonoids.

Figure 1

CONSORT (consolidated standards of reporting trials) flowchart of the study design.

Figure 2

(a) Percentage variation (mean ± standard error) in the plasma total phenol index (spectrophotometric assay, absorbance reading at 280 nm) of volunteers (N = 19) 30, 60, 120 and 180 min after consuming 100 g of Venere (square), Artemide (triangle) or Carnaroli (circle) rice. The symbol (§) indicates statistically significant differences between Carnaroli rice and the pigmented varieties (p < 0.01); the symbol (*) indicates statistically significant differences between Venere and Artemide rice (p < 0.05); (b) percentage variation (mean ± standard error) in the total polyphenol plasma levels (Folin–Ciocalteu colorimetric assay, absorbance reading at 765) of volunteers (N = 19) 30, 60, 120 and 180 min after consuming 100 g of Venere (square), Artemide (triangle) or Carnaroli (circle) rice. The symbol (§) indicates statistically significant differences between Carnaroli rice and the pigmented varieties (p < 0.01); (c) percentage variation (mean ± standard error) in the total flavonoid plasma levels (spectrophotometric assay) of volunteers (N = 19) 30, 60, 120 and 180 min after consuming 100 g of Venere (square), Artemide (triangle) or Carnaroli (circle) rice. The symbol (§) indicates statistically significant differences between Carnaroli rice and the pigmented varieties (p < 0.01); the symbol (*) indicates statistically significant differences between Venere and Artemide rice (p < 0.05).

Figure 3

(a) Percentage variation (mean ± standard error) in the plasma antiradical capacity (DPPH radical scavenging assay) of volunteers (N = 19) 30, 60, 120 and 180 min after consuming 100 g of Venere (square), Artemide (triangle) or Carnaroli (circle) rice. The symbol (§) indicates statistically significant differences between Carnaroli rice and the pigmented varieties (p < 0.01); the symbol (*) indicates statistically significant differences between Venere and Artemide rice (p < 0.05). (b) Percentage variation (mean ± standard error) of the plasma antiradical capacity (ABTS radical scavenging assay) of volunteers (N = 19) 30, 60, 120 and 180 min after consuming 100 g of Venere (square), Artemide (triangle) or Carnaroli (circle) rice. The symbol (§) indicates statistically significant differences between Carnaroli rice and the pigmented varieties (p < 0.01); the symbol (#) indicates statistically significant differences between Carnaroli and Artemide rice (p < 0.05); the symbol (*) indicates statistically significant differences between Venere and Artemide rice (p < 0.05).