Effect of ultrasonication, germination, and steaming on the properties of a black rice variety

Abstract

This study determined the combined effect of ultrasonication (50 KHz for 5 min and 7 min), germination (for 96 h), and steaming (100 °C for 10 and 20 min) that was given sequentially on colour, physicochemical, phytochemical, and antioxidant properties of Chakhao Poireiton, a black rice variety. The treated rice decreased significantly (p < 0.05) in amylose content and total starch, and increased in sediment volume, and the values were affected maximum in the samples given higher severity of treatments. There was loss of lightness with treatments and increase of redeness and yellowness, indicating the impact of steaming. Chakhao Poireiton had considerable amount of phenolic content (488.16 mg/100 g), flavonoid content (77.31 mg/100 g), and monomeric anthocyanin content (40 mg/100 g). The most severely treated sample had 167 mg/100 g of total phenolic content, which was 34.2% of the raw rice value, and showed strong DPPH scavenging activity (90.40%). GABA (γ-aminobutyric acid) level increased substantially to 334.98 mg/100 g in this sample. Surface morphology of the treated flour samples showed changes that are characteristic of the treatment. Thus, combination of ultrasonication, germination, and steaming had very high GABA levels and such treated rice can be used as a functional food.

Keywords

• Black rice
• Ultrasonication
• Germination
• Steaming
• Phenolic content
• Antioxidant activity