Post Acid Treatment on Pressurized Liquid Extracts of Sorghum (Sorghum bicolor L. Moench) Grain and Plant Material Improves Quantification and Identification of 3-Deoxyanthocyanidins

Sorghum is a unique natural food source of 3-deoxyanthocyanidins (3-DA) polyphenols. This work evaluated the effect of acidification on sorghum extracts post pressurized liquid extraction (PLE) and its ability to increase the identification and quantification of 3-DA. The sorghum genotypes included Sumac and PI570366 (bran only) and SC991 (leaf and leaf sheath tissue). The acidification of the PLE extracts was carried out with methanol-HCl solutions at various concentrations (0, 0.5, 1, 2, and 4%, v/v). Changes in color were determined using L*a*b*. The overall phenolic composition was estimated with the total phenolic content and the DPPH free radical scavenging assays. Quantitative and qualitative chromatographic methods determined the phenolic profile. Color analysis showed that the redness and color saturation increased after acidification. No statistical difference was found in the total phenolic content of the acidified extracts, except for SC991, which was increased. There were no differences in the antioxidant capacity following acidification in all samples. For chromatographic analysis, luteolinidin was predominant in the extracts and the 3-DA content increased after acid treatment. However, some flavonoid and phenolic acid concentrations decreased following acid treatment, including taxifolin, quercetin, and chlorogenic acid. Interestingly, 0.5% v/v HCl acidification was sufficient to increase the color, allow the detection of 5-methoxyluteolinidin, and to increase luteolinidin and 7-methoxyapigenidin by at least twofold.

Automated summary

This study evaluated the effect of acidification on sorghum extracts and found that acidification can increase color saturation and the identification and quantification of 3-DA. Some flavonoid and phenolic acid concentrations decreased following acid treatment, but a 0.5% v/v HCl acidification was sufficient to achieve the desired effects.