Changes of Total Phenolics, Tannins, Phytate and Antioxidant Activity of Two Sorghum Cultivars as Affected by Processing

Abstract

Sorghum (Sorghum bicolor (L.) Moench ) is a rich source of bioactive compounds such as polyphenols, tannins, and phytate. Polyphenols have been recognized as the most abundant source of anti-oxidants in our diet. The quantity and quality of polyphenols, tannins and phytate in foods are affected by processing due to their highly reactive nature, which may affect their anti-oxidant activity and the nutritional value of foods. The aim of the present study was to investigate how some domestic processing methods such as soaking (in different solutions), germination, fermentation using (Saccharomyces cerevisia) and wet cooking influence phenolic compounds, tannins, phytate content and free radical scavenging activity of two sorghum cultivars {high tannin sorghum (Assuit 14) and low tannin sorghum (Giza 15)} grown in southern Egypt. The results indicated that soaking in (distilled water, KOH 2%, NH4OH 30%, and NaOH 2%), and germination had significant reduction of total phenolic, tannin and, phytic acid content and antioxidant activity. While fermentation process of Giza 15 increased the total phenolic content and the antioxidant activity of the fermented flour, while a significant decrease of tannin and phytic acid was found. On the other hand, wet cooking treatment for 2h of Giza 15 grains showed an increase of antioxidant activity (58%), and a decrease in phytic acid, phenolic compounds and tannins contents. Our results illustrated that sorghum Assiut 14 had higher content of phenolics, tannins, phytate as well as antioxidant activity by DPPH than Giza 15. For (IC50) Assuit 14 had 7.544 while Giza15 had 22.147. All processing methods affect on phenolics, tannin and,phytic acid content and activities of antioxidant components of sorghum differentially, suggesting that treating the seed before use is able to change the bioactive compounds content of sorghum and the antioxidant activity as related.