CHAPTER 16: Sorghum Non-extractable Polyphenols: Chemistry, Extraction and Bioactivity

Sorghum grain is rich in polyphenols, and the consumption of these grains could provide antioxidant and anti-inflammation health benefits to humans. Based on their ease of solvent extractability, two types of polyphenols are present in sorghum grain – extractable and non-extractable – with the non-extractable forms being covalently bound to cell wall components such as structural proteins, non-starch polysaccharides (e.g. arabinoxylans, hemicellulose and cellulose) and lignin. Alkaline and acid hydrolysis, with the assistance of microwaves or ultrasound, have been used to release and extract these non-extractable polyphenols. The level of non-extractable polyphenols in sorghum is also influenced by food processing methods such as microbiological fermentation, germination, cooking, extrusion, baking and roasting. It is hypothesised that upon ingestion of sorghum grain foods by humans, the non-extractable polyphenols will be barely absorbed in the small intestine, whereas the majority of these polyphenols reach the large intestine and undergo transformation during the microbiological fermentation process, whence they can be released from the cell wall matrix and thus become bioavailable. This chapter provides some guidance for researchers in the chemistry, extraction and bioactivity of non-extractable polyphenols of sorghum grain. Further studies will be required in order to focus on the metabolism of these compounds in biological systems.