Effect of sorghum type and processing on the antioxidant properties of sorghum sorghum bicolor (l.) moench based foods

摘要

Antioxidant properties of sorghum are related to sorghum type and method ofprocessing into foods. Tannin and non-tannin sorghums and their products wereevaluated for total phenols, tannins and antioxidant activity. Total phenols weredetermined using the Folin Ciocalteu method, and tannins were determined by thevanillin-HCl method. Antioxidant activity was evaluated using the ABTS (2,2?-azinobis(3-ethyl-benzothiazoline-6-sulphonic acid) and DPPH (2,2?-diphenyl-Ipicrylhydrazyl)assays. Tannin sorghums and their products had higher total phenols,tannins and antioxidant activity than non-tannin sorghum grain and products.Fermentation, extrusion cooking and porridge making reduced measurable phenols,tannins and in vitro antioxidant activity. Reduction was probably due to phenolsbinding to the food components, thus reducing their solubility in the extractingsolvents; 1% HCl in methanol and 70% aqueous acetone.The procyanidin profile obtained using normal phase HPLC and fluorescentdetection showed that extrusion cooking and porridge making lowered extractability ofpolymers (DP>8), while that of oligomers (DP 2-8) and monomers in porridges wasnot significantly changed. This indicated increased interactions of procyanidinpolymers with the food matrix, especially with protein. Pepsin treatment of sorghumextrudates and porridges significantly improved the antioxidant activity and recovery.The highest antioxidant activity was in the supernatants of pepsin hydrolysates.Amylase treatment alone did not significantly affect phenol content and antioxidants, except in bread containing non-tannin white sorghum bran, where there was a slightincrease in phenols. The combination of pepsin followed by amylase treatment ofporridges and extrudates had effects similar to those of pepsin alone.Improved extractability of antioxidants on pepsin treatment was due to eitherthe release of phenolic antioxidants or protein hydrolysates high in aromatic aminoacid residues such as tyrosine, also known for their antioxidant activity. In eithersituation the improved antioxidant activity could mean that once food is digested it canpotentially protect the gastrointestinal tract against oxidative stress generated from thediet and that produced by food interactions during digestion.There is scope to explore other biological methods like use of other proteases toimprove antioxidant recovery. Further work would thus determine contribution ofphenolic compounds to improved antioxidant activity, and also identify the phenolics.