| dc.description.abstract | Antioxidant properties of sorghum are related to sorghum type and method of
processing into foods. Tannin and non-tannin sorghums and their products were
evaluated for total phenols, tannins and antioxidant activity. Total phenols were
determined using the Folin Ciocalteu method, and tannins were determined by the
vanillin-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 phenols
binding to the food components, thus reducing their solubility in the extracting
solvents; 1% HCl in methanol and 70% aqueous acetone.
The procyanidin profile obtained using normal phase HPLC and fluorescent
detection showed that extrusion cooking and porridge making lowered extractability of
polymers (DP>8), while that of oligomers (DP 2-8) and monomers in porridges was
not significantly changed. This indicated increased interactions of procyanidin
polymers with the food matrix, especially with protein. Pepsin treatment of sorghum
extrudates 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 slight
increase in phenols. The combination of pepsin followed by amylase treatment of
porridges and extrudates had effects similar to those of pepsin alone.
Improved extractability of antioxidants on pepsin treatment was due to either
the release of phenolic antioxidants or protein hydrolysates high in aromatic amino
acid residues such as tyrosine, also known for their antioxidant activity. In either
situation the improved antioxidant activity could mean that once food is digested it can
potentially protect the gastrointestinal tract against oxidative stress generated from the
diet and that produced by food interactions during digestion.
There is scope to explore other biological methods like use of other proteases to
improve antioxidant recovery. Further work would thus determine contribution of
phenolic compounds to improved antioxidant activity, and also identify the phenolics. | en |
