Effect of Chemical Treatments on Polyphenols and Malt Quality in Sorghum

Abstract

Tannin-containing sorghums, Chirimaugute and DC-75, and a tannin-free sorghum, SV2, were steeped in water, HCl (0·25 m), formaldehyde (0·017 m) and NaOH (0·075 m) for 8 and 24 h. Germination was carried out for 2 and 5 d. Steeping in NaOH enhanced water uptake of the grains compared with the other treatments. All treatments reduced the polyphenol content of the raw grain. Treatment with NaOH or formaldehyde (HCHO) was more effective than water or HCl. Malt quality was measured in terms of diastatic power (DP). Potential DP, determined after the peptone extraction, indicated higher amylase activity in DC-75 malt than in Chirimaugute and SV2 malt. Available DP, determined after water extraction, was low in malt from the tannin-containing varieties that had been treated with water or HCl. Malting alone was not an effective method of reducing the enzyme inhibitory power of the sorghum tannins. Available DP was markedly improved by the NaOH and HCHO treatments of the tannin-containing varieties. It is concluded that steeping in dilute NaOH is effective in detoxifying high-tannin sorghums, reducing the steeping period and enhancing malt quality. Steeping in NaOH appears to be a safer alternative to HCHO for treatment of high-tannin sorghums in the malting industry and for other food uses.