Evaluation of the physico-chemical properties of cassava, cocoyam, sweet potato starches and glucose syrups produced from the hydrolysis of the starches with sorghum malt enzyme extract

Some physicochemical properties of starches from cocoyam, cassava and sweet potato were compared for suitability in glucose syrup production. Glucose syrups were produced from the starch slurry using 30 g of sorghum malt per 250 g starch weight. Malts were produced from Nigerian sorghum varieties; SFF- Sorghum ‘Farafara’ and SFD-Sorghum ‘Farindawa’ (Sorghumbicolor L. Moench). The grains were steeped for 24 h with 8 h air rest and germinated for 96 h. Results showed that malted SFD and SFF-sorghum grains recorded diastatic powers (61.45 and 52.32 DU.g-1), α-amylase (38.19 and 43.3 DU.g-1) and β-amylase (14.13 and 18.15 DU.g-1) activities, respectively. Cocoyam starch contained highest amylose (28.20%) when compared with sweet potato starch (22.50%) and cassava starch (20.40%). Solubility and swelling power of cassava, sweet potato and cocoyam starches were 17.2, 16.5 and 15.3 g.g-1 and 9.6, 6.2 and 7.6% at 90℃, respectively. Cocoyam starch showed the highest transition temperatures (69.5, 73.6, 82.3℃) and gelatinization enthalpy (17.3 J.g-1) than sweet potato (67.4, 71.3, 78.4℃, 12.3 J.g-1) and cassava (61.3, 65.5, 75.6℃, 13.4 J.g-1) starches. Dextrose equivalent for cassava, sweet potato and cocoyam glucose syrups were 40, 36, 30. Cassava starch glucose syrup obtained from SFD-malt hydrolysis met most of the Standard Organization of Nigeria set specifications.