Effect of Storage Relative Humidity on Some Chemical Composition and Browning Development of Treated Cocoyam (Colocasia esculenta) Corm Flour

Abstract

Aim: Some unstable compounds namely ascorbic acid, anthocyanin and reducing sugar contents were used to monitor the stability of differently processed cocoyam flours stored under different relative humidities. Place and Duration of Study: Federal Polytechnic Idah, Nigeria; January to August 2011. Methods: Peeled cocoyam corm slices (3–5cm thick) were washed and divided into three parts that were respectively sundried (NT), blanched and sundried (BT); and sulphited, blanched and sundried (SBT). The milled samples (<200um) were stored under different relative humidities (RH) and analysed at time intervals for ascorbic acid (AA), anthocyanin (ACY) and reducing sugar contents; and for alcohol soluble colour (non-enzymatic browning) developments. Results: Ascorbic acid content of cocoyam flour ranged from 8.65mg/100g in NT to 14.13mg/100 in SBT while anthocyanin and reducing sugar contents ranged from 8.62 and 317.5mg/100g, respectively, in NT to 13.37 and 302.0mg/100g in BT flours. These values decreased with increasing storage RH and time. At seventh month, AA was retained in NT flour stored only at 11% RH and in BT and SBT flours stored at ambient, 11% and 33% RH. Similarly, only storage at 11% RH retained ACY for 5 months in NT and for 7 months in BT and SBT cocoyam flours. Reducing sugar decreased with increasing storage RH and time. Initial absorbance of flour alcohol extract was highest in NT and least in SBT, indicating greater browning in the former. Regression analysis revealed that the rate of non-enzymatic browning development was lower in the SBT cocoyam flour; and seemed to be higher in BT flour than in NT at RH of 53% and below, and vice versa at RH above 53%. Correlation coefficients of reducing sugar contents and non-enzymatic browning development were significant (P=0.05) in RH conditions studied. Conclusion: Cocoyam flour stability was improved by sulphiting and blanching treatments and low RH storage.