Influence of anti-browning agent pretreatment on drying kinetics, enzymes inactivation and other qualities of dried banana (Musa ssp.) under relative humidity-convective air dryer

Abstract

The influences anti-browning agents (citric and ascorbic acids) and relative humidity (RH) on dried banana slices were investigated. Three concentrations (0.5, 1.0 and 1.5% w/v) of each citric and ascorbic acids pretreated banana slices (5 mm) were dried under 75 °C, 10, 30 and 50% RH and 2.0 m/s air velocity in RH-convective hot air dryer. The relationship between the RH with anti-browning agents on drying kinetics, enzymes inactivation, browning index as well as other qualities of banana slices were discussed. Results showed that RH of 10 and 30% achieved 20 and 10% drying time reduction respectively when compared with untreated sample. Contrary, 50% RH increased the drying time by 10%. Results also showed that the resistivity of the enzymes studied follows the order: Peroxidase > Polyphenol oxidase > Ascorbic acid oxidase. Enzymatic browning index was observed to decrease when anti-browning agent and RH increased and decreased respectively. Lower RH (10 and 30%) was in favor of non-enzymatic reduction but 50% RH produced a contrasting result. For color, a significant (p < 0.05) decrease of L* value and an increase in a* and b* value were observed under various RH and anti-browning agents treatments for both citric and ascorbic acids. Both anti-browning agents were effective in color retention as a result of lower acidification effect on dried banana. Fewer micropores formed in higher RH indicated a more solid surface in the micrograph compare with others and therefore caused lesser damage to the tissue of the dried banana. Person’s coefficient of correlation revealed a direct relation between enzymatic browning index and residual enzymes studied. Also, browning index obtained by color parameters correlated highly with enzymatic browning index than non-enzymatic browning index.