N-Octenyl succinylation of pullulan: Effect on its physico-mechanical and thermal properties and application as an edible coating on fruits

Abstract

The esterification of pullulan (Pu) with n-octenyl succinic anhydride (OSA) was validated using Fourier Transform Infra Red (FTIR) spectroscopy. The reaction parameters viz., base concentration, reaction time, temperature, OSA concentration were optimized to obtain a maximum degree of substitution (DS). Reaction of 10 g Pu with 0.4 mol OSA/mol repeating unit of pullulan and 2 g of sodium bicarbonate at 70 °C for 5 h gave a maximum DS of 0.0604. Calorimetric analysis showed no significant change in crystallinity and scanning electron microscopy indicated cluster formation at maximum DS. Pu-OSA (DS 0.0604) films were more yellow, demonstrated ∼30% lower water vapour permeability rate, no significant change in oxygen transfer rate and 50% lower tensile strength compared to Pu. The effect of Pu-OSA as an edible coating was evaluated on sapota (Manilkara zapota) fruits of Kalipatti variety and compared with Pu and emulsified palm oil coating formulation containing Pu. The onset of ripening was monitored in terms of CO2 release, O2 absorbed, reduction in flesh firmness loss and weight loss. Coating the sapota fruits with Pu-OSA delayed the ripening and senescence and hence could be used as an effective edible coating for extending their shelf life.