Sorption behavior, thermodynamic properties and storage stability of ready-to-eat Elephant Foot Yam (Amorphophallus spp.) product: physic-chemical properties, minerals, total dietary fiber and phenolic content of stored product

Abstract

The effect of osmotic dehydration in sucrose solution followed by convective dehydration on sorption isotherms and storage stability of elephant foot yam was evaluated in the present work. The equilibrium moisture content of un-treated (Hot-air-dried) and pre-treated (Osmo-air-dried) samples were determined by static gravimetric method at different temperatures (20, 30, 40, and 50 °C) and relative humidities (11–90 %). The curves obtained for sorption can be considered as type-II according to Brunauer–Emmett–Teller (BET) classification. The higher values of net-isosteric heat of sorption and heat of vaporization was observed for un-treated samples. i.e. 6.82–14.79 and 2978.28–3548.68 kJ/kmol as compared to pre-treated samples. i.e. 6.72–14.09 and 2858.33–3315.85 kJ/kmol, respectively and decreased with increase in moisture content. The experimental data revealed that enthalpy–entropy compensation theory was satisfactorily applicable to the moisture sorption behavior of the un-treated and pre-treated EFY samples. Mineral contents of fresh EFY product viz. magnesium, potassium and calcium were 190 ± 1.0, 515 ± 2.5 and 214 ± 2.08 mg/100g, respectively. After 6 months of storage change in minerals was not significant, whereas significant increase in dietary fiber (15.95 ± 0.76−19.68 ± 0.45 g/100g) and slight but significant reduction in phenolic content (49.97 ± 0.76–46.81 ± 0.60 mgGAE/g extract) was observed.