Thermal characteristics, chemical composition and polyphenol contents of date-pits powder

Abstract

Polyphenol contents in date-pits varied from 21–62mg gallic acid equivalents (GAE)/g date-pits when acetone–water, ethanol–water, methanol–water and water alone were used as solvents for extraction at temperatures 22, 45, and 60°C. The BET and GAB monolayer values of date-pits were estimated as 4.3 and 4.1g/100g dry-solids. The DSC thermogram of freeze-dried date-pits showed an endothermic peak due to the melting of oil, and a second endothermic peak for solids-melting (i.e. non-fat). The first shift indicated the glass transition (i.e. Tg) while the second exothermic shift after solids-melting indicated the interactions of the components in melted solids. The melting peak temperature was decreased due to the plasticization of solids with water and the melting enthalpy was increased with the increasing water content due to the formation of more order in the amorphous, semi-crystallites and crystallites parts. The Flory–Huggins modelling of peak temperature estimated the water–solids interaction parameter as 0.0068. The melting peak temperature increased exponentially with increasing heating rate and the data was fitted with Mehl–Johnson–Avrami and Kissinger models. Annealing close to the onset of melting indicated that melting peak temperature increased exponentially with increasing annealing time, while melting enthalpy decreased with the increasing annealing time.