drying kinetics and quality characteristics of saffron dried with a heat pump assisted hybrid photovoltaic-thermal solar dryer

in the present study, saffron was dried using a heat pump-assisted hybrid photovoltaic-thermal solar dryer. the effect of different drying air temperatures at three levels (40, 50, and 60oc) and two different modes of the dryer (with and without heat pump system) were investigated on drying behaviour of saffron. after collecting the pertinent data, eleven drying models were used to describe drying characteristics of saffron. quality characteristics of the dried products (including: colouring, aromatic strength and bitterness) were also evaluated. the results indicated that drying time decreased by 62% with increasing air temperature from 40 to 60oc. moreover, applying heat pump with the dryer reduced rh of drying air and, consequently, enhanced drying rate and shortened drying period by 40%. a two-term drying model presented a relatively higher r2 and lower, mbe, and rmse values at both modes of drying and, therefore, was selected to explain drying behaviour of saffron among the other models. the results of saffron quality evaluation showed that colouring characteristics of saffron improved with drying temperature and heat pump system. meanwhile, aromatic strength of saffron increased with increasing air temperature. but, no significant change in bitterness was observed at different levels of temperature and heat pump system.