Effect of pretreatments and solar tunnel dryer zones on functional properties, proximate composition, and bioactive components of pumpkin (Cucurbita maxima) pulp powder

Pumpkin fruits are large in size and need to be cut into pieces for use. The quality and storage life of cuts rapidly deteriorated. Big size fruits can be converted to shelf stable product to minimize postharvest loss using solar driers. However, drying temperature and RH in long solar tunnel drier not uniform and may affects quality of dried products. Therefore this research work aimed to investigate the effects of pre-drying treatments and solar tunnel dryer zones on the functional properties, proximate composition, and bioactive components of pumpkin pulp powder. Three groups of pumpkin slices were pre-treated in 1% citric acid (20 min), 2% salt (20 min) solutions, and the other group blanched at 65 °C in 1% salt solution (2 min), untreated sample used as a control. Pre-treated samples then dried in three zones of tunnel solar drier (zone I, zone II and zone III). Treatment combinations were laid down in factorial RCBD replicated 3 times. Results showed that pulp powder from salt pre-treated slice and dried at zone III results in the highest values of shrinkage, rehydration ratio, water holding capacity, and bulk density. Moisture content decreased from zone I to III, and with salt blanching in range of 8.2 to 6.4%, no effect in crude fat content, slices pre-treated in 2% salt solution results is better crude protein and fiber contents in zones. Better retention of total polyphones, beta-carotene, ascorbic acid, with high DPPH scavenging activity and lowest IC(50) values were observed for salt pre-treated sample but dried in zone II of the drier. In general relatively better functional properties, proximate composition and bioactive compounds of the powder can be preserved when slices pre-treated in 2% salt solution and dried in zone II of solar tunnel drier characterized by 54.9 ± 3.7 °C, RH value of 31.4 ± 3.4% and air velocity of 0.45 m/s.