Determination of rational modes of pumpkin seeds drying

Abstract

Pumpkin seeds are an easily accessible source of protein and other useful substances. A purpose is to determine a rational mode of its drying, which ensures high germinability of the seeds. The physical and mechanical properties of pumpkin seeds «Stofuntovyi» of Ukrainian selection with a humidity of 0, 6, 16, 46 % have been investigated. The drying process kinetics have been investigated on a test bench of convective drying at the following conditions: the drying agent temperature in the drying chamber t = 40–80˚C, velocity V = 1,5 m/s, the moisture content of dry air d = 10 g/kg d.a. The biochemical properties of dried pumpkin seeds were determined by the amount of seeds capable of forming normally developed sprouts under optimal conditions on the 5th, 7th and 10th days of germination. The studies of the properties of pumpkin seeds variety have revealed that when the initial moisture content in the material changes from 0 to 46%, there is an increase in the seeds’ geometric sizes: the length increases by 38%, width – by 10% and thickness – by 8%. Other parameters change too. Investigation of the pumpkin seeds drying process has shown that when the temperature of the drying agent increases, the drying intensity increases also. In particular, the drying time reduces 8 times when the drying agent temperature is raised from 40 to 80 °C. The drying rate curves corresponding to the falling drying rate period with preheating indicate that the highest drying rate at the maximum critical point at a drying agent temperature of 80 °C is 2.32% / min, and the lowest at 40 °C is 0.33 %/min. The heating of the pumpkin seeds takes 3 to 5 minutes depending on the mode, then the temperature of the material does not change significantly and deviates from the temperature of the drying agent by 0.1–0.5 ºС. The generalized curve of kinetics of pumpkin seeds drying makes it possible to describe the general process at different drying modes. The drying agent temperature substantially affects the pumpkin seeds germinability. The most rational mode of drying is at a temperature of 40 °C and an air speed of 1.5 m/s.