Theoretical and Experimental Studies of Low-Temperature Dehulling Process of High-Oil Sunflower Under a Centrifugal Field

Abstract

Appearance of high-oily sunflower seeds with oil content 52–54 % in the 60’s of the last century, led to revolutionary changes in raw material base of the fat-and-oil industry, but caused difficulties in the process of its storage and processing due to the morphological structure features and biochemical composition of fruit coat. Overcoming of the main technological disadvantages for high-oily sunflower seeds during dehulling was achieved due to development of an innovative dehulling technology for seeds in frozen state to sub-zero temperatures, which was developed at the technology of fats and fermentation products department of NTU “KhPI”. This paper presents results of experimental study of sunflower variety Ukrainian F1 high-oily seeds dehulling (dehulling coefficient and kernel content coefficient) depending on the temperature change (0–-196°C) and centrifugal dehullerꞌs rotor rotation speed. It has been shown that rational dehulling conditions for dry seeds, which allow to reach maximum dehulling depth (K0 = 0,99) under conditions of minimum outputs of chaff and oilseed dust, are cooling temperature in the range of -30–-50°C and dehullerꞌs rotation speed 26,7 s-1. Based on the literature data and research results, it has been shown that one of the main reasons of dry seeds dehulling coefficient increasing, during the transition from plus to minus temperatures, is a change in basic physicochemical properties of cellulose fibers (the basis of fruit coats biochemical composition) with a solid adsorption surface towards increasing of its strength. According to a special experiment data in relation to change in aggregate state of sunflower oil in temperature range from +20ºС to -196ºС, it was shown that cellulose fibers with adsorbed oil are practically the only component of fruit coat, which increases its plasticity with decreasing temperature. It is noted that fruit coat plasticity increases most significantly in temperature range -30 – -50°C, when oil obtain a plasticine-like consistency. This is exactly what temperature range where minimum yield of chaff and oilseed dust is observed, i.e. the highest dehulling quality is achieved. Obtained scientific results of this study make a significant contribution to the theory and practice of oil seeds dehulling, which have structural and compositional features of the fruit coat.