Effects of operative conditions on products obtained of starch-oil mixtures by single-screw extrusion.

BACKGROUND: d. The aim of the study was to evaluate the fat binding and physicochemical properties of the products under conditions of potato starch extrusion containing rapeseed or linseed oil and rapeseed oil with glycerol.

METHODS: The study dealt with the extrudates of potato starch produced with the addition of rape seed or linseed oil and rapeseed oil and glycerol at 22% humidity. The extrudates were obtained at two screw speeds: 80 rpm and 100 rpm. Extrudates containing rapeseed oil and glycerol (R6G) were obtained at a temperature distribution of 115/130/150°C, while those with the participation of rapeseed oil and linseed oil were obtained at 120/135/128°C. Water solubility index (WSI), water absorption index (WAI), specific surface area (SBET) and quantity of fat permanently bound were determined for the products obtained.

RESULTS: When oils were added, the solubility of extrudates decreased as compared to the control samples (starch without oil; S). Rapeseed oil added to the starch mixture at the levels of 3 g and 6 g in had no sig- nificant effect on the solubility of the product and amounted to: 80.3–82.6% and 78–79.6%. The largest decrease in solubility (WSI, 55.4–57.1%) was demonstrated for samples with 6% addition of rapeseed oil and 10 g glycerol. For these samples (R6G), a significant increase in the index WAI (376–397%) was recorded. Extrudates obtained with the addition of 3 g of rapeseed oil absorbed slightly more water than those with 6 g of oil added. The specific surface area (SBET 230–256 m2/g) determined from the water vapor adsorption isotherm indicates no statistically significant difference at α = 0.05 for products with rapeseed oil, linseed oil, and controls. A significant increase in the specific surface area (SBET 284–347 m2/g) was observed for samples with 6g rapeseed oil and 10 g glycerol added. For samples with 3 g of rapeseed oil, the amount of bound fat was 1.9–2.1 g/100 g of starch and for 6% the starch percentage was 2.96–3.5 g/100 g.

CONCLUSIONS: The water solubility of starch extrudates with the addition of oils decreases with an increase   in screw speed. Starch extrudates with linseed oil and rapeseed oil plus added glycerol are characterized by an increase in water-absorption capacity with respect to the control extrudates. The products obtained with the addition of rapeseed oil and glycerol exhibit a significant increase in their specific surface area. The quan- tity of fat permanently bound during extrusion depended on: the oil type, its percentage in the mixture and the screw speed. The linseed oil was the least absorbed in the starch structure, but rapeseed oil binding increased with the increase in its level in the mixture.