Effect of natural extracts on the stability of sunflower oil and acrylamide formation at different thermal treatments

Abstract

This study was conducted to reduce the simulated chemical changes of sunflower oil during intermittent heating and / or frying model technique, and to improve the thermal stability of oil, and to study the effects on acrylamide formation level by some additives such as oleoresin thyme (OTE) and rosemary extracts (ORE) at different levels (100, 200, 300, 400, 500 and 600 mg-1 L oil), in comparison to standard oil sample (without addition of extracts) and / or (with addition 200 mg-1 L oil of BHA), and the chemical changes were correlated with acrylamide content aiming at establishing prediction models for estimating acrylamide content; during intermittent heating and / or frying model technique of potato chips at 175 o C for 24 hrs. at three consecutive days (8 hrs. daily). The results could be concluded that addition of OTE and/ or ORE to sunflower oil kept its characteristics from being deteriorated. During the simulated heating and / or frying model technique, the OTE or ORE act as an antioxidant taking part in the chain radical oxidation, as well as simultaneously inhibiting the thermal processes occurring in oil. Induction period (IP) was decreasedby increasing the thermal treatment period. Moreover, the addition of OTE and/ or ORE up to 400 mg-1 L oil increase IP before thermal treatment then slows down the decreasing of the IP in comparison to the control samples, and TPCs, TBA and acrylamide content of control oil samples were significantly lower than that of the oil samples treated with OTE and/or ORE.Under the conditions simulated heating and / or frying model technique, the OTE inhibits oxidative processes more strongly than ORE or BHA. The results demonstrate that the heating model technique causes a slower increase in acrylamide content during treatment at 175 o C in comparison to frying model technique, (39.18 %) under heating model technique.While, ORE reduced the acrylamide ranged by 25.54% and 27.48% fewer than500 mg-1 L oil during frying and heating model technique respectively. The correlation coefficient between acrylamide level and frying time was very high (r = 0.986) for control sample, and an equation for prediction the acrylamide was γ =-190.9 + 0.116 X. The correlation coefficient between acrylamide level and TPCs content was very high (r = 0.994) for control sample, while the correlation coefficient between acrylamide level and TPCs (r =-0.621) for oil treated with OTE at 400 mg-1 L during frying, and (r = 0.732) during heating model system.During the progressive frying of the potato chips, the sensory panel could distinguish a difference in flavor between the fried potato chips in sunflower oil with and without OTE or ORE. Panelists preferred the chips fried in oil treated with OTE or ORE.