Chemical Changes Associated with Repetitive Re-Use of Vegetable Oil during Deep Frying of Bean Cake, Plantain and Yam

Abstract

Oil re-use Chemical changes Palm oil Vegetable oil Frying Free fatty acid. Oil re-use is a common practice in households. Oxidative and hydrolytic reactions have been reported to cause significant changes in oil quality. This study was carried out to determine the chemical changes specific to beans cake (Vigna unguiculata), Plantain (Musa paradisiaca) and yellow yam (Discorea cayenensis) frying with repetitive re-use of oil. Refined vegetable and palm oil were used for five consecutive frying operations for bean cake, plantain and yam. Free fatty acids, iodine value, peroxide value and saponification value of the first, third and fifth frying operations were determined using standard methods. For refined vegetable oil, the FFA range for repeated frying operations obtained for bean cake, plantain and yam were 0.31-0.53, 0.37-0.52 and 0.40 to 0.53 % oleic respectively. While palm oil re-use had a range of 11.87 to 14.97 in the value of their FFA. Peroxide value (3.24-4.92 meq/kg), Iodine value (91.09-107.00 mg/100g) and Saponification value (125.00-152.66 mgKOH/g) were obtained for reuse refined vegetable oil while Peroxide value (27.95-77.02 meq/kg), Iodine value (131.68-210.89 g/100g) and Saponification value (179.45-197.50 mgKOH/g) were obtained for re-use palm oil. Generally, frying operation led to increase in the FFA of refined vegetable oil. Frying operation for peroxide value significantly varied for all frying operation for plantain. Significant difference existed in iodine value at p<0.05 among frying operations for bean cake and yam. Changes in chemical properties of oil were affected by frying duration and food material fried. Contribution/Originality: The present study reported variations in the chemical properties of vegetable oil as affected by the type of food material (bean cake, plantain and yam) during repeated frying operation. Extent of changes caused by hydrolytic and oxidative reactions is dependent on the food material used for deep frying operation. This work also was able to ascertain that acceptable oil re-use depended on the frying duration and food material. 1. INTRODUCTION Vegetable oils are a major part of human diet considering its energy, fat soluble vitamins and essential fatty acid contribution. Aside the nutritional, physical and chemical properties, high quality vegetable oil are determined by its ability to withstand high temperature while still retaining its high quality. In the food industry, vegetable oil found one of its uses in its ability to serve as a processing medium. Deep frying of food involves the use of high temperature which alters oil properties (Debnath et al., 2012). Frying operation in food processing is known to be intense due to high temperature of processing which induces chemical reactions in the frying medium (Weisshaar, 2014; Park and Kim, 2016). These chemical reactions