Effects of Some Weak Acids and Moringa oleifera Leaf Extract Powder on the Colour of Dried Apple

Abstract

This study aimed to find alternatives to sulphite as a preservative for dried fruits. Granny Smith apples were sanitised in a 200 ppm sodium chlorite solution, de-cored, peeled, and cut into slices. The sliced apples were pre-treated/dipped in a water solution containing the three weak acids, namely, ascorbic acid (AA), citric acid (CA), and potassium sorbate (PS) as well as Moringa oleifera leaf extract powder (MOLEP). A screening fractional factorial experiment consisting of five independent variables (AA, CA and PS, time and temperature and MOLEP) constrained at their upper and lower levels (AA: 0.5 to 2.0%, CA: 0.3 to 2.0%, MOLEP: 0.1 to 0.2%, time: 7 to 15 h and temperature: 57 to 70◦C) were evaluated for their effect on the colour of the dried sliced apples. An increase in the concentration of the CA significantly increased the lightness (p = 0.05) and decreased the redness (p = 0.0022) of the dried apple slices. AA and PS did not impact the lightness of the dried sliced apples. A dipping solution of citric acid at 2.0%, Moringa oleifera leaf extract powder at 0.1%, and drying time of 7 h at 70◦C effectively minimized the discolouration of the dried sliced apples.