Isaac O. Nyangena of the Department of Food Science and Technology, School of Food and Nutritional Sciences, Jomo Kenyatta University of Agriculture and Technology Nairobi, Kenya studied the effect of pretreatments prior to drying on antioxidant properties of dried mango slices
The author posits that chemical, thermal or osmotic pretreatments prior to drying can improve the quality aspects of dried foods. Three pretreatments prior to drying were evaluated for antioxidant capacity in two mango varieties viz. Ngowe and apple that were dehydrated in either, oven (50 and 65 °C) and solar dryer. The antioxidant properties analyzed included polyphenols, vitamin C, carotenoids, flavonoids and total antioxidant activity. Total polyphenol content was determined through Folin–Ciocalteu method and quantified using UV-Spectrophotometer. Vitamin C was analyzed by HPLC system while total carotenoids, total antioxidants, and flavonoids were analyzed using UV-Spectrophotometer at varied wavelengths.
Method of drying and pretreatment type had significant effect (p ≤ 0.01) on the flavonoid content, total carotenoids and β-carotene for differently pretreated and dried mango slices. The results showed increased content in total antioxidants, polyphenols and flavonoids for the pretreated and dried slices compared to the fresh samples of both varieties. The highest flavonoid content (43.66 ± 1.27 mg/100 g) was recorded in 1% citric acid pretreated samples dried at 50 °C while the lowest amount (16.73 ± 1.14 mg/100 g) was recorded in blanched Ngowe oven dried at 65 °C. Vitamin C decreased with increased drying temperature from 50–65 °C and the largest value (78.87 ± 0.46 mg/100 g) was observed in fresh Apple mango variety while the lowest value (28.45 mg/100 g) was observed in Ngowe variety samples oven dried at 65 °C for 10 h. β-carotene for dried mango slices ranged from 6.65 mg/100 g to 40.88 mg/100 g among the differently pretreated and dried mango slices and the values were lower than the content in fresh samples in the respective varieties. Total polyphenol content varied from 5.83–29.9 mg (GAE)/100 g.
This research demonstrated that appropriate pretreatments in this case, 1% citric acid pretreatment prior to drying at 50 °C can enhance retention of antioxidants in dried mango product.