Effects of pretreatment and drying temperatures on physicochemical and antioxidant properties of dried duku (Lansium domesticum)

Abstract

Duku (Lansium domesticum) is a native of Southeast Asia. Duku is a seasonal fruit and highly deteriorated due to high moisture content of more than 80 %, thus difficult to commercialise due to the short shelf life. The transformation of fresh into dried fruit will increase the commercial values as well as be a solution to reduce fruit loss. This study was conducted to evaluate the effects of pretreatments and drying temperatures on physicochemical and antioxidant properties in dried duku fruit. The duku fruits (whole, flesh, peels and seeds) were subjected to pretreatment process with ascorbic acid solution, sodium metabisulfite solution, sodium erythorbate solution and blanching. Then, the samples were dried at 50 °C, 60 °C, 70 °C and 80 °C, respectively. Determination of total phenolic content (TPC) was carried out based on the Folin-Ciocalteau method. The antioxidant activities were evaluated using ABTS (2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) and DPPH (2,2-diphenyl-1-picrylhydrazyl). The pH values of all parts of duku were decreased as the drying temperature increases. Seed (pretreated with sodium metabisulfite, dried at 80 °C) showed the highest total phenolic content value with 116.84 ± 0.31 mg gallic acid equivalents per g fruit extract (GAE/g), while lowest in flesh (pretreated with ascorbic acid, dried at 50 °C). Seed (pretreated with sodium metabisulfite, dried at 50 °C) has the highest antioxidant capacity with IC50 value of 41.15 µg/ml (ABTS free radical scavenging) and 121.35 µg/ml (DPPH free radical scavenging) compared to other fruit parts, pretreatments and drying temperatures. The findings of this study indicate the potential of all parts of duku fruit as a valuable source of nutrients. Information on the nutritional and antioxidant properties of this Malaysia's seasonal fruit reveals its potential to be commercialized into different food and beverage products.