Effect of different drying processes on physical properties and carotenoid content of Gac fruit (Momordica cochinchinensis Spreng.)

Abstract

Gac fruit ( Momordica cochinchinensis Spreng.) is an indigenous fruit of South and Southeast Asia. Pulp and aril of Gac fruit contain high levels of carotenoids and are known as strong antioxidants. However, the shelf life of fresh and ripened Gac fruit is limited (about 1 week). Gac powder is a good alternative source of raw material in food development. The aim of this study is to investigate the nutritional value of fresh Gac fruit and the effects of different drying processes on color characteristics, total carotenoid content, water solubility, and water holding capacity of Gac fruit powder. Fresh Gac fruit and its powders from different drying processes including freeze drying, spray drying and drum drying were analyzed to determine their physical and chemical properties. The results showed that fresh Gac fruits contained several nutrients, vitamins, minerals, and fatty acids. The moisture content of dried Gac powder was in the range of 2-8% and was found to be suitable for long-term storage and food development process. Spray drying (treated with pectinase) was found to be effective in retaining the carotenoids of Gac powders (b-carotene 57 mg/100g dried weight (DW), lycopene 139 mg/100g DW) and was similar to that of fresh Gac fruit (60.3 and 134.2 mg/100g DW respectively). In contrast, spray drying (not treated with pectinase) showed low amount of carotenoids (b-carotene 6.1 mg/100g DW and lycopene 12.5 mg/100g DW). Moreover, the drying processes significantly affected the color characteristics of Gac powder, including lightness (L*), redness (a*), yellowness (b*) and overall color difference (ΔE). Among the drying methods, the Gac fruit powder obtained from freeze drying (with ΔE 3.9) retained most of the color similar to the fresh Gac fruit. Gac powder obtained from spray drying (not treated with pectinase) provided the highest water solubility value whereas freeze drying showed the lowest water solubility value. Gac powder from freeze drying showed higher value of water holding capacity. Different drying processes provided different effects on both carotenoid content and physical properties of the product. In summary, spray drying process (treated with pectinase) retained more carotenoids and exhibited good characteristics when compared to other drying processes and can be added directly to several food products.