Bioactive compounds-rich Gac peel powder: Optimization of extraction and foam-mat drying conditions

Gac fruit (Momordica cochinchinensis Spreng) is a healthy fruit and has long been used as food and medicine. During fruit processing, the peel is often discarded as waste. However, Gac fruit peel contains a significant amount of carotenoids. This study encapsulates bioactive compounds extracted from dried Gac peels using egg albumin (EA) and xanthan gum (XG) as foaming agents and stabilizers in foam-mat drying at different temperature. The extraction process (in ethanol 60 %) was assisted by ultrasound (40 kHz, 350 W) with solvent: Gac peel ratios of 30/1–40/1, extraction temperature and time of 45–55 °C and 25–55 min, respectively. EA (9.2–15.2 %) and XG (0.1–0.38 %) were used as foaming agent and foam stabilizer, respectively, with different foam-mat drying temperatures (65–75 °C). The Response Surface Methodology (RSM) combined with a Box-Behnken Design (BBD), 3 factors - 3 levels was used to optimize the independent variables to capture the maximum level of dependent variables. The optimal extraction conditions were determined (solvent/Gac peel ratio of 36.26/1, temperature of 51.38°C and time of 43.39 min) for the extract containing high levels of lycopene 292.04 μg/g, β-carotene (515.72 μg/g) and total polyphenols (3.86 mg GAE/g). The extract was used to produce powder by foam-mat drying. EA, XG and drying temperature significantly affected the drying rate and powder quality. The optimum concentrations of EA and XG were determined to be 13.13 % and 0.3 %, respectively, at an optimum drying temperature of 72.4°C. Under these conditions, the highest drying rate (2.41 g water/g dry matter/min) was achieved to produce powder containing the with highest content of lycopene, β-carotene and total polyphenol contents, 83.42 µg/g, 97.68 µg/g and 1.09 mg GAE/g, respectively. The physical and chemical properties of foam-mat dried Gac peel powder were also investigated. Making good use of byproducts from fruit processing will help local communities and businesses while also ensuring the goal of a circular economy, contributing to long-term socioeconomic growth and enhancing public health, at least in the region and around the world.