Extraction of pectin with tunable physicochemical properties from different fruit peels by microwave assisted extraction

Fruit and vegetable peels as agricultural waste are thrown away into the environment instead of being used as value-added products including pectin, nutritional supplements or antimicrobial agents. Here, pectin extraction was carried out from three different fruit peels (lemon (L), cucumber (C) and melon (M)), and their four different mixtures (lemon-cucumber (LC), lemon-melon (LM), cucumber-melon (CM) and lemon-melon-cucumber (LMC)) with equal weight ratios in five different extractants (H2O, citric acid (0.2 N CA), acetic acid (0.2 N AA), 0.1 N HCl and 0.1 N HNO3 by microwave-assisted extraction (MAE) technique. The effects of different extractants and fruit peel mixtures on the yields and properties of extracted pectin were also evaluated. The highest pectin yield (39.55 ± 0.32%, 0.1 N HNO3) was obtained from lemon peels (L) since citrus fruits are one of the main commercial pectin sources. As expected, the yield of pectin extracted from L peels was approximately threefold higher than that obtained from M and C peels. Extractions performed in H2O, AA and HCl resulted in high-methoxyl pectin (HMP, ED ≥ 50%). However, CA, HCl and HNO3 extractants provided low-methoxyl pectin (LMP, ED < 50%). Pectins from fruit peel mixtures showed mostly quite high water holding capacity (WHC) compared to the fruit peels used alone. It has been established that the physicochemical properties of extracted pectin, which govern functional parameters such as solubility, rheological characteristics, and gelation ability and temperature, can be modulated through utilization of diverse fruit peels in various combinations. The yields and properties of extracted pectins from these mixtures were in good agreement with the estimated values. This will provide important benefit for utilization of agricultural waste without separation of each component and obtaining pectin with desired properties.