Extraction of phenolic compounds from agro-industrial wastes and evaluation of their antioxidative potential

Abstract

Constant world population growth imposes the need for the production of more food, and as a consequence, has an increase in the organic-rich wastes. These agro-industrial wastes represent problem from the environmental viewpoint, and their utilization as the raw materials for the production of value-added products has become one of the main topics of the biorefinery. The aim of this research was to use soybean meal, co-product of dietary oil production, as a model agro-industrial by-product for optimization of phenolic compounds extraction. In this paper, ethanol influenced microwave-assisted extraction is chosen since it is recognized as eco-friendly and food-safe. Optimization of the extraction included finding the optimal liquid/solid ratio, extraction duration, and microwave power. The same method was applied for the extraction of phenolics from apple pomace, apple pomace mixed with soybean meal, ultrasound-treated soybean meal, and wheat bran. Antioxidative potential of all extracts was evaluated using a fixed reaction time 2,2-diphenyl-1-picrylhydrazyl (DPPH) method as well as a steady-state measurement DPPH method. 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) i.e., ABTS and ferric reducing antioxidant power (FRAP) methods were applied as well. Under optimized conditions (liquid/solid ratio of 15 mL/g for 70 s at a microwave power of 300 W) 3.87 mg gallic acid equivalent (GAE)/g was extracted from soybean meal, which represented a substantial increase compared to 2.46 mg GAE/g obtained before optimization. Results showed that extracts had different behavior towards different radicals depending on the type of the extracted phenolics. Apple pomace extract was the most potent towards DPPH• radical, while the most effective extract towards ABTS•+ radical was obtained from apple pomace and soybean meal mixture. The soybean meal extract showed the highest reducing power assessed via the FRAP method. Results obtained in this study show that optimization of the extraction enabled a substantial increase in the extracted phenolics and that the method could be successfully applied with other agro-industrial by-products providing extracts with antioxidative potential.