By-products from the processing of herbs as sources of antioxidants

Abstract

During the processing of herbs, a significant amount of chopped biomass by-products is left behind, often discarded and underutilized. Since they are important sources of different groups of bioactives like polyphenolics, essential oils or terpenes and structural compounds like lignocellulose, they could be exploited in fermentation by different microorganisms. However, fractionation and extractions could significantly increase the effectiveness and productivity of the valorization process. We examined the possibility of extracting antioxidants from by-products of hoary willowherb (Epilobium spp.), sage (Salvia spp.), and basil (Ocimum spp.), as medicinal herbs with significant pharmaceutical and market value. Extracts of hoary willowherb, sage and basil residues were obtained by a conventional, Soxhlet extraction for polar compounds and supercritical carbon(IV)-oxide extraction as an unconventional extraction method for non-polar compounds. We measured the antioxidant content in the obtained extracts by the ABTS and DPPH spectrophotometric methods. In addition, we measured the total polyphenol content of the extracts by the Folin-Coicalteu method. According to the ABTS method, the antioxidant activity in the sage extracts obtained from Soxhlet extraction is 2.2 times greater than in the extracts obtained from supercritical carbon(IV)-oxide extraction. The antioxidant activity in the basil extracts obtained from Soxhlet extraction is 9.1 times greater than in the extracts obtained from supercritical carbon(IV)-oxide extraction, according to the DPPH method. The total polyphenol content in the hoary willowherb extracts obtained from Soxhlet extraction is 4.6 times greater than in the extracts obtained from supercritical carbon(IV)-oxide extraction. The antioxidant activity is greater in the extracts obtained by Soxhlet extraction than in the extracts obtained with supercritical carbon(IV)-oxide extraction. Because we examined residues from the tea processing industry, the content of easily volatile non-polar components is expected to be lower. The results confirm that valorization of these residues should be focused on the polar components and their microbial biotransformations.