S23 - Session O5 - Valorization of underutilized groundnut waste: a potential source of "green" antimicrobials for controlling spoilage and improving safety of fresh produce

Authors: Nimrod Tish, Yakov Vinokur, Victor Rodov *

Agricultural wastes can serve an unlimited source of active natural substances suitable for developing "green" agrochemicals. Groundnut skins (testa) are underutilized agro-industrial waste rich in phenolic compounds, in particular proanthocyanidins (procyanidins, condensed tannins) known to have wide-spectrum antimicrobial activity and beneficial effect on human health. The present study examined the potential of using antifungal and antibacterial properties of procyanidins extracted from groundnut processing waste for preservation of fresh fruits and vegetables and improving their microbiological safety. Water-soluble procyanidin fraction was extracted from the groundnut skins with > 1% yield by hot water with subsequent liquid-liquid butanol extraction, partially purified on C18 column and characterized by UV/visible spectrophotometry, HPLC and LC/MS. A-type procyanidin trimers were found as major constituents of the fraction. In a series of in-vitro tests, the fraction inhibited spore germination, germ-tube elongation and mycelial growth of the phytopathogenic fungus Botrytis cinerea , a causative agent of gray mold disease. It completely arrested the mycelial growth of the phytopathogenic oomycete Pythium aphanidermatum known as a cause of the cottony leak disease in cucumbers and other crops. In addition, the groundnut extract showed in vitro antibacterial activity against Gram-negative ( E. coli ) and Gram-positive ( Listeria innocua ) human pathogen surrogates, especially in combination with low doses of ascorbic acid. The groundnut extract treatment alleviated the gray mold disease in strawberries and cucumbers inoculated with B. cinerea , and prevented the cottony leak disease in cucumbers inoculated with P. aphanidermatum . The postharvest spray of strawberries with 5 mg/mL solution of the groundnut skins extract halved the fruit storage losses caused by fungal decay. The study has demonstrated that water-soluble procyanidin-rich extract from groundnut waste has a good potential as a basis of "green" antimicrobials for plant and human health protection.