Evaluation of the total phenolics and quercetin content of foliage in mycorrhizal grape (Vitis vinifera L.) varieties and effect of postharvest drying on quercetin yield

Secondary phenolic metabolites play an important role in plant defense mechanisms and most of them are known to be valuable in human health. There are only few studies related to the significant role of various mycorrhizal fungi on changes taking place in their host secondary metabolites. Furthermore, grapevine pruning wastes were known as a potential source of high-value phytochemicals with respect to medicinal and antimicrobial properties. Total phenols and quercetin content of four Iranian grape (Vitis vinifera L.) varieties (Asgari, Khalili, Keshmeshi and Shahroodi) were investigated following inoculation with four arbuscular mycorrhizal fungi (AMF) strains (Glomus mosseae, Glomus fasciculatum and Glomus intraradices and a mixture of three species). Moreover, quercetin content of vegetative parts (leaf and stem tissues) was studied using a simple extraction and isocratic HPLC method. Additionally the effect of a common postharvest processing treatment (oven-drying) on the quercetin content of these grape varieties were also investigated. Higher levels of quercetin were consistently found in Keshmeshi (70.8 μg/g FW) and Shahroodi (100.6 μg/g FW) varieties following inoculation with G. mosseae. The non inoculated plants of the same varieties were found to produce only 35.7 and 16.3 μg/g FW quercetin, respectively. Oven-drying did not affect the leaf quercetin content in none of samples except in Keshmeshi variety in which drying resulted to higher quercetin yield in comparison with fresh leaf tissues (72.4 vs. 37.0 μg/g FW, respectively). The present study suggests that grapevine wastes are valuable sources for extraction of flavonoid quercetin which can also be further increased following inoculation with arbuscular mycorrhizal fungi.

► Changes in total phenols and the flavonoid quercetin of grapevine following inoculation by arbuscular mycorrhizal fungi (AMF) were investigated.
► Oven-drying as a postharvest processing treatment was also applied to examine further changes in quercetin levels.
► High levels of quercetin were found in some AMF inoculated grape varieties as compared to non-inoculated control ones.
► Oven-drying resulted to higher quercetin extraction yield in one of the grape varieties.
► Grapevine wastes were found as great sources of valuable flavonoid quercetin.