Antioxidant and Antimicrobial Activities of Aqueous Extract of the Yellow and White Sweet Spanish onion (Allium cepa L.) in Isfahan

Background and Objectives: Onion (Allium cepa L.) possesses aromas and flavours, which have made them one of important ingredients of food. In addition, recent publications have reported that onion and its extract have many biological properties such as antimicrobial and antioxidant. Yellow and White Sweet Spanish onions belonging to Amaryllidaceae, are cultivated all over Iran as a condiment, vegetable, and medicinal herbs. In present study, the antioxidant and antimicrobial properties of outer and inner layers were investigated in two hybrid onion bulbs; Yellow and White Sweet Spanish. Materials and Methods: Cultivation of plant material consisting two cultivars was performed in Isfahan experimental farm 32°38′27.6″N, 51°46′50.3″E, Iran. In order to assess of sample antioxidant capacity, total phenolic, and total flavonoid contents were estimated for the various fractions. In vitro antioxidant potential of scales onion extracts was evaluated using the scavenging activity for DPPH. Furthermore, this extract was investigated for its ability to provide protection from DNA damage. Disk diffusion and micro-well dilution as some antimicrobial properties of phytochemicals extracted from onion layers were evaluated against seven bacteria and four fungi. Results: Evaluation results of onion extract biological properties showed that aqueous extract of outer layer had the highest antioxidant activity comparison inner layers. However, extract from Yellow Sweet Spanish onion had more phenolic, flavonoid, radical scavenging activities on DPPH. Thereupon, aqueous extract from outer layers of Yellow Sweet Spanish extract showed the most ability to protection against DNA damage caused by reactive oxygen species. Extracts of inner layers of Yellow Sweet Spanish had more inhibition zone and lower MIC and MMC, for all microorganisms. Conclusions: This study showed that aqueous extract of outer and inner layers of both onion lumps (Yellow and White Sweet Spanish) had antioxidant activity and inner layers of extract had antimicrobial activity. It should be noted that extract of outer layer onions had the highest antioxidant properties but no antimicrobial properties. Therefore, the aqueous extract of Yellow and White Sweet Spanish onions might be a valuable food additive and can be used as natural antimicrobial and antioxidant additives for incorporating in various food products.