EFFECTS OF THE ESSENTIAL OIL OF ZATARIA MULTIFLORA BOISS, A THYME-LIKE MEDICINAL PLANT FROM IRAN ON THE GROWTH AND SPORULATION OF ASPERGILLUS NIGER BOTH IN VITRO AND ON LIME FRUITS

Abstract

Antifungal activity of the essential oil (EO) of Zataria multiflora Boiss. against Aspergillus niger fruit rot of key lime was studied. Minimum inhibitory concentrations of the volatile fraction against mycelial growth and spore germination were 0.8 and 4.0 µL per 8 cm Petri dish. The EO median effective concentration was estimated as 819.3 ppm. The EO inhibited sporulation of A. niger with no sporulation at EO ≥1,500 ppm. In comparison with control, lower fruit rot at 200, 400 and 600 ppm of the EO was recorded for fruits stored outdoors; however, no significant difference was found between these treatments. The EO concentrations ≥400 ppm reduced the fruit rot in the cold room. At 600 ppm EO, only 15% of the fruits decayed in the cold room 50 days postinoculation. No change in taste, total soluble solid percent, titratable acidity and vitamin C content of the fruits was observed due to application of the EO. PRACTICAL APPLICATIONS Food safety is one of the major issues related to fresh fruits and vegetables. More degradable natural compounds that can be regarded as safe to human health and environment are alternatives of choice for synthetic chemicals used to control postharvest fruit rots. Results of recent studies on control of fungal rots using natural substances indicate that demands for research and development of natural fungicides are just gaining momentum globally. Despite the extensive in vitro studies on the antimicrobial effects of essential oils (EOs), in vivo experiments examining the EOs activity on a host–pathogen system are quite few. The objective of the present study was to investigate the effect of the EO of Z. multiflora on growth and sporulation of Aspergillus niger under both in vitro and in vivo (on lime fruit) conditions to achieve its potential use for controlling A. niger fruit rot of key lime. Lime is a fruit used fresh and as lime juice in many cuisines in Iran. The demand for lime is very high, and due to inappropriate transport and storage, it is decayed by many postharvest pathogens including A. niger. The authors have repeatedly isolated A. niger from limes with and without apparent symptoms of rot collected from local market and storages and picked from various lime-producing regions. Although study of mycotoxins in lime was not an objective of this study, it is conceivable that a high incidence of lime infection to A. niger in southern parts of Iran can result in contamination of lime to its hazardous mycotoxins.