Phytochemical Inhibition of Aflatoxigenicity in Aspergillus flavus by Constituents of Walnut (Juglans regia)

• Published in: Journal of agricultural and food chemistry Vol. 52; no. 7; pp. 1882 - 1889
• Main Authors: Mahoney, Noreen, Molyneux, Russell J
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 07.04.2004
• Subjects: Aflatoxins - antagonists & inhibitors; Aflatoxins - toxicity; Aspergillus flavus; Aspergillus flavus - drug effects; Biological and medical sciences; Carboxylic Ester Hydrolases - metabolism; Ellagic Acid - analysis; Ellagic Acid - pharmacology; Food industries; Food toxicology; Fruit and vegetable industries; Fundamental and applied biological sciences. Psychology; Gallic Acid - analysis; Gallic Acid - pharmacology; Hydrolysis; Juglans - chemistry; Juglans regia; Kinetics; Plant Extracts - pharmacology; Seeds - chemistry; Tannins - chemistry; Nuts; Mycotoxin; Juglans hindsii; Fungi; Tannin; Dicotyledones; Ellagic acid; Angiospermae; walnuts; Proanthocyanidin; Fungi Imperfecti; Inhibition; Aflatoxin; Constituent; Thallophyta; Juglans regia; Aspergillus flavus; Gallic acid; hydrolyzable tannins; Toxin; Juglandaceae; Walnut; Juglans nigra; Spermatophyta; Aspergillus spp
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf030812p

Tulare walnut, a cultivar highly resistant to aflatoxin formation, was investigated for endogenous phytochemical constituents capable of inhibiting aflatoxigenesis in Aspergillus flavus. The activity, located entirely in the pellicle (seed coat), was extractable to various degrees with polar solvents, although some activity remained unextractable, indicating that the bioactivity resided in a complex of hydrolyzable tannins. These tannins can be hydrolyzed by a fungal tannase present in A. flavus, yielding gallic acid and ellagic acid, testing of which showed that only gallic acid had potent inhibitory activity toward aflatoxin biosynthesis. Comparison of the gallic and ellagic acid content in the pellicle of Tulare and Chico cultivars, over the 2002 and 2003 growing seasons, showed that the gallic acid content increased rapidly with maturation of the nut and was 1.5−2 times higher in Tulare than in Chico. Gallic acid content in the pellicle at maturity of a series of commercial English walnut cultivars, and two black walnut species, was determined as an indicator of potential for inhibition of aflatoxigenesis. Regulation of gallic acid levels in the hydrolyzable tannins of walnuts by conventional breeding or genetic manipulation has the potential to provide new cultivars with high resistance to aflatoxigenesis. Keywords: Aflatoxin; Aspergillus spp.; walnuts; Juglans regia; Juglans hindsii; Juglans nigra; hydrolyzable tannins; gallic acid; ellagic acid