Seasonal variation of total phenols in leaves of walnut (Juglans regia L.)

The total phenols content was studied in walnut (Juglans regia L.) leaves of twelve different cultivars, over eight distinct harvest times (June 1st to September 15th). Total phenols content was determined by colorimetric assay and their amount ranged from 15.87 (cv. Jupanesti) to 33.67 mg GAE/100 g (cv. Valrex). Total phenols increase over the months of June and July, then decrease over the month of August, then a new increase is recorded by the beginning of September. These differences in terms of total phenols at different sampling time are supposed to be the effect of change in ecological parameters. The results obtained indicated that walnut leaves may become important in obtaining a noticeable source of compounds with health protective potential and antimicrobial activity; therefore the walnut leaves should preferentially be collected in July and early September, when phenolic content is higher.