Chlorophyll and colour changes in grapevine leaves preserved by passive modification

Grapevine leaves are used to prepare the dish called as dolma, i.e., a Turkish term for stuffed vegetable. Our study was undertaken to monitor the desirable colour changes from bright-green to olive-yellow in grapevine leaves stored under modified atmosphere (passive modification). We also determined whether microbial growth occurred after a prolonged storage (9 mo) at 20 degrees C. For this purpose, grapevine leaves from two common varieties grown in Turkey were placed in hermetically-sealed glass jars and stored at 20 degrees C for 9 mo. Since the colour is the most important quality criteria for grapevine leaves, the changes in chlorophyll-a and chlorophyll-b, and colour variables were monitored during storage. Chlorophyll-a and -b were identified and quantified by HPLC. Chlorophyll-b was more stable than chlorophyll-a in both varieties studied. Compared to varieties, chlorophylls in Narince variety were less stable than those in Sultani variety. Since consumers expect olive-yellow colour in grapevine leaves, Narince variety is more suitable for this technique. Excellent correlation was found between -a(*)b(*)colour variable and chlorophyll-a concentration (r=0.9829-0.9832). Mesophilic bacteria were found to be low level (3.2x10(1) cfu/g), whereas yeast and molds, lactic acid bacteria and Enterobacteriaceae were below the lowest detection limit (< 10 cfu/g) in the leaves stored at 20 degrees C for 9 mo. The results suggest that passive modification is very effective to achieve the desirable colour transformation of grapevine leaves in a very short period of time (2-6 days) depending on the variety. Moreover, this simple technique gives rise to a product with good microbial quality.