Danuše Lefnerová

Influence of Technological Processes on Biologically Active Compounds of Produced Grapes Juices

Grape juice quality can be substantially influenced by different processing methods and their parameters. This study deals with the influence of thermomaceration temperature and its holding time on important juice quality parameters such as the content of trans-resveratrol, trans-piceid, trans-ε-viniferin, and 2,4,6-trihydroxyphenantrene-2-O-glucoside. All the aforementioned compounds together with antioxidative capacity, total polyphenols, and antimutagenic activity were measured. This study used the following grapes: Blaufränkisch, Blaufränkisch bio, Saint Laurent, Grüner Veltliner, Grüner Veltliner bio, and Müller-Thurgau. For all tested grape varieties, the most important processing parameters were temperature and thermomaceration holding time. There were no significant differences in the content of the studied compounds. Three preservation technologies, freezing, bottle pasteurization, and high-pressure treatment, were also studied regarding the content of abovementioned biologically active compounds. Results of this study can be immediately applied to grape juice production.

Influence of UV and Ozonised Water Treatment on Trans-resveratrol Content in Berry Skins and Juices of Franc and Green Veltliner Grapes

Landfeld A., Třiska J., Balik J., Strohalm J., Novotna P., Vrchotova N., Totusek J., Lefnerova D., Hic P., Tomankova E., Halama R., Houska M. (2015): Influence of UV and ozonised water treatment on trans-resveratrol content in berry skins and juices of Franc and Green Veltliner grapes. Czech J. Food Sci., 33: 267–276. Grapes from two varieties – Franc (red) and Green Veltliner (white) were processed using UV radiation at selected powers and times. Irradiated grapes were stored for 24, 48, and 72 h at room temperature. A second set of grapes was dipped into ozonised water. We tested the influence of ozone concentration, dipping time, and storage time. All experiments were performed using grapes harvested in 2009, 2010, and 2011. The two treatments were compared relative to trans-resveratrol content in grape skins and juices (prepared from treated grapes).