Wine Grape Bioactive Production & Release Following Leaf Plucking & Pulsed Electric Field Treatment, & Wine Industry Applications
Rozhkova, Alexandra 'Sasha'
The research findings presented in this thesis describe some of the interactions that can take place between the climate and the endogenous metabolism of Vitis vinifera. Leaf plucking is a traditional vineyard management tool commercially used to mediate microclimates, optimize environmental stress exposure and minimise pathogenicity among vines. Bioactives play an important role in wine and contribute heavily to the quality and sensory attributes of the product. Pinot Noir (PN) and Sauvignon Blanc (SB) grapes from Canterbury, New Zealand were macerated to produce juice and wine used in this study. Pulsed Electric Field (PEF) treatment is a relatively new food processing method that induces electropermeabilization in the berry skins, promoting leaching and consequently extraction of vacuole bound bioactives. The main objective of this study was to investigate the individual and combined effects of leaf plucking and PEF processing over various maceration times, as a means of manipulating the bioactive content in grape juice and wine. The results of this study showed the application of a PEF treatment following crushing of the berries has the ability to regulate extraction of a variety of phenolics, such as the anthocyanins in PN, and the phenolic acids in SB. Microfermentation of the juice was carried out to produce a corresponding wine and the resultant analysed. Juice samples from PN treated grapes were also shown to increase Caco-2 cell viability following a peroxide stress exposure. It was shown that various levels of leaf plucking (field treatment) had less of an impact than PEF processing on many of the biochemical and quality parameters measured. The results of this study also indicate a varied response to the field treatment effect on the vitamin C content, antioxidant capacity and on the colour intensity in PN juice. The PN wine production was deemed unsuccessful due to poor berry quality and reduced yield. The SB juice samples showed a different response to the field treatment with respect to soluble sugar and vitamin C content. It was shown that SB wine made from PEF treated grapes required a shorter maceration period of 1.5 hours as opposed to 12 hours to reach similar levels of extracted phenolic compounds. Variation between the two cultivars was evident, primarily due to cultivar determined differences in berry morphology and physiology. It was therefore appropriate to present the two cultivars separately and independently of one another. An increase in the bioactive compound levels in juice and wine products has been shown to increase health promoting properties and improve the quality of red wines, while helping to reduce the risk of microbial contamination and spoilage of white wines. The local and international wine industry shows consistent economic growth. The optimization of leaf plucking and PEF processing has the commercial potential to modernize the wine industry, encourage exclusivity, and promote the quality of the final product.
Advisor: Burritt, David; Oey, Indrawati
Degree Name: Master of Science
Degree Discipline: Botany
Publisher: University of Otago
Keywords: Bioactives; Wine; PEF; Antioxidants; Pulsed Electric Field; Leaf Plucking; Wine Processing; Health Promoting
Research Type: Thesis