Graduate Thesis Or Dissertation
 

Use of Organoleptic Methodologies to Evaluate Wine Oligosaccharides and Wines made from Grapevine Red Blotch Virus Positive Vines Subjected to Various Vineyard Management Practices

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/8g84mt761

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  • The human senses can be used as analytical tools to evaluate many different aspects of our daily lives. The use of our senses through organoleptic methods offers unique and powerful insights into the characteristics of different stimuli. Due to the unique function of the different sensory organs we use to evaluate our surroundings, humans are incredible at evaluations that are beyond the scope of modern analytical equipment. Because of their availability to discriminate different stimuli, humans are often used in place of equipment to evaluate different foods and beverages, for sensory testing. These tests cover a wide range of scopes and applications, making them very versatile. For the research covered in this thesis, sensory methodologies were implemented to use humans’ discriminatory power to evaluate different organoleptic properties of wine and wine constituents. The first study explored the use of two vineyard treatments to alter the effects of an emerging grapevine disease caused by Grapevine Red Blotch Virus (GRBV). GRBV can affect the vines ability to fully ripen grapes and can results in many different compositional changes in the grape including lower total soluble solids, lower anthocyanins, and higher acidity. These compositional changes in turn can alter the sensory characteristics of wine made from grapes from GRBV positive vines. To counteract these effects, two vineyard treatments were employed: the exogenous application of abscisic acid (ABA), and the usage of different leaf removal techniques. Treatments were applied in the vineyard to Vitis vinifera Pinot Noir, during the 2018 and 2019 season. Grapes were harvested and made into wine using standard red wine techniques. Both juice and wine samples were collected for physiochemical analysis. Juice samples were analyzed for ⁰Brix, pH, titratable acidity (TA), and yeast assimilable nitrogen. Wine samples were then assessed for pH, TA, polymeric pigment, color density, color intensity, color shade, and ethanol. Wines were then aged in bottle for 1 year, after which they were evaluated via sensory analysis. Minimal analytical differences were found in both the juice and wine samples in both years. Sensory panels consisting of general red wine consumers were used to evaluate overall liking, color, aroma, and mouthfeel. Results showed that ABA and leaf removal treatments were not effective in altering the sensory properties of wines made from GRBV positive grapes. The only significant sensory result was within both the ABA and leaf removal treatment groups where color was rated significantly higher for the treatment groups (ABA and LR HR treatments) in 2019. These findings suggest that neither ABA nor leaf removal are adequate methods of altering the sensory characteristics of wines made from GRBV positive wines. The second study explored the effect of oligosaccharides on wine taste and mouthfeel. Two different oligosaccharide types, fructo-oligosaccharide (FOS), and galacto-oligosaccharide (GOS) at two different concentrations, 450 ppm and 900 ppm were used. These concentrations were selected as 450 ppm was previously reported to be present in Pinot noir wines, while 900 ppm was used to study the effects of greatly increasing the oligosaccharide concentration. Oligosaccharides were added to a generic wine matrix (pH 3.5, 4 g/L TA, 12% v/v ethanol) to control for potential chemical interactions. All samples including an untreated control underwent triangle testing. Triangle testing was then followed by a trained descriptive analysis panel using line intensity scaling for sweetness, bitterness, acidity, astringency, and viscosity. Two samples were found to be significantly different from each other, the FOS450 and FOS900 samples. However, neither was different from the control and there were no significant differences noticed during descriptive analysis. Polyphenols, compounds known to influence wine astringency, were then added to the wine matrix to explore sensory differences due to potential interactions. Samples then underwent additional triangle testing to evaluate differences due to oligosaccharides in the new wine matrix. However, no significant differences were notice for any of the oligosaccharide types or concentrations. Thus, the overall lack of significant results in both sets of triangle tests and descriptive analysis indicates that oligosaccharides likely do not play a large role in wine sensory. Sensory methodologies offer an in depth look at the characteristics of different foods and beverages that may or may not be predictable from compositional data. Treatments or additions intended to alter sensory characteristics does not always mean there are differences to be found. This is true for both experiments presented in this thesis. While ABA and leaf removal techniques have previously proven to alter wine sensory properties, this did not occur for wines made from GRBV positive vines. Additionally, while oligosaccharides can influence sensory perception in different food systems, the same cannot be said for wine sensory. However, these findings are not without significance. While GRBV continues to be prevalent across the globe the findings presented here allow for better focus into different mitigation efforts. The same is true for the oligosaccharide findings, these results will better inform and guide future research efforts. Overall, the sensory methods employed in the studies presented provide helpful insights into the organoleptic properties of wines and wine components.
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