APPLE ORCHARD MANAGEMENT FOR HARD CIDER PRODUCTION: INFLUENCE OF NITROGEN FERTILIZATION AND CARBOHYDRATE AVAILABILITY ON TANNIN SYNTHESIS, YEAST ASSIMILABLE NITROGEN, AND FERMENTATION KINETICS
Two areas of interest were identified to investigate how orchard management can improve cider apple orchard management: the influence of nitrogen fertilization on yeast assimilable nitrogen (YAN) concentrations, and when tannins are synthesized in apples and what factors influence their synthesis. Two experiments were carried out using soil and foliar applied nitrogen fertilizers to investigate how nitrogen influences the concentrations and composition of YAN; juice from these experiments were fermented and the production of hydrogen sulfide (H2S) tracked. Different rates of foliar urea application beginning six weeks before harvest increased YAN by as much as 319% compared to the Control. A high rate of soil applied calcium nitrate fertilizer increased juice primary amino nitrogen (PAN) by 103% relative to the Control. In both fertilizer studies PAN constituted over 90% of YAN. Fertilization increased fermentation rate, but no consistent relationship was found with fertilization rate and H2S synthesis. There was no influence of nitrogen fertilization on polyphenol concentrations. The increases in YAN demonstrate that nitrogen fertilization is an effective means of increasing juice YAN while not impacting important sensory attributes such as polyphenols. In order to investigate when polyphenols are produced in cider apples, and the influence of carbohydrate availability, light, temperature, and location within the tree canopy on fruit and juice polyphenol concentrations, five separate experiments were conducted over three years. Analysis of polyphenol concentrations in cortex tissue in developing fruit showed that most polyphenol synthesis occurred in the first five weeks after full bloom (WAFB). Shading whole trees or individual branches in the first five WAFB reduced total polyphenol concentrations by as much 23%. Bagging fruit three WAFB had variable effects on polyphenol concentrations depending on cultivar. Shading branches from four WAFB through harvest resulted in a 16% reduction of polyphenols relative to the Control. Fruit from the tops and exposed lateral sides of tree canopies had lower total polyphenol concentrations in juice than the interior of the canopy. These results suggest that most polyphenols are synthesized early in fruit development and that carbohydrate supply during this period likely influences their development.
apple; cider; polyphenol; yeast assimilable nitrogen
Cheng, Lailiang; Mansfield, Anna; Stewart, Amanda
Ph. D., Horticulture
Doctor of Philosophy
dissertation or thesis