2018 ASHS Annual Conference

Cider production relies primarily on the transformation of fresh apples. When the primary constituents are inadequate, producers often rely on additives to increase sugar, correct acid, or control the yeast assimilable nitrogen (YAN) in the pre-fermentation juice. Apple juice often has insufficient YAN for yeast, particularly Saccharomyces cerevisiae, to use for its own growth, which can prevent the completion of alcoholic fermentation and affect flavor development. In apple juice, YAN consists of individual amino acids (free amino nitrogen, or FAN) and ammonium. Nitrogenous compounds develop and change in apple fruits during fruit growth and development and in response to nitrogen fertilization, but it is unclear exactly which compounds in the juice are affected. This study investigated the concentration of 20 individual amino acids in apple juice in two ways: one looking at the development of amino acid concentrations throughout the growing season and one looking at this development in response to foliar fertilization. In the 2016 and 2017 seasons we applied weekly urea foliar sprays (5.1 g N/L solution) to Crimson Crisp® apple trees on M9 rootstock weekly after petal fall at three treatment levels: zero sprays, three sprays, and six sprays. The orchard was divided into eighteen units of ten trees. Each treatment was applied to six units in the orchard in a completely randomized design. Sprays began 7 days after full bloom ended. After the third spray was completed and every three weeks thereafter until maturity apples were collected from each unit and processed into juice. The juice was then analyzed for amino acid concentrations using high performance liquid chromatography. The results indicate that the greatest changes in amino acids within the growing season are the overall reduction in FAN concentration, the decline of asparagine concentration, and the increase in aspartic acid concentration as the fruit approaches maturity. The study found that the six-spray treatment increased the concentration of FAN in juice, but FAN concentrations in juices from the zero- and three-spray treatments were not significantly different from one another. The most notable differences in the amino acid concentrations in mature fruit were higher concentrations of aspartic acid, asparagine, methionine, and valine in the units that received six sprays. This information can be used by cider producers to better plan for their supplementation regimens during fermentation. Further research is required to investigate other forms of nitrogen fertilization as well as the effect of spray timing.