Effect of amino acid composition on the taste of 'Hakuho' peaches (Prunus persica batsch) grown under different fertilizer levels

The effect of amino acids on the taste of the peach fruit was investigated by sensory evaluation tests. Fruits were harvested from 'Hakuho' trees that were grown under three levels of complete liquid fertilizers, containing nitrogen at 40 ppm (L), 80 ppm (M), and 160 ppm (H). Major amino acids analyzed were asparagine (ASN), serine (SER), threonine (THR), arginine (ARG), and aspartic acid (ASP), which accumulated at significantly higher concentrations with increased fertilizer levels. Sensory evaluations showed that juice from the H treatment fruit was more sour and had a bitter taste, whereas that from the L treatment was equally sweet as the juice from the M treatment; the overall evaluation gave the highest mark to the M treatment. After removing amino acids from juice using ion exchange resins, the major amino acids were added again individually or cumulatively to the original concentrations of each treatment juice. SER, ARG, and ASN increased sweetness, whereas ASP increased sourness of each case. Such amino acids improved "umami" (deliciousness or deepness of the taste) and overall taste at the concentrations of those in the M treatment juice but they increased bitterness and, thereby, lowered the overall evaluation of the H treatment juice. These results indicate that amino acids improve the taste of peach fruit, but excessively high levels of ASN and ARG lower the sensory quality.