Suppression of red color development associated with anthocyanin accumulation in the epicarp of grape (Vitis labrusca × vinifera cv. Ruby Roman) berries caused by air temperature in daylight periods higher than 33°C during maturation

Abstract

The effect of high air temperature on the anthocyanin accumulation in the epicarp of 'Ruby Roman' grape (Vitis labruscana × vinifera) berries was examined. Seventeen types of anthocyanin were detected from the epicarp tissue of the matured berries using HPLC. Since a strong positive correlation (P < 0.005, R2 = 0.937) was confirmed between the degree of color density evaluated using a color chart and the total content of anthocyanins quantified separately, it seems possible to trace anthocyanin accumulation using the color chart on each berry during maturation at different air temperatures. Four conditions were designed for cooling the fruit clusters with a spot-cooling system, which can keep air temperature 4–5°C lower for 60–70 days after the full–bloom, i.e. consecutive (0:00–24:00) cooling, daytime (6:00–18:00) cooling, nighttime (18:00–6:00) cooling and no–cooling (control). The degree of color density showed statistically higher (P < 0.05) values in the consecutive–cooling treatment than that of the control through the post–cooling duration (0–15 days after cooling). To clarify the effect of temperature zones with or without daylight on the anthocyanin accumulation in the epicarp, percentage of exposure time to each temperature zone of < 21, 21–24, 24–27, 27–30, 30–33, 33–36 and 36°C ≤ were calculated for both daylight and dark periods, separately. Correlations of the ∆ time% (the amount of difference in percentage of exposure time from the control) with the ∆ color degree (the amount of difference in degree of color density from the control) in the daylight period were positive at temperature zones of < 30°C, but turned to negative at those of 30°C ≤. The fact that correlation coefficient was statistically significant (P < 0.05) at the temperature zones of 27–30°C (positive) and 33–36°C (negative) in the daylight period shows that the threshold where the anthocyanin accumulation starts to be suppressed exists within 30–33°C.