3.2. Effect of AITC treatment on surface color and firmness of mulberry fruit
Most mulberry fruit is bright red in color before full ripeness and becomes purply-black when fully ripe due to the presence of copious amounts of anthocyanins compounds, the majority as identified in the fruit extract being cyanidin-3-glucoside and cyanidin-3-rutinoside (Butkhup et al., 2011 and Jiang et al., 2013). As shown in Fig. 2A–C, the color parameters (L*, a* and b*) of fruit decreased rapidly in the control group but gradually decreased in the AITC treatment groups (5 and 15 μL L−1). The control fruit had the lowest a* value (11.90) and b* value (4.72) on day 15, namely, decreases of 51.70% and 62.69% from the initial values of 24.70 and 12.60, respectively. The decrease in a* and b* value of AITC-treated fruit was not significant during the storage. L* value tended to decrease during storage ( Fig. 2C), and it decreased severely in the control while the brightness values were well-maintained in AITC treated groups. Surface color is an important index to evaluate the quality and ripening process of mulberry fruit (Oz and Ulukanli, 2014). In the present work, significant differences in the color parameters (a* and b*) were observed between treatments and control (P < 0.05) after 15 d of storage. The results indicate that AITC treatment can slow down the ripening process of mulberry fruit.