3.2. Onion supplementation increases color quality of apple juice
Browning is responsible for degrading the color quality of apple juice. Thus, we examined whether or not onion addition and/or heating affect browning of apple juice using a colorimeter and spectrophotometer. Heating itself markedly reduced the estimated browning index, as measured by spectrophotometry, and no additional effect was observed in the heated apple juice supplemented with onion solution (Fig. 2). Consistently, colorimetry analysis found that Hunter L value representing brightness was elevated in the heated apple juice compared to unheated juice, whereas L value did not increase in heated apple juice supplemented with onion (Table 1). These data suggest that heating itself can strongly suppress browning of apple juice.