Inhibitory Effect of Onion Juice on Browning of Shredded Lettuce

The effect of Allium juice on browning of shredded lettuce was evaluated as hue angle, using a color meter. When shredded lettuce was dipped for 3-min. in Allium juice, browning of shredded lettuce stored at 5 or 10°C was significantly reduced compared to the water-dipped, control sample. Juice of onion or garlic had the strongest activity among tested Alliums. Among 11 onion cultivars, the juice of 'Kitamomiji 86' had the strongest activity. The inhibitory activity was ubiquitous in juices from all edible parts but that from the middle part of the bulb was stronger than the outer part. The inhibitory activity decreased slightly when the onion juice was heated in boiling water ; it almost ceased when the raw onion was microwaved, homogenized, then squeezed to obtain the juice. The results indicate that the inhibitory component is formed by heat labile enzyme reaction during the raw bulb is cut and homogenized.