4. Conclusions
Although the underlying mechanisms are unclear, heating can increase the functionality of onion. This study showed that the total contents of polyphenols and flavonoids as well as antioxidant capacity markedly increased in heated onion compared to unheated one (Woo et al., 2007). Consistently, in our study, although both heated and unheated apple juices supplemented with onion showed increased nutritional quality as well as inhibition of browning, onion exerted better functionality when heated. Heating itself is also an efficient way to reduce browning and increase radical scavenging activity of apple juice regardless of onion addition, although onion addition also inhibited browning and increased radical scavenging activity of unheated apple juice. Under our experimental conditions, maximal nutritional quality and anti browning effect were achieved in heated apple juice supplemented with onion solution. Therefore, heating and addition of heated onion together may greatly improve overall quality of apple juice.