Regulation of Enzymatic Browning of Mung Bean Sprout by Heat-Shock Treatment

Abstract

Mung bean sprouts turn brown during cold storage. Here we showed that heat-shock treatment inhibited this browning by repressing the induction of phenylalanine ammonia-lyase (PAL) activity and the biosynthesis of polyphenols during cold storage. Mung bean sprouts were soaked in warm water at 50℃ for 60 s as heat-shock treatment and then stored at 8℃ for 6 days. Heat-shocked mung bean sprout turned less brown than that of the control sprout. The PAL activity in the control significantly increased during cold storage, while that in heat-shocked mung bean sprouts did not. The polyphenol content in heat-shocked mung bean sprouts was lower than that in the control at 3 and 6 days. There was no significant difference in polyphenol oxidase activity between the control and heat-shocked mung bean sprouts during cold storage. These results show that mild heat treatment inhibited the enzymatic browning of mung bean sprouts by repressing the induction of PAL activity during cold storage and the accumulation of polyphenols.

Cloning of Phenylalanine Ammonia-lyase and its Role in Enzymatic Browning of Mung Bean Sprout during Cold Storage

“…This result supports our previous report (Nishimura et al, 2012) showing that heat-shock treatment repressed the accumulation of phenolics and browning of mung bean sprout, by inhibiting the induction of PAL activity during cold storage. Although the heat- shock treatment of cut lettuce also repressed the accumulation of phenolics and browning during storage (Loaiza-Velarde et al, 1997;Murata et al, 2004), the treatment did not repress PAL expression but was speculated to inhibit the translation of PAL (Campos-Vargas et al, 2005;Tanaka et al, 2011).…”

“…Change in phenolics of mung bean during cold storage The amount of phenolics was increased from 10.6 ± 0.6 mg/100 g at day 0 to 25.8 ± 1.1 mg/100 g at day 7 during storage at 8℃, results that coincide with the data of Nishimura et al (2012). Next, each phenolic was examined using HPLC.…”

“…The expression was increased during cold storage and was the highest at day 2. As the heat-shock treatment repressed the induction of PAL activity of mung bean sprout (Nishimura et al, 2012), the effect of heat-shock treatment on the expression of PAL mRNA was then examined (Fig. 4).…”

“…We previously showed (Nishimura et al, 2012) that heat-shock treatment inhibited browning by repressing the induction of phenylalanine ammonialyase (PAL; EC 4.3.1.24) activity, one of the key biosynthetic enzymes of polyphenols or phenolics. However, the PAL gene of mung bean sprout has not yet been cloned, and whether the induction of PAL activity occurs at the level of mRNA or protein remains to be elucidated.…”

Heat‐induced tolerance to browning of fresh‐cut lily bulbs ( Lilium lancifolium Thunb.) under cold storage

“…HT is an environmentally friendly physical processing technique. Heat shock or mild HT has become an effective method to inhibit discoloration of fresh‐cut fruits and vegetables in storage period (Nishimura, Sameshima, Joshita, & Murata, ). The mild HT in particular hot water that reduces browning may work by inhibiting enzymes of phenolic metabolism and leading the production of heat shock proteins (Saltveit, ).…”