Objective To identify the types of phenolic acids that result in bud explants browning of Magnolia sieboldii and determine the most effective anti-browning agent at an optimum concentration.

Method Bud explants were cultured in B5 medium for 30 days. At the beginning, three kinds of anti-browning agents were added separately to the B5 medium. The browning rates were calculated and analyzed. Then the effects of the three inhibitors on anti-browning were compared on the basis of the browning rates. In addition, the content variations of caffeic acid, chlorogenic acid, and p-coumaric acid in the bud explants were measured with HPLC using samples regularly selected during tissue culturing.

Result The results showed that the contents of caffeic acid and chlorogenic acid decreased sharply while the content of p-coumaric acid experienced a slight decrease, proving that caffeic acid and chlorogenic acid were more likely to be oxidized than p-coumaric acid. Moreover, the effects of the three inhibitors on anti-browning were sorted in a decreasing order of VC, PVP, and CA. Although PVP was inferior to CA with respect to controlling phenolic acid oxidation, its anti-browning effect was more efficient than CA. This result was explained by their different mechanisms for anti-browning. Lastly, the optimal concentration for VC was 500 mg·L^-1, and a higher concentration would result in a greater browning rate of the bud explants. Respective optimal concentrations for PVP and CA were 1 000~1 500 mg·L^-1 and 300 mg·L^-1.

Conclusion The browning substrates in bud explants of M. sieboldii are caffeic acid and chlorogenic acid rather than p-coumaric acid. VC, PVP, and CA have distinguishable anti-browning mechanisms and the anti-browning effects of them will decrease gradually.