Pectin esterase production by Rhizopus stolonifer from post‐harvest soft rots of potato tubers in Nigeria and its activity

Abstract

AbstractThe ability of Rhizopus stolonifer (Ehren ex. Fr.) Lind, a common pathogen of post‐harvest potato tubers in Nigeria to produce cellwall‐degrading enzymes was studied. When grown on a basal medium containing 0.5% (w/v) sodium polypectate at 30 °C, only pectin esterase was detected in the growth medium throughout the incubation period of 10 days. Both exo‐ and endo‐polygalacturonase activity were absent in the growth medium. The pectin esterase was found to be constitutive as it was readily produced on sources of carbon other than pectin. Partial purification was achieved by a combination of membrane filtration, ethanol precipitation, fractionation on DEAE‐cellulose and gel‐filtration on Sephadex G‐200. This resulted in a single enzyme peak with a specific activity of 58.5 and a recovery value of 4.9%. The purified enzyme was most active at pH 8.5 and a temperature of 35 °C. It lacked the ability to macerate potato tissue cells and did not induce discolouration of potato discs nor kill the cells. R. stolonifer is discussed to be probably not strongly pathogenic to post‐harvest potato tubers.