Characterization of factors affecting pectinmethylesterase activity in cucumber fruit Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/gq67jv348

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  • Pectinmethylesterase (PME) activity in fresh cucumber fruit was determined. The effects of several cationic species, temperature, pH, and acetic acid on the activity of cucumber PME was investigated. The efficacy of blanching, infiltration with CaCl₂ or acetic acid, and fermentation with 0 and 40 mM CaCl₂ on inhibition of cucumber PME activity were evaluated. Over 50% of PME activity was present in the skin and 75% occurred within the outer 3 mm of the fruit. Maximum stimulation of PME occurred at 125 mM NaCl, 200 mM KCl, and 5 mM CaCl₂. Higher levels of each cation demonstrated inhibition of PME activity. 50% inhibition was observed at 750 mM NaCl, 800 mM KCl, and 200 mM CaCl₂. Optimum pH was 8.0 and acid pH conditions greatly reduced activity. PME exhibited no activity at pH 4.0. PME activity responded typically to temperature variations with maximum activity occurring at 50°C. The temperature coefficient Q¹⁰ for PME activity between 10 and 40°C was 1.24. PME activity was slightly stimulated by increased levels of acetic acid and reached its maximum at 1.5% acetic acid at pH 7.5. No inhibitory effect on PME was detected at acetic acid levels of 0 to 2.0%. Inhibition of PME by NaCl and CaCl₂ was reversible. High levels of NaCl (1 M) stabilized PME activity while incubation of PME activity in low levels of NaCl (0.24 M) resulted in loss of activity over time. Both high (500 mM) and low (5 mM) levels of CaCl₂ imparted stability to PME activity. No detectable PME activity remained in cucumbers after 15 days of fermentation. Addition of CaCl2 (40 mM equilibrated) to the fermentation brine caused a rapid reduction in PME activity during the first 6 to 12 hours after brining. After 24 hours of brining there was no difference in PME activity due to CaCl₂ addition. Acetic acid infiltration at high levels (>10%) effectively reduced the pH of skin tissue to near 4 and resulted in complete inhibition of PME activity. The most effective treatment for controlling cucumber PME activity was rapid pH reduction by acetic acid infiltration and resulting in PME inhibition. Infiltration with very high CaCl₂ levels (>500 mM) may also be beneficial toward accomplishing PME inhibition. Rapid inactivation prior to brining or within 6 to 12 hours after brining is necessary to achieve effective control of cucumber PME activity.
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