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. / Graduation date: 1989
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27193 |
| Date | 06 February 1989 |
| Creators | Turk, Farzaneh |
| Contributors | Hudson, J. Michael |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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