The effect of different blanching treatments and
packaging materials on the enzymatic (lipoxygenase and
peroxidase) activity and fatty acid stability of two
different varieties of sweet corn on the cob (Jubilee and GH
2684) was evaluated during nine months of frozen storage at
-23.3°C.
The initial moisture content in the kernels of the two
sweet corn varieties averaged 72.5%. After nine months of
frozen storage the moisture content in the kernels of corn
depended greatly on the packaging material used. The ears
stored in Cryovac B and E bags showed the best moisture
retention (72.2% final moisture content), followed by the
polyethylene bags (71.4%) while the ears stored without
packaging material showed severe dehydration (70.1%).
The peroxidase and lipoxygenase activities were
determined using spectrophotometric assays on a crude
extract obtained from liquid nitrogen powdered corn. Both
unblanched varieties of sweet corn showed similar initial
peroxidase specific activity and general behavior during the
nine months of frozen storage. The presence of lipoxygenase
isozymes with different thermal stabilities in both
varieties was suggested by the higher lipoxygenase specific
activity found in Jubilee after freezing and nine months of
frozen storage (0.135 units/mg protein) compared with the GH
2684 variety (0.115 units/mg protein).
Complete inactivation of lipoxygenase was obtained
after 9 minutes steam blanching at 100°C. Peroxidase was
more heat resistant showing some remaining specific activity
after 9 minutes steam blanching with a complete inactivation
after 15 minutes steam blanching. No regeneration of either
enzyme was observed during the nine months of frozen storage
suggesting a permanent disruption of the active site of both
enzymes.
Relative fatty acid content was determined by gas
chromatographic analysis of fatty acids methyl esters. The
major fatty acids present in both varieties were palmitic
(14.93%), stearic (2.79%), oleic (31.54%), linoleic
(46.87%) and linolenic (1.89%) acids. Good stability of
the polyunsaturated fatty acids was observed during the nine
months storage at -23.3°C, with autoxidation as the main
mechanism responsible for the decrease in the relative percent of polyunsaturated fatty acids. Some enzymatic
oxidation also occurred, decreasing the linolenic acid
content.
The control of the degradation of polyunsaturated fatty
acids depended mostly on the frozen storage temperature
(-23.3°C) and not on the oxygen permeability of the different
packaging materials.
The results obtained in our study suggested that
blanching of the ears of sweet corn had an important effect
on reducing the enzyme activity but little effect on the
polyunsaturated fatty acid degradation after 9 months of
storage at -23.3°C. / Graduation date: 1994
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27144 |
| Date | 01 October 1993 |
| Creators | Rodriguez-Saona, Luis Enrique |
| Contributors | Selivonchick, Daniel P. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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