The effect of HTST pressure blanching processing parameters, as compared to conventional steam blanching, on enzyme activity, moisture, drip loss, shear force, sensory attributes and consumer acceptability of frozen sweet corn were determined. Complete inactivation of catalase and peroxidase required HTST treatments of 60 psi and 75 psi, respectively. No lipoxygenase activity was detected in the blanched corn. Moisture content increased slightly and maximum shear force decreased in the HTST blanched corn as compared to the steam blanched samples. No differences were observed in total work of compression and shear or drip losses in frozen corn prepared by the two blanching processes. Blanch pressures of 60 psi and 75 psi resulted in corn equivalent in sensory qualities to the control steam blanched product as judged by a trained panel. The 30 psi blanch treatment was rated higher in stale/oxidized, fishy, bitter, and other undesirable descriptors. Stale/oxidized and sweet/caramel character increased with storage time. Consumer tests resulted in no significant differences in acceptability across blanch treatments or storage time. / Graduation date: 1988

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Three varieties of sweet corn (Zea mays L.) , including two supersweet (Crisp 'N Sweet 710 and Rogers 3376) and one normal sweet (Jubilee), were harvested at six stages of maturity (80-72% moisture for supersweet and 75-68% moisture for normal sweet) at three days intervals. Changes in physical and chemical properties over the 15 day harvest period and effects of steam blanching on carbohydrate composition of both genotypes of sweet corn were determined. Moisture content of the kernels decreased with maturity. A quick microwave oven moisture method for determining moisture content of normal sweet and supersweet corn was evaluated and found to be a good alternative method for the time-consuming standard AOAC vacuum oven method. Yield (as represented by average ear weight) increased linearly with maturity. Percent soluble solids was determined to be a satisfactory maturity index for normal sweet corn but not for supersweet corn. The pericarp content in the normal sweet corn Jubilee increased 25% over the 15-day harvest period compared to a mean of 5-6% in the supersweet varieties. Values of the shear press tests were not significantly correlated to % moisture, and only values of compression work showed a positive trend to increase with maturity. Total sugars of supersweet corn averaged 2-3 times higher and decreased more slowly than those of normal sweet corn in the comparable maturity range for processing. Sucrose was the major sugar in both corn genotypes and represented about 80% of the total sugars (9-20% dry weight) in normal sweet corn versus 90% of the total sugars (30-45%) in supersweet corn. Polysaccharides consisted mainly of starch in supersweet corn and of water soluble polysaccharide (WSP) in normal sweet corn. Normal sweet corn contained about twice as much polysaccharides as did supersweet corn. Percent total polysaccharides increased with maturity. Although higher in sugars, supersweet corn had lower % total carbohydrates than normal sweet corn due to its low polysaccharide content. Blanching of corn-on-the-cob for 10 minutes in 99°C steam resulted in a significant loss of sugars. Blanching did not significantly reduce total polysaccharides of sweet corn. / Graduation date: 1990

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