Rapid Methods for Lipoxygenase Assay in Sweet Corn
Potential methods for rapid assay of sweet corn lipoxygenase (LPO) were evaluated and compared by visual inspection. Both model system (partially purified) and vegetable (LPO extract) system studies were carried out. Model system studies indicated that LPO had maximum activity at pH 6.0 and 2.0 mM linoleic acid. Methylene blue bleaching (MBB), carotene bleaching (CB), and potassium iodide-starch (KI-S) methods were evaluated both spectrophotometrically and visually. Both MBB and KI-S methods were effective for the model system. For the vegetable LPO extract systems (sweet corn and green beans), the MBB method indicated positive results for both, the CB method was not effective for either, and the KI-S method was very effective for green beans but not for sweet corn.
Effect of Blanching on Enzyme Activity and Quality Changes in Green Peas
Fresh green peas were blanched for various times/temperatures and stored at — 23°C. At 3 month intervals peas were analyzed for per-oxidase, polyphenoloxidase, lipoxygenase and catalase activity and ascorbic acid content. Samples were cooked and evaluated sensorily, and using Hunter color and Instron texture measurements. Enzymes exhibited varying degrees of activity over the first 3 months in storage. After 3 months, peroxidase and polyphenoloxidase activity decreased or remained constant. Lipoxygenase activity increased over storage, most noticeably in the long time/low temperature blanch treatment. Sensory evaluation indicated a gradual loss of quality due to poor flavor in the long time/low temperature blanch. Ascorbic acid content, greenness and firmness decreased gradually with storage.
Peroxidase Fractions from Asparagus of Varying Heat Stabilities
Chromatofocusing was used to fractionate asparagus peroxidases. Basic isozymes of pI greater than 9.0 predominated throughout the spear. In addition, a more acidic peroxidase fraction is found in the asparagus spear tip. The basic and acidic fractions were similar in heat stability, but the acidic fraction reactivated readily after heating at 70°C.