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.
LIPOXYGENASES IN DEVELOPING ZEA MAYS KERNELS
Dans les grains de Mais (Zea mays), les activites lipoxygenasiques (LOX, linoleate: oxygene oxydoreductase, EC 1.13.11.12) presentent trois optimums differents aux pH 6,8, 5,5, et 7,75. Les activites LOX ont ete suivies separement au cours du developpement des grains par leur mesure a chaque pH. Les activites LOX totales et specifiques sont plus elevees dans les tissus de l'embryon que dans ceux de l'albumen durant tout le developpement de la graine. L'augmentation de l'activite LOX dans l'embryon coincide avec le stade de developpement de la graine pendant lequel l'acide abscissique est le plus efficace dans l'inversion de la viviparite.
Changes in Peroxidase Activity, Hexanal, Ascorbic Acid and Free Sulfhydryl in Blanched Asparagus During Frozen Storage
Asparagus spears were water blanched at 88°C for 1 to 4.5 min and stored at - 18°C. Hexanal, ascorbic acid, free sulfhydryl and peroxidase activity were monitored during storage. Blanching for 2 min resulted in a 98% reduction in peroxidase activity. No hexanal was detectable in product blanched for 2 min or longer. Ascorbate stability during storage increased with increase in blanching time although not in direct relation to peroxidase activity loss. Free sulfhydryl was sensitive to heating and also decreased during storage of unblanched asparagus. However, there appeared to be a stable fraction of free sulfhydryls.