Note. Comparison of Two Rapid Methods of Lipoxygenase Assay in Blanched Green Peas, Green Beans and Potatoes

Abstract

Two rapid methods, methylene blue bleaching (MBB) and potassium iodide-starch (KI-S), for lipoxygenase assay in blanched green peas, cut green beans and diced potatoes were evaluated and compared, using as a reference a quantitative spectrophotometric procedure for lipoxygenase (LPO) activity determination. Green peas (diameter - 10-II mm), cut green beans (diameter = 10 mm; length = 20 mm) and diced potatoes (cubes of 10 mm) were water blanched at 100 'C; heating times ranged between 10 and 40 seconds. For visual comparison of the methods, two times were registered: starting time, when the color began to change, and final time, when the color change fully developed. Both rapid visual methods (MBB and KI-S) showed good performance in detecting LPO in blanched vegetable samples. KI-S method was more sensitive than MBB procedure, with its detection limit between 0.70 and 1.80 LPO units/g, depending on the product. Additionally, FT was 180 seconds for KI-S method as compared to 600 seconds for MBB procedure, therefore, KI-S method is recommended as the best option for a rapid assay of LPO in the vegetables studied.