Comparison study of conventional hot-water and microwave blanching on quality of green beans
Microwave blanching of green beans (Phaseolus vulgaris L.) was explored as an alternative to conventional hot-water blanching. Batches of raw pods were treated similarly to an industrial process employing a hot-water treatment but using a microwave oven for blanching. The effects of microwave processing time and nominal output power on physical properties (shrinkage, weight loss, texture, and color), enzyme activities (guaiacol peroxidase, L-ascorbate peroxidase, and catalase), and ascorbic acid content of pods were measured and modeled by first-order kinetics. Inactivation of peroxidase (POD) was the best indicator to assess the efficiency of microwave-blanching of green beans. No significant differences in product quality were found between hot-water blanched and microwaved pods at optimal processing conditions. Furthermore, since shorter processing times and higher ascorbic acid retention were found, microwave processing of green beans can be a good alternative to conventional blanching methods.
Industrial relevance: Microwave blanching of green bean pods has been proved as a reliable alternative method to the conventional heating process used in the vegetable canning industry. The overall quality of the product processed by microwave heating under optimal conditions was comparable to that of the current industry process. The microwave treatment of pods, in addition to an effective enzyme inactivation in less processing time, led to a better retention of ascorbic acid.