EFFECT OF BLANCHING AND KINETIC STUDY FOR THE BENEFIT OF GREEN BEANS [Vigna unguiculata (L.) Walp.]
Heat treatment; peroxidase; legume; quality control.
Green beans (green beans) have an important role in the economy and nutrition of different populations. However, the high perishability impairs commercialization, which can sometimes be discontinued. Blanching is a technological alternative that can give greater durability to green beans. This research aims to investigate the effects of blanching on physical characteristics (firmness, color, and mass gain) and enzymatic activity of peroxidase (POD) in green beans; to study the kinetic behavior of these properties, and to evaluate the shelf life of fresh and blanched green beans stored under refrigeration (4.90 ºC). Experiments were carried out with three temperatures (70, 80, and 90 ° C) and six times (1, 2, 4, 6, 8, and 10 minutes) to analyze the blanching effects and the kinetics of the studied properties. The physical-chemical, microbiological, and enzymatic (POD) changes, in addition to photographic monitoring, were evaluated throughout storage under refrigeration. A significant decrease (p <0.05) in enzymatic activity after blanching was evidenced. However, the application of high temperatures for a long period caused the grains to soften, increased mass gain, and decreased green hue. The dependence on decreased enzymatic activity, firmness, and color with temperature showed coefficients of determination (R2) that indicated a satisfactory fit of the data to the first-order kinetic model. The study of the effects and the kinetic model showed that the use of 70 ° C for 4 minutes was favorable for maintaining and / or improving the physical characteristics of the raw material. During the refrigerated storage period, the pH and the total titratable acidity of the blanched green beans suffered little change; microbiological load and POD activity showed a significant reduction (p <0.05) with blanching and remained stable (p> 0.05) until the eighth day of storage. The blanching of green beans at 70 ° C for 4 minutes increased storage under refrigeration in 5 days when compared to unblanched green beans under the same conditions. Thus, blanching is shown as an alternative for the processing of green beans, favoring an economic rise in production with guaranteed quality and safety attributes of green beans.