EFFECT OF MICROWAVE POWER LEVEL AND TIME ON ASCORBIC ACID CONTENT, PEROXIDASE ACTIVITY AND COLOR OF SELECTED VEGETABLES

Abstract

The objective of these studies was to evaluate the effects of blanching at various microwave power levels (30%, 55%, 70%, 100%) for times (0, 1, 2, 3, 4 min) on peroxidase inactivation, and ascorbic acid and color preservation in broccoli, green beans and asparagus. As power level and time increased, moisture losses increased. Actual ascorbic acid concentration (mg/100 g) increased, but when adjusted for moisture loss, it decreased. Microwave treatment at any power level for as little as 1 min reduced peroxidase activity. However, at higher powers (70% and 100%), less time was required to achieve the maximum reduction. Microwave heating at 70% or 100% caused some darkening (decreased L* value). Hue angle decreased (less green) at 55 %, 70% and 100% power after 1 min of treatment. Overall, microwave power level and time had greater effects on moisture, RAA content and on peroxidase activity than on color.