Effect of microwave blanching on slice thickness and quality analysis of star fruit

Star fruit (Averrhoa carambola L.) is one of the underutilized tropical fruits and is a good source of vitamins and minerals. Peroxidase (POD) is the most heat stable enzyme which is used as an indicator for adequacy of blanching process. Blanching is a prerequisite for the preservation of fruits and vegetables. Hot water blanching is having disadvantages like wastewater production and loss of valuable nutrients by leaching. Microwave blanching is one of the emerging and clean technology which seems to provide a better nutrient retention due to shorter heating time and zero wastewater production. Therefore, the present investigation was carried outto identify a suitable blanching method (hot water blanching and microwave blanching)for different slice thickness (5, 10 and 15 mm) of star fruit that ensures enzyme inactivation and maximum retention of therapeutic value (ascorbic acid and oxalic acid). It was observed that blanching at 600, 480, 240 and 120 W power level for aslice thickness of 5, 10 and 15 mm required blanching time of 30-60s, 40-70s, 60-80s, 80-150s and 300-720s respectively. For a given slice thickness, the moisture content of samples decreased with increase in power level. The moisture content was reduced to 84-88 % w.b. from an initial value of 90 % w.b. depending on power level and blanching time combinations. At the same time, the oxalic acid decreased significantly with increase in slice thickness and adecrease in power level. The change in ascorbic acid also showed a similar trend but the influence of slice thickness was not significant (p>0.05).