Effect of Infrared Blanching on Enzyme Activity and Retention of -Carotene and Vitamin C in Dried Mango

The objectives of this work were to evaluate infrared (IR) dry blanching in comparison with conventional water blanching prior to hot air drying of mango to inactivate polyphenol oxidase (PPO) and ascorbic acid oxidase (AAO) enzymes, and to study its effect on color change and retention of vitamin C and -carotene. Mango cylinders were blanched under similar temperature-time conditions either by IR heating or by immersion in a water bath during 2min at 90 degrees C (high-temperature-short-timeHTST) or for 10min at 65 degrees C (low-temperature-long-timeLTLT). After blanching mango was hot air dried at 70 degrees C. PPO was completely inactivated during the blanching treatments, but AAO had a moderate remaining activity after LTLT treatment (approximate to 30%) and a low remaining activity after HTST treatment (9% to 15%). A higher retention of vitamin C was observed in mango subjected to IR dry blanching, 88.31.0% (HTST) and 69.2 +/- 2.9% (LTLT), compared with water blanching, 61.4 +/- 5.3% (HTST) and 50.7 +/- 9.6% (LTLT). All-trans--carotene retention was significantly higher in water blanched dried mango, 93.2 +/- 5.2% (LTLT) and 91.4 +/- 5.1% (HTST), compared with IR dry blanched, 73.6 +/- 3.6% (LTLT) and 76.9 +/- 2.9% (HTST). Increased levels of 13-cis--carotene isomer were detected only in IR dry blanched mango, and the corresponding dried mango also had a slightly darker color. IR blanching of mango prior to drying can improve the retention of vitamin C, but not the retention of carotenoids, which showed to be more dependent on the temperature than the blanching process. A reduction of drying time was observed in LTLT IR-blanching mango. Practical Application Blanching is widely used in fruit and vegetable processing industry. This process consumes large amounts of water and can have a negative effect to the nutritional value of the fruits and vegetables by leaching out water-soluble compounds. In this study the potential of using infrared heating, dry blanching, prior to drying was studied to find solutions to improve the nutritional value of dried fruits. The results show that IR blanching of mango prior to drying can improve the retention of water-soluble vitamins, like vitamin C, but not the retention of lipid-soluble vitamins like, carotenoids. Selection of appropriate blanching conditions is necessary to enhance the nutritional value.