Thermal treatment of apple puree under oxygen-free condition: Effect on phenolic compounds, ascorbic acid, antioxidant activities, color, and enzyme activities

The effect of heating in the absence or presence of oxygen on the enzyme activity and nutritional quality of apple puree were investigated. Using designed equipment, apples were vacuum-ground, packaged, and heated under vacuum (2.67 kPa, 90 degrees C for 30 min) to limit exposure to oxygen, and compared to those heated in open air. All thermal treatments led to complete inactivation of oxidative enzymes. Heating without oxygen effectively maintained color, antioxidant activity, phenolic compounds, and ascorbic acid, as compared to fresh apples. In contrast, heating with oxygen led to considerable browning and degradation of antioxidant activities, phenolics, and ascorbic acid. The results indicate that thermal processing without oxygen can help preserve the nutritional value and retard changes in phenolic-related quality of fruits and vegetables. This study suggests that browning and nutritional loss during thermal treatment of apple may be attributed to oxidation, which is accelerated by the elevated temperature.