The effect of grinding at various vacuum levels on the color, phenolics, and antioxidant properties of apple

• Grinding apples at 101.33 kPa resulted in browning and the loss of antioxidant activity in 30 min.
• Vacuum-grinding apple effectively retarded the change in color and loss of phenolic compounds.
• Even a small amount of oxygen can have a substantial effect on the loss of antioxidant activity.

The purpose of this study was to evaluate the effect of grinding at different vacuum levels (2.67, 6.67, 13.33, 19.99, and 101.33 kPa) on key quality factors of apple. In the control apple, ground at atmospheric pressure of 101.33 kPa, the antioxidant activities rapidly decreased within the first 30 min, then plateaued thereafter, while enzymatic browning increased. When apples were ground and held under vacuum, changes in color and antioxidant activity were much less, and the least change was measured in samples prepared at the lowest pressure. Model fitting of the data showed that antioxidant activity decreased as a function of the logarithm of the absolute pressure. The results from analysis for key phenolic compounds including chlorogenic acid, procyanidin B2, and epicatechin indicated that these compounds were least changed at vacuum grinding at 2.67 kPa, compared to atmospheric grinding.