Abstract
The effect on Polyphenol Oxidase (PPO) and Peroxidase (POD) enzyme activity in red apple juice was evaluated after combined Pulsed Electric Fields (PEF) and mild temperature processing using a response surface methodology. Changes in color were also analyzed and compared with thermally treated and unpasteurized juices. The studied factors were electric field strength (10-30 kV/cm), treatment time (200-1000 μs) and temperature (20- 60°C). A significant second-order response function covering the whole range of experimental conditions was obtained for each enzyme. Treatments conducted at 30 kV/cm, 1000 μs and 60°C led to red apple juice with the lowest residual enzyme activity (0.04 and 0.16 for PPO and POD, respectively). Overall change in color was significantly lower (p<0.05), in comparison with severe thermal treatments. It was feasible to achieve comparable enzyme inactivation and better preserve natural juice color by this hurdle technique.
Highlights
Apple juice clarification leads to drastic changes in the polyphenol profile compared to whole fruit
C* = (a*2 + b*2)1/2 (3) Effect of electric field strength, treatment time and Experimental design: A face-centered central composite response surface design was used to determine the effect of Electric field strength (E), treatment time (t) and mild Temperature (T) on the residual activity of red cloudy apple juice Polyphenol Oxidase (PPO) and POD
Residual activity of the enzymes was calculated mild temperature on red apple juice PPO residual activity: Table 1 shows the results for a face-centered central composite design applied to analyze the effect of combined Pulsed Electric Fields (PEF) and mild temperature on red apple juice PPO enzyme
Summary
Apple juice clarification leads to drastic changes in the polyphenol profile compared to whole fruit. One of the major problems associated with cloudy apple juice processing is color deterioration This essential quality parameter is strongly influenced by the activity of endogenous enzymes, namely Polyphenol Oxidase (PPO) and Peroxidase (POD). Prevention of browning induced by PPO and POD is a critical subject in the juice industry. Reaction products of these enzymes affect color, flavor and texture, but when interacting with proteins, may hinder digestibility thereby reducing the nutritional value of juices (Valvi et al, 2011). Heating is the most ideal because of its capacity to destroy spoilage and pathogenic microorganisms It causes enzyme inactivation by denaturation, and negatively affects thermosensitive nutrients, flavor, color and texture of cloudy juice. Chemical anti-browning effectors, such as sulfating agents, have adverse health effects (Ozoglu and Bayindirli, 2002)
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