Polyphenol oxidase

Automatic Control of Apple Drying with Respect to Product Temperature and Air Velocity

Published in Alex Martynenko, Andreas Bück, Intelligent Control in Drying, 2018

Equally, if the goal is to deactivate enzymes such as polyphenol oxidase (PPO), which catalyze unwanted reactions, exceeding the critical temperatures for these components can be used to minimize enzymatic browning and other unwanted reactions. Thus, product temperature is one of the most crucial factors regarding product quality and its preservation.

Drying characteristics and quality of lemon slices dried under Coulomb force-assisted heat pump drying

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Journal Information

Published in Drying Technology, 2021

Yong Hong Lee, Siew Kian Chin, Boon Kuan Chung

Browning of biological material can be either caused by enzymatic or non-enzymatic processes (Caramelization or Maillard reaction). Enzymatic browning occurs when polyphenol oxidase (PPO) catalyzes the oxidation of phenolic compounds in the drying material to form quinones which consequently polymerize to form brown pigments (melanins).[39] On the other hand, Caramelization occurs due to decomposition of carbohydrates or sugars in the drying material and form brown pigment; whereas Maillard reaction produces brown nitrogenous polymers and melanoidins from the reaction between amino acid and reducing sugar in the drying material. Both enzymatic and non-enzymatic browning reactions involve the presence of heat during drying process.[40] Picture of fresh lemon slice before undergone drying process is illustrated in Figure 6a whereas pictures of freeze-dried and commercial dried lemon slices are shown in Figure 6(b, c), respectively. Meanwhile, lemon slices subjected to different drying methods are shown in Figures 7 and 8.

Polyphenol oxidase

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Automatic Control of Apple Drying with Respect to Product Temperature and Air Velocity

Drying characteristics and quality of lemon slices dried under Coulomb force-assisted heat pump drying