Abstract
The objective was to study the effect of alginate coating on polyphenol oxidase (PPO) activity and colour of ‘Starking’ apple cubes during dehydration with hot air. Apple cubes were dehydrated at 20oC, 35oC, or 40oC, with a parallel airflow. Analysis of PPO activity, colour (L*, a*, b*) and dry matter were performed along the dehydration process at each temperature. All samples presented a peak in relative PPO activity in the beginning of the drying. Exponential models fitted well the experimental data after the peak. Cubes without coating presented lower PPO activity, suggesting lower browning, than coated samples throughout the dehydration process, for all temperatures. Better results for coated samples were obtained with a perpendicular airflow drying at 40oC, after dipping the whole apple in water at 60oC for 10 min. In order to prevent coated samples from browning, drying by perpendicular airflow preceded by a thermal treatment of the whole apple is required.
Highlights
Polyphenol oxidase is an enzyme that, in the presence of oxygen, promotes oxidation of phenolic compounds to quinones [1] in fresh-cut plant tissues, giving their tissues a typical brownish colour due to the formation of insoluble brown pigments [2].This chemical reaction can be a drawback for Food Industry, but might be overcome with the application of an edible coating.An edible coating is a chemical solution that can be somewhat viscous; when applied to the food surface turns into a film, formed by polymers that give some protection to the food product by providing a modified atmosphere, retarding gas transfer, reducing moisture and aroma loss, delaying color changes and improving general appearance during storage [3]
The objective was to study the effect of alginate coating on polyphenol oxidase (PPO) activity and colour of ‘Starking’ apple cubes during dehydration with hot air
All curves of relative PPO activity presented a peak at the beginning of the dehydration process of the apple cubes, with 14% to 17% dry matter (Figure 1)
Summary
Polyphenol oxidase is an enzyme that, in the presence of oxygen, promotes oxidation of phenolic compounds to quinones [1] in fresh-cut plant tissues, giving their tissues a typical brownish colour due to the formation of insoluble brown pigments (melanin) [2].This chemical reaction can be a drawback for Food Industry, but might be overcome with the application of an edible coating. An edible coating is a chemical solution that can be somewhat viscous; when applied to the food surface turns into a film, formed by polymers that give some protection to the food product by providing a modified atmosphere, retarding gas transfer, reducing moisture and aroma loss, delaying color changes and improving general appearance during storage [3]. The use of these coating films presents evident advantages. Other functional properties of these coatings include carrying gases and solutes, and retaining aromatic compounds. Edible coatings can incorporate food additives, such as nutrients and antibiotic agents [3,5]
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