Polyphenol Oxidase Activity and Colour Changes of ‘Starking’ Apple Cubes Coated with Alginate and Dehydrated with Air

Susana Daniela Sousa Fernandes, Catarina Araújo da Silva Ribeiro, Maria Filomena de Jesus Raposo, Rui Manuel Santos Costa de Morais, Alcina Maria Miranda Bernardo de Morais

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DOI: 10.4236/fns.2011.25064                

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 20^oC, 35^oC, or 40^oC, 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 40^oC, after dipping the whole apple in water at 60^oC 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.

Keywords

Alginate Coating, Apple Cubes, Colour, Hot Air Drying, Polyphenol Oxidase

Conflicts of Interest

The authors declare no conflicts of interest.

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