Amino acid profile and Maillard compounds of sun-dried pears. Relation with the reddish brown colour of the dried fruits

Abstract

The sun-dried pear of S. Bartolomeu (Pyrus communis L. var. S. Bartolomeu) is a traditional sweet food product of unique elastic properties and reddish brown colour. Alternative drying methodologies to replace the traditional open air sun-drying procedure are under development, namely the use of greenhouses with and without air convection and a hot air tunnel. To test whether the Maillard reactions can contribute to the colour of this traditional product, the profiles of free and bound amino acids constituents of the pulp of fresh pears as well as pears processed according to different drying methodologies were evaluated. Also, the occurrence of furosine, carboxymethyllysine (CML) and carboxyethyllysine (CEL), indicative of Maillard reaction, was diagnosed and quantified. The drying of the pears affects the free amino acid profile, increasing proline content and decreasing aspartic and glutamic acids. Although the proteic amino acid profile was not significantly modified with the drying process, a loss of the relative content of Lys was observed. This loss was related with the increase in the amount of furosine, CML and CEL formed during the drying of the fruits. Although all drying methods tested promoted the increase in the amount of CML, CEL and furosine, this increase was higher in the case of the traditional sun-drying and greenhouse processing, where the fruits presented reddish brown colour, and lower for the hot air tunnel processing, where the fruits became less intense. These results allow affirming that the drying process promotes the occurrence of Maillard reaction, contributing to the characteristic reddish brown colour of the final product.