Thermal treatment effect on free amino acids in honey samples

Abstract

Free amino acids are minor constituents in honey which are responsible for the determination of botanical origin of honey. However, the composition of free amino acids was likely to be altered upon thermal treatment. Therefore, this study was conducted to investigate the profile of free amino acids before and after thermal treatment at 90°C for 30 minutes. This study revealed that phenylalanine (101.84-139.74 mg/kg), tyrosine (28.71-138.36 mg/kg) and proline (23.93-83.21 mg/kg) were found abundantly in all honey samples such as Tualang, Gelam and Acacia honey samples. After the honey were heated, it was found that proline and threonine were significantly reduced, while tyrosine, valine and lysine were increased in all honey samples. The proteolytic digestion was responsible for the increase of tyrosine, valine and lysine concentration after thermal treatment. The decrease could be attributed to the denaturation of proline and threonine themselves, apart from the reaction between the carbonyl group of reducing sugar and the amino acids upon thermal treatment.