The antioxidant activities based on the free radical scavenging, reducing power, and bleaching inhibition were investigated for the three commonly used honeys in Malaysia, namely, tualang, gelam, and acacia honey. The antioxidant capacity of the honey samples was correlated with their biochemical constituents such as total phenol, total flavonoid content, and total water-soluble vitamins (vitamin B1, B2, B3, B9, B12, and vitamin C). The total flavonoid content of honey samples was strongly correlated with the three antioxidative processes (r = 0.9276–0.9910). In contrast, the total water-soluble vitamins was found to be well correlated with the free radical scavenging activity (r = 0.8226). Vitamin B3 was likely to be in the highest concentration, which covered for 69–80% of the total vitamin content. A number of five phenolic acids, three flavonoids, and two organic acids had also been detected from the honey samples using UPLC-MS/MS, without sugar-removal procedure.

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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.