Abstract

The effects of ultrasound-assisted glycation with 1 m glycine at room temperature in comparison with thermal glycation on the colour and radical scavenging activity of nipa palm (Nypa fruticans Wurmb.) syrup were investigated. The pH of both treatments decreased with increasing reaction time. The browning development occurred after induction period of 10 min for thermal glycation and 60 min for ultrasound-assisted glycation. A shorter time of ultrasound rendered the syrup light brown to amber in colour with some green. With long-term ultrasound, the syrup turned brighter, yellower and greener. The increased DPPH^· scavenging activity of the thermal syrup was due to the brown pigments as shown by a marked increase in the A<inf>420</inf> and a* value. The scavenging activity of ultrasound-treated syrup was improved by 53–57% due to the accumulation of UV-intermediate products as shown by a higher A<inf>294</inf>/A<inf>420</inf>. Thus, ultrasonication for 30–60 min was recommended in order to prevent dark colour development of the final syrup.