Effects of liquefying crystallized honey by ultrasound on crystal size, 5-hydroxymethylfurfural, colour, phenolic compounds and antioxidant activity

The objective of this study was to explore the effects of liquefying honey by ultrasound in five honeys with different botanical source. The ultrasound treatments were at a frequency of 42 kHz for 5, 10 and 15 min. The effects on crystal size, 5-hydroxymethylfurfural (HMF), colour, phenolic acids, flavonoids and antioxidant activity 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) were investigated. The analysis of the honeys showed significant differences (p < 0.05) in all parameters. The honeys had similar but quantitatively different phenolic acid and flavonoid contents. The honeys that underwent ultrasound treatments exhibited significant differences (p < 0.05) in crystal size, colour and antioxidant activity (DPPH) but not in HMF (p > 0.05). The effect of ultrasound treatment on phenolic acids, flavonoids and antioxidant activity (ABTS) was different for each type of honey. Some honeys showed significant increases (p < 0.05) in phenolic acids, flavonoids and antioxidant activity after 15 min of ultrasound treatment. The ultrasound is an alternative to thermal treatment of the honey decrystallization without changing the HMF, and some honeys exhibit increased antioxidant activity.