Alkaline hydrolysis and discrimination of propolis at different pH values using high throughput 2D IR spectroscopy and LC-MS/MS

Abstract

Propolis has become a valuable byproduct of meliponiculture industry in recent years, due to its remarkable pharmacological importance. The propolis of Heterotrigina itama was extracted at pH 8–10 using ultrasonication. The results found that alkaline hydrolysis improved propolis quality, particularly at the mild alkaline condition. This was because higher amount of phenolics and flavonoids with higher antioxidant capacity for propolis at pH 8. The quality of propolis extracted at different pH values could be differentiated using 2D IR correlation spectroscopic analysis via the vibrational interaction of chemical functional groups under thermal perturbation. The variance could be detected by off-diagonal peaks in the region of 800–1500 cm-1, belonging to C[dbnd]C bending and C[dbnd]O stretching bands. The small variance was further confirmed by using high throughput mass screening technique of LC-MS/MS coupled with principal component analysis to reveal the signature compounds such as (xanthone C-glycosides, anthraquinone, procyanidin, procyanidin and resveratrol) in propolis.