Physicochemical and infrared spectroscopic analysis of honey samples from nine Nigerian states

Abstract

Although pure honey samples had been characterized in many parts of the World, there is a dearth of information on the physicochemical indices of quality honey in Nigeria. The present study attempted fingerprinting/characterization of honey samples in Nigeria using their physicochemical parameters. Physicochemical parameters of 36 honey samples (including two locally sourced quality honey designated standard) collected from 9 Nigerian states were analyzed for their functional groups and mineral contents using Infrared and atomic absorption spectroscopy. pH, ash and moisture contents, protein, lipid, reducing sugars, total sugar contents, colour, taste and refractive index were also determined. They all had characteristic honey smell and taste. pH and the refractive index of the samples were similar and resembled the quality of standards. The pH ranged from 6.50 to 6.59. The refractive index ranged from 1.480±0.01 to 1.498±0.02. Moisture content in samples was significantly higher in Sokoto and Kogi samples, while colours of the samples were shades of light to dark brown. Fe and Ca contents were significantly higher in Lagos sample compared to the standards while Na, K and Mg were significantly lower in the samples compared to the standards. Ash content ranged from 0.0135 ±0.002 to 0.8251±0.01 in the samples. Infra-red spectroscopy values of the two standard honey samples had maximum peaks (2360.96-2398.65) cm^-1 for Kanye (Adamawa) and (2360.84- 2398.75) cm^-1 for Makurdi (Benue) samples. The seven samples had significantly higher maximum peaks compared to the standards. Infrared spectrophotometry showed the honey samples analyzed to be mixtures of compounds such as carboxylic acids, aldehydes, alkynes, nitrites, alkynes and ethers. Samples from 6 out of 9 States analyzed showed qualities of purity. This indicates that quality orientation among cultivators of honey that may be on the rise in Nigerian cities. The infra-red and atomic absorbance spectroscopy values from this study suggest their possible use in honey fingerprinting which may be helpful in detecting honey adulteration. Some peaks from the spectra did not correspond to known constituents in pure honey and were likely contaminants introduced into the honey samples during processing not necessarily due to deliberate adulteration of the samples.