Physical and Chemical Characterization of Freshly Harvested and Factory-Processed Mangrove Honey from Kilifi County, Kenya

Abstract

Mangrove honey from the mangrove forests at the Kenyan coastal region has been in production at the commercial level by beekeepers organized and registered in self-help groups for more than a decade now. The honey is said to have medicinal properties but it has not been fully characterized to determine whether it meets the Kenyan standards on Honey – Specification (KS EAS 36:2020), European Union (EU) Directive on Honey (2001/110/EC) and International Honey Commission (2009). The objective of this study was, therefore, to characterize Kenyan mangrove honey in terms of its physicochemical properties and volatile organic compounds present. It was also important to correlate the honey VOC profiles with the mangrove tree flowers extract profiles. Unprocessed honey sampling was done from selected beekeepers from the four mangrove forest regions of Kilifi County, namely, Mida, Kilifi, Watamu and Mtwapa creeks while processed honey samples were obtained from Kwetu Training Centre. Twenty (20) honey samples weighing approximately 250 g each were collected randomly from farmers and factory in different locations in Kilifi County, packed in 500 cm3 plastic bottles, ferried for refrigeration in the lab at a temperature of 4o C. Mangrove flower volatile organic compounds (VOCs) were collected by static headspace solid phase microextraction (HS-SPME) fiber while collection of VOCs in honey samples was done by ultrasound-assisted solvent extraction (USE) method. Mangrove honey was analyzed for moisture content (by refractometry), colour index, diastase, proline and hydroxymethylfurfural (by spectrophotometry), pH and electrical conductivity (by pH/conductivity meters), free acidity (by titrimetry), sugar content (high performance liquid chromatography) and volatile organic compounds (by GC-MS). Quantitative data was analyzed using the SPSS program version 21. The results showed that the mean moisture content ranged from 23.40±0.00 to 19.23±0.06%, mean pH from 4.45±0.05 to 4.00±0.00, mean electrical conductivity ranged from 0.54±0.00 to 0.32±0.00 MS/cm. The mean acidity ranged from 30.21±0.15 to 22.20±0.00 Meq/kg. The mean proline content ranged from 734.36±4.23 to 602.24±2.68 mg/kg. The mean HMF levels were in the range of 2.86±0.14 to 0 mg/kg. The mean invertase content ranged from 9.55±0.10 to 5.54±0.11 U/kg. The mean diastase content ranged from 11.48.47±0.06 to 8.11±0.64 S/units. In the VOCs profile of mangrove flower, factory and farm, 119, 90 and 70compounds were identified, respectively. Of the identified VOCs, 35 were found both in the honeys analyzed and in mangrove flower. Three compounds docosanoic acid, palmitoleic acid and n-hexadecanoic were found in large quantities in all samples analyzed and the mangrove flowers and can be considered to be chemical markers for mangrove honey. The HMF, diastase and invertase were found to be below the set limits suggesting that the mangrove honey studied was fresh and had not been heated by farmers during harvesting and extraction. The high proline content also revealed that nectar and pollen are produced in great quantities by mangrove plants. The rest of the physicochemical parameters were found to be within the limits set by the International Honey Commission, Codex Alimentarius and the Kenya bureau of standards (through the EAS).