The influence of PH on the recovery of contaminating micro-organisms from honey
Accurate and sensitive methods for recovering contaminating micro-organisms from honey are required for an adequate control of the hygienic quality of the product. Most of these micro-organisms would be expected to be physiologically deficient (injured) due to being exposed to the antimicrobial physio-chemical components of honey such as low pH, low moisture content and high osmotic pressure The aim of this study was therefore to determine the pH of Kenyan honey and find out if recovery of contaminating micro-organisms in honey could be improved by using phosphate buffer to raise honey pH to about neutral. It was also intended to find out the levels of aerobic and anaerobic mesophilic total viable counts (TVC) encountered in processed, semi processed and home processed honey The pH of 44 (17 processed, 23 semi processed and 4 home processed) honey samples was determined before and after dilution in the ratio 1:10 with distilled water of pH 5.60 and O.lM phosphate buffers of pH 6.00, 7.00, 7.10, 7.20, 7.30, and 8.00. These same honey samples plus 4 other processed ones were diluted in sterile distilled water of pH 5.60 and O.lM phosphate buffer of pH 7.00 and cultured in Plate Count Agar (PCA, Oxoid) at 37°C for 48 hours .Half the plates were Incubated aerobically while- the other half was incubated anaerobically using the Gas Pak system. Colonies were counted according to Busta et al. (1984) and the results analysed using the paired t-test. Undiluted honey samples examined in this study had a low average pH of 3.60 (range 2.70-4.00). The average pH of the diluted honey depended on the diluent used. The mean pH of honey diluted in distilled water of pH 5.60 and O.lM phosphate buffer of pH 7.00 were 3.70 and 6.86 respectively. ix When compared to distilled water, phosphate buffer significantly improved the recovery of mesophilic anaerobic TVC from refined honey (45.4%), semi refined honey (32%) and all the honey types combined (29.0%). Recovery of aerobic micro-organisms was also improved although the numerical increment was not statistically significant In conclusion, O.lM phosphate buffer of pH 7.00 was shown to be a better diluent for recovering contaminating micro-organisms from honey than distilled water of pH 5.60. Hygienic quality of fully processed honey was 2-4 times better than that of semi refined (unpasteurized) honey. It was also established that tyndallization could not achieve sterilization of honey.