The influence of PH on the recovery of contaminating micro-organisms from honey
Abstract
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.
Citation
Master of Veterinary Public HealthPublisher
University of Nairobi Department of Public Health, Pharmacology and Toxicology, University of Nairobi, Kenya