Short CommunicationEffects of Ultraviolet (UV) Radiations at Different Wave Lengths on the Microbial Load and Yeast Viability of Palm Wine

Abstract

The effects of UV-radiation on the bacterial load and yeast viability of palm wine were investigated. In the studies 500ml of fresh palm wine sample each with initial yeast viability of 100% and bacterial load of 8.0 x 10¹⁵ Cfu/ml was exposed to UV-radiation at various wave lengths and time of 0 to 7hrs. The methlyene blue staining method was used to identify dead yeast cells based on the fact that dead cells absorbed the stain and were stained blue while the living cells reduced the stain and remained colourless. The viability of the yeast and bacterial load were determined on hourly basis for 7 hours. The result of the studies showed that bacterial load and yeast viability decreased with time and reached a minimal value of 3.0 x 10¹ Cfu/ml bacterial count and 10% yeast viability. The optimum wave length at which the least bacterial count and yeast viability was obtained was 300nm. The organoleptic properties of the wine such as taste and flavor deteriorated slightly with time. The overall result had proved that UV-radiation, though bactericidal to some extent could not be used as an effective means of preserving palm wine. A plot of the number of surviving cell against the time of exposure to the radiation at various wavelengths showed a negative slope which implies that the death of a population of UV – irradiated cells demonstrates a log linear kinetics similar to thermal death.

Nig J. Biotech. Vol. 24 (2012) 58-61