Validation of an Alternative Bacterial Enumeration Method in Powder Cosmetics - การทดสอบการใช้ได้ของวิธีทางเลือกในการตรวจนับจำนวนแบคทีเรียปนเปื้อนในผลิตภัณฑ์เครื่องสําอางชนิดผง

Abstract

             An alternative method (SPC+TTC) which additional of 0.0025% (w/v) 2,3,5-triphenyl tetrazolium chloride (TTC) was validated with a standard plate count method (SPC) used for counting viable bacterial contaminants in 90 cosmetic samples which were water immiscible or contained insoluble materials. The study has been undertaken within the Division of Cosmetics and Hazardous Substances during May-December 2005. The correlation tests showed high correlation values, for example, r² = 0.94 and r=0.97. The relative accuracy relationship between the alternative and reference method was assessed through the linear model : log Y = 0.081 +0.999 log X. Linear relationship between the two methods was indicated by the line fit and residual plots. The linearity fest using F-distribution (α=0.05) showed no statistically significant differences. Precision data in term of repeatability standard deviation (S_r) was 0.136. The critical level (LC), the limit of detection (LOD) and the limit of quantification (LOQ) of this SPC+TTC method for bacterial enumeration were 2, 3 and 20 cfu, respectively. The uncertainty of measurement of SPC+TTC method performed on 24 cosmetic samples yielded an expanded uncertainty (U) of ±0.081 log. The additional of TTC in this SPC+TTC method has proved useful in red coloring bacterial colonies which are more easily observed, hence the bacterial enumeration in powder cosmetics becomes more convenient, less time consuming and provides a valid result.