Foods of high fat content, such as peanut butter and ground beef, can be of particular interest to food microbiologists due to their role in harboring microorganisms that lead to spoilage and/or foodborne illnesses. In previous studies on raw poultry rendering materials, Glenn (2006) determined standard phosphate buffer serial dilutions produced erratic microbial enumeration results. As the material contained high fat, it was
hypothesized that the immiscibility of fat in the aqueous buffer caused the errors. This could occur by fat globules entrapping microorganisms in foods. Upon serial dilution with aqueous buffers, the fat globules may not be evenly dispersed throughout dilutions and subsequently not be transferred to plates for enumeration. This study was designed to examine the use of an emulsifier based phosphate diluent in improving the accuracy of microbial enumeration of lard, peanut butter, ground beef, poultry meal, and butter. In lard, peanut butter, ground beef, and butter testing, the use of a lecithin modified buffer yielded colony-forming unit counts that were not significantly different (p<0.05) from the control whereas the standard phosphate buffer results were significantly different
(p>0.05) from the control. In testing poultry meal, the use of lecithin modified buffer yielded different results than obtained using standard phosphate buffer for enumerating total aerobic, mesophilic bacteria and coliform bacteria. However, post-research measurement of pH of the dilution buffers five months after manufacture indicated a pH
range for phosphate buffer of 6.1-6.5 and for the lecithin buffer ranging from 6.22 to 7.2 depending on method of measurement. It is not known if this pH was in error at the time of the experiment as pH was not measured at that time.