Sampling and Preparing Food for Bacteriological Analysis One important aspect of food microbiology is that bacteria are usually heterogeneously distributed within food products. On commodities, such as fruit, vegetables, meats, and fish, the bacterial load will likely be higher on the surface when compared to the interior of the item. In addition, distribution can vary within a given product. For example, within different portions of a fish fillet, bacteria are usually unevenly distributed, with higher numbers around the fin and gut areas. This also holds true for processed foods. Often, bacteria are not distributed homogeneously through an entire lot of food. For example, if a standard plate count (SPC) was performed on a sample from a single unit of a lOOO-unit lot, one cannot know if the results are representative of the entire lot or if they are exceptions. Therefore, analyses of a greater number of samples will give a broader understanding of the food product's microbial quality. In addition, greater sample numbers increase the probability of finding a product containing high microbial numbers or even a pathogen within the sampled product. However, lab supplies, personnel, and product costs must be considered in the cost-effective operation of the laboratory prior to performing an analysis on the number of samples needed for each analysis. Statistical sampling plans can assist in determining the most appropriate sample number to assure a given level of risk in a food product. 1-3
Care must be taken in collecting food samples and transporting them to the laboratory for analysis. It is ideal to submit samples to the laboratory in unopened containers. Otherwise, leakproof containers and sterile stainless steel utensils should be used for sampling and transport. Frozen samples should remain frozen during transport; refrigerated samples should not be frozen, but should be kept between o to 4°C during transport. All samples should be examined within 24 h of reaching the laboratory. Frozen samples should be stored frozen, and perishable refrigerated items should be stored at 0 to 4°C.