Lori A. Garlock '98

Minimizing Aerobic Plate Counts and Yeast and Mold Plate Counts in Potato, Mock Crab, and Pasta Salads with Potassium Sorbate and Sodium Benzoate.


Purpose: The purpose of this study is to determine the optimum levels of potassium sorbate (PS) and sodium benzoate (SB) to inhibit aerobic growth and yeast and mold growth without affecting the taste of the three different types of salads. Optimum levels of potassium sorbate and sodium benzoate can inhibit growth and can decrease the cost of the salad by increasing its shelf life. In determining optimal levels, the direct cost of the additives can increase the cost of the salad due to the increased amount of the preservative needed to inhibit microbial growth in order to obtain a longer shelf life. Potassium sorbate and sodium benzoate are generally recognized as safe (GRAS) by the Food and Drug Administration (FDA) and are safe at the levels used in this study. Sodium benzoate is an effective inhibitor of yeast and bacteria but is less effective against mold. Sodium benzoate does have a distinctive taste and is an inexpensive ingredient. Potassium sorbate is an effective inhibitor of yeast and mold but not an effective inhibitor of bacteria. The taste and odor of potassium sorbate is almost undetectable. Potassium sorbate, however, is an expensive ingredient.

Methods: Three salads were evaluated: one with a mayonnaise/vinegar base (Potato Salad), one with a sour cream/salad dressing base (Mock Crab Salad), and one with an Italian dressing base (Pasta Salad). For each type of salad, 10--2 pound batches were produced, each with varying levels of potassium sorbate and sodium benzoate. The levels of potassium sorbate and sodium benzoate were set at concentrations above and below the current levels of the preservatives used in the three salads. Plastic bag samples were prepared from each of the ten batches for the three salads and were refrigerated. One of the plastic bag samples was tested for pH, aerobic plate count, and yeast and mold plate count on days 1 (day of production), 5, 10, 15, and 20 in order to evaluate the aerobic and yeast and mold growth on the salads not exposed to the environment on a continued basis. The pH was tested using a Corning Spear Combo pH probe (Cat. No. 476456) and an ORION pH meter (Model 420A). 3M Petrifilm Aerobic Count Plates and 3M Petrifilm Yeast and Mold Count Plates were used for the aerobic and yeast and mold plate counts, respectively.

Results and Conclusions: Based on the results, the salads are clean and contain little microbial growth that would cause spoilage at any concentration of PS and SB. As a result, an increase or decrease of PS and SB is not recommended. Any increase in the current 14-day shelf life obtained by an additional use of preservative would not be advantageous based on the physical breakdown of the salads observed at Day 20.

Faculty Mentor:  Amy Olson, PhD, RD