Food Protection Trends - February 2010 - 75

TABLE 1. Summary of triangle test sensory data to determine statistical significance between tap water–treated fresh spinach and fresh spinach treated with Bovamine® Meat Cultures at an α–level of 0.05 and 0.01 α–Level 0.05 0.01 Correct Responses Required 18a 20a Correct Responses 16 < 18 16 < 20 Decision Accept Null Accept Null Interpretation No Detectable Difference No Detectable Difference Reject the assumption of “no difference” if the number of correct responses is greater than or equal to the tabled value. bers of E. coli O157 declined over the 24 hour sampling period. E. coli O157:H7 populations recovered from the control maintained fairly consistent levels at just above 5 log CFU/g throughout the entire 24 hour study. Because there were no time by treatment interactions, Fig. 1 represents the LS means of all data points composited for each treatment. As illustrated by this figure, both water (P < 0.0001) and LAB (P < 0.0001) resulted in significant reductions in comparison to the control. Water reduced E. coli O157:H7 numbers by 0.88 log CFU/g, while LAB was successful at reducing it by 1.03 log CFU/g (Fig. 1). The improved reduction of LAB was significantly different from that of water (P = 0.0363). This indicates that LAB was significantly more effective than water at reducing E. coli O157:H7 populations on baby spinach leaves when the composite LS means of each treatment were compared over the 24 hour sampling period. lactic acid bacteria. Therefore, because the 16 correct responses obtained is less than the required responses of 18 and 20, there was no statistical significance and the null hypothesis was accepted at the α = 0.05 and α = 0.01 levels. These results are summarized in Table 1. Calculations to determine the number of discriminators estimated that 4 (10%) panelists perceived the true difference and selected the LAB sample as a result. These results suggest that a mere 25% (4 out of 16) of panelists who selected the LAB spinach truly detected a difference in the sensory properties of fresh spinach treated with Bovamine® Meat Cultures. DISCUSSION While little research has been conducted evaluating the effectiveness of LAB as an intervention for fresh spinach, the use of LAB in ground beef has been investigated. Smith et al. (19) utilized the same combined cultures included in Bovamine® Meat Cultures as an intervention to reduce the presence of E. coli O157:H7 in ground beef. The cultures were added to ground beef at a level of 109 CFU/g and stored at 5oC for 14 days. The combined cultures significantly reduced E. coli O157:H7 levels by 2.0 logs and 3.0 log cycles after 3 and 5 days of storage, respectively. Given the proven effectiveness of these LAB cultures in other food products, Bovamine® Meat Cultures may have great potential for application in the spinach industry, as well. The LAB treated spinach was evaluated for a mere 24 hours and resulted in reductions of 1.55 log CFU/g compared to the con- Sensory study Of the 40 panelists, 40% (16) correctly selected the LAB spinach as being the one “odd” sample. For a population of 40 panelists, the numbers of correct responses required for statistical significance at the α = 0.05 and α = 0.01 were 18 and 20, respectively. These values were determined using an equation outlined in Table T8 of the third edition of Sensory Evaluation Techniques (14). The null hypothesis for this triangle test states that no difference exists between the control spinach and the spinach treated with trol at the 24 hour sampling time (data not shown). Because LAB have the potential to produce inhibitory products over time, it is possible that longer exposure times could result in additional reductions in the spinach, making the present 24 hour study preliminary in nature. Additionally, these cultures may be an effective pre-harvest intervention to be applied to the crops prior to harvest. Furthermore, if the LAB-treated spinach had been held at 7oC for longer than 24 hours, perhaps the population of E. coli O157:H7 would have continued to decline in comparison to the control spinach and ultimately achieved reductions similar to those found by Smith et al. (19) in ground beef. Additionally, differences in the nutrient availability of the two products may play a role in the effectiveness of Bovamine® Meat Cultures. Meat is a nutrient dense environment with a high water activity (10), while the surface of spinach leaves has low water availability and is rather nutrient poor in comparison to the internal surfaces of the plant (20). A high level of nutrients and available water present in the food matrix will improve the metabolic activity of LAB and the resultant production of antimicrobial compounds will also increase. Before application to the spinach, the LAB concentration was determined to be 7.5 log10 CFU/ml (3.0 × 107 CFU/ ml) (data not shown). This value is the mean concentration of all three replications and is nearly 1 log CFU/ml less than the target concentration of 8.3 log10 CFU/ml (2.0 × 108 CFU/ml). This may be the result of adding the Bovamine® Meat Cultures to sterile distilled water. FEBRUARY 2010 | FOOD PROTECTION TRENDS

Food Protection Trends - February 2010

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