| dc.description.abstract | The exploration of natural antimicrobials for food preservation has received increased attention due to consumer awareness of natural food products and a growing concern of microbial adaption to conventional preservatives. Leaves of some plants like spinach are identified as important dietary sources of nutrients, antioxidants, antimicrobials, and several bioactive substances. In addition, bioactive compounds of spinach have been reported to inhibit the growth of Escherichia coli and Bacillus spp. These secondary metabolites like phenolics are altered by nitrogen uptake by plants, owing to importance of nitrogen in plant metabolism, its limited availability or deficiency resulting in reduced growth and a lower yield of plants. At the same time, a shift from N-based to C-based compound content is usually observed. Spinach accessions grown under low and high nitrogen concentrations were received into the Food Microbiology Laboratory (Texas A&M University, College Station, TX) and were stored at -80°C. Twenty grams of each sample were weighed aseptically and 100% methanol was used for extractions, and then these extracts were concentrated through solvent evaporation. Antimicrobial assays were performed to determine the inhibition of spinach extracts against a target pathogen (E. coli O157:H7, Salmonella, Listeria monocytogenes) using the micro-broth method. Micro-plates (96 well) were prepared and incubated for 24 hrs. at 35°C and checked spectrophotometrically to determine the difference in sample-specific light transmission/turbidity as a function of extract and pathogen. The total phenolic content and flavonoid content of spinach extractions were determined by using Folin-Ciocalteu reagent and aluminum chloride colorimetric methods respectively. Results indicate no statistically significant differences in bioactive compounds between low and high nitrogen groups. Though minimum inhibitory concentration (MIC) values were determined to be the same for each isolate, the doubling time at sub-minimum inhibitory concentrations statistically differed between each isolate. E. coli O157:H7 P18, E. coli O157:H7 EDL 932, L. monocytogenes LIS0072, and L. monocytogenes LIS0104 had longer doubling times compared to rest of the isolates when treated with spinach extracts. Results obtained indicated that there were great differences in the doubling time among the different genera/species studied. | en |
