Progress 11/15/15 to 11/14/17
Outputs
Target Audience:Food microbiologists, cantaloupe industry, regulatory agencies Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The project provided opportunities for training a graduate student on cantaloupedecontamination treatments. How have the results been disseminated to communities of interest?A poster entitled "Natural and Environment-Friendly Approaches for Improving the Microbiological Safety of Cantaloupes" was presentedat the USDA NIFA Project Directors Meeting for Food Safety: Addressing Critical and Emerging Food Safety Issues held at Tampa Convention Center on July 8, 2017. A poster summarizing the research on the post-harvest study has been accepted for presentation at the annual meeting of the Food Technologists to be held at Chicago from July 15 to 18, 2018. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Determine the efficacy of lactic acid bacteria (LAB) as post-harvest spray treatment for reducing Salmonella and Listeria monocytogenes (LM) on cantaloupe rind plugs and whole cantaloupes LAB isolates were chosen based on a preliminary screening study on their antimicrobial effect. For reducing Salmonella on cantaloupe rinds, LAB isolates namely Lactobacillus delbrueckii bulgaricus NRRL B-548 (LB), Lactobacillus rhamnosus NRRL B-442 (LR), Lactobacillus plantarum NRRL B-4496 (LP1) (USDA-ARS, Peoria, IL) and Lactobacillus plantarum (LP2) (canine feces isolate) were tested. Similarly, LM reducing activity were tested using Lactobacillus casei NRRL B-3065 (LC), Lactobacillus johnsonii NRRL B-2178 (LJ), Lactobacillus plantarum NRRL B-4496 and Lactobacillus plantarum (canine feces isolate). Fifteen circular cantaloupe rind plugs (2.5cm diameter; 0.5 cm thickness) were removed from fresh cantaloupes and randomly subjected to one of the following treatments: Unsprayed positive control, Chlorine spray (industrial standard), MRS spray (de Man Rogosa Sharpe broth; media spray control) and LAB whole culture spray treatments. Plug rinds were spot inoculated with a five strain mixtures of LM (Scott A, ATCC 19115, LM AP, LM 598, LM 15) or Salmonella (S. Typhimurium, S.Newport, S. Poona, S. Sandiego, S. Montevideo) (~ 6 log10 CFU), and air-dried. Fifteen milliliters of above treatments were applied on cantaloupe rind plugs. The plugs were air-dried and each plug was transferred to a sterile Whirl-PakTM bag, stored at 25°C and analyzed for surviving pathogen and LAB populations on days 0, 1, 3, 5 and 7. Triplicate samples of each treatment was included, and whole study was replicated twice for each pathogen. The most effective LAB treatments on cantaloupe plugs were selected as a spray on whole cantaloupe. These treatment included LP1 and LP2 for the Salmonella study, and LC, LP1 and LP2 against LM. Whole cantaloupes were randomly subjected to the following spray treatments: Unsprayed positive control, MRS control, Chlorine control and LAB spray treatments. Five evenly spaced circular areas (diameter 2.5 cm) on cantaloupe surface were marked, and inoculated with Salmonella or LM (~ 6 log10 CFU), and air-dried. The different treatments were applied by spraying 15 ml per whole cantaloupe. Sprayed cantaloupes were stored at 25°C. On days 0, 1, 3 and 5, two cantaloupes from each treatment group were taken and five plugs (2.5cm diameter; 0.5 cm thickness) from each cantaloupe were transferred to sterile Whirl-PakTM bags containing 50 mL of neutralizing broth. The samples were pummeled for 2 minutes in a stomacher. The surviving population of LM and Salmonella were enumerated. The whole experiment was replicated twice. Results: On Salmonella inoculated plugs, LP1 and LP2 treatments were most effective, and resulted in ~3.0-3.6 log0 CFU reduction/plug compared to unsprayed positive control by day 7 (P < 0.05). On LM treated plugs, LC, LP1 and LP2 treatments were the most effective, where a reduction in counts of 3.17, 4.42 and 6.5 log CFU/plug, respectively was observed compared to control (P < 0.05). More than 5 log CFU/plug of all LAB survived on cantaloupe surface throughout the study. On the contrary, on whole cantaloupes, a minimal level of reduction of Salmonella and LM (~ 1 log CFU/cantaloupe) was observed. Determine the efficacy of LAB for reducing LM and Salmonella spp. applied as a pre-harvest spray on cantaloupes in the field. Soil Preparation and planting: Soil bed (6-8") with soaker hose covered with plastic was prepared at the Beltsville Agricultural Research Center (BARC) farm. Cantaloupe plants (Athena cultivar) grown for 4-5 weeks in a growth chamber were transplanted in a high-tunnel and irrigated as required to maintain plant growth. Cantaloupes were grown for two successive years (2016, 2017) to conduct pre-harvest study. Cantaloupe inoculation: Cantaloupes with full netting on fruit surface (approx. 60 days) on vine were selected (n=60) for study. Selected cantaloupes were divided into four groups: PBS control (n=15), treatment with Lactobacillus. plantarum (n=15), Lactobacillus reuteri (n=15), and combination of L. plantarum and L. reuteri (n=15); and appropriately marked with flags for subsequent sampling. Two sites on each cantaloupe were marked with template (5 cm x 10 cm) and then ~ 3 ml of a cocktail of two strains of Listeria innocua (ADH001 and JI023) prepared in fecal slurry was sprayed on each site. The cantaloupes were air-dried for 30 min, and then sprayed with 3 ml of PBS control (n = 20), individual strain or a cocktail of L plantarum and L. reuteri. Three cantaloupes from each group were harvested at 0, 7, and 14 days-post-treatment, and tested for surviving Listeria populations. Three changes were made during the second year of study, (1) L. reuteri was replaced with Pediococcus pentosaceus, a probiotic strain isolated from canine feces, (2) only cocktail was used for treatment of cantaloupes as the effect of individual LAB was not significant, (3) sampling schedule was changed to 0, 5, and 7 days due to loss of cantaloupes by animal vectors. Results: The effect of lactic acid bacteria in killing Listeria on cantaloupe at the farm level was investigated for two successive years in a high tunnel. Initial Listeria populations on cantaloupe were 4.3 log CFU/cm2 on control samples and 2.78-3.8 log CFU/cm2 on LAB-treated cantaloupes (Figure 1). Listeria were recovered at higher level in all samples at 7 days irrespective of LAB treatment. On day 14, Listeria were reduced on all cantaloupes and were below their initial levels in control and LAB-treated cantaloupes. The spraying of cantaloupes with a cocktail of L. plantarum and L. reuteri reduced Listeria to 1.61 log CFU/cm2 compared to control (3.66 log CFU/cm2) (P < 0.05). During the second year study, the initial Listeria populations recovered from the cantaloupes were ~ 2.5 log CFU/cm2 immediately after the inoculation (Figure 2). Listeria populations increased to ~ 3.5 log CFU/cm2 on control cantaloupes on days 5 and 7 of harvest. The LAB treatment resulted in reduction of Listeria by 1.5 and 1.2 log CFU/cm2 on day 5 and 7, respectively (P<0.05) compared to corresponding controls. Populations of LAB were ~ 6 log CFU/cm2 on probiotic-treated cantaloupes, these bacterial populations decreased to ~ 3.5 and ~ 2.5 log CFU/cm2 on day 5 and day 7 post-inoculation. To summarize, in the plug experiments, a reduction of ~ 3 to 6.5 log and ~ 3 to 3.6 log in LM and Salmonella spp., respectively was observed, when sprayed with LAB isolates. However, on whole cantaloupes post-harvest LAB sprays resulted in only minimal reduction in pathogen counts. On whole cantaloupes pre-harvest, at farm level, LAB spray brought about ~ 1.5 to 2 log reduction in L. innocua counts on cantaloupe when treated with LAB. The antimicrobial efficacy of LAB in reducing pathogens on cantaloupes was dependent on the LAB strain, and our study suggest that a cocktail of L. plantarum and L. reuteri or P. pentosaceus were more effective.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2017
Citation:
Presented a poster entitled "Natural and Environment-Friendly Approaches for Improving the Microbiological Safety of Cantaloupes" at the USDA NIFA Project Directors Meeting for Food Safety: Addressing Critical and Emerging Food Safety Issues held at Tampa Convention Center on July 8, 2017.
- Type:
Journal Articles
Status:
Other
Year Published:
2018
Citation:
Poonam Vinayamohan, Abraham Pellissery, Meera Surendran Nair, Abhinav Upadhyay, Christine Nishimura, and Kumar Venkitanarayanan. 2018. Efficacy of probiotic bacteria for reducing L. monocytogenes and Salmonella spp. on cantaloupe surface. To be submitted for publication.
- Type:
Journal Articles
Status:
Other
Year Published:
2018
Citation:
Hsin-bai Yin, Jitu Patel, and Kumar Venkitanarayanan. 2018. Controlling Listeria on cantaloupes at farm level using probiotics. To be submitted for publication.
|