Semester of Graduation

Fall 2021

Degree

Master of Science (MS)

Department

Nutrition and Food Sciences

Document Type

Thesis

Abstract

Consumer preference and demand for natural and high-quality food products has increased due to awareness of health risk associated with chemical preservatives and undesirable effects caused by thermal processing. Both bacteriocins produced by lactic acid bacteria (LAB) and Ultraviolet-C (UV-C) radiation, either individually or in combination, may be alternatives to traditional techniques to produce safe and natural food products without undesirable effects on quality. The objective of this study was to evaluate the efficacy of UV-C radiation and LAB bacteriocins, either individually or in combination, in reducing Listeria monocytogenes and aerobic bacteria. Listeria innocua NRRL BB-33016 was used as the non-pathogenic surrogate for Listeria monocytogenes. Two bacteriocins (1) nisin and (2) pediocin, were produced from Lactococcus lactis subsp. lactis ATCC 11454 and Pediococcus acidilactici RS2-10, respectively. Bacteriocins were semi-purified and suspended. Bacteriocin suspensions of nisin, pediocin, and a combinationation of nisin and pediocin, in equal parts were tested to determine the potency of the bacteriocin suspensions antimicrobial activity. Bacteriocin dipping treatments (NB, treatment containing nisin bacteriocins; PB, treatment containing pediocin bacteriocins; and NPB, treatment containing a combination of nisin and pediocin bacteriocins) consisting of a ratio of 1:10 v/v of semi-purified bacteriocin suspension to distilled water were made. Fresh, raw peeled white shrimp were inoculated by dipping in inoculum containing L. innocua (6.20 ± 0.15 log CFU/g) and then either treated with UV-C light for 2 min with a dose of 3.6 J/cm2 and light intensity of 30 mW/cm2 (UV), dipped in bacteriocin treatments for 10 min (NB, PB, NPB), or a combination of both treatments (UV+NB, UV+PB, UV+NPB). Additional treatments included shrimp dipped in distilled water (W) and shrimp treated by UV-C light and dipped in distilled water (UV+W). Shrimp without any treatment was used as a control. Data from triplicate experiments were statistically analyzed (p ≤ 0.05). The antimicrobial activity of the semi-purified bacteriocin suspensions were 2.6x106 IU/ml for nisin and 2.7x106 IU/ml for pediocin. At time 0 h, combination treatments of UV with bacteriocins for the treatments UV + NB, UV + PB, and UV + NPB significantly reduced L. innocua by 1.29, 1.04, and 1.04 log CFU/g, respectively, compared to the control. Additionally, the bacteriocin dipping treatments NB, PB, and NPB significantly reduced L. innocua by 1.25, 1.60, and 1.29 log CFU/g, respectively. Results for shrimp stored for 24 h demonstrated that all individual and combination treatments of UV and bacteriocins also significantly reduced L. innocua on shrimp compared to the control. L. innocua counts were significantly increased for all treatments except W, UV, and UV + PB when comparing treatments at time 24 h versus time 0 h. These results demonstrated that the type of bacteriocin used for treatment does not have a significant effect on the reduction of L. innocua on shrimp. Counts of aerobic bacteria on shrimp for the control at time 0 h were 6.17 ± 0.14 log CFU/g. Aerobic bacteria count on shrimp immediately after treatment (time 0 h) was significantly lower for all shrimp treatment groups except the W treatment. Compared to the control at time 0 h, the combined UV and bacteriocin treatments UV + NB, UV + PB, and UV + NPB reduced 0.74, 0.62, and 0.70 log CFU/g of aerobic bacteria on shrimp, respectively. Additionally, bacteriocin treatments NB, PB, and NPB reduced APC on shrimp by 0.59, 0.61, and 0.66 log CFU/g, respectively. The treatment UV + PB was the only treatment that was significantly different from the control that did not show significant regrowth of L. innocua and aerobic bacteria after storage for 24 hours. Treatment of shrimp with bacteriocins and UV did not have a significant effect on the texture or lipid oxidation of the shrimp. This study demonstrated that UV-C radiation and bacteriocins dipping treatments can significantly reduce L. innocua and APC on shrimp without significantly affecting quality parameters of the shrimp such as texture or lipid oxidation. Bacteriocins such as nisin and pediocin may be a more natural and effective biopreservation method compared to current commercial processing methods for fresh seafood products such as shrimp in order to reduce the microbial pathogen Listeria monocytogenes.

Committee Chair

Sathivel, Subramaniam

DOI

10.31390/gradschool_theses.5440

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Available for download on Saturday, September 23, 2028

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Food Science Commons

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