Date Available

12-12-2012

Year of Publication

2012

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture

Department/School/Program

Animal Science

First Advisor

Dr. Youling L. Xiong

Abstract

There is demand for improved security of refrigerated ready-to-eat meats. Antimicrobial edible films and coatings could function as an added barrier against post-processing contamination. Hops and hop extracts are known for their antimicrobial efficacy which is attributed to key antimicrobial components including humulones, lupulones, xanthohumol and various terpenoids. Yet, hop ethanol extract has not been studied as an antimicrobial to incorporate into edible protein films and/or coatings. The overall objective of this research was to evaluate hop ethanol extract as an antimicrobial agent incorporated into edible soy protein isolate (SPI) films and coatings, and the influence on the shelf-life and sensory attributes of bologna.

Hop ethanol extract was examined for minimum inhibitory concentration before the extract was incorporated into a 6% SPI solution at 0, 10, and 20% levels to determine antimicrobial efficacy as a cast film and simulated coating via zone of inhibition against Listeria monocytogenes strains ATCC 4644, UKADL and ATCC 49594. The results showed that hop ethanol extract alone was inhibitory of all three strains. Moreover, the hop ethanol extract, when incorporated at 10 and 20% (v/v) into edible soy protein isolate (SPI) films and simulated coatings, exhibited antimicrobial action against all three L. monocytogenes strains. Key antimicrobial components, as mentioned above, were identified in the hop ethanol extract via mass spectrometry.

The SPI with 10% incorporated hop ethanol extract (SPI+10%hop) antimicrobial coating was applied to bologna, prepared in lab without L. monocytogenes inhibitors, where it exhibited a significant (P ≤ 0.05) bacteriostatic effect against strain ATCC 4644. The SPI+10% hop coating was then applied to a commercial bologna to examine effects on shelf-life and sensory attributes. Significant differences (P ≤ 0.05) were found in instrumental red and yellow colors, however not in sensory color. There was no significant difference (P > 0.05) found in measured lipid oxidation between the bologna with no coating, SPI coating or SPI+10%hop coating. The incorporation of hop did exhibit a slightly bitter taste. Overall, these findings indicate that the SPI+10%hop antimicrobial coating functioned as an inhibitor of L. monocytogenes while producing minimal effects on shelf-life and sensory attributes of bologna.

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