Date of Award
Doctor of Philosophy (PhD)
Kay Cooksey, Ph.D., Committee Co-Chair
Duncan Darby, Ph.D., Committee Co-Chair
E. Jeffery Rhodehamel, Ph.D.
Patrick Gerard, Ph.D.
This research consisted of formulating an antimicrobial coating containing Nisaplin® intended for large scale production and inhibition of spoilage microorganisms. Secondly, the coating formulated was applied to a flexible film surface using two trials (gravure and flexography) commonly used in large scale food package coating or printing processes. In addition, diffusion and mass transfer theory was applied to discuss the many complications of predicting nisin diffusion or release from a coated material for antimicrobial food packaging applications.
Previous work conducted by predecessors, produced an antimicrobial coating formulation using a 70/30 Methylcellulose/Hydroxypropyl methylcellulose base (MC/HPMC). Some disadvantages of this coating included haze, lack of sealability and percent solids content too low for large-scale gravure and/or flexographic coating application processes (which require 15-50% solids). Due to the characteristics, it was then determined that the coating would need to be re-formulated to maintain these qualities in addition to the ability to be up-scaled to large scale gravure and/or flexographic coating processes and lastly, maintain antimicrobial activity against desired microorganisms.
Multiple materials were tested to determine the antimicrobial coating formulation including four grades of polyvinyl alcohol, plasticizers, emulsifiers and antimicrobials. The first set of testing, differential scanning calorimetry (DSC), was used to determine the melt temperature of the base or matrix for containing this nisin. It is important to
determine the melt temperature of the resin in order to determine the sealability of the final package. DSC testing showed that 88% hydrolyzed, granular polyvinyl alcohol (Mowiol 4-88, Kuraray) resin combined with glycerin (40 phr) resulted in a decreased melt temperature from 189.7°C to 150.9°C and decreased thermal degradation via hydrolysis. These two components were determined to be part of the film forming matrix due to the potential for sealability. Dynamic contact angle testing was also utilized to determine adhesion, critical surface tension to several substrates (LLDPE coex, Bynel®2002; Elvax® 3165, Nucrel® 1202 HC and Surlyn® 1605) and wettability of the coating solution. All substrates were found to have statistically significantly different critical surface tensions from the control LLDPE substrate (ɑ = 0.05). All substrates except for corona treated Elvax® and Surlyn® were found to have statistically significantly different dynamic contact angle measurements from the control LLDPE substrate (ɑ = 0.05) (p value = 0.1231, Elvax® – corona; p value = 0.5648, Surlyn® - corona). Tape tests were conducted to select the final coating substrate, LLDPE. All of the testing parameters (pH, percent solids, melt temperature) indicated that the formulation was suitable for gravure or flexography coating applications.
Coating trials using the formulated antimicrobial coating showed the potential for implementing a coating containing nisin on large scale production processes. Gravure and flexography trials were conducted on primed and corona treated LLDPE material. Several characteristics of the liquid coating and dried, coated substrate were tested for quality and overall specifications such as pH, percent solids and blocking. Film on lawn testing indicated that treatment films coated using both processes were able to inhibit Micrococcus luteus compared to control films (Gravure: P<0.0001; Flexography: P<0.0001). This study showed that the formulated coating had potential to be produced using large scale food package converting processes while maintaining antimicrobial efficacy against a food spoilage indicator bacterium.
Mass transfer of antimicrobial components in antimicrobial packaging systems are governed by numerous variables both extrinsic and intrinsic factors. This study provided literature review and mass transfer theory to predict the diffusion or controlled release of nisin from the produced packaging system to target microorganisms on a food product. Factors such polymer structure, temperature, food product, fat content and polymer swellability and their effects of diffusion and controlled release were discussed. This study showed that antimicrobial packaging systems are complicated multivariable systems that require many assumptions in order to make diffusion prediction mathematically feasible.
The original work conducted by Franklin et al (2004) that this project was based off of was intended for frankfurters. The intended market of the produced antimicrobial film was for ready-to-eat (RTE) foods. These types of foods are those which do not need to be cooked prior to consumption. Due to the rising demand for convenient food products such as RTE foods, this material could be implemented for usage against surface contamination and spoilage microorganisms.
Perna, Michele Christine, "Formulation and Characterization of an Antimicrobial Coating Containing Nisin for Large Scale Food Package Converting Processes" (2016). All Dissertations. 2089.