Bruce Harte

Mechanical, Physical, and Barrier Properties of Poly(Lactide) Films

High molecular mass poly(lactide), (PLA), is an attractive polymer family because in addition to being thermoplastic, biodegradable, compostable, and produced from annually renewable resources, it shows mechanical and barrier behavior comparable to synthetic polymers like polystyrene (PS) and polyethylene terephthalate (PET). Furthermore, technology for large-scale fabrication of PLA has been fully developed. However, there is still a need to better understand the properties of PLA as this polymer is adapted to packaging applications, especially for food packaging. In this work, films from two PLA resins were studied by tensile testing; differential scanning calorimetry (DSC); and permeation of carbon dioxide, oxygen, and water vapor. The data from these two PLA film samples are compared to those of PS and PET.

Active Packaging of Fresh Chicken Breast, with Allyl Isothiocyanate (AITC) in Combination with Modified Atmosphere Packaging (MAP) to Control the Growth of Pathogens

Listeria monocytogenes and Salmonella typhimurium are major bacterial pathogens associated with poultry products. Ally isothiocyanate (AITC), a natural antimicrobial compound, is reportedly effective against these pathogenic organisms. A device was designed for the controlled release of AITC with modified atmosphere packaging (MAP), and then evaluated for its ability to control the growth of L. monocytogenes and S. typhimurium on raw chicken breast during refrigerated storage. In order to obtain controlled release during the test period, a glass vial was filled with AITC and triglyceride. It was then sealed using high-density polyethylene film. The release of AITC was controlled by the concentration (mole fraction) of AITC in the triglyceride and by the AITC vapor permeability through the film. The fresh chicken samples were inoculated with one or the other of the pathogens at 10(4) CFU/g, and the packages (with and without AITC-controlled release device) were flushed with ambient air or 30% CO(2)/70% N(2) before sealing, and then stored at 4 degrees C for up to 21 d. The maximum reduction in MAP plus AITC (compared to MAP alone) was 0.77 log CFU/g for L. monocytogenes and 1.3 log CFU/g for S. typhimurium. The color of the chicken breast meat was affected by the concentration of AITC. Overall, a release rate of 0.6 microg/h of AITC was found to not affect the color, whereas at 1.2 microg/h of AITC the surface of the chicken was discolored.

Postharvest shelf life extension of blueberries using a biodegradable package

Small berries are commonly packaged and sold to consumers in vented petroleum-based clamshell containers. Biodegradable and compostable packages may be used as an alternative package to reduce waste generation and landfill disposal. In addition, the current clamshell container design does not allow the development of a modified atmosphere that could prolong berry shelf life. Thus, in this study, a non-ventilated biodegradable container was evaluated as a possible alternative to the containers normally used in commercial distribution of small berries. To determine the potential of biodegradable containers for small berries, highbush blueberries were packaged in polylactide (PLA) containers and stored at 10°C for 18 days and at 23°C for 9 days. Commercial vented clamshell containers were used as controls. Physicochemical and microbiological studies were carried out in order to compare the efficacy of both packages. Results showed that the PLA containers prolonged blueberry shelf life at different storage temperatures.

Cholesterol oxidation in whole milk powders as influenced by processing and packaging

Abstract The effects of various spray-drying processes (direct-fired heating, high levels of oxides of nitrogen (NO x ); direct-fired heating, low NO x ; indirect electrical heating) and packaging systems (polyethylene pouches and crimp-sealed glass vials, with and without oxygen absorbers) on the oxidative stability of lipids in whole milk powders during storage were studied. Lipid oxidation, including the generation of cholesterol oxidation products, was greatest in samples processed by high NO x direct-fired driers. Oxygen absorbers effectively controlled cholesterol oxidation during the six month storage period, even in those samples from the high NO x drying system. There was a positive correlation ( r = 0·89) between lipid oxidation and the concentration of cholesterol oxides in the samples. It was concluded that the stability of whole milk powders during storage can be improved by using low NO x drying processes and by packaging in oxygen-impermeable packaging systems containing oxygen absorbers.

Development of a Food Packaging Coating Material with Antimicrobial Properties

Antimicrobial films may provide an effective way to control food-borne pathogens and spoilage microorganisms to thus enhance food safety and decrease product spoilage. Antimicrobial films can be produced by incorporation of chemical preservatives or antimicrobial agents into a plastic film. The agents can then diffuse into the food to control target microorganisms. In this work, antimicrobial coatings were developed by incorporation of nisin, lactoferrin (an antimicrobial peptide derived from bovine lactoferrin in cow’s milk), sodium diacetate, sorbic acid, and potassium sorbate into a coating material. Saran® F-310 resin, a copolymer of vinylidene chloride, was used to produce the base coating using a solvent casting method. The antimicrobial activity of these films was verified on laboratory media against the food-borne pathogen Listeria monocytogenes. Films containing nisin, sorbic acid, and potassium sorbate inhibited L. monocytogenes strain CWD 95. The lowest level of nisin, sorbic acid, and potassium sorbate that had antimicrobial activity was 1, 1.5, and 2% w/v respectively. Films containing sorbic acid were the most compatible with the resin solution and had the best physical appearance. The water vapor barrier of films containing sorbic acid was almost unchanged compared to the control film (no antimicrobial agent). The three-dimensional structure of the films was observed using Scanning Electron Microscope (SEM). The results show that films containing sorbic acid were the most homogenous of the sample films.

Factors Affecting Migration of Vanillin from Chitosan/Methyl Cellulose Films

The diffusion kinetics and factors affecting the migration of vanillin from chitosan/methyl cellulose (Chi/MC) films into water, cantaloupe juice (CJ), pineapple juice (PJ), and citrate buffer adjusted to pH values of 3.5, 5, and 6.5 were studied. Vanillin was incorporated into the Chi/MC films to provide an inhibitory effect against microorganisms. Initial vanillin concentration in the films, temperature, and pH of extracting solvent impacted the migration behavior of vanillin. The diffusion coefficients (D) followed the Arrhenius equation and increased as temperature increased for all the solvents. As temperature rose, the rate increment of the diffusion of vanillin into pineapple juice was higher than that into water and cantaloupe juice. Films containing lower vanillin content had a higher diffusion coefficient than those containing high vanillin content. Migration of vanillin was affected by pH rather than acid concentration. Lower pH resulted in a higher migration rate.

Detection of Escherichia coli in packaged alfalfa sprouts with an electronic nose and an artificial neural network.

A rapid method for the detection of Escherichia coli (ATCC 25922) in packaged alfalfa sprouts was developed. Volatile compounds from the headspace of packaged alfalfa sprouts, inoculated with E. coli and incubated at 10 degrees C for 1, 2, and 3 days, were collected and analyzed. Uninoculated sprouts were used as control samples. An electronic nose with 12 metal oxide electronic sensors was used to monitor changes in the composition of the gas phase of the package headspace with respect to volatile metabolites produced by E. coli. The electronic nose was able to differentiate between samples with and without E. coli. To predict the number of E. coli in packaged alfalfa sprouts, an artificial neural network was used, which included an input layer, a hidden layer, and an output layer, with a hyperbolic tangent sigmoidal transfer function in the hidden layer and a linear transfer function in the output layer. The network was shown to be capable of correlating voltametric responses with the number of E. coli. A good prediction was possible, as measured by a regression coefficient (R2 = 0.903) between the actual and predicted data. In conjunction with the artificial neural network, the electronic nose proved to have the ability to detect E. coli in packaged alfalfa sprouts.

Development of a gas-phase oxygen biosensor using a blue copper-containing oxidase.

A gas-phase oxygen biosensor based on blue copper-containing oxidases was developed. Blue-oxidase enzymes, including laccase and ascorbate oxidase, have a blue chromophore prosthetic group, type 1 Cu+2, which can be reduced and decolorized with reducing substrates. When the enzyme is reoxidized with molecular oxygen, there is a concomitant return of the blue color. The oxygen biosensor consisted of the Rhus vernicifera laccase and ascorbate as substrate enclosed in pouches of low-density polyethylene under nitrogen gas. Operational stability of the biosensor was established by exposing it to different oxygen/nitrogen gas mixtures at 5 degrees C. Gas-phase oxygen concentrations were measured by keeping it under nitrogen gas and subsequently recording the rate of reappearance of the enzyme blue color, both visually and spectrophotometrically at 610 nm. The oxygen biosensor was able to detect a wide range of oxygen concentrations. The time required to recover the blue color, namely the biosensor response time, at the optimized assay conditions of 5 degrees C and a high-water activity level, was determined. This research describes the development of an oxygen biosensor with adequate activity and stability to measure gas-phase oxygen concentrations at 5 degrees C and high-water activity levels. The oxygen biosensor could be used to indicate oxygen concentrations above acceptable levels in headspace oxygen concentration which could affect the quality and safety of products packaged under initial low levels of oxygen concentration.

Assessment of package integrity using a spray cabinet technique

A novel spray cabinet technique was developed to determine the microbial integrity of aseptically filled juice packages as an alternative to immersion techniques. The spray cabinet was constructed to include two pumps and 32 nozzles to achieve complete coverage over all surfaces of the test packages. A cell culture of Lactobacillus cellobiosus was sprayed onto the packages during testing. Standard pinhole orifices were used to determine the efficiency of the spray cabinet technique, 10-μm holes and 5-μm holes were detectable after 15 and 30 min of spraying, respectively. Aseptically filled juice packages were subjected to an abusive handling procedure designed to create package defects in order to compare package integrity by the spray cabinet technique and an immersion method. The spray cabinet technique provided better detectability than the immersion method.

Rapid method for prediction of Escherichia coli numbers using an electronic sensor array and an artificial neural network

An electronic sensor array with 12 nonspecific metal oxide sensors was evaluated for its ability to monitor volatile compounds in super broth alone and in super broth inoculated with Escherichia coli (ATCC 25922) at 37 degrees C for 2 to 12 h. Using discriminant function analysis, it was possible to differentiate super broth alone from that containing E. coli when cell numbers were 10(5) CFU or more. There was a good agreement between the volatile profiles from the electronic sensor array and a gas chromatography-mass spectrometer method. The potential to predict the number of E. coli and the concentration of specific metabolic compounds was investigated using an artificial neural network (ANN). The artificial neural network was composed of an input layer, one hidden layer, and an output layer, with a hyperbolic tangent sigmoidal transfer function in the hidden layer and a linear transfer function in the output layer. Good prediction was found as measured by a regression coefficient (R2 = 0.999) between actual and predicted data.