Joseph Miltz

The antimicrobial activity of microencapsulated thymol and carvacrol

The aim of the present study was to determine the antimicrobial (AM) properties of plastic flexible films with a coating of microcapsules containing carvacrol and thymol as natural AM agents. Microencapsulation of these agents enables their controlled release and leads to the destruction (or growth inhibition) of a broad spectrum of microorganisms such as, Escherichia coli O157:H7, Staphylococcus aureus, Listeria innocua, Saccharomyces cerevisiae and Aspergillus niger. It was found that the studied AM agents are strong inhibitors to the growth of mycelium, but they were not effective against spore germination of mold. Thymol (T) and carvacrol (C) showed a significant AM activity against the studied microorganisms, with minimal inhibitory concentrations (MIC) of 125-250 ppm and 75-375 ppm for thymol and carvacrol respectively. The synergistic effect of combinations of thymol and carvacrol was also studied and it was found that the highest synergism was achieved at a concentration of 50% T and 50% C. The release of the AM agents was carried out at 4°C during 28 days. The concentration of the microencapsulated AM agents showed a range of zones of inhibition of 4.3-11.3mm for the microorganisms at 10% of thymol and 10% of carvacrol. At these concentrations the release of the AM agents (within 48 h) was greater than required for the most resistant microorganism (E .coli O157:H7), as reflected by the relatively large zone of inhibition. The results of the present study confirm the suitability of using microencapsulated thymol and carvacrol incorporated in polymer films for AM food packaging.

Essential oils and their principal constituents as antimicrobial agents for synthetic packaging films.

Spices and herbal plant species have been recognized to possess a broad spectrum of active constituents that exhibit antimicrobial (AM) activity. These active compounds are produced as secondary metabolites associated with the volatile essential oil (EO) fraction of these plants. A wide range of AM agents derived from EOs have the potential to be used in AM packaging systems which is one of the promising forms of active packaging systems aimed at protecting food products from microbial contamination. Many studies have evaluated the AM activity of synthetic AM and/or natural AM agents incorporated into packaging materials and have demonstrated effective AM activity by controlling the growth of microorganisms. This review examines the more common synthetic and natural AM agents incorporated into or coated onto synthetic packaging films for AM packaging applications. The focus is on the widely studied herb varieties including basil, oregano, and thyme and their EOs.

Dehydration of carrots by a combination of freeze drying, microwave heating and air or vacuum drying

Abstract Carrot slices were dried by combining freeze drying with a short microwave treatment and air or vacuum drying. Total drying time, and quality parameters including color, dimensions of slices and rehydration ratio were determined. Freeze drying for 2 h at a plate temperature of 30 °C followed by 1.5 h at 55 °C was sufficient to remove all water by sublimation and reach a product moisture of about 40%. The partially freeze dried product was microwave treated for 50 s and then dried to 5% moisture in vacuum or forced air. The color, dimensions and rehydration ratio of the partially freeze dried, microwave treated and air dried product were similar to same quality parameters of the product freeze dried to the final moisture content. Final drying in vacuum oven had some beneficial effect on color. A considerable saving in freeze drying time was achieved by combining freeze drying with microwave treatment followed by air drying. Total freeze drying time at 30 °C was 9.5 h as compared to a combination of 3.5–3.75 h of partial freeze drying followed by a short microwave treatment and 3.75 h air drying.

A review of poly(lactic acid)-based materials for antimicrobial packaging.

Poly(lactic acid) (PLA) can be synthesized from renewable bio-derived monomers and, as such, it is an alternative to conventional petroleum-based polymers. Since PLA is a relatively new polymer, much effort has been directed toward its development in order to make it an acceptable and effective option to the more traditional petroleum-based polymers. Commercially, PLA has received considerable attention in food packaging applications with a focus on films and coatings that are suitable for short shelf life and ready-to-eat food products. The potential for PLA to be used in active packaging has also been recognized by a number of researchers. This review focuses on the use of PLA in antimicrobial systems for food packaging applications and explores the engineering characteristics and antimicrobial activity of PLA films incorporated and/or coated with antimicrobial agents.

Antimicrobial Activity of Biodegradable Polysaccharide and Protein-Based Films Containing Active Agents

Significant interest has emerged in the introduction of food packaging materials manufactured from biodegradable polymers that have the potential to reduce the environmental impacts associated with conventional packaging materials. Current technologies in active packaging enable effective antimicrobial (AM) packaging films to be prepared from biodegradable materials that have been modified and/or blended with different compatible materials and/or plasticisers. A wide range of AM films prepared from modified biodegradable materials have the potential to be used for packaging of various food products. This review examines biodegradable polymers derived from polysaccharides and protein-based materials for their potential use in packaging systems designed for the protection of food products from microbial contamination. A comprehensive table that systematically analyses and categorizes much of the current literature in this area is included in the review.

Thermal fractionation and identification of low-density polyethylenes

In the present publication, a method to identify and distinguish between different types of low-density polyethylene based on thermal fractionation and FTIR analysis is described. It was shown that during thermal fractionation four to seven endothermic peaks are obtained as opposed to one or two peaks obtained during regular differential scanning calorimetric analysis. The ration between band heights at 1368 and 1376 cm−1 was found to represent the length of the side chain (branch).

Antimicrobial Activity of Natural Agents Coated on Starch-Based Films against Staphylococcus aureus

This study investigated the antimicrobial (AM) activity of starch-based films coated with linalool, carvacrol, or thymol against Staphylococcus aureus in vitro or inoculated on the surface of Cheddar cheese. In solid media using the agar diffusion method, the inhibitory effect of linalool, carvacrol, or thymol coated onto the films increased significantly (P≤ 0.05) with the increase in concentration of each AM agent. All the coated films effectively inhibited the growth of S. aureus on the surface of Cheddar cheese. The sensitivity of S. aureus to the AM agents tested in the concentration range of the study is in the order of thymol > carvacrol > linalool.

Durability of Polyethylene Films

Abstract This work deals with the weather-resistance of low-density polyethylene films. The performance under controlled laboratory conditions, of well-characterized polymer grades and various combinations of stabilizers was studied. The high molecular weight and narrowly-distributed grades seemed to have a better performance. While the unstabilized films were found to fail after a relatively short period, the synergistic combinations of UV absorbers, quenchers and anti-oxidants showed a marked increase in film duration. For the protected films, increasing film thickness improved performance. The increase of crystallinity upon ageing with the resulting decrease in oxygen permeability are highlighted. The role of oxygen diffusion into the film is significant both in thermal and in photo-oxidation.

Inverse gas chromatographic studies of styrene diffusion in polystyrene and monomer/polymer interaction

The diffusion coefficients of styrene in polystyrene were studied using inverse gas chromatography (i.g.c.). Values between 4.3 × 10−10 and 5.5 × 10−9 cm2 s−1 were found in the temperature range from 110°C to 140°C respectively. An Arrhenius type dependence of the diffusion coefficient on temperature was found in this narrow temperature range with an activation energy of 13.5 kcal mol−1. The i.g.c. method was found to be fast and accurate for diffusion coefficient determination of vapours in molten polymers.

Effect of high-pressure food processing on the physical properties of synthetic and biopolymer films.

The effect of high-pressure processing on 2 plastic food packaging films, a biopolymer (PLASiOx/PLA) and a synthetic polymer (PET-AlOx), was studied. Samples in direct contact with olive oil, as a fatty food simulant, and distilled water, as an aqueous simulant, were subjected to a pressure of 500MPa for 15 min at 50 degrees C. The mechanical, thermal, and gas barrier properties of both films were evaluated after the high-pressure processing (HPP) and compared to control samples that have not undergone this treatment. Significant changes in all properties were observed in both films after the HPP treatment and in contact with the food simulants. In both films an induced crystallization was noticed. In the PLASiOx/PLA film the changes were larger when in contact with water that probably acted as a plasticizer. In the PET-AlOx film the changes in properties were attributed to the formation of pinholes and cracks during the HPP treatment. In this film, most of the properties changed more in the presence of oil as the food simulant.