Antonio Martínez-Abad

Stabilization of a Nutraceutical Omega-3 Fatty Acid by Encapsulation in Ultrathin Electrosprayed Zein Prolamine

Docosahexaenoic acid (DHA) is a long chain polyunsaturated fatty acid of the omega-3 series (omega-3), which exerts strong positive influences on human health. The target of this study was the stabilization by encapsulation of this bioactive ingredient in zein ultrathin capsules produced by electrospraying. The zein ultrathin DHA encapsulation was observed by ATR-FTIR spectroscopy to be more efficient against degradation under both ambient conditions and in a confined space (so-called headspace experiment). In the latter case, that more closely simulates a sealed food packaging situation, the bioactive DHA was considerably more stable. By fitting the degradation data to a specific auto-decomposition food lipids kinetic model, it was seen that the encapsulated omega-3 fatty acid showed a 2.5-fold reduction in the degradation rate constant and also had much higher degradation induction time. Moreover, the ultrathin zein-DHA capsules resulted to be more stable across relative humidity and temperature. Finally, headspace analysis by gas chromatography coupled with mass spectrometry showed that the presence of 3 main flavor-influencing aldehydes in the headspace was much lower in the zein encapsulated DHA, suggesting that the encapsulated bioactive also releases much less off-flavors. Electrosprayed ultrathin capsules of zein are shown to exhibit potential in the design of novel functional foods or bioactive packaging strategies to enhance the stability of functional ingredients. Practical Application: This article presents a novel methodology for the stabilization by encapsulation of omega 3 nutraceuticals via electrospraying and has potential application in the development of functional foods.

Development and Characterization of Silver-Based Antimicrobial Ethylene–Vinyl Alcohol Copolymer (EVOH) Films for Food-Packaging Applications

The use of silver as an antimicrobial in the food area has raised wide interest in recent years. In the present work, 0.001-10 wt % silver ions was satisfactorily incorporated into an ethylene-vinyl alcohol (EVOH) copolymer matrix by a solvent casting technique. The antibacterial efficacy of the composite was evaluated under laboratory conditions and in contact with some foods. The ionic compound did not affect the crystallinity or the water-induced plasticization of the materials and was homogeneously distributed across the surface and thickness of the films. When immersed in water, sorption-induced release of 50-100% of the silver ions took place in <30 min. In the bacterial minimal growth medium M9, the minimal inhibitory concentration (MIC) of the film was in the range of 0.01-0.1 ppm. High protein content food samples displayed low susceptibility to the films (<1 log reduction in any case), whereas low protein content food samples exhibited no detectable bacterial counts for films with 1 and 10 wt % silver and about 2 log reduction for films with 0.1 wt % silver. These results represent a step forward in the understanding of silver antimicrobial efficacy and its possible application in the food-packaging industry, most likely as food coatings.

Evaluation of silver-infused polylactide films for inactivation of Salmonella and feline calicivirus in vitro and on fresh-cut vegetables

There is a growing trend to develop packaging materials with an active role in guarantying that the quality and safety characteristics of packaged products will remain or improve from preparation throughout shelf-life. In the present study, 0.001-1.0 wt.% silver ions were satisfactorily incorporated into polylactide (PLA) films by a solvent casting technique. Silver migration from the films was measured by voltamperometry and then correlated with its antimicrobial efficacy against Salmonella enterica and feline calicivirus (FCV), a human norovirus surrogate, by using the Japanese industrial standard (JIS Z 2801). The PLA-silver films showed strong antibacterial and antiviral activity in vitro, with increasing effects at higher silver concentrations. Moreover, results show that FCV was less susceptible to silver than Salmonella. When films were applied on food samples, antibacterial and antiviral activity was reduced as compared to in vitro. Antimicrobial activity was very much dependent on the food type and temperature. In lettuce samples incubated at 4 °C during 6 days, 4 log CFU of Salmonella was inactivated for films with 1.0 wt.% and no infectious FCV was reported under the same conditions. On paprika samples, no antiviral effect was seen on FCV infectivity whereas films showed less antibacterial activity on Salmonella.

On the different growth conditions affecting silver antimicrobial efficacy on Listeria monocytogenes and Salmonella enterica

Silver is known to inhibit microorganisms and therefore it is an ideal candidate for its incorporation in a wide variety of materials for food applications. However, there is still a need for understanding how silver prolonged exposure to bacterial contamination affects the bioavailability of the active silver species. In the present study, growth curves of Listeria monocytogenes and Salmonella enterica were performed for 3-5 days in Tryptic Soy Broth (TSB) and M9 minimal medium (M9) in the presence of silver ions and silver solutions previously in contact with the growth media. The cultivability of the bacteria under these conditions was correlated with the viability of the bacterial populations as measured by flow cytometry analysis (FC) using a LIVE/DEAD BacLight kit. It was found that, after a period where viable counts were not detected, bacterial populations recovered and were able to proliferate in most cases. The resuscitation of the cultures was explained by both the existence of a resilient fraction of bacteria in a compromised state and the parallel inactivation of the silver species. This inactivation was found to be highly influenced by time dependant chemical reactions taking place in the environment of exposure, producing differences of at least 3 fold between results for nutrient rich environments and results for limiting environments. This study points out the need for understanding these chemical interactions and bacterial mechanisms of adaptation and may have relevance in the design of silver-based antimicrobial systems for food-related applications.

Antimicrobial beeswax coated polylactide films with silver control release capacity

Although the application of silver based antimicrobial systems is a widespread technology, its implementation in areas such as food packaging is still challenging. The present paper describes the fabrication of poly(lactic acid) (PLA) coated with beeswax with controlled release properties for sustained antimicrobial performance. Release of silver ions from the polymers was monitored voltammetrically under various conditions (surface contact, immersion in various liquid media and at different pH values) throughout at least 7days. A higher release was noted with decreasing pH while surface release was much slower than the release when immersed in liquid medium. While uncoated films demonstrated a high burst release which in some instances implied surpassing some current migration restrictions (<0.05mg/kg food), the addition of a beeswax layer allowed a sustained release of the antimicrobial compound. Increasing the thickness of the beeswax layer resulted in an increase in the water barrier properties of the films while reducing the relatively constant values of sustained release. Antimicrobial performance was correlated with the release of silver ions, indicating threshold concentrations for biocide action of <6μg/L and 9-14μg/L for surface contact and in liquid media, respectively. Either by surface contact or by immersion in growth medium or vegetable soup, the coated films displayed a strong bactericidal effect against Salmonella enterica. The application of this functional barrier thus offers the possibility of tuning the release profiles of the films to suit a specific application and puts forth the possible suitability of these materials for food packaging or other migration sensitive applications.

Stabilization of antimicrobial silver nanoparticles by a polyhydroxyalkanoate obtained from mixed bacterial culture

The incorporation of antimicrobials into polymer matrices is a promising technology in the food packaging and biomedical areas. Among the most widely used antimicrobials, silver nanoparticles (AgNPs) have emerged as one of the most researched technologies to prevent microbial outbreaks. However, it is known that AgNPs are rather unstable and present patterns of agglomeration that might limit their application. In this work, AgNPs were produced by chemical reduction in suspensions of an unpurified poly(3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) which was previously obtained from a mixed culture fermentation using a synthetic medium mimicking fermented cheese whey. The synthesis of AgNPs was carried out within the unpurified PHBV suspension (in situ) and by physical mixing (mix). The stability of crystalline and spherical nanoparticles (7±3nm) obtained in situ was found to be stable during at least 40 days. The results suggest that the unpurified PHBV appears to be a very efficient capping agent, preventing agglomeration and, thereby, stabilizing successfully the silver nanoparticles. The in situ obtained AgNP-PHBV materials were also found to exhibit a strong antibacterial activity against Salmonella enterica at low concentration (0.1-1ppm).

Ligands affecting silver antimicrobial efficacy on Listeria monocytogenes and Salmonella enterica.

Although silver is being extensively used in food or other applications as the key component to control microbial proliferation, many factors affecting its real potential are still unknown. In the present work, the presence of specific ligands or the contents in organic matter was correlated with silver speciation and its antibacterial performance. Silver was found to be only active in form of free silver ions (FSI). The presence of chloride ions produced an equilibrium of stable silver chloride complexes which were void of antimicrobial efficacy. However, even at relatively high concentrations of chlorides, a small fraction of FSI may still be present, producing a bactericidal effect with concentrations at the nanomolar level under optimum conditions. Low concentrations of thiol groups completely inactivated silver, while methylsulphur groups only affected its efficacy at very high concentrations. Antibacterial performance revealed differences of about 1000-fold between results for environments with high organic matter content and results for aqueous salt buffers. Thiol groups were nonetheless not found directly associated with the decrease in antimicrobial performance in a nutrient rich environment. These results point out the complexity of the antimicrobial systems based on silver and can have relevance in food or other applications of silver as an antimicrobial.

Antibacterial Properties of Tough and Strong Electrospun PMMA/PEO Fiber Mats Filled with Lanasol—A Naturally Occurring Brominated Substance

A new type of antimicrobial, biocompatible and toughness enhanced ultra-thin fiber mats for biomedical applications is presented. The tough and porous fiber mats were obtained by electrospinning solution-blended poly (methyl methacrylate) (PMMA) and polyethylene oxide (PEO), filled with up to 25 wt % of Lanasol—a naturally occurring brominated cyclic compound that can be extracted from red sea algae. Antibacterial effectiveness was tested following the industrial Standard JIS L 1902 and under agitated medium (ASTM E2149). Even at the lowest concentrations of Lanasol, 4 wt %, a significant bactericidal effect was seen with a 4-log (99.99%) reduction in bacterial viability against S. aureus, which is one of the leading causes of hospital-acquired (nosocomial) infections in the world. The mechanical fiber toughness was insignificantly altered up to the maximum Lanasol concentration tested, and was for all fiber mats orders of magnitudes higher than electrospun fibers based on solely PMMA. This antimicrobial fiber system, relying on a dissolved antimicrobial agent (demonstrated by X-ray diffraction and Infrared (IR)-spectroscopy) rather than a dispersed and “mixed-in” solid antibacterial particle phase, presents a new concept which opens the door to tougher, stronger and more ductile antimicrobial fibers.

Chapter 32 – Silver-Based Antibacterial and Virucide Biopolymers: Usage and Potential in Antimicrobial Packaging

The purpose of this chapter is to conduct a structured and systematic review of published literature on the current state of knowledge regarding silver-based antimicrobial packaging; in particular, the antibacterial capacity of silver nanoparticles (AgNPs) has been compiled in this chapter. The release kinetics and antimicrobial properties of AgNPs incorporated into biobased polymers such as polylactic acid and polyhydroxyalkanoates have been extensively reviewed. Additionally, enteric viruses are a growing concern in many areas, especially in foods. This chapter reviews the usage of silver to fight enteric viruses.Abstract The purpose of this chapter is to conduct a structured and systematic review of published literature on the current state of knowledge regarding silver-based antimicrobial packaging; in particular, the antibacterial capacity of silver nanoparticles (AgNPs) has been compiled in this chapter. The release kinetics and antimicrobial properties of AgNPs incorporated into biobased polymers such as polylactic acid and polyhydroxyalkanoates have been extensively reviewed. Additionally, enteric viruses are a growing concern in many areas, especially in foods. This chapter reviews the usage of silver to fight enteric viruses.

CHAPTER 11:Polymeric Materials Containing Natural Compounds with Antibacterial and Virucide Properties

This chapter deals with a very trendy topic related to the design of efficient antimicrobials based on natural extracts, which are of particular consideration in food-packaging applications. The reason why natural extracts generate significant interest lies in the fact that they are natural compounds, typically extracted from foods or plants, and are, therefore, perceived as safer antimicrobials. Additionally, viruses are a growing concern in many areas, but since more recently also in foods. This chapter uniquely reviews the usage of natural compounds to fight viruses.