PVOH/protein blend films embedded with lactic acid bacteria and their antilisterial activity in pasteurized milk

Recent advances of antibacterial starch-based materials

Starch has attracted a lot of attention because it is biodegradable, renewable, nontoxic and low cost. By adding antibacterial substances to starch, starch-based materials have antibacterial properties. The composite with other materials can improve the comprehensive performance of starch-based materials, thus broadening the application field of the material. In this paper, we focus on antibacterial starch-based materials and review their preparation and applications. It was found that antibacterial starch-based materials were most widely used in packaging, followed by medicine, and the research on smart starch-based materials was relatively less. This review may provide some reference value for subsequent studies of starch-based materials.

Development of Biodegradable Films Loaded with Phages with Antilisterial Properties

The inhibitory and bactericidal capacity of Listex P100 bacteriophage has been studied against different concentrations of Listeria monocytogenes in stationary and exponential phases. Three different matrices were employed to developed films incorporating Listex P100: (1) sodium caseinate, (2) sodium alginate mixed with gelatin, and (3) polyvinyl alcohol (PVOH). All the films were successfully developed by casting at room temperature. These active biodegradable films were optical, structural, and thermally characterized, and their antimicrobial capacities against L. monocytogenes were studied. The incorporation of phages did not affect the morphology, colour, opacity, and thermal stability of polymers. The antimicrobial analysis revealed the bacteriophage presented a high antimicrobial capacity against L. monocytogenes in the stationary phase (4.40 and 6.19 log reduction values or bactericide effect depending on the initial inoculum of the pathogen). Developed films showed antimicrobial capacity close to 1 log after 24 h of incubation at 30 °C. The effectiveness of PVOH films was greater under refrigeration conditions, reaching 2 log reduction after eight days of incubation. The use of these films as a coating in a food or as part of a packaging could improve food safety against the growth of pathogenic microorganisms such as Listeria monocytogenes.

Broadening the antimicrobial spectrum of nisin-producing Lactococcus lactis subsp. Lactis to Gram-negative bacteria by means of active packaging

Cast films obtained from polyvinyl alcohol (PVOH) blended with casein hydrolysates (HCas) in a weight ratio of 1:1 were employed to carry nisin-producing L. lactis and phytic acid in order to broaden the antimicrobial spectrum of L. lactis to Gram-positive and Gram-negative spoilage and pathogen bacteria. For this purpose, the effect of the antimicrobial activity of various film formulations and combinations of films on the growth of E. coli at 37 °C for 24 h was studied. The film system that showed antimicrobial activity against Gram-negative bacteria consisted of phytic acid and L. lactis incorporated in separate films. When the active agents were in the same film the viability of L. lactis decreased considerably and it did not exert antimicrobial activity against the bacterium. Therefore, the combination of L. lactis and phytic acid in separate films was chosen as the reliable system, and the effect of its activity on the growth of Gram-negative bacteria (E. coli, Salmonella enterica, and Pseudomonas fluorescens) and Gram-positive bacteria (Listeria monocytogenes) in liquid culture medium was tested at refrigeration temperature (4 °C), and with simulated breaks in the cold chain (14 °C and 24 °C). The survival of L. lactis in coexistence with these bacteria was also studied. The film system exerted an antimicrobial effect against the Gram-negative bacteria tested, and the activity depended on the bacteria and the temperature assayed. With regard to the antimicrobial activity against L. monocytogenes, phytic acid improved the antimicrobial capacity of L.lactis. The survival of L. lactis was maintained at 7-8 log (CFU/mL) culture in liquid medium throughout the storage period. The films developed were intended to be used as coatings in the design of a double-sided active bag for a non-fermented dairy product. The bags were filled with homemade preservative-free pastry cream, and the microbiological shelf life and evolution of pH of the packaged ready-to-eat food stored at 4 °C was studied for 20 days. The results showed a reduction in the growth of spoilage bacteria and therefore an increase in the shelf life of the packaged product. The films developed could be applied in the design of packages for perishable dairy foods in order to increase their microbiological shelf life.

Biodegradable Antimicrobial Food Packaging: Trends and Perspectives

This review presents a perspective on the research trends and solutions from recent years in the domain of antimicrobial packaging materials. The antibacterial, antifungal, and antioxidant activities can be induced by the main polymer used for packaging or by addition of various components from natural agents (bacteriocins, essential oils, natural extracts, etc.) to synthetic agents, both organic and inorganic (Ag, ZnO, TiO2 nanoparticles, synthetic antibiotics etc.). The general trend for the packaging evolution is from the inert and polluting plastic waste to the antimicrobial active, biodegradable or edible, biopolymer film packaging. Like in many domains this transition is an evolution rather than a revolution, and changes are coming in small steps. Changing the public perception and industry focus on the antimicrobial packaging solutions will enhance the shelf life and provide healthier food, thus diminishing the waste of agricultural resources, but will also reduce the plastic pollution generated by humankind as most new polymers used for packaging are from renewable sources and are biodegradable. Polysaccharides (like chitosan, cellulose and derivatives, starch etc.), lipids and proteins (from vegetal or animal origin), and some other specific biopolymers (like polylactic acid or polyvinyl alcohol) have been used as single component or in blends to obtain antimicrobial packaging materials. Where the package's antimicrobial and antioxidant activities need a larger spectrum or a boost, certain active substances are embedded, encapsulated, coated, grafted into or onto the polymeric film. This review tries to cover the latest updates on the antimicrobial packaging, edible or not, using as support traditional and new polymers, with emphasis on natural compounds.

Improving nisin production by encapsulated Lactococcus lactis with starch/carboxymethyl cellulose edible films

In this study, Lactococcus lactis was embedded in a film of corn starch (NS) and carboxymethyl cellulose (CMC) prepared using a casting method. At a CMC:NS ratio of 5:5, the composite film had the best comprehensive properties. Scanning electron microscopy images clearly showed that L. lactis was effectively embedded. The film with 1.5 % L. lactis showed the best performance and the lowest water vapor transmission rate (5.54 × 10^-11 g/m s Pa. In addition, the edible film retained a viable count of 5.64 log CFU/g of L. lactis when stored at 4 °C for 30 days. The composite film with 1.5 % L. lactis showed the highest release of nisin (3.35 mg/mL) and good antibacterial activity against Staphylococcus aureus (53.53 %) after 8 days. Therefore, this edible film is a viable alternative antimicrobial strategy for the active packaging of foods containing low moisture content.

Smart Food Packaging Designed by Nanotechnological and Drug Delivery Approaches

This paper offers a general view of the solutions that are able to confer bioactivity to the packaging materials, especially antimicrobial and antioxidant activity. These properties can be induced by the nature of the polymers blend or due to the addition of ternary components from natural agents (essential oils or other extracts) to synthetic organic and inorganic agents, including nanoparticles with a broad antimicrobial activity such as metals (e.g., Ag, Au, Cu) or metal oxide (e.g., TiO2, ZnO) nanoparticles, and even bacterial cells such as probiotics. Many times, these components are synergistically used, each of them assuring a specific role or potentiating the role of the other components. The antimicrobial activity can be induced due to the applied coatings or due to the whole bulk material. Along with an increasing food stability which means a longer shelf-life some smart packaging can be exploited in order to highlight the freshness of the food. These act as a sensor (usually pH sensitive but also other mechanisms can be exploited such as aggregation/agglomeration of AuNPs leading to color change or even aldehyde-specific reactions such as the Cannizzaro reaction), and thus, consumers can be confident about the freshness of the food, especially perishable food such as seafood or fish.