The influence of fat and monoacylglycerols on growth of spore-forming bacteria in processed cheese

Milk-derived antimicrobial peptides incorporated whey protein film as active coating to improve microbial stability of refrigerated soft cheese

Nisin is the first FDA-approved antimicrobial peptide and shows significant antimicrobial activity against Gram-positive bacteria, but only a weakly inhibitory effect on Gram-negative bacteria. The aim of this study was to prepare whey protein-based edible films with the incorporation of milk-derived antimicrobial peptides (αs2-casein151-181 and αs2-casein182-207) and compare their mechanical properties and potential application in cheese packaging with films containing nisin. These two antimicrobial peptides showed similar activity against B. subtilis and much higher activity against E. coli than bacteriocin nisin, representing that these milk-derived peptides had great potential to be applied as food preservatives. Antimicrobial peptides in whey protein films caused an increase in film opaqueness and water vapor barrier properties but decreased the tensile strength and elongation at break. Compared to other films, the whey protein film containing αs2-casein151-181 had good stability in salt or acidic solution, as evidenced by the results from scanning electron microscope and Fourier transform infrared spectroscopy. Whey protein film incorporated with αs2-casein151-181 could inhibit the growth of yeasts and molds, and control the growth of psychrotrophic bacteria present originally in the soft cheese at refrigerated temperature. It also exhibited significant inhibitory activity against the development of mixed culture (E. coli and B. subtilis) in the cheese due to superficial contamination during storage. Antimicrobial peptides immobilized in whey protein films showed a higher effectiveness than their direct application in solution. In addition, films containing αs2-casein151-181 could act as a hurdle inhibiting the development of postprocessing contamination on the cheese surface during the 28 days of storage. The films in this study exhibited the characteristics desired for active packaging materials.

Unravelling the impact of fat content on the microbial dynamics and spatial distribution of foodborne bacteria in tri-phasic viscoelastic 3D models

The aim of the current study is to develop and characterise novel complex multi-phase in vitro 3D models, for advanced microbiological studies. More specifically, we enriched our previously developed bi-phasic polysaccharide (Xanthan Gum)/protein (Whey Protein) 3D model with a fat phase (Sunflower Oil) at various concentrations, i.e., 10%, 20%, 40% and 60% (v/v), for better mimicry of the structural and biochemical composition of real food products. Rheological, textural, and physicochemical analysis as well as advanced microscopy imaging (including spatial mapping of the fat droplet distribution) of the new tri-phasic 3D models revealed their similarity to industrial food products (especially cheese products). Furthermore, microbial growth experiments of foodborne bacteria, i.e., Listeria monocytogenes, Escherichia coli, Pseudomonas aeruginosa and Lactococcus lactis on the surface of the 3D models revealed very interesting results, regarding the growth dynamics and distribution of cells at colony level. More specifically, the size of the colonies formed on the surface of the 3D models, increased substantially for increasing fat concentrations, especially in mid- and late-exponential growth phases. Furthermore, colonies formed in proximity to fat were substantially larger as compared to the ones that were located far from the fat phase of the models. In terms of growth location, the majority of colonies were located on the protein/polysaccharide phase of the 3D models. All those differences at microscopic level, that can directly affect the bacterial response to decontamination treatments, were not captured by the macroscopic kinetics (growth dynamics), which were unaffected from changes in fat concentration. Our findings demonstrate the importance of developing structurally and biochemically complex 3D in vitro models (for closer proximity to industrial products), as well as the necessity of conducting multi-level microbial analyses, to better understand and predict the bacterial behaviour in relation to their biochemical and structural environment. Such studies in advanced 3D environments can assist a better/more accurate design of industrial antimicrobial processes, ultimately, improving food safety.

Reuse of Textile Waste to Production of the Fibrous Antibacterial Membrane with Filtration Potential

Wasted synthetic fabrics are a type of textile waste source; the reuse of them brings environmental protection and turns waste into a valuable material. In this work, the used nylon (polyamide) stockings were transmuted into a fine fibrous membrane via an electrospinning process. In addition, the safety antibacterial agent, monoacylglycerol (MAG), was incorporated into a recycled fibrous membrane. The results revealed that the neat, recycled polyamide (rPA) fibers with a hydrophobic surface could be converted into hydrophilic fibers by blending various amounts of MAG with rPA solution prior to electrospinning. The filtration efficiency and air/water vapor permeability of the two types of produced membranes, neat rPA, and rPA/MAG, were tested. Their filtration efficiency (E100) was more than 92% and 96%, respectively. The membranes were classified according to Standard EN1822, and therefore, the membranes rPA and rPA/MAG were assigned to the classes E10 and E11, respectively. The air permeability was not affected by the addition of MAG, and water vapor permeability was slightly enhanced. Based on the obtained data, prepared rPA/MAG fibrous membranes can be evaluated as antifouling against both tested bacterial strains and antimicrobial against S. aureus.

Antibacterial Filtration Membranes Based on PVDF-co-HFP Nanofibers with the Addition of Medium-Chain 1-Monoacylglycerols

The efficiency of filtration membranes is substantially lowered by bacterial attachments and potential fouling processes, which reduce their durability and lifecycle. The antibacterial and antifouling properties exhibited by the added materials play a substantial role in their application. We tested a material poly(vinylidene fluoride)-co-hexafluoropropylene (PDVF-co-HFP) based on an electrospun copolymer, where an agent was incorporated with a small amount of ester of glycerol consecutively with caprylic, capric, and lauric acids. Each of these three materials differing in the esters (1-monoacylglycerol, 1-MAG) used was prepared with three weighted concentrations of 1-MAG (1, 2, and 3 wt %). The presence of 1-MAG with an amphiphilic structure resulted in the hydrophilic character of the prepared materials that contributed to the filtration performance. The tested materials (membranes) were characterized with rheological, optical (scanning electron microscopy, SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and other methods to evaluate antibacterial and antifouling activities. The pure water flux was 6 times higher than that of the neat PVDF-co-HFP membrane when the added 1-MAG attained only 1 wt %. It was experimentally shown that the PVDF-co-HFP/1-MAG membrane with high wettability improved antibacterial activity and antifouling ability. This membrane is highly promising for water treatment due to the safety of antibacterial 1-MAG additives.