Encapsulation of thyme essential oil using electrospun zein fiber for strawberry preservation

Background Strawberry is a nutrient-rich and important small fruit because of its high content of beneficial phytochemicals and several vitamins like vitamin C, vitamin E and vitamin B6. However, strawberry is highly perishable due to its susceptibility to mechanical damage, microbiological decay, and softening in texture. Recently, there has been an increasing interest in using various essential oils as natural food preservatives. Although, they have limited stability to exposure to high temperatures, light and oxygen, which could eventually affect sensory quality attributes. The electrospinning method is a simple and well-organized process that has been used to encapsulate essential oils. In this study, the effect of thyme essential oil (TEO) encapsulated into zein electrospun fiber film was assessed on extending the shelf life and preserving the quality of strawberry fruit during storage. Findings Results indicated that TEO presented potent antibacterial activity against Bacillus cereus, Escherichia coli and Aspergillus fumigatus. The scanning electron microscopy images of zein fiber had a linear shape, absence of beads, and smooth surface. The encapsulation efficiency (EE) of TEO in the zein fiber was about 75.23%. Encapsulated TEO released at a slower rate than free TEO. The zein/TEO fibers (zein fiber film loaded with TEO) significantly (p ˂ 0.05) decreased weight loss and maintained the anthocyanin content, firmness and color of the strawberries during storage. After 15 days of storage, weight loss reduced about 15% and firmness was higher about 20% in packed fruit with zein/TEO fibers compared to control. Conclusions Interestingly, after 15 days of cold storage, the strawberries firmness, appearance, and sensory evaluation, which are important quality factors from both postharvest and consumers’ viewpoint, in zein/TEO fiber treatment were acceptable and had higher scores compared to the control. In conclusion, the present study demonstrated the benefits of incorporating TEO into zein films, which could play a significant role in the active packaging and preservation of strawberry fruits. Graphical Abstract

Characterization of Lacticaseibacillus rhamnosus, Levilactobacillus brevis and Lactiplantibacillus plantarum Metabolites and Evaluation of Their Antimicrobial Activity against Food Pathogens

Lactic acid bacteria (LAB) play an important role as natural food preservatives. However, the characterization of the variety of their metabolites is limited. The objective of this study was to determine the production of specific metabolites of Lacticaseibacillus rhamnosus, Levilactobacillus brevis and Lactiplantibacillus plantarum by an optimized liquid chromatography with an ultraviolet/diode detection (HPLC-UV/DAD) method and to investigate their potential antimicrobial activity against specific food pathogens. Based on the results of this study, the main metabolites detected in Levilactobacillus brevis were 103.4 μg mL−1 DL-p-Hydroxyphenyllactic acid (OH-PLA) and 2.59 μg mL−1 vanillic acid, while 216.2 μg mL−1 OH-PLA, 19.0 μg mL−1 salicylic acid, 3.7 μg mL−1 vanillic acid, 6.9 μg mL−1 ferulic acid, 4.2 μg mL−1 benzoic acid and 1.4 μg mL−1 4-Hydrocinnamic acid were identified in the Lactiplantibacillus plantarum strain and 147.6 μg mL−1 OH-PLA and 4.9 μg mL−1 ferulic acid were identified in Lacticaseibacillus rhamnosus. This study provides alternative approaches for the molecules involved in the antimicrobial activity of food microorganism fermentation. These molecules may be used as antimicrobial ingredients in the food industry instead of conventional chemical preservatives.

Phenolic-Rich Plant Extracts With Antimicrobial Activity: An Alternative to Food Preservatives and Biocides?

In recent years, the search for natural plant-based antimicrobial compounds as alternatives to some synthetic food preservatives or biocides has been stimulated by sanitary, environmental, regulatory, and marketing concerns. In this context, besides their established antioxidant activity, the antimicrobial activity of many plant phenolics deserved increased attention. Indeed, industries processing agricultural plants generate considerable quantities of phenolic-rich products and by-products, which could be valuable natural sources of natural antimicrobial molecules. Plant extracts containing volatile (e.g., essential oils) and non-volatile antimicrobial molecules can be distinguished. Plant essential oils are outside the scope of this review. This review will thus provide an overview of current knowledge regarding the promises and the limits of phenolic-rich plant extracts for food preservation and biofilm control on food-contacting surfaces. After a presentation of the major groups of antimicrobial plant phenolics, of their antimicrobial activity spectrum, and of the diversity of their mechanisms of action, their most promising sources will be reviewed. Since antimicrobial activity reduction often observed when comparing in vitro and in situ activities of plant phenolics has often been reported as a limit for their application, the effects of the composition and the microstructure of the matrices in which unwanted microorganisms are present (e.g., food and/or microbial biofilms) on their activity will be discussed. Then, the different strategies of delivery of antimicrobial phenolics to promote their activity in such matrices, such as their encapsulation or their association with edible coatings or food packaging materials are presented. The possibilities offered by encapsulation or association with polymers of packaging materials or coatings to increase the stability and ease of use of plant phenolics before their application, as well as to get systems for their controlled release are presented and discussed. Finally, the necessity to consider phenolic-rich antimicrobial plant extracts in combination with other factors consistently with hurdle technology principles will be discussed. For instance, several authors recently suggested that natural phenolic-rich extracts could not only extend the shelf-life of foods by controlling bacterial contamination, but could also coexist with probiotic lactic acid bacteria in food systems to provide enhanced health benefits to human.

Effect of citric acid at different pH on the survival of Escherichia coli

Microorganisms are included among the major spoilers of food, they achieve this by using the nutrients present in food material. Susceptibility of microorganisms to the most currently used preservatives has been decreasing. Organic acids have been considered as valuable food preservatives. This study aimed to isolate, identify and determine the effect of citric acid at different pH levels on the survival of E. coli. The E. coli was isolated and a pure culture was obtained after series of sub-ulturing on Eosine Methylene Blue agar. The biochemical tests known as IMViC were performed to confirm the presence of the organism. The organism was also identified using polymerase chain reaction (PCR) in which the DNA was extracted, amplified and viewed by gel electrophoresis. The organism was then inoculated in nutrient broth containing citric acid at pH levels of 3.0, 4.5 and 6.0 in different test tubes. Negative controls were included. Results were analyzed using one way ANOVA to compare the means obtained. Results obtained was positive for indole and methyl red tests but negative for VogesProskauer and citrate tests which confirmed the organism. After 24 hours of inoculation, the results of spectrophotometry showed that at pH level of 3.0, the absorbance was lower than the results obtained at pH level of 4.5 and 6.0. This is an indication of higher reduction in the count of the organism at pH of 3.0. There was significant difference between the control and the test groups (p<0.05) but the difference obtained between the test groups were not significant (p>0.05). Results from this study showed that citric acid could not eliminate the whole organism but was effective in inhibiting the growth of the organism dependent on pH level. This indicates that a pH dependent citric acid can be used as a good preservative.

Galleria mellonella: The Versatile Host for Drug Discovery, In Vivo Toxicity Testing and Characterising Host-Pathogen Interactions

Larvae of the greater wax moth, Galleria mellonella, are a convenient in vivo model for assessing the activity and toxicity of antimicrobial agents and for studying the immune response to pathogens and provide results similar to those from mammals. G. mellonella larvae are now widely used in academia and industry and their use can assist in the identification and evaluation of novel antimicrobial agents. Galleria larvae are inexpensive to purchase and house, easy to inoculate, generate results within 24–48 h and their use is not restricted by legal or ethical considerations. This review will highlight how Galleria larvae can be used to assess the efficacy of novel antimicrobial therapies (photodynamic therapy, phage therapy, metal-based drugs, triazole-amino acid hybrids) and for determining the in vivo toxicity of compounds (e.g., food preservatives, ionic liquids) and/or solvents (polysorbate 80). In addition, the disease development processes are associated with a variety of pathogens (e.g., Staphylococcus aureus, Listeria monocytogenes, Aspergillus fumigatus, Madurella mycotomatis) in mammals are also present in Galleria larvae thus providing a simple in vivo model for characterising disease progression. The use of Galleria larvae offers many advantages and can lead to an acceleration in the development of novel antimicrobials and may be a prerequisite to mammalian testing.

In Vitro Evaluation of Biological Activities and Phytochemical Analysis of Different Solvent Extracts of Punica granatum L. (Pomegranate) Peels

Antimicrobial resistance is a public health concern resulting in high rates of morbidity and mortality worldwide. Furthermore, a high incidence of food poisoning diseases besides harmful implications of applying synthetic food additives in food preservation necessitates fabrication of safe food preservatives. Additionally, damaging effects of free radicals on human health has been reported to be involved in the incidence of serious diseases, including cancer, diabetes and cardiovascular diseases; hence, finding safe sources of antioxidants is vital. Therefore, the present study was carried out to assess the antibacterial, antiradical and carcinopreventive efficacy of different solvent extracts of pomegranate peels. Agar disk diffusion assay revealed that Staphylococcus aureus, MRSA, E. coli and S. typhimurium were highly susceptible to methanolic fraction of Punica granatum L. peels recording inhibition zones of 23.7, 21.8, 15.6 and 14.7 mm respectively. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the methanolic fraction of Punica granatum L. peels against S. aureus were 0.125 and 0.250 mg/mL, respectively. In addition, the pomegranate acetonic and methanolic fractions revealed an impressive antiradical efficiency against DPPH (2,2-diphenyl-1-picrylhydrazyl) radical recording radical scavenging activity percentages of 86.9 and 79.4%, respectively. In this regard, the acetonic fraction of pomegranate peels revealed the highest anti-proliferative efficiency after 48 h incubation against MCF7 cancer cells recording IC50 of 8.15 µg/mL, while the methanolic extract was highly selective against transformed cancer cells compared to normal cell line recording selectivity index of 5.93. GC–MS results demonstrated that 5-Hydroxymethylfurfural was the main active component of methanolic and acetonic extracts of pomegranate peels recording relative percentages of 37.55 and 28.84% respectively. The study recommends application of pomegranate peel extracts in the biofabrication of safe food preservatives, antioxidants and carcinopreventive agents.

Effects of Extraction Technique and Solvent on Phytochemicals, Antioxidant, and Antimicrobial Activities of Cultivated and Wild Rosemary (Rosmarinus officinalis L.) from Taounate Region (Northern Morocco)

This work was set up to investigate the effects of domestication, solvent, and extraction technique on extracts yield, total phenolics content (TPC), flavonoids content (TFC), antimicrobial (minimal inhibitory concentration, MIC), and antioxidant (IC50) activities in rosemary aerial parts at flowering stage. Although solvent was the main variability source in our data, all tested factors significantly impacted yield, TPC, TFC, MIC, and IC50. These results were confirmed via principal component analysis, which separated solvents, extraction techniques, and rosemary types on the first three components accounting for more than 99% of data variability. Better values of yield (4.17 ± 0.30 –21.58 ± 0.93% DM ), TPC (12.48 ± 1.17–34.72 ± 1.65 mg GAE/g DM), TFC (6.51 ± 1.79–25.02 ± 1.53 mg QE/g DM), MIC (8.17 ± 1.04–24.20 ± 0.98 μg/mL), and IC50 (50.02 ± 0.08–390.00 ± 1.00 µg/mL) were obtained in the case of wild rosemary with Soxhlet extraction especially when combined with more polar solvents (ethanol and methanol). It could be concluded that domestication had negative effects on rosemary phytochemicals and associated antimicrobial and antioxidant activities. Rosemary extracts could serve as important ingredients as food preservatives, antimicrobial agents, and nutraceuticals.

Genomic characterization of bacteriophage BI-EHEC infecting strains of Enterohemorrhagic Escherichia coli

Objective The aims of this research were to determine the genomic properties of BI-EHEC to control Enterohemorrhagic Escherichia coli (EHEC), which was isolated from previous study. Genomic analysis of this phage is essential for the assessment of this bacteriophage for further application as food preservatives. Results Genome of BI-EHEC was successfully annotated using multiPhATE2. Structural and lytic cycle-related proteins such as head, tail, capsid, and lysozyme (lysin) were annotated. The phylogenetic tree of tail fiber protein and BRIG results showed that BI-EHEC was similar to phages of the same host in the bacteriophage genome database. There were no indications of virulence properties, antibiotic resistance genes and lysogenic protein among annotated genes which implied BI-EHEC followed a lytic life cycle. PHACTS analysis was done to confirm this notion further and yielded a lytic cycle result. Further analysis using CARD found that BI-EHEC does not contain residual ARGs per recommended parameter. Furthermore, BI-EHEC confirmed as lytic bacteriophage, making it a good candidate for biocontrol agent.