Escherichia coli
E. coli, a member of the Enterobacteriaceae bacterial family, is the most common commensal occupant of humans and warm-blooded animals' gastrointestinal systems, as well as one of the most important pathogens. It lives in a mutually beneficial relationship with its hosts as a commensal, and it rarely causes disease. It is, nonetheless, one of the most prevalent human and animal infections, as it causes a wide range of diseases in both humans and animals. E. coli is an essential host organism in biotechnology because of its unique qualities, such as simplicity of handling, availability of the entire genome sequence, and capacity to grow in both aerobic and anaerobic conditions. E. coli is the most widely utilized microbe in the field of recombinant DNA technology, and it is used in a wide range of industrial and medical applications.
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Prior to the discovery of specific virulence factors in pathogenic strains, E. coli was predominantly categorized based on serologic detection of O (lipopolysaccharide, LPS) and H (flagellar) antigens. E. coli strains are classified as pathogenic or nonpathogenic depending on the kind of virulence factor present and the clinical symptoms experienced by the host: there are at least seven primary pathotypes for enteric E. coli, and three pathotypes for extraintestinal E. coli (ExPEC).
E. coli with enteropathogenic potential (EPEC). EPEC was the first E. coli pathotype to be identified. Despite the fact that significant outbreaks of EPEC – related baby diarrhea have virtually disappeared in developed nations, EPEC remains a major cause of potentially deadly child diarrhea in impoverished countries. The methods by which EPEC induced diarrhea were unclear for decades, and this pathotype could only be discovered by O:H serotyping. Since 1979, however, major breakthroughs in our understanding of the pathogenesis of EPEC diarrhea have been made, and EPEC is currently one of the best – understood pathogenic E. coli strains [29].
EPEC strains primarily cause diarrhea in children and animals, especially in settings of low cleanliness. Hemorrhagic colitis is caused by the bacterium EHEC and is spread through food, also known as HUS. EHEC strains release Shiga – like toxins that are similar to those produced by Shigella dysenteriae, making them the most virulent diarrhoeagenic E. coli strains discovered to date. ETEC are the most common diseases in people of all ages that cause mild to severe watery diarrhea in travelers. EAEC strains have been associated to diarrhoeal sickness epidemics over the world and have been linked to prolonged diarrhea in humans. EAEC is the world's second most prevalent cause of traveler's diarrhea, and it's found in the stomachs of asymptomatic individuals. In children in underdeveloped countries and HIV – positive patients, EAEC is usually linked to diarrhea [30].
The strain used in this experiment is Escherichia coli ATCC 8739 provided by Saigon University.
Aspergillus niger
There are more than 300 species of Aspergillus, a genus of ascomycete filamentous fungi. Aspergilli reproduce by generating extendingchyphae that branch subapically to form a mycelium, just as all filamentous fungi. This hyphal method of growth not only provides a wide surface area for nutrition intake, but it also allows the fungus to efficiently colonize its substrate. The organic material that most fungal species use as a substrate is made up of huge, complicated molecules that must be broken down before they can be used
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as a source of sustenance. Filamentous fungus release a variety of enzyme combinations that are specifically tailored to the polysaccharide they encounter [31].
Due to their potential in plant biomass degradation and a variety of industrial applications, Black Aspergilli species have been isolated from all over the world. A. niger can grow in a wide temperature range of 6 – 47°C, but prefers temperatures around 35 – 37°C, the water activity limit for growth is 0.88. A. niger can grow in a pH range ranging from 1.4 to 9.8. These properties, as well as the abundant generation of spores that are dispersed by the air, ensure the species' extensive occurrence, with a higher frequency in warm and humid environments [32]. Aspergilli, like other common soil fungi found in a variety of settings, can produce a wide range of enzyme combinations and breakdown a wide range of polysaccharides. When you consider that many Aspergilli have high levels of protein secretion and good fermentability, it is no surprise that this fungus has found applications in industries like food and feed, pulp and paper, biofuels, biodegradable plastics, and textiles, as well as serving as a host for heterologous protein production.
Especially, in food industrial, A. niger applied in production of citric acid since 1919 and had a great attribution in food and beverage productions.
A. niger is typically regarded as a non-harmful organism. However, when people are exposed to large levels of spore dust, hypersensitivity reactions have been observed in a few occasions. A. niger is a non – pathogenic fungus found in large quantities in nature. Its spores come into contact with humans on a daily basis and do not cause illness. A. niger can only enter the human body as an opportunistic invader under rare conditions, and most of these people have a history of serious illness or immunosuppressive drugs [33]. In foodborne system, Aspergillus niger can be discovered in a variety of plant and processed food products, including grapes, cereals, coffee, and derivative products [34]. Aspergillus niger used in this experiment had been isolated and grown for two weeks on potato dextrose agar ourselves and identified at the Center for Bioscience and Biotechnology of the University of Science.
Aspergillus fumigatus
The fungus Aspergillus fumigatus is part of the Aspergillus genus. It is one of the most common Aspergillus species to infect people with weakened immune systems. There are around 300 species of Aspergillus in the genus [31]. Conidiophores produce thousands of minute grey – green conidia (2–3 m) that easily get airborne in fungus colonies.
The species Aspergillus fumigatus is remarkable in that it can survive temperatures ranging from 20 to 50oC [35], with conidia surviving at 70oC (158oF) – conditions it frequently finds in self – heating compost heaps. Its spores are widely distributed in the environment, and everyone inhales hundreds of spores every day, in healthy persons, the
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immune system often destroys these spores quickly. In immunocompromised patients, such as organ transplant recipients and people with AIDS or leukemia. In immunocompromised patients, such as organ transplant recipients and people with AIDS or leukemia, the fungus is more likely to become pathogenic, overwhelming the host's weakened defenses and causing a variety of diseases known as aspergillosis. Because of the recent rise in the use of immunosuppressants to treat human ailments, A. fumigatus is thought to be responsible for approximately 600,000 deaths per year, with a mortality rate ranging from 25 to 90 % [36].
The saprotroph Aspergillus fumigatus can be found in soil and decaying organic materials like compost heaps, where it aids in carbon and nitrogen recycling. A. fumigatus has been found in cereals, rice, and wheat, as well as other foods. A. fumigatus has been found in cereals, rice, and wheat, as well as other foods. A. fumigatus.was found in more places this time, with amaranth, oil, rape, sesame, and sunflower seeds [37]. A source of A. fumigatus has been identified as cocoa. Low fat buffalo cheese and processed cheese have been shown to have A. fumigatus, which may provide a specific risk. Surprisingly, A.
fumigatus was not found in fruit, with the exception of pickled mangoes, suggesting that fruit could be beneficial to immunocompromised people. Furthermore, because A.
fumigatus is a thermophilic species, it may not thrive in temperate areas. Fruits from temperate climates, it is suggested, may be safer in general, however further research is needed [37]. Aspergillus fumigatus used in this experiment had been isolated and grown for two weeks on potato dextrose agar ourselves and identified at the Center for Bioscience and Biotechnology of the University of Science.
1.5. Researches relating to active packaging based on chitosan and CNM in the world:
In the last ten years, numerous studies on the development of natural active packaging materials have been published, with the bulk of them focusing on food applications.
Controlled moisture transfer between food and the environment, reduced oxygen partial pressure in the package, controlled release of chemical agents, antimicrobials, antioxidants, high permeability to certain substances, temperature control, structural reinforcement of food, and coating flavor compounds are some of the techniques used to extend the shelf life of food.
Natural polymers, particularly polysaccharides, are gaining popularity in a variety of technological disciplines, despite the fact that many types of synthetic polymer compositions are created industrially. CH has been investigated extensively among the polysaccharides due to its outstanding film forming capabilities, antibacterial characteristics, physical and mechanical capabilities, biocompatibility, and
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biodegradability. Agriculture, food, and pharmaceuticals could all benefit from CH film.
At the 1st Workshop on Nanotechnology in Instrumentation and Measurement (NANOFIM) in 2015, Demitri et al. presented Graphene reinforced CH – CNM derivatives films: antifungal activity and mechanical characteristics. The proposed research shows that CNM and graphite stacks in CH substrates have excellent antifungal action as well as better mechanical properties. The inclusion of graphite nano stacks, on the other hand, improved the composite material's mechanical properties. The combination of these two qualities may increase the use of these materials in the food sector as active packaging [38]. López- Mata et al. [39] investigated the mechanical, barrier, and antioxidant properties of CH films with CNM. According to a study by Xu et al. (2005), films made exclusively of CH exhibit poor water resistance and mechanical properties. Another possibility is to use CH and other hydrophilic biopolymers to create a miscible, biodegradable composite film. The purpose of this study was to create chitosan/starch composite films by combining a 90 % deacetylated CH solution with two thermally gelatinized maize starches (waxy starch and ordinary starch with 25 % amylose) [40]. Preparation and characterisation of CH film incorporating thinned young apple polyphenols as an active packaging material was published by Sun et al. in 2017. The purpose of this study was to see what physical, mechanical, and bioactive properties CH film with thinned young apple polyphenols had (YAP). According to the findings, adding YAP to CH film increased its thickness, density, swelling degree, solubility, and opacity while lowering its water content, water vapor permeability, and mechanical properties. Furthermore, YAP increased the antioxidant and antibacterial properties of CH film significantly [41]. Furthermore, Gao et al. demonstrated in 2018 that CH – CNM, as a green environmental protection chemical, may lengthen the storage time of navel orange fruit while retaining its quality by covering it with CH – CNM.
It might create a homogeneous and clear layer of coating film on the fruit surface, minimizing fruit postharvest deterioration, slowing water loss degradation, and delaying fruit storage weight loss while maintaining high commodity value [42]. Higueras et al.
developed CH – CNM Schiff base films for antibacterial food packaging in their paper Reversible Covalent Immobilization of CNM on CH Films through Schiff Base Formation and Their Application in Active Food Packaging. CH was chosen as the support matrix for the nucleophilic addition of CNM to free amino groups [43]. The findings of these experiments imply that CNM and CH could be used as coatings for preserving food products.
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