Antimicrobial textile treated with chitosan from Aspergillus niger mycelial waste

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Abstract

The waste biomass of Aspergillus niger, following citric acid production, was used as a source for fungal chitosan extraction. The produced chitosan was characterized with deacetylation degree of 89.6%, a molecular weight of 25,000 dalton, 97% solubility in 1% acetic acid solution and comparable FT-IR spectra to standard shrimp chitosan. Fungal chitosan was applied as a cotton fabric finishing agent using pad-dry-cure method. The topographical structure of chitosan-treated fabrics (CTF) was much improved compared with control fabrics. CTF, after durability tests, exhibited a powerful antimicrobial activity against both E. coli and Candida albicans, the captured micrographs for E. coli cells contacted with CTF showed a complete lysis of cell walls with the prolonging contact time. The produced antimicrobial CTF could be proposed as a suitable material for many medical and hygienic applications.

Introduction

Chitosan is an amazing natural and biodegradable biopolymer derived from chitin. It has a wide range of applications in many fields, e.g. food and nutrition (emulsifying, thickening and stabilizing agent, packaging membrane, antioxidant and dietary supplement), biotechnology (enzyme immobilization), water engineering (flocculants, chelating agent for metals), medical applications (artificial skin, blood anticoagulants, drug-delivery systems) and, recently, in gene therapy [1], [2], [3]. Commercial production of chitosan by deacetylation of crustacean chitin with strong alkali appears to have limited potential for industrial acceptance because of seasonal and limited supply, difficulties in processing particularly with the large amount of waste of concentrated alkaline solution causing environmental pollution and inconsistent physico-chemical properties [4], however, new research has been carried out on the use of alternative sources for chitosan. The studies were focused mainly on chitosan from fungi. The production and purification of chitosan, from the cell walls of fungi grown under controlled conditions, offer a greater potential for more consistent products.

The antimicrobial activity of chitosan has been studied both in terms of bacteriostatic and bactericidal activity and has been demonstrated to inhibit the growth of a wide variety of bacteria. Moreover, chitosan has several advantages over other chemical disinfectants since it possesses a stronger antimicrobial activity, a broader spectrum of activity, a higher killing rate and a lower toxicity toward mammalian cells [5], [6].

Nowadays, Aspergillus niger is almost exclusively used for industrial scale production of citric acid. More than 600,000 metric tons are produced annually worldwide [7]. The fungal mycelia produced as byproducts of fermentation industries could be considered as a promising potential source for the isolation of chitin and/or chitosan.

Cotton textiles have generally a poor resistance to microorganisms, thus antimicrobial finishing of cotton fabrics is an essential approach to prevent their harm to the human body [8]. Many chemical compounds have been employed to impart antimicrobial activity to textile fabrics [9], most of these chemicals, however, are toxic to humans and could not easily be degraded in the environment. The textile industry continues to search for eco-friendly agents that substitute for toxic textile chemicals, in this viewpoint, chitosan could be proposed as an excellent candidate [5].

The current study, however, was designed to investigate the production of fungal chitosan from A. niger mycelial waste subsequent to its production of citric acid and to apply the resultant chitosan as cotton fabric finishing agent to have a fully organic antimicrobial textiles regarding their action against different microbial strains.

Section snippets

Fungal strain

A. niger ATCC 9642 stock culture was reactivated and cultivated on potato dextrose agar (PDA) plates and incubated at 25 °C for 5 days. Spores formed were washed out twice with 10 ml distilled sterilized water each time. Spore suspensions concentration was adjusted to 105/ml and used as inoculums for the fermentation process.

Citric acid production was carried out using a 5.0 l BIOFLO 310 stirred tank bioreactor (New Brunswick Scientific Co., Edison, N.J.). The fermentor jar containing 3.5 l of

Results

The A. niger productivity of mycelia dry weight, after the completion of fermentation process, was recorded to be 11.34 g/l, whereas the produced chitosan weight was 1.32 g/l of fermentation medium. The chitosan yield (g of chitosan/g of dry biomass × 100), however, was calculated to be of 11.64%.

The physico-chemical characteristics of produced fungal chitosan were the deacetylation degree of 89.6%, a molecular weight of 25,000 dalton (Da) and 97% solubility in 1% acetic acid solution (pH 5.0)

Discussion

The application of fungal chitosan in many fields could verify its biosafety and suitability for human use, and that was reported by many researchers [1], [3], [17]. The reported characteristics for the standard chitosan are the deacetylation degree (DD) of ≥75%, partial solubility in 1% acetic acid and a molecular weight (MW) of 190,000–>375,000 Da, however the corresponding physiochemical characteristics of the produced fungal chitosan (higher solubility of 97%, higher DD of 89.6% and lower MW

Conclusion

A. niger waste biomass, after citric acid production, could be considered as a beneficial source for high quality chitosan extraction. The produced fungal chitosan could be effectively applied for cotton fabrics finishing to have enhanced textiles with powerful antimicrobial activities. Chitosan-treated fabrics proved their efficiency to control bacterial and yeast growth, which recommends their application in medical and hygienic clothes fabrication.

Acknowledgement

Always and foremost, thanks are indebted to our God ALLAH forever for his mercy guiding and helping.

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