Entsar I. Rabea

A Biopolymer Chitosan and Its Derivatives as Promising Antimicrobial Agents against Plant Pathogens and Their Applications in Crop Protection

Recently, much attention has been paid to chitosan as a potential polysaccharide resource. Although several efforts have been reported to prepare functional derivatives of chitosan by chemical modifications, few attained their antimicrobial activity against plant pathogens. The present paper aims to present an overview of the antimicrobial effects, mechanisms, and applications of a biopolymer chitosan and its derivatives in crop protection. In addition, this paper takes a closer look at the physiochemical properties and chemical modifications of chitosan molecule. The recent growth in this field and the latest research papers published will be introduced and discussed.

Antimicrobial and inhibitory enzyme activity of N-(benzyl) and quaternary N-(benzyl) chitosan derivatives on plant pathogens.

Chemical modification of a biopolymer chitosan by introducing quaternary ammonium moieties into the polymer backbone enhances its antimicrobial activity. In the present study, a series of quaternary N-(benzyl) chitosan derivatives were synthesized and characterized by (1)H-NMR, FT-IR and UV spectroscopic techniques. The antimicrobial activity against crop-threatening bacteria Agrobacterium tumefaciens and Erwinia carotovora and fungi Botrytis cinerea, Botryodiplodia theobromae, Fusarium oxysporum and Phytophthora infestans were evaluated. The results proved that the grafting of benzyl moiety or quaternization of the derivatives onto chitosan molecule was successful in inhibiting the microbial growth. Moreover, increase water-solubility of the compounds by quaternization significantly increased the activity against bacteria and fungi. Exocellular enzymes including polygalacturonase (PGase), pectin-lyase (PLase), polyphenol oxidase (PPOase) and cellulase were also affected at 1000 mg/L. These compounds especially quaternary-based chitosan derivatives that have good inhibitory effect should be potentially used as antimicrobial agents in crop protection.

Synthesis and structure-activity relationship of N-(cinnamyl) chitosan analogs as antimicrobial agents.

The current study focuses on the preparation of new N-(cinnamyl) chitosan derivatives as antimicrobial agents against nine types of crop-threatening pathogens. Chitosan was reacted with a set of aromatic cinnamaldehyde analogs by reductive amination involving formation of the corresponding imines, followed by reduction with sodium borohydride to produce N-(cinnamyl) chitosan derivatives. The structural characterization was confirmed by (1)H and (13)C NMR spectroscopy and the degrees of substitution ranged from 0.08 to 0.28. The antibacterial activity was evaluated in vitro by minimum inhibitory concentration (MIC) against Agrobacterium tumefaciens and Erwinia carotovora. A higher inhibition activity was obtained by N-(α-methylcinnamyl) chitosan with MIC 1275 and 1025 mg/L against A. tumefaciens and E. carotovora, respectively followed by N-(o-methoxycinnamyl) chitosan (MIC=1925 and 1550 mg/L, respectively). The antifungal assessment was evaluated in vitro by mycelial radial growth technique against Alternaria alternata, Botrytis cinerea, Botryodiplodia theobromae, Fusarium oxysporum, Fusarium solani, Pythium debaryanum and Phytophthora infestans. N-(o-methoxycinnamyl) chitosan showed the highest antifungal activity among the tested compounds against the airborne fungi A. alternata, B. cinerea, Bd. theobromae and Ph. infestans with EC₅₀ of 672, 796, 980 and 636 mg/L, respectively. However, N-(p-N-dimethylaminocinnamyl) chitosan was the most active against the soil born fungi F. oxysporum, F. solani and P. debaryanum (EC50=411, 566 and 404 mg/L, respectively). On the other hand, the chitosan derivatives caused significant reduction in spore germination of A. alternata, B. cinerea, F. oxysporum and F. solani compared to chitosan and the reduction in spore germination was higher than that of the mycelia inhibition. The synthesis and characterization of new chitosan derivatives are ongoing in our laboratory aiming to obtain derivatives with higher antimicrobial activities and used as safe alternatives to harmful microbicides.

Strawberry Shelf Life, Composition, and Enzymes Activity in Response to Edible Chitosan Coatings

ABSTRACT A series of active biodegradable coatings based on chitosan, gelatin, starch, and sorbitol with or without monoterpenes (geraniol and thymol) were prepared and applied on fresh strawberry fruit as postharvest treatments. The coated fruits were inoculated with fungal spores of Botrytis cinerea and stored for 7 days at 4 °C. Decay incidence, weight loss, anthocyanins, total soluble solids (TSS), total soluble phenolics (TSP), polygalacturonase (PGase), pectin-lyase (PLase), antioxidant activity, guaiacol peroxidase (G-POD), polyphenol oxidase (PPO), and catalase (CAT) were elucidated in the fruits of experimental sets and they were compared with that of controls. The coatings showed a significant effect on the development of quality variables, with the additional effect of geraniol and thymol as a function of the polysaccharide matrix. The coatings inhibited decay incidence, reduced weight loss, delayed changes in the contents of anthocyanin, TSS, and total soluble phenolics; inhibited the increase in G-POD and PPO activities; and retarded the reduction in CAT activity. Compared to the controls, all of the coatings had positive effects on the inhibition of cell wall degrading enzymes (PGase and PLase) and among all the tested coatings, T5, chitosan (1%) + starch (1%) + sorbitol (0.5%) + tween (0.05%) + thymol (0.02%) was the best. This formulation showed also the highest antimicrobial activity and the greatest effect on other physiochemical parameters and it can be suggested to use it as a useful coating agent for extending the shelf-life and maintaining quality of strawberry fruit.

Inhibitory effects on microbial growth of Botrytis cinerea and Erwinia carotovora on potato using of a biopolymer chitosan at different molecular weights

The antimicrobial efficiency of chitosan at different molecular weights (5, 37, 57 and 290 kDa) against Botrytis cinerea and Erwinia carotovora on potato (Solanum tuberosum L.) was investigated. In vitro study showed that chitosan of 37 kDa was the most active against E. carotovora (minimum inhibitory concentration (MIC) = 950 mg/L), whereas 5 kDa chitosan was the most active against B.cinerea. Coating of potato tubers with 100, 250 and 500 mg/L significantly decreased the rate of weight loss and chitosan of 37 kDa showed the best effect. The in vivo antibacterial effect indicated that all treatments (500, 1000 and 2000 mg/L) significantly inhibited the growth of E. carotovora compared with the control. The lowest decay incidence was observed with 37 kDa chitosan. However, the antifungal activity against B. cinerea inoculated of leaves showed no decay incidence at 500 and 1000 mg/L with 57 kDa chitosan after 48 h.

The Antibacterial Activity of Chitosan Products Blended with Monoterpenes and Their Biofilms against Plant Pathogenic Bacteria.

This study focuses on the biological activities of eleven chitosan products with a viscosity-average molecular weight ranging from 22 to 846 kDa in combination with the most active monoterpenes (geraniol and thymol), out of 10 tested, against four plant pathogenic bacteria, Agrobacterium tumefaciens, Erwinia carotovora, Corynebacterium fascians, and Pseudomonas solanacearum. The antibacterial activity was evaluated in vitro by the agar dilution technique as a minimum inhibitory concentration (MIC) that was found to be dependent on the type of the microorganism tested. The most active product of chitosan was used for biofilm production enriched with geraniol and thymol (0.1 and 0.5%) and the films were also evaluated against the tested bacteria. The biological bioactivities summarized here may provide novel insights into the functions of chitosan and some monoterpenes and potentially allow their use for food protection from microbial attack.

Chitosan and Its Derivatives as Active Ingredients Against Plant Pests and Diseases

Summary Considerable developments have occurred over the years in pest and disease control worldwide. Pest and disease control for the past decades relied mainly in the application of synthetic pesticides. Numerous problems arose later due to their use, such as appearance of resistant strains, harmful effects on nontarget organisms, and potential impact on human health. The need, then, is for those concerned with problems of food production and protection to provide natural alternatives that can be safely used for pest and disease control. Among these alternatives, chitosan as a biopesticide has received a great deal of attention. In this chapter, we provide collective studies for understanding the biological activities of chitosan and its derivatives against most economical agricultural pests and diseases. Moreover, the chapter provides information on technological applications in agriculture, mechanisms of action, and the future prospects of pest and disease control products based on chitosan.

Synthesis and Antimicrobial Activity of N-(6-Carboxyl Cyclohex-3-ene Carbonyl) Chitosan with Different Degrees of Substitution

Five products of -(6-carboxyl cyclohex-3-ene carbonyl) chitosan as antimicrobial agents were prepared by reaction of chitosan with tetrahydrophthalic anhydride (THPA) at different degrees of substitution (DS). The antimicrobial activity was evaluated against four plant bacteria and eight fungi. The results proved that the inhibitory property and water solubility of the synthesized chitosan derivatives, with increase of the DS, exhibited a remarkable improvement over chitosan. The product with a DS of 0.40 was the most active one with MIC of 510, 735, 240, and 385 mg/L against Erwinia carotovora, Ralstonia solanacearum, Rhodococcus fascians, and Rhizobium radiobacter, respectively, and also in mycelial growth inhibition against Alternaria alternata (EC50 = 683 mg/L), Botrytis cinerea (EC50 = 774 mg/L), Botryodiplodia theobromae (EC50 = 501 mg/L), Fusarium oxysporum (EC50 = 500 mg/L), F. solani (EC50 = 260 mg/L), Penicillium digitatum (EC50 = 417 mg/L), Phytophthora infestans (EC50 = 298 mg/L), and Sclerotinia sclerotiorum (EC50 = 763 mg/L). These compounds based on a biodegradable and biocompatible chitosan could be used as potentially antimicrobial agents in crop protection instead of hazardous synthetic pesticides.

Current Applications in Food Preservation Based on Marine Biopolymers

Marine biopolymers, including polysaccharides such as alginate, carrageenan, chitin, chitosan and gelatin, are biocompatible, biodegradable and non-toxic to mammals and are widely used in a variety of industrial applications. In food, these biopolymers perform a number of functions including gelling and thickening aqueous solutions, as well as stabilizing foams, emulsions and dispersions, inhibiting ice and sugar crystal formation, preventing spoilage and control the release of additive materials. These food biopolymers play an important role in food structure, food functional properties, food processing and shelf life. They are generally hydrophilic due to the large number of hydroxyl groups, which confer high affinity for binding water molecules, so that they can be dispersed in water in the colloidal state. In this chapter, we provide recent collaborative studies of the application of some important biopolymers in food preservation. In addition, the chapter provides the latest technological applications and prospects of these products in food applications. It provides a better understanding of the food systems, improve food qualities, and make better use of food macromolecules.

Isolation, characterisation and efficacy of the bacterial strain Lysinibacillus sphaericus YMM in biodegradation of malathion insecticide in liquid media

ABSTRACT A new isolate of bacterium Lysinibacillus sphaericus YMM capable of degrading malathion insecticide in liquid media was isolated and characterised. Biodegradation factors were investigated using Plackett–Burman factorial design, and the rest of the insecticide was monitored by high-performance liquid chromatography analysis. The near optimum conditions for degradation of 200 mg malathion/L were 30 mL medium, 2% of L. sphaericus suspension (0.70 OD600nm), pH 5,10 g/L glucose, 1.0 g/L NaCl, 0.3 g/L MgSO4, 1.0 g/L NH4Cl and incubation for 24 h without yeast extract and peptone or beef extract. In addition, the significant variables including the medium volume, inoculum and incubation time were further optimised using Box–Behnken response surface design. These conditions were found to be 30.10% medium and inoculum of 0.706 (OD600nm) for 23.636 h of incubation to achieve 98.974% degradation. Therefore, L. sphaericus YMM showed a potential degradation of malathion. Further studies should be conducted to understand the mechanism of biodegradation in liquid media.