Worldwide, millions of tons of crustaceans are produced every year and consumed as protein-rich seafood. However, the shells of the crustaceans and other non-edible parts constituting about half of the body mass are usually discarded as waste. These discarded crustacean shells are a prominent source of polysaccharide (chitin) and protein. Chitosan is a de-acetylated form of chitin obtained from the crustacean waste that has attracted attention for applications in food, biomedical, and paint industries due to its characteristic properties, like solubility in weak acids, film-forming ability, pH-sensitivity, biodegradability, and biocompatibility. We present an overview of the application of chitosan in composite coatings for applications in food, paint, and water treatment. In the context of food industries, the main focus is on fabrication and application of chitosan-based composite films and coatings for prolonging the post-harvest life of fruits and vegetables, whereas anti-corrosion and self-healing properties are the main properties considered for antifouling applications in paints in this review.

Hordein electrospun ultra-thin fibers are unstable in an aqueous environment. Chitosan was added to improve their water resistance. With increasing chitosan concentration, the viscosity and conductivity of the biopolymer blends increased, and the surface tensions remained almost constant. The structure and morphology of composite biopolymer fiber membranes showed that the average fiber diameter varied with chitosan concentration. ATR-FTIR spectra showed that the C–H stretching band changed or disappeared with increased chitosan. X-ray diffraction showed that chitosan was distributed in hordein fibers without crystallites. Compared with the hordein nanofibers, thermogravimetric analysis and derivative thermogravimetry curves showed that hordein/chitosan electrospun fibers had slightly decreased thermal stability. In conclusion, a low chitosan content improved the water resistance and other properties of hordein fibers, without changing their morphology or structure.

In this work we demonstrate that the synergistic combination of organic molecules extracted from food waste can empower different types of carboxylated gold nanoparticles (Au NPs) in removal of Cr(VI) species from both milliQ and real water solutions. In particular, chitosan extracted from shrimp’s shell and dissolved in an acidic active medium based on a 1:3 M mixture of ascorbic and citric acid allows citrate-capped Au NPs to improve their abatment efficiency from 18.4 to > 99% in milliQ and 80.6% in drinking water. When citrates are exchanged with 3-mercaptopropionic or 11-mercaptoundecanoic acids, the efficiency reaches 100% in both milliQ and drinking water. 11-mercaptoundecanoic acid is found to be the best capping agent in terms of efficiency and stability. Crossing of cyclic voltammetry and UV–Vis data enabled to define the main role of each individual component in abatment of Cr(VI). This study further advances research on the rational design of hybrid nanoparticle/polymer systems for environmental remediation, inspired by criteria of circular economy and environmental sustainability.

The synthesis of new chitin derivatives through ultrasound-assisted treatment of the chitin with 1-azido-3-chloropropan-2-ol under Green Chemistry conditions is described. This is the first example of ultrasound-assisted polymer analogues transformation of chitin unaccompanied by noticeable backbone degradation or deacetylation. The obtained water-soluble azido chitin derivatives are characterized by high antibacterial activity, which is comparable with that of commercial antibiotics ampicillin and gentamicin. At the same time, they were demonstrated almost identical in vitro toxicity as unmodified chitin and chitosan. The antibacterial activity of the obtained polymers is mainly provided by azido moiety in their macromolecules. The conjugation of azido moiety to chitin backbone strongly diminishes the toxicity of the azido pharmacophore, but preserves its antibacterial properties. The most potent chitin derivative was used for the film coating of Ricotta cheese samples. This food coating proved to be efficient for the prolongation of shelf life of Ricotta cheese.

In the present study, a well-defined set of chitosans, with different degrees of acetylation (DA) and degrees of polymerization (DP), were processed by solution electrospraying from a water-based solvent. The solution properties, in terms of surface tension, conductivity, viscosity, and pH, were characterized and related to the physico-chemical properties of the chitosans. It was observed that both DA and DP values of a given chitosan, in combination with biopolymer concentration, mainly determined solution viscosity. This was, in turn, the major driving factor that defined the electrosprayability of chitosan. In addition, the physico-chemical properties of chitosans highly influenced solution conductivity and results indicated that the chitosan solutions with low or low-to-medium values of conductivity were the most optimal for electrospraying. The results obtained here also demonstrate that a good process control can be achieved by adjusting the working conditions, i.e . applied voltage, flow-rate, and tip-to-collector distance. Finally, it was also shown that electrosprayability of chitosan with inadequate physico-chemical properties can be improved by solution mixing of very different kinds of this polysaccharide. The resultant electrosprayed submicron chitosan capsules can be applied for encapsulation of food additives and to develop bioactive coatings of interest in food packaging, where these particles alone or containing functional ingredients can be released from the package into the food to promote a health benefit.

Water-based chitosans in the forms of oligochitosan (OligoCS) and nanowhisker chitosan (CSWK) are proposed as a novel food preservative based on a minced pork model study. The high surface area with a positive charge over the neutral pH range (pH 5–8) of OligoCS and CSWK lead to an inhibition against Gram-positive (Staphylococcusaureus, Listeriamonocytogenes, and Bacilluscereus) and Gram-negative microbes (Salmonellaenteritidis and Escherichiacoli O157:H7). In the minced pork model, OligoCS effectively performs a food preservative for shelf-life extension as clarified from the retardation of microbial growth, biogenic amine formation and lipid oxidation during the storage. OligoCS maintains almost all myosin heavy chain protein degradation as observed in the electrophoresis. The present work points out that water-based chitosan with its unique morphology not only significantly inhibits antimicrobial activity but also maintains the meat quality with an extension of shelf-life, and thus has the potential to be used as a food preservative.

The potential isolation of bio-active polysaccharides from bay tree pruning waste was studied using sequential subcritical water extraction using different time-temperature combinations. The extracted polysaccharides were highly enriched in pectins while preserving their high molecular mass (10–100 kDa), presenting ideal properties for its application as additive in food packaging. Pectin-enriched chitosan films were prepared, improving the optical properties (≥95% UV-light barrier capacity), antioxidant capacity (˃95% radical scavenging activity) and water vapor permeability (≤14 g·Pa⁻¹·s⁻¹·m⁻¹·10⁻⁷) in comparison with neat chitosan-based films. Furthermore, the antimicrobial activity of chitosan was maintained in the hybrid films. Addition of 10% of pectins improved mechanical properties, increasing the Young's modulus 12%, and the stress resistance in 51%. The application of pectin-rich fractions from bay tree pruning waste as an additive in active food packaging applications, with triple action as antioxidant, barrier, and antimicrobial has been demonstrated.

PhDENV | Department of Geography and Environmental Sciences | In the past few decades, South Africa's freshwater resources have faced a severe problem of eutrophication and frequent occurrence of cyanobacterial blooms. This is of great concern since some of the cyanobacteria species have the potential to produce cyanotoxins that pose health risks to livestock and humans. Recently, there have been evidence of the toxic effects of microcystins (MCs) and cylindrospermopsin (CYN) on terrestrial plants including plants used for food. Ever since, the use of surface waters contaminated with cyanobacteria and cyanotoxins for agricultural purposes has been receiving growing attention. In hypereutrophic waters, such as commonly found in impoundments around major metros in South Africa, MCs co-exist with other pollutants such as metals and Linear Alkylbenzene Sulfonates (LAS), and these can have synergistic effects on the crops irrigated by such waters and exacerbate the human health risks posed by MCs. The current study investigated the bioaccumulation and effects of MCs on food plants, developed and evaluated the use of crosslinked chitosan (sorbents) passive samplers to monitor the bioavailability of MCs in water intended for irrigation. The findings are presented in six major sections. The first section detailed literature on the impacts of cyanotoxins on food plants with emphasis on the South African context. The reviewed literature demonstrated the potential of exposure of irrigated plants to multiple stressors such as MCs, LAS, metals, endocrine disrupting chemicals (EDCs) and high levels of dissolved salts around South Africa’s urban provinces. The literature also showed that South Africa lacks research on human exposure to cyanotoxins via irrigated crops and regulations to manage emerging pollutants such as MCs in irrigation water. Such lack of data and policies thus prompts an urgent need for local evidence-based research to guide policies and guidelines on cyanotoxins in irrigation water, food plants and, water used for livestock. In the second part of the thesis, the bioaccumulation of MCs in parts of the plants Brassica oleracea (cabbage) and Solanum tuberosum (common potato) was investigated in pot-culture experiments. Water used to irrigate the plants was collected from Roodeplaat Dam and had total MCs ranging from 0.12–2.84 μg L-1. The pH for the water was slightly alkaline (pH 7.29±0.71 to 10.03±0.29) whilst the Electrical Conductivity (EC) ranged from 296.67±13.87 to 878.67±42.44 μS cm-1. The findings showed that the two plants can bioaccumulate MCs to concerning levels when irrigated with water derived from Roodeplaat Dam. MCs accumulation levels in the two tested plants ranged from 0.00142 to 0.136 mg kg-1 DW for individual MC congeners. These findings demonstrated that terrestrial food crops can bioaccumulate MCs to levels that can pose human-health risks. v The third part of the thesis investigated the uptake and accumulation of metals Al, Mn and Sr in distinct parts of the plants Brassica oleracea and Solanum tuberosum in the presence of the anionic surfactant LAS. Pot-culture experiments were conducted to assess the effect of LAS on the accumulation of the three metals by watering the plant with Roodeplaat dam water containing 3.48 mg L-1 of LAS and Mn (0.257mgL-1), Al (0.6mgL-1) and Sr (0.16mgL-1). Findings indicated that the presence of LAS, in the irrigation water, did not enhance the uptake of Sr, Mn and Al by the two plants as demonstrated by the comparable levels of the metals in plants exposed to the metals in presence and absence of LAS. The fourth section investigated the uptake and the accumulation of MCs in distinct parts of the plants B. oleracea and S. tuberosum in the presence of the anionic surfactant LAS. Pot-culture experiments were conducted with the two plant species watered Roodeplaat dam water containing 3.48 mg L-1 of LAS and MCs with mean concentrations of: MC-LR: 10.47±3.879; MC-RR: 6.158± 4.127 and MC-YR: 8.160 ± 2.544 μg L-1. Findings indicated that the presence of LAS in the irrigation water at the levels investigated did not enhance the uptake of MCs by the two plants, even though in some cases the levels of MCs bio-accumulated by the two plants exceeded WHO-recommended tolerable daily intake (TDI). These findings imply that, the tested levels of LAS and MCs did not have any synergic effects on the two plant species. The fifth part of the thesis focused on the synthesis of a composite of glutaraldehyde-crosslinked chitosan and multiwalled carbon nanotubes (ChMWCNT) for application in the Solid Phase Adsorption Toxin Tracking (SPATT) for monitoring MCs in freshwaters. Batch experiments were conducted to evaluate the adsorption efficiency of the composite. The composite was found to be efficient in adsorbing MC-LR showing 97% removal and maximum adsorption capacity of 4.639 μg g-1 under optimized conditions of 5 μg L-1 of MC-LR, adsorbent dose of 0.03g 5 mL-1, and contact time of 30 mins. For desorption, 100% methanol was most effective, with efficiency of 84.71 %. When applied for the adsorption of MCs in raw dam water, the composite was saturated within two days of exposure and effectively adsorbed and desorbed three congeners tested in the order MC-LR>MC-RR>MC-YR. The last part of the thesis evaluated the field applicability of the newly synthesised glutaraldehyde crosslinked chitosan hydrogel (ChGLA) and the composite of glutaraldehyde-crosslinked chitosan and multiwalled carbon nanotubes (ChMWCNT) in a SPATT bag format and compare them to the commonly used DIAION HP20 resin. The constructed SPATT samplers were deployed in canals and farm dams around Roodeplaat and Hartbeespoort Dam sites. The findings elucidated a good vi correlation between the MCs detected by the two newly synthesized sorbents (ChGLA and ChMWCNT) and grab samples. The detected total MCs for the ChGLA samplers were: 0.003 and 1.742 (μg g-1) and for the ChMWCNT samplers 0.006 and 3.300 (μg g-1) (lowest and highest respectively). In conclusion, the two plants were found to accumulate MCs to levels that can pose human-health risks when water derived from the Roodeplaat Dam was used for irrigation. The effects of other pollutants such LAS found in hypereutrophic water bodies on the uptake and accumulation of MCs in food plants was for the first times tested on terrestrial food plants. The findings showed that the presence of LAS had no impact on the uptake of MCs and heavy metals such as Al, Mn and Sr. For the first time, chitosan-based sorbents were synthesized and applied in SPATT for MCs. The use of the chitosan sorbents demonstrated a lot of promise for the monitoring of MCs in water and can possibly be used as an early warning sign for the presence of MCs in irrigation water derived from eutrophicated impoundments in South Africa. | National Research Foundation (NRF)

Among oral delivery systems, oil in water nano-emulsions (O/W NEs) are of particular interest to improve pharmacokinetics of lipophilic compounds. Recently, we have implemented a successful strategy to improve O/W NEs stability, based on a polymeric coating on an oil core, namely secondary O/W NEs, through the use of pharma grade formulations. However, in the field of food supplements, food grade materials are the top choice since they combine safety and cost effectiveness. Here, we have replaced pharma grade (PG) with food grade (FG) materials in the preparation of the polymer coated O/W NEs, and performed a comparative study between the two formulations to assess the FG one. At the same time, in order to provide formulations with enhanced mucus-adhesion to the intestinal barrier, secondary O/W NEs were prepared by adding thiol groups to chitosan (Ct) via a simple non-covalent procedure based on N-acetyl-cysteine (NAC) salification, thus easily implementable to a food supplement formulation. PG and FG formulations, in different materials combinations, were prepared and physico-chemically characterized (DLS, ¹H NMR, ITC, CRYO-TEM) showing similar behaviour. FG formulations (NEs, Ct-NEs and Ct-NAC-NEs) loaded with curcumin were prepared and compared with the free drug in terms of drug bioaccessibility through the INFOGEST protocol confirming improved bioaccessibility. Very interestingly, by comparing mucus-adhesion properties of the two polymeric coatings (Ct and Ct-NAC) within an intestine on chip device able to mimic the complex intestinal functions, a significant enhancement in the mucus-adhesive properties of the proposed novel Ct-NAC-NE formulation was observed with respect to Ct due to the presence of thiol groups. Nonetheless, in-vivo assays are required as a final assessment of the proposed system.

Compatibility of CNF with three polysaccharides having different surface charges and backbones (chitosan, methyl cellulose, and carboxymethyl cellulose) was investigated. Chitosan (CH) incorporation reduced water absorption (WA) of CNF films (P < 0.05). CH molecular weight (Mw) (68, 181, 287 kDa) and amount (10 and 20 g/100 g CNF in dry basis) impacted moisture barrier, mechanical, antibacterial, thermal, and structural properties of CNF films. Regardless of Mw, CH incorporation (20 g/100 g CNF) decreased (P < 0.05) WA of CNF films, and high Mw (287 kDa) CH (20 g/100 g CNF) incorporation resulted in lower film water solubility while increasing film water vapor permeability compared with low Mw CH (68 kDa) incorporation (P < 0.05). CNF film with low Mw CH (20 g/100 g CNF) exhibited antibacterial activity against L. innocua and E. coli. Interaction mechanisms between CH and CNF were investigated through thermal, structural, and morphology analyses using DSC, FTIR, and SEM, respectively. CNF films with low or high Mw CH incorporation (20 g/100 g CNF) were further validated as surface contact films for fresh beef patties, showing effectiveness to prevent moisture transfer between the layered patties. This study demonstrated the potential of using CNF-CH composite films as water resistant and antibacterial packaging for foods with high moisture surfaces.