Browsing by Author "Mugwagwa, Lindleen Runyararo"
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- ItemFractionation of agro-waste to producebiopolymers and bioactive compounds for active food packaging(Stellenbosch : Stellenbosch University, 2020-12) Mugwagwa, Lindleen Runyararo; Chimphango, Annie F. A.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH ABSTRACT: The food packaging industry is faced with a need to find alternative raw materials to replace the non-renewable petroleum-based polymers and active compounds used in developing active food packaging material (packaging film capable of maintaining food quality by releasing antioxidants into food in response to temperature and time) and temperature-time indicators. Agricultural residues are a promising one-stop feedstock for biopolymers (hemicellulose, nanocellulose, pectin) and active compounds (polyphenols, anthocyanins) that can be used to develop renewable, biodegradable and non-toxic active food packaging and temperature-time indicators. However, the sequential or co-extraction of these raw materials from agricultural residues is hindered by the differences in the optimal extraction conditions of the products. Furthermore, the coexistence of these products with other plant material in biomass affects their effective recovery, downstream processing and end-application. On the application side, biocomposite films such as hemicellulose-based films made from agro-derivatives, completely disintegrate when in contact with aqueous solutions, hence, they cannot be used for packaging wet food, limiting their application only to dry foods packaging. In addition, the poor mechanical properties (tensile strength and Young‘s modulus) of these films hinder their application as alternative packaging to petroleum-based films such as low density polyethylene (LDPE). Manipulating and optimising the biopolymers and antioxidants extraction processes taking into consideration downstream modification processes and end-application, can be a strategy in tailor-making the properties of the agro-derivatives with the aim of developing active food packaging films with properties similar or better than LDPE-based active packaging. Furthermore, modifying and blending the biopolymers to form films and applying hydrophobic coatings to the films can further enhance film properties. Therefore, the aim of the study was to develop processes for fractionating wheat straw and mango peels to recover biopolymers and bioactive compounds and then integrate the products into bio-composite films for active food packaging applications, using LDPE films as benchmark. In addition, the application of bioactive compounds from agro-residues as temperature-time indicators was evaluated. To fulfill the aim, the first part of the project focused on optimising organosolv pre-treatment of wheat straw [ethanol (50–80 %)/sodium hydroxide (NaOH) (1–13%)/2–6 h] prior to hemicellulose extraction (10% NaOH/25 °C/24 h) so as to enhance hemicellulose acetylation, hydrophobicity, and the mechanical properties of hemicellulose-based films. A three-stage sequential extraction process was developed and optimised to recover anthocyanins (50–80% ethanol/0.1–2% acetic acid/25 °C/60–150 min), polyphenols (65–85% ethanol/75 °C/20–60 min) and pectin (0.25% ammonium oxalate-oxalic acid/85 °C/60 min) from mango peels. The second part involved the development and evaluation of hemicellulose-based films as active packaging material. The utilisation of a combination of nanocellulose (25% w/w) and pectin (hemicellulose/pectin ratio from 0% to 100%) as reinforcement and filler in hemicellulose-based films was investigated. Furthermore, the effects of modifying hemicellulose by acetylation, reinforcing the acetylated hemicellulose (AH) with acetylated nanocellulose (ACNC) of varying degrees of acetylation (DS 0–2.34) and loading (10–50%) and coating the AH/ACNC films with polycaprolactone (PCL) (0.3 g/L) on the films‘ mechanical properties, hydrophobicity and solubility in wet food simulants were assessed. Hemicellulose-based active packaging material was then formulated by doping the films with mango peel polyphenols. Antioxidant release by the hemicellulose-based active packaging material to different food simulants, was evaluated both experimentally (temperature range 5–40 °C for two days) and by using Migratest Exp. LDPE films doped with polyphenols were used as a benchmark. Lastly, the utilisation of anthocyanins as a time-temperature indicator was investigated by evaluating colour change of the anthocyanin/hydrogen phosphate buffer solution incubated at temperatures ranging from 5 °Cto 40 °C for three days. Organosolv pre-treatment optimal conditions [(1% NaOH/50% ethanol/6 h/75 °C)] of wheat straw enhanced the acetylation of the recovered hemicellulose (DS increased from 1.2 to 1.7) and in turn improved water resistivity (water contact angle (WCA) increased from 34.21° to 39.90°) of hemicellulose-based films. Increasing the reinforcing nanocellulose DS to 2.34, loading to 50% and coating the AH/ACNC films with PCL increased the films‘ Young‘s modulus from 55.23 to 335.33 MPa, tensile strength from 1.79 to 6.72 MPa, and WCA from 39.90° to 82.40°. There was no significant difference (p > 0.05) between the aforementioned results and the LDPE properties (Young‘s modulus 244.46 MPa, tensile strength 11.07 MPa and WCA 84.91°). The solubility of the hemicellulose-based films in the food simulants was reduced from 100% to 3.25% by the aforementioned modifications. Blending hemicellulose with pectin and nanocellulose improved the mechanical properties and reduced the solubility of the films in the fatty food simulant by up to 84%. Hemicellulose-based films released up to 98.54% whereas LDPE released 6.89% of the encapsulated polyphenols into food simulants, thereby increasing the antioxidant activity of the food simulant by up to 60% and 8.97% respectively. AH-based films were least soluble and had the highest antioxidant release in the fatty simulant when compared to the other simulants. Therefore, hemicellulose-based films can be utilised as alternative active packaging for short term storage (0–2 days) of fatty foods. Mango anthocyanins changed colour from orange to dark green with an increase in temperature from 0 °C to 40 °C and time 0 to 2 days, hence exhibiting temperature-time indicator properties. Overall, the study generated novel methods for manipulation of hemicellulose to increase its applications as a functional food packaging material. New information was generated when hemicellulose films were tested as active packaging in a food environment. This work also contributed to the development of agro-residue biorefineries for multiple product production and their utilisation for sustainable food packaging material development.