Browsing by Author "Matavire, Thokozani Olga"
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- ItemExtraction and modification of hemicellulose from wheat bran to produce entrapment materials for the controlled release of chemicals and bioactive substances(Stellenbosch : Stellenbosch University, 2018-03) Matavire, Thokozani Olga; Chimphango, Annie F. A.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH SUMMARY: Hydrogels are a network of cross-linked hydrophilic polymers that form an insoluble three-dimension structure capable of imbibing large amounts of fluid and they can be used as entrapment matrices for substances. However, synthetic polymers used for the formation of entrapment matrices cause health and environmental concerns, which leads to a need for environmental benign alternatives. Hemicellulose biopolymer is a potential replacement for the petroleum based materials as it is abundant, renewable and biodegradable. Agro-residues such as wheat bran are an abundant and affordable source of hemicellulose as they are not primary food products and would reduce environmental concerns related to their disposal. However, hemicellulose is bound to other components in a complex structure and extraction methods need to be carefully considered to maintain functional properties required for formation and performance of entrapment materials as slow release devices. Furthermore, hemicelluloses are water soluble due to the presence of side groups along the backbone and low molecular weight and that limits its application as insoluble entrapment matrices. The solubility of hemicellulose can be modified physically, chemically and enzymatically to produce insoluble entrapment matrices or hydrogels for the delivery of chemical and bioactive substances. The aim of this study was to develop insoluble entrapment matrices from soluble hemicellulose extracted from wheat bran agro-residue as delivery devices for chemical and bioactive substances. The type of hemicellulose extracted from wheat bran was arabinoxylan. The extraction of soluble arabinoxylan from wheat bran was performed using alkaline method after pre-treatment of wheat bran to remove starch. A full factorial design was used to determine the effects sodium hydroxide (NaOH) concentration, solid loading, extraction time and temperature on xylan extraction. A face centered central composite design was subsequently used to optimize the significant (p<0.05) factors sodium hydroxide concentration, extraction time and temperature with yield and purity as the dependent variables. The highest arabinoxylan yield and purity in terms of arabinoxylan content was 63% and 53%, respectively. The extracted arabinoxylans contained no monomeric sugars indicating that they were in polymeric form and thus were suitable to form stable hydrogels. The extracted hemicellulose was used to form insoluble hydrogels using: (1) coacervation method based on neutralizing an alkaline xylan solution with acid and (2) side chain removing enzyme α-arabinofuranosidase that cleaved the arabinose side groups along the xylan backbone. The hydrogels were applied as delivery systems for gallic acid. The hydrogels were assessed for size, stability, encapsulation efficiency of gallic acid, antioxidant activity of encapsulated gallic acid and chemical structure. The wheat bran arabinoxylan hydrogels formed were in nanosize range (469 – 678nm), however chemically formed hydrogels were smaller compared to enzymatically formed hydrogels. Enzymatically formed hydrogels had smaller size distribution with a polydispersity index (PDI) of up to 0.3 whilst chemically formed hydrogels had a broad size distribution and PDI of 1. In addition, the zeta potential of enzymatically formed hydrogels was more negative compared to chemically formed hydrogels. The more negative zeta potential indicated agglomeration of hydrogels is less, hence enzymatically formed hydrogels were more stable than chemically formed hydrogels. The encapsulation efficiency was up to 72% and 59% for chemically and enzymatically formed hydrogels, respectively. It is worth noting that encapsulating gallic acid before and after formation of hydrogels resulted in differences in encapsulation efficiency. The enzymatically formed hydrogels better preserved the integrity of encapsulated gallic acid with an antioxidant activity of 91% as compared to 80% for chemically formed hydrogels. The release of gallic acid was sustained when the encapsulation of gallic acid occurred during the formation of hydrogels as compared to encapsulation after the formation of hydrogels. Despite enzymatic hydrogels having lower encapsulation efficiency, they showed sustained release of encapsulated gallic acid. In conclusion, chemically and enzymatically modified wheat bran arabinoxylan hydrogels were formed with the ability to entrap and release gallic acid.