Extraction, encapsulation and in-vitro stomach digestion of mamaku extract : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Palmerston North, New Zealand

Abstract

Process development aimed to scale up the extraction of Mamaku, with a resulting yield of 56%wt/wt (mass of liquid extract/100kg of fronds) and 2.8%wt/wt (mass of freeze-dried material/100kg of fronds); this being higher than the yield previously obtained at a small scale (~1% freeze-dried Mamaku). The concentration of the liquid extract followed by freezing, as opposed to freeze-drying it, improved the shear-thickening properties of the Mamaku solutions. The critical temperature for processing was identified to be 63oC, whereby mamaku can be treated for 60 minutes without degradation. Higher temperatures were detrimental for the rheological properties of this polysaccharide, exhibiting a complete loss of shear-thickening when heated to 110oC. The shear- thickening properties of Mamaku solutions were also reduced when exposed to body temperature (37oC) and at the acidic pH found in the human stomach (pH 2-4). Encapsulation experiments aimed to allow mamaku to be swallowed safely, targeting release in the stomach in a hydrated form, and without incorporating calories if used as an ingredient in functional foods aiming to target weight loss. Gelatin was chosen as the encapsulating agent and 7.5%wt/v concentration was selected, being this quantity able to successfully trap concentrated mamaku (4.5%wt/wt), but also exhibiting a melting point high enough (~31oC) to avoid melting in the mouth when consumed. A number of different encapsulation techniques were trialled. The most promising technique was the fluid gel system. The nozzle techniques proved not be suitable for the properties of mamaku. The emulsion templating system showed challenges around removing the oil. The micro-injector based system produced beads likely to be too large for practical use in a food product. Limitations in the encapsulation techniques included: (i) a low mamaku concentration was used (4.5%wt/v—obtained after concentration) and (ii) the gelatin gel appeared to be unstable when transferred to an aqueous environment. The in-vitro stomach digestion results highlighted that encapsulated mamaku by gelatin will be released in the stomach, allowing the shear-thickening properties to re-form. Above 2.2%wt/v Mamaku, some shear thickening was observed (at high shear rates) after digestion of the Mamaku + gelatin mixtures. At least a 4.0%wt/v Mamaku concentration was needed in these mixtures, to obtain similar shear-thickening viscosity values after digestion, as those found by placing the mixture just under the acidic stomach conditions. Overall, a minimum of 10%wt/v of rehydrated mamaku should be delivered to the stomach to gain optimal shear-thickening properties at biological shear rates (1-10s-1) similar to those found at native pH (~pH 5.3). Overall, more research is needed to conclude about the viability of encapsulating Mamaku using gelatin as well as optimizing the encapsulation process based on fluid gel formation.