Development and optimisation of canola protein isolate and chitosan complex coacervate

Chang, P 2019, Development and optimisation of canola protein isolate and chitosan complex coacervate, Doctor of Philosophy (PhD), Engineering, RMIT University.


Document type: Thesis
Collection: Theses

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Title Development and optimisation of canola protein isolate and chitosan complex coacervate
Author(s) Chang, P
Year 2019
Abstract Complex coacervation - a process in which liquid-solid phase separation occurs as two oppositely charged polymers undergo complexation in an aqueous medium - has been of great interest in recent years due to the high strength of the complex coacervates produced.

Complex coacervates have many novel applications including for microencapsulation purposes, controlled delivery applications, edible films and many other applications in the food and pharmaceutical industries. The most important industrial application of complex coacervation is in the microencapsulation of sensitive ingredients in the food and pharmaceutical industries. Coacervates have become more important with the food and pharmaceutical industries expecting increasingly complex properties from food and pharmaceutical ingredients. Despite all the interest and previous research, there are still big opportunities for improvement in identifying a new and novel complex coacervates and its application in encapsulation. Hence, in this thesis, a new and novel complex coacervate, canola protein isolate-chitosan complex coacervate (highly nutritional, underutilised, abundantly available food waste) was identified and studied. Food-grade complex coacervates, in which the cationic and anionic polymers are both of food grade, such as canola protein isolate (CPI) and chitosan (Ch), are desired due to their nutritional benefits and superior functional properties in stabilizing unstable food ingredients such as edible oils, enzymes and flavours against oxidation or degradation, as well as providing controlled release of sensitive ingredients.  The concept of controlled release of the encapsulated ingredient at the right place and the right time is receiving more and more interest. Controlled release of the ingredients can improve the effectiveness of food additives, broaden the application range of food ingredients, and ensure optimal dosage of substances / ingredients.
The focus of this research was on the development and optimization of a complex coacervate that would be compatible with encapsulation of thermally sensitive edible oil. For this purpose, a protein and polysaccharide, namely canola protein isolate and chitosan, were selected to yield a novel, compatible pair of complex coacervate, with many potential benefits ensuing from the recycling of huge amounts of highly nutritious canola meal wastes into high-value products.

Canola protein isolate-chitosan (CPI-Ch) complex coacervates were produced through the complex coacervation process using purified canola protein isolate and chitosan with varying ratios between 1:1 and 30:1, at pH values of 4.0 to 8.0. The complex coacervation phenomenon occurring between canola protein isolate and chitosan was studied. The developed CPI-Ch complex coacervates were characterized using a variety of techniques to determine the optimum CPI-Ch complex coacervate conditions for the highest product yield and quality. The optimum CPI-Ch complex coacervate was used to test its application in encapsulating canola oil, which has good potential for commercial application in the frozen food industry.

The factors affecting the yield of CPI-chitosan complex coacervates such as CPI-to-chitosan ratio, pH and strength of the electrostatic interaction (SEI) were investigated. The optimum complex coacervation between CPI and Ch occurred at the CPI-to-chitosan mass ratio of 16:1 and a pH of 5.8-6.2, which was reflected in the high complex coacervate turbidity and yield value at that condition. This was consistent with the maximum SEI value for CPI and chitosan, which was found to be highest at pH 6.0. At this pH, CPI and chitosan exhibited their highest binding strength, an important parameter for complex coacervation.
CPI-Ch complex coacervate functional groups were determined using Fourier-transform infrared spectroscopy (FTIR). The CPI-chitosan coacervates (crosslinked and uncrosslinked) contained functional groups that were a combination of those present in CPI and chitosan, with minor shifts and domination by the CPI functional groups due to the high CPI-to-chitosan ratio. The thermal characteristics of CPI-Ch complex coacervates were determined using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The peak denaturation temperature and the denaturation enthalpy of CPI in CPI-chitosan complex were higher than those of the free CPI, indicating that the coacervation made the CPI more thermally stable. The increased thermal stability of CPI in CPI-chitosan coacervate indicates that CPI-chitosan complex coacervate would be suitable for encapsulation of thermally sensitive food and pharmaceutical ingredients.

Rheology studies were conducted and it was thereby found that the CPI-chitosan coacervates exhibited elastic behaviour, as evidenced by significantly higher elastic modulus (G') compared to viscous modulus (G") in all the tested ratios and pH ranges. They also exhibited shear-thinning behaviour during viscous flow. The complex coacervates formed at the optimum CPI-to-chitosan ratio of 16:1 and pH of 6.0 manifested the highest G' and G", which correlated well with the strength of electrostatic interaction (SEI), indicating the establishment of a strong intermolecular network in the coacervate at this CPI to chitosan ratio and pH. G' and G" were also found to decrease with temperature.

Scanning electron microscopy (SEM) micrographs were acquired to elucidate the microstructural network and explain its effects that underpin the rheological behaviour. The SEM micrographs revealed that the CPI-Ch coacervates had a sponge-like microstructure. Thick-walled, sponge-like, less porous microstructure was observed at the optimum CPI-to-chitosan ratio of 16:1 and pH of 6.0, which correlated well with the overall CPI-Ch complex coacervate characteristics and rheological results. The complex coacervates at a CPI-to-chitosan ratio of 16:1 and pH of 6.0 also showed glassy consistency at low temperatures and rubbery consistency above their glass transition temperature, demonstrating the potential application of these complex coacervates as effective encapsulants for unstable food ingredients.

Canola oil microcapsules were produced using CPI-Ch complex coacervate, aiming for controlled release and to improve the oil's oxidative stability. It was evident from the micrographs that the production of microcapsules of canola oil formed under various conditions with CPI-Ch complex coacervate as the wall material was functionally successful. They were larger in size, had lower polydispersity, and higher encapsulation efficiency. They also had superior oxidation stability overall compared to those with either CPI alone or Ch alone as the wall material, although microcapsules with CPI as the wall material did exhibit the minimum secondary oxidation (hexanal production in the 27-day accelerated storage test). It was found that the ratio of oil to CPI-Ch complex coacervate had a significant impact on the microcapsules: encapsulation efficiency increased with decreasing oil to CPI-Ch complex coacervate ratio, and the highest observed encapsulation efficiency of 86% was achieved at an oil to CPI-Ch complex coacervate ratio of 1:2.

It can be concluded from this study that the potential utilisation of CPI-Ch complex coacervate as an encapsulant for liquid capsules containing a hydrophobic ingredient such as canola oil has been proven feasible at the laboratory bench scale, and has great potential for future full-scale commercial applications requiring microcapsule wall materials.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Engineering
Subjects Food Processing
Rheology
Keyword(s) Complex coacervate
Canola protein isolate
Encapsulation
Microcapsules
Food protein
Food waste
Environmentally friendly
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Created: Wed, 03 Jul 2019, 12:46:12 EST by Adam Rivett
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