Studies of the encapsulation and release of carbon dioxide from amorphous and crystalline alpha-cyclodextrin powders and its application in food systems

Abstract

Carbon dioxide gas has been widely used in food production. Nevertheless, the conventional ways to utilize CO 2 gas have limitations in terms of safety, convenience, handling and storage. To offer a safe and convenient approach to use CO 2 gas, the production of food-grade CO 2 powder in which CO 2 release can be controlled was investigated. Conventionally, such gas powder has been produced via molecular encapsulation, accomplished by compression of the gas into either a solution of alpha-cyclodextrin (-CD) or crystalline -CD in a solid state. However, shortcomings (low yield or stability of the complex) of these techniques have prevented their actual application.In this project, an innovative method to produce CO 2 --CD complex powder with high yield and stability was investigated using amorphous spray-dried α-CD powder followed by crystallization of the complex. Due to a lack of understanding of amorphous α-CD powder properties and the complexities of conventional methods to quantify CO 2 in solid systems, the project commenced with the characterization of α-CD powders and the development of a simple system to determine the amount of encapsulated CO 2 .The study of the structure of α-CD powders revealed that spray drying of α-CD solution resulted in a completely amorphous powder (T g  83 o C). The differences in molecular structure between crystalline and amorphous α-CDs were illustrated by the analytical results of SEM, X-ray, FTIR, DSC, TGA and 13 C-NMR. The study of moisture sorption showed that an amorphous α-CD powder adsorbed more water than its crystalline counterpart at the same a w but it crystallized as it was equilibrated at higher than 65% RH (>13.70g moisture/100 g of dry solids).A simple system to quantify the CO 2 in the complex through measuring the amount of CO 2 released from the complex into an air-tight chamber headspace by using an infra-red CO 2 probe was designed and tested. The concentrations measured using this new system and conventional acidbase titration were insignificantly different (p > 0.05). This was also validated by the gas chromatography method.A study of solid encapsulation of crystalline (9.84% MC, w.b.) and amorphous (5.58% MC, w.b.) α-CD powders at 0.4-1.6 MPa for 0-96 h showed that amorphous α-CD encapsulated a much larger quantity of CO 2 than the crystalline form at low pressure and short time (p < 0.05). An increase in pressure and prolongation of the time increased encapsulation capacity (EC) of α-CD, especially for the crystalline form. The highest EC of crystalline α-CD was 1.45 mol CO 2 /mol α-CD, which was markedly higher than that of amorphous α-CD (0.98 mol CO 2 /mol α-CD). Solid encapsulation did iii not affect the structure of amorphous α-CD, but slightly altered the structure of crystalline α-CD.Peak representing the encapsulated CO 2 in the complex was clearly observed on the FTIR (2334 cm -1 ) and NMR (125.3 ppm) spectra. However, the complexes were not stable enough for actual application, especially those produced from amorphous α-CD.To impr...

Crystallisation properties of amorphous cyclodextrin powders and their complexation with fish oil

“…In a recent report by Ho (2017), an innovative encapsulation approach using CD powder which addresses the disadvantages of co-precipitation and paste methods was reported. In this approach (known as solid encapsulation), the CD powders must be in the amorphous structure, instead of the crystalline CD powders which are used in coprecipitation and paste methods.…”

“…Crystallisation of the amorphous complex powders during encapsulation process causes the guest molecules to be locked inside the CD cavity making them stable. This encapsulation approach was initially developed for CO 2 gas encapsulation using amorphous a-CD powder (Ho 2017). It was also successfully applied for tea tree oil encapsulation using amorphous b-CD powder (Shrestha et al 2017).…”