Thao M. Ho

Encapsulation of CO2 into amorphous and crystalline α-cyclodextrin powders and the characterization of the complexes formed

Carbon dioxide complexation was undertaken into solid matrices of amorphous and crystalline α-cyclodextrin (α-CD) powders, under various pressures (0.4-1.6 MPa) and time periods (4-96 h). The results show that the encapsulation capacity of crystalline α-CD was significantly lower than that of amorphous α-CD at low pressure and short time (0.4-0.8 MPa and 4-24 h), but was markedly enhanced with an increase of pressure and prolongation of encapsulation time. For each pressure level tested, the time required to reach a near equilibrium encapsulation capacity of the crystalline powder was around 48 h, which was much longer than that of the amorphous one, which only required about 8h. The inclusion complex formation of both types of α-CD powders was confirmed by the appearance of a CO2 peak on the FTIR and NMR spectra. Moreover, inclusion complexes were also characterized by DSC, TGA, SEM and X-ray analyses.

Encapsulation of CO2 into amorphous alpha-cyclodextrin powder at different moisture contents - part 1: encapsulation capacity and stability of inclusion complexes

This study investigated the effects of water-induced crystallization of amorphous alpha-cyclodextrin (α-CD) powder on CO2 encapsulation at 0.4-1.6 MPa pressure for 1-72 h through the addition of water (to reach to 13, 15 and 17% wet basis, w.b.) into amorphous α-CD powder prior to the encapsulation. The results showed that the α-CD encapsulation capacity was over 1 mol CO2/mol α-CD after pressurizing for longer than 48 h. The encapsulated CO2 concentration by the addition of water was considerably higher (p<0.05) than that of amorphous α-CD powder (5.51% MC, w.b.) without an addition of water and that of crystalline α-CD powders under the same MC and encapsulation conditions. A comparison of CO2 release properties (75% relative humidity, 25 °C) from complexed powders prepared from amorphous and crystalline α-CD powders under the same conditions is also presented.

Encapsulation of tea tree oil by amorphous beta-cyclodextrin powder.

An innovative method to encapsulate tea tree oil (TTO) by direct complexation with solid amorphous beta-cyclodextrin (β-CD) was investigated. A β-CD to TTO ratio of 90.5:9.5 (104.9mg TTO/g β-CD) was used in all complexation methods. The encapsulation was performed by direct mixing, and direct mixing was followed by the addition of water (13-17% moisture content, MC) or absolute ethanol (1:1, 1:2, 1:3 and 1:4 TTO:ethanol). The direct mixing method complexed the lowest amount of TTO (60.77mg TTO/g β-CD). Powder recrystallized using 17% MC included 99.63mg of TTO/g β-CD. The addition of ethanol at 1:2 and 1:3 TTO:ethanol ratios resulted in the inclusion of 94.3 and 98.45mg of TTO/g β-CD respectively, which was similar to that of TTO encapsulated in the conventional paste method (95.56mg TTO/g β-CD), suggesting an effective solid encapsulation method. The XRD and DSC results indicated that the amorphous TTO-β-CD complex was crystallized by the addition of water and ethanol.

Encapsulation of CO2 into amorphous alpha-cyclodextrin powder at different moisture contents - Part 2: Characterization of complexed powders and determination of crystalline structure.

This study aims to characterize CO2-α-cyclodextrin (α-CD) inclusion complexes produced from amorphous α-CD powder at moisture contents (MC) close to or higher than the critical level of crystallization (e.g. 13, 15 and 17% MC on wet basis, w.b.) at 0.4 and 1.6MPa pressure for 72h. The results of (13)C NMR, SEM, DSC and X-ray analyses showed that these MC levels were high enough to induce crystallization of CO2-α-CD complexed powders during encapsulation, by which amount of CO2 encapsulated by amorphous α-CD powder was significantly increased. The formation of inclusion complexes were well confirmed by results of FTIR and (13)C NMR analyses through an appearance of a peak associated with CO2 on the FTIR (2334cm(-1)) and NMR (125.3ppm) spectra. Determination of crystal packing patterns of CO2-α-CD complexed powders showed that during crystallization, α-CD molecules were arranged in cage-type structure in which CO2 molecules were entrapped in isolated cavities.

Methods to characterize the structure of food powders-a review

Food powders can exist in amorphous, crystalline or mixed structure depending on the order of molecular arrangement in the powder particle matrices. In food production, the structure of powders has a greatly effect on their stability, functionality, and applicability. The undesirable structure of powders can be accidentally formed during production. Therefore, characterization of powder structure as well as quantification of amorphous–crystalline proportions presenting in the powders are essential to control the quality of products during storage and further processing. For these purposes, many analytical techniques with large differences in the degree of selectivity and sensitivity have been developed. In this review, differences in the structure of food powders are described with a focus being placed on applications of amorphous powders. Essentially, applicability of common analytical techniques including X-ray, microscopic, vapor adsorption, thermal, and spectroscopic approaches for quantitative and qualitative structural characterization of food powders is also discussed. The common techniques to quantitatively and qualitatively characterize the structure (amorphous and crystallize) of food powders.

Method of Measurement of CO2 Adsorbed into α-Cyclodextrin by Infra-Red CO2 Probe

A simple CO2 probe system for quantifying CO2 gas adsorbed in solid matrix of α-cyclodextrin powder (α-CD) by measuring the gas concentration in the headspace was developed and validated. The essential components of this system are an infrared CO2 probe and an air tight chamber equipped with a two-fan system to uniformly mix the relatively high density CO2 gas. First, a known weight of dry ice (considered as pure CO2) was used to create different amounts of CO2 in the headspace of the chamber, and the resultant gas concentrations were measured by the probe and gas chromatography. The gas concentrations measured by both methods were quite similar (R2 = 0.9950), and the calculated amount of dry-ice in the headspace using the probe was highly comparable to the amount of dry ice initially added in the chamber (R2 = 0.9970). This system was then tested to measure adsorbed CO2 content in CO2-α-CD complexed powder by using water injection to release CO2 from the complexed powder into the headspace. The measured results using this system were quite similar (R2 = 0.9972) to those determined by a conventional acid-base titration method.

Spray-drying and non-equilibrium states/glass transition

In this chapter, the fundamental characteristics of spray drying are described with regards to its applications to alter the structure of food powders (crystalline or amorphous). Unlike amorphous powders which are in thermodynamically non-equilibrium state and tend to experience many phase transitions to obtain the lowest energy state, crystalline powders are stable and an alteration of its structure using spray drying involves two steps, disruption of the molecular order in crystal lattice and fast solidification to prevent molecules from orderly arrangement. As compared to other approaches, spray drying is the most effective technique to prepare amorphous powders due to its unique characteristics (fast and continuous process, diversity in capacity and designs, and ability to control crystallinity of produced powders). In the last part, differences about characteristics of crystalline and spray-dried amorphous alpha-cyclodextrin powders are shown as a case study of application of spray drying to change powder structure.

Dehydration of CO2-α-cyclodextrin complex powder by desiccant adsorption method and its release properties

Abstract Stability and release properties of CO2-α-cyclodextrin complex powder prepared by solid encapsulation (water activity, aw ≈ 0.95) followed by moisture removal using silica gel and CaCl2 desiccants during post-dehydration were investigated. The results showed that CaCl2 reduced aw much faster than silica gel did under the same conditions. After approximately 60 h, aw of complex powders reduced using silica gel was almost constant at 0.247 (±0.012), while those treated with CaCl2, aw was 0.225 (±0.005) and had not yet reached their lowest value. Moisture adsorption by silica gel and CaCl2 also led to a decrease in the CO2 concentration of complex powder (higher decrease for silica gel adsorption) without affecting the structure and morphology of complex powder. The CO2 release properties of CaCl2-aw-reduced complex powder at different relative humidities (32.73, 52.86, 75.32 and 97.30% RH), liquid environments (water and oil) and packaging methods (normal and vacuum) were also studied.

Methods to extend the shelf-life of cottage cheese - a review

Under typical refrigeration conditions (4–7 °C), unopened fresh cottage cheese only lasts for approximately 3 weeks unless preservatives are added. The spoilage of cottage cheese during storage is primarily due to the growth of Gram-negative psychrotrophic bacteria, yeasts and moulds. To extend its shelf-life, along with a strict sanitation practice throughout the manufacturing process, an appropriate preservation approach is generally applied. Many methods to preserve cottage cheese have been reported. These can be classified into three categories, namely food-grade chemicals, heat treatment and modified atmosphere packaging. In this review, factors responsible for the spoilage of cottage cheese during storage and the methods to extend its shelf-life are discussed.

Foaming properties and foam structure of milk during storage

Changes in foaming properties and foam structure of raw whole, raw skim, pasteurised whole, and pasteurised skim milk during storage at 4 °C, evaluated by mechanical mixing, air and steam injection, were investigated. The results showed that storage of milk until the end of their shelf-life (day 3 for raw milk and day 21 for pasteurised milk) did not induce any significant change in pH, particle size, viscosity and their foaming properties (foaming capacity, foam stability and size of air bubbles) although there was a slight increase in free fatty acid content. Regarding foaming methods, the air injection method produced much less foam volume than mechanical mixing and steam injection, except for raw milk where mechanical mixing showed the least foamability. However, an opposite trend was observed for foam stability. Although air injection induced the largest size of air bubbles, it produced the most stable foam, which was much more stable than foam produced by mechanical mixing and steam injection.