Nathdanai Harnkarnsujarit

Porosity and Water Activity Effects on Stability of Crystalline β-Carotene in Freeze-Dried Solids

UNLABELLED Stability of entrapped crystalline β-carotene as affected by water activity, solids microstructure, and composition of freeze-dried systems was investigated. Aliquots (1000 mm(3) , 20% w/w solids) of solutions of maltodextrins of various dextrose equivalents (M040:DE6, M100:DE11, and M250:DE25.5), M100-sugars (1:1 glucose, fructose and sucrose), and agar for gelation with dispersed β-carotene were frozen at -20, -40, or -80 °C and freeze-dried. Glass transition and α-relaxation temperatures were determined with differential scanning calorimetry and dynamic mechanical analysis, respectively. β-Carotene contents were monitored spectrophotometrically. In the glassy solids, pore microstructure had a major effect on β-carotene stability. Small pores with thin walls and large surface area allowed β-carotene exposure to oxygen which led to a higher loss, whereas structural collapse enhanced stability of β-carotene by decreasing exposure to oxygen. As water plasticized matrices, an increase in molecular mobility in the matrix enhanced β-carotene degradation. Stability of dispersed β-carotene was highest at around 0.2 a(w) , but decreasing structural relaxation times above the glass transition correlated well with the rate of β-carotene degradation at higher a(w) . Microstructure, a(w) , and component mobility are important factors in the control of stability of β-carotene in freeze-dried solids. PRACTICAL APPLICATION β-Carotene expresses various nutritional benefits; however, it is sensitive to oxygen and the degradation contributes to loss of nutritional values as well as product color. To increase stability of β-carotene in freeze-dried foods, the amount of oxygen penetration need to be limited. The modification of freeze-dried food structures, for example, porosity and structural collapse, components, and humidity effectively enhance the stability of dispersed β-carotene in freeze-dried solids.

Thermal Properties of Freeze-Concentrated Sugar-Phosphate Solutions

In order to understand the effect of phosphate salts on the freeze-concentrated glass-like transition temperature (Tg′) of aqueous sugar solutions, two types of sugar (glucose and maltose) and five types of phosphate salts (Na3PO4, Na4P2O7, Na5P3O10, K3PO4, and K4P2O7) were employed, and the thermal properties of various sugar-phosphate aqueous systems were investigated using differential scanning calorimetry. The Tg′ of glucose increased with increasing sodium phosphates up to a certain phosphate ratio, decreasing thereafter. The maximum Tg′ value was slightly higher in the order of Na3PO4 > Na4P2O7 ≥ Na5P3O10. Maltose-sodium phosphate also showed a similar trend as glucose-sodium phosphate samples. However, the degree of Tg′-rise of maltose systems was much less than that of glucose. It is thought that the Tg′ elevated by the molecular interaction between sugar and phosphate ions will be reduced by hydrated sodium ions. In comparisons between potassium phosphate and sodium phosphate, it was found that sugar-potassium phosphates showed the lower maximum Tg′ at a lower phosphate ratio than sugar-sodium phosphates. In addition, the Tg′ of potassium phosphates dropped sharply in comparison with sodium phosphates at the high phosphate ratio. These results suggest that potassium phosphates are lower Tg′ than sodium phosphates, and that potassium ion plays a better plasticizer than sodium ion. A certain amount of sodium phosphates (Na3PO4 and Na4P2O7) caused devitrification. Potassium phosphates, however, did not show devitrification which can be explained by the fact that potassium ion can be dynamically restricted by sugar.

Effect of cellulose nanocrystals from sugarcane bagasse on whey protein isolate-based films

Whey protein isolate (WPI) has been utilized as edible film or food packaging material. However, WPI films are hydrophilic due to highly polar amino acids which provide a moderate barrier to water vapor and low mechanical properties. To overcome these drawbacks, cellulose nanocrystals (CNCs) extracted from sugarcane bagasse were incorporated with whey protein. FTIR and TGA were used to confirm the changes in chemical structures and to observe the thermal properties, respectively. The CNCs had sizes of 200-300 nm and diameters of 20-40 nm using TEM and AFM technique, respectively. Different amounts of CNCs (0-8 wt% based on WPI) were added into whey protein solution and formed films. The lightness and transparency of the films tended to decrease with increasing WPI content. The water activity (aw) and water solubility of those films increased, whereas their water contact angle values decreased, implying that the film became more hydrophilic when the cellulose nanocrystal was added. The addition of CNCs increased the tensile strength and Youngs modulus and reduced the water vapor permeability of WPI-based CNC films. However, the CNCs did not change the oxygen permeability of the film. Therefore, the obtained WPI films provided good mechanical performance and may be promising as an alternative product for film packaging.

Glass-Transition and Non-equilibrium States of Edible Films and Barriers

Abstract Edible films and barriers derived from polysaccharides, proteins and lipids provide several functions which prevent mass transfer, for example, water vapor, gas, and volatile compounds, between foods and environment. The preparation of materials can be either by solution casting commonly used in the laboratory or a more commercially extrusion process. Plasticizers are used to increase deformability reducing the glass transition temperature ( T g ) of the materials which can be determined using differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). This chapter also demonstrates the effects of plasticizers, other components, and treatments on the T g values of various edible films. Moreover, the non-equilibrium state of the edible film matrices causes several time-dependent changes during storage or “aging,” for example, plasticizer loss, lipid destabilization, and crystallization which subsequently impacts functional and mechanical properties of the films.

Mechanical and Thermal Properties of Toughened PLA Composite Foams with Modified Coconut Fiber

Composite foams from PLA, natural rubber and modified coconut fibers was prepared employing a compression molding method, which is suitable for the fabrication of composites containing high fiber content. The results revealed that the incorporation of natural rubber into composite foams increases the compressive stress to 101.17 kN/m2. Further, a 10% wt increase of modified coconut fiber added into composite foams resulted in an increase of compressive stress to 105.24 kN/m2. The addition of modified coconut fibers in composite foams showed a slight decrease of the crystallization state, obtained by DSC results by about 1-3 oC. Thus, modified coconut fibers played a role as a nucleating agent. Moreover, the combination of modified coconut fibers in composite foams could lead to improved adhesion between the surface area of PLA matrix and the natural rubber phase.