Influence of collapsed structure on stability of ��-carotene in freeze-dried mangoes

This study aimed to investigate the effect of structural collapse of freeze-dried mangoes on stability of ??-carotene. Three different freeze-drying protocols were performed to produce collapse and non-collapse structures of freeze-dried mangoes. Thermal transitions of samples were determined using a differential scanning calorimeter. ??-carotene content was monitored during storage using high-performance liquid chromatography. The ??-carotene degradation followed first-order kinetics. Mangoes freeze-dried at above ice melting temperature revealed structural collapse which decreased ??-carotene degradation rate. These dense and collapsed structures formed prevented oxygen penetration through the solids. Liquid nitrogen freezing also gave structural collapse coincided with surface cracking on freeze-dried mangoes. Such structure showed no protective effect on ??-carotene as similar degradation rate to non-collapsed systems was observed. The cracking on mango surface potentially allows high oxygen penetration through the solids thus promoting ??-carotene loss. These findings give benefit to the production of freeze-dried fruits to increase storage stability of ??-carotene.     

Development of starch-based peelable coating for edible packaging

This research characterised properties and stability of starch-based peelable coating film layers via mould dipping. Different ratios between rice starch (RS) and hydroxypropyl cassava starch (HS) containing agar blends were characterised for fluid rheology and properties of solid films. Layer-by-layer mould dipping in starch blend suspensions produced peelable shells. Rheology indicated that formability of thin-film layer on solid surface subsequently affected integrity of the shells. HS highly adsorbed water which plasticised matrices giving lower relaxation temperature (~10 °C) than RS and caused shrivelling and non-stable shell structures. RS increased crystallinity and non-homogeneity of films and reduced network flexibility and light transmission. IR spectra indicated modified hydrophobicity and hydrogen bonding of starch blends which governed water and oxygen permeability. Higher RS ratios significantly increased crystallinity which affected physical, mechanical and barrier properties during storage for three months. Findings indicated that HS provided flexibility and stability while RS improved formability of peeled shells.     

Characterisations of cassava starch and poly(butylene adipate-co-terephthalate) blown film with silicon dioxide nanocomposites

Films with high permeability are necessary for the packaging of agricultural products that respire to avoid anoxic conditions. This research developed and characterised bioplastic nanocomposite films with enhanced permeation and increased strength. Thermoplastic starch (TPS) was compounded with silicon dioxide (SiO₂) and blended with poly (butylene adipate-co-terephthalate) (PBAT) to produce bioplastic PBAT/TPS blend films via blown-film extrusion. Different SiO₂ contents (0.5%–1%) were dispersed in the matrices, causing interaction via hydrogen bonding with the TPS phase. SiO₂ at 1% significantly improved melting of the polymer blends, giving increasing amorphous ratios of the polymeric films. Microstructures and surface topography indicated voids between incompatible components and porous structures that improved permeation. Increasing SiO₂ content linearly enhanced oxygen and water vapour permeability by up to 39% and 16%, respectively. Tensile strength and elongation at break increased and decreased up to 40% and 32%, respectively, indicating increased rigidity due to adding solid nanoparticles to 1%. Migration phenomena of the film components, that is molecules with diol structures and silicon compounds depended on types of simulant and microstructures that induced swelling and release of the compounds. Film permeabilities increased, thereby facilitating air and humidity flow through the packaging.     

Properties and release kinetics of pine bark incorporated agar and carrageenan film

Effects of plasticisers (glycerol, sorbitol and polypropylene glycol) and blend ratios on release behaviour, molecular vibration, mechanical and water barrier properties in agar and carrageenan films incorporating pine bark extract were investigated. Infrared spectra indicated hydrogen bonding of sorbitol and polypropylene glycol with film polymers which improved water diffusion and agar solubility but showed no effect in carrageenan films due to high water affinity. Hydrophilicity of the plasticisers modified dissolution of films and strongly affected the release behaviours of polyphenols and antioxidant capacity (DPPH• and FRAP). Film solubility showed high correlation to release behaviours. Fick’s diffusion kinetics fitted well to release behaviour of pine bark to aqueous media (water, 3% acetic acid and 10% ethanol). Agar gave a higher diffusion coefficient that was improved by the addition of sorbitol and polypropylene glycol. Increased diffusion coefficients enhanced degree of release, with some diversions suggesting that solvent modified matrices and, hence, release properties.     

Structure–property modification of microcrystalline cellulose film using agar and propylene glycol alginate

Microcrystalline cellulose gum (MCG) forms edible films with poor physical and barrier properties. This study investigated the effects of incorporated agar and propylene glycol alginate (PGA) on structure and property of MCG films. The addition of agar and PGA modified the microstructure and reduced pinholes contributed to lower water vapor permeability (WVP) and improved tensile property of agar–MCG films. However, PGA–MCG had reduced tensile strength possibly due to incompatibility between polymer networks, however, showed a synergistic light barrier. The increased surface hydrophobicity (θ ～ 30°–75°) correlated well with decreased WVP for agar, PGA, and their composites which diverted from pure MCG films. The MCG reduced the thermal stability of agar; however, the PGA had no effect. Conversely, agar and PGA increased the thermal stability of the MCG component. The infrared spectra revealed insignificant H‐bonding and molecular interaction between polymers. Therefore, the results indicated that agar and PGA improved stability, mechanical, and barrier properties of edible MCG films via physical entanglement. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45533.     

Edible packaging from hydroxypropyl thermoplastic cassava starch,agar and maltodextrin blends produced by cast extrusion

Edible packaging from hydroxypropyl cassava starch with different degrees of substitution (DS), agar and maltodextrin films was produced by conventional cast extrusion. Microstructures showed hydrophobic agar aggregates (100–200 µm) dispersed in film matrices, giving nonsmooth surfaces that enhanced wettability (17%–31%). Higher DS increased interaction between agar and maltodextrin via hydrogen bonding due to greater plasticisation and enhanced formation of agar networks. Lower DS starch showed instability with lower tensile strength (23% of higher DS), giving poor processability that was greatly improved by agar (20%). Water vapour and oxygen permeability depended on microstructures and hydrophilic–hydrophobic properties of the matrices which were decreased by 25% and 58% with combined agar and maltodextrin, respectively. Crystallinity of the films depended on plasticisation, with enhanced mobility that reduced transparency. Agar and maltodextrin inhibited recrystallisation of starch. Findings suggested that higher DS starch and agar enhanced extrusion processability, while maltodextrin increased plasticisation and reduced network strength.     

Effect of water activity on sugar crystallization and β-carotene stability of freeze-dried mango powder

Storage water activity (a_w) affects the stability of freeze-dried food. The sugar crystallization and storage stability of β-carotene in freeze-dried mango powder was investigated following storage under various relative vapor pressures (11.3-80.9%). Sugar crystallization was revealed by the loss of sorbed water in the water sorption experiment. However, the sorption isotherms showed unclear divergence between the experimental and predicted values. X-ray powder diffraction and scanning electron microscopy were used to confirm the crystallization. The results showed that increased a_w resulted in higher sugar crystallization. The loss of β-carotene was monitored by high-performance liquid chromatography with a diode-array detector and fitted to a first-order reaction. The rate constant decreased as a_w increased up to 0.43, due to the collapse of the mango powder. An increase in the rate constant above this value of a_w coincided with pronounced sugar crystallization. Choosing the appropriate value of a_w for storage can prevent sugar crystallization and enhance β-carotene stability in freeze-dried fruit powder.     

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

Abstract: Stability of entrapped crystalline β‐carotene as affected by water activity, solids microstructure, and composition of freeze‐dried systems was investigated. Aliquots (1000 mm³, 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.