Effect of the viscoelastic properties of modified starch as a wall material on the surface morphology of microcapsules

Study of the interfacial viscoelasticity of human serum albumin microcapsules using a viscoelasto-electrohydrodynamic technique

Crosslinked proteins are widely used as the encapsulating membranes in microcapsules for many biomedical and food industries. The interfacial rheological properties of these capsules are due to the complex microstructure of cross-linked globular proteins owing to structural changes at quaternary, tertiary and secondary levels. These changes in structure can be induced by high protein concentration, hydrophobic-hydrophillic interfaces, and pH. In this work, the interfacial viscoelastic rheological properties of human serum albumin (HSA) microcapsules are estimated using a novel electrodeformation technique exhibiting creep and oscillatory responses. Insights into the microstructure-rheology relationship are obtained using FTIR and SEM studies. The results show a complex dependence of the interfacial properties on the size, concentration and pH of the capsules. An interplay of inter-molecular interactions, adsorption and multilayer formation, accessibility to reactive functional groups, and dependence on the relative content of alpha helix, beta sheet and beta turn is observed. The interfacial rheological properties are estimated using the Burger model and creep is found to sensitively affect the rheological properties due to irreversible changes in microstructure. Furthermore, the electrodeformation technique allows analysis of interfacial rheology at high frequencies, 10 Hz to 1 kHz, which is otherwise not easily possible with conventional rheometers.

Study of the Effect of Hydrolysis Time on the Mechanical Properties of Polysiloxane Microcapsules

It is known that the microstructure and thereby the mechanical properties of membranes constituting microcapsules are sensitive to parameters such as precursor concentration and pH. In the case of polysiloxane microcapsules, the oligomers, which are already formed in the continuous oil phase, because of the inherent moisture content in the oil phase, deposit on the membrane surface, resulting in the formation of a microstructure with a hairy layer. An electrodeformation investigation shows that the deposition of these oligomers is predominant in the smaller microcapsules compared to the larger ones and results in strain hardening and plasticity in the microcapsule membrane at high deformation. However, if the hydrolysis time during the synthesis of microcapsules is controlled, a smooth morphology (with a diminished hairy layer) can be realized for smaller capsules, as well. This work, using the electrodeformation method, demonstrates significant viscoelasticity and plasticity in the response of the capsules to applied electric stress and establishes an equivalence between simple spring and dashpot element-based phenomenological models with respect to the membrane properties using a linearized viscoelastic elasto-electrohydrodynamic model. The model can capture plasticity and strain hardening that are otherwise missed in simplified elasticity-based models.

Effects of particle formation behavior on the properties of fish oil microcapsules fabricated using a micro-fluidic jet spray dryer

Fish oil was encapsulated with whey protein isolate (WPI) as wall material using a Micro-Fluidic Jet Spray Dryer. The effects of core/wall material ratio, drying temperature and total solids content on the properties of microcapsules were studied. Low core/wall material ratios at 1:5 and 1:3 resulted in high encapsulation efficiency (EE) and excellent oxidative stability of microparticles during storage. Reducing the inlet temperature from 160 to 110 °C remarkably decreased EE from around 99 to 64.8%, associated with substantial increases in peroxide value during storage. The total solids content mainly altered the morphology of microcapsules, showing little influence on EE and oxidative stability. We proposed that the different drying conditions impacted on particle formation behavior during spray drying, which could be a crucial factor responsible for the differences in the quality attributes of microparticles. A low core/wall material ratio and high drying temperature facilitated the formation of a rigid protein skin at droplet surface during drying, whereas a high solids fraction in the droplets could limit possible droplet shrinkage. These factors contributed positively to the encapsulation of the lipophilic core material.

A Novel Shell Material-Highland Barley Starch for Microencapsulation of Cinnamon Essential Oil with Different Preparation Methods

Highland barley starch (HBS), as a carbohydrate shell material with excellent performance in microcapsule applications, has rarely been reported. In the present study, three different microcapsules (CEO-SWSM, CEO-PM, and CEO-UM) were synthesized successfully via saturated aqueous solution method, molecular inclusion method and ultrasonic method, respectively, using HBS as shell material coupled with cinnamon essential oil (CEO) as the core material. The potential of HBS as a new shell material and the influence of synthetic methods on the performance of microcapsules, encapsulation efficiency (EE), yield, and release rate of CEO-SWSM, CEO-PM, and CEO-UM were determined, respectively. The results confirmed that CEO-PM had the most excellent EE (88.2%), yield (79.1%), as well as lowest release rate (11.5%, after 25 days of storage). Moreover, different kinetic models were applied to fit the release process of these three kinds of microcapsules: CEO-SWSM, CEO-PM, and CEO-UM had the uppermost R-squared value in the Higuchi model, the zero-order model, and the first-level model, respectively. Over all, this work put forward a novel perspective for the improved encapsulation effect of perishable core materials (e.g., essential oil) for the food industry.