Encapsulation and microwave technologies to preserve/improve quality of foods

This dissertation discusses the details of research conducted on two independent projects. Although independent, these two approaches carry a common thread towards preserving/improving quality of food products. Summary of these two projects is as follows. First project explores microwave heating as an emerging and commercially applicable thermal processing technique to process perishable fruit products such as strawberry puree. Strawberry is a fruit best known for its characteristic red color, delicate flavor and nutritional benefits such as antioxidant capacity. However, high susceptibility of strawberries and strawberry products to fungal spoilage makes it necessary to process them for shelf life enhancement. Microwave heating is known to have advantages such as short come-up times, due to volumetric heating which, can be exploited in inactivating yeasts and molds responsible for spoilage of strawberry products without compromising their quality. In this investigation, strawberry puree was thermally processed by microwave radiation on a batch system at 80ºC and on continuous flow pilot (100 kW) and laboratory (6 kW) scale systems at 80, 91 and 102ºC at different holding times. Strawberry puree was also processed by conventional tubular heating methods to compare with microwave processing under similar processing conditions. In spite of the differences in processing conditions and results for batch, small and large continuous systems, overall, it could be summarized that microwave processing showed higher retention of anthocyanin content, color and viscosity of strawberry puree as compared to conventionally heated and untreated puree over a storage period of up to 12 weeks with no significant differences among three processing temperatures. These findings support the efficacy of microwave heating in preserving quality of food products when compared to conventional heating methods as well as its potential commercial applicability due to the continuous nature of the system. The second project sets a background for a potential application of solid lipid nanoparticles (SLN), an encapsulation technique commonly used in pharmaceutical industry, for encapsulation of food bioactive compounds such as lipophilic vitamins. Ergocalciferol or vitamin D2 is a fat-soluble compound essential for the development of bones in human body. It is susceptible to degradation by oxygen and light and hence was chosen as a model compound for encapsulation in this study. In this research study, ergocalciferol was encapsulated in tripalmitin solid lipid nanoparticles stabilized by polysorbate 20. SLN dispersions (5% w/w) with Ergocalciferol concentrations at 0, 5, 10, 15 and 20% (w/w of lipid phase) were prepared by hot high pressure homogenization. As the proportion of ergocalciferol in the SLN increased from 0 to 20%, size (Z-average values) of these particles, as measured by dynamic light scattering, gradually decreased (p≤0.05) from ∼120 nm to ∼65 nm. Differential scanning calorimetry (DSC) results of freeze dried SLN samples showed gradual decrease in enthalpies of fusion and crystallization for the stable β-subcell polymorphic form, whereas for SLN dispersions, the enthalpy of fusion of unstable α-subcell crystal form increased with increased ergocalciferol loading. This suggests that increasing ergocalciferol concentration slows down the crystallization process and results in predominant presence of more unstable crystal forms. Transmission electron microscopy (TEM) images of ergocalciferol loaded SLNs showed the presence of spherical as well as rod-shaped nanoparticles. It was also observed that the turbidity of the SLN dispersions noticeably decreased with increased ergocalciferol loading, indicating the potential application of ergocalciferol-loaded SLNs for the fortification of clear beverages