John Flanagan

Microemulsions: A Potential Delivery System for Bioactives in Food

Microemulsions are thermodynamically stable, transparent, low viscosity, and isotropic dispersions consisting of oil and water stabilized by an interfacial film of surfactant molecules, typically in conjunction with a cosurfactant. Microemulsions (so-called due to their small particle size; 5–100 nm) have found application in a wide variety of systems, such as pharmaceutical and oil recovery, but their application in food systems has been hindered by the types of surfactant permissible for use in food. The objective of this review is to provide an overview of the structures and phase behavior of microemulsions, methods of microemulsion formation, and techniques which may be used for characterization. A comprehensive review of previous work on both food-grade microemulsion systems, and non-food-grade systems of specific food interest is included. The application of microemulsions as reaction media, their ability to solubilize proteins and hence their use as a separation technique is also documented. In addition, attention is focused on the application of microemulsions as delivery systems for delivery of bioactive compounds, and the links between microemulsions and increased bioavailability. Future research, both applied and fundamental, should focus on surfactants which are not restricted for use in foods.

Preparation and characterization of nanoparticles formed by chitosan-caseinate interactions

Intermacromolecular complexation between chitosan and sodium caseinate in aqueous solutions was studied as a function of pH (3-6.5), using absorbance measurements (at 600 nm), dynamic light scattering (DLS), and transmission electron microscopy (TEM). The chitosan-caseinate complexes formed were stable and soluble in the pH range 4.8-6.0. In this pH range, the biopolymers had opposite charges. At higher concentrations of chitosan (0.15 wt%), the soluble complexes associated to form larger particles. DLS data showed that, between pH 4.8 and 6.0, the particles formed by the complexation of chitosan and caseinate had sizes between 250 and 350 nm and these nanoparticles were visualized using negative staining TEM. Above pH 6.0, the nanoparticles associated to form larger particles, causing phase separation. Addition of NaCl increased the particle size. The pH dependence of the zeta potential of the mixture solutions was appreciably different from that of the pure protein and pure chitosan solutions.

Functional properties of Bacillus proteinase hydrolysates of sodium caseinate incubated with transglutaminase pre- and post-hydrolysis

The effects of hydrolysis with Protamex (a Bacillus proteinase), cross-linking with microbial transglutaminase, and combinations of these treatments on the functional properties of sodium caseinate (NaCN) were investigated. Higher (P<0.005) emulsifying activity index (EAI) values were observed between pH 4.0 and 10.0 on hydrolysis of transglutaminase cross-linked NaCN to 0.5% degree of hydrolysis (DH) compared to either the 0.5% DH hydrolysate, the cross-linked NaCN or unmodified NaCN control. Reversing the order of modification (cross-linking after hydrolysis to 0.5% DH) generated a product which displayed 1433% foam expansion (FE) at pH 6.0, compared to 735% FE for the control. Cross-linking with transglutaminase after hydrolysis to 1.3% DH resulted in significant improvements (P<0.005) in EAI at low pH, compared to control. In addition, the latter sample exhibited greater FE than the control between pH 3.0 and 10.0 (P<0.005). Extensive transglutaminase-catalysed cross-linking of NaCN per se resulted in increased viscosity (P<0.005) at alkaline pH.

Functionality of Bacillus proteinase hydrolysates of sodium caseinate

Sodium caseinate (NaCN) was digested with Protamex, a Bacillus proteinase, at 40°C and pH 7.0 to degree of hydrolysis (DH) values of 2.7%, 5.3% and 13.3%. The solubility, emulsifying, foaming and viscosity properties of the hydrolysates were investigated between pH 2.0 and 10.0. Foam expansion of >1300% was observed for the 5.3% DH hydrolysate at pH 4.0, compared to 670% for unheated NaCN. Significantly improved foam expansion properties (P<0.005) were observed over the entire pH range examined for the 13.3% DH hydrolysate compared to unheated or heat-treated NaCN. Hydrolysis resulted in significantly improved solubility (P<0.005) around the isoelectric point and significant improvements in the emulsifying activity and stability (P<0.005) at alkaline pH compared to unheated NaCN. Hydrolysis with Protamex increased the apparent viscosity of NaCN at the isoelectric point. Reversed-phase HPLC profiles showed that high DH samples contained high levels of hydrophilic peptides.

Chapter 14 – Interactions between Milk Proteins and Micronutrients

Milk proteins can interact with micronutrients through a variety of mechanisms, with hydrophobic interactions being of particular importance. This chapter focuses on the interactions of milk proteins with a range of micronutrients, including vitamins, fatty acids, sugars, and minerals. Milk proteins can potentially be used as micronutrient carriers in foods, thereby increasing the nutritional benefit of milk and milk-based products. It is widely known that the processing of milk proteins via heat or high pressure can result in the modification of protein structure, resulting in altered interactions between proteins and micronutrients. Interestingly, the presence of some micronutrients can retard the denaturation of some milk proteins. The addition of specific micronutrients may therefore be used as a processing tool to prevent denaturation of milk proteins under physical conditions that normally result in denaturation.