Microencapsulation of supercritical CO2 extracted rice bran oil in pea proteins

Abstract

Rice bran oil is a source of bioactive molecules such as sterols, tocols, -oryzanols and unsaturated fatty acids [1,2]. In this work, the encapsulation of rice bran oil extracted using supercritical CO2 under the conditions optimized by Benito-Román et al. [3] has been studied. Microencapsulation processes are sequential and involve the emulsion formation and then, the emulsion drying. In a first stage, the emulsification process by high pressure homogenization was studied and optimized. High pressure homogenization, also known as microfluidization, is a high energy emulsification method affected by several parameters: pressure and number of homogenization cycles (together determine the energy input), the carrier material, the carrier to core ratio, and the solids content in the emulsion. Microfluization also exhibits an important advantage: the industrial application due to flexibility to control the emulsion droplet size (EDS) and the ability to produce emulsions from a variety of materials [4]. Among the different encapsulation materials, vegetable proteins are trendy, due to their properties and the possibility to be used in pharma, cosmetics and food industries [5]. More specifically, pea proteins present the most interesting properties such as emulsifying easiness, high nutritional value and non-allergenic characteristics [6]. For these reasons, and the wall forming properties pea proteins have, key in microencapsulation processes, they were used in this work. The effect of working pressure (60-150 MPa), composition of the carrier (mixtures of pea protein isolate (PPI) and maltodextrin (MD), (from 50 to 90% of PPI) and carrier to oil ratio (COR) (from 2 to 4) on the emulsion droplet size (EDS) was studied, using the response surface methodology. The number of passes through the homogenization chamber was previously determined and set in 7. The experimental work, revealed that in order to minimize the EDS, moderate pressures (114 MPa), a carrier composed mainly by PPI (64%) and carrier to oil ratios around 3.2 are required. Important interactions between the experimental factors were also observed. In the second stage, the emulsion obtained in the optimal conditions (EDS=189±3nm) was dried using different technologies: spray-drying (Buchi B-290 mini Spray-dryer, inlet temperature 155 ºC, outlet temperature 92-96 ºC and emulsion flow rate of 3 g/min); PGSS-drying (apparatus extensively described by Melgosa et al. [7], being the main working conditionsgas to product ratio (GPR) equal to 30 g/g temperature and pressure in the static mixer of 105 ºC and 10 MPa, respectively) and freeze drying (Labconco Freeze Dry System, 0.15 mbar for, at least, 48 h). All of them were suitable to get dry powders, spray drying provided high encapsulation efficiencies (around 73%) and monomodal powders (around 18 μm), whereas PGSS drying provided lower encapsulation efficiencies (around 52%) but perfect spheres with lower particle size (around 11 μm). Freeze drying yielded powders with almost complete encapsulation efficiencies, and higher stability when stored at 4 ºC, since spray-dried and PGSS-dried powders increased the amount of free oil after two weeks of storage.