Ultrasound-Assisted Water-in-Oil Emulsions for the Microencapsulation of Beet Extract (Beta Vulgaris L.) by Spray Chilling Technique

Abstract

In order to incorporate bioactive compounds in foods and beverages from substances with coloring and antioxidant properties such as betalains, pigments of natural origin from beet disposal, it is necessary to analyze the main operational variables that influence its stability. Thus, the importance of encapsulation technologies by spray chilling and emulsion homogenization from ultrasonic devices is highlighted. Therefore, three independent variables were studied: lipid binary treatments (carrier agents), containing stearic acid (SA) and oleic acid (OA), prepared in an ultrasonic probe homogenizer, in proportions of 50/50, 60/40, and 70/30, respectively; permanence time (1, 2, and 3 min) in the homogenizer and power (200 W and 280 W) of the equipment. Then, the mixtures were evaluated for kinetic stability (creaming index) and rheology (consistency index) and, from these results, the optimum power and time were selected to obtain ideal colloidal systems aimed at microencapsulation of the particles in spray chilling. In general, the increase in the proportion of stearic acid directly influenced the increase in viscosity and stability of the emulsion. Such behavior allowed setting the sonicator operating parameters at the limit of 2.75 min and 200 W, in addition to indicating that the SA would have better atomization performance than the OA. Morphological analyzes showed that the microspheres (70/30) had larger particle size, spherical shape and smooth surface; however, lower encapsulation yields. The lipid matrix with the highest content of unsaturated fats (OA), especially the treatment with 50% of this component, showed greater agglomeration of particles, demonstrating a pasty and sticky consistency, which made handling difficult. From the FTIR spectrum it was possible to verify that the beet extract was incorporated into the lipid matrix, that is, demonstrating that the spray chilling technique did not destroy the primary structures. Over the storage time, it was possible to observe greater degradation of the pigments present in the microspheres with 50/50 and 60/40 of stearic acid/oleic acid and, consequently, greater visual color change, when compared to the 70/30 treatment. The research showed that, with a high potential for early release and greater retention of betalains, the microsphere made with a lower concentration of stearic acid proves to be viable for application in refrigerated foods, such as gelatine, jellies, yogurts, and ice cream. In contrast, the increase in stearic acid promotes a larger particle size and, at higher temperatures, had a better visual appearance, being ideal for foods that have good melting properties in the mouth, such as chocolates, flavored milks and cake mixes. Thus, the spray chilling technique under the conditions of the tested operations proved to be a promising alternative for the encapsulation of water-soluble extracts and maintenance of its stability, which contributes to its application in the future projects in the food industry.