Microencapsulation of betanin in monodisperse W/O/W emulsions
Graphical abstract
Introduction
Consumers prefer foods and beverages containing raw natural materials to artificial substances (Oplatowska-Stachowiak & Elliott, 2017; Román, Sánchez-Siles, & Siegrist, 2017). Products without (or with reduced amount of) artificial substances are classified as clean label and have been associated to putative health benefits and lower environmental impact (Asioli et al., 2017). Betanin (betanidin 5-O-glucoside, EEC #E162), the major pigment of the red beetroot, is a water-soluble nontoxic natural pigment belonging to the class of betalains that was approved by the FDA and has been used in foods since 1967 (Herbach, Stintzing, & Carle, 2006). Betalains show higher tinctorial strength compared to anthocyanins, and keep their color in low-acid food (within the pH 3 to 7 range), where the color of anthocyanins is loss due to hemiketal formation (Quina & Bastos, 2018). However, betanin is sensitive to thermal and photochemical decomposition and subject to acid- and base-catalyzed hydrolysis that may cause color alterations that limit its application as a food additive (Attoe & von Elbe, 1981; Attoe & von Elbe, 1984; Bastos & Gonçalves, 2017; Esteves et al., 2018; Goncalves, Da Silva, DeRose, Ando, & Bastos, 2013; Herbach, Stintzing, & Carle, 2004; Khan, 2016).
The encapsulation of betalains in complex matrices increases its persistence in food products (Khan, 2016), and may be useful to expand the application of natural and artificial derivatives as food colorants (Fernandes et al., 2016; Goncalves et al., 2013; Goncalves, Da Silva, et al., 2013; Pavliuk et al., 2017; Rodrigues et al., 2018). There are several techniques for microencapsulation, which include emulsification followed by solvent removal, spray drying and milling. These techniques usually produce polydisperse material, i.e., non-uniform particle sizes, and heat that may not be adequate for temperature-sensitive samples, such as betalains. Water-in-oil (W/O) emulsions, where oil refers to any water-insoluble liquid, are suitable for encapsulating polar substances. However, multiple water-in-oil-in-water (W/O/W) emulsions allow the encapsulation of hydrophilic substances in water with a protecting layer of oil (Dias, Ferreira, & Barreiro, 2015). W/O/W emulsions have been used as delivery systems for plant bioactives, in preventing the exposure of sensitive substances to light oxygen and heat, and for the manufacture of food products with improved sensorial characteristics (Lamba, Sathish, & Sabikhi, 2015; Muschiolik & Dickinson, 2017). Homogenization of water and oil mixtures using a rotor-stator, ultrasound or high rotation result in polydisperse W/O/W emulsions. However, microchannel emulsification (MCE) produces monodisperse emulsions with improved physical stability (Khalid et al., 2014; Kobayashi & Nakajima, 2006; Souilem et al., 2013).
Aqueous beet extract was encapsulated in W/O/W type double-layer emulsion to study intestinal digestion in vitro, but the emulsion obtained is polydisperse and unstable, producing cream after storage at room temperature (Kaimainen, Marze, Järvenpää, Anton, & Huopalahti, 2015). Here we describe the encapsulation of three different sources of betanin in monodisperse W/O/W emulsions prepared by MCE of water, soybean oil and food-grade surfactants. The emulsion formulation was optimized by varying the volume fraction of the internal aqueous phase, the concentration of the hydrophobic and hydrophilic emulsifiers, and the flux of the dispersed phase. The tinctorial strength and color variability of encapsulated E162, powdered beetroot juice and betanin as well as the physical stability of the emulsions kept at 4 °C, 25 °C and 60 °C were monitored over 7 days and compared.
Section snippets
General
All chemicals were purchased from commercial sources with the highest purity available and were used without further purification. Refined soybean oil, d(+)-glucose, and polyoxyethylene (n = 20) sorbitan monolaurate (Tween 20) were purchased from Wako Pure Chemical Industries. Tetraglycerin monolaurate condensed ricinoleic acid ester (CR-310) was obtained from Sakamoto Yakuhin Kogyo Co. Ltd. Aqueous solutions were prepared with deionized water (conductivity 18.2 MΩ cm at 25 °C, Milli-Q,
Formulation of W/O/W emulsions loaded with betanin
E162 (sample A) was encapsulated in a W/O/W emulsion formulated using a W/O emulsion as the dispensed phase and an aqueous solution of Tween 20 as the continuous phase. The effect of formulation conditions on droplet size distribution, average droplet diameter (d3,2) and degree of emulsion dispersion was investigated. Initial experimental conditions were defined as follows: volume fraction of the internal aqueous phase (ϕAi): 30% v/v, concentration of CR-310 (CCR-310): 4% w/w, concentration of
Conclusions
Betanin was encapsulated in W/O/W emulsions using the microchannel emulsification (MCE) technique. The droplets formed have a size of 46 ± 10 μm and are monodisperse. Emulsifying agents suitable for use in food and the use of soybean oil resulted in a W/O/W emulsion that can be used in the preparation of functional foods kept under refrigeration for up to 7 days. The emulsification conditions were optimized and the dispersed phase flux was the most important factor influencing the capillary
Author contributions
APEP, NK, IK and MN performed the experiments. IK, MN, MAN, ELB contributed with reagents, materials, analysis costs and technology. APEP and ELB prepared the manuscript. All authors analyzed the data and revised the manuscript.
Conflict of interest
The authors declare no competing financial interest.
Acknowledgements
We thank the São Paulo Research Foundation – FAPESP (ELB, 2014/22136-4, 2016/21445-9), the Brazilian National Council for Scientific and Technological Development – CNPq (ELB, 303341/2016-5), and the University of Tsukuba for financial and fellowship support.
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