Spray-dried novel structured lipids enriched with medium-and long-chain triacylglycerols encapsulated with different wall materials: Characterization and stability
Graphical abstract
Introduction
Structured lipids (SLs) can be produced enzymatically or chemically via interesterification, acidolysis, and/or esterification processes from the conventional fats/oils in order to improve their nutritional and functional properties (Lu, Jin, Wang, & Wang, 2017; Zhao et al., 2014). SLs are available in a number of commercial zero- or low- calorie food ingredients, for example salatrim (Nabisco, USA) and diacylglycerol (Kao Cooperation, Japan). Medium and long-chain triacylglycerols (MLCTs) are a special kind of SLs found in food products like Resetta™ (Nisshin Oillio Group Ltd., Japan) that have been found with many physiological benefits, such as anti-obesity effect and the maintenance of good cholesterol (Lee et al., 2015). Furthermore, MLCTs possess the capability to provide the body with quick energy and essential fatty acids such as arachidonic acid (ARA) by an easy way, thus they are very useful for humans, in particular for infants (Korma et al., 2018; Matsuo & Takeuchi, 2004). ARA is one of the omega-6 long-chain polyunsaturated fatty acids, exists in human milk. It has been used in the supplementation of infant formula for more than two decades since it has a functional role as an essential fatty acid for normal growth, visual acuity, and brain development of infants. Moreover, ARA plays a fundamental role in many physiological functions in human health, for instance acting as a precursor of eicosanoid hormones (prostaglandins, leukotrienes, and thromboxanes) and the prevention of several kinds of diseases in human (Korma et al., 2018; You et al., 2011). Despite their health benefits, ARA is prone to rapid oxidative degradation and stability problems (Kikuchi et al., 2006). Therefore, it is important to reduce the oxidation of ARA, in order to improve their quality in food applications.
Microencapsulation process is a technique for transferring liquid oil into powder form through micro- and nano-particles in order to protect the unsaturated fatty acids from degradation during exposure to environmental factors such as, light, moisture, and oxygen, thus contributing to the increased shelf life of the product. Moreover, microencapsulation also has the capability to mask the unacceptable odor, and improve the solubility and handling properties of the final product (Bakry et al., 2016). Spray drying is the most commonly technology used for fats and/or oils encapsulation at large scale because of its low cost and easier accessible equipment. In addition, it is a reasonably simple technique and continuously operated unlike other microencapsulation techniques. It also reinforces the microbiological and chemical stability of the final product (Hartwig, Ponce Cevallos, Schmalko, & Brumovsky, 2014).
It was reported that emulsion properties, such as stability, viscosity, droplets size, and the other characteristics including surface oil, particle size, density, morphology, and oxidative stability after drying and during storage of the encapsulated products are affected by the materials used on the wall (Jafari, Assadpoor, He, & Bhandari, 2008). The use of whey proteins as an encapsulating agent in the food industry is very attractive due to its great nutritional benefits (Khem, Bansal, Small, & May, 2016). In addition, the existence of hydrophilic and hydrophobic amino acids of whey protein facilitates encapsulation of hydrophobic compounds (Liu, Chen, Cheng, & Selomulya, 2016). Whey proteins are known to be great encapsulating agents for fats and/or oils and volatile compounds (Bae & Lee, 2008). In addition, whey proteins have been applied in combination with carbohydrates in order to stabilize spray-dried emulsions (Bakry et al., 2017; Botrel, Borges, Fernandes, & Lourenço Do Carmo, 2014; de Barros Fernandes et al., 2017). Maltodextrin (MD) is a polysaccharide produced by partial hydrolysis of starch with acid or enzymes. It is commonly used as a secondary wall material in microencapsulation process of food ingredients (Gharsallaoui, Roudaut, Chambin, Voilley, & Saurel, 2007; Goula & Adamopoulos, 2012). The rheological and functional properties of MD are mainly characterized by a dextrose equivalent value lower than 20 (Pycia, Juszczak, Gałkowska, Witczak, & Jaworska, 2016). The use of MD as a secondary wall material provides many advantages, such as low cost, neutral aroma and taste, low viscosity at high solid concentrations, protection of flavours against oxidation, and ease of digestion by humans. However, on the other hand, MD had poor emulsification properties and its application led to marginal retention of volatile compounds during the process of spray-drying (Otálora, Carriazo, Iturriaga, Nazareno, & Osorio, 2015; Pourashouri et al., 2014). In order to minimize these shortfalls, MD is generally used in mixtures with other wall materials. Inulin (IN) is a natural source of carbohydrates extracted from chicory roots, wheat, Jerusalem artichoke, asparagus, yacon tubers, and onions (Castro, Céspedes, Carballo, Bergenståhl, & Tornberg, 2013). It can be considered as a polysaccharide mixture of fructose unit chains linked by β-(2 → 1) D-fructosyl-fructose bonds of different lengths and commonly ended by a glucose unit (Sébastien N Ronkart et al., 2007). The physicochemical characterizations of IN are related to the polymerization degree. Long-chain IN has higher viscosity and lower solubility than the native product (Meyer, Bayarri, Tárrega, & Costell, 2011), and can be used as a fat replacer, texture modifier, and also as a stabilizer of emulsions because of its capacity for binding water. In addition, it has a broad range of health benefits, for example promotion of gastro intestinal tract work, improving the absorption of minerals, and reduction of appetite modulation and colon cancer occurrence (Cho & Samuel, 2009). Also, IN may be an interesting secondary wall material for the encapsulation of food components dried by a spray dryer. The utilization of IN, MD, and WPI affected the quality of the obtained spray-dried capsules, since it was reported that the existence of IN and MD for the production of spray-dried fish oil microcapsules decreased the separation of oil on the surface of particles, and improved the particle's wettability as compared to WPI. In the presence of IN, the particles became more spherical with fewer dents (Botrel, de Barros Fernandes, Borges, & Yoshida, 2014). Furthermore, the addition of IN to WPI wall matrix resulted in a suitable carrier formulation in the production of spray-dried rosemary essential oil when ratios of 1:1 and 3:1 for WPI/IN mixtures were used (R. V. d. B. Fernandes, Borges, Botrel, & Oliveira, 2014).
In order to improve the applicability of MLCTs-rich SLs as lipid ingredient in nutritional and functional food applications especially in infant formula, MLCTs-rich SLs could be transformed into powder and encapsulated on food products by spray drying technology. Hence, the aims of this study were to investigate the influence of the partial replacement of WPI as the primary wall material by using prebiotic carbohydrates, such as MD and IN as the secondary wall materials on the encapsulation of MLCTs-rich SLs by spray drying, and to evaluate the physicochemical characteristics and oxidative stability of the encapsulated MLCTs-rich SLs during storage.
Section snippets
Materials
ARA-rich fungal oil (ARASCO) from Mortierella alpina was purchased from Qingdao Keyuan Marine Biochemistry Co., Ltd. (Qingdao, China) as the source of long chain triacylglycerols. Medium-chain triacylglycerols (MCTs) was purchased from Britz Networks Sdn., Bhd. (Shanghai, China). The fatty acids composition of ARASCO and MCTs were studied in our previous study (Korma et al., 2018). Immobilized lipase, Lipozyme 435 (a recombinant lipase from Candida antarctica, immobilized on a lewatit VP OC
Oxidative stability of MLCTs-rich SLs
The oxidation induction time (OIT) is a good indicator of oil resistance to degradation by oxidation. MLCTs-rich SLs had an OIT of 1.63 h, indicating that MLCTs-rich SLs are prone to rapid oxidative degradation. This is probably due to the presence of ARA with high unsaturated double bonds (Kikuchi et al., 2006). MLCTs-rich SLs emulsions were therefore selected for the study of the physicochemical properties and oxidative stability of MLCTs-rich SLs microcapsules.
Viscosity
Fig. 1 shows the relation
Conclusions
In this study, novel SLs enriched with MLCTs were encapsulated and spray-dried into a powder. Three treatments including WPI, WPI/MD (1:1), and WPI/IN (1:1) were used as wall material combinations, and all of them exhibited well visible microcapsules. The partial replacement treatments WPI/MD (1:1) and WPI/IN (1:1) produced microparticles with improved properties for microencapsulation efficiency, moisture content, water activity, wettability, solubility, and oxidative stability. The
Acknowledgements
The first author thanks the Chinese Scholarship Council (CSC) for funding his study. This work was also financially supported by National Natural Science Foundation of China Grant (31701558) and Fundamental Research Funds for the Central Universities (JUSRP11734).
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