Phytopharmaceuticals. Группа авторов

Phytopharmaceuticals - Группа авторов


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Drying

      Microencapsulation is defined as the entrapment of tiny particles of an active agent inside coating materials [151]. Spray drying is the most commonly used microencapsulation technique, due to its low cost and high efficiency, fast and continuous operation and significant increment of the bioactive shelf life [149–151].

      Spray drying has different stages: first, the coating materials are solubilized, generally in aqueous solution and then the bioactive compound is added to this coating dispersion. In case of oils, this dispersion is homogenized to generate a stable emulsion. Then, this emulsion is atomized into the spray dryer chamber where hot dry air circulates and quickly dries the droplets and the powder (microcapsules) is collected in a mechanical cyclone. Drying rate is influenced by the emulsion characteristics, such as viscosity and particle size. Emulsions with high viscosity form elongated and bigger droplets, which interfere with the atomization process, affecting adversely the drying rate [149]. The emulsion viscosity can be modified by varying the feed temperature. Some process conditions that have to be controlled are the inlet and outlet air temperature, atomization pressure, feed rate, the concentration of fed flow [150, 151]. The selection of the atomizer type (nozzle or disc) is also important.

      To obtain a gradual release, it is necessary to include other hydrophobic compounds, such as proteins or other polymers in the coating material formulation [148–154]. Chitosan and alginate may be used to generate pH-sensitive encapsulation systems. In the intestinal tract (pH >6) alginate (a polyanionic water-soluble polysaccharide) disintegrates, and the bioactive compounds are released [155]. Although it is extensively used in food and pharmaceutical industry, alginate is barely been used as wall material for spray-drying encapsulation [156]. Moreover, other polysaccharides that are described for their health benefits as prebiotic or bifidogenic, such as inulin, have been used as colonic release polymers. Their glycosidic linkages are stable during the human digestive enzymatic action but they are fermented by colonic bacteria, releasing the bioactive compounds properly [157].

      Oleurepin bioaccesibility (from olive leaves) is influenced by the type of the encapsulation system, polymer type and process conditions [158]. In this context, works in this line are scarce but necessary because the digestive mechanisms related to phenolic compounds remain unknown. Moreover, the most consumed compounds are not necessarily the most active in the organism, since their concentrations in the bloodstream depend on its modifications during metabolism in the gastrointestinal tract.

Coating material Spray dryer Process conditions Results Ref.
Flaxseed oil MD, GA, WPC, Hi-Cap 100, Capsul TA Laboratory scale spray dryer Flow rate 12 ± 2 g/min. I/O T: 180 °C/110 °C. High encapsulation efficiency: Good stability. [159]
Chia oil WPC, MG, GA Nichols/Niro spray-drier, Turbo spray-drier PLA Feed rate 40 ml/min I/O T: 135 °C/80 °C. Pressure 4 bar WPC:MG and WPC:GA blends promoted good encapsulation efficiency [160]
Olive oil MD, agave inulin (IN), AG Niro Minor pilot scale spray dryer Flow rate 57.6 g/min I/O T 180 ±5 °C/90 ± 5 °C. Pressure 5 bar MD-AG and IN-AG blends generate high microencapsulation yield. [161]
Pomegranate oil Skimmed milk powder Pilot scale spray dryer, Buchi, B-191 Feed rate 1.75 ± 0.05 g/min Inlet temperature 150–190 °C Pressure 5 bar Core to wall material ratio defined the encapsulation yield. [162]
Avocado oil WPI and MD Small scale spray dryer, Model SL10, Saurin Group of Companies I/O T 180 °C/80 °C Microencapsulated avocado oil showed a good oxidative stability. [163]

      AG, acacia gum; GA, gum Arabic; Hi-Cap 100 and Capsul TA, modified starchs; I/O, Inlet/outlet MD, maltodextrin; MG, mesquite gum; WPC, whey protein concentrate; WPI, whey protein isolate; T, temperature.

       2.3.3.2 Coacervation

      Coacervation may be simple or complex, according to the involved phase separation. In simple coacervation, only one polymer is in aqueous solution, occurring the polymer separation when electrolytes or water-miscible solvents are added, a temperature change is produced, or an inorganic salt is added. In complex coacervation, two or more polymers are in aqueous solution, occurring the separation phenomenon when electrostatically oppositely charged biopolymers are brought together, under certain specific conditions [165].

Active agent Wall material Process conditions Results Ref.
Chia oil Protein and gums
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