Microencapsulation is a novel trend to increase the stability of bioactive compounds. Microencapsulation is the process in that small particles like a liquid or gas can be entrapped within a layer of encapsulating or a matrix with microscopic size for protecting the coated materials against adverse reactions and promoting the controlled release of the encapsulates [1]. Selecting the correct encapsulating materials is a crucial step to stabilize the micro-particles [2]. Among many various encapsulating materials, Maltodextrin (MD) has been widely used in microencapsulation of bioactive compounds due to its low cost, neutral taste and aroma. Major advantages of MD are regarded as good film-forming property, high water solubility, low viscosity [3], and great ability against the oxidation of core materials. Gum Arabic (GA) is a hetero-polysaccharide that is generally used as wall materials in microencapsulation. It is well known as a good emulsifier with several properties like non-toxic, odorless, tasteless, high water solubility and low viscosity [4]. Chitosan is one of the natural biodegradable groups of polymers which is also extensively applied in microencapsulation. Besides, its good film-forming ability [5], it has some limitations such as low solubility in water and organic solvent, which decreases its exploitation for specific functions [6]. Regarding microencapsulation technique, spray drying is normally used for the production of aromas and flavors, and non-heat sensitive/non-labile compounds [7], while freeze drying is often applied for heat sensitive/labile compounds and high-value products. The principle of freeze-drying is the sublimation under low pressure of ice formed by rapid freezing and the removal of bound water molecules through the process of desorption.
The moisture content and water activity of powdered samples are two important factors influencing the chemical reactions and microbiological spoilage in foods, which decide the stability, shelf-life, and other technical properties of the powder. The main benefit of wall materials is to prevent the absorption of moisture from the outside environment, hence the moisture content and water activity of microencapsulated samples are lower and the dehumidification process occurs more slowly, which prolongs the shelf-life and enhances the quality of samples [8].
Theobroma cacao L. is known to originate from Central and South America. Cocoa was first cultivated in Mexico, South America, and then spread throughout the Caribbean islands. Currently, West Africa produces appropriately 75% of worldwide cocoa which becomes their important source of export earnings [9]. According to the World Cocoa Foundation in 2016, the world market value of the annual cocoa crop is the US $5.41 billion. Cultivated cocoa is spilled into 4 varieties including Forastero, Criollo, Trinitario, and Nacional [10]. In Vietnam, cocoa trees are mainly grown in the Central Highlands and Southern provinces, with cocoa bean yield approximately 2500 tons in 2016.
The cocoa pod husk (CPH) is considered as a major by-product, which accounts for 67–76% of total fresh fruit weight and cocoa bean only accounts for 24–33% of the fruit. The CPH can be potentially applied in many fields such as food processing, cosmetic manufactory, pharmaceutical production, fuel industry, etc. [11]. The CPH has been recently used to produce animal feeds and organic fertilizer, hence their value is underrated and they may become a pollution risk for the environment [12]. Recent studies indicated that the extracts from the CPH possesses high levels of phenolic, saponin and alkaloid compounds. Main phenolics and alkaloids have been found in the CPH being catechin, quercetin, epicatechin, gallic acid, coumaric acid, protocatechuic acid, theobromine, and theophylline [13, 14]. In which, alkaloid compounds have been used in prevention and treatment of many chronic diseases such as theobromine, which may act as antitumoral, anti-inflammatory or cardiovascular protector molecule [15], while theophylline is used to prevent and treat wheezing, shortness of breath, and chest tightness caused by asthma, chronic bronchitis, emphysema, and other lung diseases [16]. However, they are unstable when exposed to oxygen, UV light, high temperature, and humidity [17].
Recovery of natural bioactive compounds from the CPH can decrease pollution risk for the environment and apply them in functional foods or drugs to replace synthetic compounds. Recently, some studies on proximate composition and extraction of pigments, phenolic, saponin and alkaloid compounds from CPH have been performed. However, no investigations have been reported on microencapsulation of alkaloid-enriched CPH extract. Thus, this study aimed to microencapsulate the CPH extract rich in alkaloid compounds using different encapsulating materials in terms of maltodextrin, gum Arabic and chitosan and to evaluate the physicochemical, phytochemical, and antioxidant properties of powdered CPH extract without and with microencapsulation.