Dragon fruit, known for its distinct look and delicate texture, belongs to the family of Cactaceae and is a vine climbing cactus of the Hylocereus genus (Hua et al., 2018). Dragon fruit used to be a backyard plant grown only for table consumption and medicinal uses. But now, there is a global growth of dragon fruit production from which growers are getting benefitted (Balendres & Bengoa, 2019). The pulp of dragon fruit has a high concentration of vitamin C as well as water-soluble fiber. The reddish color imparted to the peels of \(Hylocereus undatus\) is associated with persistent nitrogen containing pigment known as betacyanin, which are water soluble (Al-Mekhlafi et al., 2021). The peel of the fruit was a major byproduct of the dragon fruit juice processing industry and generally dumped onto the ecosystem. Recent research on dragon fruit peel was aimed at extracting polyphenols, betacyanin (G. V.S. Bhagya Raj & Dash, 2020b), and pectin ( Tien et al., 2022).
The temperature during food processing and storage significantly impacts betacyanin stability since heating induces the breakdown of this pigment (Gengatharan et al., 2015; Herbach et al., 2006). In addition to these factors that degrade the stability of betacyanin were light exposure, pH, water activity, soluble metals, and enzymatic reactions (Edia Rahayuningsih et al., 2021). Degradation and low stability of betacyanin can be the major issue in use as a food colorant in the food matrix. As natural dyes’ potential and drawback, some innovation is necessary to minimize natural dyes’ disadvantages as food colorants (E. Rahayuningsih et al., 2019). The utilization of betacyanin in food processing can be increased by enhancing its stability, which can be accomplished by the encapsulation method. Therefore encapsulation of can be a substantial alternative approach for boosting the stability of bioactive substances.
Encapsulation is a technique in which targeted compounds are entrapped by encapsulant in order to form capsules or microcapsules at micrometer or nanometer scale and eventually released at the time of requisite (Bamidele & Emmambux, 2021). The encapsulation method was extensively applied in food processing industries to encapsulate phytochemicals such as polyphenols, micronutrients, enzymes, and antioxidants by creating protective barriers against the light, oxygen, pH, moisture, heat, shear, or other extreme conditions during processing and storage. It improves the stability of the product when transiting through the gastrointestinal tract (Dima et al., 2015). Different methods were implemented to achieve the encapsulation of phytochemicals from food materials, including wet heat processing (pasting, kneading, and co-precipitation), spray drying, spray cooling/chilling, extrusion coating, fluidized bed coating, liposome entrapment, coacervation, inclusion complexation, centrifugal suspension separation, co-crystallization, liposomes, nanoparticles, freeze-drying, emulsion and rotational suspension separation ( Boger et al., 2021; Carpentier et al., 2021; Lengyel et al., 2019). Usually, the encapsulation process consists of two main steps, such as homogeneous mixing of components and drying. Ultrasound treatment can be applied for homogeneous mixing, and it is an effective, non-toxic, and environmentally friendly process that shortens the drying time (Colucci et al., 2018; Yazicioglu et al., 2015).
The freeze-drying encapsulation technique was commonly utilized to entrap phytochemicals from agricultural products into another material because the core molecules are heat sensitive (Cheng et al., 2017; Yamashita et al., 2017). As mass transfer in freeze drying does not occur by evaporation but rather through freezing, sublimation, and desorption for dehydrating the material, the powder is formed when the frozen feed emulsion is sublimated. (Ozkan et al., 2019). The freeze drying technique was successfully implemented to microencapsulate bioactive compounds from fruits and vegetables with different wall materials such as encapsulation of betanin (a natural dye of red beets) in a combination of maltodextrin and xanthan gum, bioactive compounds of Malpighia emarginata DC fruit pulp extracts using gum arabica and maltodextrin (Rezende et al., 2018), Anthocyanin of purple Roselle with maltodextrin as carrier agent (Nafiunisa et al., 2017), betalain extract from Cactus pear fruit by starch and maltodextrin as wall materials (Morales et al., 2021), anthocyanins from pomegranate peel using maltodextrin and calcium chloride (Azarpazhooh et al., 2019), red beet root extract using carrier agents as maltodextrin and whey protein isolate (Faridnia et al., 2020) and curcumin with various wall materials (Guo et al., 2020).
Maltodextrin is a polysaccharide that is commonly used as a carrier agent for microencapsulation due to its high solubility in water (Galves et al., 2021 ). The solutions formed from maltodextrin are colorless, with low viscosity and sugar content, and are inexpensive (Akhavan Mahdavi et al., 2016; Robert et al., 2010). Gum Arabic is a natural polysaccharide and exudate gum of acacia that is widely utilized as an efficient wall material in various food applications (Carpentier et al., 2022). Gum Arabic is preferred as a carrier agent due to emulsion formation and excellent volatile retention ability (Rajabi et al., 2015). Gelatin has good biocompatibility and biodegradability and is a polypeptide with high molecular weight derived by regulated hydrolysis of collagen from bones and skin (Elzoghby, 2013; Nezhadi et al., 2009). It has the ability to form a film and a gel with excellent mechanical properties that also serve as barriers to oxygen, carbon dioxide, and volatile compounds (Tongnuanchan et al., 2012). Xanthan gum is a colorless, tasteless, odorless, and smooth texture. Xanthan gum has low viscosity at high shear rates and high viscosity at low shear rates. It has stability against heat, acid, and alkali conditions and is a clear weak gel-like liquid that can be used in a variety of industrial applications (Jo et al., 2018). Use of one carrier agent or wall material for encapsulation is not preferable as it does not maintain all necessary properties to retain the core material. As a result, a wall material comprising two or more carrier agent mixtures could be employed to increase the encapsulation characteristics of the compound of interest. This could be accomplished by combining carbohydrates with proteins and polysaccharides in various proportions.
The artificial neural network is considered a powerful tool to develop mathematical models with higher accuracy and flexibility for modeling processes and predicting responses (G. V.S. Bhagya Raj & Dash, 2020a; Huang et al., 2017). In many of the ANN modeled food processing methods, genetic algorithm (GA) was used for optimizing the process parameters such as microwave puffing (K. K. Dash & Das, 2021), ultrasound-assisted extraction (G. V.S. Bhagya Raj & Dash, 2020b), convective drying (Chasiotis et al., 2020), spray drying (Przybył et al., 2018), and microwave vacuum drying (Khawas et al., 2016). Many researchers integrated ANN with GA for modeling and optimizing the encapsulation process, such as phenolic extracts from different agricultural produces (Espinosa-Sandoval et al., 2019), blueberry anthocyanin extract (Tao et al., 2017), and olive pomace phenols (Aliakbarian et al., 2018). There has only been a little research on the effect of hydrocolloids and ultrasound on the encapsulation process. Based on this, the objective of this study is to encapsulate the phytochemicals of dragon fruit peel by using the freeze drying technique using three different wall materials such as maltodextrin, gum arabica, and gelatin. The influence of wall materials and ultrasonication power on encapsulation efficiency, antioxidant activity, hygroscopicity, and solubility of the encapsulated product was studied using a feed-forward back propagation neural network, and the process was optimized by using integrating ANN–GA approach.