**1. Introduction**

Human metabolism continuously produces reactive oxygen species (ROS) by normal respiration and cellular functions. These species may cause cellular damage by affecting the DNA, stimulating free radical chain reactions, and provoking more than one hundred diseases [1]. To counteract the reactive oxygen species (ROS), human body produces antioxidant compounds that may scavenge free radicals either by transferring free electrons or hydrogen atoms [2]. However, an over production of oxidative species and a weak immune system, may result in an imbalance in the body, developing oxidative stress (OS). This OS can generate changes in cell volume, and make other biomolecules (i.e., proteins, lipids and nucleic acids) to malfunction, leading to other major degenerative diseases such as cancer, diabetes, atherosclerosis, stroke, asthma, arthritis, dermatitis and aging, among others [3]. Thus, one approach to reduce OS is a regular consumption of antioxidants, which are found in fruits, vegetables, leafs and roots. There are various types of antioxidants in nature, among them are found flavonoids and stilbenoids structures such as quercetin 3-D-galactoside, resveratrol, myricetin and kaempferol [4,5]. Among these compounds, resveratrol (3,4',5-trihydroxystilbene) is a polyphenolic

compound that exists in the *cis*- and *trans*- isomeric forms, synthesized by plants as a phytoalexin in response to injury, fungal attack and exposure to UV light [6]. It is one of the most potent antioxidants against ROS and OS, and its intake is beneficial for human health, in the modulation of vascular cell function, suppression of platelet aggregation, reducing myocardial damage, inhibiting kinase activity, as anti-inflammatory and e ffective against the carcinogenesis [1,3]. Particularly, resveratrol is abundant in red wine, grape berry skins and seeds, berries, nuts and roots such as the Itadori plant (*Polygonum cuspidatum*) [7,8]. According to Tomé-Carneiro et al. the cardiovascular risk factor is reduced with a dose of 8 mg/day of resveratrol for one year [9]. In terms of red wine consumption, this dose would be equivalent to drinking 1–3 L of wine per day, depending on wine variety [10]. Additionally to a large volume ingestion of antioxidants containing products, utilization of resveratrol in the food industry is limited by factors such as low stability against oxidation, high photosensitivity, insolubility in water and short biological half-life (i.e., rapid metabolism and elimination) [11,12]. Thus, it is necessary to develop food products containing a high concentration of resveratrol, o ffering a reduced volume, while keeping the stability and bioavailability of antioxidants.

Both, flavor and high content of antioxidants in blueberry (*Vaccinium corymbosum*) juice (BJ) has triggered its consumption and popularity in regions such as Europe, Asia, North America and Latin America, but the short harvest season of the fruit and rapid perishability, limit its availability in the market [13]. In consequence, more than 50% of the total production must be processed in food products that may support a long shelf life such as juices, nectars, yogurts, marmalades, syrups and juice powders. Unfortunately, thermal degradation of antioxidants may occur during processing at temperatures higher than 60 ◦C. Spray drying of fruit juices is an alternative that o ffers a solution to this issue. In this sense, several studies have reported spray drying of di fferent fruit juices with carrying agents. These agents are employed as aids in the drying process because of their relative high glass transition temperature (Tg). Fruit juices such as orange, pineapple, apple, watermelon, mango and blueberry, have been successfully dried with carrying agents such as inulin, maltodextrins, starch, Arabic gum and sodium alginate [14–20]. Maltodextrins are polysaccharides obtained from the acidic hydrolysis of starch, with a nutritional contribution of only 4 calories per gram. Besides, maltodextrins are commercially found in a wide range of molecular weight distributions (MWD), which lead to di fferent thermal properties and potential applications [21]. Recently, Saavedra-Leos et al. used a set of four maltodextrins as carrying agents in spray drying of BJ [22]. Through analysis of variance (ANOVA) and response surface plots (RSP), they determined the e ffect of processing conditions, found an optimal set of experimental variables for drying the juice and conserving of quercetin 3-D-galactoside, and set the application limits of maltodextrins based on their MWD. Although there is a large number of works published on the subject of conservation of resveratrol, few have addressed the issue of optimization of processing conditions. For example, Lim, Ma and Dolan carried out a systematic experiment for testing the spray drying conditions of blueberry by-products. They found a yield of 94% when employing a ratio of blueberry solid to maltodextrin of 30:70, and an outlet temperature of 90 ◦C [19]. Jiménez-Aguilar et al. studied the spray drying conditions of blueberry and mesquite gum on color and degradation of anthocyanins, and found a direct relation between color and concentration of anthocyanins [23]. Tatar Turan et al. studied the e ffect of an ultrasonic nozzle on spray drying of blueberry juice with maltodextrin and Arabic gum as carrier agen<sup>t</sup> and coating material, respectively [24]. They reported the optimal drying conditions as inlet temperature of 125 ◦C, ultrasonic power of 9 W, and feed pump rate of 8%. Correia et al. encapsulated the polyphenolics in wild blueberry with di fferent protein-food ingredients, by two-way ANOVA and Tukey's test; they found that soy protein produced the highest total phenolic content [25]. Darniadi, Ho and Murray, also used ANOVA for comparing two methodologies in drying of blueberry juice: Foam-mat freeze-drying (FMFD) and spray drying. They concluded that the highest powder yield was achieved with FMFD methodology and a ratio of maltodextrin to whey protein of 1.5 [26]. Shimojo et al. employed a 22 full factorial experimental design for evaluating the process parameters on the properties of resveratrol

loaded in nanostructured lipid carriers [27]. Additionally, other works have also studied the drying processing conditions of alternative drying methodologies [28–30].

Therefore, in the present work, ANOVA and RSP were employed for setting the optimal processing conditions of blueberry juice-maltodextrin (BJ-MX) mixtures. The e ffects of inlet temperature, concentration and type of maltodextrin, were studied on content, and retention of resveratrol, and the results were compared with those reported by Saavedra-Leos et al. (2019) for quercetin 3-D-galactoside. This work contributes to understanding the application limits of maltodextrins when used as carrying agents in the spray drying of sugar-rich systems, and for conservation of antioxidants.

#### **2. Materials and Methods**
