## 1 Introduction  
Functional foods consist of nutraceuticaltals, pharma foods, medical foods, probiotics, prebiotic dietary fibers, and vitamin foods [1]. Foods enriched with probiotic microorganisms, such as lactic acid bacteria (LAB) and/or bifidobacteria, make up a large part of the commercial market. According to the most recent definition by the FAO/WHO, \"probiotics are microorganisms (bacteria or yeasts) which, when administered in adequate concentrations, provide health benefits to the host\" [2]. One of the main ways that probiotics exert their beneficial effects is through alterations in the composition of intestinal microbiome [3]. The effect of functional (probiotic) microorganisms and prebiotic dietary fibers on the composition of the intestinal microbiota has been well documented over the last years [4]. Prebiotic dietary fibers constitute of compounds that display health benefits towards digestive health. Cereals contain fiber, nutrients, and are rich in vitamins and minerals. Daily cereal intake has been associated with a decreased risk of chronic diseases, such as obesity, type-1 diabetes (T1 DM) and type-2 diabetes mellitus [5], and cardiovascular disease [6]. Fiber acts as a substrate for microbial fermentation in the gut, thereby facilitating the maintenance and/or growth of beneficial microbial populations. Consumption of dried fruits [7] and nuts has been linked to beneficial health and glycemic control benefits [8]. Raisins (_Vitis vinifera_ L.) are rich in vitamins, minerals, and antioxidants, such as polyphenols (e.g., resveratrol). Metabolites of phenolic compounds have the ability to promote the growth of specific microbial species [9,10]. Pistachios (_Pistacia vera_ L.) contain high loads of monounsaturated fatty acids (MUFA), fiber, and phytochemicals, which have beneficial effects on health [11]. More specifically, they contain high percentages of oleic acid, along with phenolic compounds, such as resveratrol and pro-anthocyanins [12]. The beneficial effects of pistachio consumption on gut microbiome and lipid profiles have been recently demonstrated in a streptozotocin-induced T1 DM animal model [13,14]. Cereals, pistachios, and raisins could therefore be proposed as foods with prebiotic properties, which may potentially regulate the levels of microbial populations contributing to maintenance of human health [13,15]. Similarly, three-day consumption of a granola meal improved glycemic regulation in a recent study [16]. Immobilization technology enables enhanced survival of probiotic cells [17] and can be employed in the production of novel functional foods, enriched with immobilized functional cultures in natural food carriers. Immobilization is defined as limiting cells to a solid matrix, separated from the main liquid phase. Many studies have demonstrated that the use of immobilized cultures in the production of probiotic foods led to increased cell viability [17, 18, 19], while the delivery vehicle is possible to affect the adhesion and therefore the colonization properties of functional cells [20,21]. The use of natural food carriers, containing prebiotic dietary fibers for the immobilization of probiotic cells, may lead to the production of symbiotic functional components [22]. Prebiotics and probiotics contribute to intestinal microbiome homeostasis by enhancing the presence of beneficial bacterial species and exerting benefits for the host immune system in diseases, such as T1 DM [23]. In general, dried products are preferred by the food industry as they have an extended shelf life, are easy to store and transport, and reduce storage costs since refrigeration is not required. Freeze-drying is usually used for sensitive ingredients, as it is employed under vacuum and at low temperatures [24]. However, freeze-drying can cause many negative effects on cells, such as rupture of cell walls, due to water vapor transport to the surface and sublimation of water molecules, protein destruction, and cell shrinkage.