# The Sensory Quality and Volatile Profile of Dark
## 3 Results and Discussion
### Viability of Probiotic Bacteria  
According to the definition given by FAO/WHO [30] probiotics are \"live microorganisms which, when administrated in adequate amounts, confer a health benefits on the host\". To have a positive effect in the intestinal tract, probiotics should be able to survive low pH, gastric acid and bile secretions and should succeed in competing with the resident intestinal microbiota. The bacteria should also be able to selectively stimulate the growth and/or activity of bacteria in the colon [31; 32]. Probiotic bacteria have been reported to have numerous health benefits such as balancing of intestinal microbiota, stimulation of immune system, blood cholesterol reduction, enhancement of the digestibility of protein and vitamin synthesis, anti-bacterial activities, treatment of lactose intolerance, food-related allergies, amongst others [33; 34; 35; 36]. Most of probiotic bacteria belong to the _Lactobacillus_ genera and _Bifidobacterium_ strains [37]. However, variety of food grade lactic acid bacteria, have been evaluated for their potential probiotic ability. Furthermore, some of autochthonous facultative heterofermetative lactobacillus isolated from traditional dairy products, such as _Lactobacillus casei_, _Lactobacillus plantarum_, _Lactobacillus rhamnus_ can also have probiotic properties [38]. Many destabilizing factors in food production could affect viability of probiotic bacteria. In production of dark chocolate, the factors such as temperature, oxygen, osmotic pressure, water activity and so forth could be critical for bacterial cell survival. Therefore, it is very important to incorporate probiotic bacteria in dark chocolate mass at very low temperature during manufacturing process, so their viability will not be impaired. In this experiment, probiotic bacteria were added after the process of tempering when the temperature reached around 30 \({}^{\circ}\)C. However, chocolate composition, such as protein and fat content, sugar concentration, including high buffering capacity, remains an important factor affecting the viability of probiotic bacteria [39], not only after production but also during storage. Based on the development of functional foods such as probiotic dark chocolate, one of the main goals is achieving the desired amount of probiotic bacteria in dark chocolate during the production and storage in order to provide a therapeutic effect on human health. To have a beneficial effect on health, probiotics must be viable in the product at the time of consumption. The threshold cell number should be above 10\({}^{6}\) cfu/g during manufacturing process and storage [40; 41]. The viability of probiotic bacteria can be affected by many factors, particularly physicochemical properties of dark chocolate (fat and protein content, type of sugars, etc.) and addition of certain food ingredients (stabilizers, sweeteners, etc.) [42]. Different approaches that increase the viability of probiotic bacteria have been adopted, including appropriate selection of acid- and bile-resistant strains, use of oxygen impermeable containers, two-step fermentation, incorporation of micronutrients and microencapsulation [43]. Microencapsulation by spray-drying is presumably the most effectiveand economic method. Also, spray drying is suitable for large-scale, industrial applications [44]. Although high temperature of hot air can be a disadvantage of spray-drying, proper readjustments of processing conditions can achieve better viability of probiotic bacteria [45; 46]. According to the literature, an air outlet temperature of 80 to 85 \({}^{\circ}\)C was optimal for spray drying to preserve _Lb. paracasei_ and _Lb. salivarius_ strains with probiotic potential [47; 48]. Our previous studies [29] demonstrated a high viability and survival rate of spray dried _Lb.