## 1 Introduction  
Milk is a food produced by mammals to feed their offspring. Due to its high nutritional value and its good flavor, milk has been one of the main components of human nutrition since ancient times [1]. Aside from its direct consumption, milk has been used to produce a wide range of dairy products. These products are usually prepared by fermentation with specific microorganisms. The variety of these products, especially in recent years, is large (sour milk, yogurt, cheese, butter, etc.) [2, 3]. One of the most representative dairy products around the world is yogurt [2]. Yogurt is a very nutritious and easily digestible food that is suitable for all ages, making it one of the most frequently consumed foods [3]. In addition to the above, the popularity of yogurt among consumers depends mainly on its sensory characteristics, of which aroma, taste and texture are most important.  
In fact, the properties of foods that can be perceived by the senses (e.g., color, texture, flavor) influence the choice of the product by consumers more than its nutritional value [4].  
For example, a food may have an extremely high nutritional value, but its appearance may not be attractive to consumers, or its taste and aroma may prevent consumers from buying it [5]. Therefore, the sensory properties of foods greatly contribute to product quality and acceptability by consumers.  
Volatile compounds are responsible for the aroma of foods. As aroma is critical for the acceptance of a food, it plays an important role in its commercialization. For this purpose, various studies have been carried out in order to identify the volatile compounds of foods including yogurt [6; 7; 8; 9; 10; 11; 12; 13; 14; 15]. Of course, a number of volatile compounds are not always perceived as characteristic odors, as the compound contributing to a particular odor should be at a concentration greater than a minimum threshold [7]. It should be noted, however, that most odors are not attributed solely on a single volatile component, but to a mixture of compounds, some of which may be present at sub-threshold levels.  
In addition, it has been observed that in yogurts deriving from milk of different animal origin (i.e., cow vs. goat vs. ewe), the profile of the volatile compounds differs significantly, giving yogurts different organoleptic properties. Aside from the above, the fermentation process and other phenomena such as the oxidation of lipids contribute specific aromatic notes. As such, the aroma of the dessert yogurts is also affected by the type of microorganism strain used for the fermentation of the milk. More specifically, the formation of VOCs in fermented dairy products is complex and includes the glycolysis, lipolysis as well as the proteolysis of milk components, which is brought about by the enzymatic mechanisms of microflora within the dairy matrix [16].  
Finally, in order to achieve optimum health benefits for the consumer, probiotics are usually added to yogurts which, in turn may affect product sensory properties. Based on the above, the objective of the present study was to determine the effect of (i) milk type (cow vs. goat), (ii) starter culture (sweet-mild, classic and acidic) and (iii) type of probiotic culture (_Bifidobacterium_ BB-12 in cow milk and _Lactobacillus acidophilus_ LA-5 in goat milk) on the aroma and the flavor (aroma + taste) of dessert yogurt. To the best of our knowledge, the above-mentioned experimental parameters have not been previously studied simultaneously in yogurts or dessert yogurts. The present study attempts to illustrate that an optimum selection with regard to starter culture and probiotic culture may result in a dessert yogurt (cow or goat) with the most desirable aroma profile and overall consumer acceptability.