## 3 Discussion  
Although investigation on the VOC profile of dairy products is a field largely investigated, the studies available for buffalo dairy products are scanty and, in addition, they adopted different analytical techniques, thus making the data comparison difficult [40]. Moreover, the cheese making processes, including the starter cultures and ripening, can also strongly influence cheese VOC profile [22; 35; 37; 44], therefore further limiting any direct comparison. As a matter of fact, the VOCs of buffalo milk [4; 45] and mozzarella [6; 23], were numerically higher than those that we found, and the application of different extraction methodologies is probably the origin of these discrepancies. Nevertheless, although distillation and solid phase micro-extraction (SPME) are two non-comparable extraction procedures, our technique was able to detect two compounds (i.e., nonanal and 3-hydroxy-2-butanone) among the eight volatile compounds reported in the literature for buffalo and bovine mozzarella cheese [46]. From a sensorial point of view, these two compounds can exert a significant role in the aroma of mozzarella cheese, being characterized by a very low odor threshold. To the best of our knowledge, this is the first paper reporting the VOCs of buffalo milk and mozzarella cheese determined by the headspace solid phase micro extraction (HS-SPME), technique that allows a negligible sample manipulation, so potentially avoiding solvent residues, contaminants, or artifacts [17]. Hydrocarbons (toluene), aldehydes (hexanal and pentanal), alcohols (2-ethyl-1-hexanol), and esters (ethyl acetate and propyl acetate), were the key compounds of the Exp milk, while ketones and FFA were the key compounds for the Ctl milk. Except for FFA, these observations are in accordance with the trends indicated by [PERSON] et al. [20] for cow milk from three diets based on fresh forage, silage, or hay. Toluene can originate from \(\beta\)-carotene degradation [41] that is present in larger amount in fresh forages compared with hays or silage [12; 47]. Therefore, the buffalo cows on Exp diet likely took more \(\beta\)-carotene, and this may explain the higher levels of toluene in milk. Pentanal and hexanal ('cut grass' flavor note) could derive from the higher levels in milk of PUFA, from which aldehydes are formed by the lipoxygenase (LOX) pathway [5; 20]. However, there is not a strong explanation for the higher nonanal in Ctl milk, a compound that can be produced from MUFA by the LOX pathway [5], but also by lipid auto-oxidation [48]. Esters can be produced in the mammary gland by esterification of FFA with alcohols [46]. The Ctl diet, containing a higher quantity of silage, showed a significantly greater FFA content with chain lengths from 3 (acetic acid) to 14 (tetradecanoic acid) carbons. This observation is consistent both with the significantly higher content in milk/cheese of the FA from 4 to 10 carbons [26] and the enhancement of milk lipolysis detected in cows fed silage [49]. In addition, fresh forage is well known to reduce the lipolytic processes and free fatty acid release [50]. The acetic acid, might potentially derive from silage, being a main product of carbohydrate fermentation during the ensiling process, but very limited information is available on the carry-over of acids from silage to milk and cheese [51; 52]. Ketones are common VOCs of most dairy products, in particular of surface-mould ripened and blueveined cheeses [40]. Ketones can arise from \(\beta\)-oxidation of saturated fatty acid [17], so their higher content in Ctl milk is in agreement with the FA composition. Moreover, even the higher content in Ctl milk of acetone and 2-butanone, which are reputed to originate from animal feeds [53], is consistent with the fact that silage is a main source of ketone compounds [54; 55]. Overall, the differences in milk VOC profiles appear related to both the higher silage incidence in the Ctl diet and the presence of fresh forage in the Exp diet.