## 3 Results and Discussion
### Quantification of Volatiles in Pasteurized Milk  
Volatile compounds were produced in pasteurized milk as a result of storage time and temperature. A total of 20 volatile compounds were quantified in milk samples, ranging from 0.01 \(\pm\) 0.01 \(\upmu\)g/L to 139.6 \(\pm\) 6.7 \(\upmu\)g/L, which agrees with previous reports [9; 19]. Freshly pasteurized milk (Table 1, day 0) at 4 \({}^{\circ}\)C resulted in the measurement of 6 compounds, including ketones (2), alcohols (2) and aldehydes (2), which were increased to 12 compounds, with 3 ketones, 7 alcohols and 2 aldehydes, at the end of storage (day 19). A comparable volatile profile was described by [PERSON] [20] for cow's milk with low fat content, at day 0. Carbonyl compounds are secondary products of lipid photo-oxidation, as product of light exposure and a microbial metabolite [21]. Of the above compounds, acetone was measured the compound with the maximum amount of 75.6 \(\pm\) 1.13 \(\upmu\)g/L, at 0 day, and 93.3 \(\pm\) 2.14 \(\upmu\)g/L at day 19. Butanone, ethanol and pentanal were also quantified compounds, which increased proportionally with storage time at 4 \({}^{\circ}\)C.  
A similar volatile profile was detected for milk stored at 7 \({}^{\circ}\)C (Table 2). At day 0, the same 6 compounds were measured, but at the end of storage, the total number of volatile compounds increased to 14, including ketones (4), aldehydes (4) and alcohols (6). The acetone amount was 73.5 \(\pm\) 1.12 \(\upmu\)g/L at day 0 and 99.6 \(\pm\) 2.17 \(\upmu\)g/L at day 19, being slightly higher than at 4 \({}^{\circ}\)C. Two new compounds were detected at this temperature: acetaldehyde at day 17 and 3-Meth-1-Butanol at day 18, which was likely photo-oxidation of milk. This deterioration in packaging materials arises in milk inthe presence of a photosensitizer (e.g., riboflavin), which excites oxygen to its singlet state, a requisite for oxygen to react with the unsaturated lipid moiety, producing hydroperoxide [22].  
The number of volatile compounds in pasteurized milk stored at 10 \({}^{\circ}\)C, at day 0, was almost similar to that at 4 \({}^{\circ}\)C and 7 \({}^{\circ}\)C, but high at end of storage. A total of 20 different compounds were observed, including aldehydes (5), ketones (4) and alcohols (11) (Table 3). At day 0, acetone (72.8 \(\pm\) 1.32 \(\upmu\)g/L) was the highest quantified compound, followed by butanone (7.56 \(\pm\) 0.03 \(\upmu\)g/L), pentanal (1.13 \(\pm\) 0.02 \(\upmu\)g/L) and ethanol (0.04 \(\pm\) 0.01 \(\upmu\)g/L). These compounds slightly increased at the 19 th day of storage, being respectively, 139.6 \(\pm\) 6.7, 15.4 \(\pm\) 2.20, 11.2 \(\pm\) 2.06 and 5.29 \(\pm\) 1.17. These results are in close agreement with that obtained by [PERSON] et al. [23] and a similar profile of off-flavoring compounds was detected in pasteurized milk by [PERSON] et al. [24]. Analyzing the trend of volatile compound production, mostly all compounds increased in quantity as the storage interval increased, but some decreased as the storage period increased, at all studied temperatures. At the same time, the rate of increase was higher at 10 \({}^{\circ}\)C. Adequate reproducibility was achieved for most compounds (relative standard deviation \(<\) 15%).