# Dietary Compounds Influencing the Sensorial, Volatile and Phytochemical Properties of Bovine Milk
## 2 Results and Discussion
### Volatile Analyses (Feed, Raw and Pasteurized Milk)
Moreover, the levels of certain compounds present on day three of analysis increased or decreased over storage, highlighting that storage time has an effect on the volatile profile of bovine milk (Table 2 and Supplementary Table S5). [PERSON] et al. [65] investigated the effect of storage time on the concentrations of volatiles known to cause off-flavors in milk. Results showed the ability of certain compounds to both increase and decrease over time at 4 and 7 \({}^{\circ}\)C. Any fluctuations occurring throughout storage are likely due to lipid hydrolysis [32], lipid oxidation [66], microbial changes by indigenous or bacterial lipases [49], or by enzymatic action [20]. Esters and aldehydes were more closely correlated with TMR milk samples. Esters of short chain fatty acids (C4-C10) are important aroma active compounds [26] that are responsible for fruity off-flavors in milk [67; 68]. It is possible for esters to be formed through esterification reactions (the formation of esters from alcohols and carboxylic acids) or alcoholysis (the production of esters from alcohols and acylglycerols or from alcohols and fatty acyl-CoAs derived from metabolism of fatty acids, amino acids and/or carbohydrates) [26]. Esters in pasteurized milk are occasionally present as a result of post-pasteurization microbial contamination and microbial activity [69; 70]. Ethyl butanoate (fruity) was identified in rGRS and rTMR samples at day 14 of storage and ethyl hexanoate (fruity, malty pineapple, waxy) was identified in r and p GRS milk at day nine and increased at day 14. It was also identified in rCLV and rTMR samples at day 14 only. Ethyl butanoate was identified in rGRS and rTMR milk at day 14 of storage but was not identified in any p milk samples. The contribution of esters to the flavor of milk is concentration-dependent, and at low levels, esters contribute positively to the overall flavor balance; but at high concentrations they can cause a fruity defect as mentioned previously [26]. Hydrocarbons and sulphur compounds were more closely associated with GRS and CLV milk samples. [PERSON] et al. [71] reported that sulfur compounds such as hydrogen sulfide, methanthiol, dimethyl sulfide, and dimethyl trisulfide were present in commercial ultra-heat-treated milk samples at levels above their documented odor thresholds. The same study identified carbon disulfide, dimethyl sulfide, dimethyl sulfoxide, and dimethyl disulfide in pasteurized milk samples, although below their reported threshold values. Sulphur compounds are thought to be important contributors to the cooked flavor in milk. Significant differences were observed between the GRS, CLV, and TMR milk samples based on storage time, feeding system, and pasteurization (Figure 2a-c, respectively). Differences between the rGRS, rCLV, and rTMR milk samples at day three were dominated by alcohols (3) and aldehydes (2). Differences between the p milk samples based on feeding system at day three were dominated by aldehydes (3), alcohols (2) and hydrocarbons (2). Raw milk samples at day nine were dominated by aldehydes (6), alcohols (3) and ketones (3). Pasteurized milk samples at day nine were dominated by esters (6), ketones (6) and alcohols (4). r milk samples were significantly (\(p<0.05\)) dominated by esters (9), ketones (7), alcohols (4), aldehydes (3) and hydrocarbons (4) after 14 days of storage while p milk samples contained higher levels of aldehydes (7), ketones (6), and hydrocarbons (5) at day 14. All results for the concentrations of volatile organic compounds identified in r and p milk samples are outlined in Table 2 and Supplementary Table S5, respectively.