# Dietary Compounds Influencing the Sensorial, Volatile and Phytochemical Properties of Bovine Milk
## 2 Results and Discussion
### Volatile Analyses (Feed, Raw and Pasteurized Milk)
Seventy eight compounds were identified in the milk samples at day 14, 15 of which varied significantly between the milk types: (_Z_)-2-heptenal (green, fatty); 1-octanol (waxy, green, mushroom) is a fatty alcohol that could be derived from octanal; 1-Pentanol increased in pGRS samples at day 14; 2-Butanone remained correlated with pTMR samples at day 14; 3,5-(_E_,_E_)-Octadien-2-one (grassy, fruity, green) is a product of linolenic acid degradation [89] and was significantly higher in pTMR samples, which may explain the perceived hay-like flavor in the pTMR samples; 4-Methyl-3-penten-2-one (honey, vegetable, earthy) was identified in pGRS and pCLV samples only, and was found to be more closely correlated with the pCLV samples; acetone, as previously mentioned, is thought to originate from the diet of cows [19] and was also higher in the pTMR sample;butanal (chocolate, pungent, musty), a primary aldehyde product of lipid oxidation [90] was detected in the pGRS and pTMR samples only, being most abundant in pTMR samples; heptanal, hexanal, nonanal and octanal were all more closely correlated with TMR samples at day 14, as these are all products of lipid oxidation [90] their increased concentrations in pTMR samples could indicate quality deterioration and an increase in off-flavors; pentanal remained correlated with pCLV samples after 14 days of storage; p-cresol (barnyard, cowy, phenolic) is derived from the metabolism of \(\beta\)-carotene and aromatic amino acids (mainly tyrosine) in the rumen and may be a potential biomarker for dairy products derived from pasture [5; 91; 92]. Further, p-Cresol was strongly correlated with pGRS milk. Tyrosine has been shown to be a precursor for the production of both p-cresol and phenol [93], and both compounds follow the same trend across all p milk samples with the exception of TMR samples at day nine. Additionally, p-Cresol may also be present from the metabolism of isoflav in the feed [33]. Toluene was also found to be significantly correlated with the pGRS samples. In addition to the number of compounds increasing in the p milk samples throughout the storage period, the levels of numerous VOCs decreased, possibly due to the degradation and/or formation of secondary compounds. It is well known that pasteurization has an effect on certain volatile compounds in milk and can lead to losses or changes [1]. This can be seen as some compounds that are present in the r milk samples are absent in the corresponding p milk samples or vice versa. This is very evident for esters which could have been formed by heat-catalyzed esterification reactions [1; 60], some aldehydes (possibly from the activation of lipid oxidation after heat treatment, autooxidation or light induced oxidation) and some ketones [46]. It has been noted that enzymatic and metabolic reactions that occur in raw milk during storage may also lead to the loss of compounds post pasteurization [46; 94]. Storage time was also shown to have an effect on the volatile profile and this could be due to enzymatic reactions from microbes.