# Dietary Compounds Influencing the Sensorial, Volatile and Phytochemical Properties of Bovine Milk
## 2 Results and Discussion
### Sensory Analyses of Pasteurized Milk Samples  
It can be observed from Figures 4 and 5 that there is considerable discrimination between the three milk samples. Three significant differences (\(p<0.05\)) were observed between the three milk types; creaminess, color and hay-like flavor. A post hoc [PERSON]'s test showed that the difference in creaminess exists between GRS and CLV milk, the difference in color exists between TMR and the other two millks, with TMR milk scoring highest for white color and GRS and CLV millks scoring highest for creamy color. The significant difference in creaminess is likely to be linked to the higher level of fat in the CLV milk, as creaminess is linked to milk fat globules in dairy products [95]. Fat is in the form of emulsified globules in liquid dairy products which are perceived as smooth and creamy [96]. The fatty acid profile of milk also has an impact on texture, the ratio of oleic acid (C18:1; low melting point) to palmitic acid (C16:0; high melting point) has been used as a measure of hardness in cheese and butter [97]. [PERSON], et al. [1] reported that milk samples produced from pasture scored significantly higher for viscosity, possibly due to the lower ratio of oleic acid to palmitic acid. In this study, CLV samples scored significantly higher for creaminess and contained a lower ratio of oleic acid to palmitic acid followed by GRS and TMR samples, which is in agreement with the previous studies [97]. Free FA profile also impacts the surface tension and foaming capacity of milk, which contribute to texture [21]. \(\beta\)-Carotene content is responsible for the difference in color with the study by [PERSON], et al. [97] who concluded that dairy products produced from cows fed pasture have a higher yellow intensity. Figure 4: Multivariate data analysis partial least squares (PLS) regression plot of sensory descriptors for pasteurized milk samples; grass (GRS), grass/clover (CLV) and total mixed ration (TMR). AE denotes after effect. \(p\) = 0.05%. Figure 5: Hierarchical clustering analysis (Heatmap) of the average values for each sensory descriptor applied to the 3 pasteurized milk samples (grass (GRS), clover (CLV) and total mixed ration (TMR)) as determined by full descriptive sensory analysis (\(n\) = 7). Positive and negative correlations between diet treatment and sensory descriptors is denoted by +1 (red) and \(-\)1 (blue). AE: aftereffect. A difference in hay-like flavor was found between TMR milk and the other two milks, being significantly higher in the TMR samples. Previous studies have found that the oxidation of unsaturated fatty acids, yielding a complex mixture of volatile compounds can be involved in the formation of a hay-like flavor in food products [98; 99]. [PERSON] and [PERSON] [100] speculated that the compound 3-methyl-2,4-nonanedione could be responsible for a hay-like off-flavor in dried parsley. Interestingly, 3-methyl-2,4-nonanedione has been found to be the main contributor to the light-induced off-flavor of butter and butter oil [101]. While this specific compound was not identified in the present study, the compound 3,5-(_E,E_)-ocatden-2-one has been described as having a grassy aroma and present at higher levels in TMR samples, this may be contributing to the hay-like flavor. Other compounds have also previously been linked to a hay-like sensory note, including, hexanal [99], 1-hexanol and _trans_-2-hexen-1-ol [102]. However, 1-hexanol was present in rTMR samples, but not pTMR samples. The thermal oxidation of vitamin A palmitate has also previously been attributed to hay-like off-flavor in non-fat milk powder [103]. Further, 2,3-pentanedione (buttery, sweet, nutty) may have been formed from 3-methyl-2,4-nonanedione through photoxidation [104] and was only detected in TMR milk samples at day nine. It is also possible that the hay-like off-flavor is being caused by a complex mixture of compounds rather than a single compound.