# Dietary Compounds Influencing the Sensorial, Volatile and Phytochemical Properties of Bovine Milk
## 1 Introduction  
The effect of bovine diet on the composition and flavor profile of milk is well documented [1; 2; 3]. However, conflicting results exist on the effect of feeding systems on the flavor and abundance of volatile organic compounds (VOCs) in dairy products, and their impact on the sensory perception of milk. Studies suggest that certain VOCs in milk could prove to be useful metabolic markers in tracing animal diets [4; 5]. Alterations to feeding systems have been shown to effect milk fat composition, protein content, urea, citrate, and soluble calcium (list not exhaustive), which can subsequently influence the oxidative stability and flavor of the milk [6]. The review by [PERSON], et al. [7] summarized the effectsof forage type on milk fat and composition, and highlighted the need to evaluate the impact of feeding systems on other aspects of milk fat quality, such as flavor and oxidative stability. Milk produced from many supplemented and altered diets have been investigated, including supplementation with flaxseed [8], lipid complex [9], crude protein [10], iodine [11] marine algae [12], oregano and caraway essential oils [13], hull-less barley [14] and sunflower/fish oil [15]. These studies focused mainly on animal production performance, milk composition, milk yield, milk fatty acid composition, and to a lesser extent on the flavor and sensory characteristics of milk. The study by [PERSON], et al. [16] investigated the influence of four supplemental feed choices for pasture-based cows on the fatty acid and volatile profile of milk. Some studies have also evaluated the effect of storage conditions on the microbiological quality of milk [17; 18]. In the present study, the volatile profile and free fatty acid (FFA) content of the milk samples were evaluated over a 14-day storage period at 4 \({}^{\circ}\)C in order to ascertain the level of lipid oxidation occurring within the milk, and to track volatile compounds forming or changing during refrigerated storage. Free fatty acids (FFAs) in milk are produced by two mechanisms, namely incomplete esterification in the mammary gland before lipid excretion [19] or lipid hydrolysis after milking and during storage [20]. The FFAs influence product quality, flavor, nutrition, and texture, and thus accurate quantification is important for quality control as well as research and development purposes [21]. FFA levels > 1.5 mmol/L are unacceptable to most consumers [22]. A number of factors including individual animals, feeding system, stage of lactation, farm practices, bacterial contamination, and storage quality influence the level of FFA in milk [23]. Increased levels of unsaturated fatty acids bound in the lipid molecules (triacylglycerglycerol or phospholipids) or as FFA have been shown to increase the susceptibility of milk to lipid oxidation [24], thus impacting negatively on quality and sensory properties. Increased levels of short and medium chain FFA in particular have been shown to be responsible for off-flavors described as rancid, butyric, and astringent [25]. Increased levels of ethyl esters of short-chain fatty acids, particularly ethyl butanoate and ethyl hexanoate, impart a fruity off-flavor in milk [26]. Furthermore, four important isoflav (apigenin, diadzein, formononetin, and genistein) with potentially important sensory implications were also investigated. Isoflavones are a group of phytoestrogens with estrogenic or hormone-like properties, and are known to have positive effects on various diseases, including atherosclerosis, osteoporosis, and some cancers [27], but may also act as substrates for biomarkers of pasture feeding and influence sensory properties through the degradation of odor active compounds [1; 5]. Isoflavones in bovine milk are likely present as a result of the direct transfer from feeds including leguminous plants such as clover and soybean, which are naturally rich in phytoestrogens. Dairy produce from pasture-based farming systems is considered more natural by consumers from an animal welfare and environmental standpoint [28].