Abstract
Aroma-active compounds in raw bovine milk produced from cows fed perennial ryegrass (GRS) or total mixed ration (TMR) consisting of grass silage, maize silage, and concentrates were identified by direct immersion sorptive extraction (DI Hi-Sorb), coupled with gas-chromatography-mass spectrometry and olfactometry using odour intensity (OI) and aroma extraction dilution analysis (AEDA). Ninety-nine volatile organic compounds (VOC) were identified in these raw GRS and TMR milk samples; 33 of which were also present in the feed and rumen samples from these diets. Only the abundance of 13 VOC varied significantly based on diet. However, the odours of both raw milks were quite distinct as aroma perception is not influenced by abundance alone but also by the odour activity of each VOC. Approximately, 30% of the VOC influenced the aroma perception of these raw milks. This study clearly highlighted the significant impact of VOC transferring from the diet that influenced the aroma perception of both raw GRS and TMR milk. The aroma of the raw TMR milk was more complex than that of the raw GRS milk, and many of the key dietary-derived-odour-active VOC likely arose during the production of the TMR feed as most were either derived from Maillard reactions or impacted by heat. Seventeen of the 44 odour activities detected differed between both sample types. This study has clearly demonstrated the impact of diet on the aroma perception of raw bovine milk.
Highlights
Previous studies have demonstrated a significant effect of the feeding system on the composition of raw milk and, its impact on the fatty acid content (1)
The volatile compounds identified in the feed, RF, RB, and raw milk samples by DI-HiSorb GCMS are outlined in Supplementary Table 1
Ninety-nine volatile organic compounds (VOC) were identified in raw milk by DI-HiSorbGC-MS, which is significantly more than previous studies (10–15) and highlights the capability of the DI-HiSorb extraction technique (Table 1)
Summary
Previous studies have demonstrated a significant effect of the feeding system on the composition of raw milk and, its impact on the fatty acid content (1). VOC in bovine milk consists of a range of different chemical classes, including aldehydes, ketones, lactones, esters, alcohols, acids, terpenes, furans, hydrocarbons, pyrazines, and phenolic and sulphur compounds (1, 5–7). Their potential impact on sensory perception depends upon their relative concentration and odour activity. Previous studies have reported direct transfer of VOC from bovine feed to milk (4, 8), and that compounds such as phytochemicals in the feed may be metabolised in the rumen to more volatile odour-active compounds in the milk (7). Further processing to generate commodity dairy products may positively or negatively alter and/or exacerbate specific odours that may impact consumer preference
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