The Flavor of Dairy Products from Grass-Fed Cows

2-Heptanone, 2-nonanone, and 2-undecanone confer oxidation off-flavor in cow milk storage

Flavor sensation is one of the most prevalent characteristics of food industries and an important consumer preference regulator of dairy products. So far, many volatile compounds have been identified, and their molecular mechanisms conferring overall flavor formation have been reported extensively. However, little is known about the critical flavor compound of a specific sensory experience in terms of oxidized off-flavor perception. Therefore, the present study aimed to compare the variation in sensory qualities and volatile flavors in full-fat UHT milk (FFM) and low-fat UHT milk (LFM) samples under different natural storage conditions (0, 4, 18, 25, 30, or 37°C for 15 and 30 d) and determine the main component causing flavor deterioration in the FFM and LFM samples using sensory evaluation, electronic nose, and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). In addition, the Pearson correlation between the volatile flavor components and oxidative off-flavors was analyzed and validated by sensory reconstitution studies. Compared with the LFM samples, the FFM samples showed a higher degree of quality deterioration with increased storage temperature. Methyl ketones of odd carbon chains (i.e., 2-heptanone, 2-nonanone, 2-undecanone, 2-tridecanone, and 2-pentadecanone) reached a maximum content in the FFM37 samples over 30 d storage. The combined results of the Pearson correlation and sensory recombination study indicated that 2-heptanone, 2-nonanone, and 2-undecanone conferred off-flavor perception. Overall, the present study results provide potential target components for detecting and developing high-quality dairy products and lay a foundation for specific sensory flavor compound exploration in the food industry.

Ingested versus inhaled limonene in sheep: A pilot study to explore potential different transfer to the mammary gland and effects on milk and Caciotta cheese aroma

Concentration is a key determinant in the overall positive impact of terpenes on milk and cheese aroma; additionally, route of intake may affect the achievable concentrations of dietary terpenes in milk and cheese. In this study, we explored the possibility that the amount of the monoterpene limonene transferred to sheep milk and its corresponding cheese could differ depending on the route of intake and that the aroma profile of these products could also differ. To this aim, 12 lactating dairy ewes were repeatedly exposed to limonene by the oral or respiratory route during a 48-h test period, according to a 3 × 3 Latin square experimental design. Limonene content was measured in individual and bulk milk samples, in 1-d-old and 15-d-old Caciotta cheese obtained from that milk, in the related whey and curd, and in the air inhaled by the ewes in the respiratory treatment group (to obtain an estimate of the dose actually supplied by this route). Bulk milk and fresh (1-d-old) cheese underwent sensory analysis by ortho-olfactory evaluation. Both intake routes demonstrated transfer of limonene to milk, but the respiratory route transferred limonene with greater efficiency than the oral route. Moreover, according to the protocol used in this study, a short period of respiratory exposure induced a slightly higher limonene content in milk compared with oral exposure. As to the fate of limonene during cheesemaking, an important part of it was lost into the whey, perhaps through volatilization. The differences between milk and cheese tended to dissipate in curd and fresh cheese and disappeared completely after 15 d of ripening. Finally, it was possible to distinguish between the 2 routes of limonene intake using sensory analysis, even though no direct relationship was identified between the different aroma profiles of milks and cheeses from the oral and respiratory groups and their respective limonene contents. Overall, our results expand current knowledge on the biological pathways of terpene transfer from feed to sheep milk and cheese, as well as on the role played by terpenes in the formation of aroma in these products. Our observations may contribute to future development of strategies for external control and better standardization of the presence of odor compounds in milk and cheese from dairy ruminants.

Production of Hydroxy Fatty Acids, Precursors of γ-Hexalactone, Contributes to the Characteristic Sweet Aroma of Beef

Aroma is an essential factor for meat quality. The meat of Japanese Black cattle exhibits fine marbling and a rich and sweet aroma with a characteristic lactone composition. The mechanism of lactone formation associated with beef aroma has not been elucidated. In this study, we examined the precursors of γ-hexalactone, an indicator of the sweet aroma of beef and identified the mechanism underlying γ-hexalactone production. A low-temperature vacuum system was used to prepare beef tallow from Japanese Black cattle and Holstein cattle. The odor components were identified using headspace–gas chromatography. The analysis revealed that γ-hexalactone, γ-dodecalactone, δ-tetradecalactone, and δ-hexadecalactone were present as sweet aroma components of beef tallow prepared from marbling and muscle. Since we previously reported that γ-hexalactone formation correlates with linoleic acid content in beef, we analyzed ten oxidized fatty acids derived from linoleic acid by liquid chromatography–triple quadrupole mass spectrometry and detected two hydroxy-octadecadienoic acids (9S-HODE and 13S-HODE) in beef tallow. Significant differences in arachidonic acid 15-lipoxygenase and cyclooxygenase protein expression levels among subcutaneous fat, intramuscular fat, and muscle tissue were observed. Our results suggest that the combination of linoleic acid and the expression of lipid oxidase derived from beef muscle and intramuscular fat produce hydroxy fatty acids that result in a sweet aroma.

The Influence of Pasture and Non-pasture-Based Feeding Systems on the Aroma of Raw Bovine Milk

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.