Concentrations of Volatile 4-Alkyl-Branched Fatty Acids in Sheep and Goat Milk and Dairy Products

Widely Targeted Metabolomic Analysis Revealed the Diversity in Milk from Goats, Sheep, Cows, and Buffaloes and Its Association with Flavor Profiles

The milk flavor can be attributed to the presence of numerous flavor molecules and precursors. In this study, we employed widely targeted metabolomic analysis techniques to analyze the metabolic profiles of various milk samples obtained from goats, sheep, dairy cows, and buffaloes. A total of 631 metabolites were identified in the milk samples, which were further categorized into 16 distinct classes. Principal component analysis (PCA) suggested that the metabolite profiles of samples from the same species exhibit clustering, while separated patterns of metabolite profiles are observed across goat, sheep, cow, and buffalo species. The differential metabolites between the groups of each species were screened based on fold change and variable importance in projection (VIP) values. Five core differential metabolites were subsequently identified, including 3-(3-hydroxyphenyl)-3-hydroxypropanoic acid, inosine 5'-triphosphate, methylcysteine, N-cinnamylglycine, and small peptide (L-tyrosine-L-aspartate). Through multiple comparisons, we also screened biomarkers of each type of milk. Our metabolomic data showed significant inter-species differences in the composition and concentration of some compounds, such as organic acids, amino acids, sugars, nucleotides, and their derivatives, which may affect the overall flavor properties of the milk sample. These findings provided insights into the molecular basis underlying inter-species variations in milk flavor.

Effects of Allium mongolicum Regel ethanol extract on three flavor-related rumen branched-chain fatty acids, rumen fermentation and rumen bacteria in lambs

The objective of this study was to evaluate the effect of Allium mongolicum Regel ethanol extract (AME) on the concentration of three branched-chain fatty acids (BCFAs) related to flavor, fermentation parameters and the bacteria and their correlations in the rumen of lambs. A total of thirty 3-month-old male, Small-tailed Han sheep (33.60 ± 1.23 kg) were randomly distributed into 2 groups as follows: control group (CON) was fed a basal diet and AME group was fed a basal diet supplemented with 2.8 g⋅lamb–1⋅d–1A. mongolicum Regel ethanol extract. AME supplementation decreased (P = 0.022) 4-methyloctanoic acid (MOA) content and tended to lower (P = 0.055) 4-methylnonanoic acid (MNA) content in the rumen. Compared to CON group, the ruminal concentrations of valerate and isovalerate were higher (P = 0.046 and P = 0.024, respectively), and propionate was lower (P = 0.020) in the AME group. At the phylum level, the AME group had a lower abundance of Bacteroidetes (P = 0.014) and a higher abundance of Firmicutes (P = 0.020) than the CON group. At the genus level, the relative abundances of Prevotella (P = 0.001), Christensenellaceae_R-7_group (P = 0.003), Succiniclasticum (P = 0.004), and Selenomonas (P = 0.001) were significantly lower in the AME group than in the CON group, while the relative abundances of Ruminococcus (P < 0.001), Quinella (P = 0.013), and Lachnospiraceae_XPB1014_group (P = 0.001) were significantly higher. The relative abundances of Prevotella (P = 0.029, R = 0.685; P = 0.009, R = 0.770), Christensenellaceae_R-7_group (P = 0.019, R = 0.721; P = 0.029, R = 0.685), and Succiniclasticum (P = 0.002, R = 0.842; P = 0.001, R = 0.879) was positively correlated with MOA and MNA levels, and the relative abundance of Lachnospiraceae_XPB1014_group (P = 0.033, R = −0.673) was negatively correlated with MOA. The relative abundance of Christensenellaceae_R-7_group (P = 0.014, R = −0.744) and Prevotellaceae_UCG-003 (P = 0.023, R = −0.706) correlated negatively with the EOA content. In conclusion, these findings suggest that the AME affected the concentration of BCFAs, fermentation parameters and the rumen bacteria in the rumen of lambs.

Genome-wide analysis of the acyl-coenzyme A synthetase family and their association with the formation of goat milk flavour

Goat milk is rich in fat and protein, thus, has high nutritional values and benefits human health. However, goaty flavour is a major concern that interferes with consumer acceptability of goat milk and the 4-alkyl-branched-chain fatty acids (vBCFAs) are the major substances relevant to the goaty flavour in goat milk. Previous research reported that the acyl-coenzyme A synthetases (ACSs) play a key role in the activation of fatty acids, which is a prerequisite for fatty acids entering anabolic and catabolic processes and highly involved in the regulation of vBCFAs metabolism. Although ACS genes have been identified in humans and mice, they have not been systematically characterized in goats. In this research, we performed genome-wide characterization of the ACS genes in goats, identifying that a total of 25 ACS genes (without ACSM2A) were obtained in the Capra hircus and each ACS protein contained the conserved AMP-binding domain. Phylogenetic analysis showed that out of the 25 genes, 21 belonged to the ACSS, ACSM, ACSL, ACSVL, and ACSBG subfamilies. However, AACS, AASDH, ACSF, and ACSF3 genes were not classified in the common evolutionary branch and belonged to the ACS superfamily. The genes in the same clade had similar conserved structures, motifs and protein domains. The expression analysis showed that the majority of ACS genes were expressed in multi tissues. The comparative analysis of expression patterns in non-lactation and lactation mammary glands of goat, sheep and cow indicated that ACSS2 and ACSF3 genes may participate in the formation mechanisms of goaty flavour in goat milk. In conclusion, current research provides important genomic resources and expression information for ACSs in goats, which will support further research on investigating the formation mechanisms of the goaty flavour in goat milk.

Influence of dietary cardoon meal on volatile compounds and flavour in lamb meat

Cardoon meal is a by-product retained after oil extraction from the seeds of cultivated Cynara cardunculus var. altilis that has been proposed as a valuable resource for animal feeding. The study aimed to assess the influence of its dietary inclusion on volatile profile and flavour of meat and kidney fat from lambs. Fifteen Sarda × Comisana male lambs were randomly divided in two groups and fed for 75 days with a concentrate-based diet containing 15% cardoon meal (CMD, n = 7) or dehydrated alfalfa (CON, n = 8). Cardoon meal inclusion reduced the "barnyard/animal" odour perceived by a trained panel in kidney fat, which could be associated with the aromatic compound p-cresol (4-methylphenol), detected only in CON diet. Considering the other aroma volatiles regarded as the main contributors for the characteristic lamb flavour, both diets were characterized by moderate to low levels of 4-methyloctanoic acid, skatole and indole while 4-methylnonanoic acid and 4-ethyloctanoic acid were not detected.

Factors affecting levels of volatile 4-alkyl branched-chain fatty acids in sheep milk from 2 contrasting farming systems in New Zealand

Knowledge of factors influencing the levels of 4-alkyl branched-chain fatty acid (vBCFA), and consequently the "sheepy flavor" intensity of New Zealand sheep milk, is currently limited. In this study, we investigated the effects of 2 contrasting farming systems (fully housed/mid-lactation or pasture-grazed/late lactation) on the levels of vBCFA in sheep milk on a commercial farm in the North Island of New Zealand. Fully housed/mid-lactation ewes were housed 24 h/d and fed a total mixed ration. Pasture-grazed/late-lactation ewes were grazed 24 h/d and offered approximately 40% supplements because of poor pasture growth resulting from dry and hot climatic conditions. Any effects of genetics, age, lactation stage, feed composition, lambing date, or the environment in the housing barn or outdoors were confounded. The results obtained in this study were descriptive rather than definitive, because of the limitations of the experimental design. Levels of 4-methyloctanoic acid and 4-methylnonanoic acid in milk from fully housed/mid-lactation ewes increased during the trial period, but remained low in milk from pasture-grazed/late-lactation ewes. Levels of 4-ethyloctanoic acid in milk from the 2 groups of ewes were comparable throughout the trial. Increases in levels of 4-methyloctanoic acid and 4-methylnonanoic acid in sheep milk were associated with lactation stage and the proportion of lucerne silage fed to ewes. The level of free-form 4-ethyloctanoic acid was positively correlated with the proportion of soy meal in the diet and negatively correlated with the proportion of barley. Milk from fully housed/mid-lactation ewes had a higher flavor values than milk from pasture-grazed/late-lactation ewes because of its higher total amounts of vBCFA.

Effect of Spices on the Formation of VOCs in Roasted Mutton Based on GC-MS and Principal Component Analysis

Peppertree prickly ash, Amomum tsao-ko, cumin, and ginger have long been used in Asian countries to modify the flavor and to partially neutralize any unpleasant odors present in roast lamb. The purpose of this study was to evaluate the change in the amount of volatile components present in roast lamb compared to meat added with peppertree prickly ash, Amomum tsao-ko, cumin, and ginger. Principal component analysis was carried out on the 27 initially selected from 88 volatile substances, and 15 substances with a projection of more than 0.25 in the load matrix were used as indicators to study the different contents in roasted mutton and lamb prepared by adding peppertree prickly ash, Amomum tsao-ko, cumin, and ginger. The types of VOCs (volatile organic compounds) detected in roast meat without adding spices were the least. Roast meat with the addition of cumin leads to the strongest content of aldehydes, followed by the addition of Amomum tsao-ko. Additionally, roast meat with the addition of Chinese prickly ash leads to the strongest content of terpenes, followed by the addition of ginger. Moreover, with the addition of spices, the content of volatiles responsible for the presence of a mutton odor (such as hexanal, heptanal, pentanal, (z)-4-decenal, benzaldehyde, p-propyl-anisole, and dimethyl ether) was not significantly decreased, and in fact some volatiles increased in amount such as pentanal, hexanal, octanal, and (z)-4-decenal. In conclusion, the effect of addition of spices on the volatile profile of roasted mutton and lamb can be attributed to the generation of flavor volatiles mainly derived from raw spices’ hot action, with few additional volatiles formed during boiling.

Volatile Profile of Grilled Lamb as Affected by Castration and Age at Slaughter in Two Breeds

The aim of this study was to assess the effect of castration and slaughter age on the volatile profile of cooked meat from Scottish Blackface (SB) and Texel × Scottish Blackface (T × SB) lambs. M. longissimus thoracis et lumborum was sampled at slaughter and subjected to volatile analysis by SPME-GC-MS. Rams had higher relative proportions, expressed as relative abundance (RA), in lipid oxidation products while castrates had higher RA in pyrazines and benzenoid compounds. There was no consistent age effect on the RA of volatiles, although rams in November and January had a different volatile profile to castrates. There were higher proportions of free branched-chain fatty acids in muscle from SB compared to T × SB lambs. Overall, the results showed that production factors affected the volatile profile of cooked lamb meat which may explain differences in lamb flavor.

PRACTICAL APPLICATION

Lamb meat has a characteristic flavor which, according to the evidence to date, may be influenced by farm production factors like gender or slaughter age. Our results showed variations in the proportions of some flavor compounds in cooked lamb between rams and castrated lambs while an increase in slaughter age did not have a consistent effect on proportions of compounds.

Gas-phase chemical ionization of 4-alkyl branched-chain carboxylic acids and 3-methylindole using H3 O+ , NO+ , and O2+ ions

RATIONALE

4-Methyloctanoic acid, 4-ethyloctanoic acid, 4-methylnonanoic acid, and 3-methylindole are primary contributors to the distinctive aroma and flavor of lamb meat. The reactions of H₃ O⁺ , NO⁺ , and O₂⁺ with these compounds, and identification of the product ions and their distribution, are fundamental to their characterization and rapid, real-time trace analysis using selected ion flow tube mass spectrometry (SIFT-MS).

METHODS

The chemical ionization of pure standards of 4-ethyloctanoic acid, 4-methyloctanoic acid, 4-ethylnonanoic acid, and 3-methylindole was carried out using the H₃ O⁺ , NO⁺ , and O₂⁺ reagent ions of a V200™ SIFT mass spectrometer. Kinetic data were calculated using the Langevin collision rate with parameterized trajectory equations. Identification of product ions, distribution, and interferences was performed by further evaluation of the pertinent ion-molecule reaction mechanisms, careful spectral analyses, and molecular mass-molecular structure pairing.

RESULTS

The collisional capture rate constants of the reaction of the precursor ions H₃ O⁺ , NO⁺ , and O₂⁺ , their extended hydrates and the analytes, which were assumed to occur at or near the collisional rate, were all of the order of 10^-9  cm³ molecule s^-1 - typical for bimolecular ion-molecule reactions. Positive identification of the primary and secondary product ions, fragmented ionic species, and potential ion conflicts and interferences, from each reagent ion channel, was determined for each compound.

CONCLUSIONS

We have established the ion chemistry involved in the ionization of the 4-alkyl branched-chain fatty acids and 3-methylindole using the precursor ions, H₃ O⁺ , NO⁺ , and O₂⁺ in SIFT-MS. The ion-molecular chemistry and the associated kinetics serve as a fundamental basis for the accurate characterization of these compounds by SIFT-MS.

High enantiomeric excess of the flavor relevant 4-alkyl-branched Fatty acids in milk fat and subcutaneous adipose tissue of sheep and goat

Volatile 4-alkyl-branched fatty acids are characteristic flavor compounds of sheep and goat. Due to the methyl branch, the carbon C-4 represents a stereogenic center with the possible presence of one or both enantiomers in the respective samples. In this study, we used enantioselective gas chromatography to study the enantiomeric composition of 4-methyloctanoic acid (4-Me-8:0) and 4-ethyloctanoic acid (4-Et-8:0) in milk and dairy products from sheep and goat as well as in goat subcutaneous tissue. Different columns coated with modified cyclodextrins were tested to resolve racemic 4-alkyl-branched fatty acid methyl ester standards. The best enantiomer resolution was obtained on 25% octakis(2,3,6-tri-O-ethyl)-γ-cyclodextrin (γ-TECD) diluted in OV-1701. For analysis of the food samples, the lipids were extracted and fatty acids in the extracts were converted into fatty acid methyl esters. Non-aqueous reversed-phase high-performance liquid chromatography was used to fractionate the samples in order to gain one solution enriched in 4-Me-8:0 methyl ester and one solution enriched with 4-Et-8:0 methyl ester. Subsequent analysis by enantioselective gas chromatography with mass spectrometry allowed only the detection of one enantiomer of 4-Me-8:0 and 4-Et-8:0 in the samples. By means of a non-racemic standard of 4-Me-8:0, it was found that the predominant enantiomer was (R)-4-Me-8:0.