An overview on the presence of cyclopropane fatty acids in milk and dairy products

Novel odd-chain cyclopropane fatty acids: detection in a mammalian lipidome and uptake by hepatosplanchnic tissues

Microbe-produced molecules (xenometabolites) found in foods or produced by gut microbiota are increasingly implicated in microbe-microbe and microbe-host communication. Xenolipids, in particular, are a class of metabolites for which the full catalog remains to be elaborated in mammalian systems. We and others have observed that cis-3,4-methylene-heptanoylcarnitine is a lipid derivative that is one of the most abundant medium-chain acylcarnitines in human blood, hypothesized to be a product of incomplete β-oxidation of one or more "odd-chain" long-chain cyclopropane fatty acids (CpFAs). We deduced two possible candidates, cis-11,12-methylene-pentadecanoic acid (cis-11,12-MPD) and cis-13,14-methylene-heptadecanoic acid (cis-13,14-MHD). Authentic standards were synthesized: cis-11-pentadecenoic acid and cis-13-heptadecenoic acid were generated (using Jones reagent) from cis-11-pentadecene-1-ol and cis-13-heptadecene-1-ol, respectively, and these were converted to CpFAs via a reaction involving diiodomethane. Using these standards in mass spectrometry analyses, we determined the presence/absence of cis-11,12-MPD and cis-13,14-MHD in archived piglet biospecimens. Both CpFAs were detected in rectal contents of sow and soy-fed piglets. Archived mass spectra were analyzed post hoc from a second independent study that used tissue-specific catheterization to monitor net metabolite flux in growing pigs. This confirmed the presence of both CpFAs in plasma and revealed a significant net uptake of the odd-chain CpFAs across the splanchnic tissue bed and liver. The results confirm that the novel xenolipids cis-11,12-MPD and cis-13,14-MHD can be components of the mammalian lipidome and are viable candidate precursors of cis-3,4-methylene-heptanoylcarnitine produced from partial β-oxidation in liver or other tissues.

Establishing authenticity of hay milk: Detection of silage feeding through cyclopropane fatty acids analysis using 1H NMR spectroscopy

Cyclopropane fatty acids (CPFAs) serve as indicators of silage feeding, verifying the authenticity of hay milk where silage feeding is forbidden. In this study, the authenticity of hay milk was determined by detecting CPFAs using proton nuclear magnetic resonance (1H NMR) spectroscopy. 245 milk samples were collected in South Tyrol (Italy), categorized as follows: 98 from grass silage-fed cows, 98 from maize silage-fed cows, and 49 authentic hay milk. The limit of detection of CPFAs was 12 µM, corresponding to 70 mg/kg of freeze-dried milk. The CPFAs were absent in all of the hay milk samples, verifying their authenticity. In contrast, 97 % of maize silage and 77 % of grass silage samples exhibited distinct CPFAs signals. These findings were further corroborated by gas chromatography-mass detector (GC-MS) analysis. The study highlights 1H NMR as a robust, and rapid technique for hay milk authentication, supporting alpine dairy production and increasing consumer trust in food authenticity.

Improved Detection and Quantification of Cyclopropane Fatty Acids via Homonuclear Decoupling Double Irradiation NMR Methods

Over the years, NMR spectroscopy has become a powerful analytical tool for the identification and quantification of a variety of natural compounds in a broad range of food matrices. Furthermore, NMR can be useful for characterizing food matrices in terms of quality and authenticity, also allowing for the identification of counterfeits. Although NMR requires minimal sample preparation, this technique suffers from low intrinsic sensitivity relative to complementary techniques; thus, the detection of adulterants or markers for authenticity at low concentrations remains challenging. Here, we present a strategy to overcome this limitation by the introduction of a simple band-selective homonuclear decoupling sequence that consists of double irradiation on 1H during NMR signal acquisition. The utility of the proposed method is tested on dihydrosterculic acid (DHSA), one of the cyclopropane fatty acids (CPFAs) shown to be a powerful molecular marker for authentication of milk products. A quantitative description of how the proposed NMR scheme allows sensitivity enhancement yet accurate quantification of DHSA is provided.

Study on the Effect of Ensiling Process and Ruminal Digestion on the Synthesis and Release of Cyclopropane Fatty Acids in Cow Feeding

Cyclopropane fatty acids (CPFA) were found in milk fat from cows fed maize silage and suggested to be synthesized by lactic acid bacteria during ensiling. This study aimed to elucidate some gaps of knowledge about the microbial synthesis of CPFA, to strengthen the current authentication method based on their detection in cheese fat and performed for Parmigiano Reggiano (UNI11650), whose Specifications forbid the use of silage. CPFA were screened in different ensiled cows' feeding by gas chromatography-mass spectrometry, and the effect of feed ingredients and ruminal digestion on CPFA microbial production were further examined by in vitro tests. Results showed that solely the environmental conditions developed in silos for specific plant materials (e.g., maize) are essential for the bacterial synthesis of CPFA, whereas rumen activity did not affect CPFA levels in feeds. This supports the suitability of using CPFA as biomarkers of a crop silage-based diet forbidden by certain PDO feedstock regulations.

Cyclopropane Fatty Acids as Quality Biomarkers of Cheeses from Ewes Fed Hay- and Silage-Based Diets

This study aimed to investigate cyclopropane fatty acids (CPFAs) as quality biomarkers of forage feedings in cheese fat obtained from ewe's milk, based on two different dietary treatments (hay and silage). The gas chromatography-mass spectrometry (GC-MS) analysis detected CPFAs in most cheese samples, both from hay and silage-based diets. CPFA levels in cheese fat from hay feeding were positively correlated to the total trans-monounsaturated fatty acids (MUFAs) and n-6 polyunsaturated fatty acids (PUFAs), whereas they were negatively correlated to cis-MUFAs, odd- and branched-chain fatty acids (i.e., C13:0 anteiso, C16:0 iso, and C17:1), and C22:5n-3, which are mainly associated with a low starch intake and grass pasture. Overall, the presence of CPFAs in ovine cheese fat suggests the use of silage, but it can also be an indicator of poor-quality hay forages. This approach confirmed the reliability of CPFAs as biomarkers of forage quality, especially in relation to the use of conserved forages and good livestock practices.

High-throughput virtual screening and microsecond MD simulations to identify potential sugar mimic of the solute-binding protein BlAXBP of the ABC transporter from Bifidobacterium animalis subsp. Lactis

Xylotetraose is a prebiotic oligosaccharide can be utilized by the ABC transporter of the gut microbiota Bifidobacteria. BlAXBP is the solute binding protein of the ABC transporter, and its complex with xylotetraose has been solved by X-ray crystallography. Here, we have identified novel sugar mimic of BlAXBP by applying a high-throughput virtual screening of ZINC database containing a huge library with ∼22 M compounds. To begin with, we identified 18,571 ligands by a ligand-based virtual screening. Further, a total of 3968 compounds were selected for molecular docking due to their Tanimoto coefficient's value were larger than a cutoff of 0.08. The molecular mechanics-generalized born surface area was used to evaluate the binding free energies, and the top 10 ligands with free energies below an energy threshold of -35.22 kcal/mol were selected. ZINC13783511 formed the most stable complex with BlAXBP and its recognition mechanism were further explored by microsecond MD simulations in explicit solvent. Free energy landscapes were used to evaluate conformational changes of BlAXBP in its ligand free and binding states. Collectively, this work identified potential novel sugar mimics to BlAXBP, providing novel atomic-level understanding of the binding mechanism.

Occurrence of Cis-11,12-Methylene-Hexadecanoic Acid in the Red Alga Solieria pacifica (Yamada) Yoshida

Fatty acids in marine algae have attracted the attention of natural chemists because of their biological activity. The fatty acid compositions of the Solieriaceae families (Rhodophyceae, Gaigartinales) provide interesting information that unusual cyclic fatty acids have been occasionally found. A survey was conducted to profile the characteristic fatty acid composition of the red alga Solieria pacifica (Yamada) Yoshida using gas chromatography-mass spectrometry (GC-MS), infrared spectroscopy (IR), and proton nuclear magnetic resonance spectroscopy (¹H-NMR). In S. pacifica, two cyclopentyl fatty acids, 11-cyclopentylundecanoic acid (7.0%), and 13-cyclopentyltridecanoic acid (4.9%), and a cyclopropane fatty acid, cis-11,12-methylene-hexadecanoic acid (7.9%) contributed significantly to the overall fatty acid profile. In particular, this cyclopropane fatty acid has been primarily found in bacteria, rumen microorganisms or foods of animal origin, and has not previously been found in any other algae. In addition, this alga contains a significant amount of the monoenoic acid cis-11-hexadecenoic acid (9.0%). Therefore, cis-11,12-methylene-hexadecanoic acid in S. pacifica was likely produced by methylene addition to cis-11-hexadecenoic acid.

Enzymatic hydrolysis of monoacylglycerols and their cyclopropanated derivatives: Molecular structure and nanostructure determine the rate of digestion

Colloidal lipidic particles with different space groups and geometries (mesosomes) are employed in the development of new nanosystems for the oral delivery of drugs and nutrients. Understanding of the enzymatic digestion rate of these particles is key to the development of novel formulations. In this work, the molecular structure of the lipids has been systematically tuned to examine the effect on their self-assembly and digestion rate. The kinetic and phase changes during the lipase-catalysed hydrolysis of mesosomes formed by four synthetic cyclopropanated lipids and their cis-unsaturated analogues were monitored by dynamic small angle X-ray scattering and acid/base titration. It was established that both the phase behaviour and kinetics of the hydrolysis are greatly affected by small changes in the molecular structure of the lipid as well as by the internal nanostructure of the colloidal particles.

An Overview on Cyclic Fatty Acids as Biomarkers of Quality and Authenticity in the Meat Sector

A survey was conducted to determine the content of cyclopropane fatty acids (CPFAs) and ω-cyclohexyl fatty acids (CHFAs) by using gas chromatography- mass spectrometry (GC-MS) and proton nuclear magnetic resonance (¹H NMR) techniques in various meat samples from different species, including commercial samples and complex and thermally processed products (i.e., Bolognese sauce). The CPFAs concentration (as the sum of two isomers, namely dihydrosterculic acid and lactobacillic acid) in bovine meat fat (ranging between 70 and 465 mg/kg fat) was positively related to a silage-based diet, and therefore, they are potential biomarkers for monitoring the feeding system of cattle. CHFAs, such as 11-cyclohexylundecanoic and 13-cyclohexyltridecanoic acids, were only found in lipid profiles from ruminant species, and a linear trend was observed in their content, together with iso-branched fatty acids (iso-BCFAs) deriving from ruminal fermentation, as a function of bovine meat percentage in both raw and cooked minced meat. Thus, CHFAs are potential biomarkers for the assurance of the meat species and, combined with iso-BCFAs, of the beef/pork ratio even in complex meat matrices. The proposed approaches are valuable novel tools for meat authentication, which is pivotal in the management of meat quality, safety, and traceability.

Identification of Cyclopropane Fatty Acids in Human Plasma after Controlled Dietary Intake of Specific Foods

Cyclopropane fatty acids (CPFAs) are an investigated class of secondary fatty acids of microbial origin recently identified in foods. Even though the dietary daily intake of this class of compounds it has been recently estimated as not negligible, to date, no studies specifically have investigated their presence in human plasma after consumption of CPFA-rich sources. Therefore, the aims of this study were (i) to test CPFAs concentration in human plasma, thus demonstrating their in vivo bioaccessibility and potential bioavailability, (ii) to investigate a dose-response relationship between medium term chronic intake of CPFAs-rich foods and both CPFAs and plasma total fatty acid profiles in healthy subjects. Ten healthy normal weight adults were enrolled for conducting an in vivo study. Participants were asked to follow a CPFA-controlled diet for 3 weeks, consuming 50 g of Grana Padano cheese (GP) and 250 mL of whole cow milk, which correspond to a total of 22.1 mg of CPFAs. Fasting CPFAs concentration were monitored for eight timepoints during the whole study and plasma total fatty acids composition was determined by GC-MS. CPFAs, mainly dihydrosterculic acid (DHSA), were identified in plasma total fatty acids profile at the beginning of the study and after dietary treatment. A significant (p < 0.05) increase of CPFAs mean plasma concentration (n = 10) were observed at the end of the dietary intervention. Contrarily, the total fatty acids composition of the general plasma fatty acids profile did not significantly change (p ≥ 0.05) during the dietary intervention period. This is the first investigation demonstrating that CPFAs are bioaccessible in vivo and, as expected, their plasmatic concentration may be affected by consumption of CPFAs-rich foods. This research will open the door to further detailed research, which may better elucidate the role of these compounds in human health.

Virtual screening of potentially endocrine-disrupting chemicals against nuclear receptors and its application to identify PPARγ-bound fatty acids

Nuclear receptors (NRs) are key regulators of energy homeostasis, body development, and sexual reproduction. Xenobiotics binding to NRs may disrupt natural hormonal systems and induce undesired adverse effects in the body. However, many chemicals of concerns have limited or no experimental data on their potential or lack-of-potential endocrine-disrupting effects. Here, we propose a virtual screening method based on molecular docking for predicting potential endocrine-disrupting chemicals (EDCs) that bind to NRs. For 12 NRs, we systematically analyzed how multiple crystal structures can be used to distinguish actives and inactives found in previous high-throughput experiments. Our method is based on (i) consensus docking scores from multiple structures at a single functional state (agonist-bound or antagonist-bound), (ii) multiple functional states (agonist-bound and antagonist-bound), and (iii) multiple pockets (orthosteric site and alternative sites) of these NRs. We found that the consensus enrichment from multiple structures is better than or comparable to the best enrichment from a single structure. The discriminating power of this consensus strategy was further enhanced by a chemical similarity-weighted scoring scheme, yielding better or comparable enrichment for all studied NRs. Applying this optimized method, we screened 252 fatty acids against peroxisome proliferator-activated receptor gamma (PPARγ) and successfully identified 3 previously unknown fatty acids with Kd = 100-250 μM including two furan fatty acids: furannonanoic acid (FNA) and furanundecanoic acid (FUA), and one cyclopropane fatty acid: phytomonic acid (PTA). These results suggested that the proposed method can be used to rapidly screen and prioritize potential EDCs for further experimental evaluations.

Determination of Cyclopropenoid Fatty Acids in Ewe Milk Fat by GC-MS after Intravenous Administration of Sterculic Acid

Cyclopropenoid fatty acids (CPEFA), found in oilseeds from Malvaceae and Sterculiaceae, have been shown to interfere with the endogenous synthesis of several bioactive lipids of dairy fat, such as cis-9, trans-11 18:2 and cis-9 18:1, by inhibiting Δ9-desaturase. No previous study has reported the presence of sterculic acid in animal fat and its incorporation in tissues after its administration, due to the lack of a proper methodology. In the present research, a GC-MS method based on cold base derivatization to fatty acids methylesters was developed to determine CPEFA in ewe milk triglycerides, after infusing sterculic acid (0.5 g/day) to six lactating ewes. An alternative derivatization based on silanyzation followed by GC-MS analysis was also tested, showing its possible applicability when CPEFA are present in the form of free fatty acids. Sterculic acid was detected in ewe milk triglycerides, demonstrating its incorporation from the bloodstream into milk by the mammary gland. The mean transfer rate represented 8.0 ± 1.0% of the daily dose. This study provides, for the first time, the presence of sterculic acid in milk fat, supporting the importance of understanding its occurrence in vivo and encouraging further research to determine whether it can be present in foods, such as dairy products, obtained under practical farming conditions.

Chemometric authentication of farming systems of origin of food (milk and ripened cheese) using infrared spectra, fatty acid profiles, flavor fingerprints, and sensory descriptions

Milk samples from 1264 cows in 85 farms were authenticated for different farming-systems using a 10-fold cross-validated linear-discriminant-analysis using Fourier-transform infrared spectra (FTIRS) and gas-chromatographic fatty-acid (FA) profiles. FTIRS gave correct classification greater than FAs (97.4% vs. 81.1%) during calibration, but slightly worse in validation (73.5% vs 77.3%) and their combination improved the results. All milk samples were processed into ripened model-cheeses, and analyzed by near-infrared-spectrometry (NIRS), by proton-transfer-reaction time-of-flight mass-spectrometry for their volatile organic compound (VOCs) fingerprint and by panel sensory profiling (SENS). Farming-system authentication on cheese samples was less efficient than on milk, but still possible. The instrumental methods yielded similar validation results, better than SENS, and their combination improved the correct classification rate. The efficiency of the different technics was affected by specific farming systems. In conclusion, dairy products could be discriminated for farming-systems with acceptable accuracy, but the methods tested differ in sampling procedure, rapidity and costs.

Presence of cyclopropane fatty acids in foods and estimation of dietary intake in the Italian population

Cyclopropane fatty acids (CPFAs) are the most abundant cyclic fatty acids in microorganisms with unknown role(s) regarding their dietary relevance and biological effects in humans. This work was aimed to draw up a list of CPFAs-containing foods for estimating their dietary intake in the Italian population to provide a basis for evaluating their nutritional relevance and potential health-related effects. The CPFAs content of more than 500 food items was investigated and a preliminary dietary intake was assessed (12.0 ± 6.0 mg/day), based on the data reported by the Italian National Food Consumption Survey INRAN-SCAI 2005-06. CPFAs should be considered of dietary relevance in view of their potential physiological activity in humans and their presence in significant amounts in dairy products, as Grana Padano cheese (9.0-30.0 mg/100 g), and in bovine meat (0.7-4.0 mg/100 g). Future studies should elucidate whether this uncommon class of fatty acids has a biological role in human health.

Determination of Cyclopropane Fatty Acids in Food of Animal Origin by 1H NMR

Cyclopropane fatty acids (CPFAs) are unusual fatty acids of microbial origin, recently detected in milk and dairy products. CPFAs have been demonstrated to be interesting molecular markers for authentication of dairy products obtained without ensiled feeds. Moreover, they can also be recognized as a new secondary component of human diet. Information is lacking on the presence of cyclic fatty acids in other food sources. Cyclopropane fatty acids have been detected by GC-MS analysis in cheese and other animal fats in concentration ranging from 200 to 1000 mg/kg fat, but in some cases, the complex fatty acid profile and the possible presence of interfering peaks make the separation not straightforward and the quantification uneasy. Therefore, a new reliable ¹H NMR method was developed to detect and measure CPFA content in different foods of animal origin, based on the detection of the characteristic signals of cyclopropane ring. The ¹H NMR (600 MHz) method showed detection limits comparable with those of full scan GC-MS, and it allowed the identification and quantitation of the cyclopropane fatty acids in different foods.

Comparative studies of immobilized lipase- and acid-catalyzed fatty acid methyl ester synthesis for seed lipid analysis

Fatty acids are one of the most important nutrients in food. Acid- or base-catalyzed transesterification methods are commonly used for the analysis of fatty acids. However, several drawbacks were reported for these methods, including the isomerization and degradation of fatty acids. Lipase-catalyzed reactions are usually undertaken at mild conditions, preventing such problems. In this study, commercial resin-bound lipase from Candida antartica was tested for possible application in fatty acid methyl ester analysis. Experimental parameters, including temperature, reaction time, and re-cycling were evaluated. The optimized condition was (5-10 mg lipid, 0.5 mL of MeOH, and 50 mg Novozyme 435 in 2 mL toluene, 80°C for 1 h). In optimized condition, the lipase-catalyzed methods yielded similar results with the chemical method. In overall, lipase-catalyzed transesterification can be a useful alternative to acid-catalyzed methods for fatty acid analysis.

Development of a Quantitative GC-MS Method for the Detection of Cyclopropane Fatty Acids in Cheese as New Molecular Markers for Parmigiano Reggiano Authentication

Cyclopropane fatty acids (CPFA), as lactobacillic acid and dihydrosterculic acid, are components of bacterial membranes and have been recently detected in milk and in dairy products from cows fed with corn silage. In this paper, a specific quantitative gas chromatography-mass spectrometry (GC-MS) method for the detection of CPFA in cheeses was developed, and the quality parameters of the method (limit of detection, limit of quantitation, and intralaboratory precision) were assessed. Limit of detection and quantitation of CPFA were, respectively, 60 and 200 mg/kg of cheese fat, and the intralaboratory precision, determined on three concentration levels, satisfied the Horwitz equation. This method was applied to 304 samples of PDO cheeses of certified origin, including Parmigiano Reggiano (Italy), Grana Padano (Italy), Fontina (Italy), Comté (France), and Gruyère (Switzerland). Results showed that CPFA were absent in all of the cheeses whose Production Specification Rules expressly forbid the use of silages (Parmigiano Reggiano, Fontina, Comté, and Gruyère). CPFA were instead present in variable concentrations (300-830 mg/kg of fat) in all of the samples of Grana Padano cheese (silages admitted). A mix of grated Parmigiano Reggiano and Grana Padano was also prepared, showing that the method is able to detect the counterfeiting of Parmigiano Reggiano with other cheeses up to 10-20% Grana Padano content. These results support the hypothesis that CPFA can be used as a marker of silage feedings for cheeses, and the data reported can be considered a first attempt to create a database for CPFA presence in PDO cheeses.

Increased Serum Level of Cyclopropaneoctanoic Acid 2-Hexyl in Patients with Hypertriglyceridemia-Related Disorders

We recently reported the presence of various cyclopropane fatty acids—among them, cyclopropaneoctanoic acid 2-hexyl—in the adipose tissue of obese women. The aim of this study was to verify whether the presence of cyclopropaneoctanoic acid 2-hexyl in human serum was associated with obesity or chronic kidney disease (both being related to dyslipidemia), and to find potential associations between the serum level of this compound and specific markers of the these conditions. The serum concentration of cyclopropaneoctanoic acid 2-hexyl was determined by gas chromatography–mass spectrometry (GC–MS) in non-obese controls, obese patients, obese patients after a 3-month low-calorie diet, and individuals with chronic kidney disease. Obese patients and those with chronic kidney disease presented with higher serum levels of cyclopropaneoctanoic acid 2-hexyl than controls. Switching obese individuals to a low-calorie (low-lipid) diet resulted in a reduction in this fatty acid concentration to the level observed in controls. Cyclopropaneoctanoic acid 2-hexyl was also found in foods derived from animal fat. Serum concentrations of triacylglycerols in the analyzed groups followed a pattern similar to that for serum cyclopropaneoctanoic acid 2-hexyl, and these variables were positively correlated with each other among the studied groups. Patients with hypertriglyceridemia-related conditions presented with elevated serum levels of cyclopropaneoctanoic acid 2-hexyl. Our findings suggest that its high serum level is related to high serum triacylglycerol concentrations rather than to body mass or BMI.