**2. Cyclic fatty acids: natural occurrence and biosynthesis**

#### **2.1 Cyclopropane and cyclopropene fatty acids**

Cyclopropane fatty acids (CPFA), containing three carbon rings located at different sites of the fatty acid chain (**Figure 1**), occur widespread in several microorganisms as major lipid component [8] and in certain eukaryotes, including protozoa, fungi, and plants [9, 15]. Many cyclopropane-containing natural compounds have shown biological activity, and their presence in the cellular membrane seems to be related to its physicochemical properties [16]. However, the real significance of these compounds in their natural context is often less well known as well as their occurrence in higher animals. The major investigations which have been

**33**

amounts [22].

*Cyclic Fatty Acids in Food: An Under-Investigated Class of Fatty Acids*

published about their occurrence, biosynthesis, and their physiological role in the cellular membrane are described in more detail in the following paragraphs.

A study of the fatty acid composition of *Lactobacillus arabinosus* first reported the isolation of lactobacillic acid (cis-11,12-methylene octadecanoic acid), a 19 carbon cyclopropane analogue of cis-vaccenic acid, the major unsaturated fatty

Subsequently, lactobacillic acid and other cyclopropane fatty acids have been

CPFA are suggested to be associated with the occurrence of unsaturated fatty acids (UFA) in the bacterial membrane, generally palmitoleic (cis-9-hexadecenoic acid), cis-vaccenic (cis-11-octadecenoic acid), and oleic (cis-9-octadecenoic acid) acids [5]. Furthermore, it seems that they predominate at the end of the growth cycle of bacteria, when the majority of UFA are converted to cyclopropane fatty acids by the

Cyclopropane and the structurally related cyclopropene fatty acids have also been found in certain eukaryotes, including trypanosomatid protozoa and plants

In plants, cyclopropene fatty acids, such as sterculic acid (cis-9,10-methylene-9-octadecenoic acid) and malvalic acid (cis-8,9-methylene-heptadecenoic acid), are distributed across several families, mainly in Sterculiaceae, Malvaceae, Bombacaceae, Tiliaceae, and Sapindaceae. It has been reported that cyclopropene fatty acids are often accompanied by smaller proportion of cyclopropanic fatty acids, such as dihydrosterculic and dihydromalvalic acids, which are the dihydro

*Sterculia foetida* is a tropical tree belonging to the Sterculiaceae family of order Malvales. Its seeds are rich in oil (55% dry weight) and contain up to 78% of cyclopropenoid fatty acids (especially sterculic and malvalic acids), representing one of

CPFA were the major lipid component (42%) in the seed oil of *Litchi chinensis,* belonging to Sapindaceae family. The CPFA fraction in *Litchi chinensis* seed oil mainly contains dihydrosterculic acid, and cis-7,8-methylenehexadecanoic acid, cis-5,6-methylene-tetradecanoic acid, and cis-3,4-methylenedodecanoic acid in smaller

the highest source of carbocyclic fatty acids reported in nature [19].

identified in a variety of microorganisms of both Gram-negative and Grampositive bacteria such as Lactobacilli, Streptococci, Enterobacteria, Clostridia, and Brucellaceae [18]. Some microorganisms contain cis-9,10-methylene octadecanoic acid (dihydrosterculic acid), derived from oleic acid, together with other isomers

(C16 or C20 in chain length, as cis-9,10-methylene hexadecenoic acid).

*DOI: http://dx.doi.org/10.5772/intechopen.80500*

*Most commonly found cyclopropane fatty acids in bacteria.*

*2.1.1 Distribution*

**Figure 1.**

acid in *L. arabinosus* membrane [17].

cyclopropane synthase [8].

analogues of cyclopropene fatty acids [21].

[19, 20].

*Cyclic Fatty Acids in Food: An Under-Investigated Class of Fatty Acids DOI: http://dx.doi.org/10.5772/intechopen.80500*

#### **Figure 1.**

*Biochemistry and Health Benefits of Fatty Acids*

atoms and linear hydrocarbon chains, although some of them, found primarily in bacteria, may contain branched or cyclic structures [5–7]. Fatty acids containing a carbocyclic unit naturally occur in specific genera of bacteria and in plants.

In some cases, alicyclic fatty acids, such as cyclopropane (CPFA) and omegacyclohexyl fatty acids (CHFA), are essential for cell survival, as they could affect the membrane fluidity that enables certain microorganisms to survive under extreme environmental conditions [8]. In plants, CPFA are usually minor components, where cyclopropene fatty acids are the most abundant. *Sterculia foetida* seed oil contains 65–78% of cyclopropene fatty acids (principally sterculic acid), sug-

CPFA, especially dihydrosterculic (9,10-methylene-octadecanoic acid) and lactobacillic (11,12-methylene-octadecanoic acid) acids, have been identified as minor component of lipid profile in a wide range of milk and dairy products [10, 11] and, more recently, in meat and fish [12] representing important foodstuffs in human

CPFA concentration ranges from 200 to 1000 mg/kg fat in dairy products and bovine meat [13]; therefore, their dietary intake may not be negligible, and their

However, due to their recent identification, so far CPFA have not been yet considered for their occurrence in humans, and several aspects related to their bioavailability and putative bioactivity as well as the bacterial strains producing CPFA in

ω-Cyclohexyl fatty acids (CHFAs), mainly cyclohexyl-undecanoic and tridecanoic acids, occur in several acido-thermophilic bacteria such as *Alicyclobacillus acidocaldarius* and can be biosynthesized by these bacteria species, even by adding cyclohexyl acid to the bacteria culture [11]. 11-cyclohexyl undecanoic acid was first isolated as a minor component of butter fat, then in sheep fat but it is almost certainly produced by bacteria in the rumen. 13-cyclohexyltridecanoic acid has been considered as a potential marker of ruminal acidosis in cow [11]. Recently, both ω-cyclohexyl fatty acids, 11-cyclohexylundecanoic acid and 13-cyclohexyltridecanoic acid, were detected in meat fat, especially in bovine meat but not in pork and horse meat. Therefore, the presence of ω-cyclohexyl fatty acids in foods was related to a ruminal origin and, combined with other fatty acids as branched chain fatty acids, could be

This chapter reviews the literature data about the origin and natural occurrence of cyclic fatty acids, their presence in foods, especially in meat and dairy products, and their potential bioavailability and bioactivity in mammals. Finally, the application of some cyclic fatty acids as molecular markers for food authenticity will be

Cyclopropane fatty acids (CPFA), containing three carbon rings located at different sites of the fatty acid chain (**Figure 1**), occur widespread in several microorganisms as major lipid component [8] and in certain eukaryotes, including protozoa, fungi, and plants [9, 15]. Many cyclopropane-containing natural compounds have shown biological activity, and their presence in the cellular membrane seems to be related to its physicochemical properties [16]. However, the real significance of these compounds in their natural context is often less well known as well as their occurrence in higher animals. The major investigations which have been

**2. Cyclic fatty acids: natural occurrence and biosynthesis**

**2.1 Cyclopropane and cyclopropene fatty acids**

gested to have antifungal and enzyme inhibitor activities [9].

potential role in human health should not be underestimated.

feeds and in which conditions still must be explored.

proposed as marker of species [14].

**32**

provided.

diet.

*Most commonly found cyclopropane fatty acids in bacteria.*

published about their occurrence, biosynthesis, and their physiological role in the cellular membrane are described in more detail in the following paragraphs.

#### *2.1.1 Distribution*

A study of the fatty acid composition of *Lactobacillus arabinosus* first reported the isolation of lactobacillic acid (cis-11,12-methylene octadecanoic acid), a 19 carbon cyclopropane analogue of cis-vaccenic acid, the major unsaturated fatty acid in *L. arabinosus* membrane [17].

Subsequently, lactobacillic acid and other cyclopropane fatty acids have been identified in a variety of microorganisms of both Gram-negative and Grampositive bacteria such as Lactobacilli, Streptococci, Enterobacteria, Clostridia, and Brucellaceae [18]. Some microorganisms contain cis-9,10-methylene octadecanoic acid (dihydrosterculic acid), derived from oleic acid, together with other isomers (C16 or C20 in chain length, as cis-9,10-methylene hexadecenoic acid).

CPFA are suggested to be associated with the occurrence of unsaturated fatty acids (UFA) in the bacterial membrane, generally palmitoleic (cis-9-hexadecenoic acid), cis-vaccenic (cis-11-octadecenoic acid), and oleic (cis-9-octadecenoic acid) acids [5]. Furthermore, it seems that they predominate at the end of the growth cycle of bacteria, when the majority of UFA are converted to cyclopropane fatty acids by the cyclopropane synthase [8].

Cyclopropane and the structurally related cyclopropene fatty acids have also been found in certain eukaryotes, including trypanosomatid protozoa and plants [19, 20].

In plants, cyclopropene fatty acids, such as sterculic acid (cis-9,10-methylene-9-octadecenoic acid) and malvalic acid (cis-8,9-methylene-heptadecenoic acid), are distributed across several families, mainly in Sterculiaceae, Malvaceae, Bombacaceae, Tiliaceae, and Sapindaceae. It has been reported that cyclopropene fatty acids are often accompanied by smaller proportion of cyclopropanic fatty acids, such as dihydrosterculic and dihydromalvalic acids, which are the dihydro analogues of cyclopropene fatty acids [21].

*Sterculia foetida* is a tropical tree belonging to the Sterculiaceae family of order Malvales. Its seeds are rich in oil (55% dry weight) and contain up to 78% of cyclopropenoid fatty acids (especially sterculic and malvalic acids), representing one of the highest source of carbocyclic fatty acids reported in nature [19].

CPFA were the major lipid component (42%) in the seed oil of *Litchi chinensis,* belonging to Sapindaceae family. The CPFA fraction in *Litchi chinensis* seed oil mainly contains dihydrosterculic acid, and cis-7,8-methylenehexadecanoic acid, cis-5,6-methylene-tetradecanoic acid, and cis-3,4-methylenedodecanoic acid in smaller amounts [22].

Malvalic, sterculic, and dihydrosterculic acids have also been detected in Baobab seeds oil from plant belonging to Adansonia species (Bombacaceae family) of Madagascar. Seed lipids containing CPFA are extensively consumed by humans, especially in those tropical areas [19, 23].

However, carbocyclic fatty acids seemed not to be confined to seeds. Long-chain cyclopropane fatty acids have been described in various polar lipid classes of leaves of early spring plants, whereas both cyclopropane and cyclopropene fatty acids were found in root, leaf, stem, and callus tissue in plants of the Malvaceae [9].

The presence of CPFA has also been documented in some aquatic invertebrates, marine isolates [24, 25] and in the lipid composition of mushrooms, mainly belonging to the family *Boletaceae* [15]. Overall, the natural distribution of CPFA among eukaryotes appears much less common than among bacteria.

### *2.1.2 Biosynthesis and physiological aspects*

CPFA synthesis involves the transfer of a methylene group from S-adenosyl methionine by the CPFA synthase to the cis double bond of the precursor unsaturated fatty acids, already integrated into phospholipids of cellular membrane [5]. A proposed pathway for the biosynthesis of dihydrosterculic acid from oleic acid is shown in **Figure 2**.

The reaction is a post synthetic modification and has been widely studied in microorganisms such as *E. coli* [26–29], Pseudomonas, Mycobacterium, *Lactobacillus* spp. and *Leishmania* spp. [20, 30, 31].

Cyclopropane fatty acids are not essential fatty acids, but the bacterial production of cyclopropane ring seems to be related to changes in the membrane fatty acid composition of that microorganisms. In fact, the presence of these specific fatty acids seems to favor the stress tolerance of several bacteria strains to adverse environments (including ethanol, osmotic and oxidative stress, hot temperature, and low pH) and likely plays a role in the pathogenesis of bacterial infections [32].

The acid tolerance of individual strains of *E. coli* appears to be correlated with membrane cyclopropane fatty acid content and may enhance the survival of microbial cells exposed to low pH [29]. During acid habituation, monounsaturated fatty acids (cis-16:1 and cis-18:1) are either converted to their cyclopropane derivatives or replaced by saturated fatty acids. On the contrary, *E. coli* mutants deficient in CPFA seemed to be more sensitive to adverse conditions such as repeated freeze-drying and pressure [33].

Natural CPFA occur widespread with a cis configuration about cyclopropane moiety [5]; however, trans cyclopropane fatty acids are common in the cell

**35**

**Figure 3.**

*Cyclic Fatty Acids in Food: An Under-Investigated Class of Fatty Acids*

envelope of *Mycobacterium tuberculosis* and play a role in regulating virulence. Cyclopropanation of mycolic acids has been suggested to be correlated with the persistence of the pathogen and modulates the innate immune response of the host

Cyclopropane fatty acids tend to promote the fluidity of lipid bilayers by interfering with lipid packing, improving the formation of gauche defects originating partly from the steric restraints caused by the methylene moieties and increasing lipid diffusion [31]. This could explain how cyclopropane fatty acids can improve the stability of the membrane against adverse conditions and, at the same time,

CPFA are cellular components of lactic acid bacteria (LAB), such as *Lactobacillus bulgaricus*, *L. helveticus*, *L. sanfranciscensis*, and *L. acidophilus*, and are synthetized to strength their membrane, improving their resistance to unfavorable conditions to which LAB are exposed during their proliferation and lactic fermentation in foods

Recently, we reported the presence of CPFA in ensiled feeds (as maize silage) and in milk and cheeses from cow fed with silages [10, 11]. Some LAB strains, both homofermentative such as *Lactobacillus plantarum* and heterofermentative (i.e., *Lactobacillus buchneri* and *Lactobacillus brevis*), are known to represent major constituents of the microbial ecosystem in silages [36]. Crop ensiling technology is based on the natural fermentation of plant tissue juice mediated by the lactic acid bacteria naturally present in the plant leaves. LAB convert soluble carbohydrates to organic acids, mainly lactic acid, under anaerobic conditions, resulting in a pH drop from 6.0–6.5 to 5.0–3.7 [36]. Therefore, the presence of CPFA in milk was related to their presence in ensiled products, where they are released by bacteria during silage fermentation conditions. Further studies on dairy products [10] demonstrated that LAB, ubiquitous in fermented milk and cheeses, were not able to release significant amount of CPFA in the medium during milk fermentation, and their presence in

fermented milk products derives only from their starting content in milk.

*Chemical structure of 11-cyclohexylundecanoic and 13-cyclohexytridecanoic acids.*

Omega-cyclohexyl fatty acids (CHFAs), as 11-cyclohexyl undecanoic and 13-tridecanoic acids (**Figure 3**), occur in several acido-thermophilic bacteria, mainly in

Cyclohexanecarboxylic acid starter unit in omega-cyclohexyl fatty acid synthesis is derived from shikimic acid, and it is probably related to glucose metabolism [37].

*DOI: http://dx.doi.org/10.5772/intechopen.80500*

reduce its permeability against toxic compounds.

**2.2 Omega-cyclohexyl fatty acids**

*Alicyclobacillus acidocaldarius* [8, 37, 38].

as well as the response to osmotic and ethanol stresses [30].

[34, 35].

**Figure 2.** *Biosynthesis of dihydrosterculic acid from oleic acid by CPFA synthase.* *Cyclic Fatty Acids in Food: An Under-Investigated Class of Fatty Acids DOI: http://dx.doi.org/10.5772/intechopen.80500*

*Biochemistry and Health Benefits of Fatty Acids*

especially in those tropical areas [19, 23].

*2.1.2 Biosynthesis and physiological aspects*

*Lactobacillus* spp. and *Leishmania* spp. [20, 30, 31].

*Biosynthesis of dihydrosterculic acid from oleic acid by CPFA synthase.*

shown in **Figure 2**.

and pressure [33].

Malvalic, sterculic, and dihydrosterculic acids have also been detected in Baobab

However, carbocyclic fatty acids seemed not to be confined to seeds. Long-chain cyclopropane fatty acids have been described in various polar lipid classes of leaves of early spring plants, whereas both cyclopropane and cyclopropene fatty acids were found in root, leaf, stem, and callus tissue in plants of the Malvaceae [9].

The presence of CPFA has also been documented in some aquatic invertebrates, marine isolates [24, 25] and in the lipid composition of mushrooms, mainly belonging to the family *Boletaceae* [15]. Overall, the natural distribution of CPFA among

CPFA synthesis involves the transfer of a methylene group from S-adenosyl methionine by the CPFA synthase to the cis double bond of the precursor unsaturated fatty acids, already integrated into phospholipids of cellular membrane [5]. A proposed pathway for the biosynthesis of dihydrosterculic acid from oleic acid is

The reaction is a post synthetic modification and has been widely studied in microorganisms such as *E. coli* [26–29], Pseudomonas, Mycobacterium,

Cyclopropane fatty acids are not essential fatty acids, but the bacterial production of cyclopropane ring seems to be related to changes in the membrane fatty acid composition of that microorganisms. In fact, the presence of these specific fatty acids seems to favor the stress tolerance of several bacteria strains to adverse environments (including ethanol, osmotic and oxidative stress, hot temperature, and low pH) and likely plays a role in the pathogenesis of bacterial infections [32]. The acid tolerance of individual strains of *E. coli* appears to be correlated with membrane cyclopropane fatty acid content and may enhance the survival of microbial cells exposed to low pH [29]. During acid habituation, monounsaturated fatty acids (cis-16:1 and cis-18:1) are either converted to their cyclopropane derivatives or replaced by saturated fatty acids. On the contrary, *E. coli* mutants deficient in CPFA seemed to be more sensitive to adverse conditions such as repeated freeze-drying

Natural CPFA occur widespread with a cis configuration about cyclopropane

moiety [5]; however, trans cyclopropane fatty acids are common in the cell

seeds oil from plant belonging to Adansonia species (Bombacaceae family) of Madagascar. Seed lipids containing CPFA are extensively consumed by humans,

eukaryotes appears much less common than among bacteria.

**34**

**Figure 2.**

envelope of *Mycobacterium tuberculosis* and play a role in regulating virulence. Cyclopropanation of mycolic acids has been suggested to be correlated with the persistence of the pathogen and modulates the innate immune response of the host [34, 35].

Cyclopropane fatty acids tend to promote the fluidity of lipid bilayers by interfering with lipid packing, improving the formation of gauche defects originating partly from the steric restraints caused by the methylene moieties and increasing lipid diffusion [31]. This could explain how cyclopropane fatty acids can improve the stability of the membrane against adverse conditions and, at the same time, reduce its permeability against toxic compounds.

CPFA are cellular components of lactic acid bacteria (LAB), such as *Lactobacillus bulgaricus*, *L. helveticus*, *L. sanfranciscensis*, and *L. acidophilus*, and are synthetized to strength their membrane, improving their resistance to unfavorable conditions to which LAB are exposed during their proliferation and lactic fermentation in foods as well as the response to osmotic and ethanol stresses [30].

Recently, we reported the presence of CPFA in ensiled feeds (as maize silage) and in milk and cheeses from cow fed with silages [10, 11]. Some LAB strains, both homofermentative such as *Lactobacillus plantarum* and heterofermentative (i.e., *Lactobacillus buchneri* and *Lactobacillus brevis*), are known to represent major constituents of the microbial ecosystem in silages [36]. Crop ensiling technology is based on the natural fermentation of plant tissue juice mediated by the lactic acid bacteria naturally present in the plant leaves. LAB convert soluble carbohydrates to organic acids, mainly lactic acid, under anaerobic conditions, resulting in a pH drop from 6.0–6.5 to 5.0–3.7 [36]. Therefore, the presence of CPFA in milk was related to their presence in ensiled products, where they are released by bacteria during silage fermentation conditions. Further studies on dairy products [10] demonstrated that LAB, ubiquitous in fermented milk and cheeses, were not able to release significant amount of CPFA in the medium during milk fermentation, and their presence in fermented milk products derives only from their starting content in milk.

#### **2.2 Omega-cyclohexyl fatty acids**

Omega-cyclohexyl fatty acids (CHFAs), as 11-cyclohexyl undecanoic and 13-tridecanoic acids (**Figure 3**), occur in several acido-thermophilic bacteria, mainly in *Alicyclobacillus acidocaldarius* [8, 37, 38].

Cyclohexanecarboxylic acid starter unit in omega-cyclohexyl fatty acid synthesis is derived from shikimic acid, and it is probably related to glucose metabolism [37].

**Figure 3.** *Chemical structure of 11-cyclohexylundecanoic and 13-cyclohexytridecanoic acids.*

In the following paragraph, information about the distribution of omegacyclohexyl fatty acids, their biosynthesis, and their role on the cellular membrane will be provided.

#### *2.2.1 Distribution and structure*

Omega-cyclohexyl fatty acids are the principal lipid component of saponifiable fraction of *Alicyclobacillus acidocaldarius*. They also occur in thermoacidophile strains, such as *A. acidoterrestis* and *A. cycloheptanicus*, and in the mesophile *Curtobacterium pusillum*, where the percentage concentration of these fatty acids in the cellular membrane increases at pH 3–4 as well as at elevated temperatures [8, 37]. In fact, omega-cyclic fatty acids are suggested to have special physiological importance for the cells both at hot temperature and acid pH. Model membranes, consisting of lipids containing omega-cyclohexyl fatty acids, are relatively dense and closely packed even at the phase transition temperature [8].

The occurrence of a fully saturated and monosubstituted cyclohexane ring is rare but derivatives of cyclohexyl acid, precursor of omega-cyclohexyl fatty acid biosynthesis, have been isolated from the extract soil and shoots of *Achyranthes aspera* and from several *Streptomyces* antibiotics, including ansatrienin A synthetized by *S. collinus* [8]. However, in this case, omega-cyclohexyl fatty acids do not seem to play a similar membrane stabilizing role as in *A. acidocaldarius*.

In eukaryotes, the identification of 11-cyclohexylundecanoic fatty acid has been documented as a minor component of butter fat [40], then in sheep fat (0.05% of the total weight of fatty acids) [39] and more recently in cow milk [11]. In this previous work [11], they focused on the identification and characterization of cyclic fatty acids in cow milk to study the effect of diverse types of dairy diet on milk fat composition. 13-cyclohexyl tridecanoic acid methyl ester was well detectable in all milk samples by GC-MS analysis of fatty acid methyl esters (FAME), and its presence was confirmed by mass spectra and the synthetized standard.

The presence of omega-cyclic fatty acids in milk could be related to acidic ruminal fermentation patterns. An increase in starch as well as a decrease of less digestible fiber content favors the growth of amylolytic bacteria. This leads to an increased concentration of rumen volatile fatty acids such as butyric and propionic acids, a decrease of rumen odd and branched fatty acids [41] and lactate accumulation, resulting in a pH drop, which favors not only the development of the subacute ruminal acidosis (SARA) [42] but also the growth of thermo-acidophilus bacteria, which produce omega-cyclohexyl fatty acids. In this context, the presence of omega-cyclohexyl fatty acids in milk, especially 11-cyclohexylundecanoic and 13-cyclohexyltridecanoic acids, could be represented as a parameter to detect SARA, as proposed by other authors for odd- and branched-chain fatty acids [41]. However, this hypothesis has never been confirmed by experimental data.

#### **2.3 Cyclic fatty acids in human nutrition**

Cyclic fatty acids are generally secondary compounds in fatty acid profiles of food; however, due to the recent discovery, some gaps of knowledge must be fulfilled. In some cases, especially cyclopropane fatty acids, they could reach the g/kg of total fat content in meat and dairy products [12, 43] and their dietary intake may be not negligible.

Therefore, it would be interesting to investigate on their metabolism in humans and eventual physiological effects, considering that bacteria produce cyclic fatty acids to enforce their membranes. The aim of these studies is to achieve a first never reported picture of the occurrence of CPFA in humans and their possible health effects.

**37**

**Table 1.** *CPFA food sources.*

*1*

*2*

*Cyclic Fatty Acids in Food: An Under-Investigated Class of Fatty Acids*

In the following paragraphs, we focused on the investigation of CPFA content in foods to estimate their dietary intake and on their potential bioaccessibility in humans. Finally, a review of literature data about their potential biological effects

Data reported on CPFA, mainly in dairy products, meat, and fish, were obtained in previous publications [10–12]. The content of cyclopropane fatty acids has also been evaluated in other food categories such as probiotic food supplements, vegetable edible oils (e.g., extra virgin olive, corn, soy, and peanuts oils) and cocoa butter, soy-derived products, and mushrooms (data not published). CPFA content in food

Results showed that among all the analyzed food categories, the most important

CPFA food source is Grana Padano cheese, reaching concentration levels of 1 g/ kg total fat (**Table 1**). CPFA were detected not only in commercial bovine meat (200–400 mg/kg total fat) but also in some species of fish (eels and mullets) with concentrations between 400 and 800 mg/kg total fat [12], probiotics, and in mushrooms (data not published). On the contrary, poultry, pork meat, vegetable oils commonly consumed (e.g., extra virgin olive, corn, soy, and peanuts oils), and cocoa butter were all negative to CPFA (data not shown), indicating that CPFA presence in foodstuffs of animal origin is correlated with the use of silages in the animal feedings, whereas plant organisms generally do not produce CPFA. As a whole, our results demonstrate the bacterial and fungal origin of CPFA in foods [16, 44]. Finally, the estimated daily, weekly and monthly CPFA dietary intake in the total Italian population (all sex and ages) [45] resulted in the milligrams order, so not negligible in view of a possible physiological action by CPFA on humans. Furthermore, food processing, manufacturing, seasoning steps, and fermentation [10] seemed not to affect CPFA content in the analyzed food matrices. Certainly,

**to CPFA2**

**/tot**

Cow milk 49/50 310 ± 240 70–830 Grana Padano (Lombardy, Italy) 72/72 540 ± 110 300–1000 Other cow cheeses 30/79 360 ± 180 180–1000 Commercial butter 6/10 200 ± 100 90–335 Yoghurt/fermented cow milk 4/4 200 ± 20 170–240

Commercial beef meat 5/5 200 ± 100 200–400

Eel 2/2 500 ± 250 400–590 Mullet 1/1 700 ± 100 600–800

*CPFA = cyclopropane fatty acids as the sum of total isomers (dihydrosterculic and lactobacillic acids) as reported by* 

**Mean ± SD (mg/ kg total fat)**

**Range (mg/ kg total fat)**

categories, resulted positive in previous analysis, is shown in **Table 1**.

**Food No. of positive samples** 

*Results obtained combining previous analysis [10–12, 43].*

*Dairy products*<sup>1</sup>

*Meat*<sup>1</sup>

*Fish*<sup>1</sup>

*Caligiani et al. [43]. SD = standard deviation.*

*DOI: http://dx.doi.org/10.5772/intechopen.80500*

*2.3.1 Cyclopropane fatty acids presence in food*

on mammals will be provided.

In the following paragraphs, we focused on the investigation of CPFA content in foods to estimate their dietary intake and on their potential bioaccessibility in humans. Finally, a review of literature data about their potential biological effects on mammals will be provided.
