Production of conjugated linoleic acid by food-grade bacteria: A review

Factors influencing conjugated linoleic acid content of dairy products: challenges and strategies

Conjugated linoleic acid (CLA), a bioactive fatty acid that provides various physiological benefits, has gained increasing attention in the food industry, and various studies have focused on enhancing its content in dairy products. The factors influencing CLA content in dairy products vary significantly, including lactation stage, breed type, seasonality, feed, management methods of the animals, the manufacturing processes, storage, and ripening periods of the product. Additionally, the incorporation of CLA-producing probiotic bacteria, such as Lactobacillus, Lactococcus, Bifidobacterium, and Propionibacterium, is an emerging study in this field. Studies have revealed that factors affecting the CLA content in milk affect that in dairy products as well. Furthermore, the species and strains of CLA-producing bacteria, fermentation conditions, ripening period, and type of dairy product are also contributing factors. However, production of CLA-enhanced dairy products using CLA-producing bacteria while maintaining their optimal viability and maximizing exposure to free linoleic acid remains limited. The current review emphasized the factors affecting the CLA content and related mechanisms, challenges in the application of CLA-producing probiotic bacteria, and strategies to address these challenges and enhance CLA production in dairy products. Therefore, the development of functional dairy products with enhanced CLA levels is expected to be possible.

Production of Conjugated Linoleic Acid (CLA) by Lactiplantibacillus plantarum: A Review with Emphasis on Fermented Foods

The term Conjugated Linoleic Acid (CLA) refers generically to a class of positional and geometric conjugated dienoic isomers of linoleic acid. Among the isomers of linoleic acid cis9, trans11-CLA (c9, t11-CLA) and trans10, cis12-CLA (t10, c12-CLA) are found to be biologically active isomers, and they occur naturally in milk, dairy products and meat from ruminants. In addition, some vegetables and some seafoods have also been reported to contain CLA. Although the CLA levels in these natural sources are insufficient to confer the essential health benefits, anti-carcinogenic or anti-cancer effects are of current interest. In the rumen, CLA is an intermediate of isomerization and the biohydrogenation process of linoleic acid to stearic acid conducted by ruminal microorganisms. In addition to rumen bacteria, some other bacteria, such as Propionibacterium, Bifidobacterium and some lactic acid bacteria (LAB) are also capable of producing CLA. In this regard, Lactiplantibacillus plantarum (formerly Lactobacillus plantarum) has demonstrated the ability to produce CLA isomers from linoleic acid by multiple enzymatic activities, including hydration, dehydration, and isomerization. L. plantarum is one of the most versatile species of LAB and the bacterium is widely used in the food industry as a microbial food culture. Thus, in this review we critically analyzed the literature produced in the last ten years with the aim to highlight the potentiality as well as the optimal conditions for CLA production by L. plantarum. Evidence was provided suggesting that the use of appropriate strains of L. plantarum, as a starter or additional culture in the production of some fermented foods, can be considered a critical factor in the design of new CLA-enriched functional foods.

Advances in research on microbial conjugated linoleic acid bioconversion

Conjugated linoleic acid (CLA) is a functional food ingredient with prebiotic properties that provides health benefits for various human pathologies and disorders. However, limited natural CLA sources in animals and plants have led microorganisms like Lactobacillus and Bifidobacterium to emerge as new CLA sources. Microbial conversion of linoleic acid to CLA is mediated by linoleic acid isomerase and multicomponent enzymatic systems, with CLA production efficiency dependent on microbial species and strains. Additionally, complex factors like LA concentration, growth status, culture substrates, precursor type, prebiotic additives, and co-cultured microbe identity strongly influence CLA production and isomer composition. This review summarizes advances in the past decade regarding microbial CLA production, including bacteria and fungi. We highlight CLA production and potential regulatory mechanisms and discuss using microorganisms to enhance CLA content and nutritional value of fermented products. We also identify primary microbial CLA production bottlenecks and provide strategies to address these challenges and enhance production through functional gene and enzyme mining and downstream processing. This review aims to provide a reference for microbial CLA production and broaden the understanding of the potential probiotic role of microbial CLA producers.

Conjugated linoleic acid (CLA) as a functional food: Is it beneficial or not?

Conjugated linoleic acid (CLA) has attracted great attention in recent years as a popular class of functional food that is broadly used. It refers to a group of geometric and positional isomers of linoleic acid (LA) with a conjugated double bond. The main natural sources of CLA are dairy products, beef and lamb, whereas only trace amounts occur naturally in plant lipids. CLA has been shown to improve various health issues, having effects on obesity, inflammatory, anti-carcinogenicity, atherogenicity, immunomodulation, and osteosynthesis. Also, compared to studies on humans, many animal researches reveal more positive benefits on health. CLA represents a nutritional avenue to improve lifestyle diseases and metabolic syndrome. Most of these effects are attributed to the two major CLA isomers [conjugated linoleic acid cis-9,trans-11 isomer (c9,t11), and conjugated linoleic acid trans-10,cis-12 isomer (t10,c12)], and their mixture (CLA mix). In contrast, adverse effects of CLA have been also reported, such as glucose homeostasis, insulin resistance, hepatic steatosis and induction of colon carcinogenesis in humans, as well as milk fat inhibition in ruminants, lowering chicken productivity, influencing egg quality and altering growth performance in fish. This review article aims to discuss the health benefits of CLA as a nutraceutical supplement and highlight the possible mechanisms of action that may contribute to its outcome. It also outlines the feasible adverse effects of CLA besides summarizing the recent peer-reviewed publications on CLA to ensure its efficacy and safety for proper application in humans.

Development of a whey-based beverage with enhanced levels of conjugated linoleic acid (CLA) as facilitated by endogenous walnut lipase

In this study, optimization of fermentation conditions, and applying endogenous walnut lipase were investigated for the manufacture of a fermented, whey-based beverage containing conjugated linoleic acid (CLA). Among different commercial starter and probiotic cultures, the culture containing Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus showed high potency for CLA synthesis. The fermentation time and the type of walnut oil (lipolyzed or non-lipolyzed) had significant effects on CLA production, as the highest CLA content (36 mg/g fat) was synthesized in the sample containing 1 % lipolyzed walnut oil fermented at 42 °C for 24 h. Moreover, fermentation time had the highest contribution on viable cell counts, proteolysis, DPPH scavenging activity, and final pH. A significant and positive correlation between cell counts and CLA content was also observed (r = +0.823, p < 0.05). This study establishes a cost effective approach for converting cheese whey to a value added beverage enriched with CLA.

Probiotic Properties of Lactic Acid Bacteria with High Conjugated Linoleic Acid Converting Activity Isolated from Jeot-Gal, High-Salt Fermented Seafood

Conjugated linoleic acid (CLA) isomers are potent health-promoting fatty acids. This study evaluated the probiotic properties of 10 strains of high CLA-producing lactic acid bacteria (LAB) isolated from Jeot-gal, a high-salt, fermented seafood. Two isolates, Lactiplantibacillus plantarum JBCC105683 and Lactiplantibacillus pentosus JBCC105676, produced the largest amounts of CLA (748.8 and 726.9 μg/mL, respectively). Five isolates, L. plantarum JBCC105675, L. pentosus JBCC105676, L. pentosus JBCC105674, L. plantarum JBCC105683, and Lactiplantibacillus paraplantarum JBCC105655 synthesized more cis-9, trans-11-CLA than trans-10, cis-12-CLA (approximately 80:20 ratio). All the strains survived severe artificial acidic environments and showed antimicrobial activity and strong adhesion capability to Caco-2 cells as compared to the commercial strain Lactocaseibacillus rhamnosus GG. Among them, Pediococcus acidilactici JBCC105117, L. paraplantarum JBCC105655, and L. plantarum JBCC105683 strongly stimulated the immunological regulatory gene PMK-1 and the host defense antimicrobial peptide gene clec-60 in Caenorhabditis elegans. Moreover, three strains showed a significant induction of tumor necrosis factor-α, interleukin (IL)-1β, IL-6, IL-12, and IL-10 production in RAW 264.7 macrophages, indicating that they were promising candidates for probiotics with high CLA-converting activity. Our results indicate that the newly isolated CLA-producing LAB might be useful as a functional probiotic with beneficial health effects that modulate the immune system.

Novel Yeasts Producing High Levels of Conjugated Linoleic Acid and Organic Acids in Fermented Doughs

Traditional fermented foods are obtained by a complex consortium of autochthonous microorganisms producing a wide variety of bioactive compounds, thus representing a reservoir of strains with new functional properties. Here, doughs obtained using five different wholegrain flours were singly fermented with selected yeast strains, which were evaluated for their functional traits. Lactate, volatile fatty acids and conjugated linoleic acid isomers produced by fermented doughs were detected by HPLC, while dough anti-inflammatory capacity was measured on human peripheral blood mononuclear cells by flow cytometry. Yeast potential probiotic activity was assessed by evaluating their resistance to simulated gastric and intestinal fluids. For the first time we report evidence of yeast strains producing high levels of the conjugated linoleic acid (CLA) isomer CLA 10-12tc and propionic acid, which are known for their specific health benefits. Moreover, such yeast strains showed an anti-inflammatory capacity, as revealed by a significantly decreased production of the strongly pro-inflammatory cytokine IL-1β. All our Saccharomyces cerevisiae strains were remarkably resistant to simulated gastric and intestinal fluids, as compared to the commercial probiotic strain. The two strains S. cerevisiae IMA D18Y and L10Y showed the best survival percentage. Our novel yeast strains may be exploited as valuable functional starters for the industrial production of cereal-based innovative and health-promoting fermented foods.

Starter bacteria as producers of CLA in ripened cheese

The profile of polyunsaturated fatty acids in cheeses obtained through fermentation by lactic acid bacteria Lactobacillus helveticus and Streptococcus thermophilus were evaluated. The milk used to make the cheeses came from cows fed with flaxseed oil and annato. The cheeses presented microbiological and physic-chemical quality with in the standards established by the legislation for Staphylococci and Listeria. With maturation, there was a reduction in the coliform values ​​for both treatments. Regarding the counts of lactic acid bacteria, these remained viable until the 30th day of maturation and the proteolytic bacteria decreased. For antioxidant capacity, the treatment containing the combination of the strains obtained high ABTS values. There was no significant difference between the treatments with respect to the color of the samples. For texture, there was a significant difference for the parameters cohesion and elasticity. No increase in CLA content was observed in the form of its two main isomers, however, the levels of polyunsaturated fatty acids were increased.

Current Trends of Enterococci in Dairy Products: A Comprehensive Review of Their Multiple Roles

As a genus that has evolved for resistance against adverse environmental factors and that readily exchanges genetic elements, enterococci are well adapted to the cheese environment and may reach high numbers in artisanal cheeses. Their metabolites impact cheese flavor, texture, and rheological properties, thus contributing to the development of its typical sensorial properties. Due to their antimicrobial activity, enterococci modulate the cheese microbiota, stimulate autolysis of other lactic acid bacteria (LAB), control pathogens and deterioration microorganisms, and may offer beneficial effects to the health of their hosts. They could in principle be employed as adjunct/protective/probiotic cultures; however, due to their propensity to acquire genetic determinants of virulence and antibiotic resistance, together with the opportunistic character of some of its members, this genus does not possess Qualified Presumption of Safety (QPS) status. It is, however, noteworthy that some putative virulence factors described in foodborne enterococci may simply reflect adaptation to the food environment and to the human host as commensal. Further research is needed to help distinguish friend from foe among enterococci, eventually enabling exploitation of the beneficial aspects of specific cheese-associated strains. This review aims at discussing both beneficial and deleterious roles played by enterococci in artisanal cheeses, while highlighting the need for further research on such a remarkably hardy genus.

Effectiveness of probiotics, prebiotics, and prebiotic-like components in common functional foods

The bioactive ingredients in commonly consumed foods include, but are not limited to, prebiotics, prebiotic-like components, probiotics, and postbiotics. The bioactive ingredients in functional foods have also been associated with beneficial effects on human health. For example, they aid in shaping of gut microflora and promotion of immunity. These functional components also contribute in preventing serious diseases such as cardiovascular malfunction and tumorigenesis. However, the specific mechanisms of these positive influences on human health are still under investigation. In this review, we aim to emphasize the major contents of probiotics, prebiotics, and prebiotic-like components commonly found in consumable functional foods, and we present an overview of direct and indirect benefits they provide on human health. The major contributors are certain families of metabolites, specifically short-chain fatty acids and polyunsaturated fatty acids produced by probiotics, and prebiotics, or prebiotic-like components such as flavonoids, polyphenols, and vitamins that are found in functional foods. These functional ingredients in foods influence the gut microbiota by stimulating the growth of beneficial microbes and the production of beneficial metabolites that, in turn, have direct benefits to the host, while also providing protection from pathogens and maintaining a balanced gut ecosystem. The complex interactions that arise among functional food ingredients, human physiology, the gut microbiota, and their respective metabolic pathways have been found to minimize several factors that contribute to the incidence of chronic disease, such as inflammation oxidative stress.

Conjugated linoleic acid producing potential of lactobacilli isolated from goat (AXB) rumen fluid samples

OBJECTIVE

The present investigation was aimed to explore the potential of lactobacilli for conjugated linoleic acid (CLA) production, isolated from rumen fluid samples of lactating goats.

METHODS

A total of 64 isolates of lactobacilli were obtained using deMan-Rogosa-Sharpe (MRS) agar from rumen fluid of goats and further subjected to morphological and biochemical characterizations. Isolates found as gram-positive, catalase negative rods were presumptively identified as Lactobacillus species and further confirmed by genus specific polymerase chain reaction (PCR). The phylogenetic tree was constructed from the nucleotide sequences using MEGA6.

RESULTS

Out of the 64 isolates, 23 isolates were observed positive for CLA production by linoleate isomerase gene-based amplification and quantitatively by UV-spectrophotometric assay for the conversion of linoleic acid to CLA as well as gas chromatography-based assay. In all Lactobacillus species cis9, trans11 isomer was observed as the most predominant CLA isomer. These positive isolates were identified by 16S rRNA gene-based PCR sequencing and identified to be different species of L. ingluviei (2), L.salivarius (2), L. curvatus (15), and L. sakei (4).

CONCLUSION

The findings of the present study concluded that lactic acid bacteria isolated from ruminal fluid samples of goat have the potential to produce bioactive CLA and may be applied as a direct fed microbial to enhance the nutraceutical value of animal food products.

Substitutions between dairy products and risk of stroke: results from the European Investigation into Cancer and Nutrition-Netherlands (EPIC-NL) cohort

The association between intake of different dairy products and the risk of stroke remains unclear. We therefore investigated substitutions between dairy product subgroups and risk of stroke. We included 36 886 Dutch men and women. Information about dairy product intake was collected through a FFQ. Dairy products were grouped as low-fat milk, whole-fat milk, buttermilk, low-fat yogurt, whole-fat yogurt, cheese and butter. Incident stroke cases were identified in national registers. We used Cox proportional hazards regression to calculate associations for substitutions between dairy products with the rate of stroke. During a median follow-up of 15·2 years we identified 884 stroke cases (503 ischaemic and 244 haemorrhagic). Median intake of total dairy products was four servings/d. Low-fat yogurt substituted for whole-fat yogurt was associated with a higher rate of ischaemic stroke (hazard ratio (HR) = 2·58 (95 % CI 1·11, 5·97)/serving per d). Whole-fat yogurt as a substitution for any other subgroup was associated with a lower rate of ischaemic stroke (HR between 0·33 and 0·36/serving per d). We did not observe any associations for haemorrhagic stroke. In conclusion, whole-fat yogurt as a substitution for low-fat yogurt, cheese, butter, buttermilk or milk, regardless of fat content, was associated with a lower rate of ischaemic stroke.

Substitutions of dairy product intake and risk of stroke: a Danish cohort study

Low fat dairy products are part of dietary guidelines to prevent stroke. However, epidemiological evidence is inconclusive with regard to the association between dairy products and stroke. We therefore investigated associations for substitutions between dairy product subgroups and risk of total stroke and stroke subtypes. We included 55,211 Danish men and women aged 50-64 years without previous stroke. Baseline diet was assessed by a food frequency questionnaire. Cases were identified through a national register and subsequently verified. The associations were analyzed using Cox proportional hazard regression. During a median follow-up of 13.4 years, we identified 2272 strokes, of which 1870 were ischemic (318 large artery atherosclerotic, 839 lacunar, 102 cardioembolic, 98 other determined types, 513 of unknown type), 389 were hemorrhages (273 intracerebral, 116 subarachnoid) and 13 of unknown etiology. Substitution of semi-skimmed fermented milk or cheese for whole-fat fermented milk was associated with a higher rate of ischemic stroke [semi-skimmed fermented milk: hazard ratio (HR) = 1.20 (95% confidence interval (CI) 0.99-1.45), cheese: HR = 1.14 (95% CI 0.98-1.31) per serving/day substituted] and substitutions of whole-fat fermented milk for low-fat milk, whole-fat milk or buttermilk were associated with a lower rate [low-fat milk: HR = 0.85 (95% CI 0.74-0.99), whole-fat milk: HR = 0.84 (95% CI 0.71-0.98) and buttermilk: HR = 0.83 (95% CI 0.70-0.99)]. We observed no associations for substitutions between dairy products and hemorrhagic stroke. Our results suggest that intake of whole-fat fermented milk as a substitution for semi-skimmed fermented milk, cheese, buttermilk or milk, regardless of fat content, is associated with a lower rate of ischemic stroke.

Isolation, molecular characterization and screening of indigenous lactobacilli for their abilities to produce bioactive conjugated linoleic acid (CLA)

Ingestion of conjugated linoleic acid poised many health benefits; however, amount of CLA one can get through generalized diet in is inadequate in exerting the desired benefits. Therefore, presence of CLA producing lactobacilli in dairy fermented foods has a tremendous potential to increase the CLA content. Therefore, present study was focused to isolate and characterize CLA producing lactobacilli from different dairy products and human faeces. Arguably, 283 lactobacilli were isolated from various sources and tested for CLA production. Fifty-seven CLA producing (≥20 µg/ml) lactobacilli were selected from screening in de Man, Rogosa and Sharpe (MRS) broth and reconstituted with skim milk (SM), supplemented with 0.5 mg/ml of linoleic acid. Positive strains were classified into-L. plantarum (44%), L. gasseri (30%), L. fermentum (21%) and L. salivarius (5%) species. Nineteen most efficient strains (CLA ≥25 µg/ml) were further assessed in SM for CLA production. Total 08 strains produced significantly higher CLA in SM than MRS and also produced cis 9, trans 11, trans 10, cis 12 and trans 9, trans 11 isomers. Overall, L. plantarum HIF15 was reported as the best producer of CLA and other 08 lactobacilli may be utilized for the formulation of CLA-enriched functional foods to support these bacteria to synthesize CLA in the human gut.

Screening of Lactobacillus strains for their ability to produce conjugated linoleic acid in milk and to adhere to the intestinal tract

Conjugated linoleic acid (CLA) has been shown to provide beneficial effects on health; however, the amount consumed in food is far from that required for the desired effects. Thus, increasing the CLA content in dairy foods through milk fermentation with specific lactic acid bacteria (LAB) offers an interesting alternative. Moreover, some LAB may be able to adhere to the intestinal mucosa and produce CLA through endogenous synthesis. Therefore, the objective of this study was to screen LAB isolates for their ability to produce CLA in skim milk and in simulated gastrointestinal conditions. Additionally, the ability of selected CLA-producing LAB to adhere to the intestinal mucosa in a murine model was assessed. Results showed that of 13 strains of Lactobacillus tested, only 4 were able to produce CLA in skim milk supplemented with linoleic acid (13.44 ± 0.78 to 50.9 ± 0.26 µg/mL). Furthermore, these 4 Lactobacillus strains were able to survive and produce CLA in simulated gastrointestinal conditions and to adhere to the intestinal mucosa of Wistar rats after 7 d of oral inoculation with fluorescently labeled bacteria. Accordingly, these 4 Lactobacillus strains may be used to manufacture fermented dairy foods to increase CLA content, and consumption of these fermented milks may result in CLA produced endogenously by these LAB.

Identification of conjugated linoleic acid (CLA) isomers by silver ion-liquid chromatography/in-line ozonolysis/mass spectrometry (Ag+-LC/O3-MS)

A novel method for the identification of conjugated linoleic acid (CLA) isomers has been developed in which silver ion liquid chromatography is coupled to in-line ozonolysis/mass spectrometry (Ag(+)-LC/O3-MS). The mobile phase containing CLA isomers eluting from the Ag(+)-LC column flows through a length of gas-permeable tubing within an ozone rich environment. Ozone penetrating the tubing wall reacts with the conjugated double bonds forming ozonolysis product aldehydes. These, and their corresponding methanol loss fragment ions formed within the atmospheric pressure photoionization (APPI) source, were detected by in-line MS and used for the direct assignment of double bond positions. Assignment of positional isomers is based entirely on the two pairs of diagnostic ions seen in the in-line O3-MS mass spectra. In this way, de novo identification of CLA positional isomers, i.e. without requiring comparison to CLA standards, was achieved. The Ag(+)-LC/O3-MS method was applied to the analysis of CLA isomers in a commercial CLA supplement, milk fat, and the lipid extract from a Lactobacillus plantarum TMW1460 culture. The results demonstrate how Ag(+)-LC/O3-MS can be used for the direct and fast determination of CLA isomers at low concentrations and in complex lipid mixtures.

Antifungal lipids produced by lactobacilli and their structural identification by normal phase LC/atmospheric pressure photoionization−MS/MS

Lactobacillus hammesii converts linoleic acid into an antifungal hydroxy fatty acid. High speed counter-current chromatography (HSCCC) using a hexane/ethyl acetate/methanol/water solvent system [3.5:1.5:3:2 (v/v/v/v)] allowed isolation of the antifungal hydroxy fatty acid. A method was developed for characterization of antifungal hydroxy fatty acids using normal phase liquid chromatography combined with atmospheric pressure photoionization-tandem mass spectrometry (LC/APPI-MS/MS). The position of unsaturations and hydroxyl groups was determined directly from crude lipid extracts and their hydroxylated derivatives. The antifungal compounds were identified as a racemic mixture of 10-hydroxy-cis-12-octadecenoic and 10-hydroxy-trans-12-octadecenoic acid. Additionally, HSCCC and LC/APPI-MS/MS methods were used to elucidate the pathway of conversion of linoleic acid by Lactobacillus sanfranciscensis , Lactobacillus plantarum , and L. hammesii to hydroxy fatty acids and conjugated linoleic acid. This study links previously reported 10-hydroxy-12-octadecenoic acid producing Lactobacillus strains to antifungal activities.