3-Ácido fenilláctico

Otros Nombres

(2R)-2-Hydroxy-3-phenylpropanoic acid(2R)-2-Hydroxy-3-phenylpropionic acid(2S)-2-Hydroxy-3-phenylpropanoic acid(2S)-2-Hydroxy-3-phenylpropionic acid(R)-2-Hydroxy-3-phenylpropanoic acid(R)-2-Hydroxy-3-phenylpropionic acid(R)-3-Phenyl-2-hydroxypropanoic acid(R)-3-Phenyllactic acid(S)-2-Hydroxy-3-phenylpropanoic acid(S)-2-Hydroxy-3-phenylpropionic acid(S)-3-Phenyllactic acid2-Hydroxy-3-phenylpropanoic acid2-Hydroxy-3-phenylpropionic acid3-Phenyl-2-hydroxypropanoic acid3-Phenyl-D-lactic acid3-Phenyl-DL-lactic acid3-Phenyl-L-lactic acid3-Phenyllactatealpha-Hydroxy-benzenepropanoic acidalpha-hydroxy-beta-phenyl-propionic acidalpha-Hydroxyhydrocinnamic acidb-Phenyl-D-lactic acidb-Phenyl-L-lactic acidbeta-Phenyllactic acidD-(+)-3-Phenyllactic acidD-(+)-Phenyllactic acidD-beta-Phenyllactic acidD-β-Phenyllactic acidDL-2-Hydroxy-3-phenylpropionateDL-2-Hydroxy-3-phenylpropionic acidDL-3-Phenyllactic acidDL-alpha-Hydroxyhydrocinnamic acidDL-beta-Phenyllactic acidDL-Phenyllactic acidL-(−)-Phenyllactic acidL-3-Phenyllactic acidL-beta-Phenyllactic acidL-β-Phenyllactic acidPLAα-Hydroxybenzenepropanoic acidβ-Phenyllactic acid

Sinopsis

3-Phenyllactic Acid: A Comprehensive Reference

1. Identity and Chemical Characterization

1.1 Nomenclature and Chemical Identity

3-Phenyllactic acid (2-hydroxy-3-phenylpropionic acid) (PLA) is an organic acid with broad-spectrum antimicrobial activity against bacteria, molds, and yeasts, making it a promising natural preservative and antimicrobial agent. The compound is also widely known under the synonyms β-phenyllactic acid, α-hydroxyhydrocinnamic acid, and 2-hydroxy-3-phenylpropanoic acid. Its linear formula is C₆H₅CH₂CH(OH)COOH and its empirical formula is C₉H₁₀O₃.

PLA is an organic phenolic acid, naturally found in honey and foods and produced by lactic acid bacteria (LAB). It exists in two optical isomeric forms known as enantiomers, d-PLA and l-PLA, with d-PLA demonstrating greater antimicrobial activity than l-PLA. (S)-3-phenyllactic acid is the (S)-enantiomer and is a (2S)-2-hydroxy monocarboxylic acid. The racemic (DL) mixture carries CAS number 828-01-3, the L-(S)-enantiomer carries CAS 20312-36-1, and the D-(R)-enantiomer carries CAS 7326-19-4.

3-Phenyllactic acid is a carboxylic acid that can undergo deracemisation through lipase-catalyzed kinetic resolution, followed by racemisation of the non-reacting enantiomer, as demonstrated in biotransformation processes. PLA has low kinetic solubility in water, and its pKa has been measured at approximately 3.46, a property with direct relevance to its antimicrobial mechanism of action.

1.2 Natural Sources

3-Phenyllactic acid (PLA) is an organic acid widely existing in honey and lactic acid bacteria fermented food, and can be produced by many microorganisms, especially lactic acid bacteria. PLA, which is detected in honey, is known to be produced by Geotrichum candidum and Bacillus coagulans. Some PLA-producing lactic acid bacteria (LAB), such as Lactobacillus, Enterococcus, Leuconostoc, and Pediococcus, have also been reported.

PLA was first identified as an antifungal compound in lactic acid bacteria in 2002. Geotrichum candidum excretes D-3-phenyllactic acid, which was one of the early-characterized natural sources demonstrating inhibition of Listeria monocytogenes. Among fermented foods, PLA has been documented in sourdough bread, fermented dairy products, kimchi, silage, and various other LAB-fermented matrices. Three antifungal compounds from Lactobacillus plantarum MiLAB 393 have been identified, including the organic acid PLA at an l/d isomer ratio of approximately 9:1.

In honey, PLA plays a notable supporting antimicrobial role. Manuka honey is known for its unique antibacterial activity, which is due to methylglyoxal (MGO). Studies showed that honey differs in its growth-retarding effect on Bacillus subtilis despite the same content of MGO, indicating the presence of potentially synergistic compounds. In model studies using artificial honey with varying amounts of MGO and 3-PLA, it was shown that 3-PLA in concentrations above 500 mg/kg enhances the bacteriostatic effect of honeys containing 250 mg/kg MGO or more. It is notable that the two honeys with the highest 3-PLA and gallic acid equivalent (GAE) content are also the honeys with the highest growth delay against B. subtilis; for example, "honey 1" containing 734 mg/kg 3-PLA and 636 mg/kg GAE required less MGO to achieve a growth delay of five compared to a honey with lower 3-PLA content.

1.3 Common Forms and Preparations

PLA is encountered in its pure crystalline form in laboratory and research settings, as it can be crystallized from water, methanol, ethanol, or other suitable solvents. In industrial and food-technology contexts, it is produced as a fermentation metabolite of LAB cultures, typically recovered from cell-free supernatants. Because PLA has low kinetic solubility in water, strategies to improve its solubility are necessary to facilitate certain delivery applications. Using biocompatible cations, choline and carnitine, researchers have successfully transformed both d- and l-enantiomers of crystalline PLA into amorphous low-melting ionic liquids (ILs) with high water solubility. For food preservation applications, PLA has been incorporated into active packaging materials and antibacterial nanofiber films prepared by electrospinning with gelatin and chitosan.

2. Traditional and Historical Use

3-Phenyllactic acid does not have an established history as an intentionally isolated or named compound in pre-modern traditional medicine. Rather, it exists as a naturally occurring constituent of widely used traditional preparations, and its documented history is therefore embedded within the history of fermented foods and honey use across many cultures.

Fermentation as a food preservation and health-promoting technology has a history spanning millennia in cultures worldwide. Fermentation has been used for hundreds of years to preserve food, with many fermentations relying on the metabolic activity of lactic acid bacteria. Traditional fermented foods including sourdough bread, fermented dairy products, and various vegetable ferments — all known to contain PLA-producing LAB — were employed historically not only for their preservation properties but also for their perceived beneficial effects on digestion and health. The antimicrobial properties of such foods, partly attributable to what is now known as PLA, contributed to their empirical value in food safety and preservation across diverse agricultural traditions.

Honey, another naturally rich source of PLA, has one of the longest documented therapeutic histories of any natural product. It has been used in wound care, the treatment of oral and gastrointestinal complaints, and as a general tonic in ancient Egyptian, Greek, Roman, Ayurvedic, and Chinese medical traditions. The antimicrobial properties of honey, to which PLA makes a measurable contribution, formed the rational basis of many of these traditional applications. The compound itself, however, was not characterized or isolated from these preparations until the modern era of analytical chemistry.

The formal scientific identification of PLA as a discrete antimicrobial compound produced by LAB occurred in 2002, after which research into its properties, biosynthesis, and applications accelerated substantially. Prior to that point, any therapeutic or preservative effects attributable to PLA were not distinguished from the general antimicrobial activity of fermented foods and honey.

3. Biosynthesis, Key Constituents, and Active Compounds

3.1 Biosynthetic Pathways

Two biosynthetic pathways for PLA are known in lactic acid bacteria. In the first, named the "de novo pathway," glucose is the precursor for the biosynthesis of PLA and does not require the activity of an aminotransferase. In the second, called the "core pathway," phenylalanine is the precursor. Phenylalanine is thereby converted into phenylpyruvic acid by the action of an aminotransferase. Phenylpyruvic acid is subsequently reduced to PLA by a dehydrogenase.

For PLA biosynthesis in LAB, the most important biochemical pathway is reported to be amino acid metabolism, which involves the transamination of phenylalanine to phenylpyruvic acid (PPA) and the subsequent PPA reduction to PLA by lactate dehydrogenase (LDH). Phenylalanine can be generated from either the phenylalanine biosynthesis pathway or protein degradation. Phenylpyruvate is one of the intermediate products of phenylalanine biosynthesis, and it is produced by transamination of phenylalanine. Phenylpyruvate can be decarboxylated, reduced, and chemically oxidized, resulting in phenylacetaldehyde, PLA, and benzaldehyde, respectively.

The initial phenylalanine conversion step to PPA is considered the rate-limiting step in PLA production, and this limitation can be overcome by adding PPA as the direct precursor. The conversion from PPA to PLA by LDH has been regarded as the key factor in the improvement of PLA production by LAB.

3.2 Producing Organisms

PLA-producing lactic acid bacteria include species of Lactobacillus, Enterococcus, Leuconostoc, and Pediococcus. Among the best-characterized producers is Lactobacillus plantarum, which has been studied extensively in the context of sourdough fermentation, silage, and dairy products. Since PLA-producing LAB are generally regarded as safe (GRAS) microorganisms, these strains are gaining wide attention. PLA production has also been documented in Pediococcus acidilactici, Pediococcus pentosaceus, and, in selected in vitro conditions, Clostridium sporogenes.

Since PLA is produced in natural and fermented foods in low amounts, De Man Rogosa Sharpe (MRS) broth or dairy whey broth with additional supplementation of phenylalanine or PPA has been widely used to increase production yields.

3.3 Structural Features Relevant to Activity

Structurally, PLA has a phenyl ring in place of the methyl hydrogen found in lactic acid, which differentiates it from lactic acid. It is suggested that this contributes to the amphiphilic nature of PLA and perhaps facilitates its interaction with bacterial membrane lipids and proteins. This amphiphilicity — possessing both hydrophilic (carboxylic acid, hydroxyl) and hydrophobic (phenyl ring) functional groups — is considered central to its superior antimicrobial potency relative to simple organic acids such as lactic acid.

4. Mechanisms of Action

4.1 Weak Acid Mechanism and Intracellular Acidification

The PLA mode of action is related to its undissociated form (pKa 3.46), which is able to cross the microbial membrane. Other studies have shown that the antimicrobial activity of some acids is ascribable to the ability of undissociated forms to freely cross the cytoplasmic membrane, inducing damage to membrane permeability. The inhibitory mechanism is attributable in part to pH reduction, which induces proton release from undissociated molecules in the cytoplasm, leading to a decrease in intracellular pH and inhibiting essential microbial metabolic reactions.

4.2 Cell Membrane Disruption

Scanning electron microscope studies on the effect of D-3-phenyllactic acid on L. monocytogenes showed that it caused changes in bacterial behavior and structure. The bacteria formed aggregates and secreted polysaccharides; their cell walls lost their rigidity, causing the cells to swell. Finally the bacteria broke down completely and the cells disintegrated.

A study evaluated the antimicrobial activity of PLA against foodborne Enterococcus faecalis and its effect on the cell membrane. The minimum concentration of PLA to inactivate E. faecalis in brain heart infusion broth was 5 mg/mL. PLA solutions of 5 and 10 mg/mL could inactivate E. faecalis population ≥6 log CFU/mL within 60 and 30 minutes, respectively. The cell membranes of most E. faecalis cells were damaged after PLA treatment according to scanning electron microscopy and transmission electron microscopy images.

4.3 Dual Target: Membrane Integrity and Genomic DNA

Investigations were performed to elucidate the antibacterial mechanism of PLA against Listeria monocytogenes and Escherichia coli. Flow cytometry analysis stained with propidium iodide demonstrated that PLA could damage the membrane integrity of L. monocytogenes, while it could not disrupt that of E. coli in the same way. Uptake of 1-N-phenylnaphthylamine (NPN) indicated that PLA interrupted the outer membrane permeability of E. coli. The study proposed dual antibacterial targets for PLA, namely the cell membrane and genomic DNA.

Several studies have pointed toward the dual mechanism of antibacterial action of PLA, namely the disruption of membrane integrity and genomic DNA stability by intercalation. Phenyllactic acid may exhibit direct antimicrobial activity by disrupting cell wall membrane integrity and interfering with genomic DNA function.

4.4 Quorum Sensing Inhibition and Anti-Virulence

Pseudomonas aeruginosa depends on its quorum sensing (QS) system for virulence factor production and biofilm formation. Biofilms of P. aeruginosa on the surface of indwelling catheters are often resistant to antibiotic therapy. Alternative approaches employing QS inhibitors alone or in combination with antibiotics are being developed. Studies on the mechanism of action of 3-phenyllactic acid (PLA), a QS inhibitory compound produced by Lactobacillus species, against P. aeruginosa PAO1 revealed that PLA inhibited the expression of virulence factors such as pyocyanin, protease, and rhamnolipids that are involved in biofilm formation. Swarming motility, another important criterion for biofilm formation, was also inhibited by PLA.

4.5 Anti-Biofilm Activity

PLA is associated with multifaceted antibacterial mechanisms of action, such as damaging the cell membrane and intercalating DNA. There are emerging reports on the anti-biofilm activity of PLA against Enterobacter cloacae, Pseudomonas aeruginosa, Listeria monocytogenes, and Enterococcus faecalis. Thus, PLA has potential as an antimicrobial and anti-biofilm candidate against other pathogenic microorganisms.

Studies have shown that PLA is effective against Klebsiella pneumoniae with a minimum inhibitory concentration of 2.5 mg/mL. Furthermore, PLA inhibited the growth and biofilm formation of KP in a time- and concentration-dependent manner.

4.6 Anti-Inflammatory and Immunomodulatory Properties

PLA can be produced by a variety of lactic acid bacteria, including vaginal Lactobacillus species, which are healthy constituents of the vaginal microbiome with a protective role against invading pathogenic bacteria and/or fungi. Additionally, PLA has been shown to exhibit anti-inflammatory and immunomodulatory properties, overall indicating its therapeutic potential as an intravaginally delivered compound for modulation of the vaginal microbiome. The precise molecular mechanisms underlying these anti-inflammatory effects remain under investigation and have not yet been characterized in clinical human studies.

5. Scientific Evidence by Area of Use

5.1 Broad-Spectrum Antibacterial Activity

Evidence level: Predominantly preclinical (in vitro and animal). No controlled human clinical trials identified.

Geotrichum candidum excretes D-3-phenyllactic acid, which inhibits the growth of Listeria monocytogenes. It was found to inhibit a range of gram-positive bacteria found in humans and foodstuffs, such as Staphylococcus aureus and Enterococcus faecalis, and gram-negative bacteria from humans, such as Providencia stuartii and Klebsiella oxytoca. This 1998 study was among the first systematic characterizations of PLA's antibacterial spectrum.

PLA exhibits effective antagonistic activity against pathogenic bacteria such as Listeria monocytogenes, Salmonella enterica, Escherichia coli O157:H7 and Staphylococcus aureus, and Enterococcus faecalis. A dose of 1.5% PLA was effective in curbing E. coli O157:H7, O26:H11, O103:H2, and O121:H19 and Salmonella typhimurium DT104, whereas the same dose of lactic acid was ineffective.

Against drug-resistant organisms, as Klebsiella pneumoniae has acquired high levels of resistance to multiple antibiotics and is considered a worldwide pathogen of concern, 3-phenyllactic acid has been reported to have antimicrobial activity against this food-borne bacterium. In vivo (mouse) studies showed that PLA could significantly increase the survival rate of infected mice and reduce pathological tissue damage. These animal data are promising but require human clinical validation.

In a study using Listeria innocua as a model organism, PLA produced by various LAB was confirmed to possess broad-spectrum antimicrobial activity. The effect of PLA against Listeria innocua was studied, and a pH-dependent behavior, typical of a weak acid, was detected. The antilisterial effect of PLA was compared to that produced by lactic acid and phenolic acids (gallic, caffeic, and ferulic acids) evaluating minimum inhibitory concentration (MIC), MBC, and survival kinetic parameters. PLA showed MIC values and death kinetic parameters significantly different from those exhibited by lactic acid and the tested phenolic acids. It is hypothesized that the antilisterial mechanism of action due to PLA is associated with its affinity to the cell surface, which contributes to cellular damage.

5.2 Antifungal Activity

Evidence level: In vitro laboratory studies. No human clinical trials identified.

Phenyllactic acid has been found in cultures of Lactobacillus plantarum that show antifungal activity in sourdough breads. The fungicidal activity of PLA and growth inhibition by PLA were evaluated by using a microdilution test and 23 fungal strains belonging to 14 species of Aspergillus, Penicillium, and Fusarium isolated from bakery products, flours, or cereals. Less than 7.5 mg of PLA per mL was required to obtain 90% growth inhibition for all strains, while fungicidal activity against 19 strains was shown by PLA at levels of ≤10 mg/mL.

The three citrinin-producing strains that were tested were also inhibited by PLA (MIC₉₀, 7.5 mg/mL), indicating potential relevance not only for pathogen control but also for mycotoxin-producing mold inhibition in food products. PLA is also effective against fungi such as Candida and Rhodotorula species, as well as Fusarium, Aspergillus, and Penicillium. All antifungal data identified are from in vitro studies; no clinical trials in human fungal infections have been identified.

5.3 Role as a Synergistic Antibacterial Compound in Manuka Honey

Evidence level: In vitro model studies; no direct human clinical trials on PLA's specific contribution.

After establishing a suitable assay for measuring the bacteriostatic effect in liquid culture, researchers demonstrated that honey differs in its growth-retarding effect on Bacillus subtilis despite the same content of MGO, indicating the presence of potentially synergistic compounds. In model studies using artificial honey, it was shown that 3-PLA in concentrations above 500 mg/kg enhances the bacteriostatic effect of model honeys containing 250 mg/kg MGO or more. It was shown that the effect correlates with the contents of 3-PLA and polyphenols in commercial manuka honey samples. Additionally, yet unknown substances further enhance the antibacterial effect of MGO in manuka honey. This work, published in 2023 (Thierig et al., Foods), used model honey systems and commercial manuka samples, not direct human subjects.

5.4 Anti-Biofilm and Quorum Sensing Inhibition

Evidence level: In vitro laboratory studies and one animal model. No human clinical trials identified.

Nisin and 3-phenyllactic acid in combination displayed excellent combinatorial antibacterial activity against foodborne pathogens including S. xylosus and M. luteus. The potential application in food preservation was verified via microbial analysis during the storage of meat and milk, and determination of strawberry rot rate. Scanning electron microscopy observation indicated a distinct mode of PLA with nisin, which may target the dividing cell, contributing to their combinatorial antibacterial effect.

A dedicated PMC-indexed study on Aggregatibacter actinomycetemcomitans (a periodontal pathogen) showed that the inhibition of cell growth and biofilm formation, and the breakdown of the preformed biofilm of A. actinomycetemcomitans by PLA, were significantly higher than those by lactic acid. The MIC for this organism was determined at 20 mM or 3.3 mg/mL. This preclinical data could have implications for oral health applications, but no human clinical studies on PLA in periodontal disease have been identified.

5.5 Vaginal Microbiome Modulation

Evidence level: In vitro cytotoxicity studies and mechanistic research. No human clinical trials identified.

PLA is a naturally produced, broad-spectrum antimicrobial compound with activity against bacteria and fungi. PLA can be produced by a variety of lactic acid bacteria, including vaginal Lactobacillus species, which are healthy constituents of the vaginal microbiome with a protective role against invading pathogenic bacteria and/or fungi. Additionally, PLA has been shown to exhibit anti-inflammatory and immunomodulatory properties, overall indicating its therapeutic potential as an intravaginally delivered compound for modulation of the vaginal microbiome.

In a 2024 study published in RSC Advances, microscopic visualization of cellular morphology using crystal violet staining and MTT cell proliferation assay revealed that PLA ionic liquids (ILs) result in minimal morphological changes and low cytotoxicity to human cervical epithelial cells. It was successfully demonstrated that transforming PLA into ILs efficiently enhances its solubility in water, and these formulations are not toxic to human epithelial cells. This investigation lays the groundwork for future testing of PLA ILs for their antimicrobial properties and metabolic activity within the cervicovaginal microenvironment. This work represents preliminary formulation science rather than a clinical intervention study.

5.6 Food and Feed Preservation

Evidence level: Applied food science studies (controlled food matrix experiments). No clinical endpoint human trials.

Applications of PLA-producing LAB in dairy, bakery, fruits, vegetables, meat, and fish products as well as active packaging have been analyzed, demonstrating their effectiveness in controlling microbial spoilage and pathogens while preserving sensory quality. PLA has been proved as an ideal antimicrobial compound with broad and effective antimicrobial activity against both bacteria and fungi. In addition, it could be used as feed additive to replace antibiotics in livestock feeds. These findings are based on food science and animal nutrition research rather than human health outcome studies.

5.7 Potential as a Biomarker

Evidence level: Observational clinical data; not a therapeutic application.

Clinical observations reveal a marked accumulation of specific aromatic microbial metabolites in sepsis cases irrespective of etiology, including phenyllactic acid (PhLA), p-hydroxyphenyllactic acid, and p-hydroxyphenylacetic acid. Under physiological conditions, aromatic metabolite biosynthesis primarily occurs in the intestinal environment, where microbial communities process intermediate compounds, with only minimal amounts of final metabolites entering systemic circulation. Experimental evidence confirms a statistically significant elevation in PhLA concentrations within gut pathobiota samples obtained from sepsis patients, compared to normobiota controls (p = 0.002). This observational finding positions PLA as a potential microbiome-derived biomarker in certain disease states but does not establish a therapeutic or causal role.

6. Body Systems and Health Areas of Association

Gastrointestinal and gut microbiome: PLA is a metabolite naturally produced by gut-resident LAB species. Its presence in the gut microbiome context has been studied in relation to pathobiota alterations in sepsis, and it contributes to the antimicrobial environment maintained by commensal LAB populations in the human gut.
Vaginal/urogenital microbiome: PLA can be produced by vaginal Lactobacillus species, which are healthy constituents of the vaginal microbiome with a protective role against invading pathogenic bacteria and/or fungi.
Oral health: Preclinical evidence shows anti-biofilm activity against Aggregatibacter actinomycetemcomitans, a key periodontal pathogen. No clinical studies exist.
Immune and inflammatory pathways: PLA has been shown to exhibit anti-inflammatory and immunomodulatory properties, indicating therapeutic potential. The exact mechanisms and clinical relevance remain to be established in human trials.
Food and agricultural safety: The most thoroughly documented area of application is food biopreservation, where PLA contributes to the control of spoilage organisms, molds, and foodborne pathogens in diverse food matrices.

7. Dosage Forms and Dosages Reported in Studies

The following dosages and concentrations are those reported in the scientific literature cited above; they are not clinical dosing recommendations for human use, as no clinical dosing studies for PLA as a dietary supplement or pharmaceutical have been identified.

Minimum inhibitory concentration (MIC) against Enterococcus faecalis: The minimum concentration of PLA to inactivate E. faecalis in brain heart infusion broth was 5 mg/mL.
MIC against Klebsiella pneumoniae: PLA was effective against KP with a minimum inhibitory concentration of 2.5 mg/mL.
MIC against Aggregatibacter actinomycetemcomitans: An MIC of 20 mM (approximately 3.3 mg/mL) was determined in cell-free supernatant biofilm inhibition experiments.
Antifungal MIC (bakery molds): Less than 7.5 mg of PLA per mL was required to obtain 90% growth inhibition for all 23 fungal strains tested; fungicidal activity against 19 strains was shown at levels of ≤10 mg/mL.
Bacteriostatic synergy in honey model systems: 3-PLA in concentrations above 500 mg/kg enhances the bacteriostatic effect of model honeys containing 250 mg/kg MGO or more.
Food preservation dose (E. coli and Salmonella): A dose of 1.5% PLA was effective to curb multiple E. coli O157 strains and Salmonella typhimurium DT104.
Fermentation production yield: Starting with 0.6 g/L phenylalanine, PLA was continuously accumulated reaching a maximum amount of 4.25 ± 0.18 mM after 158 hours of fed-batch fermentation.

8. Safety Considerations

8.1 Natural Origin and GRAS Context of PLA-Producing Organisms

PLA-producing lactic acid bacteria, such as Lactobacillus, Enterococcus, Leuconostoc, and Pediococcus, are generally regarded as safe (GRAS) microorganisms, and PLA-producing LAB strains are gaining wide attention. PLA is considered a natural, environmentally friendly organic acid, and its antimicrobial activity is regarded as safe and efficient. The GRAS designation applies formally to the producing organisms and their use in food production; PLA itself as a pure isolated ingredient does not currently appear on the FDA's GRAS list as a standalone food additive.

8.2 Low Cytotoxicity to Human Cells

Because of its low cytotoxicity, PLA is frequently used as a natural preservative and antimicrobial agent in the food processing industry. In the context of intravaginal delivery research, microscopic visualization of cellular morphology using crystal violet staining and MTT cell proliferation assay revealed that PLA ionic liquids result in minimal morphological changes and low cytotoxicity to human cervical epithelial cells.

8.3 Regulatory and Toxicological Gaps

Clinical data should be supplemented with the metabolic kinetics of PLA in humans and to evaluate animal toxicology, in order to enable regulatory use of PLA as a food additive. This published assessment reflects the current state of the evidence: while PLA has accumulated substantial in vitro and in vivo (animal) data confirming low toxicity to mammalian cells at the concentrations used in food science, comprehensive formal toxicological profiling in humans has not been completed, and PLA has not yet achieved approval as a standalone food additive in major regulatory jurisdictions.

8.4 pH Dependence and Formulation Considerations

The antimicrobial efficacy of PLA is pH-dependent due to its weak acid character (pKa ~3.46). PLA's mode of action is related to its undissociated form, which is able to cross the microbial membrane. At higher pH values, the compound becomes more dissociated and correspondingly less effective as an antimicrobial. This is a formulation consideration in any application context.

8.5 Water Solubility Limitation

PLA has low kinetic solubility in water. Hence, strategies to improve the solubility of PLA are necessary to facilitate its intravaginal or other systemic delivery applications. This property affects bioavailability in aqueous biological environments and is an active area of formulation research.

8.6 Absence of Drug Interaction Data

No published human studies were identified that characterize interactions between 3-phenyllactic acid and pharmaceutical drugs, dietary supplements, or specific medical conditions in humans. All interaction-relevant data available pertain to combinatorial antimicrobial effects with other agents (e.g., nisin) in food science contexts.

9. Summary of Evidence Landscape

The scientific literature on 3-phenyllactic acid is concentrated in the fields of food microbiology, fermentation biotechnology, and food preservation. PLA is an organic acid widely existing in honey and lactic acid bacteria fermented food and can be produced by many microorganisms. It has been proved as an ideal antimicrobial compound with broad and effective antimicrobial activity against both bacteria and fungi. Its mechanisms are increasingly well-characterized at the molecular level, involving cell membrane disruption, genomic DNA intercalation, and quorum sensing inhibition.

Notably, no randomized controlled human clinical trials for PLA as a therapeutic agent or dietary supplement have been identified in this review. The evidence base is primarily composed of in vitro microbiological studies, a smaller number of animal studies, and applied food matrix experiments. Exploratory work in formulation science for vaginal delivery and in characterizing its role in honey's antimicrobial action represents the frontier of translational research. Future research directions highlighted by experts include supplementing clinical data with metabolic kinetic studies of PLA in humans and completing animal toxicology evaluations.

References

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