Table 2.

Main metabolites produced by whey fermentation and their industrial applications.

Fermentation Methods	Main Metabolites Produced	Functional Properties Highlighted in Various Studies	Industrial Applications	References
Lactic fermentation	Lactic acid	Lactic acid inhibits Propionibacterium acnes at concentrations above 60 mg/mL, which supports its role in the treatment of acne and skin whitening. Its efficacy may vary depending on the stability and concentration of the formulation.	Food preservation, dairy products, bioplastics, cosmetics, pharmaceuticals	[13,38,99,136,137,138,139]
	EPS	EPSs exhibit a wide range of strain-specific bioactivities: EPS from Leuconostoc pseudomesenteroides increased Lactobacillus counts by 20% and reduced E. coli by 15% in rats; EPS from Bifidobacterium longum reduced lung eosinophils by 40% in an asthma model; sulfonated EPS from Lactiplantibacillus plantarum increased antioxidant activity by 35%, while EPS from L. lactis subsp. cremoris lowered cholesterol by 25% in rats. HePS inhibited biofilms by 70%, and Lactobacillus gasseri EPS suppressed E. coli, L. monocytogenes, and S. aureus by 60%. EPS-loaded nanoparticles reduced tumor volume by 70%, indicating a promising but context-dependent therapeutic potential.	Functional foods, dairy products, prebiotics, biopolymers	[140,141,142,143,144]
	Bacteriocins	Bacteriocins exhibit strong antimicrobial activity, positioning them as effective natural food preservatives. In situ production using starter cultures is promising for fermented foods; however, their application still depends on strain compatibility and product matrix. Commercial examples include Lactococcus lactis subsp. lactis BS-10 (BioSafe™) for cheese and Leuconostoc carnosum (Bactoferm™ B-SF-43) or Lactobacillus sakei (Bactoferm™ B-2) for vacuum-sealed meat. Lacticin 3147 has been shown to improve the quality of cheddar cheese by controlling non-starter LABs. Bacteriocin-producing LABs are also used to preserve plant-based foods, seafood, and fermented vegetables, although their wider industrial use may be limited by production stability, regulatory approval, and interaction with complex food systems.	Food preservation, pharmaceuticals, antimicrobial coatings	[145,146,147,148,149,150,151,152,153]
	Bioactive peptides and free amino acids	The antihypertensive effect of peptides from whey is primarily associated with angiotensin-converting enzyme (ACE) inhibition, with whey protein hydrolysate lowering systolic blood pressure by 30% in hypertensive rats. Co-fermentation of Lactobacillus paracasei and Saccharomyces cerevisiae has shown that novel ACE inhibitory and antioxidant peptides can be produced from whey protein concentrate, increasing serum antioxidant capacity by 40%. These peptides also showed antimicrobial activity by inhibiting the growth of Listeria and E. coli by 80% at 0.2 mg/mL and increasing the proliferation of immune cells by 50% in vitro. While these multifunctional properties suggest considerable therapeutic potential, their efficacy and stability in various biological systems and routes of administration need to be further validated for practical applications.	Functional foods (infant formula, sports nutrition, medical nutrition), nutraceuticals, pharmaceuticals	[145,154,155,156,157,158]
	γ-aminobutyric acid (GABA)	Fermented rice flour that contains 750.55 ± 26.03 mg GABA/100 g has been shown to reduce oxidative stress and improve neuroprotection. GABA also contributes to blood pressure regulation, as shown by a reduction in systolic pressure of 5.5 ± 3.9 mmHg over 12 weeks after daily consumption of 50 g cheddar cheese containing 16 mg GABA. A single dose of chocolate enriched with 28 g GABA from Lactobacillus hilgardii K-3 reduced stress levels. These results underline the multifunctional health potential of GABA. The physiological effects of GABA may vary depending on delivery matrix, dosage, and individual response, so further studies on standardized use in functional foods are needed.	Functional beverages, food supplements, pharmaceuticals	[159,160,161,162,163]
Alcoholic fermentation	Ethanol	Fermentation studies have reported ethanol concentrations reaching 4.52% after 20 days, though such yields are strongly influenced by fermentation conditions and substrate composition. Kluyveromyces marxianus produces ethyl acetate under aerobic conditions, which can be economically recovered from bioreactors for use in flavors and solvents. Recent studies indicate that metabolite production by K. marxianus is significantly dependent on oxygen availability, medium composition, and fermentation mode, which may affect process consistency and scalability in industrial applications.	Bioethanol production, pharmaceutical solvents, beverages	[164,165,166,167,168,169,170]
	Acetic acid	Dekkera anomala thrives under aerobic conditions and produces acetic acid with remarkable antimicrobial and preservative activity. Fermentation with D. anomala yields 9.18 g/L acetic acid after 34 days, supporting its potential use in food preservation at concentrations of 0.1–0.5%. Ethanol and acetic acid produced by these yeasts serve as effective antimicrobial agents; ethanol from whey-based disinfectants significantly reduced bacterial contamination, while acetic acid inhibited Listeria monocytogenes and E. coli in food matrices. L. monocytogenes was reduced by 90% at 0.5% and 99.9% at 2% acetic acid, while E. coli was reduced by 99% at 1.5% and 99.9% at 3%. A 2.5% acetic acid solution reduced L. monocytogenes in meat products by 3.7 log CFU/g after 24 h at 4 °C. Despite these promising results, the relatively slow fermentation rate and the concentration-dependent efficacy underline the need for process optimization and product-specific validation in industrial applications.	Food industry, pharmaceuticals, polymers, textiles, agrochemicals, cosmetics, chemical industry	[171,172,173,174,175,176,177,178]
	Higher alcohols and aromatic compounds	Higher alcohols from whey fermentation improve sensory properties and show antimicrobial activity. Isoamyl and phenylethyl alcohol produced during alcoholic fermentation inhibit spoilage organisms—phenylethyl alcohol at a concentration of 0.3% suppresses ~95% of Zygosaccharomyces bailii, while isoamyl alcohol at a concentration of 0.5% inhibits 90% of Penicillium species. Although these effects are promising, their application may be limited by concentration thresholds and product compatibility.	Biofuels, alcoholic beverages, chemical synthesis; dairy industry, flavoring agents, bakery products
	Glycerol	Glycerol is frequently used in pharmaceutical formulations and cosmetics due to its moisture-retaining and stabilizing effect in concentrations of 5–30%. In biotechnology, it acts as a metabolic regulator at 0.5–10% (w/v) and can be converted by microbial fermentation into high-value products such as 1,3-propanediol and polyhydroxyalkanoates (PHAs). Although its multifunctionality is well documented, optimization of conversion efficiency remains essential for broader industrial integration.	Cosmetics, pharmaceutical stabilizers, food processing
Propionic fermentation	Propionic acid	Propionic acid serves as a natural preservative for food and effectively inhibits mold growth in baked goods and dairy products. Studies indicate strong antifungal activity, particularly against Aspergillus fumigatus, Penicillium roqueforti, Pichia anomala, and Kluyveromyces marxianus, with minimum inhibitory concentration (MIC) values between 20 and 120 mM at pH 5 and below 10 mM at pH 3. P. roqueforti was the most sensitive, showing inhibition at 50 mM even at pH 7. While the pH-dependent efficacy highlights its potential, optimization of formulation conditions is key to ensuring consistent antifungal performance in different food systems.	Food preservatives, bioplastics, functional foods, nutraceuticals, pharmaceuticals, feed supplements, cosmetics agrochemicals	[12,179,180,181,182,183,184,185,186,187]
	Acetic acid	Acetic acid shows remarkable antimicrobial activity, with MIC values of 30–120 mM at pH 5 and effective suppression of fungal growth. The enhanced antifungal activity observed when combined with other organic acids, such as propionic acid, highlights its potential for natural food preservation, although the synergy of the formulation and pH sensitivity require careful optimization for consistent efficacy.	Food industry, pharmaceuticals, polymers, textiles; agrochemicals, cosmetics, chemical industry
	Succinic acid	Succinic acid from whey fermentation can achieve yields of 25–30 g/L with over 98% purity after processing. It is used as a flavor enhancer, acidity regulator, and gelling agent in foods, while succinic acid and its derivatives, such as sodium succinate, are used in packaging and as slow-raising agents. As an important precursor for biodegradable plastics, it supports the production of co-polyesters for sustainable food packaging. It also acts as an ion chelator and surfactant in pharmaceuticals and as an acidifier and stabilizer in cosmetics. Despite its versatility, wider industrial application may depend on cost-efficient production and integration into existing manufacturing processes.	Polymers, pharmaceuticals, food industry, cosmetics, chemical industry, agriculture
	Vitamin B12	Propionibacterium freudenreichii subsp. shermanii efficiently synthesizes vitamin B12 under optimal conditions: pH 6–7, lactate as carbon source, and fed-batch fermentation. Whey is a cost-effective medium when using a 24 h inoculum, 5 mg/L iron, 4% lactose, and 0.5% (NH4)2HPO4, with fermentation typically involving anaerobic and aerobic phases at 30 °C. While yields are promising, maintaining these specific parameters is critical for consistent B12 production on a large scale.	Pharmaceuticals, nutraceuticals, food industry, animal nutrition, biotechnology, cosmetics
Butyric fermentation	Butyric acid	Butyric acid has been shown to be effective against pathogens such as Salmonella and E. coli while supporting beneficial gut microbiota. Supplementation with 0.63 g/kg reduced Salmonella colonization in chickens, and 0.4% in broilers improved weight gain and feed conversion, and reduced E. coli levels, comparable to antibiotics. This dose also lowered pH in the upper part of the digestive tract, increased villus length and crypt depth, improved carcass yield, and reduced abdominal fat. While these results highlight its potential as an alternative to antibiotics in poultry feed, consistent performance under variable rearing conditions is worth further validation.	Polymers, chemical industry, food and nutraceutical industry, feed industry, pharmaceuticals, bioenergy	[188,189,190,191]
	Acetic acid	Acetic acid strongly inhibits Saccharomyces cerevisiae and outperforms sorbic acid at higher concentrations. Its antifungal effect is pH dependent: 100–115 mM completely inhibited Fusarium oxysporum at a pH of 4.8 (tomato), and 45–60 mM reduced spore germination of Penicillium expansum by 78–86% at a pH of 4.2 (apple juice). Although the effect is effective in acidic foods, the results may vary depending on the matrix and strain.	Food industry, pharmaceuticals, polymers, textiles, agrochemicals, cosmetics, chemical industry	[192,193,194,195]
	Acetate and butyrate	Clinical studies report that 2–5 g/day of butyrate increases Faecalibacterium prausnitzii by 28–47% and reduces inflammatory markers by 23–35%. Acetate at a concentration of 10–30 mM in the colon decreases E. coli adhesion by 42%. In bioplastics, acetate-based PHAs (15–25% acetate) are 76% biodegradable within 180 days. In livestock, 0.3–0.5% sodium butyrate improves poultry feed conversion by 8.7–12.3% and reduces intestinal pathogens by 18.5%. Acetate at 1–3 g/kg increases soil microbial biomass by 27% and organic carbon by 9–15%. Both acids are used as industrial solvents, with global production of acetate and butyrate exceeding 3.2 million and 80,000 tons, respectively. Despite their broad functionality, application efficiency varies by sector and depends on formulation, dosage, and environmental conditions.	Food and nutraceutical industry, pharmaceuticals, bioplastics, chemical industry, agriculture, feed industry, biofuels	[193,196,197,198,199]
	Hydrogen	Fermentative hydrogen production yields 1.5–2.8 mol H2/mol glucose with 15–24% conversion efficiency in optimized bioreactors. It plays a key role in biofuels and industrial cooling, where hydrogen systems operate at –253 °C with a coefficient of performance of 0.3–0.5. Blending hydrogen with natural gas (5–20%) reduces carbon emissions from heating by 7–13%. In the chemical industry, green hydrogen reduces the carbon footprint of ammonia synthesis by 65–90%, with modern Haber–Bosch plants consuming 28–37 GJ/ton of ammonia. Despite its potential, scalability and energy consumption remain critical factors for sustainable use.	Renewable energy, chemical industry, fertilizers	[200,201,202]
	Carbon dioxide (CO2)	CO2, a by-product of fermentation, is often used in the food industry to carbonate beverages at 3.5–7.0 g/L. In refrigeration, it is considered an environmentally friendly alternative with a GWP of 1, far lower than conventional refrigerants (GWP 1430–4000), and it achieves energy efficiency values of 2.5–3.8 in transcritical cycles. In greenhouse agriculture, CO2 enrichment at 800–1200 ppm increases tomato yields by 27–42% and lettuce biomass by 25–35% compared with ambient levels (~410 ppm). While the benefits are well documented, the efficiency of implementation depends on system design, cost, and sector-specific integration.	Food industry, industrial refrigeration, greenhouse agriculture	[203,204,205,206]
Acetic fermentation	Acetic acid	Acetic acid is widely known for its antimicrobial properties. It reduces E. coli O157:H7 by 99.7% at 0.1–0.5% in 24 h and lowers Listeria monocytogenes by 3–5 log CFU/g at 2–3% in meat. In pharmaceuticals, 0.25–1.0% solutions inhibit Pseudomonas aeruginosa at MICs of 0.16–0.31%. It is also used in acetate fibers (25–30 MPa tensile strength; >1.5 Mt/year production) and cosmetics (0.1–0.5%) to regulate pH (3.5–5.0) and improve the skin barrier by 18–27%. With a global production of over 13.8 Mt/year, acetic acid is an important chemical intermediate. Despite its versatility, its efficacy and safety depend on the exact formulation and context of use.	Food industry, pharmaceuticals, polymers, textiles, agrochemicals, cosmetics, chemical industry	[207,208,209,210,211,212,213]
	Acetate	An acetate content of 60–80 mM in the gut increases butyrate-producing bacteria by 35–40% and reduces inflammatory markers by 25%. In pharma, sodium acetate buffers enhance protein stability by 28–42%. Acetate-based PHAs (15–25%) show 76–90% in soil within 180 days. In animal feed and agriculture, 0.2–0.5% acetate improves digestion, increases feed conversion in poultry by 7–12%, and reduces CH4 emissions in ruminants by 15–22%. The chemical industry uses acetate in solvents, adhesives, and coatings, with a global production of over 3.5 Mt/year. Although it is versatile, its effectiveness depends on the formulation and sector-specific conditions.	Food and nutraceutical industry, pharmaceuticals, bioplastics, chemical industry, agriculture, feed industry	[214,215,216]
	EPS	EPS increases the viscosity of yogurt by 150–300% at 0.05–0.2% and reduces syneresis by 45–60%. In pharmaceuticals, 1.5–3 g/day increases SCFA production by 24–36% and bifidobacteria by 18–27%. In biotechnology, 2–5 g/L EPS increases the binding of heavy metals by 65–80% through biofilm formation. Biomedical applications include wound healing and drug delivery, where EPS hydrogels improve wound closure by 40–55% and prolong drug release by 30–45%. Despite their broad functionality, their efficacy is context- and formulation-dependent.	Food industry, pharmaceuticals	[217,218,219,220]
	CO2	Controlled CO2 levels can enhance the productivity of industrial fermentation by 15–30% by optimizing dissolved CO2 and improving kinetics and metabolite synthesis. Specific CO2 concentrations also reduce unwanted by-products by 25–40% through effects on metabolic flux and substrate uptake. In penicillin production, precise CO2 control increases antibiotic titers by 18–24% and improves microbial performance. In addition, CO2 optimization reduces energy consumption by 12–19% through improved glucose–oxygen efficiency. While these results are promising, they depend on tightly controlled process conditions.	Food industry, biotechnology
Mixed fermentation for microbial polymer production	PHAs	PHAs containing 10–30% hydroxyvalerate exhibit greater flexibility, with elongation at break increasing from 5–10% to 30–450% compared with pure PHB, making them ideal for bioplastics. In tissue engineering, PHA-based scaffolds improve cell adhesion and proliferation. They exhibit 75–90% better biocompatibility and 65–85% higher cell viability than conventional synthetic polymers. PHAs with 10–30% hydroxyvalerate show increased flexibility, with elongation at break rising from 5–10% to 30–450% versus pure PHB, supporting their use in bioplastics. In tissue engineering, PHA scaffolds enhance cell adhesion and proliferation, with 75–90% better biocompatibility and 65–85% higher viability than synthetic polymers. Despite these advantages, performance can vary with composition and application context.	Polymers	[141,221,222,223,224]
	Biohydrogen	Biohydrogen is gaining relevance as a renewable energy source, with fermentative yields of 1.8–2.5 mol H2/mol glucose under optimized conditions. Hydrogen-enriched fuels (15–20% H2) reduce CO2 emissions by 10–15% and NOx by 20–50%. Microbial reactors achieve up to 40% energy efficiency and produce 0.5–3.5 L H2/day in continuous operation. Practical scalability depends on whether these performance levels can be maintained in real systems.		[225,226,227,228]
	Polymalic acid (PMA)	PMA, a biodegradable polyester, is widely studied for biomedical and pharmaceutical purposes. PMA nanocarriers enable 50–70% extended drug release over 7–21 days with 15–30% loading efficiency. In bioplastics, PMA films offer a tensile strength of 20–35 MPa and an oxygen permeability of 2.5–8.7 cm3-mm/m2-day-atm, making them suitable for sustainable packaging. During composting, PMA biodegrades 85–95% within 90 days. Despite its promising properties, performance can vary depending on the formulation and application environment.
	EPS	EPS-based hydrogels improve water retention by 60–80%, retain 20–35 g water/g dry matter, and are suitable for biomedical dressings and agriculture. In biopolymers, EPS improves the flexibility of films by reducing the modulus of elasticity by 30–45%. Plastics with 5–15% EPS degrade 85% faster and achieve 90–95% biodegradation in 60–180 days compared with more than 365 days for conventional plastics. While the effect is effective, performance can vary depending on matrix compatibility and environmental conditions.
Methanogenic fermentation	CH4	CH4 is an important renewable fuel in biogas production, with optimized anaerobic digestion of whey yielding 0.3–0.5 m3 CH4/kg COD. CH4-fueled engines reduce CO2 emissions by 15–25% compared with diesel, while bio-CNG in public transportation reduces NOx by 40–60% and particulates by 85–95%. Biogas plants using cheese whey achieve 0.34–0.48 m3 CH4/kg COD, with 55–68% energy recovery and 3.5–7 years payback. Despite strong potential, the results depend on the plant scale and process optimization.	Renewable energy, fuel for heating, transportation	[16,229,230,231,232,233,234,235,236]
	CO2	Optimized CO2 levels in sparkling water (5.8–6.2 g/L) increase consumer preference by 32–41%, while sparkling wines require more than 1.2 g/L for perceptible mouthfeel. At retail, transcritical CO2 systems reduce energy consumption by 18–26%, with advanced designs (e.g., two-phase ejector, heat exchanger) improving COP by 12% and energy efficiency by 16% and reducing electricity consumption by 10%. Cascade CO2 systems achieve an efficiency of 3.2–4.1 for medium-temperature cooling. In biotechnology, controlled CO2 increases the expression of recombinant proteins by 25–33%. Although the benefits are significant, system design and application context remain critical for consistent performance.	Food industry, industrial refrigeration, greenhouse agriculture
	Volatile fatty acids (VFAs)	VFAs can be converted to PHAs with yields of 0.2–0.6 g PHA/g VFA. Industrial processes using mixed VFAs from wastes achieve 50–150 g/L PHA and 1.0–3.5 g/L/h productivity. The resulting PHAs have a tensile strength of 20–40 MPa and an elongation at break of 5–500%, with an oxygen permeability of 3–55 cm3-mm/m2-day-atm and a water vapor permeability of 1–5 g-mm/m2-day, suitable for sustainable packaging. VFAs also support the production of solvents and coatings, with acetate to ethanol conversion at 85–92% and propionate-based adhesives achieving bond strengths of 2.5–4.8 MPa. While performance and efficiency are promising, they are highly dependent on feedstock variability and process control.	Polymers
Fungal fermentation for SCPs production	SCPs	SCPs-enriched bread formulations with 5–10% fungal protein increase the protein content by 18–25%, with sensory acceptability at 85% of control products. SCP (mycoprotein) derived from Fusarium venenatum has been shown to reduce postprandial blood glucose levels by 20–35% and insulin response by 15–27% compared with reference proteins, thus supporting metabolic health. In the animal feed industry, SCPs are used as a high-protein supplement for livestock and aquaculture. Replacing 20–40% of fishmeal with SCPs from Aspergillus oryzae in aqua feed improves fish growth rates by 10–18% and increases feed conversion in tilapia and rainbow trout by 12–20. In poultry, the inclusion of 5–15% fungal SCPs in feed increases weight gain by 8–14% while improving gut health by reducing Salmonella by 22–30% and increasing Lactobacillus populations in the cecum by 15–22%. The production of SCPs for waste utilization and enzyme production is being researched. Trichoderma reesei efficiently utilizes whey as a carbon source and achieves biomass yields of 0.45–0.65 g/g lactose, with protein contents of 45–55% and cultivation productivity of 0.8–1.2 g/L/h in optimized bioreactors. In addition, SCP-producing fungi secrete valuable enzymes such as proteases and cellulases, which can be used for biofuels and increase enzyme activity by 50–75% under optimized fermentation conditions. T. reesei, which grows on lignocellulosic substrates, reaches cellulase activities of 1.2–2.8 FPU/mL. Fungal SCPs are analyzed for their bioactive properties. SCP-derived peptides show antimicrobial effects, with Saccharomyces cerevisiae protein hydrolysates inhibiting E. coli and Staphylococcus aureus by 65–80% at 0.5–1.5 mg/mL, with MIC of 0.18–0.42 mg/mL against common foodborne pathogens. In addition, SCP-derived β-glucans improve immune function by increasing macrophage activity by 40–60% and natural killer (NK) cell cytotoxicity by 25–38% at a dosage of 100–250 mg/day, making them promising functional ingredients for immunological supplements. SCP bread enriched with 5–10% mushroom protein increases the protein content by 18–25% while retaining 85% of the sensory acceptability. Trichoderma reesei also produces enzymes such as cellulases (1.2–2.8 FPU/mL), with 50–75% higher activity under optimized conditions. SCP-derived peptides show antimicrobial activity and inhibit E. coli and S. aureus by 65–80% at 0.5–1.5 mg/mL (MIC 0.18–0.42 mg/mL), while β-glucans improve immune function by increasing macrophage activity by 40–60% and NK cell cytotoxicity by 25–38% at 100–250 mg/day. Although SCPs show multifunctional potential in various areas, consistent bioactivity and integration into existing systems require further standardization and validation.	Food industry, feed industry, biotechnology, pharmaceuticals	[237,238,239,240,241,242]