Hypoglycemic and Antioxidant Activities of Exopolysaccharides Produced by Lactic Acid Bacteria: A Systematic Review

Abstract

Lactic acid bacteria (LAB) are widely utilized in various fermented food products and possess a Generally Recognized as Safe status. LAB produce exopolysaccharides (EPS), which are one of the components of postbiotics. Studies on EPS from LAB have attracted considerable interest because of their potential biological functions and associated health benefits, including hypoglycemic and antioxidant functions. However, there is still a lack of reviews that summarize available studies regarding the relationship between EPS characteristics and hypoglycemic and antioxidant activities. Therefore, the present systematic review aimed to identify the characteristics of EPS that influence its hypoglycemic and antioxidant activities. This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Twenty-seven articles from Google Scholar, PubMed, and Scopus, which reported the sources of EPS-producing LAB, fermentation media, and conditions, as well as their EPS yields, molecular weights (MWs), and monosaccharide components, were selected based on the inclusion and exclusion criteria and whole literature screening. The MWs of EPS ranged from 10.75 to 9,549 kDa and from 2.4 to 9,549 kDa based on hypoglycemic and antioxidant activity assays, respectively. Generally, glucose and mannose were found in almost all EPS that were produced. This study indicated that MW and monosaccharide components influence hypoglycemic and antioxidant activities (in vitro). Further investigations with more comprehensive supporting data are needed to understand how all related factors influence EPS bioactivity.

INTRODUCTION

Lactic acid bacteria (LAB) are widely utilized as starter cultures to ferment various food products. Most LAB are food-grade bacteria and possess a Generally Recognized as Safe status. Some LAB strains act as probiotics. LAB can also produce metabolites with various biological functions. These metabolites are known as postbiotic components (Salminen et al., 2021). According to the International Scientific Association for Probiotics and Prebiotics, a postbiotic is defined as a preparation of inanimate microorganisms and/or their components that confer health benefits to the host. Exopolysaccharides (EPS), peptidoglycan, teichoic acid, bacteriocins, enzymes, vitamins, and short-chain fatty acids such as butyric acid are metabolites produced by LAB and considered as postbiotics (Bourebaba et al., 2022).

Postbiotics, including cell components and metabolites, offer benefits and successfully mimic the therapeutic effects of probiotics. Compared with probiotics, postbiotics have a longer shelf life and are easy to store, handle, and transport. Postbiotics possess metabolic, immunomodulatory, antiobesogenic, anticancer, and antioxidant functions. Therefore, they can be used to develop new food products with specific physiological effects (Hernández-Granados and Franco-Robles, 2020).

EPS are metabolites produced by microbes, mainly food-grade bacteria such as LAB, that can act as postbiotics and possess characteristics attractive to the food industry. EPS produced by LAB can be classified as homopolysaccharides (HoPS) and heteropolysaccharides (HePS). HoPS are produced extracellularly from one type of monosaccharide, whereas HePS are produced intracellularly from several monosaccharides and then secreted from the cell. EPS can be secreted as a slimy polymer or attached to the cell wall to form a capsule (Guérin et al., 2020). Aside from Leuconostoc sp., Weissella sp., Lactococcus sp., Streptococcus sp., Pediococcus sp., and Bifidobacterium sp., Lactobacillus sp. is one of the LAB that produces the most EPS (Guérin et al., 2020).

Extracellular enzymes, including glucansucrase or fructansucrase, play a role in HoPS biosynthesis. These enzymes transfer monosaccharides from specific substrates to form polysaccharides. Both of these enzymes belong to the glycosyltransferase (GTF, E.C.2.4xy) group, which catalyzes sugar hydrolysis and produces monosaccharide residues that attach to the glycan acceptor chain (Zhou et al., 2019). HoPS are primarily produced by Lactobacillus, Leuconostoc, Oenococcus, and Weissella (Lynch et al., 2018).

Meanwhile, HePS biosynthesis occurs in several stages: (1) transport of sugar into the cytoplasm from bacterial cells, (2) synthesis of nucleotide sugars and sugar-1-phosphate (donor substrates for nucleotide sugars), (3) synthesis of repeating units, and (4) polymerization of repeating sugar units and export of elongated chains (Oleksy and Klewicka, 2018). The following enzymes are involved in HePS biosynthesis: phospho-β-galactosidase, β-galactosidase, glucokinase, galactokinase, galactose-1-phosphate uridyltransferase, α-phosphoglucomutase, β-phosphoglucomutase, UDP-glucose pyrophosphorylase, dTDP-glucose pyrophosphorylase, UDP-galactose 4-epimerase, dTDP-glucose 4,6-dehydratase, UDP-glucose dehydrogenase, flippase (wzx), polymerase (wzy), phosphoglucose isomerase, fructose-1,6-bisphosphatase, 6-phosphofructokinase, fructose-1,6-diphosphate aldolase, galactose 6-phosphate isomerase, tagatose 6-phosphatase kinase, and tagatose-1,6-di-phosphate aldolase (Xu et al., 2019). HePS are primarily produced by Lactobacillus, Lactococcus, and Streptococcus (Lynch et al., 2018).

Recently, EPS produced by LAB have received considerable interest because of their potential biological functions and associated health benefits, including hypoglycemic and antioxidant functions. Several studies have found that EPS produced by certain LAB strains, including Lactobacillus plantarum PFC308, PFC309, PFC310, PFC311, PFC312, and PFC313 (Yılmaz and Şimşek, 2020); Lactococcus garvieae C47 (Ayyash et al., 2020a); L. plantarum LS5 and LU5 (Hashemi et al., 2022); Lactobacillus rhamnosus LB1lac1 (Wang et al., 2022); Lactobacillus delbrueckii MW725385.1 and Lacticaseibacillus rhamnosus MW725389.1 (Tarique et al., 2023); Enterococcus faecalis 84B (Ali et al., 2023); Levilactobacillus brevis (Kwun et al., 2024); Lactiplantibacillus plantarum MY04 (Mao et al., 2024); L. rhamnosus ACS5 (İnanan et al., 2024); and Limosilactobacillus reuteri C66 (Kober et al., 2025), possess hypoglycemic biological properties. Meanwhile, several studies have investigated the antioxidant activity of EPS produced by certain LAB strains, including Lactobacillus helveticus MB2-1 (Xiao et al., 2020); Weissella cibaria MD2 (Lakra et al., 2021); Lactobacillus kimchi SR8 (Zhang et al., 2021b); Lactococcus lactis subsp. lactis IMAU11823 (Li et al., 2022); L. plantarum NA (Xu et al., 2023); L. plantarum MC5 (Zhao and Liang, 2023); Lactococcus hircilactis CH4 and L. delbrueckii GRIPUMSK (Srinivash et al., 2023); Limosilactobacillus fermentum LAB-1 (Tarannum et al., 2024); L. rhamnosus ACS5 (İnanan et al., 2024); L. fermentum YL-11 (Wei et al., 2024); and L. reuteri C66 (Kober et al., 2025).

Diabetes is a serious chronic condition where the body does not produce enough insulin or cannot use it effectively, leading to hyperglycemia. Diabetes is a significant health concern that has reached alarming levels. According to data from the International Diabetes Federation (IDF) Diabetes Atlas 2025, type 2 diabetes mellitus (T2DM) is the most common type of diabetes, accounting for over 90% of all diabetes globally. In 2024, an estimated 588.7 million adults aged 20－79 years (11.1% of all adults in this age group) were living with diabetes worldwide. By 2050, the number of adults living with diabetes is projected to reach 852.5 million. Although the world’s population is estimated to grow by 25% over the following years, the number of people with diabetes is estimated to increase by 45% (IDF, 2025).

Reactive oxygen species (ROS), including superoxide anions, hydroxyl radicals, hydrogen peroxide radicals, and nitric oxide, are the products of single-electron oxygen reduction in the body and are unavoidable byproducts of normal cellular metabolism. High ROS concentrations can trigger oxidative damage, leading to diabetes, cancer, atherosclerosis, liver disease, and chronic degenerative diseases (Jomova et al., 2023).

T2DM is a metabolic disorder characterized by chronic hyperglycemia and an insufficient response to circulating insulin in peripheral tissues, resulting in insulin resistance (Yaribeygi et al., 2020). One of the factors affecting insulin resistance is oxidative stress. Oxidative stress occurs from an imbalance between free radical production and the antioxidant system, which reduces peripheral insulin sensitivity and contributes to T2DM development (Yaribeygi et al., 2020). Previous studies have shown that EPS produced by LAB exhibit antioxidant and hypoglycemic activities (Ayyash et al. 2020a, 2020b; Ali et al., 2023; Bamigbade et al., 2023; Tarique et al., 2023). Therefore, as oxidative stress is one of the factors affecting DM, the present review covers the bioactivity of EPS in terms of antioxidant and hypoglycemic activities.

There are several molecular mechanisms between oxidative stress and β-cell dysfunction that can lead to insulin resistance: (1) increasing apoptotic processes; (2) decreasing metabolic pathways in β-cells; (3) disrupting KATP channels; (4) inhibiting transcription factors, such as Pdx-1 (insulin promoter factor 1) and MafA (a transcription factor); (5) reducing β-cell neogenesis; (6) mitochondrial dysfunction; (7) activating Toll-like receptors; and (8) inducing molecular pathways, such as the nuclear factor kappa B, c-Jun NH(2)-terminal kinase/stress-activated protein kinase, p38 mitogen-activated protein kinase, and hexosamine pathways (Yaribeygi et al., 2020). As a natural product with hypoglycemic and antioxidant functions, EPS produced by LAB can be used to develop functional foods or as starter culture in fermented dairy products or similar beverages to prevent or reduce DM occurrence.

EPS produced by LAB have attracted considerable attention because of their diverse chemical structure, unique properties, and intriguing relationship between their chemical structure and function (Erdem et al., 2023). Different LAB strains can produce EPS with other structures, which can play various roles (Korcz and Varga, 2021). According to Zhang et al. (2023), the bioactivity of EPS is influenced by their structure, including monosaccharide composition, glycosidic bonds, and molecular weight (MW).

However, there is a lack of available studies correlating EPS characteristics (MW and monosaccharide composition) with their hypoglycemic and antioxidant biological functions. Therefore, the present systematic review examined how EPS characteristics (MW and monosaccharide composition) affect their hypoglycemic and antioxidant activities.

MATERIALS AND METHODS

Search strategy and study selection

This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (Page et al., 2021). Google Scholar, PubMed, and Scopus databases were searched for English language articles published in the last 10 years (2014－2024) until February 2024. The keywords used a combination of Boolean operators “AND” and “OR” for the search. The following keywords were used in the databases: EPS AND “lactic acid bacteria” AND (“antioxidant activity” OR “hypoglycemic activity” OR “antidiabetic activity” OR “alphα-glucosidase inhibitor activity” OR “alphα-amylase inhibitor activity”). Publish or Perish was used to assist in the search for studies on databases. The studies were then collected using the Zotero reference manager. Subsequently, we identified the collected articles and removed duplicate articles.

The articles were selected based on their titles and abstracts. Irrelevant articles, including those not published in English, duplicate reviews, and others (e.g., books, overviews, theses, encyclopedias, and proceedings), were removed. The eligibility of the full-text articles was determined by the participants, intervention, comparison, and outcome criteria. The inclusion and exclusion criteria are presented in Table 1. For the inclusion criteria, the participants were LABs that produced EPS. The desired intervention was the characteristics of LAB without treatment. For comparison, acarbose was used as the positive control for hypoglycemic activity assay, whereas vitamin C was used for antioxidant activity assay. The expected outcome was the hypoglycemic and antioxidant activities (in vitro study) of EPS from LAB.

Table 1.

Inclusion and exclusion criteria

Criteria	Inclusion	Exclusion
Participants	Lactic acid bacteria that produce EPS	Other microbes (besides lactic acid bacteria, such as bifidobacteria, molds, yeasts, thermophilic bacteria, or others) that produce EPS
Intervention	Characteristics of EPS produced by LAB (MW and monosaccharide composition) without intervention on the hypoglycemic and antioxidant activities	The influence of irradiation, ultrasonication, radioprotective agents, interaction with casein or other compounds, and other processes on the antioxidant and hypoglycemic activities of EPS produced by LAB
Comparison	The positive control for hypoglycemic activity is acarbose, and for antioxidant activity, it is ascorbic acid	-
Outcome	Hypoglycemic and antioxidant activities (in vitro study) possessed by EPS from LAB	Biological activities other than hypoglycemic and antioxidant (such as for food processing, ointment, anti-aging, antimicrobial, antibiofilm, lowering cholesterol, and other biological functions). In vivo and cellular studies for antioxidant and hypoglycemic activities
Study design	Research journal, scientific report	Review (narrative/systematic), proceeding, book chapter
Year of publication	The last 10 years	Besides the last 10 years
Language	English	Other languages

EPS, exopolysaccharides; LAB, lactic acid bacteria; MW, molecular weight.

Articles involving interventions (e.g., the influence of irradiation processes, ultrasonication, radioprotective agents, and others on hypoglycemic and antioxidant activities), those that were irrelevant (e.g., in vivo and cellular studies on antioxidant and hypoglycemic activities), those with insufficient data (no data on MW and monosaccharide composition of EPS), and those with inaccessible full text were excluded. The selected articles were used to investigate the influence of the MW and monosaccharide composition of EPS on the resulting hypoglycemic and antioxidant activities.

Data extraction

After identifying articles that fulfilled the criteria, data, including the name of EPS-producing LAB, source of LAB (from which it was isolated), media/carbon source in the fermentation media, conditions, HoPS/HePS, EPS yield, country, MW, constituents, composition, hypoglycemic/antioxidant activity (in vitro), and references, were extracted from the selected studies.

Hypoglycemic activity was expressed as a percentage of α-glucosidase inhibitor (AGI) and α-amylase inhibitor (AAI). Meanwhile, antioxidant activity was expressed as a percentage of 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity, hydroxyl radical scavenging (HRS) activity, superoxide anion scavenging (SAS) activity, and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) scavenging activity (%). The half-maximal inhibitory concentration (IC₅₀) values or hypoglycemic/antioxidant activities of EPS and positive controls were determined/plotted on a graph using OriginPro 2024 (OriginLab Corp.), and the extracted data were organized using Microsoft Excel.

Analysis and data representation

The data that were collected from the articles, including the EPS concentration for in vitro hypoglycemic and antioxidant assays, relationship between EPS MW and hypoglycemic and antioxidant activities, relationship between the monosaccharide composition and hypoglycemic and antioxidant activities, and comparison between the IC₅₀ values of EPS and positive control, were analyzed. Acarbose and ascorbic acid were used as positive controls for hypoglycemic and antioxidant assays, respectively. The data are presented as tables/images or in textual form.

RESULTS AND DISCUSSION

Results of the search and selection of studies

The PRISMA flowchart for the study search and selection strategy is shown in Fig. 1. A total of 5,987 articles were collected across Google Scholar (n=5,432), PubMed (n=20), and Scopus (n=535). A total of 863 articles were removed using the Zotero reference manager, resulting in 5,124 articles for the title selection stage.

Fig. 1.

PRISMA flowchart for the study search and selection strategy. ¹⁾Book, overview, thesis, encyclopedia, and proceedings.

A total of 4,855 articles were excluded because of irrelevant titles (e.g., EPS produced by microbes other than LAB, use of EPS from LAB for food processing, and others), non-English language, review articles, duplication, and others (e.g., books, overviews, theses, encyclopedias, and proceedings). A total of 269 articles were included in the abstract selection stage. Among them, 190 articles were excluded because they were irrelevant, reviews, not in English, or others. Seventy-nine articles, with seven additional articles from the list (n=86), were included into the full-text selection stage for eligibility. Full-text screening was performed on the basis of the inclusion and exclusion criteria. A total of 59 articles were excluded because of interventions (e.g., the influence of irradiation, radioprotective agents, and others), irrelevance (e.g., postbiotics in general, cellular antioxidant activity, in vivo, wastewater media, and bifidobacteria), lack of data (no data on MW and monosaccharide composition of EPS), and inaccessible full text. Finally, 27 articles were selected for this study. Table 2 lists the LAB used for EPS production in the 27 selected studies.

Table 2.

LAB used for EPS production

No.	EPS producer	The source of the LAB (isolated from)	The media/carbon source in the fermentation media	Fermentation condition	HoPS/HePS	EPS yield (g/L)	Country	Reference
1	Lactobacillus plantarum YO175 L. plantarum OF101	Traditional fermented cereal beverage	Modified MRS/mMRS (sucrose 20 g/L)	Incubator shaker, 170 rpm	HePS HoPS	1.36 (EPS-YO175) 2.18 (EPS-OF101)	Nigeria	Adesulu-Dahunsi et al. (2018a)
2	Weissella cibaria GA44	Gari (Nigerian fermented food)	Modified MRS (sucrose 20 g/L)	30°C, 24 h	HePS	4.80	Nigeria	Adesulu-Dahunsi et al. (2018b)
3	Levilactobacillus brevis NCCP 963	Black carrot drink (kanji)	10.56% glucose, 9.2% sucrose, 0.75% tryptone, 0.446% CaCl2, and 0.385% K2HPO4	37°C, 3－4 d, anaerobic	HoPS	0.97	Pakistan	Afreen et al. (2023)
4	Enterococcus faecalis 84B	NR	MRSB supplemented with sucrose 20 g/L	25.0±0.1°C, 48 h	HePS	0.16	Egypt	Ali et al. (2023)
5	Lactococcus garvieae C47	Fermented camel milk	Reconstituted Camel Milk supplemented with glucose 2%	37°C, 48 h	HePS	NR	United Arab Emirates	Ayyash et al. (2020a)
6	Pediococcus pentosaceus M41	Marine source	MRSB supplemented with sucrose 20 g/L	25.0±0.1°C, 48 h	HePS	NR	United Arab Emirates	Ayyash et al. (2020b)
7	Lactococcus lactis subsp. lactis C15	Raw camel milk	M-17 Broth (contain sucrose 20 g/L)	25°C, 48 h	HePS	NR	United Arab Emirates	Bamigbade et al. (2023)
8	Lactiplantibacillus plantarum RO30	Romi cheese	MRS-sucrose 5%	37°C, 72 h	HePS	4.23	Egypt	Elmansy et al. (2022)
9	L. plantarum EB-2	Armenian feta cheese	MRSB	37°C, 48 h, aerobic	HePS	0.25	Uzbekistan	Elova et al. (2019)
10	Lactobacillus casei K7/3	Sauerkraut	MRSB	2% Inokulum, 37°C, 48 h, aerobic, 150 rpm	HePS	0.02	Uzbekistan	Elova et al. (2020)
11	L. plantarum H31	Pickled cabbage	MRSB	37°C, 24 h	HePS	0.83	China	Huang et al. (2020)
12	Lactiplantibacillus pentosus B8	Sichuan Pickle	MRS supplemented with sucrose 40 g/L	30°C, 48 h	HePS	1.40	China	Jiang et al. (2022b)
13	P. pentosaceus E8	Cereal vinegar	MRS contain sucrose 4%	48 h	HePS	1.37	China	Jiang et al. (2022a)
14	Streptococcus thermophilus CC30	Raw milk	Skim milk lactose medium: 11% skim milk, 0.35% yeast extract, 1% lactose, and 1.5% agar	30°C, 24 h	HePS	1.95	India	Kanamarlapudi and Muddada (2017)
15	L. plantarum NS1905E	Yoghurt	MRSB	37°C, overnight	HePS	NR	China	Lei et al. (2023)
16	Lactobacillus helveticus MB2-1	Traditional Sayram ropy fermented milk	Reconstituted whey medium: lactose 80 g/L, soya peptone 20 g/L, and MgSO4 3 g/L	37°C, 24 h	HePS	0.75	China	Li et al. (2014b)
17	L. plantarum HY	Home-made Sichuan pickle	SDM contain (per 100 mL): 4.0 g lactose, 4.0 g yeast nitrogen base, 0.5 g sodium acetate, 0.1 g ammonium sulphate, and 0.1 mL Tween 80	37°C, 48 h	HePS	1.43	China	Liu et al. (2019a)
18	Leuconostoc lactis KC117496	Naturally fermented idli batter	MRS-sucrose and glucose 2%	30°C, 48 h	HoPS	4.55	India	Saravanan et al. (2019)
19	L. plantarum BR2	Jack fruit	Media contain (in g/100 mL): yeast extract (4.0), lactose (4.0), Tween 80 (0.1), sodium acetate (0.5), and ammonium sulphate 0.5	37°C, 72 h, static condition	HePS	2.80	India	Sasikumar et al. (2017)
20	Lactobacillus delbrueckii ssp. bulgaricus B3 and L. plantarum GD2	Yoghurt (B3) Stoll (GD2)	NR	NR	HePS	0.44; 0.38 (B3; GD2)	Turkey	Sirin and Aslim (2020)
21	L. delbrueckii MW725385.1 (EPS-LB3) Lacticaseibacillus rhamnosus MW725389.1 (EPS-MLB3)	Traditional yoghurt-like products (Labaneh)	MRSB contain sucrose: 0%; 2%; 4%	pH: 5.5; 6; 7 T: 25°C; 34°C; 43°C t: 24 h; 48 h; 72 h	HePS	0.28 (EPS-LB3) 0.24 (EPS-MBL3)	United Arab Emirates	Tarique et al. (2023)
22	L. plantarum YW32	Kefir grains	SDM: glucose (20 g/L), bactocasitone (10 g/L), yeast nitrogen base (5 g/L), sodium acetate (5 g/L), ammonium citrate (2 g/L), MnSO4 (0.05 g/L), MgSO4･7H2O (0.1 g/L), K2HPO4 (2 g/L), dan Tween 80 (1 ml/L), pH adjusted to 6.6 (with acetic acid 1 M)	37°C, 24 h	HePS	NR	China	Wang et al. (2015)
23	Lactobacillus fermentum S1	Fermented Fuyuan pickles	Liquid medium: 20 g of glucose (20 g/L), ammonium citrate (5 g/L), soya peptone (10 g/L), yeast extract (6 g/L), MnSO4 (0.05 g/L), FeSO4 (0.04 g/L), MgSO4 (0.2 g/L), and Tween 80 (1 mL/L)	3% inoculum, 33°C, 24 h	HePS	NR	China	Wang et al. (2020)
24	L. rhamnosus LB1lac10	Homemade pickles	MRSB	37°C, 18 h, anaerob	HePS	8.24 (crude EPS)	China	Wang et al. (2022)
25	L. casei NA-2	Chinese Northeast sauerkraut	MRSB	37°C, 24 h, anaerob	HePS	NR	China	Xu et al. (2022)
26	L. plantarum YW11	Tibetan kefir grains	Pasteurized skim milk medium	37°C, 18 h	HePS	NR	China	Zhang et al. (2017)
27	Leuconostoc mesenteroides LM187	Sichuan paocai samples	Sugar production medium (180 g sucrose, 10 g peptone, 5 g dipotassium phosphate, 2 g sodium chloride)	2% (v/v) inoculum, 30°C, 36 h	HePS	NR	China	Zhang et al. (2021a)

LAB, lactic acid bacteria; EPS, exopolysaccharides; NR, not reported; HoPS, homopolysaccharides; HePS, heteropolysaccharides; MRS, de Man Rogosa Sharpe; MRSB, de Man Rogosa Sharpe Broth; SDM, semi-defined medium.

Among the 27 articles, 18 articles mainly discussed antioxidants, two articles discussed hypoglycemics, and seven articles discussed both (Fig. 2A). This indicates that the hypoglycemic effects of EPS produced by LAB have not been extensively studied. Combined studies on antioxidant and hypoglycemic effects have shown a correlation. The distribution of selected studies on EPS from LAB shows that research over the past 10 years has been primarily conducted in China, followed by the United Arab Emirates and India, with a total of 12, 4, and 3 studies, respectively (Fig. 3). Moreover, EPS from L. plantarum have been the most extensively researched in almost all countries except the United Arab Emirates and Pakistan (Fig. 3).

Fig. 2.

(A) Distribution of selected studies on the antioxidant and hypoglycemic properties of EPS produced by LAB. Methods for analyzing the (B) hypoglycemic and (C) antioxidant activities of EPS from the selected studies. EPS, exopolysaccharides; LAB, lactic acid bacteria; AAI, α-amylase inhibitor; AGI, α-glucosidase inhibitor; SD, superoxide dismutase scavenging activity; FRAP, ferric reducing antioxidant power; LP, lipid peroxidation inhibitory activity; HP, hydrogen peroxide scavenging activity; TAC, total antioxidant capacity; MC, metal (ferrous) ion chelating activity; RP, reducing power; ABTS, 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) scavenging activity; SAS, superoxide anion scavenging activity; HRS, hydroxyl radical scavenging activity; DPPH, 2,2-diphenyl-1-picrylhydrazyl scavenging activity.

Fig. 3.

Distribution of selected studies on exopolysaccharides produced by lactic acid bacteria in several countries.

EPS production by LAB

Various LAB species and strains produce EPS, with L. plantarum being the most extensively studied (36.7%). There are 11 strains of L. plantarum that produce EPS, including L. plantarum YW11, YW32, GD2, BR2, HY, NS1905E, H31, EB-2, YO175, OF101, and RO30 (Table 2).

Other LAB that produce EPS include L. delbrueckii MW725385.1, L. delbrueckii ssp. bulgaricus B3, Pediococcus pentosaceus E8, P. pentosaceus M41, L. rhamnosus LB1lac10, L. rhamnosus MW725389.1, Lactobacillus casei NA-2, L. casei K7/3, Leuconostoc mesenteroides LM187, Leuconostoc lactis KC117496, L. helveticus MB2-1, Streptococcus thermophilus CC30, Lactiplantibacillus pentosus B8, L. lactis subsp. lactis C15, L. garvieae C47, E. faecalis 84B, L. brevis NCCP 963, W. cibaria GA44, and Lactobacillus fermentum S1 (Table 2).

EPS-producing LAB come from various fermented products, including fermented cereal drinks, fermented camel milk, sauerkraut, pickles, cereal vinegar, yogurt, kefir grains, and others. Various media are used as a carbon source in the fermentation media for EPS production, including various concentrations of sucrose, glucose, and lactose. MRS-sucrose is the medium commonly used for EPS production, with a concentration range of 2%－5% (Table 2). As a carbon source, sucrose increases EPS production. The mechanism of sucrose utilization for EPS biosynthesis from Latilactobacillus sakei L3 is related to the induction of sucrose metabolism, which increases sucrose utilization to produce EPS. Meanwhile, genes associated with the uridine monophosphate, fatty acid, and folate synthesis pathways are significantly inhibited (Wang et al., 2024). As shown in Table 2, the fermentation conditions for EPS production vary, with fermentation temperature and fermentation times ranging from 30°C to 37°C and from 12 to 96 h, respectively. The most common fermentation conditions were maintained at 37°C for 48 h. L. plantarum M101 produced crude EPS under fermentation conditions of 37°C for 96 h (Kusmiati et al., 2025).

HoPS are only produced by L. plantarum OF101, L. brevis NCCP 963, and L. lactis KC117496. HePS have been extensively studied for their hypoglycemic and antioxidant functions. The yield of EPS produced by LAB varied from 0.02 to 8.24 g/L. L. rhamnosus LB1lac10 produces the highest yield of HePS (8.24 g/L). Studies have shown that the diversity of LAB species and strains, LAB sources, carbon sources, and fermentation conditions can affect EPS production (Jiang et al., 2020; Zhang et al., 2021c; Fuso et al., 2023; Georgieva et al., 2023; Zanzan et al., 2023; Zhang, 2024).

EPS constituents

According to studies related to the hypoglycemic function of EPS from LAB (Table 3), all EPS producers (10 LAB isolates) produce HePS. With regard to antioxidant function (Table 4), 24 out of 27 EPS producers (88.89%) are HePS producers. Meanwhile, the rest are HoPS producers. Most EPS produces are HePS, typically comprising 3－8 units of D-glucose, D-galactose, and L-rhamnose (Hussein et al., 2024).

Table 3.

Hypoglycemic activity of HePS produced by LAB

No.	EPS producer	MW (kDa)	Constituent	Composition	EPS concentration (mg/mL)	Enzyme concentration (mg/mL)	AAI (%)	AGI (%)	Reference
1	Lacticaseibacillus rhamnosus MW725389.1	1,272.19	Ribose, mannose, xylose, galacturonic acid, arabinose	7.1:1.6:4.8:1.0:9.0 (molar ratio)	0.5	NR	85.05	78.78	Tarique et al. (2023)
2	Lactococcus garvieae C47	7,300	Glucose, arabinose, xylose	6.8:1.0:0.4 (molar ratio)	1) 0.1 2) 0.2	NR	1) 91.00 2) 90.10	1) 88.80 2) 87.90	Ayyash et al. (2020a)
3	Enterococcus faecalis 84B	604.8	Arabinose, glucose	1.0:2.0 (molar ratio)	1) 0.1 2) 0.2	NR	1) 89.60 2) 87.90	1) 90.00 2) 90.50	Ali et al. (2023)
4	L. rhamnosus LB1lac10	88.65	Mannose, glucuronic acid, glucose, xylose, galactose, arabinose	NR	NR	1) 0.01 2) 0.10 3) 0.15 4) 0.20	−	1) 95.90 2) 37.51 3) 25.97 4) 15.33	Wang et al. (2022)
5	Lactobacillus delbrueckii MW725385.1	3,762.43	Glucose, ribose, mannose, xylose	1.0:16.4:4.6:6.6 (molar ratio)	0.25	NR	79.84	90.98	Tarique et al. (2023)
6	Lactobacillus plantarum BR2	2,380	Glucose, mannose	NR	1) 0.1 2) 0.8 3) 0.3	NR	1) 10.00 2) 21.00 3) −	1) − 2) − 3) 67.00	Sasikumar et al. (2017)
7	L. plantarum H31	10.75	Mannose, glucose	9.85:0.77 (molar ratio)	100	1	89.10 (crude EPS) 69.23 (pure fraction)	−	Huang et al. (2020)
8	L. plantarum HY	9,549	Mannose, galactose, glucuronic acid, glucose	72.99%:17.27%: 6.99%: 2.75%	0.8	NR	26.06	−	Liu et al. (2019a)
9	Lactococcus lactis subsp. lactis C15	880	Arabinose, xylose, mannose, glucose	2.0:2.7:1.0:21.3 (molar ratio)	1) 0.1 2) 0.2	NR	1) 88.00 2) 89.30	1) 87.20 2) 85.00	Bamigbade et al. (2023)
10	Pediococcus pentosaceus M41	682.7	Arabinose, mannose, glucose, galactose	1.2:1.8:15.1:1.0 (molar ratio)	1) 0.1 2) 0.2	NR	1) 86.80 2) 90.00	1) 90.80 2) 90.40	Ayyash et al. (2020b)

HePS, heteropolysaccharides; LAB, lactic acid bacteria EPS, exopolysaccharides; MW, molecular weight; NR, not reported; AAI, α-amylase inhibitor; AGI, α-glucosidase inhibitor.

Table 4.

Antioxidant activity of EPS produced by LAB

No.	EPS producer	MW (kDa)	Constituent	Composition	Method of antioxidant	Concentration of EPS (mg/mL)	Scavenging activity of EPS (%)	Scavenging activity of ascorbic acid (%)	IC50 of EPS (mg/mL)	IC50 of ascorbic acid (mg/mL)	Reference
HePS
1	Lactiplantibacillus plantarum RO30	49.6	Glucuronic acid, mannose, glucose, arabinose	2.2:0.1:0.5:0.1 (molar ratio)	DPPH	5	43.60	77.86	NR	NR	Elmansy et al. (2022)
2	Lactobacillus casei K7/3	5.6	Dextrose, mannose, galactose	2.7:1.5:1 (molar ratio)	DPPH	1) 2 2) 3 3) 4	1) 12.00 2) 12.00 3) 26.00	NR	NR	NR	Elova et al. (2020)
3	Lactobacillus plantarum GD2	2.4	Mannose, glucose, arabinose, N-acetyl glucosamine	71.03%:25.97%: 2.73%:0.27%	1) DPPH 2) HRS 3) SAS	1) 1.25 2) 1.25 3) 1.25	1) 58.00 2) 48.00 3) 36.00	1) 95 (0.5 mg/mL) 2) 60 (0.5 mg/mL) 3) 98.00	NR	NR	Sirin and Aslim (2020)
4	L. plantarum YO175	1,200	Glucose, galactose	NR	1) DPPH 2) HRS 3) SAS	1) 4 2) 4 3) 4	1) 56.90 2) 66.00 3) 89.40	1) 82.10 2) 83.10 3) 83.10	NR	NR	Adesulu-Dahunsi et al. (2018a)
5	Lactococcus garvieae C47	7,500	Glucose, arabinose, xylose	6.8:1.0:0.4 (molar ratio)	1) DPPH 2) DPPH 3) ABTS 4) ABTS	1) 5 2) 10 3) 5 4) 10	1) 51.92 2) 67.52 3) 18.49 4) 61.06	NR	NR	NR	Ayyash et al. (2020a)
6	Enterococcus faecalis 84B	604.8	Arabinose, glucose	1:2 (molar ratio)	1) DPPH 2) DPPH 3) ABTS 4) ABTS	1) 5 2) 10 3) 5 4) 10	1) 81.10 2) 93.20 3) 35.20 4) 41.70	NR	NR	NR	Ali et al. (2023)
7	Lacticaseibacillus rhamnosus MW725389.1	1,272.19	Ribose, mannose, xylose, galacturonic acid, arabinose	7.1:1.6:4.8: 1.0:9.0 (molar ratio)	1) DPPH 2) HRS 3) SAS 4) ABTS	1) 250 2) 0.5 3) 0.25 4) 0.25	1) 37.50 2) 84.80 3) 54.70 4) 56.60	NR	NR	NR	Tarique et al. (2023)
8	Lactiplantibacillus pentosus B8	A) 11.2 (LPB8-0) B) 178 (LPB8-1)	A) Mannose, glucose B) Mannose, glucose, galactose Backbone: (1→2)-linked α-D-Manρ and (1→6)-linked α-D-Manρ	NR	A 1) DPPH 2) HRS 3) ABTS B 1) DPPH 2) HRS 3) ABTS	A 1) 10 2) 10 3) 10 B 1) 10 2) 10 3) 10	A 1) 50.62 2) 47.91 3) 47.17 B 1) 62.82 2) 72.52 3) 58.36	A 1) 88.86 2) 98.98 3) 97.96 B 1) 88.86 2) 98.98 3) 97.96	A 1) 6.82 2) 5.17 3) NR B 1) 4.75 2) 5.17 3) 6.18	A 1) 1.09 2) 1.06 3) 1.05 B 1) 1.09 2) 1.06 3) 1.05	Jiang et al. (2022b)
9	L. casei NA-2	538.5	Glucose, mannose, galactose, rhamnose	NR	1) DPPH 2) HRS 3) SAS	1) 10 2) 1.2 3) 0.1	1) 80 2) 42 3) 76	1) 88.84 2) 81.28 3) 64.78	1) 7.09 2) NR 3) 0.03	1) 1.08 2) 0.40 3) 0.07	Xu et al. (2022)
10	Lactobacillus delbrueckii MW725385.1	3,762.43	Glucose, ribose, mannose, xylose	1.0:16.4:4.6:6.6 (molar ratio)	1) DPPH 2) HRS 3) SAS 4) ABTS	1) 250 2) 0.25 3) 0.25 4) 0.25	1) 34.00 2) 88.80 3) 53.90 4) 47.30	NR	NR	NR	Tarique et al. (2023)
11	L. delbrueckii ssp. bulgaricus B3	12	Mannose, glucose, sucrose+maltose, fructose, acetyl glucosamine	88.25%:9.54%: 1.10%:1.04%: 0.07%	1) DPPH 2) HRS 3) SAS	1) 1.25 2) 1.50 3) 1.25	1) 58.00 2) 54.00 3) 48.00	1) 95.00 (0.5 mg/mL) 2) 60.00 (0.5 mg/mL) 3) 98.00	NR	NR	Sirin and Aslim (2020)
12	Lactobacillus fermentum S1	A) 4,450 B) 2,820	Glucose, galactose, mannose, arabinose	NR	A 1) DPPH 2) HRS 3) ABTS B 1) DPPH 2) HRS 3) ABTS	A 1) 4 2) 4 3) 4 B 1) 4 2) 4 3) 4	A 1) 15.55 2) 15.18 3) 57.13 B 1) 37.92 2) 47.03 3) 97.54	A 1) 94.47 2) 99.92 3) 100 B 1) 94.47 2) 99.92 3) 100	A 1) NR 2) NR 3) 3.36 B 1) NR 2) NR 3) 1.23	A 1) NR 2) NR 3) NR B 1) NR 2) NR 3) NR	Wang et al. (2020)
13	Lactobacillus helveticus MB2-1	200	Galactose, glucose, mannose	1.00:1.69:3.54 (molar ratio)	1) DPPH 2) HRS 3) SAS	1) 4 2) 4 3) 4	1) 47.44 2) 80.24 3) 71.82	1) 88.34 2) 100 3) 56.35	1) 6.83 2) 0.52 3) 0.63	1) 0.08 2) 0.09 3) 1.44	Li et al. (2014b)
14	L. plantarum BR2	2,380	Glucose, mannose	NR	DPPH	2	29.80	NR	NR	NR	Sasikumar et al. (2017)
15	L. plantarum EB-2	31.6	Mannose, glucose, galactose, rhamnose	21.7:12.4:2:1 (molar ratio)	DPPH	1) 2 2) 3 3) 4	1) 14.60 2) 24.00 3) 42.00	1) 35.00 2) 37.00 3) 39.00	NR	NR	Elova et al. (2019)
16	L. plantarum HY	9,549	Mannose, galactose, glucuronic acid, glucose	72.99%:17.27%: 6.99%:2.75%	DPPH	10	92.27	98.36	1.41	0.16	Liu et al. (2019a)
17	L. plantarum NS1905E	265.8	Glucose, arabinose, rhamnose, mannose, galactose	58.83:17.4:6.31: 5.86:2.74 (molar ratio)	DPPH	1) 5 2) 10	1) 90.94 2) 96.54	1) 97.02 2) 97.02	NR	NR	Lei et al. (2023)
18	L. plantarum YW11	110	Glucose, galactose	2.71:1 (molar ratio)	1) DPPH 2) HRS 3) SAS	1) 3 2) 3 3) 3	1) 35.11 2) 75.10 3) 62.71	1) 80.07 2) 84.47 3) 80.03	1) NR 2) 1.22 3) 1.54	1) 0.74 2) 0.47 3) 0.71	Zhang et al. (2017)
19	L. plantarum YW32	103	Mannose, fructose, galactose, glucose	NR	1) DPPH 2) HRS 3) SAS	1) 5 2) 5 3) 5	1) 30.00 2) 77.50 3) 66.50	1) 97.06 2) 95.71 3) 95.67	1) NR 2) 2.51 3) 2.75	1) 0.12 2) 0.15 3) 0.57	Wang et al. (2015)
20	Lactococcus lactis subsp. lactis C15	880	Arabinose, xylose, mannose, glucose	2.0:2.7:1.0:21.3 (molar ratio)	1) DPPH 2) DPPH 3) ABTS 4) ABTS	1) 5 2) 10 3) 5 4) 10	1) 41.80 2) 50.30 3) 22.50 4) 46.40	NR	NR	NR	Bamigbade et al. (2023)
21	Pediococcus pentosaceus M41	682.7	Arabinose, mannose, glucose, galactose	1.2:1.8:15.1:1.0 (molar ratio)	1) DPPH 2) DPPH 3) ABTS 4) ABTS	1) 5 2) 10 3) 5 4) 10	1) 69.64 2) 76.90 3) 22.28 4) 48.97	NR	NR	NR	Ayyash et al. (2020b)
22	Leuconostoc mesenteroides LM187	775.7	Glucose (mainly), galactose, rhamnose, mannose, ribose, arabinose, galacturonic acid	NR	1) DPPH 2) HRS 3) SAS	1) 5 2) 7 3) 3	1) 50.20 2) 71.00 3) 33.10	1) 94.90 2) 81.00 3) 76.10	1) 4.99 2) 3.50 3) NR	1) NR 2) NR 3) 2.00	Zhang et al. (2021a)
23	P. pentosaceus E8	50.2	Mannose, glucose, galactose Major backbone: →2)-α-D-Manp-(1→2,6)-a-D-Glcp-(1→6)-α-D-Manp-(1→	NR	1) DPPH 2) HRS 3) ABTS	1) 10 2) 10 3) 8	1) 50.62 2) 58.91 3) 52.17	1) 91.60 2) 100 3) 100	1) 9.26 2) 8.53 3) 9.61	1) 1.23 2) 0.98 3) 1.12	Jiang et al. (2022a)
24	Weissella cibaria GA4	280	Glucose, rhamnose	NR	1) DPPH 2) HRS 3) SAS	1) 4 2) 4 3) 4	1) 48.90 2) 88.00 3) 77.1	1) 82.10 2) 83.21 3) 83.10	1) NR 2) 0.88 3) 1.22	1) 1.19 2) 1.02 3) 1.01	Adesulu-Dahunsi et al. (2018b)
HoPS
1	L. plantarum OF101	440	Glucose	NR	1) DPPH 2) HRS 3) SAS	1) 4 2) 4 3) 4	1) 51.30 2) 52.30 3) 45.30	1) 82.10 2) 83.10 3) 83.10	NR	NR	Adesulu-Dahunsi et al. (2018a)
2	Leuconostoc lactis KC117496	4,428	Glucose	NR	1) DPPH 2) HRS	1) 0.5 2) 0.5	1) 74.00 2) 97.80	1) 75.61 2) 98.20	NR	NR	Saravanan et al. (2019)
3	Levilactobacillus brevis NCCP 963	54.8	Glucose	NR	1) DPPH 2) HRS 3) SAS 4) ABTS	1) 10 2) 10 3) 10 4) 0.8	1) 76.10 2) 73.74 3) 68.00 4) 68.37	1) 88.45 2) 86.78 3) 82.45 4) 86.64	1) 2.43 2) 5.62 3) 8.30 4) 0.31	1) 1.56 2) 0.74 3) 0.70 4) 0.07	Afreen et al. (2023)

EPS, exopolysaccharides; LAB, lactic acid bacteria MW, molecular weight; HePS, heteropolysaccharides; HoPS, homopolysaccharides; NR, not reported; DPPH, 2,2-diphenyl-1-picrylhydrazyl scavenging activity; HRS, hydroxyl radical scavenging activity; SAS, superoxide anion scavenging activity; ABTS, 2,2'-azino-bis(3-ethyl-benzene-thiazoline-6-sulphonic acid) scavenging activity.

HePS produced by LAB consist of several monosaccharides and their derivatives (Table 3 and 4). The constituents of EPS from LAB include glucose, galactose, fructose, sucrose, maltose, rhamnose, mannose, ribose, arabinose, xylose, dextrose, galacturonic acid, glucuronic acid, and N-acetyl glucosamine. The EPS components vary with different LAB strains. Several factors influence the variation of EPS components, including genetic diversity (Wei et al., 2019; Xiao et al., 2021; Zhang et al., 2023), environmental conditions, and carbon sources used in the fermentation media (Bomfim et al., 2020; Vosough et al., 2022; Fuso et al., 2023). The diverse structure of EPS produced by LAB is related to the variety of their gene clusters, particularly GTF genes, which determine the monosaccharide composition (Zhang et al., 2023).

Fig. 4 shows the constituents of EPS produced by LAB with a hypoglycemic activity analysis. In the AAI assay, the most abundant components of EPS include glucose (29.41%), mannose (22.53%), and arabinose (17.65%). In the AGI assay, glucose, mannose, and arabinose are still the most abundant components. However, their proportions differ: glucose (22.95%), arabinose (21.31%), and mannose (18.03%).

Fig. 4.

Constituents of EPS produced by LAB with hypoglycemic activity test: (A) AAI and (B) AGI. EPS, exopolysaccharides; LAB, lactic acid bacteria; AAI, α-amylase inhibitor; AGI, α-glucosidase inhibitor; Glc, glucose; Ara, arabinose; Man, mannose; Xyl, xylose; Gal, galactose; GlcA, glucuronic acid; Rib, ribose; GalA, galacturonic acid.

When grouped based on monosaccharide constituent (Table 3), out of 10 EPS producers tested for hypoglycemic activity, there are nine groups/variations of monosaccharide constituents of EPS (all of which are HePS). The simplest monosaccharide components comprise two types of monosaccharides, including arabinose and glucose, and glucose and mannose. The other group consists of three to six types of monosaccharides/constituent components. The EPS produced by L. plantarum BR2 and H31 have the same monosaccharide components: glucose and mannose. Meanwhile, uronic acid is one of the components of EPS produced by L. rhamnosus MW725389.1 (galacturonic acid) and L. rhamnosus LB1lac10 (glucuronic acid). Glucose and mannose are monosaccharides found in almost all EPS produced.

The molar ratio or percentage composition of EPS components varies among strains (Table 3). Some EPS contain the highest molar ratio of glucose/mannose/arabinose/ribose. Generally, among the EPS components, glucose has the highest molar ratio. According to the available data, EPS with the highest glucose molar ratio show activity (AAI and AGI) above 85%. These EPS demonstrate enhanced hypoglycemic activity.

Fig. 5 shows the constituents of EPS produced by LAB. DPPH, HRS, SAS, and ABTS assays were used to evaluate antioxidant activity. In the DPPH, HRS, and SAS assays, glucose, mannose, and galactose are the three most common constituents of EPS, with percentages of 26.56%, 21.88%, and 16.41% for DPPH assay; 30%, 21.67%, and 16.67% for HRS assay; and 26.83%, 17.07%, and 12.20% for SAS assay, respectively. In the ABTS assay, glucose (28.25%), mannose (21.15%), and arabinose (21.15%) are the three main components of EPS.

Fig. 5.

Constituents of EPS produced by LAB with antioxidant activity test: (A) DPPH, (B) HRS, (C) SAS, and (D) ABTS. EPS, exopolysaccharides; LAB, lactic acid bacteria; DPPH, 2,2-diphenyl-1-picrylhydrazyl scavenging activity; HRS, hydroxyl radical scavenging activity; SAS, superoxide anion scavenging activity; ABTS, 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) scavenging activity; Glc, glucose; Man, mannose; Gal, galactose; Ara, arabinose; Rha, rhamnose; Xyl, xylose; Rib, ribose; Dex, dextrose; Fru, fructose; GalA, galacturonic acid; GlcA, glucuronic acid; Suc, sucrose; Mal, maltose; GlcNAc, N-acetyl glucosamine.

Among the 27 EPS producers exhibiting antioxidant activity, EPS comprise 21 distinct groups of monosaccharides when categorized by their constituent monosaccharides (Table 4). There are 20 groups classified as HePS and one group classified as HoPS (Table 4). The most basic monosaccharide is glucose. Combinations of two types of monosaccharides include glucose and galactose, arabinose and glucose, glucose and mannose, and glucose and rhamnose. The other group has three to seven varieties of monosaccharides or constituent components.

The EPS produced by L. plantarum OF101, L. lactis KC117496, and L. brevis NCCP 963 contain glucose as the monosaccharide component. Meanwhile, the EPS produced by L. pentosus B8 (LPB8-0) and L. plantarum BR2 have the same monosaccharide components: glucose and mannose. Those produced by L. pentosus B8 (LPB8-1), P. pentosaceus E8, and L. helveticus MB2-1 have glucose, mannose, and galactose as the monosaccharide components. For L. casei NA-2 and L. plantarum EB-2, the EPS have the same monosaccharide components: glucose, mannose, galactose, and rhamnose. Meanwhile, those produced by L. fermentum S1 and P. pentosaceus M41 contain glucose, mannose, galactose, and arabinose. Glucose and mannose are monosaccharides found in almost all EPS produced.

EPS derived from several LAB strains may include identical components, including glucose and galactose, which are the constituents of EPS synthesized by L. plantarum YO175 and L. plantarum YW11. Uronic acid is present in the EPS produced by L. rhamnosus MW725389.1 (galacturonic acid) and L. plantarum HY (glucuronic acid). In the EPS synthesized by L. plantarum GD2 and L. delbrueckii subsp. bulgaricus B3, N-acetyl glucosamine is present.

Table 4 shows that the molar ratio or percentage composition of EPS components varies among strains. Some EPS contain the highest molar ratio of glucose/mannose/dextrose/glucuronic acid/arabinose/ribose. Generally, among the EPS components, glucose has the highest molar ratio. According to the available data, EPS with the highest glucose molar ratio show antioxidant activity above 80%. These EPS demonstrate enhanced antioxidant activity.

Glycosidic linkages (including α or β and 1→2, 3, 4, and 6) influence the functionality of EPS beyond their monosaccharide constituents (Zhang et al., 2023). According to Table 4, the glycosidic bond data for EPS constituents are exclusively found in the EPS generated by L. pentosus B8 (Jiang et al., 2022b) and P. pentosaceus E8 (Jiang et al., 2022a). EPS from L. pentosus B8 (LPB8-1) contain a backbone (1→2)-linked α-D-Manp and (1→6)-linked α-D-Manp, whereas those from P. pentosaceus E8 contain a major backbone →2)-α-D-Manp-(1→2,6)-a-D-Glcp-(1→6)-α-D-Manp-(1→. Both HePS produced have the same components: mannose, glucose, and galactose. The majority of EPS derived from LAB comprise many glycosidic bonds, including (1→3), (1→6), (1→4), and (1→2), complicating the analysis of individual glycosidic bond functions. Therefore, further studies are needed to elucidate the precise mechanisms of these glycosidic linkages (Zhang et al., 2023).

Hypoglycemic activity of EPS

The hypoglycemic activity of EPS produced by LAB was analyzed in vitro using AAI and AGI assays, with acarbose as the positive control. The combination of AAI assay with AGI assay is the most common approach for evaluating the hypoglycemic activity of EPS produced by LAB (Fig. 2B). This approach is likely aimed at understanding, viewing, or comparing the results and studying the mechanism of EPS inhibition on both enzymes.

The EPS-producing LAB used in the hypoglycemic activity assay include L. delbrueckii MW725385.1, L. rhamnosus MW725389.1, L. plantarum H31, L. garvieae C47, E. faecalis 84B, P. pentosaceus M41, L. plantarum HY, L. plantarum BR2, L. lactis subsp. lactis C15, and L. rhamnosus LB1lac10 (Table 3). The results of AAI and AGI assays showed that the most used EPS concentrations are 0.1 and 0.2 mg/mL. The enzyme concentration used for AAI assay was 1 mg/mL, whereas that used for AGI assay ranged from 0.1 to 0.3 mg/mL. The MW of the produced EPS ranged from 10.75 to 9,549 kDa for AAI assay and 88.65 to 3,762 kDa for AGI assay. The percentage of AAI produced ranged from 10% to 90.1%, whereas that for AGI ranged from 15.33% to 95.9% (Table 3).

The structure of EPS, including the monosaccharide composition, glycosidic bonds, and MW, affects their bioactivity (Zhang et al., 2023). Several factors can also affect the hypoglycemic effects of natural polysaccharides, including MW, monosaccharide composition, backbone structure (glycosidic bonds), advanced structure, structural modifications, and uronic acid content (Ji et al., 2023). According to AAI and AGI assays, EPS with a lower MW (approximately below 2,000 kDa) generally inhibited α-amylase and α-glucosidase by 87.9%－90% and 85%－90.5%, respectively, at an EPS concentration of 0.2 mg/mL (Fig. 6A). These results indicated that EPS with a lower MW could produce better hypoglycemic activity. According to Ji et al. (2023), there is still controversy regarding the relationship between the MW and hypoglycemic activity. Thus, further studies with adequate data are needed to verify the actual relationship between the MW and hypoglycemic activity of EPS.

Fig. 6.

Relationship between molecular weight and the percentage of (A) α-amylase and α-glucosidase inhibition from EPS at a concentration of 0.2 mg/mL (AAI, blue; AGI, orange) and (B) scavenging activity of EPS at a concentration of 10 mg/mL (DPPH, blue; HRS, green; SAS, orange; and ABTS, purple). EPS, exopolysaccharides; AAI, α-amylase inhibitor; AGI, α-glucosidase inhibitor; DPPH, 2,2-diphenyl-1-picrylhydrazyl scavenging activity; HRS, hydroxyl radical scavenging activity; SAS, superoxide anion scavenging activity; ABTS, 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) scavenging activity.

With regard to the monosaccharide components, glucose and mannose were most commonly found in all EPS produced. EPS with the highest glucose molar ratio show high hypoglycemic activity (above 85%) (Table 3). Polysaccharides with a more complex monosaccharide composition generally have better hypoglycemic activity (Ji et al., 2023).

EPS H31-2 produced by L. plantarum H31 with mannose as the dominant component, can inhibit pancreatic α-amylase by increasing glucose absorption by insulin-resistant HepG2 cells, thereby enhancing the expression of GLUT-4, Akt-2, and AMPK, which play roles in glycometabolism. This finding indicates the potential to prevent DM (Huang et al., 2020). The mechanism of EPS produced by L. plantarum in lowering blood glucose concentration is through the inhibition of the activity of enzymes associated with T2DM (Liang et al., 2024).

L. rhamnosus MW725389.1 contains galacturonic acid as one of its EPS components, exhibiting α-amylase inhibition of 85.05% (Tarique et al., 2023). Meanwhile, L. rhamnosus LB1lac10 contains glucuronic acid as one of its EPS components. It exhibits α-glucosidase inhibition of 95.9% at an enzyme concentration of 0.01 mg/mL (Wang et al., 2022). Polysaccharides with higher uronic acid content tend to form hydrogen bonds with water, which create relatively more dispersed conditions, thereby potentially enhancing their hypoglycemic activity (Ji et al., 2023).

With regard to the influence of backbone structure/glycosidic bonds, advanced structures (e.g., triple helix forms), and structural modifications (e.g., sulfation, acetylation, and hydroxymethylation) on the hypoglycemic effects of EPS, these cannot be explained in this study. Therefore, further investigations are needed. Some mechanisms behind the hypoglycemic activity of polysaccharides derived from natural sources include modulating gut microbiota; regulating signaling pathways, enzyme activity, and insulin; and reducing damage because of oxidative stress (Ji et al., 2023).

Antioxidant activity of EPS

According to the examined studies, DPPH (n=24), HRS (n=14), SAS (n=10), and ABTS (n=9) assays are the four most common methods for evaluating the antioxidant activity of EPS in vitro (Fig. 2C). The EPS concentration that was mostly used in DPPH and ABTS assays is 10 mg/mL, whereas that in HRS and SAS assays is 4 mg/mL (Table 4).

In DPPH assay, three EPS-producing LAB had the highest antioxidant activity, including L. plantarum NS1905E (96.54%), E. faecalis 84B (93.2%), and L. plantarum HY (92.27%) at an EPS concentration of 10 mg/mL. In HRS assay, L. lactis KC117496 (97.8%), L. delbrueckii MW725385.1 (88.8%), and W. cibaria GA44 (88%) had the highest antioxidant activity at EPS concentrations of 0.5, 0.25 mg/mL, and 4 mg/mL, respectively. In SAS assay, L. plantarum YO175 (89.4%), W. cibaria GA44 (77.1%) at an EPS concentration of 4 mg/mL, and L. casei NA-2 (76%) at an EPS concentration of 0.1 mg/mL had the highest antioxidant activity. In ABTS assay, L. fermentum S1 (97.54%), L. brevis NCCP 963 (68.37%), and L. garvieae C47 (61.06%) had the highest antioxidant activity at EPS concentrations of 4, 0.8, and 10 mg/mL, respectively (Table 4).

The MW of EPS produced by LAB ranges from 2.4 to 9,549 kDa for DPPH assay, 2.4 to 4,450 kDa for HRS assay, 2.4 to 3,762 kDa for SAS assay, and 11.2 to 7,500 kDa for ABTS assay (Table 4). EPS with a MW of about 2,000 kDa or less exhibits scavenging activity against DPPH, HRS, SAS, and ABTS at a concentration of 10 mg/mL (Fig. 6B). HePS produced from L. plantarum NS1905E had the highest scavenging activity against DPPH (96.54%), with a MW of 265.8 kDa. This HePS comprises glucose, arabinose, rhamnose, mannose, and galactose, with glucose having the highest molar ratio (Lei et al., 2023). These results indicated that EPS with lower MW can produce better antioxidant activity than those with higher MW.

At an EPS concentration of 4 mg/mL, HePS from W. cibaria GA44, which has a MW of 280 kDa, had the highest activity against HRS, with an 88% success rate (Adesulu-Dahunsi et al., 2018b). Meanwhile, HePS from L. plantarum YO175, which has a MW of 1,200 kDa, exhibited the highest scavenging activity against SAS (89.4%) (Adesulu-Dahunsi et al., 2018a). With a MW of 2,820 kDa, HePS from L. fermentum S1 had the highest ABTS scavenging activity (97.54%) (Wang et al., 2020). HePS with a reduced MW resulting from the depolymerization of EPS derived from L. plantarum LPC-1 exhibit enhanced antioxidant action (Yan et al., 2024).

With regard to the monosaccharide components, glucose and mannose are present in almost all EPS produced. EPS with the highest glucose molar ratio showed higher antioxidant activity, with scavenging activity above 80% (Table 4). The antioxidant activity of EPS is related to the monosaccharide composition, MW, degree of branching, glycosidic bonds, and functional groups (Andrew and Jayaraman, 2020; Salimi and Farrokh, 2023; Liang et al., 2024). EPS containing galactose, glucose, and rhamnose as the main components exhibit potent antioxidant activity (Wang et al., 2023). EPS produced from L. helveticus contain galactose, glucose, and mannose, and both crude and pure EPS show strong DPPH, HRS, SAS, and MC free radical scavenging activity (Li et al., 2014a). Meanwhile, EPS from L. plantarum strains PRK7 and PRK11 contain glucose, galactose, xylose, and mannose, exhibiting high DPPH free radical scavenging activities (89.77 and 93.11%) (Kowsalya et al., 2023).

The glucuronic acid content of EPS produced by L. plantarum HY shows a high DPPH radical scavenging activity of 92.27% (Table 4). Studies have shown that the presence of uronic acid in EPS can enhance their ability to capture free radicals as it can provide a negative charge that can activate the hydrogen atom of sugar residues through electric fields and induction (Yang et al., 2021).

Aside from the monosaccharide composition (including their composition ratio), other factors can influence the antioxidant activity of EPS, including the type of glycosidic bonds and branching patterns. However, the influence of glycosidic bonds still remains unclear, and further research is needed. Meanwhile, EPS with a high branching pattern exhibit high antioxidant activity. The changes in fermentation conditions (e.g., pH) can also impact the structure of EPS, which will affect their antioxidant activity (Wang et al., 2023). In addition, extraction and purification (Werning et al., 2022) and sulfonation methods (Liu et al., 2019b) can affect the resulting antioxidant activity of EPS.

The IC₅₀ value of EPS produced by L. brevis NCCP 963 was 1.56 times that of ascorbic acid in DPPH assay. Meanwhile, the IC₅₀ value of EPS produced by W. cibaria GA44 was 0.86 times that of ascorbic acid in HRS assay. In SAS assay, the IC₅₀ value of EPS produced by L. casei NA-2 was 0.44 times that of ascorbic acid (Fig. 7). Based on these findings, EPS has increasingly more potent antioxidant activity.

Fig. 7.

IC₅₀ values of EPS produced by LAB and ascorbic acid in (A) DPPH, (B) HRS, and (C) SAS assays. IC₅₀, half-maximal inhibitory concentration; EPS, exopolysaccharides; LAB, lactic acid bacteria; DPPH, 2,2-diphenyl-1-picrylhydrazyl scavenging activity; HRS, hydroxyl radical scavenging activity; SAS, superoxide anion scavenging activity.

The antioxidant activity of EPS is associated with the presence of hydroxyl and various functional groups, which contribute to the formation of more stable radicals. The presence of negatively charged groups induces acidic environmental conditions, thereby promoting EPS hydrolysis. This process leads to the generation of additional hemiacetal hydroxyl groups, which exhibit notable antioxidant activity (Andrew and Jayaraman, 2020; Werning et al., 2022). Monosaccharides possess an aldose or ketose structure or can interconvert into either form. Thus, they are classified as reducing sugars. The functional groups present in microbial EPS, including hydroxyl, carboxyl, sulfate, sulfhydryl, acetyl, carbonyl, thioether, and amide groups, can provide electron pairs, release protons, or promote metal binding, converting free radicals into more stable molecules (Fadlillah et al., 2021; Salimi and Farrokh, 2023).

The findings of the present study may be subject to several limitations, including the accuracy of keyword selection; the methods employed for article searches; and the quantity or incompleteness of data with regard to glycosidic bonds, molecular ratios, branching patterns, advanced structures, and structural modifications. These factors may influence the antioxidant and hypoglycemic activities of EPS produced by LAB. Therefore, additional studies are needed in the future. Through an in-depth examination of the factors that may affect the activity of EPS, subsequent research can be oriented toward developing customized EPS exhibiting the intended biological functions. However, future research should focus on in vivo studies for practical application, detailed analysis of higher-order structures, and establishing quantitative correlations to advance the field further.