Beta-glucosidase

Beta-Glucosidase: A Comprehensive Reference

1. Identity, Nomenclature, and Classification

The enzyme β-glucosidase (β-d-glucopyrranoside glucohydrolase) is formally classified as EC 3.2.1.21. Beta-glucosidase (BGL) is defined as an enzyme that catalyzes the hydrolysis of β-glucosidic linkages in various substrates, playing essential roles in biological processes across bacteria, fungi, plants, and animals. The systematic name under the IUBMB enzyme nomenclature is β-d-glucoside glucohydrolase, and it belongs to the broad class of glycoside hydrolases (GHs).

Glycoside hydrolases constitute the most prevalent enzyme class, with over 180 GH families currently listed in the Carbohydrate-Active enZymes (CAZy) database. Within this system, the GH1, GH5, and GH30 β-glucosidases fall in GH Clan A, which consists of proteins with (β/α)₈-barrel structures. In contrast, the active site of GH3 enzymes comprises two domains, while GH9 enzymes have (α/α)₆ barrel structures.

Family 1 (GH1) contains β-glucosidases from some archaea, bacteria, fungi, plants, and mammals, whereas Family 3 (GH3) comprises β-glucosidases of some bacterial, fungal, and plant origins. Family 3 contains β-glucosidases produced from fungi, bacteria and plants having a characteristic two-domain structure.

Anomer-retaining β-glucosidase (BGL, EC 3.2.1.21) is a major exo-type GH that acts on a β-d-glucopyranoside bond at the non-reducing end of oligomeric (and sometimes polymeric) substrates, releasing β-glucose.

Human Endogenous Forms

In humans, three native β-glucosidase enzymes have been identified: glucocerebrosidase, deficiency of which causes Gaucher's disease; lactase phlorizin hydrolase, deficiency of which causes lactose intolerance; and β-glucosidase, a cytosolic enzyme of broad specificity that is abundant in the kidney, liver, and small intestine of mammals and plays a crucial role in the transport and/or digestion of dietary sugars.

In humans, tissues within the liver, small intestine, spleen, and kidney contain a cytosolic β-glucosidase (CBG) that hydrolyses various β-d-glycosides. This human enzyme shows significant activity towards many xenobiotics commonly found in the human diet including glycosides of phytoestrogens, flavonoids, simple phenolics, and cyanogens, and human CBG hydrolyses a broad range of dietary glucosides, possibly playing a critical role in xenobiotic metabolism.

Liposomal β-glucosidase (glucocerebrosidase), found in human lysosomes, plays an important role in the degradation of glycosphingolipids, breaking down glucosylceramide into ceramide and glucose.

Common Preparations and Commercial Forms

Commercially, β-glucosidase is produced using Aspergillus species. Aspergillus isolates showed the highest β-glucosidase activity (in particular A. niger), followed by Trichoderma and Fusarium. The two fungal species Trichoderma reesei and Aspergillus niger are predominantly used by enzyme manufacturers to produce enzymes effective on lignocellulosic material. As a dietary supplement, beta-glucosidase is available as a purified enzyme powder or in capsules, and is frequently included in multi-enzyme digestive blends. Dosage in supplement contexts varies widely based on specific formulation and intended use, typically measured in activity units (e.g., BGU — beta-glucosidase units).

2. Natural Sources

Beta-glucosidases are ubiquitous and commonly found in bacteria, fungi, plants, and animals, which produce them intracellularly as well as extracellularly in various organisms.

Fungal Sources

Among microorganisms, filamentous fungi are the most important sources of β-glucosidases. Phanerochaete chrysosporium, Paecilomyces sp., Penicillium brasilianum, P. decumbens, A. oryzae, and A. niger are important producers of β-glucosidases. β-glucosidase production has also been reported by yeast (mostly Candida) and some bacteria. Even Clostridium (anaerobic bacteria) produces β-glucosidase along with other cellulolytic components.

Plant Sources

β-Glucosidase is naturally present in plant materials such as grapes and can be produced by some microorganisms. In plants, the enzyme catalyzes β-glucan synthesis during cell wall development, fruit ripening, pigment metabolism, and defence mechanisms. β-Glucosidases act on polysaccharide degradation for energy harvesting in bacteria and fungi, and vital developmental processes in plants, such as growth, pathogen defence, and hormone hydrolysis.

Bacterial Sources

The bioavailability of polyphenol glycosides requires conversion of glucosides into the bioactive aglycones via the action of intestinal β-glucosidases from small-intestine bacteria (Lactobacillus, Bifidobacterium). In addition to endogenous β-glucosidase activity present in raw material, the function of β-glucosidases in fermenting microorganisms has been progressively clarified and increasingly appreciated. Several lactic acid bacteria, including Lactiplantibacillus plantarum, showed high β-glucosidase activity, which can be considered as a valid biotechnological resource in different food sectors.

3. Traditional and Historical Use

Beta-glucosidase as a defined, isolated enzyme is a product of modern biochemistry. However, the enzyme's activity has been intrinsic to traditional fermented foods and herbal preparations across many cultures, where it acts invisibly as part of the biochemical transformation of plant glycosides during processing and fermentation.

East Asian Fermented Soy Foods

Natto is a traditional food fermented by Bacillus subtilis natto with soybean as raw material and widely consumed in Japan, Asia, and other countries as a healthy food with a long history. Natto is a traditional food fermented by Bacillus subtilis natto and contains a variety of active substances, especially flavonoids. Flavonoids in soybean usually exist in the form of inactive glycosides, which can only play biological activities when being decomposed into free isoflavone aglycone by β-glucosidase. Similar β-glucosidase-driven transformations occur during the preparation of traditional fermented soy products including miso, tempeh, and doenjang.

Traditional Cassava Processing

Populations in sub-Saharan Africa, South America, and parts of Asia have relied for centuries on cassava (Manihot esculenta) as a dietary staple, developing elaborate processing techniques that depend critically on β-glucosidase activity to manage the plant's cyanogenic glycoside content. Traditional food preparation methods are effective at reducing or eliminating the cyanogenic risk. The goal of processing is twofold: allowing the activating enzymes to break down the glycosides and facilitating the removal of the volatile hydrogen cyanide gas. This process has been developed over centuries in cultures that rely on cyanogenic plants for sustenance. Methods like grating or pounding the raw material intentionally damage the tissue and mix the glycosides with the β-glucosidase enzyme. Soaking the grated plant material in water for prolonged periods, often several days, allows the water-soluble glycosides and the liberated hydrogen cyanide to leach out. Boiling and cooking are effective, as the heat facilitates the spontaneous decomposition of the unstable cyanohydrins into HCN, which readily volatilizes into the air.

Traditional Chinese Medicine and Bitter Almond Preparations

Common cyanogenic glycosides include amygdalin found in bitter almonds and peach kernels (both used in Chinese medicine), and prunasin in wild cherry bark (Prunus serotina). In these preparations, the endogenous plant β-glucosidase catalyzes hydrolysis of amygdalin; this activity was not understood mechanistically in pre-modern eras but was empirically modulated through processing steps such as roasting or boiling that inactivate the enzyme.

Wine and Beer Production

Yeast and lactic acid bacteria have been suggested as the main source of β-glucosidase in winemaking. Modern winemaking techniques often use exogenous enzymes to compensate for insufficient enzyme activity in grapes, mostly by the addition of specific strains of Saccharomyces or non-Saccharomyces yeasts with known β-glucosidase activity. Traditional winemaking and brewing, practised for millennia, thus incorporated β-glucosidase activity through native microflora. The phenolic compounds found in wort and beer, especially phenolic acids and flavonoids, are derived mainly from barley malt and hops and are often present as glycosides. The β-glucosidase activity promotes the bioavailability of these compounds by releasing the aglycones.

4. Key Biochemical Constituents and Mechanisms of Action

Core Catalytic Chemistry

β-glucosidases hydrolyse glycosidic bonds to release non-reducing terminal glucosyl residues from glycosides and oligosaccharides via catalytic mechanisms. Two principal stereochemical outcomes of catalysis are recognized:

• Retaining mechanism: Retaining β-glycosidases generally employ the Koshland double-displacement mechanism with a catalytic nucleophile and acid/base for catalysis. The first step is a nucleophilic attack by the catalytic amino acid to the anomeric carbon of the glycosidic substrate. Catalysis involves two carboxylic acid/carboxylate side chains with one serving as an acid/base and the other as a nucleophile. The first step of the reaction is the formation of a glycosyl-enzyme intermediate facilitated by protonation of the glycosidic bond oxygen by the catalytic acid to promote departure of the aglycone leaving group. In the second step of the reaction, the catalytic acid/base now serves as a base to deprotonate water or another incoming nucleophile to allow it to displace the catalytic nucleophile from the glycosyl-enzyme intermediate, thereby releasing the sugar from the enzyme.
• Inverting mechanism: The inverting mechanism is seen in family GH9 glycoside hydrolases, including β-glucosidases. A single displacement of the aglycone by water leads to an anomeric carbon with inverted chirality.

These enzymes employ two standard catalytic mechanisms involving two carboxylic acid (Asp or Glu) residues as catalytic groups: either retaining or inverting the α/β-anomeric configuration of sugar after hydrolysis. The anomer-retaining mechanism is more widespread than the inverting mechanism, utilized by over half of the GH families.

Substrate Range

β-glucosidase substrates include the plant cyanogenic glucosides linamarin, dhurrin, prunasin, and its precursor amygdalin. Other defense-related glycosides include DIMBOAGlc and the flavonoids apigenin 7-O-β-d-glucoside, the isoflavonoids daidzin and genistin, and phloridzin.

β-glucosidase also exhibits substantial glycosyl hydrolase activities with natural glycosyl substrates, such as sophorose, cellobiose, cellotriose, cellotetraose, and cellopentaose.

Cellulase Complex Role

The cellulase enzymatic system consists of three individual enzymes — endoglucanase, exoglucanase, and β-glucosidase — which act synergistically to degrade cellulose molecules into glucose. Beta-glucosidase not only hydrolyzes cellobiose and short-chain cellooligosaccharides to glucose, but also removes the inhibitory effect of cellobiose on the β-1,4-endoglucanase and exoglucanase.

Aglycone Liberation and Bioactivation

With the aid of β-glucosidase enzymes, cyanogenic glycosides and plant glycosides are transformed into sugar moiety and aglycones. These aglycone compounds are employed as aromatic compounds in the food processing and brewing industries; they are also used as medications and dietary supplements based on their pharmacological qualities.

Enzymes including lactase phlorizin hydrolase (LPH) at the enterocyte membrane, and β-glucosidase (CBG, cytosolic, for polar glycosides) hydrolyze glycosylated flavonoids, and then aglycones enter epithelial cells by passive diffusion.

5. Scientific Evidence by Area of Use

5.1 Polyphenol and Isoflavone Bioavailability

The most thoroughly studied health-relevant function of β-glucosidase is its role in converting glycosidically bound polyphenols — including isoflavones, flavonols, and anthocyanins — into their bioavailable aglycone forms.

Almost all isoflavones (daidzein, genistein, and formononetin) exist as glucosides and therefore are not absorbed across enterocytes due to their high polarity and molecular weight. These flavonoids are present almost exclusively in plants from the Fabaceae family (soy, lentils, beans, and chickpeas). Their bioavailability requires therefore conversion of glucosides into the bioactive aglycones via the action of intestinal β-glucosidases from small intestine bacteria (Lactobacillus, Bifidobacterium). These aglycones are then taken up to the peripheral circulation.

In vitro fermentation studies: One study determined beta-glucosidase activity of commercial probiotic organisms for hydrolysis of isoflavone to aglycones in fermenting soymilk. Soymilk made with soy protein isolate was fermented with Lactobacillus acidophilus LAFTI L10, Bifidobacterium lactis LAFTI B94, and Lactobacillus casei LAFTI L26 at 37°C for 48 hours. All the bacteria produced beta-glucosidase, which hydrolyzed isoflavone β-glycosides to isoflavone aglycones. The decrease in the concentration of β-glycosides and the increase in the concentration of aglycones were significant (P < 0.05) in the fermented soymilk. Increased isoflavone aglycone content in fermented soymilk is likely to improve the biological functionality of soymilk.

A further study evaluated β-glucosidase and β-galactosidase activities of probiotic organisms including Lactobacillus acidophilus ATCC 4461, Lactobacillus casei 2607, and Bifidobacterium animalis ssp. lactis Bb12 in soymilk and correlated them with the increase in concentration of isoflavone aglycones during fermentation. In all micro-organisms, beta-glucosidase activity was found greater than that of beta-galactosidase. There was an increase in the aglycone concentration with incubation time because of the apparent hydrolytic action on isoflavone glycosides. Aglycone concentration increased by 5.37-, 5.52- and 6.10-fold, respectively, after 15 hours of fermentation at 37°C. Beta-glucosidase played a greater role in isoflavone glycoside hydrolysis.

Human clinical data (limited): Richelle et al. investigated whether the bioavailability of isoflavones could be enhanced by enzymatic hydrolysis with β-glucosidase of a non-fermented soy drink in postmenopausal women. The hydrolysis of isoflavone glucosides to aglycones before consumption did not alter the plasma and urinary pharmacokinetics of individual isoflavones (daidzein, genistein, and glycitein) or their microbial metabolites. This could indicate abundant endogenous β-glucosidase along the gastrointestinal tract, sufficient to hydrolyze isoflavone glucosides. In a previous study with healthy women, even a higher bioavailability was observed when genistein and daidzein were administered as β-glycosides than their corresponding aglycones.

Evidence strength: The biochemical and fermentation data are robust and consistent. Human pharmacokinetic data specifically examining exogenously administered β-glucosidase as a supplement are limited; available clinical evidence suggests that endogenous intestinal β-glucosidase capacity may already be sufficient under normal conditions, though individual variation (linked to gut microbiota composition) is significant.

5.2 Flavonoid Aglycone Release and Antioxidant Bioavailability

Flavonoids are the largest class of polyphenols, naturally distributed in plant foods as glycosides containing single or multiple sugar moieties. Flavonoid aglycones are generally more bioavailable than their respective glycosides. Several studies have shown that flavonoid aglycone content in plant-based foods can increase after fermentation due to the microbial β-glucosidase. Therefore, fermentation by lactic acid bacteria (LAB) possessing this specific enzymatic activity is an effective strategy to increase the bioavailability of natural antioxidants present in fermented plant-based products.

Several studies have demonstrated that the content of aglycones in soy products was increased after microbial fermentation by LAB, which may be due to the changes of β-glucosidase activity. Therefore, the use of these bacteria as starters, with the aforementioned enzymatic activity, in soymilk fermentation could contribute to increasing bioavailable isoflavones, thereby increasing the nutritional values and health benefits of fermented soy products.

Evidence strength: Evidence for this mechanism is primarily in vitro and ex vivo (fermentation studies). Well-designed, adequately powered human randomized controlled trials (RCTs) specifically testing exogenous β-glucosidase enzyme supplementation for antioxidant bioavailability outcomes are lacking as of 2024.

5.3 Gut Microbiota and Isoflavone Metabolism

One of the most active isoflavones, daidzein, is metabolized in two different ways depending on subjects and their gut microbiota. Lactobacillus converts glycosides into aglycones to improve their bioavailability and bioactivity by producing extracellular β-glucosidase. It has been demonstrated that soybean isoflavone daidzin is converted to daidzein and equol by Bifidobacterium spp., Eubacterium spp., Blautia spp., and Adlercreutzia spp.

To explore possible theoretical knowledge for developing functional probiotics, researchers can screen and isolate gut microbes capable of biotransforming phytoestrogens by β-glucosidase activity and characterize how these microbes influence the response of phytoestrogen metabolism. A study found that fecal cultures from women with an equol producer phenotype produced equol when fermented with isoflavones in vitro, so transplanting certain fecal microbiota from equol producers may help improve the body's bioavailability of phytoestrogens.

Evidence strength: This area is supported by solid mechanistic and in vitro data, with early-phase human observational data. Prospective interventional human clinical trials examining β-glucosidase supplementation specifically (as distinct from probiotic supplementation) for gut microbiota-mediated isoflavone metabolism are not yet established in the literature.

5.4 Colon Enzyme Activity and Xenobiotic Metabolism

Bacterial β-glucuronidase (EC 3.2.1.31) and β-glucosidase (EC 3.2.1.21) in the human colon are involved in the metabolism and activation of xenobiotics derived from dietary compounds. The enzymes are known to be mediators of colon cancer (CRC).

It is important to note that the majority of research specifically associating gut enzymatic activity with colon carcinogenesis focuses on β-glucuronidase rather than β-glucosidase, and these are distinct enzymes (EC 3.2.1.31 vs. EC 3.2.1.21). Much published literature uses these terms in proximate but not interchangeable contexts. The role of colonic β-glucosidase specifically in carcinogenesis remains an area requiring further dedicated investigation.

Evidence strength: Preliminary and largely mechanistic. Human RCT data for β-glucosidase supplementation specifically targeting colon health are absent.

5.5 Ginsenoside Bioconversion

β-Glucosidase has been shown to convert the major ginsenoside Rb1 into the pharmaceutically active minor ginsenoside Rd within 24 hours. This biotransformation is relevant because minor ginsenosides such as compound K are associated with higher pharmacological activity than their parent glycosidic forms; gut microbial β-glucosidases mediate this conversion in vivo. Evidence for this conversion is primarily enzymatic and in vitro; clinical trials evaluating β-glucosidase supplementation specifically to enhance ginsenoside bioavailability in humans are not established in the peer-reviewed literature.

Evidence strength: Mechanistic and in vitro only.

5.6 Cyanogenic Glycoside Processing (Toxicological Relevance)

Cyanogenic glycosides found in plants are not toxic on their own. However, when cell structures of plants are disrupted, cyanogenic glycoside will be brought together with the corresponding hydrolytic β-glucosidase enzyme. The hydrolysis of the cyanogenic glycosides is accomplished by the β-glucosidase enzymes, which facilitate the cleavage of the carbohydrate moiety of the cyanogenic glycoside to yield corresponding cyanohydrins, which further decompose to release hydrogen cyanide and an aldehyde or ketone.

According to pharmacological data, the free HCN released by the β-glucosidase enzyme present in the gut accounts for the high oral toxicity of amygdalin compared to parenteral administration. Maceration of edible parts of plants as they are eaten can release β-glucosidase. The β-glucosidase is then active until the low pH in the stomach deactivates the enzyme. Additionally, it is possible that part of the enzyme fraction can become reactivated in the alkaline environment of the gut.

Evidence strength: Well-established mechanistic and toxicological data. This is a key safety consideration for β-glucosidase supplementation in the context of co-ingestion with cyanogenic plant foods.

6. Body Systems and Health Areas

• Digestive system: Beta-glucosidase catalyzes the hydrolysis of β-glucosidic linkages in various substrates, playing essential roles in cellulose hydrolysis, β-glucan synthesis, and the metabolism of glycosylated compounds.
• Small intestine and flavonoid absorption: Following the ingestion of flavonoids, sugar moieties are cleaved from the phenolic backbone in the small intestine and absorbed here. Enzymes including cytosolic β-glucosidase (CBG) hydrolyze glycosylated flavonoids, and then aglycones enter epithelial cells by passive diffusion.
• Gut microbiome: Microbial β-glucosidases produced by Lactobacillus, Bifidobacterium, and related species are critical mediators of polyphenol metabolism, isoflavone activation, and interindividual variation in phytonutrient bioavailability.
• Liver and xenobiotic metabolism: The cytosolic β-glucosidase (CBG) in human liver hydrolyses various β-d-glycosides including glycosides of phytoestrogens, flavonoids, simple phenolics, and cyanogens, possibly playing a critical role in xenobiotic metabolism.
• Lysosomal/lipid metabolism: Glycosyl hydrolases are carbohydrate-active enzymes that hydrolyze a specific β-glycosidic bond in glycoconjugate substrates; β-glucosidases degrade glucosylceramide, a ubiquitous glycosphingolipid.
• Plant cell wall digestion: The β-glucosidase enzyme is used in biorefineries for cellulose degradation, where β-glucosidase is the rate-limiting enzyme for the final glucose production from cellobiose.

7. Dosage Forms and Reported Dosages

Beta-glucosidase as an isolated supplement is measured in enzymatic activity units rather than mass. Dosage varies widely based on specific formulation and intended use, typically measured in activity units (e.g., BGU).

In the context of food enzyme safety assessments by regulatory bodies, specific dosing parameters have been characterized. Dietary exposure to the food enzyme total organic solids (TOS) was estimated to be up to 4.054 mg TOS/kg body weight per day in European populations for the β-glucosidase preparation from Penicillium guanacastense evaluated by EFSA. In the toxicological studies underpinning that assessment, the systemic toxicity was assessed by means of a repeated dose 90-day oral toxicity study in rats. The Panel identified a no observed adverse effect level of 943 mg TOS/kg body weight per day, the highest dose tested, which when compared with the estimated dietary exposure, resulted in a margin of exposure of at least 233.

For a second food enzyme preparation from Aspergillus tubingensis, dietary exposure was estimated to be up to 0.609 mg TOS/kg body weight per day in European populations. The Panel identified a no observed adverse effect level of 2,217 mg TOS/kg bw per day, the highest dose tested, resulting in a margin of exposure of at least 3,640.

In the fermentation research context, soymilk was fermented with probiotic organisms at 37°C for 48 hours to generate endogenous β-glucosidase activity sufficient to hydrolyze isoflavone glycosides to aglycones; this represents a food-matrix dose rather than a supplemental dose.

No established standard human supplemental dose for exogenous β-glucosidase, expressed in activity units with clinical endpoint data, is documented in the peer-reviewed literature as of 2024.

8. Safety Considerations and Interactions

Regulatory Safety Assessments

The food enzyme β-glucosidase (β-d-glucoside glucohydrolase; EC 3.2.1.21) produced with the non-genetically modified Penicillium guanacastense strain AE-GLY has been evaluated by the EFSA Panel on Food Enzymes. Genotoxicity tests did not raise a safety concern. The systemic toxicity was assessed by means of a repeated dose 90-day oral toxicity study in rats. The Panel identified a no observed adverse effect level of 943 mg TOS/kg bw per day, the highest dose tested, resulting in a margin of exposure of at least 233.

A search for the similarity of the amino acid sequence of the food enzyme to known allergens was made and no match was found for the Penicillium guanacastense preparation.

For the Aspergillus tubingensis-derived preparation, the outcome was different: a search for the homology of the amino acid sequence of the food enzymes to known allergens found four matches with food allergens and 22 matches with respiratory allergens. Known sources of food allergens were used in the food enzyme manufacturing process. The Panel considered that the risk of allergic reactions upon dietary exposure cannot be excluded.

Cyanogenic Glycoside Interaction (Critical Safety Issue)

Co-administration of beta-glucosidase with amygdalin to rats substantially increased its toxicity compared to amygdalin given alone. Oral laetrile (amygdalin) could be up to 40 times more toxic than parenterally administered doses. This is probably due to the free HCN released by the β-glucosidase enzyme present in the gut. This pharmacological interaction is well documented and represents a direct, mechanism-based safety concern for individuals taking β-glucosidase supplements alongside amygdalin-, apricot kernel-, or bitter almond-containing products.

Upon enzymatic hydrolysis by β-glucosidase after maceration of cassava as it is eaten, cyanogenic glycosides are broken down to release HCN, which is toxic to both animals and humans. Supplemental β-glucosidase could theoretically enhance HCN liberation from inadequately processed cassava or other cyanogenic foods.

Heat Inactivation

The food enzyme has a temperature optimum between 60°C and 70°C (pH 4.5) and a pH optimum between pH 4.5 and 5.0 (37°C). Thermostability tests showed that enzyme activity decreased above 60°C, with no residual activity after pretreatment above 80°C. This indicates that β-glucosidase in cooked foods is substantially inactivated by normal cooking temperatures; cold or raw preparations preserve greater enzymatic activity.

Maceration of edible plant material as it is eaten can release β-glucosidase; the enzyme is then active until the low pH in the stomach deactivates it.

Fecal Enzyme Activity and Gut Inflammatory Conditions

Bacterial β-glucuronidase and β-glucosidase in the human colon are involved in the metabolism and activation of xenobiotics derived from dietary compounds. Research indicates that fecal β-glucosidase activity may be altered in inflammatory bowel disease, though the clinical implications of supplementing this enzyme in gastrointestinal disease states have not been established in controlled trials.

Source-Related Allergenicity

As noted in the EFSA assessments above, the allergenicity profile of β-glucosidase preparations depends substantially on their production organism. Preparations from Aspergillus tubingensis exhibited sequence homology to known allergens, and the Panel considered that the risk of allergic reactions upon dietary exposure cannot be excluded. Individuals with mold or fungal allergies should be aware that most commercial β-glucosidase preparations derive from Aspergillus or Penicillium species.

Limitations of the Evidence Base

A consistent limitation across all health-relevant areas of β-glucosidase research is the paucity of well-designed human RCTs specifically evaluating exogenous β-glucosidase supplementation. The health effects of polyphenols depend upon their bioavailability, which in general is very low and shows high interindividual variability. The low bioavailability of polyphenols is mainly attributed to their low absorption in the upper gastrointestinal tract. Although many studies have investigated how technological and biotechnological processes affect phenolic composition of fruits and vegetables, limited information exists regarding their effects on polyphenol bioavailability in humans. The vast majority of mechanistic data comes from in vitro, ex vivo, and animal studies. Clinical claims for β-glucosidase as a standalone dietary supplement ingredient therefore remain insufficiently substantiated by direct human trial evidence.

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