Rhizopus oryzae: A Comprehensive Reference
1. Identity and Taxonomy
1.1 Scientific Classification and Nomenclature
Rhizopus oryzae is a filamentous heterothallic microfungus that occurs as a saprotroph in soil, dung, and rotting vegetation. Taxonomically, it occupies the position: Domain: Eukarya, Kingdom: Fungi, Phylum: Zygomycota, Class: Zygomycetes, Order: Mucorales, Family: Mucoraceae, Genus: Rhizopus, and Species: oryzae — a species of filamentous fungi within the group Mucormycetes, largely found in decaying organic matter.
The nomenclature surrounding this organism has been a subject of sustained scientific debate. The classification published by Schipper (1984) separated the genus into three groups — R. microsporus, R. stolonifer, and R. arrhizus (=oryzae) — based on rhizoid branching, growth temperature and the size of sporangia and sporangiophores. A molecular phylogenetic study of the genus Rhizopus by Abe et al. (2010) recognised eight species including R. arrhizus (= R. oryzae). The controversy surrounding which species name to use for R. oryzae / R. arrhizus has been resolved in favour of the latter (Ellis 1985, de Hoog et al. 2015). As a result, the current authoritative name in medical and taxonomic literature is Rhizopus arrhizus, while R. oryzae persists broadly in food science, industrial microbiology, and dietary supplement contexts.
Rhizopus oryzae was first described by Frits Went and Hendrik Coenraad Prinsen Geerligs in 1895. The genus Rhizopus (family Mucoraceae) was erected in 1821 by the German mycologist Christian Gottfried Ehrenberg.
1.2 Morphological and Genetic Characteristics
This species is very similar to Rhizopus stolonifer, but it can be distinguished by its smaller sporangia and air-dispersed sporangiospores. It differs from R. oligosporus and R. microsporus by its larger columellae and sporangiospores. In contrast to Dikaryomycota fungi that form hyphae divided by septa, the hyphae of R. oryzae are multinucleate but not divided into separate cells (coenocytic).
R. oryzae was relegated to a distinct section because it grows well at 37 °C but fails to grow at 45 °C. The highly repetitive 45.3 Mb genome assembly contains abundant transposable elements (TEs), comprising approximately 20% of the genome, and 13,895 protein-coding genes not overlapping TEs, many of which are paralogous gene pairs. The order and genomic arrangement of the duplicated gene pairs and their common phylogenetic origin provide evidence for an ancestral whole-genome duplication (WGD) event.
Rhizopus oryzae is subdivided into two groups based on genetic and phenotypic differences: Type-I isolates accumulate primarily lactic acid when grown in the presence of a fermentable carbon source and contain two lactate dehydrogenase genes, ldhA and ldhB, while Type-II isolates synthesize predominantly fumaric acid and only have an ldhB gene.
1.3 Natural Habitat and Distribution
Among the Zygomycetes fungi, some of the best-known and most studied species can be found within the genus Rhizopus. These fungi are generally saprophytes and can be found living on dead and decaying organic material, for example, on leaves or in the soil. They are well spread and can be encountered in several different niches from the warm and moist Southern Asia to the colder Northern Europe. Many strains of R. oryzae have been isolated from sweet potato, mulberry, lily, and the human body.
1.4 Common Forms and Preparations
In the context of dietary supplements and food applications, R. oryzae appears in several distinct forms:
- Fermented foods (whole-culture form): Tempeh is a traditional Indonesian food made from fermented soybeans, produced by a natural culturing and controlled fermentation process that binds soybeans into a cake form; Rhizopus oligosporus or Rhizopus oryzae is used in the fermentation process and is also known as tempeh starter.
- Enzyme preparations (isolated): Microbial enzymes derived from fermentation include products such as Nortase®, which contains a lipase from Rhizopus oryzae, a protease from Aspergillus oryzae, and an amylase from Aspergillus oryzae.
- Fermentation starter culture: Used in solid-state and submerged fermentation processes for rice wine, vinegar, and various Asian fermented foods.
- Biomass for beta-glucan extraction: The fungus has traditionally been used in Asian countries to produce fermented foods and beverages, and β-glucans, polysaccharide macromolecules, can be found in the cell walls of molds such as R. oryzae.
2. Traditional and Historical Use
2.1 Southeast Asian Tempeh Production
One long-time use of these fungi is in tempe, a dish from soybeans fermented by R. oryzae or the related Rhizopus microsporus, which has been indigenous to Southeast Asia since 500 years ago, and used as a common meal. Tempeh is native to the island of Java, where it is a staple source of protein; like tofu, tempeh is made from soybeans, but it is a whole-soybean product with different nutritional characteristics and textural qualities, and its fermentation process and retention of the whole bean give it a higher content of protein, dietary fiber, and vitamins.
This fermented indigenous food has its origin in the Indonesian region, produced as a compact cake where traditionally soybean kernels are utilized, but diverse materials can also be used such as cereals, legumes, coconut cakes, or nuts. In general, this fermentation is carried out by Rhizopus and Aspergillus species, with frequent use of R. oryzae and R. oligosporus as safe strains, because there are no reports of production of mycotoxins (rhizonina A and B) which can cause mycotoxicoses.
2.2 East Asian Fermented Beverage and Condiment Traditions
The members of fungus Rhizopus (R. microsporus, R. oligosporus, and R. oryzae) have been used for thousands of years as major components of starter cultures for mixed-culture, solid state rice fermentation of Chinese sweet rice wine ('daqu').
Both jiu and chang (ancient Chinese fermented beverages) were likely made by mold saccharification, a uniquely Chinese contribution to beverage-making. In brief, amylolysis fermentation, which remains the traditional method for making fermented beverages in modern China, exploits the fungi of the genera Aspergillus, Rhizopus, Monascus, and others to break down the carbohydrates of rice and other grains into simple, fermentable sugars. Unlike the use of enzymes drawn from malt in western brewing practices, in Chinese fermentation the needed enzymes are produced from a diverse community of microorganisms making up the qu starter; these key microorganisms include molds such as Monascus, Aspergillus, and Rhizopus, which are essential for producing amylases, proteases, and other enzymes that break down starches and proteins into fermentable sugars and amino acids.
Within the world of Chinese fermentation, there are three related starters: Daqu, Xiaoqu, and Fuqu. Daqu, or "big qu," is used for both alcohols and vinegars and is usually a cake; it is typically made from peas, barley, or wheat and contains a variety of molds including Aspergillus terreus, Rhizopus oryzae, Rhizopus javanicus, and Amylomyces rouxii, among others.
In the past, strains were identified through isolating active components of the species that were commonly found in food and alcoholic drinks in Indonesia, China, and Japan.
2.3 Use in Korean and Indonesian Starters
The use of R. oryzae extends into Korean and Indonesian fermentation traditions. Korean starters contain Mucor circinelloides, M. javanicus, M. rouxii, and Rhizopus oryzae. Indonesians predominantly use ragi to make fermented snacks out of rice or cassava called tapé. The preparation of traditional ragi involves inoculating cooked, starchy substrates with mixed starter cultures that include Rhizopus species, then incubating in controlled conditions of warmth and humidity until fungal mycelium binds the substrate into a cohesive product.
3. Key Constituents and Active Compounds
3.1 Enzyme System
The many strains of R. oryzae produce a wide range of enzymes such as carbohydrate digesting enzymes and polymers along with a number of organic acids, ethanol and esters, giving it useful properties within the food industries, bio-diesel production, and pharmaceutical industries.
The principal enzymes produced by R. oryzae include:
- Lipase (triacylglycerol lipase; EC 3.1.1.3): Because of the outstanding traits of Rhizopus oryzae lipase (ROL) — including 1,3-specificity, high enantioselectivity and stability in organic media — its application in the energy, food, and pharmaceutical industrial sectors has been widely studied. The native structure of Rhizopus oryzae lipase (ROL) comprises a signal sequence of 26 amino acids, a prosequence of 97 amino acids, and a mature lipase region of 269 amino acids (mROL).
- Glucoamylase and α-amylase: In the production of Chinese traditional alcoholic beverages by solid-state fermentation, several species of the filamentous fungus genus Rhizopus have been widely applied in brewing processes as microorganisms for saccharification; they can secrete large amounts of hydrolytic enzymes and play a very important role in converting the starch present in grains into sugars.
- Protease: During fermentation, Rhizopus' amylase, lipase, and protease activity increases the bioavailability of nutrients and their ability to use many compounds as an energy and carbon source.
- Phytase: Rhizopus oryzae produces a wide spectrum of metabolites, in the form of enzymes, esters, organic acids, volatile materials, polymers and bioalcohols, including phytase, which is significant in enhancing mineral bioavailability from plant-based foods.
- β-Glucosidase: Another characteristic of Tempeh fermentation is the activity of β-glucosidases, which are primarily found in LAB and Rhizopus molds; these enzymes hydrolyze isoflavone glycosides in soybeans to produce aglycones such as genistein and daidzein, which exhibit more pronounced estrogenic and antioxidant actions and better intestinal absorption.
3.2 Organic Acids
R. oryzae is known for its ability to produce the sustainable platform chemicals l-(+)-lactic acid, fumaric acid, and ethanol. During glycolysis, all fermentable carbon sources are metabolized to pyruvate and subsequently distributed over the pathways leading to the formation of these products. The yields are in excess of 85% of the theoretical yield for l-(+)-lactic acid and ethanol and over 65% for fumaric acid.
The first references on the ability of Rhizopus species to produce organic acids appeared in 1911: Saito (1911) described lactic acid production by Rhizopus chinensis, and Ehlich (1911) reported the production of primarily fumaric acid, together with lactic acid, succinic acid, and malic acid by R. nigricans species.
3.3 Cell Wall Polysaccharides
β-Glucans are polysaccharide macromolecules that can be found in the cell walls of molds such as Rhizopus oryzae. They provide functional properties in food systems and have immunomodulatory activity, anticancer and prebiotic effects, reduce triglycerides and cholesterol, and prevent obesity, among other benefits.
3.4 Secondary Metabolites Produced During Fermentation
A total of 718 metabolites from 18 compound classes were identified in adlay millet seeds fermented by R. oryzae, of which 184 became more abundant and 19 got less abundant; many components such as amino acids, nucleotides, vitamins, flavonoids, terpenoids, and phenols significantly increased after the fermentation process. Notably, R. oryzae was found to synthesize high levels of two important beneficial compounds, S-adenosylmethionine (SAMe) and β-nicotinamide mononucleotide (β-NMN), with their contents increasing markedly after fermentation.
This fungus has a very rich secondary metabolism, producing a high number of compounds with sensorial and nutritional interest.
4. Mechanisms of Action
4.1 Enzymatic Hydrolysis and Nutrient Liberation
The primary mechanism by which R. oryzae exerts its effects in fermented foods and as an isolated enzyme preparation is direct enzymatic hydrolysis. R. oryzae produces amylase, lipase, and protease activity to increase the nutrient's ability to use many compounds as an energy and carbon source. During tempeh fermentation, the mycelium penetrates the substrate and secretes these extracellular hydrolases, which break down complex macromolecules into biologically available forms including free amino acids, monosaccharides, and free fatty acids.
During fermentation, free amino acids, soluble nitrogen compounds, free fatty acids and various types of vitamins and minerals increase by enzymatic digestion and synthesis.
4.2 Reduction of Antinutritional Factors
Isoflavone glycosides are converted to aglycones by genes that encode β-glucosidases, which are more potent antioxidants and estrogens. An association between genes coded to phytase and reduced phytate concentrations and enhanced mineral bioavailability exists. Phytate (phytic acid) is a potent chelator of minerals including iron, zinc, calcium, and magnesium; its enzymatic removal during fermentation releases these minerals into bioavailable forms.
4.3 Lipase: 1,3-Positional Specificity
The main reason for industrial interest in R. oryzae lipase is its catalytic versatility, as it carries out several industrially relevant reactions including hydrolysis of fats at the water/lipid interface and synthesis reactions in solvent-free or non-aqueous media such as transesterification, interesterification, and esterification. Because of the outstanding traits of ROL — 1,3-specificity, high enantioselectivity and stability in organic media — its application in energy, food, and pharmaceutical industrial sectors has been widely studied. In a digestive context, this 1,3-specificity means the enzyme hydrolyzes ester bonds at the sn-1 and sn-3 positions of triglycerides, liberating fatty acids and partial glycerides as digestion intermediates.
4.4 Organic Acid Metabolic Pathways
R. oryzae is known for its ability to produce l-(+)-lactic acid, fumaric acid, and ethanol. During glycolysis, all fermentable carbon sources are metabolized to pyruvate and subsequently distributed over the pathways leading to the formation of these products. Type-I isolates accumulate primarily lactic acid when grown in the presence of a fermentable carbon source and contain two lactate dehydrogenase genes, ldhA and ldhB, while Type-II isolates synthesize predominantly fumaric acid and only have an ldhB gene.
5. Scientific Evidence by Area of Use
5.1 Digestive Enzyme Supplementation
The most direct human-health application of isolated R. oryzae-derived enzymes is in digestive enzyme supplement formulations intended to support fat, carbohydrate, and protein digestion. Several enzyme formulations containing a mixture of exogenous digestive enzymes are available in the market to aid food digestion, though few clinical studies have shown the significance of enzyme supplements in improving digestion and treating digestive disorders.
In one clinical study, supplementation with N-SORB® (a multi-enzyme complex) for 90 days showed improvement in gut health and gastrointestinal and metabolic functions. In another investigation, supplementation of DigeZyme® (a penta-enzyme complex of α-amylase, lactase, cellulase, lipase, and protease) for 60 days showed significant improvement in efficacy parameters and reduction in gastric and intestinal symptoms. It should be noted, however, that these multi-enzyme trials were not conducted with R. oryzae-derived enzymes in isolation; they employed complex formulations from multiple fungal sources. Isolating the contribution of R. oryzae lipase specifically from these results is not possible. Evidence from these trials is preliminary and limited in applicability to the individual enzyme from this organism.
Microbial enzyme products on the market include Nortase®, which contains a lipase from Rhizopus oryzae, a protease from Aspergillus oryzae, and an amylase from Aspergillus oryzae. However, no large-scale randomized controlled human trials have been identified in the peer-reviewed literature specifically assessing isolated R. oryzae lipase as a standalone dietary supplement in healthy or disease populations.
Evidence strength: Weak to preliminary for human outcomes specific to R. oryzae-derived enzymes as standalone supplements. The mechanistic rationale for digestive enzyme support is well established; clinical confirmation specific to this organism's enzymes is limited.
5.2 Nutritional Enhancement Through Tempeh Fermentation
This is the area with the most established evidence base for R. oryzae's role in human nutrition, though most evidence pertains to the fermented food product (tempeh) rather than the organism administered as an isolated supplement.
Tempeh fermentation increases the bioavailability of proteins, fiber, vitamins, and minerals and produces isoflavones and bioactive peptides with health benefits.
A 2023 study published in ScienceDirect investigated the effects of fermenting a wild African legume (Senegalia macrostachya) with R. oryzae. Fermentation for 48 hours caused significant decreases in lipid content (by 30%) and insoluble dietary fiber (by 22%), and resulted in a complete elimination of phytate. This is consistent with the known enzymatic capabilities of the fungus and represents a positive outcome for mineral bioavailability.
An 86% reduction in β-glycosides was reported after 48-hour fermentation of soybeans with Rhizopus oryzae. This conversion of bound isoflavone glycosides to free aglycones (genistein, daidzein) is nutritionally significant because these aglycones exhibit more pronounced estrogenic and antioxidant actions and better intestinal absorption.
A 2024 metabolomic study published in Scientific Reports used R. oryzae fermentation of adlay millet seeds. A total of 718 metabolites from 18 compound classes were identified; the fermentation with R. oryzae varied 203 differential metabolites, of which 184 became more abundant and 19 got less abundant, with many components such as amino acids, nucleotides, vitamins, flavonoids, terpenoids, and phenols significantly increasing after the fermentation process. These findings are from in vitro and analytical studies; no clinical human trials were included.
Evidence strength: Moderate for the nutritional improvement of plant-based fermented foods prepared with R. oryzae; these are predominantly bench and food-science studies. Clinical human evidence linking fermented-food consumption (tempeh) to specific health outcomes independent of overall dietary patterns is limited and confounded.
5.3 Antioxidant Activity
As fermentation time progressed, GABA, total phenolics content (TPC), and flavonoids increased rapidly. Rhizopus oryzae-fermented oats had the highest total phenolics content. Fungal-fermented okara (soybean pulp) exhibited elevation of phenolic compounds by 2.19- to 4.13-fold and correspondingly possessed superior antioxidant properties compared to non-fermented okara.
In an assessment of strains isolated from traditional rice wine starters, strains W17 and W42 (R. arrhizus) exhibited the highest enzyme activities and antioxidant capacities, with a total phenolic content of 828 mg/L, total flavonoids of 215 μg/L, and an ABTS scavenging rate of 96.3%.
Evidence strength: All antioxidant data for R. oryzae or its fermentation products are currently from in vitro analytical studies. No human clinical trials on antioxidant outcomes specific to this organism have been identified.
5.4 Immunomodulation via Beta-Glucans
β-Glucans are polysaccharide macromolecules found in the cell walls of molds including Rhizopus oryzae. They provide functional properties in food systems and have immunomodulatory activity, anticancer and prebiotic effects, reduce triglycerides and cholesterol, and prevent obesity, among other benefits. These attributions to R. oryzae cell wall β-glucans are derived from the broader scientific literature on fungal β-glucans generally and from production studies rather than human clinical trials in which isolated R. oryzae β-glucans were tested.
Evidence strength: Preclinical / mechanistic. Clinical evidence supporting immunomodulatory benefits specific to R. oryzae-derived β-glucans in human subjects has not been identified in the peer-reviewed literature.
5.5 Fat Digestion Support (Lipase)
Studies of fungal lipases from Rhizopus oryzae and Rhizopus niveus have been used in the INFOGEST static in vitro simulation of digestion to study fat hydrolysis. These in vitro digestion simulation studies demonstrate that R. oryzae lipase can function across relevant physiological pH ranges to hydrolyze dietary triglycerides. However, translation of these findings to clinical outcomes has not been established through controlled human trials.
Evidence strength: Mechanistic and in vitro evidence supports the lipase's functional capacity for fat hydrolysis. Human clinical trial evidence is absent or limited for this specific enzyme source.
5.6 Lactic Acid Production and Gut Health
R. oryzae is classified as a GRAS filamentous fungus, commonly used for production of some oriental traditional foods, and is mainly recognized as a good producer of lactic acid. The L-(+)-lactic acid produced by R. oryzae during fermentation contributes to the preservation and organoleptic properties of fermented foods, and fermentation-derived lactic acid has well-established roles in food safety through pH reduction. However, no human clinical data specifically linking the lactic acid productivity of R. oryzae to gut health outcomes in supplement form has been identified.
Evidence strength: The biochemistry is well characterized; clinical supplementation evidence is absent.
6. Body Systems and Health Areas of Association
6.1 Gastrointestinal System
The primary body system with which R. oryzae is associated, through its enzyme activities, is the gastrointestinal tract. Its amylase, protease, and lipase contribute to macronutrient digestion. The reduction of anti-nutritional factors (phytate, trypsin inhibitors) in fermented foods prepared with this organism also improves the overall digestibility and nutritional quality of the food matrix.
6.2 Metabolic / Nutritional System
Through the conversion of isoflavone glycosides to bioavailable aglycones, and through increases in free amino acids, vitamins, and minerals during fermentation, R. oryzae contributes to improved macronutrient and micronutrient availability. The complex mixture of microbial species produces numerous enzymes, alcohol, amino acids, and many other flavor and bioactive compounds, which improve the nutritional value, sensory properties, and functional qualities of fermented foods.
6.3 Immune System
Cell-wall β-glucans derived from R. oryzae are associated in the broader fungal β-glucan literature with immunomodulatory activity, though specific human clinical data on R. oryzae-sourced β-glucans are lacking, as detailed in Section 5.4.
6.4 Cardiovascular System (Indirect Association)
β-Glucans from R. oryzae are noted to reduce triglycerides and cholesterol, and prevent obesity, among other benefits, according to general fungal β-glucan literature. These associations are derived from research on fungal β-glucans broadly and are not from human clinical studies specifically conducted with R. oryzae-derived material.
7. Dosage Forms and Dosages Reported in Studies
Dosages reported in the scientific literature pertain primarily to isolated enzyme preparations or toxicological safety studies, not to standardized supplement recommendations. The following are reported values from the identified literature:
- Lipase safety study (subchronic oral toxicity): A lipase enzyme obtained from Rhizopus oryzae, produced by a fermentation process, was subjected to a series of toxicological tests; administration of the lipase at dosages of 50, 200, and 1,000 mg/kg body weight/day for 90 days did not induce noticeable signs of toxicity.
- EFSA safety study (NOAEL): The systemic toxicity of a Rhizopus arrhizus-derived lipase was assessed by means of a repeated-dose 90-day oral toxicity study in rats, and the Panel identified a no observed adverse effect level of 1,806 mg TOS/kg body weight per day, the highest dose tested.
- Enzyme activity in traditional rice wine starters: Significant variation in enzyme activities was observed among R. arrhizus strains isolated from rice wine starters, with acidic protease activity ranging from 280 to 1,023 U/g, amylase from 557 to 1,681 U/g, and esterase from 370 to 2,949 U/g.
- Fermentation duration (tempeh): The tempeh production process involves the use of legumes or cereals and simple steps such as cleansing, soaking, hull removal, boiling, acidifying, tightly packing, and fermentation for around 2 days with a food-grade inoculum.
- β-Glucan production study: Rhizopus oryzae M10A1 produced the greatest amount of β-glucans after six days of culture at 30 °C.
No established or consensus human therapeutic dosages for R. oryzae as a dietary supplement (in the form of the whole organism or its isolated metabolites) exist in the identified peer-reviewed literature.
8. Safety Considerations
8.1 GRAS Status and Regulatory Recognition
Rhizopus oryzae is considered GRAS (Generally Recognized as Safe) by the FDA and thus recognized as safe to use industrially. It is classified as a GRAS filamentous fungus, commonly used for production of some oriental traditional foods. Applications have been introduced to EFSA by Amano Enzyme Inc. for the authorization of food enzymes including triacylglycerol lipase from Rhizopus oryzae (strain AE-TL).
8.2 Toxicological Data for Isolated Enzymes
A lipase enzyme obtained from Rhizopus oryzae, produced by a fermentation process, was subjected to a series of toxicological tests including acute, subacute, and subchronic oral toxicity and mutagenic potential. An extensive literature search on the production organism was also conducted. No evidence of (sub)acute oral toxicity or mutagenic potential was found. A few minor changes in the chemical composition of the blood in the highest dose group were of no toxicological significance. The no-observed-adverse-effect level (NOAEL) of the lipase in the subchronic toxicity study was 1,000 mg/kg body weight/day.
Genotoxicity tests for a Rhizopus arrhizus-derived lipase food enzyme did not indicate a safety concern. A search for the similarity of the amino acid sequence of this food enzyme to known allergens was made and no match was found.
8.3 Pathogenic Risk: Mucormycosis
The most significant safety consideration associated with R. oryzae is its dual identity as both a food-safe fermentation organism and a recognized human pathogen. Rhizopus oryzae is a species of filamentous fungi within the group Mucormycetes found in decaying organic matter and responsible for causing infections in immunocompromised individuals; it is the principal causative agent of the third most common invasive fungal infection in humans, after aspergillosis and candidiasis, known as mucormycosis.
R. oryzae is one of the most common causes of mucormycosis, characterized by growing hyphae within and surrounding blood vessels. The causal agents of mucormycosis may also produce toxins like agroclavine, which is toxic to humans, sheep, and cattle. This infection usually occurs in immunocompromised individuals but is rare.
Risk factors have been well described and include diabetes mellitus, malignancy, solid organ transplantation, iron overload, neutropenia, and prednisolone use. Mucormycoses are high-mortality infections. They predominantly affect immunocompromised hosts and are associated with a spectrum of disease.
Mucoralean fungi, including Mucor and Rhizopus spp., have caused cutaneous, hematological, gastrointestinal, rhinocerebral, and sinopulmonary infections with a high probability of dissemination and mortality. Across all types of sepsis, the mortality rate for mucormycosis is around 50%, with infection dissemination increasing mortality to 96%.
Treatment of mucormycosis includes amphotericin B, posaconazole, itraconazole, and fluconazole.
8.4 Risk in Immunocompromised Individuals Consuming Fermented Foods
As an example of the potential food safety risk to immunocompromised individuals regarding consumption of foodborne filamentous fungi, mucoralean fungi represent a particularly pertinent class. Significant food spoilage and fermentation genera in this class, including Mucor and Rhizopus spp., have caused cutaneous, hematological, gastrointestinal, rhinocerebral, and sinopulmonary infections. The possible relationship between fungal food fermentation and invasive fungal infections was described in a structured review by Benedict et al. (2016), in which the authors queried case reports of fungal infections putatively linked to consumption of fermented or spoiled food, beverages, and dietary supplements; of 11 reports, five were attributed to mucormycetes.
8.5 Absence of Mycotoxins in Food-Grade Strains
In general, R. oryzae and R. oligosporus are used as safe strains in tempeh fermentation because there are no reports of production of mycotoxins (rhizonina A and B) which can cause mycotoxicoses. This is an important distinction between food-grade strains selected and characterized for fermentation use and environmental or clinical isolates.
8.6 Summary of Safety Profile
For healthy, immunocompetent individuals, the consumption of foods fermented with certified food-grade strains of R. oryzae (such as tempeh) has a long history of safe use across multiple cultures. Isolated enzyme preparations derived from R. oryzae have undergone formal toxicological evaluation and demonstrated no mutagenicity, genotoxicity, or significant subchronic oral toxicity in animal studies. However, individuals who are immunocompromised — including those with uncontrolled diabetes mellitus, hematological malignancies, receiving systemic corticosteroids, or who have undergone organ transplantation — face a documented and potentially life-threatening risk of mucormycosis from exposure to viable Rhizopus spores, including from dietary sources. Isolated enzyme preparations, which are free of viable cells of the production organism, do not carry this infectious risk.
References
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