Recent developments in tempe research

Microbiology of fermented soy foods in Asia: Can we learn lessons for production of plant cheese analogues?

The food industry is facing the challenge of creating innovative, nutritious, and flavored plant-based products, due to consumer's increasing demand for the health and environmental sustainability. Fermentation as a unique and effective tool plays an important role in the innovation of food products. Traditional fermented soy foods are popular in many Asian and African countries as nutritious, digestible and flavorful daily staples or condiments. They are produced by specific microorganisms with the unique fermentation process in which microorganisms convert the ingredients of whole soybean or soybean curd to flavorful and functional molecules. This review provides an overview on traditional fermented food produced from soy, including douchi, natto, tempeh, and sufu as well as stinky tofu, including the background of these products, the manufacturing process, and the microbial diversity involved in fermentation procedures as well as flavor volatiles that were identified in the final products. The contribution of microbes to the quality of these five fermented soy foods is discussed, with the comparison to the role of cheese ripening microorganisms in cheese flavor formation. This communication aims to summarize the microbiology of fermented soy foods in Asia, evoking innovative ideas for the development of new plant-based fermented foods especially plant-based cheese analogues.

Analysis of functional ingredients of tempe-like fermented Moringa oleifera seeds (Moringa tempe) prepared with Rhizopus species

Tempe is a fermented food prepared by fermenting soybeans with Rhizopus species. However, there have recently been concerns about the stable supply of raw soybeans due to global warming and other factors. Moringa is a plant whose cultivation area is expected to expand in the future, and its seeds contain abundant proteins and lipids, and thus could be used as an alternative to soybeans. To develop a novel functional Moringa food, we fermented dehulled Moringa seeds with Rhizopus oligosporus and Rhizopus stolonifer using the solid fermentation method of tempe and investigated changes in the functional components, such as free amino acids and polyphenols, of the respective obtained Moringa tempe Rm and Rs. After 45 h of fermentation, the total content of free amino acids, mainly including gamma-aminobutyric acid and l-glutamic acid, in Moringa tempe Rm was about three times higher, while that in Moringa tempe Rs was almost the same, compared to that in unfermented Moringa seeds. Moreover, after 70 h of fermentation, both Moringa tempe Rm and Rs had approximately four times higher polyphenol content and significantly higher antioxidant activity than did unfermented Moringa seeds. Further, the content of each residual chitin-binding protein of defatted Moringa tempe Rm and Rs was almost the same as that of unfermented Moringa seeds. Taken together, Moringa tempe was rich in free amino acids and polyphenols, exhibited better antioxidant activity, and retained the levels of its chitin-binding proteins, suggesting that Moringa seeds could be used as an alternative to soybean for tempe preparation.

Fungal Cell Factories for Efficient and Sustainable Production of Proteins and Peptides

Filamentous fungi are a large and diverse taxonomically group of microorganisms found in all habitats worldwide. They grow as a network of cells called hyphae. Since filamentous fungi live in very diverse habitats, they produce different enzymes to degrade material for their living, for example hydrolytic enzymes to degrade various kinds of biomasses. Moreover, they produce defense proteins (antimicrobial peptides) and proteins for attaching surfaces (hydrophobins). Many of them are easy to cultivate in different known setups (submerged fermentation and solid-state fermentation) and their secretion of proteins and enzymes are often much larger than what is seen from yeast and bacteria. Therefore, filamentous fungi are in many industries the preferred production hosts of different proteins and enzymes. Edible fungi have traditionally been used as food, such as mushrooms or in fermented foods. New trends are to use edible fungi to produce myco-protein enriched foods. This review gives an overview of the different kinds of proteins, enzymes, and peptides produced by the most well-known fungi used as cell factories for different purposes and applications. Moreover, we describe some of the challenges that are important to consider when filamentous fungi are optimized as efficient cell factories.

Tempeh: A semicentennial review on its health benefits, fermentation, safety, processing, sustainability, and affordability

Tempeh is a fermented food made of mainly soybeans and is a nutritious, affordable, and sustainable functional source of protein. Globally, tempeh is a widely accepted fermented product. Although there is a growing body of literature on tempeh, most research has focused on unfermented soybeans, thus the impact of tempeh fermentation on biological properties of soybeans has been largely left scattered. The objective of this review is to summarize the literature of tempeh fermentation over the past 60 years. A search of articles on tempeh published from 1960 to 2020 was performed using the Cochrane Library, Web of Science, EBSCOhost FSTA database, and Google Scholar. References from identified articles were reviewed for additional sources. In total, 321 papers were selected for this review, of which 64 papers were related to the health benefits of tempeh. This review concluded that sufficient evidence exists in the literature supporting tempeh fermentation as a low-cost, health-promoting, and sustainable food processing technology to produce protein-rich foods using various beans, legumes, and grains. This comprehensive review suggests further studies are needed on tempeh fermentation and its impact on human health; research and standardization of nonsoy tempeh; assessment of food safety-improving modification in tempeh production system; and initiatives supporting the sourcing of local ingredients in tempeh production.

Biochemical characterization of two new Aspergillus niger aspartic proteases

Two new aspartic proteases, PepAb and PepAc (encoded by pepAb and pepAc), were heterologously expressed and biochemically characterized from Aspergillus niger F0215. They possessed a typical structure of pepsin-type aspartic protease with the conserved active residues D (84, 115), Y (131, 168) and D (281, 326), while their identity in amino acid sequences was only 19.0%. PepAb had maximum activity at pH 2.5 and 50 °C and PepAc at 3.0 and 50 °C. The specific activities of PepAb and PepAc toward casein were 1368.1 and 2081.4 U/mg, respectively. Their activities were significantly promoted by Cu²⁺ and Mn²⁺ and completely inhibited by pepstatin. PepAb exhibited higher catalytic efficiency (k _cat/K _m) toward soy protein isolates than casein, while PepAc showed higher catalytic efficiency toward casein. The hydrolysis capacities of PepAb and PepAc on soy protein isolates were slightly lower than that of previously identified A. niger aspartic protease, PepA (aspergillopepsin I), while the resultant peptide profiles were remarkably different for all three proteases.

Occurrence and species diversity of human-pathogenic Mucorales in commercial food-stuffs purchased in Paris area

Mucormycoses are life-threatening fungal diseases that affect a variety of patients including those with diabetes mellitus or hematological malignancies. The responsible agents, the Mucorales, are opportunistic pathogens originating from the environment such as soil or decaying organic matter. The aim of the present study was to assess the prevalence and diversity of human-pathogenic species of Mucorales in commercially available foodstuffs in France. All food samples were purchased from January 2014 to May 2015 in France. A total of 159 dried food samples including spices and herbs (n = 68), herbal tea (n = 19), cereals (n = 19), vegetables (n = 14), and other foodstuffs (n = 39) were analyzed. Each strain of Mucorales was identified phenotypically, and molecular identification was performed by ITS sequencing. From the 28 (17.6%) samples that were culture-positive for Mucorales, 30 isolates were recovered. Among the isolates, 13 were identified as Rhizopus arrhizus var. arrhizus, 10 R. arrhizus var. delemar, two Rhizopus microsporus, one Lichtheimia corymbifera, three Lichtheimia ramosa, and one Syncephalastrum racemosum. Culture-positive samples originated from different countries (Europe, Asia) and brands. The samples most frequently contaminated by Mucorales were spices and herbs (19/68, 27.9%), followed by herbal tea (2/19, 10.5%), cereals (2/19, 10.5%), other food products (5/39, 12.8%). The present study showed that human-pathogenic Mucorales were frequently recovered from commercially available foodstuffs in France with a large diversity of species. The potential danger represented by Mucorales present in food for immunocompromised patients should be further analyzed.

What is the cobalamin status among vegetarians and vegans in Australia?

Water-soluble vitamin B12 (cobalamin) plays a vital role in normal blood function and neurological functioning. Clinical and subclinical B12 deficiency has been notably reported in vegans, vegetarians, the elderly and metformin-treated diabetics. Currently, the prevalence of cobalamin deficiency among vegans and vegetarians in Australia is lacking; data on dietary intake including supplements and nutritional status are also limited. The increasing multiculturalism of Australia has seen an influx of imported foods, of which some may contain considerable vitamin B12. However, values for such foods are not included in the food composition databases. This review highlights the need to update the food composition database with culturally diverse foods containing vitamin B12. Moreover, the need for assessing dietary intakes and status using the most current best evidence and best practice on nutritional indicators (biochemical and functional biomarkers) to estimate the risk of deficiency and/or depletion is discussed.

Controlled fermentation of rapeseed presscake by Rhizopus, and its effect on some components with relevance to human nutrition

The use of rapeseed protein could contribute to meeting the increasing demand for plant proteins with high biological value in human nutrition. In order to make rapeseed presscake fit for human consumption, the presscake was fermented by using the tempeh mould, Rhizopus microsporus var. oligosporus. Fermentation was satisfactory at initial levels of added acetic acid of 40-60 mmoles/Kg, a_w of 0.97, pasteurization, surface inoculation and incubation at 32 °C and 90-95% relative humidity. It was crucial to stop the fermentation once the mould had grown and metabolized sufficiently but before a major rise in pH and subsequent growth of acid-sensitive sporeforming bacteria occurred. Some degradation of glucosinolates, cell wall polysaccharides and phenolic compounds was found, but there was some evidence that growth and metabolism of the mould also depended on the texture of the presscake, as these factors affect the oxygen supply to the mould. In conclusion, it is possible to ferment rapeseed presscake by using the "Tempeh starter" Rhizopus oligosporus, but in order to use the resulting product to enrich various foods with protein or replace other proteins, the degree of degradation of undesired compounds should be further standardized, especially by the control of the pH, oxygen supply, and fermentation time.

Next-Generation Sequencing Analyses of Bacterial Community Structures in Soybean Pastes Produced in Northeast China

Fermented soybean foods contain nutritional components including easily digestible peptides, cholesterol-free oils, minerals, and vitamins. Various fermented soybean foods have been developed and are consumed as flavoring condiments in Asian regions. While the quality of fermented soybean foods is largely affected by microorganisms that participate in the fermentation process, our knowledge about the microorganisms in soybean pastes manufactured in Northeast China is limited. The current study used a culture-independent barcoded pyrosequencing method targeting hypervariable V1/V2 regions of the 16S rRNA gene to evaluate Korean doenjang and soybean pastes prepared by the Hun Chinese (SPHC) and Korean minority (SPKM) populations in Northeast China. In total, 63399 high-quality sequences were derived from 16 soybean paste samples collected in Northeast China. Each bacterial species-level taxon of SPHC, SPKM, and Korean doenjang was clustered separately. Each paste contained representative bacterial species that could be distinguished from each other: Bacillus subtilis in SPKM, Tetragenococcus halophilus in SPHC, and Enterococcus durans in Korean doenjang. This is the 1st massive sequencing-based study analyzing microbial communities in soybean pastes manufactured in Northeast China, compared to Korean doenjang. Our results clearly showed that each soybean paste contained unique microbial communities that varied depending on the manufacturing process and location.

Vitamin B12 among Vegetarians: Status, Assessment and Supplementation

Cobalamin is an essential molecule for humans. It acts as a cofactor in one-carbon transfers through methylation and molecular rearrangement. These functions take place in fatty acid, amino acid and nucleic acid metabolic pathways. The deficiency of vitamin B12 is clinically manifested in the blood and nervous system where the cobalamin plays a key role in cell replication and in fatty acid metabolism. Hypovitaminosis arises from inadequate absorption, from genetic defects that alter transport through the body, or from inadequate intake as a result of diet. With the growing adoption of vegetarian eating styles in Western countries, there is growing focus on whether diets that exclude animal foods are adequate. Since food availability in these countries is not a problem, and therefore plant foods are sufficiently adequate, the most delicate issue remains the contribution of cobalamin, which is poorly represented in plants. In this review, we will discuss the status of vitamin B12 among vegetarians, the diagnostic markers for the detection of cobalamin deficiency and appropriate sources for sufficient intake, through the description of the features and functions of vitamin B12 and its absorption mechanism.

Food preparation with mucoralean fungi: A potential biosafety issue?

Mucorales have been used for production of fermented food in Asia and Africa since time immemorial. Particularly Rhizopus species are rapidly growing, active producers of lipases and proteases and occur naturally during the first stages of soybean fermentation. Two biosafety issues have been raised in recent literature: (1) pathogenicity, Rhizopus species being prevalent opportunists causing erosive infections in severely compromised patients, and (2) toxicity, strains harbouring endosymbiotic Burkholderia producing toxic secondary metabolites. At the molecular level, based on different gene markers, species identity was found between strains used for food processing and clinical strains. In this study, we screened for bacterial symbionts in 64 Rhizopus strains by light microscopy, 16S rRNA sequencing, and HPLC. Seven strains (11 %) carried bacteria identified as Burkholderia rhizoxinica and Burkholderia endofungorum, and an unknown Burkholderia species. The Burkholderia isolates proved to be able to produce toxic rhizoxins. Strains with endosymbionts originated from food, soil, and a clinical source, and thus their presence could not be linked to particular habitats. The presence of Burkholderia in Rhizopus producing toxins could not be excluded as a potential risk for human health. In contrast, given the type of diseases caused by Rhizopus species, we regard the practical risk of infection via the food industry as negligible.

Reduction of phytic acid and enhancement of bioavailable micronutrients in food grains

More than half of the world populations are affected by micronutrient malnutrition and one third of world's population suffers from anemia and zinc deficiency, particularly in developing countries. Iron and zinc deficiencies are the major health problems worldwide. Phytic acid is the major storage form of phosphorous in cereals, legumes, oil seeds and nuts. Phytic acid is known as a food inhibitor which chelates micronutrient and prevents it to be bioavailabe for monogastric animals, including humans, because they lack enzyme phytase in their digestive tract. Several methods have been developed to reduce the phytic acid content in food and improve the nutritional value of cereal which becomes poor due to such antinutrient. These include genetic improvement as well as several pre-treatment methods such as fermentation, soaking, germination and enzymatic treatment of grains with phytase enzyme. Biofortification of staple crops using modern biotechnological techniques can potentially help in alleviating malnutrition in developing countries.

Fermented soybeans by Rhizopus oligosporus reduce femoral bone loss in ovariectomized rats

BACKGROUND/OBJECTIVES

Soy isoflavones are structurally similar to estrogen and bind to estrogen receptors, suggesting that they exhibit estrogenic activities; therefore, they are referred to as phytoestrogens. Fermentation may affect the bioavailability of isoflavones altering soy isoflavone glycosides in the form of aglycones. Thus, this study investigated the effects of fermented soybeans by Rhizopus oligosporus on bone metabolism in both young rats as a pilot test and in ovariectomized (ovx) old rats as a model of menopause.

MATERIALS/METHODS

In the pilot test, a total of 24 seven-week-old female Sprague-Dawley (SD) rats were fed one of three diets for a period of four weeks: casein, unfermented soybean product, or fermented soybean product by R. oligosporus. In the ovx rat model, 20-week-old SD rats weighing 260-290 g underwent either sham-operation (n = 10) or bilateral ovariectomy (n = 30) and were then fed the AIN-93M diet for one week. Thereafter, rats were fed sham-casein, ovx-casein, ovx-soybean, or ovx-fermented soybean diet for five weeks. After decapitation, femoral bones were isolated and preserved in 9% formalin for assessment of bone mineral density (BMD), bone mineral content (BMC), and bone-breaking strength (BBS).

RESULTS

Ovx rats showed significantly increased weight gain and decreased uterine wet weight. Of particular interest, ovx rats fed fermented soybeans showed increased uterine wet weights compared to control rats. Fermented soybean diet caused a significant increase in plasma 17-β estradiol concentrations in young rats, and 17-β estradiol levels were enhanced in ovx rats to match those of sham-operated ones. Significantly lower femoral BMD and BMC were observed in ovx rats compared to sham-operated controls, whereas bone areas did not differ statistically among the groups. In addition, BBS tended to be increased in ovx rats fed soybeans and fermented soybeans.

CONCLUSIONS

Supplementation of fermented soybeans could have preventive and therapeutic effects against osteoporosis in postmenopausal women.

Vitamin B₁₂-containing plant food sources for vegetarians

The usual dietary sources of Vitamin B₁₂ are animal-derived foods, although a few plant-based foods contain substantial amounts of Vitamin B₁₂. To prevent Vitamin B₁₂ deficiency in high-risk populations such as vegetarians, it is necessary to identify plant-derived foods that contain high levels of Vitamin B₁₂. A survey of naturally occurring plant-derived food sources with high Vitamin B₁₂ contents suggested that dried purple laver (nori) is the most suitable Vitamin B₁₂ source presently available for vegetarians. Furthermore, dried purple laver also contains high levels of other nutrients that are lacking in vegetarian diets, such as iron and n-3 polyunsaturated fatty acids. Dried purple laver is a natural plant product and it is suitable for most people in various vegetarian groups.

Microbial diversity and dynamics of microbial communities during back-slop soaking of soybeans as determined by PCR-DGGE and molecular cloning

Tempe is a traditional fermented food in Indonesia. The manufacture process is quite complex, which comprises two stages, preparatory soaking of soybeans and fungal solid state fermentation. Daily addition of previous soak water (back-slopping) during the soybean soaking step is considered to be crucial in the manufacture of high quality tempe. The microbial diversity and dynamics of the microbial communities evolving during back-slop soaking of soybeans for tempe making was investigated by culture-independent PCR-DGGE and molecular cloning. Both DNA and total RNA were isolated and included in this study, to obtain a view on the succession of total and viable bacteria in the complex microbiota. DGGE profiles indicated that Enterobacter sp., Enterococcus sp., Pseudomonas putida, Leuconostoc fallax, Pediococcus pentosaceus, and Weissella cibaria, were the predominant bacteria. Their occurrence shifted dramatically during the back-slop soaking procedure. This study combined with previous culture-dependent studies could gain a better understanding of the complex microbiota of traditional fermented food and give useful information for its quality control.

Biologically active vitamin B12 compounds in foods for preventing deficiency among vegetarians and elderly subjects

The usual dietary sources of vitamin B12 are animal-source based foods, including meat, milk, eggs, fish, and shellfish, although a few plant-based foods such as certain types of dried lavers (nori) and mushrooms contain substantial and considerable amounts of vitamin B12, respectively. Unexpectedly, detailed characterization of vitamin B12 compounds in foods reveals the presence of various corrinoids that are inactive in humans. The majority of edible blue-green algae (cyanobacteria) and certain edible shellfish predominately contain an inactive corrinoid known as pseudovitamin B12. Various factors affect the bioactivity of vitamin B12 in foods. For example, vitamin B12 is partially degraded and loses its biological activity during cooking and storage of foods. The intrinsic factor-mediated gastrointestinal absorption system in humans has evolved to selectively absorb active vitamin B12 from naturally occurring vitamin B12 compounds, including its degradation products and inactive corrinoids that are present in daily meal foods. The objective of this review is to present up-to-date information on various factors that can affect the bioactivity of vitamin B12 in foods. To prevent vitamin B12 deficiency in high-risk populations such as vegetarians and elderly subjects, it is necessary to identify plant-source foods that contain high levels of bioactive vitamin B12 and, in conjunction, to prepare the use of crystalline vitamin B12-fortified foods.

Soyfoods and soybean products: from traditional use to modern applications

Soybean products (soyfoods), reported as potential functional foods, are implicated in several health-enhancing properties, such as easing the symptoms of postmenopausal women, reducing the risk of osteoporosis, preventing cardiovascular disease, and antimutagenic effects. Isoflavone, for example, is one of the most important compounds abundantly found in soybean, mainly accounting for the health-enhancing properties as mentioned earlier. However, most biological activities of isoflavones are mainly attributed to their aglycone forms. It has also been demonstrated that isoflavone aglycones are absorbed faster and in greater amount than their glycosides in human intestines. Fortunately, deglycosylation of isoflavones can be achieved during fermentation process by several strains such as lactic acid bacteria, basidiomycetes, filamentous fungus, and Bacillus subtilis with their β-glucosidase activity. This article presents an overview of soybean's chemistry, application, state-of-the-art advances in soybean fermentation processing and products as well as their applications in food and pharmaceutical industries. Different compounds, such as isoflavone, dietary fibers, and proteins which exhibit significant bioactivities, are summarized. The roles of different microorganisms in bioconversion and enhancement of bioactivities of fermented soybean are also discussed.

Effects of non-fermented and fermented soybean milk intake on faecal microbiota and faecal metabolites in humans

The effects of non-fermented soybean milk (NFSM) and fermented soybean milk (FSM) intake on the faecal microbiota and metabolic activities in 10 healthy volunteers were investigated. Soybean oligosaccharides, raffinose and stachyose were utilized by bifidobacteria except for Bifidobacterium bifidum, but most strains of Escherichia coli and Clostridium perfringens could not use them. During the dietary administration of FSM, the number of bifidobacteria and lactobacilli in the faeces increased (p < 0.05), and clostridia decreased (p < 0.05). Moreover, the concentrations of faecal sulphide were decreased (p < 0.01) in the intake of FSM. During the dietary administration of NFSM, the number of bifidobacteria tended to increase. These results indicate that the consumption of soybean milk, especially FSM, is related to improvement of the intestinal environment.

Carbohydrate-active enzymes from the zygomycete fungus Rhizopus oryzae: a highly specialized approach to carbohydrate degradation depicted at genome level

BACKGROUND

Rhizopus oryzae is a zygomycete filamentous fungus, well-known as a saprobe ubiquitous in soil and as a pathogenic/spoilage fungus, causing Rhizopus rot and mucomycoses.

RESULTS

Carbohydrate Active enzyme (CAZy) annotation of the R. oryzae identified, in contrast to other filamentous fungi, a low number of glycoside hydrolases (GHs) and a high number of glycosyl transferases (GTs) and carbohydrate esterases (CEs). A detailed analysis of CAZy families, supported by growth data, demonstrates highly specialized plant and fungal cell wall degrading abilities distinct from ascomycetes and basidiomycetes. The specific genomic and growth features for degradation of easily digestible plant cell wall mono- and polysaccharides (starch, galactomannan, unbranched pectin, hexose sugars), chitin, chitosan, β-1,3-glucan and fungal cell wall fractions suggest specific adaptations of R. oryzae to its environment.

CONCLUSIONS

CAZy analyses of the genome of the zygomycete fungus R. oryzae and comparison to ascomycetes and basidiomycete species revealed how evolution has shaped its genetic content with respect to carbohydrate degradation, after divergence from the Ascomycota and Basidiomycota.

Effect of fermentation with Rhizopus oligosporus on some physico-chemical properties of starch extracts from soybean flour

Studies were carried out on the changes that occurred on some selected physico-chemical properties of starch extracts from soybean flour when fermented with Rhizopus oligosporus. This was done in order to increase the utilization potentials of the flour. Starch extracts were obtained from flour obtained from fermented soybean using R. oligosporus with a fermentation period of between 0 and 72h. Some physico-chemical properties, as well as the amylose, amylopectin, and the pasting characteristics of the starch extracts were determined using standard methods. Increasing trends with increasing fermentation period were observed with respect to most of the physico-chemical characteristics investigated, except for the reconstitution index that showed decreasing trends. While the peak, breakdown and final viscosities also decreased, the swelling power and solubility slightly increased with increase in fermentation period. The proportion of amylopectin which was constantly high showed further slight increases with fermentation, apparently because of the decreasing proportion of amylose probably due to utilization by the mould R. oligosporus used for fermentation.

Vitamin B12 sources and bioavailability

The usual dietary sources of vitamin B(12) are animal foods, meat, milk, egg, fish, and shellfish. As the intrinsic factor-mediated intestinal absorption system is estimated to be saturated at about 1.5-2.0 microg per meal under physiologic conditions, vitamin B(12) bioavailability significantly decreases with increasing intake of vitamin B(12) per meal. The bioavailability of vitamin B(12) in healthy humans from fish meat, sheep meat, and chicken meat averaged 42%, 56%-89%, and 61%-66%, respectively. Vitamin B(12) in eggs seems to be poorly absorbed (< 9%) relative to other animal food products. In the Dietary Reference Intakes in the United States and Japan, it is assumed that 50% of dietary vitamin B(12) is absorbed by healthy adults with normal gastro-intestinal function. Some plant foods, dried green and purple lavers (nori) contain substantial amounts of vitamin B(12), although other edible algae contained none or only traces of vitamin B(12). Most of the edible blue-green algae (cyanobacteria) used for human supplements predominantly contain pseudovitamin B(12), which is inactive in humans. The edible cyanobacteria are not suitable for use as vitamin B(12) sources, especially in vegans. Fortified breakfast cereals are a particularly valuable source of vitamin B(12) for vegans and elderly people. Production of some vitamin B(12)-enriched vegetables is also being devised.

Morphological characteristics of sporangiospores of the tempe fungus Rhizopus oligosporus differentiate it from other taxa of the R. microsporus group

The fungus Rhizopus oligosporus (R. microsporus var. oligosporus) is traditionally used to make tempe, a fermented food based on soybeans. Interest in the fungus has steadily increased, as it can also ferment other substrates, produce enzymes, and treat waste material. R. oligosporus belongs to the R. microsporus group consisting of morphologically similar taxa, which are associated with food fermentation, pathogenesis, or unwanted metabolite production (rhizonins and rhizoxins). The ornamentation pattern, shape, and size of sporangiospores of 26 R. microsporus group strains and two R. oryzae strains were studied using low-temperature SEM (LT-SEM) and LM. This study has shown that: (1) LT-SEM generates images from well-conserved sporangiophores, sporangia, and spores. (2) Robust spore ornamentation patterns can be linked to all different taxa of the R. microsporus group, some previously incorrectly characterized as smooth. Ornamentation included valleys and ridges running in parallel, granular plateaus, or smooth polar areas. Distribution of ornamentation patterns was related to spore shape, which either was regular, ranging from globose to ellipsoidal, or irregular. Specific differences in spore shape, size, and ornamentation were observed between Rhizopus taxa, and sometimes between strains. (3) R. oligosporus has a defect in the spore formation process, which may be related to the domesticated nature of this taxon. It had a high proportion, 10-31%, of large and irregular spores, and was significantly differentiated from other, natural Rhizopus taxa as evaluated with partial least squares discriminant analysis. It is remarkable that the vehicle of distribution, the sporangiospore, is affected in the strains that are distributed by human activity. This provides information about the specificity and speed of changes that occur in fungal strains because of their use in (food) industry.

Image analysis for monitoring the barley tempeh fermentation process

AIMS

To develop a fast, accurate, objective and nondestructive method for monitoring barley tempeh fermentation.

METHODS AND RESULTS

Barley tempeh is a food made from pearled barley grains fermented with Rhizopus oligosporus. Rhizopus oligosporus growth is important for tempeh quality, but quantifying its growth is difficult and laborious. A system was developed for analysing digital images of fermentation stages using two image processing methods. The first employed statistical measures sensitive to image colour and surface structure, and these statistical measures were highly correlated (r=0.92, n=75, P<0.001) with ergosterol content of tempeh fermented with R. oligosporus and lactic acid bacteria (LAB). In the second method, an image-processing algorithm optimized to changes in images of final tempeh products was developed to measure number of visible barley grains. A threshold of 5 visible grains per Petri dish indicated complete tempeh fermentation. When images of tempeh cakes fermented with different inoculation levels of R. oligosporus were analysed the results from the two image processing methods were in good agreement.

CONCLUSION

Image processing proved suitable for monitoring barley tempeh fermentation. The method avoids sampling, is nonintrusive, and only requires a digital camera with good resolution and image analysis software.

SIGNIFICANCE AND IMPACT OF THE STUDY

The system provides a rapid visualization of tempeh product maturation and qualities during fermentation. Automated online monitoring of tempeh fermentation by coupling automated image acquisition with image processing software could be further developed for process control.

The fibrinolytic activity of a novel protease derived from a tempeh producing fungus, Fusarium sp. BLB

Tempeh is a traditional Indonesian soybean-fermented food produced by filamentous fungi, Rhizopus sp. and Fusarium sp. We isolated and sequenced the genomic gene and a cDNA clone encoding a novel protease (FP) from Fusarium sp. BLB. The genomic gene was 856 bp in length and contained two introns. An isolated cDNA clone encoded a protein of 250 amino acids. The predicted amino acid sequence of FP showed highest homology, of 76%, with that of trypsin from Fusarium oxysporum. The hydrolysis activity of FP toward synthetic peptide was higher than that of any other protease tested, including Nattokinases. Furthermore, the thrombolytic activity of FP was about 2.1-fold higher than that of Nattokinase when the concentration of plasminogen was 24 units/ml. These results suggest that FP is superior to Nattokinases in dissolving fibrin when absorbed into the blood.

Age-related uterotrophic response of soy isoflavone intake in rats

This study investigated the effects of soy isoflavone intake on uterotrophic responses in growing (juvenile) and adult female rats. In the growing rats, feed intake showed a decreasing trend as the level of dietary isoflavones increased to 0.02%, 0.1%, and 0.2% of the diets. However, in the case of the adult rats there were no significant differences among groups. Weight gains were significantly lower in the rats fed 0.1% and 0.2% isoflavones than the controls in both juvenile and adult rats. The urinary excretion of daidzein and genistein was significantly increased with increasing levels of dietary isoflavones. The calculated urinary recoveries of daidzein and genistein were significantly lower in the groups fed 0.1% and 0.2% isoflavones compared to the juvenile and adult rat groups fed 0.02% isoflavones; no significant difference was observed between the 0.1% and 0.2% groups. The calculated urinary recoveries of daidzein and genistein in the adult rats were significantly higher than in the juvenile rats. The differences in the urinary recoveries between ages may be due to greater availability of the isoflavones in the adult rats. Isoflavone supplementation did not alter the histological phenotype of endometrial cells in growing rats, but a hyperplastic response of endometrium was shown in the adult rats. Dietary isoflavones, therefore, may not have an estrogenic effect on the uterus at these dose levels during the growth period, but this organ would be expected to be a likely target for isoflavone action in adults. We observed in the present study that isoflavones are more bioavailable in adult rats than in the juvenile rats. Therefore, soy isoflavone supplementation may not act as an endocrine disrupter during the growth period but may exert a phytoestrogenic effect on the uterus of adult rats.

Production of volatile compounds by Rhizopus oligosporus during soybean and barley tempeh fermentation

Rhizopus oligosporus Saito can ferment soybeans or cereal grains to tempeh, a sliceable cake with improved nutritional properties. Volatiles produced by different R. oligosporus strains grown on malt extract agar (MEA), barley and soybean were investigated. The effect of co-cultivation with Lactobacillus plantarum on the production of volatiles was also studied. Volatile compounds were collected in situ by headspace diffusion and identified by GC-MS. The ten R. oligosporus strains that had different colony morphologies on MEA produced very similar volatile profiles, except for slight variations among the minor volatile compounds (e.g. sesquiterpenes). Likewise, practically no differences in volatile profiles were observed between three of the strains grown on soybeans. In contrast, the R. oligosporus volatile profile on soybean was different from that on barley from the same strain. Co-cultivation with L. plantarum did not influence volatile production by R. oligosporus. The dominant compounds produced on all three substrates were ethanol, acetone, ethyl acetate, 2-butanone, 2-methyl-1-propanol, 3-methyl-1-butanol and 2-methyl-1-butanol. Acetaldehyde and 2-methyl-propanal were also produced on MEA and barley, while 2-pentanone, methyl acetate, 2-butanol and 3-methyl-3-buten-1-ol were observed on soybeans. Ethanol, 2-methyl-1-butanol and 3-methyl-1-butanol were the most abundant volatile compounds produced on MEA and barley, while 2-butanone was the dominant volatile metabolite on soybean. The mushroom odour compounds, 3-octanone and 1-octen-3-ol, were only detected from soybean and soybean tempeh.