White Sufu Research Articles

Distinct bacterial community of a solid-state fermented Chinese traditional food huase sufu revealed by high-throughput sequencing.

The online version contains supplementary material available at 10.1007/s10068-021-00963-3.

Molecular identification and relative abundance of microorganisms in douchi koji and salted egg white sufu during processing.

A novel animal protein-based douchi koji-inoculated steamed salted egg white sufu (SEWS) has been developed. This study determined the relative abundance of microorganisms in the douchi koji and semi-finished (5-day fermentation) and finished (5-day fermentation and 14-day ripening) SEWS by using 16S and 18S ribosomal DNA and gene-cloning methods. The results revealed that Bacillus spp. and Aspergillus oryzae were dominant in the douchi koji. In the semi-finished SEWS, the percentages of Bacillus amyloliquefaciens and Bacillus subtilis were considerably lower, whereas those of Enterococcus and Staphylococcus were substantially higher. In the finished SEWS, Bacillus spp. became dominant again and A.oryzae was the only fungus detected. In conclusion, by using molecular techniques, microbial population dynamics in SEWS can be evaluated. During processing, the relative abundance of microorganisms in SEWS changed and Bacillus spp. and A.oryzae remained dominant. This study provides crucial information for designing starter cultures for producing SEWS.

Inhibition of Bacillus cereus by garlic (Allium sativum) essential oil during manufacture of white sufu, a traditional Chinese fermented soybean curd

This study aimed to apply garlic essential oil (GEO) to control the Bacillus cereus content in white sufu, a traditional Chinese fermented soybean curd. The effect of GEO on the Bacillus cereus count, bacterial composition, and the metabolic changes during the fermentation process were investigated. After treatment with GEO, B. cereus was reduced from 5.26 to 4.58 log CFU/g in the finished product, meeting the Hong Kong Food Microbiological Guidelines. Three Lactic acid bacteria genera (Lactococcus, Weissella, and Leuconostoc), which showed a positive correlation with desirable metabolites, were present in greater numbers after the treatment. Hierarchical cluster analysis and principal component analysis showed that GEO caused no significant differences in polar metabolites (carbohydrates, organic acids, biogenic amines, nitrogen compounds, and free amino acids) and volatile compounds in the end-product. Thus, GEO appears to have great potential in sufu manufacture and preservation.

High-Throughput Sequencing and Metabolomics Reveal Differences in Bacterial Diversity and Metabolites Between Red and White Sufu.

Sufu is a traditional fermented soybean food produced in China. However, the microbial compositions and metabolites of different types of sufu have not been studied in detail. Accordingly, in this study, we evaluated the differences in bacterial communities and metabolites between commercial red sufu (RS) and white sufu (WS). Principal coordinate analysis and the unweighted pair group method with arithmetic means analysis of 16S rRNA genes revealed that the bacterial community structures of RS and WS differed dramatically. At the phylum level, the relative abundances of Firmicutes and Proteobacteria were significantly different between RS and WS (P < 0.01). Moreover, the abundances of Lactococcus and Tetragenococcus genera were significantly different between RS and WS (P < 0.01). Among metabolites, most free amino acids, few of volatile flavor compounds, and some organic acids showed significant differences between RS and WS (P < 0.05). Additionally, correlations between microbiota and metabolites were determined. Aggregated boosted tree analysis showed that formic acid had the highest relative influence (20.27%) on bacterial community diversity (Chao 1), following by arginine (5.38%), propanol (4.57%), oxalic acid (4.46%), and hexanol (4.43%). Moreover, Streptococcaceae and Moraxellaceae had the highest relative influence on the concentration of formic acid (12.84% and 8.75%, respectively). The profiles obtained in this study improve our understanding of the relationships between bacterial flora and metabolites in different types of sufu. These findings may help us interpret the roles of bacterial communities in the flavor and characteristics of sufu.

Characterisation of aroma-active compounds in Guilin Huaqiao white sufu and their influence on umami aftertaste and palatability of umami solution

Sufu is a traditional fermented soybean curd, and Guilin Huaqiao white sufu is one of the most famous mould-fermented white sufu in China. The volatile compounds in sufu were extracted by vacuum simultaneous steam distillation and extraction (V-SDE) and analysed by gas chromatography–mass spectrometry–olfactometry (GC–MS–O). The aroma-active compounds were identified by aroma extract dilution analysis (AEDA) and odour activity values (OAVs), and their influence on umami aftertaste and palatability of umami solution was identified by sensory evaluation analysis in the follow-up research. A total of 88 volatile compounds, contained 20 aroma-active compounds were identified, of which (E,E)-2,4-decadienal, 1-octen-3-ol, (E,E)-2,4-nonadienal, eugenol, ethyl hexanoate and phenylacetaldehyde were not only the aroma-active compounds in Guilin Huaqiao white sufu, but also played an important role in enhancing the umami aftertaste and palatability of umami solution because of the congruency of the aroma and umami taste.

Influences of fermentation and ripening temperatures on the enzymatic activity and physicochemical and sensory properties of salted egg white sufu.

This study developed a novel form of sufu. Salted egg white sufu (SEWS) was produced by fermenting steamed salted egg white with douchi koji and ripening at 25°C, 35°C, or 45°C for 19days. The results show that the protease activity of the koji reduced pronouncedly during fermentation, whereas the one in the SEWS initially increased but subsequently decreased. The total nitrogen and amino nitrogen contents and degree of protein hydrolysis increased during fermentation and decreased during preripening. SEWS, particularly processed at 35°C, contained more free amino acids, notably glutamic acid and leucine, than steamed salted egg white did. After processing, SEWS had darker colors, particularly when manufactured at higher temperatures, and hardness and springiness decreased. The 35°C and 45°C SEWS had higher sensory acceptability. In conclusion, ripening at 35°C for 19days is recommended for producing this novel animal protein-based sufu.

Characterization of the Changes in Opened Sufu Bottles During Storage with Mathematical Model

Artificial Neural Network (ANN) is a type of nonlinear empirical model, which can clarify the complex relation between the inputs and outputs that allows it to approximate any nonlinear function for making predictions. The objective of this study is to monitor the Biogenic Amines (BAs) content and selected physicochemical properties of sufu (a traditional Chinese fermented soybean product) along time. Simultaneously, based on initial values, a grey model and an ANN were developed to predict the influence of storage process parameters on the quality changes during storage. Results revealed that the total amounts of BAs in newly opened bottles of white, red and grey sufu were 419.61, 311.52 and 603.10 mg kg-1, respectively, no sufu samples posed the total biogenic amines tolerance level (over 1000 mg kg-1). Results showed that slight changes in the individual BAs were detected at 4°C, 15°C, 25°C and the formation of BAs was promoted at 35°C in grey sufu. Furthermore, grey model was developed with average relative errors within ±7%, the statistical parameters (R2) of pH, water activity and amino nitrogen was all above 0.90. In the ANN, the number of neurons in the hidden layer was optimized, ten neurons revealed a positive correlation between the values obtained experimentally and those predicted values (R2 = 0.99). So ANN with highest R2 was selected to predict biogenic amines and our results demonstrated that grey sufu were not edible on the 25th days at 4°C (BAs＞ 1000 mg kg-1) and it would be better if white and red sufu are consumed within 40 days. We envision that our works can be used for proving a reference for consumers and offer new perspectives by mathematical model to avoid difficult, costly and time-consuming quality inspection, particularly in the field of storage.

Changes in bioactive compounds and their relationship to antioxidant activity in white sufu during manufacturing

SummaryIn this article, samples of white sufu were collected at different manufacture stages and their content of water‐soluble protein (WSP) and amino nitrogen (AN); the distribution of peptides in WSP and isoflavones, as well as the antioxidant activities, was analysed. Results indicated that the peptides with molecular weight of 500–1000 Da increased 13.09 times from 0.11 to 1.44 g 100 g−1 dry matter (DM) during the whole manufacturing, while isoflavone glucosides were almost entirely converted to aglycones after ripening for 15 days. Ferric reducing power (FRAP) and 2,2′‐azinobis‐3‐ethylbenzothiazoline‐6‐sulphonic acid radical scavenging activity (ABTS RSA) were significantly increased by 2.80‐ and 1.60‐fold, respectively. Correlation analysis suggested that ABTS RSA was significantly related to WSP (especially for the 500–1000 Da peptides; P &lt; 0.01) and the content of aglycones (P &lt; 0.05), while FRAP was only correlated to WSP (P &lt; 0.05). It is concluded the peptides were the most important components contributing to the antioxidant activities of sufu.

Safety assessment of the biogenic amines in fermented soya beans and fermented bean curd.

To evaluate the safety of biogenic amines, high performance liquid chromatography (HPLC) was used to evaluate the levels of biogenic amines in fermented soya beans and fermented bean curd. In fermented soya beans, the total biogenic amines content was in a relatively safe range in many samples, although the concentration of histamine, tyramine, and β-phenethylamine was high enough in some samples to cause a possible safety threat, and 8 of the 30 samples were deemed unsafe. In fermented bean curd, the total biogenic amines content was more than 900 mg/kg in 19 white sufu amples, a level that has been determined to pose a safety hazard; putrescine was the only one detected in all samples and also had the highest concentration, which made samples a safety hazard; the content of tryptamine, β-phenethylamine, tyramine, and histamine had reached the level of threat to human health in some white and green sufu samples, and that may imply another potential safety risk; and 25 of the 33 samples were unsafe. In conclusion, the content of biogenic amines in all fermented soya bean products should be studied and appropriate limits determined to ensure the safety of eating these foods.

Investigation of biogenic amines in sufu (furu): A Chinese traditional fermented soybean food product

This study was carried out to investigate the biogenic amine content and chemical properties of sufu (furu, in Chinese mandarin), a traditional cheese-like fermented soybean food product produced in China. Thirty-eight samples of sufu collected from the retail market and factories, which had been manufactured in various regions in China, were divided into white, red and grey sufu according to the dressing mixtures used for maturing the product. The biogenic amines and chemical properties exhibited large variations among samples of the same type and brand. Moreover, no consistent significant correlation between the biogenic amines and the chemical properties among the three types of sufu was observed. At least five of the ten biogenic amines studied were found in each type of sufu. In the three types of sufu, putrescine and cadaverine were the most commonly found biogenic amines, and putrescine and tyramine were those in the largest proportions. Serotonin and agmatine were not detected in any sample. The mean total biogenic amine content in grey sufu (570.5 ± 386.4 mg/kg, wet weight basis) was higher than that in white sufu (153.6 ± 160.2 mg/kg) and red sufu (10.9 ± 11.6 mg/kg). Five out of 28 white sufu samples posed histamine intoxication risk (over 50 mg/kg). Therefore, avoidance of excessive consumption of sufu on a regular basis is recommended. The findings suggest sufu should be manufactured under strict hygienic conditions to minimize the biogenic amine content of sufu and its associated risks to health.

Amino acid profiles of sufu, a Chinese fermented soybean food

Sufu is a Chinese soybean cheese-like product obtained by solid-state fungal fermentation and ripening of tofu. The resulting “pehtze” is salted, followed by maturation in brine. Total (TAA) and free amino acid (FAA) profiles were determined during consecutive stages of sufu manufacture, i.e., tofu, pehzte (fungal fermented tofu), salted pehtze and in white, red and grey sufu, ripening in dressing mixtures of different salt content (8%, 11%, and 14% w/w). TAA in tofu, pehtze and salted pehtze totalled 547, 551 and 351 mg/g dry matter, respectively. FAA increased from total 1.3 to 15.6 mg/g dm in pehtze after fermentation of tofu by Actinomucor elegans and to 11.9 mg/g dm in salted pehtze. During ripening up to 80 days, total FAA in red sufu increased from 28 to 88 mg/g (8% salt), 28–63 mg/g (11% salt) or 26–42 mg/g (14% salt). In white sufu the levels of FAA were generally higher and the effect of salt was less inhibitory. Levels of FAA in white sufu increased in 80 days from 33 to 104 mg/g (8% salt), 27–92 mg/g (11% salt) and 19–73 mg/g (14% salt). The pattern of essential amino acids compared favourably with those of eggs and cow's milk. While FAA increased during ripening of red and white sufu, the ratio of each amino acid remained essentially constant, and glutamic acid, leucine, aspartic acid, alanine, phenylalanine and lysine were found in large quantities. However, in grey sufu the ratio was different, with large proportions of leucine, alanine, isoleucine, valine and phenylalanine found after ripening.

Radical-Scavenging Activity and Isoflavone Content of Sufu (Fermented Tofu) Extracts from Various Regions in China

Water extracts and 50% ethanol extracts of 14 samples of sufu (fermented tofu) produced in various regions of China were prepared, and their DPPH (α,α-Diphenyl-β-pricryl-hydrazyl) radical-scavenging activity and isoflavone content were determined. Although the extracts showed different radical-scavenging activity levels depending on their color and region of production, all contained highly active components. Radical-scavenging activity in the water extracts ranged from 2.03 to 11.93 μg α-tocopherol/mg, while that for the 50% ethanol extracts ranged from 2.14 to 14.62 μg α-tocopherol/mg. Radical-scavenging activity in extracts from grey sufu was higher than that found in red or white sufu. Samples from the same regions showed similar radical-scavenging activity, but there was no clear directional tendency (north/south, east/west) for the produced sufu to have high activity. Most of the isoflavone in sufu was shown to be in the form of aglycone. Isoflavone aglycones in water extracts ranged from 50.2 to 179.3 μg/g of dry matter, and that in 50% ethanol extracts ranged from 199.0 to 706.9 μg/g of dry matter.

Effect of NaCl on textural changes and protein and lipid degradation during the ripening stage of sufu, a Chinese fermented soybean food

AbstractSufu is made by solid state fungal fermentation (using Actinomucor elegans) of tofu, followed by salting and maturation in dressing mixtures containing salt, alcohol and various other ingredients. NaCl in dressing mixtures strongly affected the changes in textural properties and the hydrolysis of protein and lipid of sufu. Higher salt contents (14% w/w) resulted in increased hardness (+100%) and elasticity (+18%) and reduced adhesiveness (−30%). Hardness and elasticity could be used to judge the extent of sufu ripening. SDS‐PAGE showed the disappearance of all protein subunits at 80 and 110 g kg−1 salt content; however, some protein subunits were still detectable at 140 g kg−1 salt content after 60 days of ripening. Higher ratios of free amino nitrogen to total nitrogen (FAN/TN = 0.4–0.45) and free amino acids to crude protein (FAA/CP = 0.24–0.26) were observed in sufu with lower (80 g kg−1) salt content. FAN/TN and FAA/CP in white sufu (obtained with dressing mixtures containing only salt and alcohol) were higher than those in red sufu (obtained with dressing mixtures containing angkak or kojic red rice) owing to different dressing mixture compositions. Increases in free fatty acids (FFA) were also observed during ripening. FFA levels in sufu with lower salt content increased rapidly during the first 30–40 days and then increased slowly, probably resulting from the formation of fatty acid esters. Lowering the salt content (80 g kg−1) can shorten the ripening time to 40 days, which is of benefit to manufacturers. However, sufu will spoil, ie undergo souring, during the ripening stage at salt contents of 50 g kg−1 or lower. Copyright © 2003 Society of Chemical Industry

Microbiological safety and quality of commercial sufu – a Chinese fermented soybean food

In this study, the microbiological safety and quality of commercial sufu were investigated. Twenty-three samples of three different types of sufu were obtained, mainly in China and some in The Netherlands. Chemical parameters analysed included moisture, pH, free amino N, NaCl, ethanol, sucrose, glucose, and fructose. Concentrations of NaCl, ethanol, glucose and fructose varied from 6.2%, 0.5%, 0% and 0% to 14.8%, 6.3%, 6.2% and 4.8%, respectively. Microbiological analyses were done for total count of mesophilic aerobic bacteria (TMAB), bacterial endospores, total count of halotolerant bacteria at 10% (THB10) and at 17.5% NaCl (THB17.5), lactic acid bacteria (LAB), fungi, Enterobacteriaceae, and the following pathogens: Bacillus cereus, Clostridium perfringens, Staphylococcus aureus and Listeria monocytogenes. High levels (>10 5 CFU/g) of TMAB and bacterial endospores were found in most samples, and 85% of TMAB was identified as Gram-positive. Considerable levels (10 5 and 10 7 CFU/g) of LAB were detected in two samples of white sufu, and isolates of LAB were identified as most probably Lb. casei. One-third of the samples contained less then 10 3 CFU/g B. cereus, but three samples had over 10 5 CFU/g indicating potential hazard to consumers. All samples had less than 10 3 CFU/g C. perfringens, except sample R11 (∼10 5 CFU/g). S. aureus could not be detected in any of the samples tested since the competitive microflora (usually bacilli) disturbed typical features on the selective medium used; however S. aureus enterotoxin A was detected in some of the white and grey sufu samples. Fungi, Enterobacteriaceae, and L. monocytogenes were not detected in any of the samples. Based on these results, a microbiological guideline for safe commercial sufu is proposed.