Effect of nitrate/nitrite on the quality of sausage (sucuk) during ripening and storage

The effects of nitrate/nitrite on the microbial and chemical properties and sensory quality of Turkish‐style sausage (sucuk) were investigated during 15 days of ripening and 45 days of storage. Aerobic plate count, mould and yeast count, pH, 2‐thiobarbituric acid value, residual nitrite level, nitrosomyoglobin conversion and sensory characteristics (flavour, colour and cutting scores) were monitored. Aerobic plate count increased (P < 0.05) during the first 8 days of ripening and decreased (P < 0.05) during further ripening and storage. Mould and yeast count increased (P < 0.05) during the first 4 days of ripening and decreased (P < 0.05) during further ripening and storage. Overall sensory quality increased (P < 0.05) during the first 12 days of ripening and decreased (P < 0.05) during further ripening and storage. Increasing the nitrate/nitrite concentration increased (P < 0.05) the overall sensory quality. During the first 4 days of ripening, the pH of all sausages decreased (P < 0.05) from 5.98 to 4.53–4.81, owing to the action of lactic acid bacteria. Residual nitrite level decreased (P < 0.05) sharply during the first 8 days of ripening, from 150 to about 2 mg kg^?1 in sausage samples B3 (prepared with 150 mg kg^?1 nitrite, 300 mg kg^?1 nitrate and starter culture) and from 75 to about 1 mg kg^?1 in samples B2 (prepared with 75 mg kg^?1 nitrite, 150 mg kg^?1 nitrate and starter culture). The conversion of haem pigments to nitrosomyoglobin increased (P < 0.05) during the first 12 days of ripening and decreased (P < 0.05) during further ripening and storage. Copyright © 2004 Society of Chemical Industry     

Injury,Inhibition and Inactivation ofEscherichia coli O157:H7 by Potassium Sorbate and Sodium Nitrite as Affected by pH and Temperature

The effect of potassium sorbate (0–2 g litre⁻¹) and sodium nitrite (0–1 g litre⁻¹) on the growth of four strains of Escherichia coli O157: H7 in tryptic soya broth at various pH levels (pH 4·0–7·0 for sorbate, pH 5·0–8·0 for nitrite) were determined at 37°C and 4°C. Among the pH levels tested, sorbate and nitrite exhibited the highest antimicrobial activity at pH 4·0 and 5·0, respectively. At pH 5·0 and 37°C, the presence of 500 mg litre⁻¹ sorbate or 200 mg litre⁻¹ nitrite completely inhibited the growth of E coli O157: H7. While at higher pH levels, 2 g litre⁻¹ sorbate or 1 g litre⁻¹, nitrite, the highest concentration tested, did not show significant antimicrobial action against the test organisms. At 4°C and pH 5·0, the inoculated test organisms did not showed any significant growth in preservative-free control media. Different degree of inactivation and injury was observed when E coli O157: H7 strain 933 was stored in TSB (pH 5·0) containing 1 g litre⁻¹ sorbate or nitrite at 37°C. At 4°C, inactivation and injury of E coli O157: H7 cells was not observed in the medium containing sorbate or nitrite throughout the 24 h experimental period.     

EFFECTS OF INITIAL NITRITE LEVEL, HEATING AND STORAGE ON RESIDUAL NITRITE AND SPOILAGE OF CANNED HAM ROLL

Canned ham rolls with initial nitrite levels of 0, 125, 200, 300 and 400 mg/kg were processed to an Fo of 1.07 and 1.49 and stored for 8 months. Ham rolls before processing contained 10⁵–10⁷ cfu/g total bacteria and less than 3 MPN/g of putrefactive anaerobic bacterial spores. The initial nitrite level, the storage time and the heat treatment significantly affected residual nitrite in the product. Samples stored for 1 and 3 days had significantly higher residual nitrite levels than those stored for 6–31 days. Samples processed with 0, 125 and 200 mg/kg nitrites contained significantly lowered residual nitrite levels than those formulated with 300 and 400 mg/kg nitrite. Samples heated to an Fo of 1.07 contained less residual nitrite (P ≤ 0.05) than those heated to Fo 1.49. No swelled cans were observed after 8 months of storage and the nitrosamine levels detected in the samples were lower than the safety limit proposed by Pneussman (1974).     

PRESERVATION OF FISH SPREAD WITH ENTEROCINS 1071A AND 1071B, TWO ANTIMICROBIAL PEPTIDES PRODUCED BY ENTEROCOCCUS FAECALIS BFE 1071

Enterocins 1071A and 1071B, produced by Enterococcus faecalis BFE 1071, kept the total aerobic cell numbers in fish spread between 8 × 10⁴ and 2 × 10⁵ cfu/g for the first 6 days of storage. The total aerobic cell numbers in a batch preserved with a combination of sodium benzoate (0.045%, w/w) and potassium sorbate (0.059%, w/w) remained between 8 × 10⁴ and 2 × 10⁵ cfu/g during the first 18 days of storage. In a batch containing no preservatives, cell numbers gradually increased from 1 × 10⁵ to 1 × 10⁸ cfu/g over 21 days. The spoilage organisms were identified as Staphylococcus epidermidis and atypical Proteus vulgaris. The pH of all batches remained constant over the 21‐day storage period, with minimal variations recorded in textural and organoleptic qualities. The number of microbial cells recorded in fish spread preserved with enterocins 1071A and 1071B was 8 × 10⁶ after 21 days of cold storage (4C), whereas microbial cell numbers of 1 × 10⁸ were recorded in fish spread that had not been preserved.     

Effect of Sodium Acid Pyrophosphate in Combination with Sodium Nitrite or Sodium Nitrite/Potassium Sorbate on Clostridium botulinum Growth and Toxin Production in Beef/Pork Frankfurter Emulsions

Combinations of sodium acid pyrophosphate (SAPP) with added sodium nitrite and/or potassium sorbate were tested at various pH levels to determine effectiveness in delaying Clostridium botulinum growth and toxin production in frankfurter emulsions. Formulations containing sodium nitrite (40 ppm), potassium sorbate (0.26%) and SAPP (0.4%) resulted in a greater delay of toxin production (12–18 days) than other combinations (6–12 days) having similar pH values. Treatments containing 0.4% SAPP appeared to be more inhibitory than their counterparts without SAPP, displaying less numbers of toxic samples during the 53-day storage period at 27°C. Aerobic mesophilic colony counts and residual nitrite data showed little difference among treatments.     

Defined Starter Cultures used for Fermentation of Salmon Fillets

The integration of defined starter cultures into a fish fermentation process was studied. Six lactobacilli and 5 staphylococci strains were tested in a salmon model system. Dependence of bacterial growth and pH reduction on sucrose, NaCl and sodium nitrite concentrations, and fermentation temperature was evaluated. A combination of Lactobacillus sake and Staphylococcus carnosus was then applied to whole salmon fillets to which NaCl and sucrose had been added. The influence of sucrose and NaCl concentrations, temperature and the addition of sodium nitrite on pH, color and microbiological stability was evaluated. Optimal conditions were 25g-kg^?1 NaCl, 15gkg^?1 sucrose, fermentation at 12°C for 3 days, subsequent storage at 4°C.     

亚硝酸盐添加量对西式培根贮藏期安全品质的影响

为了解亚硝酸盐添加量对西式培根产品品质及安全性的影响,在西式培根加工过程中分别按低（0.08 g/kg,low nitrite content,LNC）、中（0.12 g/kg,medium nitrite content,MNC）、高（0.15 g/kg,high nitrite content,HNC）水平添加亚硝酸盐,并设不添加亚硝酸盐的对照（control check,CK）组,测定4 组真空包装西式培根在（4±1） ℃冷藏0、5、10、15、20、50 d的感官评分、菌落总数、pH值、硫代巴比妥酸反应物（thiobarbituric acid reactive substances,TBARs）值、亚硝酸盐残留量、生物胺及N-亚硝胺含量。结果表明：贮藏期间,CK组西式培根色泽灰暗,整体外观较差,而HNC、MNC和LNC组色泽美观,贮藏50 d时,MNC组仍能保持枣红色,香味浓郁,感官评分最高。随着贮藏期的延长,4 组产品的各项指标变化有所不同,菌落总数在2.0～2.5 （lg（CFU/g））波动,后期缓慢增长至4.0 （lg（CFU/g））;pH值和TBARs值先缓慢降低后升高,HNC组的TBARs值一直保持最低值;亚硝酸盐残留量从高到低依次为HNC组＞MNC组＞LNC组＞CK组,在贮藏期间均呈降低趋势;生物胺含量未呈规律性变化,整体处于安全水平;各组N-亚硝胺形成量随贮藏期延长整体呈降低趋势,N-二甲基亚硝胺（N-nitrosodimethylamine,NDMA）检出量随亚硝酸盐添加量增加而升高,MNC和HNC组的NDMA含量均超过3.0 μg/kg的限量。由此说明,亚硝酸盐添加量影响西式培根的安全性,在保证西式培根产品品质及安全的前提下,亚硝酸盐添加量应低于0.12g/kg。     

Supercritical CO<Subscript>2</Subscript> extraction of <Emphasis Type="Italic">Alkanna</Emphasis> species and investigating functional characteristics of alkannin-enriched yoghurt during storage

Alkannin is a potent pharmaceutical substance with a wide spectrum of biological activities. In the scope of this study, supercritical CO₂ extraction and sonication with hexane were applied to various Alkanna species, which were then subjected to hydrolysis. Total alkannins were quantified by HPLC/DAD and incorporated into yoghurt. Viscosities, pH values and microbial analyses were reported at 7 days of intervals for 21 days of storage. A. tinctoria possessed the highest amounts of alkannins and total phenols (686.3 mg GAE/g extract). The results revealed no significant changes in pH values (4.1–4.0), viable counts of Streptococcus salivarius ssp. thermophilus (80–150 × 10⁶ cfu g⁻¹) and slightly lower viscosities of enriched yoghurts (8,250–6,750 cPs) compared with the control (4.15–4.0; 110–105 × 10⁶ cfu g⁻¹; 12,600–11,310 cPs) during storage. However, viable counts of Lactobacillus delbrueckii ssp. bulgaricus of enriched yoghurts (87 × 10³ cfu g⁻¹) were much better than the control (191 × 10³ cfu g⁻¹), indicating a significant decrease in post acidification and generation of bitter peptides. Among the species investigated, A. tinctoria is the most promising source, obtained at higher yields via supercritical fluid extraction technology as a green alternative to solvent extraction and thus can be utilized at industrial scale in order to develop yoghurt products with improved health benefits.     

Effectiveness of Zataria multiflora Boiss essential oil and grape seed extract impregnated chitosan film on ready-to-eat mortadella-type sausages during refrigerated storage

BACKGROUND: The effectiveness of chitosan films containing Zataria multiflora Boiss essential oil (ZEO) (5 and 10 g kg^?1) and grape seed extract (GSE) (10 g kg^?1) on lipid oxidation and microbial (lactic acid bacteria, aerobic mesophiles and inoculated Listeria monocytogenes) characteristics of mortadella sausage at 4 °C for 21 days was evaluated. The release of total phenolics (TPs) into sausage was also assessed. RESULTS: All films exhibited antibacterial activity against L. monocytogenes on agar culture media. Chitosan films containing ZEO were the most effective on the growth of bacteria. The growth of L. monocytogenes was significantly inhibited by ZEO‐GSE containing films especially during storage of the sausages for 6 days. Aerobic mesophiles and lactic acid bacteria were the most sensitive and resistant groups to films by 0.1–1.1 and 0.1–0.7 log cycles reduction, respectively. Sausages wrapped by 10 g kg^?1 GSE + 10 g kg^?1 ZEO films had the lowest degrees of lipid oxidation, which was 23% lower than the control. The TPs of ZEO films decreased to zero after 6 days, whereas TPs of GSE films followed a slight decrease during the storage. CONCLUSION: Antimicrobial/antioxidant chitosan film could be developed by incorporating GSE and ZEO for extending the shelf life of mortadella sausage. Copyright © 2011 Society of Chemical Industry     

Effects of salt, acid, and MSG on cold storage survival and subsequent acid tolerance of Escherichia coli O157:H7

The combined effects of salt, monosodium glutamate (MSG), and pH on cold storage survival and subsequent acid tolerance of Escherichia coli O157:H7 were determined. Cold storage survival was evaluated in tryptic soy broth (TSB) with combinations of pH (7.2, 5.0, or 4.0), MSG (0, 0.5, 1%) and salt (0, 2, 4%). Survival through 21 d at 5°C and acid tolerance in simulated gastric fluid were evaluated weekly. In separate experiments, strains were tested individually for the effect of growth in the presence of MSG on subsequent acid resistance and for the ability of MSG to impact growth under acid conditions. The impact of salt on cold storage survival was greater at pH 4.0 and 7.0 compared to pH 5.0. MSG did not enhance cold storage survival. The presence of MSG alone enhanced acid tolerance following cold storage at pH 5.0 and 7.2 compared to control cells. At pH 4.0, MSG alone enhanced acid tolerance compared to control cells following 21 days cold storage. Overnight growth in TSB containing MSG did not affect subsequent acid tolerance in acidified TSB (pH 2.0). The presence of MSG in TSB (37°C) did not enable growth at lower pH.     

EXPOSURE TIME ON BACTERIA FLORA/COUNT AND SHELF LIFE OF CANNED SARDINE (SARDINELLA PILCHARDUS) UNDER AMBIENT AND COLD STORAGE CONDITIONS

This study is aimed at investigating the exposure time on bacteria flora/count and shelf life of conned sardine (Sardinella pilchardus) under ambient and cold storage conditions. Twenty‐five cans with an average weight of 165.05 g of the Titus (with an expiration date of 4 years (September 30, 2004 to September 30, 2008 of batch no. 1432) were purchased and stored at the ambient temperature of 27C and cold (?4C) storage conditions as samples for 12 weeks (precisely between June 15 and September 10, 2005 when the experiment lasted). Proximate analysis of the samples was taken at the beginning of the experiment and at the end for both the ambient and cold stored (after an exposure time of 24 h). Initial baseline and biweekly studies were carried out for 12 weeks for: (1) organoleptic (odor, taste, texture, appearance, rigidity of flesh, color and reaction of fish with can); (2) chemical (trimethylamine [TMA], peroxide values [PVs] and thiobarbituric acid [TBA]); and lastly (3) microbiological analysis for bacteria count and identification of the bacteria on the samples from each storage environment after an exposure time of 24 h in each case. All the chemical parameters (TMA, TBA and PV) were significantly (P < 0.05) correlated with exposure/storage time. Correlation coefficients r = 0.60, 0.66 and 0.54 were low in all classes therefore indicating spoilage rate increases slightly with exposure time/storage period. The highest PV (0.023–0.715), TBA (0.057–1.056) and TMA (1.01 × 10³–3.63 × 10³) ranges were recorded for canned sardines stored at ambient temperature of 27C. However, these are still within acceptable tolerance limit (i.e., organoleptic score of 4–7). Organoleptic assessment with average scores of 5.5 and 6.0 was recorded for cold and ambient stored samples. No viable bacteria count was recorded for cold‐stored samples throughout the experiment. However, the range initial 1.0 × 10⁵ and final 5.0 × 10⁴ cfu/g total plate counts recorded for ambient storage were still below the minimum bacteria count for spoilage that could cause significant or deleterious effect that could result in food poisoning. Traces of the following bacterial species were recorded at ambient temperatures: (1) Bacillus subtilis (1.2 × 10⁴ cfu/g); (2) Streptococcus faecium (9.0 × 10³ cfu/g); (3) Proteus vulgaricus (7.0 × 10⁵ cfu/g); (4) Pediococcus halophilus (6.0 × 10⁵ cfu/g); (5) Micrococcus acidophilus (4.0 × 10³ cfu/g); (6) Streptococcus lactis (4.0 × 10³ cfu/g); and (7) Aerobacter aerogenes (4.0 × 10³ cfu/g), while fungal species Aspergillus terreus (1.0 × 10³ cfu/g) and Aspergillus niger (3.0 × 10³ cfu/g) were recorded also for samples stored at ambient temperature of 27C. Hence, in view of this, the 4‐year recommended expiration date may be upheld for canned sardine (S. pilchardus fish products in oil sources) provided the hazard analysis and critical control points, and closely monitored. It is, therefore, recommended that exposure of canned sardine in oil should not exceed 12–24 h under whatever food storage temperatures to avoid food poisoning.     

Quality Assessment of Tiger Tooth Croaker (Otolithes ruber) During Ice Storage

Quality and shelf life of tiger tooth croaker (Otolithes ruber) during 19 days of iced storage were investigated in terms of sensory, chemical (total volatile basic nitrogen (TVB-N), thiobarbituric values (TBA), peroxide value (PV), free fatty acid (FFA), and pH) and microbiological (total viable count, TVC and total psychrotrophic count. TPC) aspects. Acceptability quality of Tiger tooth croaker determined by panelists was 15–17 days. Limiting factors for acceptability were eye, gills, peritoneum, smell of gills and abdominal cavity, internal organs and flesh. Bacterial loads in samples were higher than limiting level (3 × 10⁶ CFU g^?1) between 15–17 days of ice storage. Of the chemical indicators of spoilage, the initial value of pH was 6.71 and increased to 7.35 at the end of storage. TVB-N content was 15.31mg N/100g on day 0 and reached to 36.52 on day 19. The acceptability of tiger tooth croaker decreased as FFA, PV and TBA values increased (P < 0.05). The release of FFA increased from an initial value of 4.15 (expressed as % of oleic acid) to a final value of 12.75 during the storage period. The initial PV value was 11.69 meq/kg and it increased to 50.75 meq/kg on day 12 and then started to decrease to 35.82 meq/kg at the end of storage period. The initial and final values of TBA were 0.83 and 3.75, respectively.     

Quality maintenance of minimally processed Chinese cabbage with low temperature and citric acid dip

Chinese cabbage (Brassica campestris L pekinensis group) was minimally processed using best preparation techniques and stored at 0 and at 5°C with and without dips in either citric acid, calcium chloride or ascorbic acid, all at 10 g litre⁻¹. The visual quality, degree of chilling injury, pH and taste were evaluated. The most deleterious effects on quality were produced by black speck (gomasho) and browning. Citric acid inhibited the development of black speck and extended storage life from 10 days of the control to 14 days at 5°C. At 0°C the storage life was not extended by any dip, but citric acid improved quality by reducing black speck. Minimally processed Chinese cabbage treated with citric acid showed only a slight reduction of pH from 6·3 of the control to 6·1 (P⩽0·05) and taste was not significantly affected (P>0·05). Microbial spoilage was not apparent during storage at 0°C for 35 days and 5°C for 21 days under any treatment. © 1997 SCI.     

Bacteria Associated with Spoilage of Braunschweiger

Refrigerated braunschweiger was spoiled mainly by Gram positive, catalase negative coçci identified as Streptococcus faecalis and Pediococcus pentosaceus. P. pentosaceus was isolated from sausage without nitrite held at refrigeration for 12 wk and from sausages made with 156 ppm nitrite stored at 22°C for 21 days. It produced souring and a low pH in the sausage. S. faecalis was isolated from refrigerated sausages and produced a perfumy or scented odor under anaerobic conditions. S. faecalis survived 65°C for 5 min and 60°C for 60 min. P. pentosaceus at levels of 10⁸ cells/ml of broth survived 65°C for 5 min but did not survive when the number of cells was 10³/ml.     

Modelluntersuchungen zu Bedingungen der Bildung vonN ε-Carboxymethyllysin in Lebensmitteln

In model experiments with equimolar mixtures of lysinemonohydrochloride and glucose [88% (w/v) water content, 100° C heating temperature] the influence of several conditions (hydrolysis, pH) and ingredients (iron, phosphate, and nitrite) on the formation ofN ^ε-carboxymethyllysine (CML) were evaluated. CML was analysed using a reversed-phase HPLC-method after derivatisation witho-phthaldialdehyde. CML, which is an oxidative derivative of fructoselysine, is also formed during the acid hydrolysis applied for amino acid determination in food products. In model mixtures without hydrolysis only 8–21% CML compared to that in hydrolysed samples was found. Therefore, in food products all hydrolyses for CML must be performed after borohydride reduction in order to destroy fructoselysine. This can be controlled by the determination of furosine. The pH of the model mixtures considerably influenced the formation of CML. At pH 4.0 only 70 mg, at pH 7.0 370 mg, and at pH 9.0 3170 mg CML/kg lysine were determined. The CML concentration also clearly increased with higher concentrations of iron, phosphate, and nitrite. This is explained by a promoting effect on the oxidation of fructoselysine to CML.     

THE ROLE OF BACILLUS spp. IN N-NITROSAMINE FORMATION DURING WORT PRODUCTION

The relative importance of bacterial and acid catalysed formation of Apparent Total N-Nitrosocompounds (ATNC) and N-nitrosodimethylamine (NDMA) following reduction of nitrate by a strain of Bacillus coagulans was investigated. The bacterium was isolated from the brewhouse and could grow and reduce nitrate at temperatures up to 70°C. Although evidence of thermophilic denitrification was observed, the predominant end products of nitrate reduction were ammonia and nitrous oxide. Bacterial catalysis of ATNC formation in sweet wort at pH 5.3 coincided with high nitrate and nitrite reductase activities and was, at 741 μg h^?1 (mg cell protein)^?1, three times faster than would be expected due to acid catalysis alone. The formation of NDMA at pH 7.8 was 300–500 times faster in the presence of nitrite than in the presence of nitrate possibly implicating the involvement of nitrite reductase .     

Effects of modified atmosphere packaging with different sizes of silicon gum film windows on Salicornia bigelovii Torr. storage

BACKGROUND: Salicornia bigelovii Torr. is a promising seasonal plant using seawater production but perishable with short shelf‐life under ambient conditions. To develop a modified atmosphere packaging (MAP) for extension of S. bigelovii shelf‐life, a nonselective polyethylene/polyamide (PE/PA) bag combining different sizes (0.6, 1.0 and 1.4 cm²) of silicon gum film (SGF) windows was tested, and low‐density polyethylene (LDPE) and perforated (1.0 cm²) PE/PA bags were used as controls. RESULTS: During 36 days of storage at 2 °C, the equilibrium compositions of O₂/CO₂ in LDPE, SGF1 (0.6 cm²), SGF2 (1.0 cm²) and SGF3 (1.4 cm²) were 3.0–5.0/4.5–6.5 kPa, 0.5–1.5/8.5–19.0 kPa, 2.5–5.0/5.5–10.0 kPa, and 6.0–13.0/4.0–6.5 kPa, respectively. Passive MAP treatments improved the quality attributes of S. bigelovii during initial storage; however, the 0.6 cm² SGF package markedly accelerated deterioration over the latter storage. The 1.0 cm² SGF package was observed to provide the optimal condition for S. bigelovii storage. CONCLUSION: The results show that passive MAP with optimized sizes of SGF windows could be an effective technique for prolonging shelf‐life of S. bigelovii. Copyright © 2009 Society of Chemical Industry     

In vitro antioxidant activity of papain‐treated grass carp (Ctenopharyngodon idellus) protein hydrolysate and the preventive effect on fish mince system

Antioxidant activities of papain‐treated grass carp protein hydrolysate (HP) were investigated using in vitro methods and in grass carp mince system. Lipid oxidation, colour changes and cooking loss in grass carp mince added with 0% (control), 0.5%, 1.0%, 2.0% and 4.0% HP during refrigerated storage (4 °C) for 8 days was studied. HP could chelate 50% of Fe²⁺ and scavenge 50% of hydroxyl radicals at the concentration of 0.81 and 8.12 mg mL^?1, respectively. And HP could effectively decrease peroxide values and inhibit the formation of thiobarbituric acid reactive substances in fish mince throughout storage (P < 0.05), at the application level range from 0.5% to 4.0%. In HP‐treated samples the formation of conjugate dienes (CDs) was retarded 5–30% at day 6 of storage compared to control. In addition, HP could significantly decrease cooking loss of fish mince samples, at the application level range from 1.0% to 4.0%.     

Saccharomyces cerevisiae Biodiversity During the Brewing Process of an Artisanal Beer: A Preliminary Study

In this study we investigated the biodiversity of Saccharomyces cerevisiae during the brewing of an artisanal beer, as well as during its storage in the bottle for 107 days at 20°C. After inoculation with an active dried yeast (ADY), the yeast counts were followed during fermentation and after bottling. Yeast loads remained stable at 10⁶–10⁷ colony forming units (cfu)/mL, and only after day 21, were they were reduced to 10⁴ cfu/mL. After three months in the bottle they spanned 10²–10⁵ cfu/mL. Almost all isolated yeasts were identified as S. cerevisiae and after molecular characterization, unexpected results were obtained. The ADY did not take over the fermentation process and only after 21 days did isolates from the beer share similarities with the inoculated strain. During storage, a high diversity was found, underlining that each bottle developed its own micro‐ecosystem. This study highlighted the necessity for better investigations of S. cerevisiae population dynamics during artisanal brewing. Even when the chemical parameters measured confirmed a correct fermentation process, the inoculated strain was not the main yeast involved in the fermentation and consequently, the final product may have different sensory characteristics from the ones expected by the producers.     

Expression and characterization of β-1,3-1,4-glucanase of Aspergillus usamii in Escherichia coli and its application in sourdough bread making

A β-1,3-1,4-glucanase gene (Auglu12A) from Aspergillus usamii was successfully expressed in Escherichia coli BL21(DE3). The recombinant enzyme, reAuglu12A was efficiently purified using the one-step nickel-nitrilotriacetic acid affinity chromatography. The specific activity of reAuglu12A was 694.8 U/mg, with an optimal temperature of 55°C and pH of 5.0. The reAuglu12A exhibited stability at temperatures up to 60°C and within the pH range of 4.0–5.5. The reAuglu12A hydrolytic activity was increased in the presence of metal ions, especially K⁺ and Na⁺, whereas it exhibited a K_m and V_max of 8.35 mg/mL and 1254.02 µmol/min/mg, respectively, toward barley β-glucan at pH 5.0 and 55°C. The addition of reAuglu12A significantly increased the specific volume (p < 0.05) and reduced crumb firmness and chewiness (p < 0.05) of wheat–barley sourdough bread during a 7-day storage period compared to the control. Overall, the quality of wheat–barley sourdough bread was improved after incorporation of reAuglu12A (especially at 3000 U/300 g). These changes were attributed to the synergistic effect of acidification by sourdough and its metabolites which provided a conducive environment for the optimal action of reAuglu12A in the degradation of β-glucans of barley flour in sourdough. This stabilized the dough structure, thereby enhancing the quality, texture, and shelf life of the bread. These findings suggest that reAuglu12A holds promise as a candidate for β-glucanase application in the baking industry.