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• Fermentation conditions were optimized for protease production. • L. fermentum R6 protease had activity at pH 6 and 40 °C. • L. fermentum protease can hydrolyse myofibrillar and sarcoplasmic proteins. This study investigated the purification and biochemical characterization of the protease produced by Lactobacillus fermentum R6 isolated from Harbin dry sausages. The optimized fermentation conditions were as follows: a fermentation time of 48 h, an initial pH of 6 and a fermentation temperature of 37 °C. The 37.7 kDa extracellular protease was purified using ammonium sulphate deposition, an ion exchange layer system and gel filtration. The protease produced by L. fermentum R6 had the highest initial velocity and k cat / K m at pH 6, 40 °C. The microbial protease activity could be inhibited by ethylene diamine tetraacetic acid disodium salt (EDTA). The V max and K m of the protease were 58.2 ± 1.42 mg/min and 17.3 ± 0.85 mg/mL, respectively. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) reflected the ability of the protease to hydrolyse myofibrillar and sarcoplasmic proteins, in particular, myosin heavy chain, paramyosin, phosphorylase and creatine kinase-M type. In conclusion, L. fermentum R6 can be used as a starter culture or an enzyme-producing strain for the inoculation of Harbin dry sausages. [ABSTRACT FROM AUTHOR]

The effects of partially replacing NaCl with sodium substitutes (SS) on the lipid and protein oxidation and flavor development of Harbin dry sausage was investigated. There were three salt formulations, including a control (100% NaCl), NaCl partially substituted with KCl (SS1) (70% NaCl and 30% KCl), and NaCl partially substituted with KCl combined with other components (SS2) (70% NaCl, 20% KCl, 4% lysine, 1% alanine, 0.5% citric acid, 1% Ca-lactate and 3.5% maltodextrin). The levels of lipid and protein oxidation increased in all sausages during fermentation (P < 0.05). In addition, lower oxidation of lipids and proteins were found in the SS2 treatment (P < 0.05) due to the lower NaCl concentration. The SS, especially the SS2, promoted the formation of volatile compounds originated from carbohydrate and amino acid metabolism, β-lipid oxidation and esterification; however, this substitute inhibited the formation of volatile compounds originated from lipid autooxidation (P < 0.05). Overall, SS2 could improve the flavor development of Harbin dry sausage and reduce NaCl by 30%. • Sausage with sodium substitute SS2 had a higher water activity and a lower pH. • Sodium substitute (SS) reduced the lipid and protein oxidation in dry sausages. • SS promoted the formation of 3-hydroxy-2-butanone, 1-octen-3-ol and ethyl acetate. • SS reduced 30% NaCl and improved the flavor in Harbin dry sausage. [ABSTRACT FROM AUTHOR]

This study investigated the purification and biochemical characteristics of the protease produced by Pediococcus pentosaceus isolated from Harbin dry sausages. The optimized fermented conditions were as follows: fermentation time 36 h, initial pH 5 and fermentation temperature 30 °C. A 29.6 kDa extracellular protease was purified using ammonium sulphate deposition, ion exchange layer system and gel filtration. The protease produced by P. pentosaceus had a certain pH and thermal stability at pH 6 and 30 °C. The microbial protease activity could be inhibited by ethylene diamine tetraacetic acid disodium salt (EDTA). V max and K m of the protease were 43.9 mg/min and 8.3 mg/mL, respectively. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) reflected the ability of the protease to hydrolyse sarcoplasmic and myofibrillar proteins, particularly those of myosin heavy chain, paramyosin, actin, phosphorylase and creatine kinase-M types. 3D structure modelling of the P. pentosaceus protease found two domains in the protease protein and the correlation of the active sites with protease properties and substrate specificity. In conclusion, P. pentosaceus can be used as a starter culture or enzyme producing strain for inoculation in Harbin dry sausages. • Fermentation conditions were optimized for the protease production from strain. • Enzymatic properties of the purified protease were investigated. • P. pentosaceus protease can hydrolyse myofibrillar and sarcoplasmic protein. • P. pentosaceus protease structures were simulated by homology modelling. [ABSTRACT FROM AUTHOR]

The effect of partial replacement of NaCl by using sodium substitutes (SS) on the physical, microbial and sensory characteristics of Harbin dry sausage was investigated. There were three salt formulations, including control (100% NaCl), NaCl partly substituted by KCl (SS1) (70% NaCl and 30% KCl), and NaCl partly substituted by KCl combined with other components (SS2) (70% NaCl, 20% KCl, 3.5% maltodextrin, 4% L-Lys, 1% L-Ala, 0.5% citric acid and 1% Ca-lactate). After a 12-day fermentation, the higher moisture content and Aw and lower pH were found in the SS2 treatment, compared to the control and SS1 treatments (P <.05). A decreased microbial diversity during fermentation was found in all sausages, and Staphylococcus spp. and Lactobacillus spp. became the dominant genera. Additionally, the SS2 treatment showed a higher L *-value and lower hardness and chewiness values (P <.05). Therefore, the formulation of SS2 could achieve a NaCl reduction of 30% in Harbin dry sausages with a better sensory acceptability. • Sausages with sodium substitutes had higher moisture content and water activity. • Lactobacillus and Staphylococcus became the dominant bacteria in the sausages. • Sodium substitute SS2 could replace 30% NaCl in Harbin dry sausage. [ABSTRACT FROM AUTHOR]

The traditional dry sausage is highly appreciated in China because of its unique flavor characteristics. This study aimed to characterize and compare the flavor profile of traditional dry sausage, inoculated with lactic acid bacteria (LAB), including Lactobacillus plantarum MDJ2, Lactobacillus sakei HRB10, Lactobacillus curvatus SYS29, Weissella hellenica HRB6, and Lactococcus lactis HRB0 using headspace solid-phase microextraction gas chromatography-mass spectrometry coupled with electronic nose (E-nose). The control (non-inoculated) sausage presented higher water activity and moisture content compared to the inoculated sausages whereas, the inoculation led to decreased pH values and increased LAB counts during fermentation of dry sausages. Inoculation with LAB increased volatile compound contents and decreased total contents of free amino acids of sausages. E-nose and sensory analysis confirmed that inoculation with LAB, especially W. hellenica HRB6, Lb. sakei HRB10, and Lb. curvatus SYS29 enriched the pleasant odors of dry sausage. Correlation analysis demonstrated that sausages inoculated with W. hellenica HRB6 and Lb. sakei HRB10 showed a correlation with most of the key volatile compounds. In conclusion, W. hellenica HRB6 and Lb. sakei HRB10 are promising starter cultures to enhance the flavor characteristics of dry sausages. • Seventy-four volatile compounds were detected in dry sausages. • The discrimination of E-nose corresponded well to the sensory results. • Sensory characteristics correlated with the key volatile compounds. • Most of the key volatile compounds were positively associated with phenylalanine. • Lb. sakei HRB10 and W. hellenica HRB6 could improve the flavor of dry sausage. [ABSTRACT FROM AUTHOR]

[Display omitted] • L. curvatus , W. hellenica , and L. plantarum promoted free amino acid release. • The E-tongue result was consistent with the sensory evaluation by PLSR analysis. • The taste compounds were correlated to the sensory properties using PLSR analysis. • W. hellenica and L. plantarum could improve the taste of reduced-salt dry sausage. The purpose of this study was to investigate the effects of lactic acid bacteria (LAB) including Lactobacillus curvatus , Lactobacillus sakei , Weissella hellenica , and Lactobacillus plantarum on the taste profiles of reduced-salt dry sausage. The results showed that the inoculation of LAB increased the moisture content and water activity and decreased the pH values of the sausages. Higher contents of total free amino acids (FAAs) were observed in the inoculated sausages (P < 0.05), especially for the sausages inoculated with L. curvatus , W. hellenica , and L. plantarum. The sausage inoculated with W. hellenica also had higher contents of organic acids than the other sausages (P < 0.05). In addition, partial least squares regression analysis demonstrated that the taste properties characterized by electronic tongue were consistent with the sensory evaluation results, and FAAs and organic acids contributed to the taste properties of the reduced-salt dry sausage. These results highlight the potential of W. hellenica and L. plantarum for the production of reduced-salt dry sausage with improved taste profiles. [ABSTRACT FROM AUTHOR]

The effects of different sodium substitutes on the physical and bacterial properties, flavour profile and sensory evaluation of dry fermented sausage were investigated. There were three different salt formulations, including control (C: 100%NaCl), S1 (70%NaCl and 30%KCl) and S2 (70%NaCl, 20%KCl and 10% flavour enhancers). Higher moisture content and lactic acid bacteria count, and lower pH and Staphylococcus count were observed in NaCl substitution treatments compared to the control (P < 0.05). Sixty-two volatiles were detected in sausages, and 26 compounds were regarded as key volatile compounds based on the odour activity values. The electronic tongue result and sensory evaluation showed that the taste profile of S2 treatment was similar to control treatment; and the electronic nose, volatile compound results and hierarchical cluster analysis showed that the sodium substitutes had a more significant effect on the odour profile. Overall, S2 may be an ideal low-sodium substitute to achieve a 30% reduction in NaCl and provide a better flavour profile of fermented sausages. • A total of 62 volatile compounds in sausages were identified using HS-SPME-GC–MS. • E-nose and E-tongue distinguished sausages with different sodium substitutes. • Sodium substitute with flavour enhancers (S2) replaced 30% of the NaCl in sausages. • Sodium substitute S2 improved the flavour development of dry fermented sausage. [ABSTRACT FROM AUTHOR]