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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]

Thirty-seven lactic acid bacteria (LAB) strains were isolated from traditional dry sausages collected from Northeast China, including Latilactobacillus sakei (29 strains), Lactiplantibacillus plantarum (4 strains), Latilactobacillus curvatus (2 strains), Weissella hellenica (1 strain), and Lactococcus lactis (1 strain). Some LAB strains had tolerance to high concentrations of sodium chloride (6%), sodium nitrite (150 mg/L NaNO 2), and acid (pH 4.0). They showed good growth and acidification properties and antimicrobial activity. Among them, five LAB strains that exhibited the best technological properties were selected and inoculated in the sausage model to explore their roles in flavor development. The contents of total free amino acids (FAAs) decreased ranging from 109.11 mg/g to 58.06 mg/g. A total of 46 volatile compounds were identified and the contents of volatile compounds increased in the sausage model during fermentation. Partial least squares regression analysis showed that Lb. sakei HRB10, Lb. plantarum MDJ2, W. hellenica HRB6, and Lc. lactis HRB0 promoted the generation of FAAs and volatile compounds in the sausage model. These findings demonstrated that the autochthonous LAB species are promising for the production of sausage with better flavor and fermentation performance. [Display omitted] • Thirty-seven LAB strains were isolated from traditional dry fermented sausages. • The selected strains exhibited high tolerance to salt, sodium nitrite, and acid. • LAB inoculation promoted free amino acid (FAA) and flavor generation. • The FAAs were responsible for the differences in the flavor of sausage models. [ABSTRACT FROM AUTHOR]

The traditional dry sausage is highly appreciated in China because of its unique quality characteristics, but it contains high salt content. Hence, this study aimed to evaluate the effects of lactic acid bacteria (LAB) comprising Lactobacillus sakei (LS), Lactobacillus curvatus (LC), Lactobacillus plantarum (LP), and Weissella hellenica (WH) on the quality attributes of the reduced-salt dry fermented sausages. The results indicated that the LP sausage showed higher (P < 0.05) shear force value compared to the other sausages, while the LP, LC, and WH sausages had higher (P < 0.05) lightness values than the control sausages. Seventy-six volatile compounds were detected, and nine compounds were identified as the key differential volatile compounds among the sausages based on partial least squares discriminant analysis. Clustering analysis of electronic nose results corresponded well to the volatile compound results. The sensory evaluation confirmed that the inoculation with LC and LP had a positive impact on the aroma, color, and hardness attributes of the reduced-salt sausages. Besides, partial least squares regression analysis further indicated that L. curvatus and L. plantarum could be used as the potential starter cultures to manufacture reduced-salt dry fermented sausage having improved texture, color, and flavor. [Display omitted] • The LP sausage shows higher shear force value compared to the other sausages. • The LP, LC, and WH sausages have higher lightness values than the control sausages. • Seventy-six volatile compounds are detected in dry fermented sausage. • Sensory attributes correlate with the key volatile compounds using PLSR analysis. • L. curvatus and L. plantarum can improve the quality of reduced-salt 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]

This study was to investigate the succession of the bacterial community in Harbin dry sausages during fermentation and its correlation to the sausage flavour. The results showed that Staphylococcus count increased but the moisture content and water activity decreased (P < 0.05). The lactic acid bacteria count first increased and then decreased, while the pH showed an opposite trend during a twelve-day fermentation (P < 0.05). According to a single molecule real time sequencing analysis, Lactobacillus sakei and Staphylococcus xylosus were the predominant bacterial species over the entire fermentation period. A total of 79 volatile compounds were detected using the headspace solid phase microextraction gas chromatography-mass spectrometry. Furthermore, the correlation between the core bacteria (top 30) and the major volatile compounds was explored, which highlighted that three bacterial species (Lb. sakei , S. xylosus and Weissella hellenica) were significantly correlated with the major volatile compounds, such as 2,3-butanediol, ethanol, 3-hydroxy-2-butanone, ethyl hexanoate and ethyl lactate. The results may provide a theoretical basis for improving the flavour and overall quality of dry sausage. • Lactobacillus sakei and Staphylococcus xylosus were the dominant bacterial species. • Seventy-nine volatile compounds were detected in Harbin dry sausages. • L. sakei , S. xylosus and W. hellenica were correlated with the volatile compounds. [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]

The objective of this study was to explore the correlation between bacterial communities and volatile compounds in traditional dry sausages from different regions in Northeast China. The bacterial community structure of dry sausages from five different regions as determined by high-throughput sequencing technology demonstrated that Firmicutes and Proteobacteria were the predominant phyla; Lactobacillus , Staphylococcus , Leuconostoc , Lactococcus and Weissella were the predominant genera; and Staphylococcus xylosus , Lactobacillus sakei , Weissella hellenica , Leuconostoc citreum , Lactococcus raffinolactis and Lactobacillus plantarum were the predominant species. Meanwhile, a total of 120 volatile compounds were detected in sausages from five different regions and mainly included alcohols, acids, aldehydes, ketones, esters and terpenes. Furthermore, the potential correlations between the core bacteria and major volatile compounds (64) were explored based on Spearman's correlation analysis. Positive correlations were found between W. hellenica , Lb. sakei , Lactococcus lactis , Lactobacillus alimentarius , Lb. plantarum and carboxylic acids and alcohols. Lc. lactis , Lb. alimentarius and Lb. plantarum were associated with the production of most esters, aldehydes and ketones. This study provides a deep insight into the relationship between the bacterial community and the volatile flavour profile of dry sausages, which may be helpful for the production of fermented dry sausages. Image 1 • The pdredominant phyla were Firmicutes and Proteobacteria in traditional dry sausage. • A total of 120 volatile compounds were detected in the five traditional sausages. • Five core bacteria improved the formation of volatile compounds in dry sausage. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the effects of NaCl reduction (2.5% 2.0%, 1.5% and 1.0%) on the bacterial growth, physicochemical characteristics, flavour profile and sensory traits of fermented dry sausage. The moisture content, water activity and lactic acid bacteria count increased as the NaCl level decreased (P < 0.05), contributing to decreases in pH (P < 0.05). A total of 50 volatile compounds were identified, and increases in volatile compounds, such as acetone, 3-hydroxy-2-butanone, with high odour activity values derived from carbohydrate metabolism and lipid oxidation may contribute to flavour development (P < 0.05). Additionally, the increased Staphylococcus spp. counts in sausages with 2.0% and 2.5% NaCl contributed to the increased contents of ethyl octanoate, ethyl butyrate and ethyl acetate (P < 0.05). Sensory evaluation showed higher scores for taste, chewiness and aroma in sausages with 2.0% and 2.5% NaCl. Therefore, it can be concluded that 2.0% NaCl can be employed as the desired addition level in fermented sausage to achieve better quality and flavour. • Sausages with reduction in NaCl level had higher moisture content and water activity. • The reduction of NaCl level increased lactic acid bacteria population. • Volatile compounds in fermented sausage during fermentation were identified. • 2.0% NaCl can be employed as the desired addition level in fermented sausage. [ABSTRACT FROM AUTHOR]

The technological properties and flavour formation potential of yeast strains isolated from traditional dry fermented sausages were evaluated. A total of 46 yeast strains were isolated and characterized at the strain level by genotyping. Among them, 34 strains were selected for evaluation of technological properties (tolerance to acid, salt, and sodium nitrite stresses; proteolytic and lipolytic activities; and biogenic amine formation capacity) based on their genetic profiles. Then, seven strains (Debaryomyces hansenii HRB2, SH4, and HG2; Torulaspora delbrueckii DQ3 and HG7; Pichia kudriavzevii MDJ1; and Candida zeylanoides DQ7) were selected to investigate their flavour formation potential in a fermented sausage model. A total of 56 volatile compounds were detected in all models, of which 17 volatile compounds were the most important flavour contributors with an odour activity value (OAV) > 1. The most remarkable result was the significant production of acid, alcohol, and esters in the inoculated models, such as acetic acid, hexanoic acid, ethanol, phenethyl alcohol, ethyl acetate, and ethyl hexanoate. Of all the strains, D. hansenii SH4 was considered to be the best flavour producer because it produced multiple compounds with the highest OAVs, which are associated with the development of desirable sensory characteristics in dry sausages. • A total of 46 yeast strains were isolated from traditional dry fermented sausages. • Intraspecific genetic diversity of yeast strains was explored using ISSR-PCR. • Eight strains exhibited high tolerance to acid, salt, and sodium nitrite stresses. • Seven strains showed specific capacities to produce acids, alcohols, and esters. • Debaryomyces hansenii SH4 produced multiple compounds with high odour activity value. [ABSTRACT FROM AUTHOR]