Improving the bacterial community, flavor, and safety properties of northeastern sauerkraut by inoculating autochthonous Levilactobacillus brevis.

The effect of Levilactobacillus brevis as a starter in northeastern sauerkraut fermentation is still unknown, and further evaluation is worthwhile. Hence, this study aimed to evaluate the effect of autochthonous L. brevis inoculation on the bacterial community succession and formation of flavor and harmful substances in sauerkrauts. Inoculation with L. brevis lowered the pH and increased the total acid content of sauerkrauts (P < 0.05). The nitrite content of the inoculated sauerkraut was significantly lower than that of control (P < 0.05). Moreover, the spoilage bacteria of the inoculated sauerkraut were decreased and nitrogen metabolism was improved. The contents of aldehydes, alcohols, esters, acids, and alkanes increased significantly (P < 0.05), and the sensory attributes such as aroma, sourness, and gloss were also improved. L. brevis was positively and negatively correlated with flavor metabolites and nitrite, respectively, which proved to be a potential starter culture to manufacture sauerkraut.

Targeted inhibition of biogenic amine-producing strains by spice extracts and control of biogenic amine accumulation in reduced-salt dry sausages.

This study aimed to screen spice extracts that can target the inhibition of biogenic amine (BA)-producing bacteria and reduce the BA accumulation in reduced-salt dry sausages. A total of 59 bacterial strains were isolated from reduced-salt dry sausages; among them, three isolates, namely, Staphylococcus epidermidis S1, S. saprophyticus S2, and S. edaphicus S3, had the strongest ability to produce BA. Eight spice extracts, i.e. Angelica dahurica, cinnamon, ginger, clove, fennel, Amomum, nutmeg, and orange peel, were extracted. The inhibition zone diameter and minimum inhibitory concentration indicated that A. dahurica, Amomum, and clove elicited the strongest inhibitory effect on BA-producing strains. Growth kinetics showed the strongest inhibitory effect of clove extracts, followed by Amomum and A. dahurica. In the medium system, clove extract was the most effective in controlling the total BA content by inhibiting of BA-producing strains S. epidermidis S1, S. saprophyticus S2, and S. edaphicus S3; their contents were reduced by 23.74%, 31.05% and 21.37%, respectively. In the dry sausage system, the control of BA accumulation by clove was quite prominent, and the total BA content was reduced from 373.70 mg/kg to 259.05 mg/kg on day 12.

Screening and evaluating microorganisms with broad-spectrum biogenic amine-degrading ability from naturally fermented dry sausage collected from Northeast China.

This study aimed to screen autochthonous strains with broad-spectrum biogenic amine (BA) degradation ability from traditional dry sausages and to evaluate their BA-degrading ability in dry sausages. A total of 120 strains were isolated from dry sausages collected from various regions in Northeast China, and 35 of 120 isolates were identified as non-BA producing strains by the in vitro agar method. The random amplified polymorphic DNA polymerase chain reaction technique genotyped these 35 isolates into 18 biotypes. Moreover, high performance liquid chromatography (HPLC) quantification showed that six strains (Latilactobacillus sakei MDJ6; Lactiplantibacillus plantarum SH7; Weissella hellenica DQ9; Staphylococcus saprophyticus JX18 and SYS8; and Macrococcus caseolyticus SYS11) of the 18 biotypes exhibited broad-spectrum BA-degrading ability, all of which had various levels of amine oxidase activity with monoamine oxidase and diamine oxidase activities ranged of 6.60-619.04 and 26.32-352.81 U/mg protein, respectively. These six strains were subsequently inoculated into dry sausages and the results showed that they exhibited varying degrees of BA-degrading ability, of which strain Lat. sakei MDJ6 allowed to have less BA production on dry sausage with a final concentration of 61.33 mg/kg.

Effect of Yeast Inoculation on the Bacterial Community Structure in Reduced-Salt Harbin Dry Sausages: A Perspective of Fungi-Bacteria Interactions.

Yeast strains are promising starters to compensate for the flavor deficiencies of reduced-salt dry sausages, but their influence on the bacterial community's structure has not yet been clarified. In this study, the effect of separately inoculating Pichia kudriavzevii MDJ1 (Pk) and Debaryomyces hansenii HRB3 (Dh) on the bacterial community structure in reduced-salt dry sausage was investigated. The results demonstrated that the inoculation of two yeast strains significantly reduced the pH, and enhanced the total acid content, lactic acid bacteria (LAB) counts, and total bacterial counts of reduced-salt sausages after a 12-day fermentation (p < 0.05). Furthermore, high-throughput sequencing results elucidated that the inoculation of yeast strains significantly affected the bacterial composition of the dry sausages. Especially, the relative abundance of bacteria at the firmicute level in the Pk and Dh treatments exhibited a significant increase of 83.22% and 82.19%, respectively, compared to the noninoculated reduced-salt dry sausage treatment (Cr). The relative abundance of Latilactobacillus, especially L. sakei (0.46%, 2.80%, 65.88%, and 33.41% for the traditional dry sausage (Ct), Cr, Pk, and Dh treatments, respectively), increased significantly in the reduced-salt sausages inoculated with two yeast strains. Our work demonstrates the dynamic changes in the bacterial composition of reduced-salt sausages inoculated with different yeast strains, which could provide the foundation for the in-depth study of fungi-bacteria interactions in fermented foods.

Analysis and comparison of the quality and flavour of traditional and conventional dry sausages collected from northeast China.

In this study, the physicochemical properties and flavour profile of traditional dry sausages (T-SH, T-DXAL, T-HG, T-MDJ, T-HRB) collected from various wet markets were compared with those of conventional dry sausages (C-QL, C-ND, C-YSD, C-YC, C-HRL) collected from various food companies in northeast China. Traditional dry sausages were characterised by a low moisture content, a low water activity, and a high shear force after a long fermentation time compared with conventional dry sausages. Electronic nose and electronic tongue signals combined with chemometrics methods were applied for a comprehensive qualitative analysis of the odour and taste of dry sausages. A total of 61 volatile compounds were identified using gas chromatography-mass spectrometry, and the multivariate chemometrics analysis confirmed the difference in volatile compounds between traditional and conventional samples. Moreover, the sensory evaluation revealed that conventional dry sausages lacked the characteristic fermented flavour of traditional dry sausages.

Exploring potential correlations between bacterial communities, organic acids, and volatile metabolites of traditional fermented sauerkraut collected from different regions of Heilongjiang Province in Northeast China.

In this study, the bacterial communities and flavor metabolites of 27 traditional naturally fermented sauerkraut samples collected from nine regions of Heilongjiang Province in Northeast China were investigated. The dominant genera were Lactobacillus, Pseudomonas, Alcaligenes, Arcobacter, Pseudarcobacter, Lactococcus, Comamonas, Pediococcus, Prevotella, and Insolitispirillum. A total of 148 volatile compounds were detected in seven categories; esters and acids were the most abundant volatiles. Additionally, the highest content (15.96 mg/g) of lactic acid was detected in YC1. Acetic acid, oleic acid, palmitic acid, elaidic acid, and dehydroacetic acid were the key differential volatile compounds, which may be related to the bacterial communities. Spearman's correlation analysis revealed that Lactococcus and Lactobacillus were significantly positively correlated with flavor metabolites, suggesting that they may play a more significant role in flavor formation. The results of this study can help in the development of better quality of fermented vegetables.