Effects of community ecological network construction on physicochemical, microbial, and quality characteristics of inoculated northeast sauerkraut: A new insight in food fermentation processes.

The enhancement of the quality of northeast sauerkraut can be achieved by inoculation with lactic acid bacteria. However, a comprehensive ecological understanding of the intricate dynamic processes involved is currently lacking, which could yield valuable insights for regulating sauerkraut fermentation. This study compares spontaneously sauerkrauts with the sauerkrauts inoculated with autochthonous Lactiplantibacillus plantarum SC-MDJ and commercial L. plantarum, respectively. We examine their physicochemical properties, quality characteristics, bacterial community dynamics, and ecological network interactions. Inoculation with L. plantarum leads to reduced bacterial community richness and niche breadth, but an increase in robustness, interactions, and assembly processes. Notably, there appears to be a potential correlation between bacterial community structure and quality characteristics. Particularly, sauerkraut inoculated with L. plantarum SC-MDJ may produce a sourness more quickly, possibly attributed to the enhanced ecological role of L. plantarum SC-MDJ. This study establishes a foundation for the targeted regulation of sauerkraut fermentation.

Myofibrillar protein hydrolysis under hydroxyl radical oxidative stress: Structural changes and their impacts on binding to selected aldehydes.

In this study, a hydroxyl radical oxidation system was established to simulate the oxidation process in fermented meat products. This system was employed to examine the structural changes in myofibrillar proteins (MPs) resulting from tryptic hydrolysis after a hydroxyl radical oxidative regime. The effect of these changes on the ability of MPs to bind selected aldehydes (3-methyl butanal, pentanal, hexanal, and heptanal) was also investigated. Moderate oxidation (H2O2 ≤ 1.0 mM) unfolded the structure of MPs, facilitating trypsin-mediated hydrolysis and increasing their binding capacity for the four selected aldehydes. However, excessive oxidation (H2O2 ≥ 2.5 mM) led to cross-linking and aggregation of MPs, inhibiting trypsin-mediated hydrolysis. The oxidised MPs had the best binding capacity for heptanal. The interaction of the oxidised trypsin-hydrolysed MPs with heptanal was driven by hydrophobic interactions. The binding of heptanal affected the structure of the oxidised trypsin-hydrolysed MPs and reduced their α-helix content.

Flavour Profile of Traditional Dry Sausage Prepared with Partial Substitution of NaCl with KCl.

The effects of partial substitution of NaCl with 0%, 20%, 30% and 40% KCl on the physical characteristics, bacterial community and flavour profile of traditional dry sausage were investigated in this study. With the increase in KCl substitution ratio, the moisture content, astringency, bitterness and umami increased significantly, and the saltiness gradually decreased (p < 0.05). The high-throughput sequencing results showed that the dry sausages with KCl substitution had relatively high abundances of Staphylococcus. For volatile compounds, increasing the KCl substitution ratio reduced the formation of aldehydes, ketones and some alcohols, but promoted the formation of acids and esters (p < 0.05). Sensory evaluation and partial least square regression analysis showed that the dry sausages with 20% and 30% KCl were similar in overall physical and microbial properties, flavour profiles and sensory attributes, and the sausages with 40% KCl were characterized by taste defects. Overall, partial substitution of NaCl with 30% KCl could ensure the acceptable flavour and sensory attributes of dry sausages.

Flavour Compensation Role of Yeast Strains in Reduced-Salt Dry Sausages: Taste and Odour Profiles.

The effects of different yeast strains including Pichia kudriavzevii, Torulaspora delbrueckii, and Debaryomyces hansenii on the taste and odour profiles of reduced-salt dry sausages were explored. Inoculation of P. kudriavzevii and D. hansenii compensated for the lack of saltiness and umami tastes of reduced-salt sausages. Furthermore, inoculation of P. kudriavzevii and T. delbrueckii resulted in an odour profile in the reduced-salt dry sausages that was similar to traditional dry sausages. According to the volatile analysis, the contents of certain alcohols, acids, esters and terpenes were higher in the inoculated sausages. Finally, the sensory evaluation indicated that the inoculation of P. kudriavzevii and D. hansenii contributed positively to the aroma and saltiness of reduced-salt dry sausages. In conclusion, P. kudriavzevii and D. hansenii can be employed as effective starter cultures to compensate for the flavour deficiencies of reduced-salt dry sausages.

Fungal community succession and volatile compound dynamics in Harbin dry sausage during fermentation.

This study investigated the fungal community succession and volatile compound dynamics of Harbin dry sausage during a twelve-day fermentation using high-throughput internal transcribed spacer amplicon sequencing and headspace solid-phase microextraction gas chromatography-mass spectrometry. Aspergillus pseudoglaucus was found to be the primary species in the sausages during fermentation, whereas Lasiodiplodia theobromae, Alternaria alternata, Aspergillus caesiellus, and Trichosporon asahii were also prevalent. Additionally, a total of 72 volatile compounds were identified in the dry sausages, of which 24 key compounds (odor activity value > 1) dominated flavor development, including 3 aldehydes, 1 ketone, 4 alcohols, 9 esters, 4 alkenes, and 3 other compounds. Furthermore, correlation analysis suggested that most of the core fungi were positively correlated with the key volatile compounds, particularly A. pseudoglaucus, Aspergillus gracilis, Trichosporon caseorum, Debaryomyces hansenii, and T. asahii. Our findings provide novel insights into the fungal ecology and flavor development of Harbin dry sausages.

The potential correlations between the fungal communities and volatile compounds of traditional dry sausages from Northeast China.

The fungal communities and volatile compounds of traditional dry sausages collected from five different regions in Northeast China, including Harbin (HRB), Daqing (DQ), Suihua (SH), Hegang (HG) and Mudanjiang (MDJ) were investigated in this study. The results revealed clear differences among the fungal community structures of the sausages. Aspergillus pseudoglaucus, Debaryomyces hansenii, and Trichosporon asahii were found to be the predominant species in the sausages from HRB, HG, and MDJ, respectively. Candida zeylanoides was the predominant species in the sausage from DQ and SH. Additionally, 88 volatile compounds were identified in all sausages, of which 31 volatile compounds were the most important flavor contributors (odor activity value > 1). Potential correlation analysis revealed that 8 fungi (D. hansenii, C. zeylanoides, T. asahii, A. pseudoglaucus, Aspergillus sydowii, Penicillium expansum, A. alternata, and Alternaria tenuissima) showed significant positive correlations with ≥3 key volatile compounds. Among these fungi, D. hansenii was regarded as a core functional fungus responsible for the formation of the volatile compounds, given its strong connection with the highest number of key volatile compounds. These results provide detailed insight into the fungal communities of traditional dry sausages and a deeper understanding of the contribution of these fungi to sausage flavor.

High-throughput sequencing approach to reveal the bacterial diversity of traditional yak jerky from the Tibetan regions.

A high-throughput sequencing approach was used to investigate the bacterial community diversity of traditional Tibetan yak jerky, which was collected from three different regions in Tibet and with different natural drying times. Tibetan yak jerky from different regions had different bacterial communities, which was mainly reflected in the relative abundance levels of unclassified Cyanobacteria, Psychrobacter and Acinetobacter. The unclassified Cyanobacteria was the dominant genus of Qamdo yak jerky, Acinetobacter was the dominant genus of Shigatse yak jerky, and Psychrobacteria was the dominant genus of Nyingchi yak jerky. With increasing natural drying time, the diversity of bacterial communities in yak jerky decreased, and unclassified Cyanobacteria become the dominant genus. Spearman's correlation analysis and canonical correspondence analysis revealed that physicochemical factors (moisture content, water activity, shear force and pH) were significantly correlated with bacterial community. Our results will be beneficial to improve and standardize the safety and quality of traditional Tibetan yak jerky.

Ultrasound-assisted immersion freezing reduces the structure and gel property deterioration of myofibrillar protein from chicken breast.

The effects of air freezing (AF), immersion freezing (IF) and ultrasound-assisted immersion freezing (UF) at different power levels (125, 165, 205 and 245 W) on the structure and gel properties of the myofibrillar protein (MP) of chicken breast were investigated. UF at 165 W (UF-165) had no obvious negative impact on the primary structure of the MP and effectively reduced the change in the secondary and tertiary structure. In addition, UF-165 significantly reduced the losses in the elastic modulus (G'), gel strength, and gel water holding capacity (P < 0.05). According to low field nuclear magnetic resonance analysis, the T21 and T22 of the UF-165 MP gels were shorter than those of the AF and IF samples, which meant that the UF-165 reduced the mobility of the immobilized water and free water in MP gel. A scanning electron microscopy analysis showed that the appropriate ultrasonic power promoted the formation of a compact and homogeneous protein gel network. These results suggested that the appropriate ultrasonic power maintained the MP structure and reduced the loss of gel quality.