The effect of different sterilization methods on the shelf life and physicochemical indicators of fermented pork jerky.

Background: To determine the effect of different sterilization methods on shelf life and physicochemical parameters of fermented pork jerky. Methods: Various sterilization techniques, including boiling, pasteurization, medium-temperature steam sterilization, high-temperature steam sterilization, ultrasonic sterilization, and ultraviolet sterilization, were employed in this study to treat vacuum-sealed fermented pork jerky. Changes in microbial populations, physicochemical parameters, and sensory evaluations were monitored throughout the storage period. Results: The results indicated the presence of Staphylococcus aureus on the 24th, 21st, 33rd, 24th, 18th, and 15th days in pork jerky subjected to boiling (100°C, 20 min), pasteurization (85°C, 15 min), medium-temperature steam sterilization (105°C, 0.5 Pa, 30 min), high-temperature steam sterilization (121°C, 1.0 Pa, 20 min), ultrasonic sterilization (480 W, 30 kHz, 30 min), and ultraviolet sterilization (254 nm, 100 W/m2, 60 min), respectively. Coliforms, salmonella, and Shigella were not detected in any group during storage. The medium-temperature steam sterilization method yielded the most favorable microbiological results, with an aerobic plate count of less than 1.0 lg CFU/g. However, other physicochemical parameters and sensory evaluations were moderate, with total volatile basic nitrogen (TVB-N) and thiobarbituric acid reactive substances (TBARS) measuring 14.023 mg N/100 g and 0.427 mg MDA/kg, respectively, remaining within acceptable limits. Conclusion: Therefore, considering microbiological indicators as the primary determinant of shelf life and taking into account other physicochemical parameters, the medium-temperature steam sterilization method was identified as the most suitable approach for extending the shelf life of fermented pork jerky while preserving its flavor.

Isolation of Aroma-Producing Wickerhamomyces anomalus Yeast and Analysis of Its Typical Flavoring Metabolites.

In this study, 21 strains of aroma-producing yeast were isolated from Sichuan paocai juice of farmers in western, eastern and southern Sichuan. One strain, Y3, with the best aroma-producing characteristics, was screened using an olfactory method and a total ester titration method, and was identified as Wickerhamomyces anomalus. The total ester content of Y3 fermentation broth was as high as 1.22 g/L, and there was no white colonies or film on the surface. Meanwhile, the Y3 strain could tolerate 14% salt concentration conditions and grow well in a pH range of 3-4. Through sensory analysis, the fermented mustard with a ratio of Lactiplantibacillus plantarum to Y3 of 1:1 showed the highest overall acceptability. Ethyl acetate with its fruit and wine flavor was also detected in the fermented Sichuan paocai juice with a mixed bacteria ratio of 1:1, analyzed with SPME-GC-MS technology, as well as phenylethyl alcohol, isobutyl alcohol, isothiocyanate eaters, myrcene and dimethyl disulfide. These contributed greatly to the unique flavor of Sichuan paocai. In general, Wickerhamomyces anomalus Y3 enhanced the aroma of the fermented Sichuan paocai.

Production of fermented spicy rabbit meat using Lactobacillus paracasei.

Lactobacillus paracasei was used to produce fermented spicy rabbit meat. A series of indexes were determined, including pH value, free amino acid content, true protein content, texture, microstructure and the volatile compounds of fermented spicy rabbit meat and unfermented spicy rabbit meat. The results showed that Lactobacillus paracasei could reduce the pH value of spicy rabbit meat (from 6.85 to 4.65), could degrade the proteins of spicy rabbit meat, could increase the content of free amino acids (from 205.1 mg/100 g to 505.6 mg/100 g), and could improve its textural properties and organoleptic quality of the spicy rabbit meat. The microstructure of the fermented spicy rabbit meat and unfermented spicy rabbit meat was observed by scanning electron microscope. The results showed that the microstructure of the fermented spicy rabbit meat changed obviously, the arrangement of muscle fibers was loose or even seriously broken, and many small pieces were formed, which indicated that the fermentation could improve the tenderness of the rabbit meat. The kinds of volatile flavor compounds after fermentation were increased from 14 to 40 as estimated by solid phase microextraction and GC-MS. Therefore, utilization of microbial fermentation technology can improve the quality, texture, tenderness and flavor of spicy rabbit meat, and enhance the digestion and absorption capacity.

Application of ε-polylysine in extending the storage period of pork jerky.

In this experiment, natural nontoxic preservative ε-polylysine (ε-PL) was used as a natural preservative in pork jerky. The pork jerky samples with ε-PL (experimental group) and without ε-PL (blank group) were stored at the 27 and 37℃. Then, the number of microorganisms, total volatile basic nitrogen (TVB-N), pH, and water activity (Aw) of each group were tested to test the antiseptic effect of ε-PL. The results showed that due to the Staphylococcus aureus was detected, the storage period of the blank group at 27 and 37°C was 15 and 9 days, respectively. However, Coliforms, Staphylococcus aureus, Salmonella, and Shigella were not detected in the experimental group on the 60th day. The experimental group all accord with the national standard for the quantity of microorganisms in meat jerky. The TVB-N content of the blank group reached 14.00 mg/100 g (15th day, 27°C) and 14.93 mg/100 g (9th day, 37°C) at the end of the storage period, while the TVB-N content of the experimental group was 11.20 mg/100 g (60th day, 27℃) and 15.86 mg/100 g (60th day, 37℃), and the increase rate of TVB-N in the blank group was greater than the experimental group, indicating that ε-PL can play a better microbial stabilization effect in pork jerky. The test of pH and Aw showed that ε-PL can stabilize the quality of pork jerky. Finally, the antiseptic effect of ε-PL was comparable to many chemical preservatives. This experiment confirms that ε-PL played an important role in extending the storage period of pork jerky.

Study on metabolites of Bacillus producing soy sauce-like aroma in Jiang-flavor Chinese spirits.

Jiang-flavor Chinese spirits are one of the four basic liquor types in China. It has thousands of years of history in China and is widely enjoyed because of its unique flavor and broad application. Although Jiang-flavor Chinese spirits have a unique soy sauce flavor, the associated key compounds and production mechanism remain unknown. To investigate this process, soy sauce flavor-producing strains were obtained, and their metabolites were evaluated. Using wheat as the fermentation medium, we observed changes in total acid, amino nitrogen, and reducing sugar in three strains of Bacillus cerberus with high yield of tetramethylpyrazine during the fermentation process. The results showed that total acid and amino nitrogen contents increased and reducing sugars decreased in a time-dependent manner. Additionally, detection of volatile compounds via solid-phase microextraction and gas chromatography-mass spectrometry that total pyrazine content reached 43.175%, 50.461%, and 45.955% in wheat fermentation medium fermented by strains Q1, Q2, and Q5, respectively, suggesting that this important flavor compound might be related to the flavor of soy sauce. Moreover, we found that fermentation time was an important factor in soy sauce flavor, as volatile compounds were detected at different times by the three strains, with pyrazines not detected before 48 hr and peaking at 50.461% after 144 hr. These results indicated that strain Q2 exhibited optimal fermenting performance and might be useful for fermentation of Jiang-flavor Chinese spirits.

Reconstruction and analysis of a genome-scale metabolic model of Methylovorus sp. MP688, a high-level pyrroloquinolone quinone producer.

Methylovorus sp. MP688 is a methylotrophic bacterium that can be used as a pyrroloquinolone quinone (PQQ) producer. To obtain a comprehensive understanding of its metabolic capabilities, we constructed a genome-scale metabolic model (iWZ583) of Methylovorus sp. MP688, based on its genome annotations, data from public metabolic databases, and literature mining. The model includes 772 reactions, 764 metabolites, and 583 genes. Growth of Methylovorus sp. MP688 was simulated using different carbon and nitrogen sources, and the results were consistent with experimental data. A core metabolic essential gene set of 218 genes was predicted by gene essentiality analysis on minimal medium containing methanol. Based on in silico predictions, the addition of aspartate to the medium increased PQQ production by 4.6- fold. Deletion of three reactions associated with four genes (MPQ_1150, MPQ_1560, MPQ_1561, MPQ_1562) was predicted to yield a PQQ production rate of 0.123 mmol/gDW/h, while cell growth decreased by 2.5%. Here, model iWZ583 represents a useful platform for understanding the phenotype of Methylovorus sp. MP688 and improving PQQ production.

Genome-scale metabolic reconstruction and analysis for Clostridium kluyveri.

Clostridium kluyveri is an anaerobic microorganism that is well-known for producing butyrate and hexanoate using ethanol and acetate. It is also an important bacterium in the production of Chinese strong flavour baijiu (SFB). To obtain a comprehensive understanding of its metabolism, a curated genome-scale metabolic model (GSMM) of C. kluyveri, including 708 genes, 994 reactions, and 804 metabolites, was constructed and named iCKL708. This model was used to simulate the growth of C. kluyveri on different carbon substrates and the results agreed well with the experimental data. The butyrate, pentanoate, and hexanoate biosynthesis pathways were also elucidated. Flux balance analysis indicated that the ratio of ethanol to acetate, as well as the uptake rate of carbon dioxide, affected hexanoate production. The GSMM iCKL708 described here provides a platform to further our understanding and exploration of the metabolic potential of C. kluyveri.

Screening of Bacillus Strains from Sun Vinegar for Efficient Production of Flavonoid and Phenol.

The aim of this study was to screen out a bacillus from Sichuan sun vinegar grains capable of producing a high total amount of flavonoids and total phenols. Forty-eight strains were initially screened out from Sichuan sun vinegar grains. The sodium nitrite-aluminum nitrate-sodium hydroxide colorimetry method was used to determine the total flavonoids, and the Folin-phenol method was used to determine the total phenols. Based on the results of total flavonids and total phenol producing capacities of the strains, one strain was singled out for use in this study. This strain, which was named YB-19, is capable of producing a total amount of 96.55 µg/mL flavonoids and 86.69 µg/mL phenols. YB-19 was identified by its strain morphology, physiological and biochemical characteristics. DNA sequencing was performed on YB-19. The results of the DNA sequencing showed that the sequence similarity between strain YB-19 and Bacillus toyonensis strain BCT-7112 was 99 %, and the two strains were housed on the same branch in the phylogenetic tree. Combined with the results of the strain morphology and the observed physiological and biochemical characteristics, YB-19 was identified as B. toyonensis. The screened strain YB-19 can be applied to the traditional brewing process of sun vinegar to improve vinegar quality and to enrich the microbial resources for vinegar fermentation.