发酵乳杆菌RC4对咸肉亚硝酸盐含量及挥发性风味物质的影响

为降低咸肉中亚硝酸盐含量, 将具有高效降解亚硝酸盐的发酵乳杆菌RC4应用于咸肉制作中, 研究其对咸肉亚硝酸盐含量、品质和风味的影响. 通过单因素实验及正交实验, 对添加发酵乳杆菌RC4的实验组咸肉制作工艺进行优化, 比较接菌组和未接菌发酵对照组在感官评分、亚硝酸盐含量、pH、色差、水分、硫代巴比妥值及挥发性风味成分的差异. 结果表明: 实验组咸肉亚硝酸盐含量降解显著, 降解率为78.60%; 实验组咸肉的最佳发酵条件为接种2.0%(μL·mL^-1)的发酵乳杆菌RC4菌液, 18℃发酵10d. 与对照组相比, 实验组咸肉pH降低; 色差及水分含量与对照组差异不显著(P＞0.05); TBA值的变化量明显小于对照组(P＜0.05). 在鉴定出的87种挥发性物质中, 庚醛为RC4发酵产生, 苯甲醛等的含量显著高于对照组, 而这几种醛均为特征风味化合物. 由此可知, 在咸肉制备工艺中, 添加发酵乳杆菌RC4能显著降低咸肉的亚硝酸盐含量, 提高咸肉保质期, 增加其特征风味化合物含量.     

Cell-Free Supernatant from Lactobacillus and Streptococcus Strains Modulate Mucus Production via Nf-κB/CREB Pathway in Diesel Particle Matter-Stimulated NCI-H292 Airway Epithelial Cells

Airway epithelial cells are a major site of airway inflammation and may play an important role in the pathogenesis of chronic obstructive pulmonary disease (COPD). Diesel particulate matter (DPM) is associated with mucus hypersecretion and airway inflammation and has been reported to overexpress airway mucin in the NCI-H292 airway epithelial cells. Therefore, regulation of mucin hypersecretion is essential for developing novel anti-inflammatory agents. This study aimed to investigate the effects of cell-free supernatant (CFS) from Lactobacillus and Streptococcus on nitro oxide (NO) production in RAW264.7 and proteins associated with mucus production in NCI-H292 cells. We observed that NO production was reduced by CFS from Lactobacillus and Streptococcus in RAW 264.7, and MUC4, MUC5AC, and MUC5B gene expression was increased by phosphorylation of nuclear factor kappa B (NF-κB) p65 and cAMP response element-binding protein (CREB) in DPM-stimulated NCI-H292 cells. However, CFS from L. paracasei MG4272, MG4577, L. gasseri MG4247, and S. thermophilus MG5140 inhibited mRNA expression related to mucus production by downregulating the CREB/NfκB signaling pathway. These results suggest that CFS from L. paracasei MG4272, MG4577, L. gasseri MG4247, and S. thermophilus MG5140 can contribute as a strategic candidate to the prevention of airway inflammatory diseases caused by DPM.     

锆基金属有机骨架材料用于四甲基硅烷/异戊烷分离

在半导体工业中，从四甲基硅烷（TMS）/异戊烷混合物中高效捕获异戊烷从而获得超高纯度的TMS是非常重要的。在本工作中，我们选择了具有笼结构的MOF-801，通过其对TMS和异戊烷吸附能力的差异，实现了TMS与异戊烷的分离。气体吸附测试结果表明，在298 K和60 kPa时，MOF-801对异戊烷吸附量为2.56 mmol·g^-1，而其对TMS的吸附量为1.20 mmol·g^-1。理想吸附溶液理论（IAST）计算结果表明，MOF-801对TMS/异戊烷（95∶5，体积比）混合物的分离选择性达到105.8。而之后的液相吸附分离实验进一步验证了MOF-801的分离效果，最终可以得到体积分数大于99.98%的TMS。     

Sensitive lactate determination based on acclimated mixed bacteria and palygorskite co-modified oxygen electrode

A sensitive bacteria biosensor was prepared for the detection of trace lactate. The sensitive bioelement, Lactobacillus bulgaricus and Streptococcus thermophilus mixed cultrue, and palygorskite, a perfect matrix for bacteria, was co-immobilized on the surface of oxygen electrode. The biosensor possesses fine selective specificity, good sensitivity and longer operational life time, which were due to the mutual help relationship of symbiotic bacteria and 240 days acclimation with lactate as the carbon source. Hydrodynamic amperometry, an advanced electrochemical method, is suitable for on-line monitoring the concentration change of dissolved oxygen that is closely accompanied with the metabolism of lactate. Electrochemical data show that the current is very sensitive to the changes of the concentration of lactate. The response current was linear with lactic acid concentration in the range from 0 to 300 μmol L^? 1, where the response time is no more than 240 s (R = 0.9952), and the sensitivity was 1.87 mA mol^? 1 L. Experiments show the biosensor is also very useful for long time on-line monitoring of lactate, such as fermentation progress.     

Quantification of <Emphasis Type="Italic">Lactobacillus</Emphasis> in fermented milk by multivariate image analysis with least-squares support-vector machines

This paper reports an approach for quantification of Lactobacillus in fermented milk, grown in a selective medium (MRS agar), by use of digital colour images of Petri plates easily obtained by use of a flatbed scanner. A one-dimensional data vector was formed to characterize each digital image on the basis of the frequency-distribution curves of the red (R), green (G), and blue (B) colour values, and quantities derived from them, for example lightness (L), relative red (RR), relative green (RG), and relative blue (RB). The frequency distributions of hue, saturation, and intensity (HSI) were also calculated and included in the data vector used to describe each image. Multivariate non-linear modelling using the least-squares support vector machine (LS-SVM) and a linear model based on PLS regression were developed to relate the microbiological count and the frequency vector. Feasibly models were developed using the LS-SVM and errors were below than 10% for Lactobacillus quantification, indicating the proposed approach can be used for automatic counting of colonies.     

Effect of Lactobacillus challenge on Gardnerella vaginalis biofilms

Bacterial vaginosis (BV) is the most common infectious condition in women. It is caused primarily by anaerobic bacteria which rapidly form biofilms recalcitrant to antibiotic treatment, elevate vaginal pH, induce inflammatory processes and displace indigenous lactobacilli from the vault. Gardnerella vaginalis is commonly associated with these infections. Microscopy analysis showed that within 72 h, viable G. vaginalis covered a surface area of 567 μm², reached a depth of 16 μm and a density of approximately 104 μm³. They maintained these levels for a further 3 days unless challenged with lactobacilli strains. Lactobacillus reuteri RC-14 produced the biggest displacement of Gardnerella. This was not due to pH, which remained between 4.7 and 5.1 for all experiments, nor by hydrogen peroxide which is produced in low amounts by strain L. reuteri RC-14, high amounts by L. crispatus 33820 and not at all by L. rhamnosus GR-1. Deconvolution microscopy showed changes in structure and viability of the biofilms, with loss of dense Gardnerella biofilm pods. For the first time, a strain of L. iners, the most commonly isolated vaginal Lactobacillus in healthy women, was tested for potential probiotic properties. It was found to disrupt Gardnerella biofilm surface area, density and depth, albeit to a lesser extent than L. reuteri RC-14. These studies help to provide insight into the clinical situation in which probiotic and indigenous vaginal lactobacilli can interfere with Gardnerella's presence and reduce the risk of bacterial vaginosis.     

Combined cup loading, bis(2-hydroxyethyl) disulfide, and protein precipitation protocols to improve the alkaline proteome of Lactobacillus hilgardii

Despite the large number of papers dealing with bacterial proteomes, very few include information about proteins with alkaline pI's, because of the limits inherent in 2-DE technology. Nonetheless, analyses of in silico proteomes of many prokaryotes show a bimodal distribution of their proteins based on their pI's; the most crowded areas lying between pI 4-7 and 9-11. The aim of the present research was to set up a general, simple, and standardizable 2-DE protocol suitable for studying the alkaline proteome of Lactobacillus hilgardii, a Gram-positive bacillus isolated from wine. The method has also been tested on a Gram-negative bacterium able to degrade aromatic pollutants, Acinetobacter radioresistens S13. Optimization of the method was mainly focused on improving protein extraction and IEF (pI 6-11) separation protocols. Concerning IEF, different methods for sample loading (in-gel rehydration and cup loading), and different reducing agents (DTT and bis(2-hydroxyethyl) disulfide (HED)) were tested and compared. The proposed protocol was found to resolve efficiently alkaline proteins from both of our Lactobacillus and Acinetobacter strains, in spite of their different external layers, thus, enabling a more comprehensive study of their proteomes.     

Nature of the antimicrobial activity of Lactobacillus caseiBifidobacterium bifidum and Bifidobacterium animalis against foodborne pathogenic and spoilage microorganisms

The antimicrobial activities as well as the nature of the inhibitory compounds obtained from Lactobacillus casei, Bifidobacterium bifidum and Bifidobacterium animalis strains were assayed on foodborne pathogenic – Staphyloccoccus aureus subsp. aureus (CCUG ATCC® 25926?) and Escherichia coli (ATCC® 25922?) – and spoilage microorganisms – Pseudomonas aeruginosa (ATCC® 27853?). Test producer strains showed inhibitory effect on all indicator microorganisms in diffusion of cell-free concentrated supernatant by agar in well methods (10.0–22.5 mm) in periods of 24, 48 and 72 h. Inhibitory compounds showed no sensitivity to the action of proteolytic enzyme trypsin and were completely inactivated by adjusting the pH of the cell-free 20 × concentrated supernatant to 7.0. The results demonstrated that antimicrobial substances do not have proteinaceous nature and are caused by the action of organic acids with decreasing medium pH.     

Essential Oils Extracted from Organic Propolis Residues: An Exploratory Analysis of Their Antibacterial and Antioxidant Properties and Volatile Profile

The industrial processing of crude propolis generates residues. Essential oils (EOs) from propolis residues could be a potential source of natural bioactive compounds to replace antibiotics and synthetic antioxidants in pig production. In this study, we determined the antibacterial/antioxidant activity of EOs from crude organic propolis (EOP) and from propolis residues, moist residue (EOMR), and dried residue (EODR), and further elucidated their chemical composition. The EOs were extracted by hydrodistillation, and their volatile profile was tentatively identified by GC-MS. All EOs had an antibacterial effect on Escherichia coli and Lactobacillus plantarum as they caused disturbances on the growth kinetics of both bacteria. However, EODR had more selective antibacterial activity, as it caused a higher reduction in the maximal culture density (D) of E. coli (86.7%) than L. plantarum (46.9%). EODR exhibited mild antioxidant activity, whereas EOMR showed the highest antioxidant activity (ABTS = 0.90 μmol TE/mg, FRAP = 463.97 μmol Fe²⁺/mg) and phenolic content (58.41 mg GAE/g). Each EO had a different chemical composition, but α-pinene and β-pinene were the major compounds detected in the samples. Interestingly, specific minor compounds were detected in a higher relative amount in EOMR and EODR as compared to EOP. Therefore, these minor compounds are most likely responsible for the biological properties of EODR and EOMR. Collectively, our findings suggest that the EOs from propolis residues could be resourcefully used as natural antibacterial/antioxidant additives in pig production.     

Continuous production of lactic acid in a cell recycle reactor

The production of lactic acid from glucose has been demonstrated using a CSTR (continuous stirred-tank reactor) with cell recycle. Studies were conducted withLactobacillus delbrueckii at a fermentation temperature of 42°C and a pH of 6.25. A cell density of 140 g dry weight/L and a volumetric productivity of 150 g/L.h, with complete glucose consumption, were obtained. It was not possible to obtain a lactic acid concentration above 60 g/L because of product inhibition. A cell purge was not necessary to maintain high viability bacteria culture or to obtain a steady state. At steady state the net cell growth appeared to be negligible. The specific glucose consumption for cell maintenance was 0.33 g glucose/g cells-h.