Membrane disruption and DNA binding of Staphylococcus aureus cell induced by a novel antimicrobial peptide produced by Lactobacillus paracasei subsp. tolerans FX-6

Previously, we have isolated a novel bacteriocin, peptide F1 from Tibetan Kefir, and demonstrated its superior antimicrobial activity. However, its antimicrobial mechanism is still undefined. This study was aimed to elucidate the antimicrobial mechanism of peptide F1 against Staphylococcus aureus. The antimicrobial effects of peptide F1 were characterized by the following methods: chemical assay to quantify cytoplasmic β-galactosidase leakage, atomic absorption spectrometry to measure the released potassium ions, transmission electron microscopy to visualize the cellular morphological changes, and electrophoresis analysis and atomic force microscopy together to exam the DNA binding activity. Our results revealed that peptide F1 exerted its bactericidal effects by damaging bacterial cell membranes and by binding to the genomic DNA in the cytoplasm, which both led to rapid cell death.     

Artificial simulated gastrointestinal digestion of four carbohydrates containing beta‐d‐1 → 4 linkages and new GC‐TQ/MS‐MS method for characterising released monosaccharides

Four types of carbohydrates, including Dendrobium officinale polysaccharide, Dendrobium aphyllum polysaccharide and β‐glucans from yeast and barley, were examined, and their structures were found to mainly contain 1,4‐linked‐β‐d ‐Glcp. Artificially simulated gastrointestinal digestion was conducted to characterise the changes of molecular weight, reducing sugars and released free monosaccharides by high‐performance liquid chromatography, kits and the newly developed gas chromatography (GC)‐mass spectrometry (MS)/MS analysis, which indicated that high molecular weight and complex spatial structures contributed to delayed monosaccharide release following exposure to digestive solution. The spatial structures of carbohydrates were changed during gastric digestion, but their primary structures were destroyed during intestinal digestion. Additionally, for the developed 7890A/7000 GC‐TQ/MS‐MS, the new analytical method was successfully used to analyse very low concentrations of monosaccharides in the simulated gastrointestinal digestive system.     

基于复检机构视角的食品复检工作风险识别与防控措施

食品复检既是市场监管部门对不合格产品核查处置的重要环节,也是法律法规赋予食品生产经营者维护自身合法权益和切身利益的救济措施。食品复检结论作为最终结论,对市场监管部门、检验机构、食品生产经营者都有很大影响。该文通过识别食品复检机构在合同评审、样品接收与保存、复检实施、复检观察、复检结果报告等环节的潜在风险,提出相应风险防控措施,以期为食品复检机构检验工作的合规性、检验结果的准确性、检验结论的科学性以及市场监管部门对食品复检机构的监管提供参考。     

Combination of nisin and ε-polylysine with chitosan coating inhibits the white blush of fresh-cut carrots

Effects of the combination of nisin and ε-polylysine with chitosan coating on quality maintenance and white blush inhibition were investigated in fresh-cut carrots. Fresh-cut carrots were treated with 1% lactic acid solution (v/v), 1% chitosan solution (w/v), or 1% chitosan solution containing 64 μg/mL nisin and 250 μg/mL ε-polylysine (LA + CH + Nisin + ε-PL). The samples were packed in polyethylene plastic bags and stored at 4 °C for 9 days. Changes in sensory attributes, physicochemical indices, respiration rate, microbiological counts and white blush were measured. Results showed that LA + CH + Nisin + ε-PL significantly (P < 0.05) inhibited respiration rate, decline of ascorbic acid and growth of microorganism (yeast and mold, total viable counts, total coliforms counts, Staphylococcus aureus and Pseudomonas spp.), and increased total phenol content and phenylalanine ammonialyse (PAL) activity compared with the control after 9-day storage. It was also strongly effective in inhibiting the white blush of fresh-cut carrots. Furthermore, LA + CH + Nisin + ε-PL significantly (P < 0.05) reduced the lignin synthesis in fresh-cut carrots by inhibiting the cinnamate-4-hydroxylase (C4H) and 4-coumarate-CoA ligase (4CL) activity, as well as Dc4CL and DcC4H gene expression. Our results may provide some basis for the use of the combination of nisin and ε-polylysine with chitosan coating as an alternative preservation method for fresh-cut carrots.     

浓香型白酒窖池空间位置及窖龄对窖泥原核微生物群落的影响

采用高通量测序技术解析4年和40年窖龄窖池不同部位窖泥原核微生物群落组成,并分析窖泥理化性质差异以及其对原核微生物的影响。结果表明,除总酸外,4年窖龄窖池窖泥样品的平均含水量、pH值、铵态氮含量、有效磷含量和α-多样性指数均低于40年窖龄窖池窖泥,40年窖龄上、中、下、底层窖泥理化性质及α-多样性均相对稳定,且4年和40年窖龄窖池窖泥理化指标的差异主要体现在上层和中层。从门和属水平组成上分析,40年窖龄窖池窖泥样品微生物群落结构相对稳定,且与4年窖龄窖池下层和底层窖泥样品更为相似。冗余分析（RDA）结果表明,总酸、有效磷和pH是影响不同窖龄和不同窖池位置窖泥中优势微生物菌群分布的主要理化因子。     

魔芋葡甘聚糖保润剂对烟丝吸湿特性的影响

利用烟草等温吸脱附性能检测装置考察施加了魔芋葡甘聚糖(KGM)保润剂的烟丝样品的吸湿特性,结果表明:KGM有助于增强烟丝的持水能力,减缓水分散失过程,KGM不同程度地降低了各部位烟丝的干燥速率常数;烟丝样品的等温吸湿—解湿曲线呈Ⅲ型吸附曲线,且KGM的施加会加剧吸湿滞后现象,吸湿滞后行为随温度升高有减弱趋势,中上部烟丝的吸湿滞后现象强于下部烟丝,DLP经验模型可较好地描述烟丝样品的等温吸湿—解湿行为。     

Structural characterisation and immunomodulatory effects of polysaccharides isolated from Dendrobium aphyllum

A crude polysaccharide extract of Dendrobium aphyllum (cDAP, yield 38.15 ± 0.20%) was generated. The D. aphyllum polysaccharide (DAP, M_w 471.586 kDa), purified by DEAE‐Sepharose and Sephadex‐G200 Fast Flow, was composed of mannose (71.3%) and glucose (28.7%), according to GC–MS analysis. Its backbone was composed of β‐d ‐mannopyranose and β‐d ‐glucopyranose residues, as revealed by infrared spectroscopic analysis. Its glycosidic bond was mainly 1, 4‐linked, and the O‐acetyl groups were mainly linked to mannose residues, according to periodate oxidation and Smith degradation analysis. The DAP units polymerised into a filiform‐shaped spatial pattern, as characterised by atomic force microscopy and scanning electron microscopy. DAP treatment enhanced cytokine secretion (nitric oxide, interleukin‐6 and tumour necrosis factor‐α) and pinocytic and phagocytic capacities of RAW 264.7 mouse macrophages. The complement receptor 3 and mannose receptor were identified to be the receptors of DAP on RAW 264.7 cells, indicating that the Akt/mTOR/MAPK and IKK/nuclear factor‐?B pathways could be involved in DAP‐activated immunomodulation.     

双酶协同转化龙眼汁中蔗糖生成低聚果糖

目的 探究葡萄糖氧化酶协同果糖基转移酶转化龙眼汁中蔗糖生成低聚果糖、并减少龙眼汁葡萄糖含量的效果,实现减少龙眼汁中热量糖含量制备出低热量龙眼汁。方法 以天然龙眼汁为原料,通过控制不同的酶添加次序、酶添加量、龙眼汁体系pH和酶处理时间的单因素变量法,探究葡萄糖氧化酶协同果糖基转移酶转化龙眼汁中蔗糖生成低聚果糖的较优工艺条件;采用高效液相色谱法测定龙眼汁中游离糖组成及含量。结果 采用两种酶分段处理的方法,控制葡萄糖氧化酶添加量为60 U/g、反应温度为35℃、初始pH值6.0、饱和碳酸钙溶液添加量9.6%、通氧处理时间4 h,可有效消耗龙眼汁中原始葡萄糖和转化过程中产生的葡萄糖,使葡萄糖消耗率达到93.56%,并使龙眼汁中低聚果糖占比由果糖基转移酶单独处理时的31.72%提高到了58.08%。结论 采用葡萄糖氧化酶协同果糖基转移酶处理龙眼汁的方法,能有效降低龙眼汁中热量糖含量,制备出低热量龙眼汁。     

金刚烷胺残留化学发光酶免疫法的建立

建立金刚烷胺残留的化学发光酶免疫方法。对酶标抗原与磁标抗体的最佳稀释倍数、反应时间、底物发光时间进行优化,建立标准曲线,同时对方法的检测限、准确度和精密度进行评价。结果表明:50%抑制浓度(IC₅₀)为0.481 μg/L,线性范围是0.085~2.729 μg/L;在动物组织、兽药、饲料中的检测限为0.1 μg/kg,样本添加回收率为80.2%~94.5%,批内、批间相对标准偏差均<10%。该方法灵敏度高、操作简便,可广泛用于动物组织、兽药、饲料中金刚烷胺残留量的测定。     

On-line monitoring of key nutrients in yoghurt samples using digitally labelled Raman spectroscopy

On-line monitoring of the fermentation process is essential for improving the quality of yoghurt products. We developed an on-line monitoring system based on digitally labelled Raman spectroscopy (DLRS). In DLRS, the strategy of Monte Carlo competitive adaptive reweighted sampling selection was proposed to isolate spectral bands according to a high-density discrete wavelet transform domain, which greatly suppressed the matrix effect on the calibration models. We demonstrated the feasibility of DLRS using 72 practical samples, and 4 key nutrients protein, fat, sucrose and total solids were determined simultaneously. The satisfactory results indicate that the DLRS system has capability for on-line monitoring of 4 key nutrients during yoghurt fermentation, thus enabling intelligent control of yoghurt production.