Detection of acylated homoserine lactones in gram-negative proteolytic psychrotrophic bacteria isolated from cooled raw milk

Through a mechanism called quorum sensing, bacteria are able to express specific genes in response to population density. Cell-to-cell communication in bacteria is mediated by signal molecules such as acylated homoserine lactones (AHLs). This work aimed to detect AHL production in Gram-negative psychrotrophic bacteria isolated from raw milk. A total of 84.9% of the bacteria were identified as AHL producers eliciting a diversity of responses in the AHL-monitor systems. These results demonstrate that AHL-production is common among psychrotrophic bacteria isolated from milk, and indicate that quorum sensing may play an important role in the spoilage of this product.     

副溶血性弧菌毒力因子及耐药机制研究进展

副溶血性弧菌是水产品中主要的致病菌之一,既可造成养殖水产品的疾病与死亡,也可引起人类的胃肠炎等疾病,不仅具有潜在的食品安全隐患,也对消费者健康造成潜在危害。该文主要阐述了副溶血性弧菌的毒力因子耐热直接溶血素(thermostable direct hemolysin, TDH)以及分泌系统T3SS1、T3SS2在菌株体内的作用机理,并对副溶血性弧菌产生耐药性的5种机制——产生生物被膜、质粒介导耐药、产生灭活酶或钝化酶类、外排泵主动排出抗菌药物、药物靶点发生改变进行了综述。     

Recent advances in shelf life prediction models for monitoring food quality

Each year, 1.3 billion tons of food is lost due to spoilage or loss in the supply chain, accounting for approximately one third of global food production. This requires a manufacturer to provide accurate information on the shelf life of the food in each stage. Various models for monitoring food quality have been developed and applied to predict food shelf life. This review classified shelf life models and detailed the application background and characteristics of commonly used models to better understand the different uses and aspects of the commonly used models. In particular, the structural framework, application mechanisms, and numerical relationships of commonly used models were elaborated. In addition, the study focused on the application of commonly used models in the food field. Besides predicting the freshness index and remaining shelf life of food, the study addressed aspects such as food classification (maturity and damage) and content prediction. Finally, further promotion of shelf life models in the food field, use of multivariate analysis methods, and development of new models were foreseen. More reliable transportation, processing, and packaging methods could be screened out based on real-time food quality monitoring.     

The impact of recrystallisation on the freeze-thaw cycles of red seabream (Pagrus major) fillets

Recrystallisation often occurs in the freeze-thaw cycles and results in poor food quality. This study was undertaken to analyse the effects of recrystallisation on the changes of protein conformation and moisture migration within red seabream fillets after the freeze-thaw cycles. The UV second-derivative spectroscopy, intrinsic fluorescence measurement and Raman spectroscopy were employed to evaluate the protein conformational changes. The Low-field NMR spectra analysis was used to evaluate moisture migration. The results indicated that the freeze-thaw cycles altered the secondary and tertiary structure of proteins. It was noticed that interactions between water and protein molecules were decreased gradually and eventually induced the thermal instability of the myosin molecules. The immobilised water content declined and the free water content increased. There were significant destructions in fillet muscle microstructure. These observations unambiguously reflect how the recrystallisations affect the protein conformation and moisture migration patterns of red seabream fillets during freeze-thaw cycles.     

插层水滑石/果胶纳米复合保鲜膜对鲤鱼的保鲜效果

目的 制备一种新型可降解复合保鲜膜,并探究其对鲤鱼的保鲜效果。方法 采用离子交换法合成一种新型插层水滑石-脱氢乙酸插层水滑石（MgAl-DHA-LDHs）。以果胶为主要成膜材料,甘油为增塑剂,脱氢乙酸根插层水滑石纳米材料为填充物, 合成MgAl-DHA-LDH/果胶复合保鲜膜。分别用 X 射线衍射（X-ray diffraction, XRD）、红外光谱（Fourier transform infrared spectrometer, FI-IR）分别对插层水滑石和复合保鲜膜进行表征, 并研究脱氢乙酸根插层水滑石复合物的添加量对鲤鱼保鲜效果的影响。结果 实验结果表明,脱氢乙酸根成功插入水滑石中,当MgAl-DHA-LDHs质量分数为0.2%时鲤鱼的保鲜效果最佳, 其菌落总数、硫代巴比妥酸值(TBARs)、挥发性盐基氮（TVB-N）、pH值均低于空白对照组。结论 此种复合保鲜膜对鲤鱼具有较好的保鲜效果, 可延长货架期5~6 d。     

市售西班牙自然发酵香肠的食用品质特征分析

以销量较高的市售西班牙自然发酵香肠为研究对象,通过感官评价筛选出喜好度较高的发酵香肠,测定香肠水分含量、pH值、色泽、质地等指标,采用顶空固相微萃取-气相色谱-质谱联用（headspace-solid phase microextraction-gas chromatography-mass spectrometry,HS-SPME-GC-MS）法分析香肠挥发性风味成分。结果表明,总体可接受性较高的自然发酵香肠具有以下特征：光泽度高、色泽暗红（亮度值16.028～31.399,红度值13.80～16.31）,组织紧密、质地均一、硬度（4 721.859 0～6 360.352 0 g）适中,pH值（5.68～5.89）、水分含量（20.12%～28.09%）较低,咀嚼感好、干燥度适中,果香味、清香味、甜味、乳香味、鲜味明显,咸味、酸味适中,胡椒味较淡。总体接受性最高的香肠（1号香肠）中检出81 种挥发性风味成分,其中乙醛、异戊醛、2,3-丁二酮、月桂烯、3-甲基丁酸乙酯、顺-4-羟基-6-十二烯酸内酯、乙酸为主要风味成分（香气活力值＞50）。     

蓝莓叶多酚单体化合物对TMAO-Fe(II)体系中TMAO热分解的影响

以氧化三甲胺-铁(Ⅱ)(trimethylamine oxide-Fe(Ⅱ),TMAO-Fe(Ⅱ))体外体系为研究对象,研究蓝莓叶多酚单体化合物对TMAO热分解的影响,并从自由基角度研究其反应机制。结果表明:蓝莓叶多酚单体化合物抑制TMAO-Fe(Ⅱ)体系中TMAO的热分解,显著降低体系中三甲胺、二甲胺和甲醛含量。质量分数越大,抑制效果越显著,槲皮素-3-D-半乳糖苷抑制效果优于绿原酸;随温度的升高,绿原酸和槲皮素-3-D-半乳糖苷对TMAO热分解有显著抑制作用。加热时间小于75 min,绿原酸和槲皮素-3-D-半乳糖苷抑制效果显著。槲皮素-3-D-半乳糖苷和绿原酸p H值分别为8.0和5.0时,抑制TMAO热分解效果最好。TMAO-Fe(Ⅱ)体系中TMAO的热分解过程中产生了自由基,绿原酸和槲皮素-3-D-半乳糖苷能够抑制自由基的产生,质量分数越高,则(CH3)3N自由基信号越弱;绿原酸和槲皮素-3-D-半乳糖苷通过抑制自由基的产生来抑制甲醛的形成。     

Purification of novel bacteriocin produced by Lactobacillus coryniformis MXJ 32 for inhibiting bacterial foodborne pathogens including antibiotic-resistant microorganisms

Bacteriocins produced by LAB comprise a variety of antimicrobial proteins or peptides which can be used as food biopreservatives and/or possible antibiotic alternatives. Bacteriocin-producing Lactobacillus coryniformis MXJ 32, which was identified based on its 16S rRNA gene sequence, was isolated from a traditional fermented vegetable (Jiangshui Cai) of Xixiang county, Shaanxi province, China. Thereafter bacteriocin (designated as lactocin MXJ 32A) produced by L. coryniformis MXJ 32 was purified by ammonium sulfate precipitation, dialysis and ion exchange chromatography. The molecular mass of lactocin MXJ 32A was 3520 Da determined by LC-ESI/MS and the N-terminal sequence of lactocin MXJ 32A was NH₂-GEPGPMGPAGAD. Lactocin MXJ 32A had a broad antimicrobial spectrum including many Gram-positive and Gram-negative foodborne pathogens, in which even some antibiotic-resistant foodborne pathogenic strains could also be inhibited. The MIC of lactocin MXJ 32A for Staphylococcus aureus and Escherichia coli was 10 mg/mL. Lactocin MXJ 32A showed good pH-stability and heat stability and was sensitive to proteolytic enzymes. It was shown by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) that the possible mode of action of lactocin MXJ 32A was pore formation of the cytoplasmic membrane of target cells.     

Passivity-based control for a non-isothermal tank used in the production of pineapple syrup

This short paper presents a design technique based on passivity for single input single output (SISO) systems through a process of feedback passivisation. The controller is implemented in the control of a tank non-isothermal for the production of pineapple syrup. The design of a model and the implementation to laboratory scale allowed the validation of the controller.