An antibacterial film using κ-carrageenan loaded with benzyl isothiocyanate nanoemulsion: Characterization and application in beef preservation.

Benzyl isothiocyanate (BITC) is a naturally active bacteriostatic substance and κ-carrageenan (KC) is a good film-forming substrate. In the present study, a nanoemulsion incorporating BITC was fabricated with a particle size of 224.1 nm and an encapsulation efficiency of 69.2 %. Subsequently, the acquired BITC nanoemulsion (BITC-NE) was incorporated into the KC-based film, and the light transmittance of the prepared composite films was lower than that of the pure KC film. Fourier transform infrared spectroscopy and scanning electron microscopy revealed that BITC-NE was compatible with the KC matrix. BITC-NE incorporation enhanced the tensile strength of the KC-based films by 33.7 %, decreased the elongation at break by 33.8 %, decreased the water vapor permeability by 60.1 %, increased the maximum thermal degradation temperature by 48.8 %, and decreased the oxygen permeability by 42 % (p < 0.05). Furthermore, the composite films showed enhanced antimicrobial activity against Staphylococcus aureus, Salmonella typhimurium, and Pseudomonas fluorescens. The developed KC-based composite films were applied to wrap raw beef, which significantly delayed the increase in total viable count, total volatile base nitrogen content, and thiobarbituric acid reactive substances, and prolonged the shelf-life of the raw beef by up to 10 days. These results indicated that the composite films prepared by incorporating BITC nanoemulsions into KC matrices have great antimicrobial application potential.

The N270 as an index of consumer commodity color preference in the S1-S2 paradigm.

Introduction: Affective decision-making is a prominent topic in consumer psychology research, with its core assumption being that consumers tend to purchase brands and commodities they like. However, the reasons behind why we develop emotional responses of liking or disliking toward certain commodities, as well as what the underlying neural mechanisms are, remain largely unknown. Methods: This study utilized the S1-S2 paradigm in an experiment wherein S1 presented 12 types of commodities and S2 displayed 48 distinct colored squares. Participants were instructed to assess whether they "Like" or "Dislike" the commodity in S1, which was colored with the S2 color. Electroencephalogram (EEG) recordings were obtained during the reaction process and subsequently analyzed to examine the components of S2-induced event-related potentials (ERPs). Results: The analysis revealed that S2 elicited a significant N270 in the prefrontal scalp area under both the "Like" and "Dislike" conditions. Interestingly, the amplitude of the N270 was significantly higher during the "Dislike" condition compared to the "Like" condition. Discussion: The N270 component was shown to reflect the conflict in physical attributes between S1 and S2, as well as the conflict between commodity and color. This highlights the potential utility of this component as an objective EEG indicator of consumer commodity color preferences in future marketing research.

In-situ growth of metal-organic frameworks on cellulose nanofiber aerogels for rapid adsorption of heterocyclic aromatic amines.

Heterocyclic aromatic amines (HAAs) are the main carcinogens produced during thermal processing of protein-rich foods. In this paper, a composite aerogel (TOCNFCa) with a stabilized dual-network structure was prepared via a template for the in-situ synthesis of UiO-66 on cellulose for the adsorption of HAAs in food. The dual-network structure of TOCNFCa provides the composite aerogel with excellent wet strength, maintaining excellent compressive properties. With the in-situ grown UiO-66 content up to 71.89 wt%, the hierarchical porosity endowed TOCNFCa@UiO-66 with the ability to rapidly adsorb HAAs molecules with high capacity (1.44-5.82 µmol/g). Based on excellent thermal stability, adsorption capacity and anti-interference, TOCNFCa@UiO-66 achieved satisfactory recoveries of HAAs in the boiled marinade, which is faster and more economical than the conventional SPE method. Moreover, TOCNFCa@UiO-66 could maintain 84.55 % of the initial adsorption capacity after 5 times of reuse.

Defective UiO-66/cellulose nanocomposite aerogel for the adsorption of heterocyclic aromatic amines.

Heterocyclic aromatic amines (HAAs), arising as chemical derivatives during the high-temperature culinary treatment of proteinaceous comestibles, exhibit notable carcinogenic potential. In this paper, a composite aerogel (AGD-UiO-66) with high-capacity and fast adsorption of HAAs was made with anchoring defective UiO-66 (D-UiO-66) mediated by lauric acid on the backbone of cellulose nanofibers (CNF). AGD-UiO-66 with hierarchical porosity reduced the mass transfer efficiency for the adsorption of HAAs and achieved high adsorption amount (0.84-1.05 µmol/g) and fast adsorption (15 min). The isothermal adsorption model demonstrated that AGD-UiO-66 belonged to a multilayer adsorption mechanism for HAAs. Furthermore, AGD-UiO-66 was successfully used to adsorb 12 HAAs in different food (roasted beef, roasted pork, roasted salmon and marinade) with high recoveries of 94.65%-104.43%. The intrinsic potential of AGD-UiO-66 demonstrated that it could be widely applicable to the adsorption of HAAs in foods.

Rapid and large-capacity adsorption of heterocyclic aromatic amines on heat resistant two-dimensional metal organic layer/cellulose nanofiber aerogels constructed by a thawing cross-linking strategy.

Composite aerogels, formed by the combination of nanoscale polymers and highly efficient adsorbents, offer the potential to deploy adsorbent distinct separation properties into a processable matrix. This paper presents a method for the fabrication of low energy bio-aerogels with high ductility, excellent wet strength and favorable heat resistance, based on cellulose nanofibers (CNFs) bound by calcium carbonate particles (CaCO3) via a simple process of ice induction, cross-linking during freezing and freeze-drying. Due to induced defects, two-dimensional metal-organic layers (MOLs) were rich in mesoporous structure and embedded in the aerogel (AGCa-MOL), which exhibited a powerful adsorption capacity. AGCa-MOL could take full advantage of their hierarchical pores and available surface area to obtain high adsorption capacity (0.694-5.470 µmol/g) and rapid adsorption kinetics (5 min) for 14 heterocyclic aromatic amines (HAAs). Moreover, the CaCO3 particles and MOLs gave the AGCa-MOL excellent thermal stability, so that it could maintain excellent adsorption capacity at a high temperature (100 °C) and be applied as an adsorbent to remove HAAs in the boiling marinade. The intrinsic potential of composite aerogels was revealed due to the synergistic properties of the various components in the composite aerogel.

Amino carboxymethyl chitosan//dialdehyde starch/polyvinyl alcohol double-layer film loaded with ε-polylysine.

To develop food packaging with good antibacterial activity and mechanical performance, four amino carboxymethyl chitosan (ACC)//dialdehyde starch (DAS) /polyvinyl alcohol (PVA) films were prepared by Schiff base and hydrogen bond interactions for efficient loading and release of ε-polylysine (ε-PL). The effects of the Schiff base reaction on the physicochemical properties of the films were explored based on the different aldehyde group contents in DAS. The ACC//DAS4/PVA film exhibited a tensile strength of 62.5 MPa, and the water vapor and oxygen permeability was 8.77 × 10-3·g·mm/m2·d·kPa and 0.15 × 103·cm3·mm/m2·d, respectively. By leveraging the Schiff base reaction, the film swelling properties were improved by adjusting the cross-link density, mesh size, and molecular mass between the cross-links. The ACC//DAS4/PVA film could efficiently load ε-PL with a value of 98.44% and long-term release in a food simulant of 10% ethanol at 25 °C for 120 min. Moreover, the ACC-ε-PL//DAS4/PVA film was successfully used for salmon preservation.

Preoperative Range of Motion in Extension May Influence Postoperative Cervical Kyphosis After Laminoplasty.

STUDY DESIGN: Retrospective observational study. OBJECTIVE: The objective of this study was to investigate factors associated with cervical kyphosis after laminoplasty. SUMMARY OF BACKGROUND DATA: Many factors are reportedly associated with the deterioration of cervical curvature after laminoplasty, including cervical lordosis angle, cervical spine range of motion (ROM), T1 slope, and C2-C7 sagittal vertical axis. Postlaminoplasty kyphosis or deterioration of cervical curvature is likely caused by multiple factors. There is currently no consensus on these issues. MATERIALS AND METHODS: Data of patients treated with laminoplasty for degenerative cervical myelopathy at our institution during 2008-2018 were reviewed. The following variables were collected for each patient: age and sex; follow-up time; surgery involving C3 (yes or no); surgery involving C7 (yes or no); distribution of segments operated on; number of laminae operated on; flexion, extension, and total ROM; cervical lordotic angle; longitudinal distance index; curvature index; C2-C7 sagittal vertical axis; and T1 slope. Logistic regression analysis was used to assess possible risk factors for postoperative kyphosis. Receiver operating characteristic curves were constructed to determine the cutoff values of risk factors. RESULTS: The study cohort comprised 151 patients. Logistic regression analysis indicated that sex, number of laminae operated on, and preoperative extension ROM were significantly associated with postoperative cervical kyphosis ( P <0.05). There was significantly greater postoperative kyphosis in women than in men; the more segments operated on, the greater the risk of postoperative kyphosis, and the larger the preoperative extension ROM, the lower the risk of postlaminoplasty kyphosis. Receiver operating characteristic curve analysis showed that the cutoff value for preoperative extension ROM is 22.1°. CONCLUSIONS: Preoperative extension ROM may be associated with the development of postoperative kyphosis. The cutoff value of preoperative extension ROM that suggested the prospect of postoperative kyphosis in our sample was 22.1°.

Hierarchical Porous Nanocellulose Aerogels Loaded with Metal-Organic Framework Particles for the Adsorption Application of Heterocyclic Aromatic Amines.

This work overcomes the long-standing challenge of cumbersome pretreatment methods in the detection of heterocyclic aromatic amines (HAAs). A UiO-66/nanocellulose composite aerogel (CMC-CNC-UiO-66) with layered pores and low density prepared by a self-cross-linking method is applied as a simple and rapid adsorbent for capturing 14 HAAs via strong electrostatic interactions, van der Waals force, and the steric effect. The adsorption capacity of CMC-CNC-UiO-66 to 14 HAAs reached 98.00-188.00 nmol/mg at equilibrium within 10 min. The adsorption and desorption abilities of CMC-CNC-UiO-66 were retained with values of 93.36 and 97.34% after two cycles. In the meantime, the kinetics study demonstrated the chemisorption between HAA molecules and CMC-CNC-UiO-66 due to the excellent agreement with the pseudo-second-order adsorption models. The fit with the Freundlich isotherm models suggested a multilayer adsorption mechanism between HAA molecules and materials with heterogeneous surfaces. Moreover, coupled with the ultrahigh-performance liquid chromatography-tandem mass spectrometry detection, the CMC-CNC-UiO-66 extraction process can be completed with a high average recovery ranging from 86.68 to 115.33%, indicating a potential application of CMC-CNC-UiO-66 in HAA adsorption for further quantitative analysis.

Preparation of chitosan-cellulose-benzyl isothiocyanate nanocomposite film for food packaging applications.

To improve the mechanical and barrier properties of cellulose and chitosan (CS) and to allow the application of volatile antibacterial benzyl isothiocyanate (BITC) in active packaging, a double-layer nanocomposite film was prepared. Cellulose nanofibers (CNF) were crosslinked with CS via genipin to build the substrate. Quaternized cellulose nanocrystals (QCNC) were synthesized for carrying BITC as the coating material. By the layer-by-layer self-assembly approach, CS-CNF/QCNC-BITC film was fabricated. This film possessed the tensile strength of 33.75 MPa, low permeabilities of oxygen (6.9 × 10-17 m3/s·m·Pa) and moisture (1.2 × 10-11 g/s·m·Pa), and good antibacterial activity with the inhibition zone diameters of 4.9, 4.2 and 2.7 cm against Escherichia coli, Salmonella typhimurium and Staphylococcus aureus. The total viable count, total volatile basic nitrogen and thiobarbituric acid-reactive substances of the chicken wrapped CS-CNF/QCNC-BITC were only 4.4 log CFU/g, 17.7 mg/100 g and 0.44 mg/kg at 14 days, indicating a potential application of CS-CNF/QCNC-BITC for food packaging.

Novel procyanidins-loaded chitosan-graft-polyvinyl alcohol film with sustained antibacterial activity for food packaging.

Active food packaging materials containing procyanidins (PC) exhibits outstanding antimicrobial activity, but PC is easy to be hydrolyzed by acid. A novel water-soluble chitosan (CS)-based copolymer was prepared to be used as a carrier to provide a pH-stable environment for loading PC. CS was copolymerized with polyvinyl alcohol (PVA) via a coupling reagent-mediated approach. The CS-graft-PVA film exhibited a desirable PC encapsulation efficiency of over 95% and excellent long-term release sustainability, which was better than the conventional CS and CS-blend-PVA films. Moreover, CS-graft-PVA film had satisfactory mechanical properties and barrier properties, as well possessed a desirable antibacterial activity and biofilm inhibition against foodborne pathogenic microbes and spoilage bacteria. The film was also applied in the salmon muscle perseveration and showed a potential ability to prevent microorganism contamination and texture deterioration in 10 days. These results suggested that the CS-graft-PVA film has an excellent promise for future food packaging applications.

Antibacterial Activity and Potential Application in Food Packaging of Peptides Derived from Turbot Viscera Hydrolysate.

As a good choice for food preservation, antimicrobial peptides (AMPs) have received much attention in recent years. In this paper, peptides derived from the turbot viscera hydrolysate were identified by ultraperformance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS/MS), and the physicochemical properties and structural characteristics were analyzed by in silico tools. Furthermore, three cationic peptides with potential hydrophobicity and amphipathy were synthesized; their cytotoxicity, hemolysis, and antibacterial activities were investigated. In particular, Sm-A1 (GITDLRGMLKRLKKMK), a peptide with 16 amino acids, showed an outstanding antibacterial activity against both Gram-positive and Gram-negative bacteria by damaging the cell membrane integrity. Moreover, Sm-A1 was successfully loaded into hydroxyl-rich poly(vinyl alcohol) (PVA)/chitosan (CS) hydrogel to improve the antibacterial activity and biofilm inhibition effect. PVA/CS+7.5‰ Sm-A1 hydrogel can satisfactorily protect the salmon muscle from the microbiological contamination and texture deterioration.

Detection of Histamine Based on Gold Nanoparticles with Dual Sensor System of Colorimetric and Fluorescence.

Gold nanoparticles (Au-NPs), with the dual sensor system of colorimetric and fluorescence responses, were developed for the determination of histamine as a spoilage monitor for distinguishing lifetime and freshness of aquatic products. Upon addition of histamine, the absorption coefficient orders of magnitude via the interaction of free electrons and photons were affected, and the characteristic absorption peak of Au-NPs was red-shifted from 520 nm to 664 nm. Meanwhile, the large amino groups in the networks of histamine-Au-NPs with high molecular orbital exhibited excellent fluorescence behavior at 415 nm. Au-NPs offered a range of 0.001-10.0 µM and 0.01-1.0 µM with a limit of detection of 0.87 nM and 2.04 nM by UV-vis and fluorescence spectrum assay, respectively. Moreover, Au-NPs could be used to semiquantitatively analyze histamine with the naked eye, since the significant colorimetric and fluorescence reaction of Au-NPs solution that coincided with different concentrations of histamine can be observed as the histamine concentration was 0.1-1.0 µM. Both of the dual-sensor systems of Au-NPs were successfully applied to the quantitative analysis of histamine in fresh salmon muscle, suggesting the simplicity and rapidity in the dual detection approaches of Au-NPs might be suitable for spoilage assay of aquatic food to ensure food safety.

Transcriptomic Analysis, Motility and Biofilm Formation Characteristics of Salmonella typhimurium Exposed to Benzyl Isothiocyanate Treatment.

Salmonella typhimurium (S. typhimurium) is a common foodborne pathogen that not only causes diseases and contaminates food, but also causes considerable economic losses. Therefore, it is necessary to find effective and feasible methods to control S. typhimurium. In this study, changes in S. typhimurium after treatment with benzyl isothiocyanate (BITC) were detected by transcriptomics to explore the antibacterial effect of BITC at subinhibitory concentration. The results showed that, in contrast to the control group (SC), the BITC-treated group (SQ_BITC) had 197 differentially expressed genes (DEGs), of which 115 were downregulated and 82 were upregulated. We screened out eight significantly downregulated virulence-related genes and verified gene expression by quantitative Real-time Polymerase Chain Reaction (qRT-PCR). We also selected motility and biofilm formation to observe the effects of BITC on the other virulence related factors of S. typhimurium. The results showed that both swimming and swarming were significantly inhibited. BITC also had a significant inhibitory effect on biofilm formation, and showed an effect on bacterial morphology. These results will be helpful for understanding the mechanism of the antibacterial action of BITC against S. typhimurium and other foodborne pathogens.

AHLs Regulate Biofilm Formation and Swimming Motility of Hafnia alvei H4.

The aim of this study was to evaluate the role of N-acyl homoserine lactones (AHLs) in the regulation of swimming motility of Hafnia alvei H4 and its biofilm formation on 96-well plate, glass and stainless-steel surfaces. The luxI gene, which codes for an enzyme involved in AHL synthesis, was deleted to generate a luxI mutant (ΔluxI). The mutant produced no AHL, and the relative expression of the luxR gene was significantly (P < 0.05) decreased. In addition, qRT-PCR analysis showed that the relative expression of the luxR gene in ΔluxI was stimulated by the presence of exogenous AHLs (C4-HSL, C6-HSL, and 3-o-C8-HSL) added at concentrations ranging from of 50-250 µg/ml. Among the three AHLs, C6-HSL had the strongest effect. The ability of ΔluxI to form biofilm on 96-well plate, glass and stainless-steel surfaces was significantly reduced (P < 0.05) compared with the wild type (WT), but was increased when provided with 150 µg/ml C4-HSL, whereas C6-HSL and 3-o-C8-HSL had no effect. Scanning electron microscopy analysis of the biofilm revealed less bacteria adhering to the surface of stainless-steel and fewer filaments were found binding to the cells compared with the WT. Furthermore, ΔluxI also exhibited significant (P < 0.05) decrease in the expression of biofilm- and swimming motility-related genes, flgA, motA and cheA, consistent with the results observed for biofilm formation and swimming motility. Taken together, the results suggested that in H. alvei H4, C4-HSL may act as an important molecular signal through regulating the ability of the cells to form biofilm, as well as through regulating the swimming motility of the cell, and this could provide a new way to control these phenotypes of H. alvei in food processing.

Bottom-up and top-down factors of motion direction learning transfer.

Perceptual learning of motion discrimination has long been believed to be motion direction specific. However, recent studies using a double-training paradigm, in which the to-be-transferred condition was experienced through practicing an irrelevant task, found that perceptual learning in various visual tasks, including motion direction discrimination, can transfer completely to new conditions. This transfer occurred when the transfer stimulus was subconsciously presented, or when top-down attention was allocated to the transfer stimulus (which was absent). In the current study, observers were exposed subconsciously, or directed top-down attention, to the transfer motion direction, either simultaneously or successively with training. Data showed that motion direction learning transferred to the transfer direction, and suggest that motion direction learning specificity may result from under-activations of untrained visual neurons due to insufficient bottom-up stimulation and/or lack of top-down attention during training. These results shed new light on the neural mechanisms underlying motion perceptual learning and provide a constraint for models of motion perceptual learning.

Transcriptomic Analysis of Vibrio parahaemolyticus Reveals Different Virulence Gene Expression in Response to Benzyl Isothiocyanate.

Vibrio parahaemolyticus isolated from seafood is a pathogenic microorganism that leads to several acute diseases that are harmful to our health and is frequently transmitted by food. Therefore, there is an urgent need for the control and suppression of this pathogen. In this paper, transcriptional analysis was used to determine the effect of treatment with benzyl isothiocyanate (BITC) extracted from cruciferous vegetables on V. parahaemolyticus and to elucidate the molecular mechanisms underlying the response to BITC. Treatment with BITC resulted in 332 differentially expressed genes, among which 137 genes were downregulated, while 195 genes were upregulated. Moreover, six differentially expressed genes (DEGs) in RNA sequencing studies were further verified by quantitative real-time polymerase chain reaction (qRT-PCR). Genes found to regulate virulence encoded an l-threonine 3-dehydrogenase, a GGDEF family protein, the outer membrane protein OmpV, a flagellum-specific adenosine triphosphate synthase, TolQ protein and VirK protein. Hence, the results allow us to speculate that BITC may be an effective control strategy for inhibiting microorganisms growing in foods.

Influence of Oxygen-Containing Sulfur Flavor Molecules on the Stability of ß-Carotene under UVA Irradiation.

The influence of 11 kinds of oxygen-containing sulfur flavor molecules was examined on ß-carotene stability under UVA irradiation in ethanol system. Both the effects of sulfides on dynamic degradation of ß-carotene and the relation between structure and effect were investigated. The oxidation products of ß-carotene accelerated by sulfides under UVA irradiation were also identified. The results indicated that the disulfides had more obvious accelerative effects on the photodegradation of ß-carotene than mono sulfides. The degradation of ß-carotene after methyl (2-methyl-3-furyl) disulfide (MMFDS), methyl furfuryl disulfide (MFDS) and bis(2-methyl-3-furyl) disulfide (BMFDS) exposure followed first-order kinetics. Furan-containing sulfides such as MMFDS and BMFDS showed more pronounced accelerative effects than their corresponding isomers. The oxidation products were identified as 13-cis-ß-carotene, 9,13-di-cis-ß-carotene and all-trans-5,6-epoxy-ß-carotene. These results suggest that both the sulfur atom numbers and the furan group in oxygen-containing sulfides play a critical role in the photooxidation of ß-carotene.

A consumer-grade LCD monitor for precise visual stimulation.

Because they were used for decades to present visual stimuli in psychophysical and psychophysiological studies, cathode ray tubes (CRTs) used to be the gold standard for stimulus presentation in vision research. Recently, as CRTs have become increasingly rare in the market, researchers have started using various types of liquid-crystal display (LCD) monitors as a replacement for CRTs. However, LCDs are typically not cost-effective when used in vision research and often cannot reach the full capacity of a high refresh rate. In this study we measured the temporal and spatial characteristics of a consumer-grade LCD, and the results suggested that a consumer-grade LCD can successfully meet all the technical demands in vision research. The tested LCD, working in a flash style like that of CRTs, demonstrated perfect consistency for initial latencies across locations, yet showed poor spatial uniformity and sluggishness in reaching the requested luminance within the first frame. After these drawbacks were addressed through software corrections, the candidate monitor showed performance comparable or superior to that of CRTs in terms of both spatial and temporal homogeneity. The proposed solution can be used as a replacement for CRTs in vision research.

The Time Course of Inhibition of Return: Evidence from Steady-State Visual Evoked Potentials.

Inhibition of return (IOR) refers to slower responses to targets at a previously cued location than that at an uncued location. The time course of IOR has long been a topic of interest in the field. Investigations into the time course of IOR are typically performed by examining the magnitude of IOR under various cue-target onset asynchrony (CTOA) conditions. Therefore, the results are vulnerable to influence of factors that could affect the target processes (e.g., the frequency of the target type). In the present study, steady-state visual evoked potentials (SSVEPs) were implemented to directly take a continuous measurement of the degree to which cued location is processed, eliminating the influence mentioned above. The results indicate that, relative to the baseline interval (-400 to 0 ms), the presence of peripheral cues generated a typical two-stage effect on the SSVEP amplitude evoked by a 20 Hz flicker. Specifically, after the onset of the peripheral cues, the SSVEP amplitude first showed a significant increase, which subsequently turned into a significant inhibition effect after 200 ms. These results provide a continuous time course diagram of the cueing effect and suggest an effective way for future investigations of controlling the masking effects of target stimuli processing on IOR.

Characteristics of N-Acylhomoserine Lactones Produced by Hafnia alvei H4 Isolated from Spoiled Instant Sea Cucumber.

This study aimed to identify N-acylhomoserine lactone (AHL) produced by Hafnia alvei H4, which was isolated from spoiled instant sea cucumber, and to investigate the effect of AHLs on biofilm formation. Two biosensor strains, Chromobacterium violaceum CV026 and Agrobacterium tumefaciens KYC55, were used to detect the quorum sensing (QS) activity of H. alvei H4 and to confirm the existence of AHL-mediated QS system. Thin layer chromatography (TLC) and high resolution triple quadrupole liquid chromatography/mass spectrometry (LC/MS) analysis of the AHLs extracted from the culture supernatant of H. alvei H4 revealed the existence of at least three AHLs: N-hexanoyl-l-homoserine lactone (C6-HSL), N-(3-oxo-octanoyl)-l-homoserine lactone (3-oxo-C8-HSL), and N-butyryl-l-homoserine lactone (C4-HSL). This is the first report of the production of C4-HSL by H. alvei. In order to determine the relationship between the production of AHL by H. alvei H4 and bacterial growth, the ß-galactosidase assay was employed to monitor AHL activity during a 48-h growth phase. AHLs production reached a maximum level of 134.6 Miller unites at late log phase (after 18 h) and then decreased to a stable level of about 100 Miller unites. AHL production and bacterial growth displayed a similar trend, suggesting that growth of H. alvei H4 might be regulated by QS. The effect of AHLs on biofilm formation of H. alvei H4 was investigated by adding exogenous AHLs (C4-HSL, C6-HSL and 3-oxo-C8-HSL) to H. alvei H4 culture. Biofilm formation was significantly promoted (p < 0.05) by 5 and 10 µM C6-HSL, inhibited (p < 0.05) by C4-HSL (5 and 10 µM) and 5 µM 3-oxo-C8-HSL, suggesting that QS may have a regulatory role in the biofilm formation of H. alvei H4.