Bacterial Quorum Sensing and Food Industry

Abstract: Food spoilage and biofilm formation by food‐related bacteria are significant problems in the food industry. Even with the application of modern‐day food preservative techniques, excessive amounts of food are lost due to microbial spoilage. A number of studies have indicated that quorum sensing plays a major role in food spoilage, biofilm formation, and food‐related pathogenesis. Understanding bacterial quorum‐sensing signaling systems can help in controlling the growth of undesirable food‐related bacteria. This review focusses on the various signaling molecules produced by Gram‐negative and Gram‐positive bacteria and the mechanism of their quorum‐sensing systems, types of signaling molecules that have been detected in different food systems using biosensors, the role of signaling molecules in biofilm formation, and significance of biofilms in the food industry. As quorum‐sensing signaling molecules are implicated in food spoilage, based on these molecules potential, quorum‐sensing inhibitors/antagonists can be developed to be used as novel food preservatives for maintaining food integrity and enhancing food safety. Practical Application: Bacteria use signaling molecules for inter‐ and intracellular communication. This phenomenon of bacterial cell‐to‐cell communication is known as quorum sensing. Quorum‐sensing signals are implicated in bacterial pathogenicity and food spoilage. Therefore, blocking the quorum‐sensing signaling molecules in food‐related bacteria may possibly prevent quorum‐sensing‐regulated phenotypes responsible for food spoilage. Quorum‐sensing inhibitors/antagonists could be used as food preservatives to enhance the shelf life and also increase food safety.     

Attachment and biofilm formation of Pseudomonas fluorescens PSD4 isolated from a dairy processing line

The effects of different nutrient sources and temperatures on attachment and biofilm formation of Pseudomonas fluorescens PSD4, a dairy isolate, were studied. Initial adherence and attachment capabilities among different strains were studied using microtitre plate assays. Biofilm development was observed using confocal microscopy. Strongly adherent cells were seen in protein rich media. Citrate as a carbon source enhanced biofilm formation. Glucose did not favor biofilm development. Psychrotrophic P. fluorescens PSD4 formed strongly adherent biofilms having high metabolic activities at low temperatures. P. fluorescens PSD4 with spoilage potential was capable of forming strong biofilms in dairy processing environments. Biofilm formation was influenced by nutrient availability and growth conditions. These factors should be considered for design of effective anti-biofilm strategies.     

Dissociation Energies of S2, SO,Te2, SeO and P2 Molecules

The ground state dissociation energies of S₂, SO, Te₂, SeO and P₂ molecules have been estimated by fitting the Szöke and Baitz electronegativity potential energy curves to the experimental RKRV curves. The estimates of dissociation energies obtained have been compared with earlier calculations.     

Electrical and Thermal Properties of Twin-Screw Extruded Multiwalled Carbon Nanotube/Epoxy Composites

This paper presents the experimental results of dispersing multiwalled carbon nanotubes (MWNTs) into epoxy (space grade structural adhesive) nanocomposites using co-rotating twin screw extrusion process. Two sets of specimens were prepared; set 1 with ultrasonication for predispersing MWNT before extrusion and set 2 direct dispersion of MWNT in the extruder. MWNT was loaded up to 8 vol.% in both the sets. The specimens were characterized for room temperature volume and surface resistivities as per ASTM D257 using Keithley Model 6517 and for thermal conductivity in the temperature range ?50 to 150 °C as per ASTM E 1530 using Thermal Conductivity Instrument (TCI) 2022 SX211. The volume resistivity of sets 1 and 2 decreased to an extent of 10¹¹ and 10⁹ respectively. The surface resistivity drop was of the order of 10⁹ for both the sets. These drops corresponded to the maximum MWNT loading of 8 vol.%. Electrical conductivity values of the specimens were fitted into the Power Law Model to evaluate the critical exponent. Both sets 1 and 2 showed increase in thermal conductivity with increase in temperature in the testing range. Thermal conductivity increased with increase in filler loading and the maximum increase was 60% at 150 °C in case of 8 vol.% MWNT nanocomposites for set 1. The corresponding value for the set 2 was 25%. Thermal conductivity values were predicted using Lewis Nielson model. DSC of the specimens showed increase in glass transition temperature with increase in filler loading. The dispersion of the nanofillers was studied using SEM and the surface morphology using AFM.     

A risk management approach to safety assessment of trenchless technologies for culvert rehabilitation

Proper functioning of culverts is not only critical to protecting the transportation system from flooding but also critical to maintaining the expected service life of the overall transportation system. During the service life of culverts, they deteriorate due to many reasons such as corrosion caused by road salt, blockage by debris and sediment, poor construction techniques, etc. Trenchless technologies have been used by several State Departments of Transportation (DOTs) to rehabilitate deteriorated drainage structures without disrupting the traffic and within a relatively short span of time. These technologies provide many benefits in terms of cost, time, quality, and expected service life. However, the safety aspects of these techniques have not been discussed and documented in detail probably due to the complexity and the lack of safety standards and specifications directly associated with the techniques. This paper discusses the application of a risk assessment framework to assess potential safety issues of currently available trenchless technologies for culvert rehabilitation. The findings of the study will provide additional information to improve the decision making process in selecting and planning culvert rehabilitation projects.     

Heat-induced Maillard reaction of the tripeptide IPP and ribose: Structural characterization and implication on bioactivity

Maillard reaction products (MRPs) were prepared from aqueous model mixtures containing 60 g L^? 1 ribose and 30 g L^? 1 of the bioactive tripeptide IPP (Ile-Pro-Pro), heated at 98 °C. MRP and associated reactions with changes in IPP were observed within one hour of heat-treatment. The pH of MRPs decreased significantly during the heat treatment of IPP–ribose mixtures from 9.0 to 7.6 after one hour. The amino group content, IPP and ribose concentration decreased significantly during heat treatment. The fluorescence intensity of the IPP–ribose MRPs reached the maximum within 2 h. Modification of the UV/vis spectra for IPP–ribose MRPs was mainly due to a condensation reaction of IPP with ribose. Compounds with molecular weight between 300 and 650 Da were dominant while compounds smaller than 250 Da were also produced during the reactions, as characterized by size exclusion chromatography. Mass spectrometry revealed that IPP was conjugated to ribose at the N-terminal (m/z of 458.3) upon heat-treatment. The presence of ribose also promoted peptide degradation to dehydrated IP (m/z of 211.1). IPP–ribose MRPs lost the known angiotensin-I-converting enzyme (ACE) inhibitory activity of IPP; however, strong antioxidant properties were detected.     

A computer approach for reliability evaluation of telecommunicationnetworks with heterogeneous link-capacities

The authors present a computer approach to obtaining a survivability index called capacity related reliability (CRR) in large telecommunication networks where links have different capacities. The method is a two-step approach. The first step deals with composite path enumeration (CPE). A k-composite path is defined as the union of the set of edges in any k simple paths and relates link capacity and network connectivity. The CPE approach is an improvement over the algorithms proposed by the authors earlier (1991). In step two, k-composite paths information is manipulated to generate the CRR. The authors use CAREL (computer aided reliability evaluator) to solve this step. The technique is automated using C on the Encore Multimax System. The results on CRR for three networks with various values of minimum message capacity are presented. An exhaustive technique is used to verify these results. An informal proof of the CPE approach is also included     

Studies in surface chemistry of carbon blacks-vi. adsorption isotherms of benzene on carbons associated with different surface oxygen complexes

Adsorption isotherms of benzene (35°C) on carbon blacks are of Type II and show complete reversibility. The presence of CO₂-complex, which imparts polar and hydrophilic character to the surface, suppresses the sorption of benzene but its elimination and the emergence of CO-complex as the only predominant complex enhances the sorption at all r.v.p's. The additional sorption amounts roughly to one molecule of benzene per quinonic oxygen as obtained by sodium borohydride treatment. This indicates probability of interaction of π electrons of benzene ring with partial positive charge on carbonyl carbon atom. The isosteric heat of adsorption is also higher in the presence of quinonic oxygen. The use of benzene isotherms for estimating surface area or pore volume of carbons may, therefore, be looked upon with caution. The isotherm on sugar charcoal also shifts bodily upward with the emergence of CO-complex but the adsorbed benzene cannot be recovered even on prolonged evacuation, showing that the benzene complexed at the quinonic sites within the microporous system requires activation energy to diffuse out of the pores. The interaction of benzene, due to the presence of π electrons, seems to be specific, since the isotherms of cyclohexane on a given carbon black are identical irrespective of the nature or amount of any of the surface oxygen complexes present in it.