Assessment of factors influencing antimicrobial activity of carvacrol and cymene against Vibrio cholerae in food

Carvacrol and cymene, phenolic compounds naturally present in the essential oil of oregano and thyme, were examined for their antimicrobial activity against Vibrio cholerae (ATCC 14033, VC1, and VC7) inoculated in carrot juice. Carvacrol exhibited a dose dependent inhibitory effect on the bacteria. Although cymene did not have antimicrobial activity against the bacteria, it enhanced the inhibitory ability of carvacrol. At 25 °C, the lowest concentrations of carvacrol and cymene required for zero detectable viable count varied depending on bacterial strains; 5 and 5 ppm, respectively, for VC7; 5 and 7.5 ppm, respectively, for VC1; and 7.5 and 7.5 ppm, respectively, for ATCC 14033. This study also examined several factors influencing the antimicrobial activity of carvacrol and cymene against V. cholerae ATCC 14033, including temperature, bacterial cell number, and food substrate. Carvacrol and cymene inhibited the bacterium in carrot juice at 25 °C more efficiently than at 15 and 4 °C. The doses of both compounds required for zero detectable viable count increased as the number of the bacterial cells in the carrot juice increased. The fat content and the complexity of foods were shown to decrease the antimicrobial activity of the compounds.     

Use of the gfp gene in monitoring bacteriocin-producing Lactobacillus plantarum N014, a potential starter culture in nham fermentation

Lactobacillus plantarum N014 is a bacteriocin-producing lactic acid bacteria originally isolated from nham, a traditional Thai fermented sausage, and in the process of development to be used as a starter culture for nham fermentation. During the fermentation process, there is a need to identify the starter culture among several naturally occurring bacteria. In this study, a new plasmid carrying the gfp (green fluorescent protein) gene was constructed based on pGKV210, an Escherichia coli/ Lactococcus shuttle vector containing an erythromycin resistance marker. The gfp gene derived from pGFPuv was placed under the control of an L-lactate dehydrogenase promoter and then inserted at the EcoRI site of pGKV210, leading to pN014-GFP. The novel plasmid was used to transform L. plantarum N014, which is a bacteriocin-producing lactic acid bacteria isolated from nham. The resulting transformant, L. plantarum N014-GFP+, was brightly fluorescent and harbored the expected plasmid. A plasmid stability test revealed that pN014-GFP was stable after 100 generations of growth under nonselective pressure. L. plantarum N014-GFP+ and its parent strain were shown to be very similar in growth rate, bacteriocin production, and lactate production. L. plantarum N014-GFP+ was able to survive in a nham model. The survival clones were still fluorescent and harbored pN014-GFP.     

Incidence of nisin Z production in Lactococcus lactis subsp. lactis TFF 221 isolated from Thai fermented foods

Lactic acid bacteria isolated from various Thai fermented foods were screened for the presence of nisin gene by using PCR with primers specific to nisin A structural gene. Only one strain, Lactococcus lactis subsp. lactis TFF 221, isolated from kung jom, a traditional shrimp paste, was found to carry a nisin gene. The TFF 221 nisin had antimicrobial activity against not only closely related lactic acid bacteria but also some foodborne pathogens. It was heat stable and inactivated by alpha-chymotrypsin and proteinase K. Some characteristics of TFF 221 nisin were found to be very similar to those of nisin A produced by Lactococcus lactis subsp. lactis NCDO 2111. Both of them had the same antimicrobial spectrum and MICs against all indicator bacteria. However, when assayed with indicator organisms, in all cases the TFF 221 nisin produced larger zones of inhibition in agar diffusion assays than the nisin A did. Sequencing of the TFF 221 nisin gene showed that it was the natural nisin variant, nisin Z, as indicated by the substitution of asparagine residue instead of histidine at position 27. The nisin determinant in strain TFF 221 was found to be located on a conjugative transposon residing in the chromosome. The ability of the nisin produced by L. lactis subsp. lactis TFF 221 to inhibit a wide range of foodborne pathogens may be useful in improving the food safety of the fermented product, especially in the Thai environment, which suffers from perennial problems of poor food hygiene.     

Structure-forming processes in Ca-induced whey protein isolate cold gelation

The structure-forming process of Ca²⁺-induced whey protein isolate (WPI) gels was studied, at 24°C, in the presence of 10 and 120 m CaCl₂. Pre-heating WPI suspensions (10% protein) at 90°C dramatically increased specific viscosity, but did not change the number of accessible sulfhydryl groups, compared to pre-heating at 70°C. The most important factor governing the process appeared to be CaCl₂ concentration, rather than the reactive sulfhydryl groups. At 10 m CaCl₂, the increase in aggregate size and network connectivity over time was achieved by clustering of adjacent aggregates. At 120 m CaCl₂, the increase in aggregate size and connectivity was by enlargement of the aggregates which formed connected paths and filled up interstitial spaces.     

Anionic and Cationic Surfactant Synergism: Minimizing Precipitation,Microemulsion Formation,and Enhanced Solubilization and Surface Modification

Anionic–cationic surfactant mixtures are known to exhibit synergistic effects (e.g., low critical micelle concentration, ultralow interfacial tension, middle phase microemulsion formulation, and increased solubilization and adsolubilization). However, the anionic–cationic surfactant mixtures are also prone to form other unique phases such as precipitates, gels, and coacervates in place of middle-phase microemulsions. Research summarized in this article demonstrates that asymmetric anionic–cationic surfactant mixtures have been shown to promote middle-phase microemulsions instead of these other phases, albeit with a slight decrease in synergism when using these asymmetric mixtures. The use of anionic–cationic surfactant mixtures also is shown to enhance or decrease surfactant adsorption depending on anionic–cationic surfactant ratios. Middle-phase microemulsion formation is demonstrated using anionic-rich or cationic-rich alcohol-free microemulsions by anionic–cationic ratio scans while also reducing or eliminating electrolyte requirement. Solubilization and adsolubilization are shown to increase for mixed anionic–cationic surfactant systems, especially for hydrophobic solutes. Thus, by exploiting these synergisms while avoiding phase separation, properly designed anionic–cationic surfactant mixtures can be advantageous for a wide range of applications.     

Lowering the Maillard reaction products (MRPs) in heated whey protein products and their cytotoxicity in human cell models by whey protein hydrolysate

This study investigated the potential use of reconstituted whey protein hydrolysate as an antibrowning agent in thermally processed foods and as a chemopreventive ingredient in biological systems. Hydrolysates were prepared by tryptic (EC 3.4.21.4) hydrolysis of whey protein concentrate (WPC) or heated (80 °C for 30 min) whey protein concentrate (HWPC). Tryptic hydrolysis of WPC and HWPC increased the oxygen radical absorbance capacity-fluorescein (ORAC_FL) antioxidant capacity from 0.2 to 0.5 ??mol Trolox equivalent (TE)/mg protein in both whey protein hydrolysate (WPH) and heated whey protein hydrolysate (HWPH) (p < 0.05). The reconstituted WPH and HWPH could prevent the formation of Maillard reaction products (MRPs) induced by a thermal process employed on WPC suspensions between 80 and 121 °C in the presence of lactose up to 0.25 M (p < 0.05). The MRPs in HWPC were cytotoxic to both normal human intestinal FHs 74 Int cells and human epithelial colorectal carcinoma Caco-2 cells. The IC₅₀ of HWPC was around 3.18-3.38 mg/mL protein. Nonetheless, when both cell types were grown in media supplemented with WPH prior to the uptake of MRPs in HWPC at 3.5 mg/mL, they were able to survive (p < 0.05). Overall, this study indicated the efficacy of WPH and HWPH in the prevention of MRP cytotoxicity. It was suggested that the ORAC_FL antioxidant capacity of WPH and HWPH needed to be high enough to provide a chemopreventive effect against MRP cytotoxicity.     

Isolation and preliminary characterization of a bacteriocin produced by Lactobacillus plantarum N014 isolated from nham, a traditional Thai fermented pork

Lactobacillus plantarum N014 was isolated from nham, a traditional Thai fermented pork, and exhibited antimicrobial activity against Listeria monocytogenes. Its bacteriocin had a broad inhibitory spectrum toward both gram-positive and gram-negative bacteria. The bacteriocin activity was sensitive to all proteolytic enzymes used in this study, including papain, pepsin, pronase E, proteinase K, and trypsin, but was resistant to the other enzymes, such as alpha-amylase, lipase A, and lysozyme. Furthermore, activity was stable over various heat treatments and pH values. The bacteriocin exerted a bacteriolytic mode of action. It was produced during the exponential growth phase and reached its highest level as producer cells entered the stationary phase. Adsorption of the bacteriocin onto producer cells was pH-dependent. No bacteriocin adsorption was detected at pH 1 to 3, whereas 100% bacteriocin adsorption was found at pH 7. Plasmid isolation revealed that L. plantarum N014 contained no plasmids. From Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis and growth inhibition testing against L. monocytogenes, the estimated molecular mass of L. plantarum N014 bacteriocin was 8 kDa.     

Effect of Surfactant Systems,Alcohol Types,and Salinity on Cold-Water Detergency of Triacylglycerol Semisolid Soil. Part II

Our prior work found that detergency of coconut oil was relatively poor using C_14-15-8PO-SO₄Na alone but showed promising improvement with the presence of linear intermediate-chain alcohols (C7–C9 alcohols) in the surfactant formulation. The maximum detergency exceeded 90% removal using 0.1 w/v% C_14-15-8PO-SO₄Na/0.2 w/v% 1-octanol/4 w/v% NaCl (final optimized surfactant system) at 10 °C. The current work thus seeks to further investigate surfactant formulations capable of providing improved detergency performance. Different 50% linear anionic extended surfactant structures (LC_14-15-8PO-SO₄Na, LC_14-15-8PO-3EO-SO₄Na, and LC_14-15-8PO-7EO-SO₄Na) were compared with the branched C_14-15-8PO-SO₄Na previously studied. Detergency of coconut oil using C_14-15-8PO-SO₄Na at 8 w/v% NaCl (S*) still performed more effectively than these new surfactant systems. The addition of octanol as a detergency additive was further studied, and it showed that S* reduced from 8 w/v% NaCl to 4 w/v% NaCl for 1-octanol and to 2 w/v% NaCl for 2-octanol and 2-ethyl-hexanol in the C_14-15-8PO-SO₄Na surfactant formulation. Coconut oil removal significantly improved detergency from roughly 49% for no alcohol with 8 w/v% NaCl, to 83% for 2-ethyl-hexanol with 2 w/v% NaCl, to 95% for 1-octanol with 4 w/v% NaCl, and to 98% for 2-octanol with 2 w/v% NaCl. Further studies on octanol concentration showed that decreasing 1-octanol from 1.2% (90 mM) to 0.2% (15.3 mM) and 2-octanol from 1.2% (90 mM) to 0.5% (38.5 mM) still maintained detergency over 90% removal. In this work, cold-water detergency was found to correlate with low interfacial tension above the melting point, improved wetting of the semisolid soil, and oil solubilization in surfactant micelles.     

Kinetics of aniline degradation by Fenton and electro-Fenton processes

Aniline degradation at pH 2 by Fenton and electro-Fenton processes was kinetically investigated in this study. Electro-Fenton process was found to be superior to ordinary Fenton process with the current impacts of 1.2 to 3.1 for removal efficiency and 1.2 to 5.8 for degradation rate depending on initial Fe2+ concentration. This is mainly due to the rapid electrochemical regeneration of Fe2+. Overall rate equations for aniline degradation by Fenton and electro-Fenton processes (in units of molar and minute) are: [EQUATION: SEE TEXT]. With current application, aniline degradation rate seems to be autonomous from Fenton's reagent concentrations and approaching a half order with respect to aniline. In addition, for complete removal of 0.01 M aniline, the delay in current supply at the initial stage could save up to one-third of the total energy required by the ordinary electro-Fenton process. As a result, significant reduction in energy consumption and operating cost could be obtained by the current-delay operating mode.