Fate of Salmonella Tennessee in peanut butter at 4 and 22 degrees C

ABSTRACT:  This study was undertaken to determine survival characteristics of inocula of a 3-strain mixture of Salmonella Tennessee in 5 commercial brands of peanut butter (A, B, C, D, and E). Inoculated peanut butter was stored at 4 (refrigerator temperature) and 22 °C (room temperature) for up to 14 d. After 1, 3, 5, 7, and 14 d, surviving cells, including injured cells, were enumerated on appropriate selective agar, including use of the agar overlay method. Populations in samples inoculated with 10^6–7 CFU/g and stored for 14 d at 4 and 22 °C decreased by 0.15 to 0.65 and 0.34 to 1.29 log CFU/g, respectively, depending on the formulation. Peanut butter A showed a significantly lower number of S . Tennessee cells when stored at 22 °C for 14 d, compared to 4 °C ( P < 0.05). However, there was no significant difference between the levels of S. Tennessee at 4 and 22 °C in products B, C, D, and E ( P > 0.05).     

The use of bacterial alkaline phosphatase assay for rapid monitoring of bacterial counts on spinach

ABSTRACT:  This study was undertaken to evaluate the applicability of bacterial alkaline phosphatase (ALP) activity for rapid monitoring of total mesophilic bacteria counts in spinach. A set of fresh and decayed spinach mixtures were tested to rapidly (10 min) monitor spinach bacterial counts. To assay ALP activity, Lumigen APS-5 was used as a substrate. Bovine ALP was reduced after heat treatment at 75 °C for 1 min; in contrast, bacterial ALP activity increased. To differentiate bacterial ALP from other ALP, heat treatment (75 °C, 1 min) was applied before measurement. As a result, a regression equation was established between the actual mesophilic aerobic bacteria count and ALP activity of spinach mixtures ( r = 0.90). The predicted total mesophilic aerobic bacterial count calculated from the fitted regression line (predicted log₁₀ CFU/g = 0.00056 × ALP values + 1.4002) showed a high correlation with the actual observed total bacterial count ( r = 0.93). The ALP assay is a simple and rapid method to utilize for estimation of existing or contaminating microorganism levels on spinach.     

优化制动转矩分布以提高四轮驱动混合电动车辆的稳定性(二)

四轮驱动混合电动车辆稳定性控制逻辑建议采用后马达能量回收制动和一个电液制动器(EHB)。采用一个通常的算法,求得能量回收制动和EHB转矩之间最佳的转矩分布。根据已知输入的所要求的偏转转矩和道路摩擦系数,用该通常算法计算出最佳能量回收制动转矩和最佳的EHB转矩。基于最佳的制动转矩分布,相应驾驶员转向角和车辆速度,用模糊控制算法,车辆稳定控制逻辑建议形成所要求的偏转转矩,去补偿侧滑角和偏转率的误差。对单车道变更机动性用比较固定能量回收制动和最佳能量回收制动,判断车辆稳定性控制逻辑的性能。由仿真结果可以看到,在满足车辆稳定性的情况下,最佳能量回收制动可以比固定的能量回收制动增大能量回收。     

Interaction of antiparallel transverse domain walls in ferromagnetic nanowires

The interaction of antiparallel transverse domain walls in ferromagnetic nanowires was investigated via micromagnetic simulation with systematic variations of the external field strength as well as the wire thickness. The interaction of antiparallel transverse walls after domain wall collision exhibited damped multiple collisions due to the rigid structure of the antiparallel transverse walls. The detailed process during the multiple collisions was analyzed via the Fast Fourier Transform technique, along with a careful examination of the inner spin structures of the colliding domain walls. It was found that a frequency peak of multiple collisions shifted to a higher peak position as the external field strength increases. With a stronger field strength of around a few hundred mT, it was found that two antiparallel transverse walls were finally annihilated with formation of complex antivortex structures.     

KINETIC STUDIES ON OXIDATION OF ALLYL ALCOHOL BY YEAST ALCOHOL DEHYDROGENASE

The kinetics of the oxidation of allyl alcohol by yeast alcohol dehydrogenase (YADH) was studied with stopped-flow technique. The experimental results showed that the specific activity of YADH remained constant within theYADH concentration range ofO-16.4mg/dm₃ and YADH exhibited maximum activity at pH 7.9 and a phosphate buffer concentration of 0.25 mol/dm₃ The oxidation rate of allyl alcohol by YADH followed the Arrhenius equation within the temperature range of 10 to 40°C The YADH was denatured irreversibly at the temperatures above 40°C. The rate equation for the YADH-catalyzed oxidation of allyl alcohol was obtained. A mixed-type substrate inhibition occurred when the concentration of allyl alcohol was higher than 200 mmol/dm₃ The presence of LiCl, NaCl and KG could enhance the activity of YADH. The YADH lost activity significantly in the presence of organic solvents, particularly benzene and its derivatives.     

Supercritical fluid chromatography reduction of hydrogen/deuterium back exchange in solution-phase hydrogen/deuterium exchange with mass spectrometric analysis

The single biggest problem with solution-phase H/D exchange as a mass spectrometric probe of surface exposure in a protein (or protein complex) is back-exchange of H for D after the initial H/D exchange has been quenched. Back-exchange results in loss of pertinent data and also greatly hampers data analysis. Previously, very fast, cold (0-4 degrees C) HPLC was performed to help reduce back-exchange, but calculated back-exchange still averages approximately 30%. In this report, supercritical fluid chromatography replaces HPLC as the desalting/separation technique prior to mass analysis, providing a dramatic reduction in back-exchange compared to the fast, cold HPLC methods.     

Optimum management scheme to control nonpoint pollution in Korea.

Comprehensive measures to control nonpoint source were developed by the Office of the Prime Minister, Korea in March 2004. These management measures present the government's policies and directions relating to nonpoint source management by 2020. However, the government has encountered difficulties since the government implemented such policies without preparing legal and institutional arrangements associated with nonpoint source management practices. Particularly, there was no legal system to manage the workplaces and construction sites that discharge the polluted runoff. To provide legal arrangements to achieve efficient implementation of the government's nonpoint source management policies, amendments to the "Water Quality Preservation Act" were proposed in the congress in March 2005 and took effect from April 2006. Subsequently, the nationally mandated nonpoint source control system was to be applied to such industries and construction sites. This paper attempts to propose the scope of the nonpoint source control system and effective strategies applied to the construction sites and industrial workplaces in Korea.     

Monoclonal-based enzyme-linked immunosorbent assay for the detection of zearalenone in cereals.

A monoclonal antibody against zearalenone (ZEA) was produced and used successfully to develop a direct competitive enzyme-linked immunosorbent assay (DC-ELISA) for the analysis of ZEA in cereals. This DC-ELISA had a limit of detection of 0.15 +/- 0.02 microg l(-1) and an IC50 value of 1.13 +/- 0.16 microg l(-1). Matrix interference was minimized by dilution of the sample extract before ELISA assays. Aqueous methanol (80%) gave good extraction efficiencies, and the recovery from spiked rice, barley, and corn samples averaged between 87 and 112%. Although ZEA was detected in seven (9%) of 80 rice samples and in eight (16%) of 50 barley samples, the concentration of ZEA in samples was around or below the limit of detection of DC-ELISA. Among 38 corn samples, ZEA was detected in nine (24%) samples in the range 41.0-909.8 microg kg(-1). Re-analysis of the ELISA-positive corn samples by high-performance liquid chromatography (HPLC) confirmed that seven (18%) corn samples were positive. The ZEA results for corn showed very good agreement between DC-ELISA and a commercial AgraQant zearalenone kit (r2 = 0.98). Thus, the monoclonal antibody-based DC-ELISA could be applied to the preliminary screening of ZEA contamination when analysis of a large sample number is needed.     

Estimated daily intakes of butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tert-butyl hydroquinone (TBHQ) antioxidants in Korea.

The study was conducted to establish the estimated daily intake (EDI) of antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tert-butyl hydroquinone (TBHQ) in Korea. The EDIs were obtained from two sources. One of the estimations was based on the analytical determination of BHA, BHT and TBHQ in 12 food categories (ten food categories for TBHQ) and on individual dietary intake data obtained from the National Health and Nutrition Survey in 1998 (n=11 525, age > 1 year). The other EDIs of BHA, BHT and TBHQ were based on the maximum permitted levels specified in national food standards in Korea and on individual dietary intake data obtained from the National Health and Nutrition Survey in 1998 (n=11 525, age > 1 year). To establish the EDIs based on the analytical determination and on individual dietary intake data, 133 food samples in 12 food categories were selected from the foods considered to be representative sources of BHA, BHT and TBHQ in the Korean diet. Selected samples were analysed by GC with FID. BHA was not detected in any of the samples analysed. BHT and TBHQ were detected in the samples, but the levels were significantly lower than their maximum limits. The EDIs1 of BHT, and TBHQ for average consumers were 0.0156(-3), and 0.0012(-3) mg kg(-1) body weight bw day(-1) and as a proportion of the ADI were 0.0052 and 0.0002%, respectively. For 95th percentile consumers, the EDIs of BHT and TBHQ were 0.0080 and 0.0006 mg kg(-1) bw day(-1), and as a proportion of the ADI were 2.67 and 0.09%, respectively. EDIs for BHA, BHT and TBHQ based on the maximum permitted levels and on individual dietary intake data were 0.04, 0.04 and 0.04 mg kg(-1) bw day(-1), respectively. The EDIs of BHA, BHT and TBHQ for average consumers ranged from 6.00 to 14.42% of the ADI of each antioxidant. According to these results, the EDIs of BHA, BHT and TBHQ in Korea were significantly lower than ADI of these antioxidants established by the JECFA.     

Determination of molecular weights of caprine milk proteins by matrix-assisted laser desorption/ionization mass spectrometry

Molecular weights (MW) of major proteins in milk of 3 Korean dairy goat breeds were determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, after treatment of milk samples with the reduction buffer used in capillary electrophoresis. The MW of caprine milk proteins were compared with those of Holstein milk counterparts using commercial bovine milk protein standards. The MW of α-lactalbumin, β-lactoglobulin, and α- and β-casein standards were 14,197±3.4, 18,326±26.3, 23,591±13.0, and 23,967±12.8 m/z, respectively, whereas those of Holstein milk treated with the reduction buffer were 14,199±8.3, 18,397±25.9, 23,614±64.8, and 23,984±75.6 m/z, respectively. The respective MW of α-lactalbumin in Saanen, Toggenberg, and Alpine milk were 14,194±27.2, 14,266±105.9, and 14,241±13.2 m/z, which were not different from those of the bovine milk. The respective MW of β- lactoglobulin in corresponding caprine milk were 18,840±31.5, 18,856±26.3, and 18,857±21.3 m/z, which were higher than those in the bovine milk. The MW of β-casein in corresponding caprine milk were 23,860±27.2, 23,886±12.3, and 23,901±8.4 m/z, which were lower than those in the bovine milk. The results indicated that matrix-assisted laser desorption/ionization time-of-flight mass spectrometry could be used for rapid determination of MW of Korean caprine milk proteins without protein separation steps.