Earticle

This study investigated the heat stability of L-ascorbic acid (AA) in acetic acid solution. To analyze the degradation of AA using high performance liquid chromatography (HPLC), AA was measured at a wavelength of 244 nm in acetic acid and 265 nm in distilled water. During the storage of AA in acetic acid or distilled water at 37℃, degradation of AA was slower in acetic acid than in distilled water. On examining various ratios of AA to acetic acid, the stability of AA at 100℃ for 30 min was the highest when the concentration of acetic acid was 10 times higher than the concentration of AA. After acetic acid was added into AA degraded by heating, the AA is stabilized by reheating. Ultimately, these results indicate that degraded AA is reduced by hydrogen ions dissociated from acetic acid, and the rate of reduction of degraded AA in acetic acid solution is improved with heat processing.

A mathematical model was developed for predicting the growth rate of Enterobacter sakazakii in tryptic soy broth medium as a function of the combined effects of temperature (5, 10, 20, 30, and 40℃), pH (4, 5, 6, 7, 8, 9, and 10), and the NaCl concentration (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10%). With all experimental variables, the primary models showed a good fit (R²=0.8965 to 0.9994) to a modified Gompertz equation to obtain growth rates. The secondary model was 'In specific growth rate=-0.38116+(0.01281*Temp)+(0.07993*pH)+(0.00618*NaCl)+(-0.00018*Temp²)+(-0.00551*pH²)+(-0.00093*NaCl²)+(0.00013*Temp*pH)+(-0.00038*Temp*NaCl)+(-0.00023*pH*NaCl)'. This model is thought to be appropriate for predicting growth rates on the basis of a correlation coefficient (r) 0.9579, a coefficient of determination (R²) 0.91, a mean square error 0.026, a bias factor 1.03, and an accuracy factor 1.13. Our secondary model provided reliable predictions of growth rates for E. sakazakii in broth with the combined effects of temperature, NaCl concentration, and pH.

In order to enhance the efficacy of norovirus detection by reverse transcriptase-polymerase chain reaction (RT-PCR) and nested PCR, this study developed a norovirus mRNA concentration method using poly oligo dT-conjugated magnetic beads. An efficient norovirus detection protocol was performed on commercial ham using 2 viral elution buffers (glycine buffer and Tris beef extract buffer) and 2 concentration solutions [polyethylene glycol (PEG) and zirconium hydroxide]. The different approaches were verified by RT-PCR and nested PCR. This method was performed on ham in less than 8 hr by artificial inoculation of serial dilutions of the virus ranging from 1,000 to 1 RT-PCR unit/mL. The viral extraction and concentration method had 10-fold higher sensitivity using the combination of Tris beef extract buffer and PEG as compared to glycine buffer and zirconium hydroxide. This method proved that RT-PCR and nested PCR have the sensitive ability to detect norovirus in commercial ham, in that norovirus was successfully detected in artificially contaminated samples at a detection level as low as 1-10 RT-PCR unit/mL. Overall, such a detection limit suggests this protocol is both quick and efficient in terms of its potential use for detecting norovirus in meat products.

Although arabinose isomerase (E.C. 5.3.1.4), a commercial enzyme for edible tagatose bioconversion, can be expressed in an Escherichia coli system, this expression system might leave noxious by-products in food. To develop an eligible tagatose bioconversion with food-safe system, we compared the tagatose production activity of immobilized arabinose isomerase expressed in Bacillus subtilis (a host generally recognized as safe) with that of the enzyme expressed in E. coli. A 48% increase in tagatose production (4.3 g tagatose/L at 69.4㎍/Lㆍhr) was found using the B. subtilis-expressed immobilized enzyme system, compared to the E. coli-expressed enzyme system (2.9 g tagatose/L). The increased productivity with safety of the B. subtilis-expressed arabinose isomerase suggests that it is a more eligible candidate for commercial tagatose production.

The diffusivity of aerosol sanitizers may be determined by the weight and droplet size of the aerosol. To test the effects of droplet size, 2 types of aerosol sanitizers were prepared using different ultrasonic nebulizer frequencies (1.6 and 2.4 MHz) and their reduction activities were determined against Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella typhimurium. A sodium hypochlorite aerosol was treated for 10, 30, or 60 min in a model aerosol cabinet. When the aerosol prepared by nebulizing at 1.6 MHz was treated for 30 min, a 0.2 log reduction was observed in E. coli O157:H7 and 0.3 log reductions were exhibited in L. monocytogenes and S. typhimurium, respectively. After 60 min, the 3 pathogens were reduced by 1.7, 0.6, and 0.8 log units, respectively. However, when the aerosol prepared by nubulizing at 2.4 MHz was treated, the microbes presented 1.6, 0.5, and 0.6 log reductions at 30 min, and 1.8, 0.9, and 1.1 log reductions at 60 min of treatment, respectively.

Zanthoxylum schinifolium and Zanthoxylum piperitum A.P. DC. belong to the Rutaceae family and are perennial, aromatic, and medicinal herbaceous plants. In this study, their aroma compounds were isolated by steam distillation extraction using a Clevenger-type apparatus, and then further analyzed by gas chromatography (GC) and gas chromatograph/mass spectrometry (GC/MS). The yields of the essential oils from Z. schinifolium and Z. piperitum AP. DC. were 2.5 and 2.0%(w/w), respectively, and the color of their oils was quite similar, a pale yellow. From the distilled oil of Z. schinifolium, 60 volatile compounds which make up 87.24% of the total composition were tentatively identified, with monoterpenes predominating. β-Phellandrene (22.54%), citronellal (16.48%), and geranyl acetate (11.39%) were the predominantly abundant components of Z. schinifolium. In the essential oil of Z. piperitum AP. DC., 60 volatile flavor components constituted 94.78% of the total peak area were tentatively characterized. Limonene (18.04%), geranyl acetate (15.33%), and cryptone (8.52%) were the major volatile flavor compounds of Z. piperitum A.P. DC.

Permeability of resveratrol, piceid, rhapontigenin, and rhaponticin in Caco-2 cell assays using high-performance liquid chromatography were compared. Caco-2 cell monolayers were used to evaluate the transport rates of stilbene analogues from the apical to the basolateral sides. All stilbenes experimented in this study were transported to the basolateral side by times. For comparing the permeability of 4 stilbenes, we calculated the slope of the cumulative concentration of each stilbene in basolateral sides over time, resulting in those values of resveratrol, piceid, rhapontigenin, and rhaponticin with 3.766×10(5), 4.330×10(-6), 5.430×10(-5), and 2.458×10(-5)㎛/sec, respectively. Apparent permeability coefficient of resveratrol and rhapontigenin were calculated to 9.994×10(-6) and 1.441×10(-6)cm/sec, respectively, while those of piceid and rhaponticin were to 1.149×10(-7)cm/sec and 6.523×10(-7)cm/sec, respectively. These results suggest that aglycones would be absorbed more effectively than glycosides in stilbenoids.

A lactic acid bacterium producing an antimicrobial substance against Escherichia coli O157:H7 was isolated from raw milk and identified as Lactobacillus amylovorus ME-1. In addition to E. coli O157 :H7, the antimicrobial substance also inhibited the growth of Bacillus cereus, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella typhimurium, Staphylococcus aureus, Streptococcus agalactiae, Streptococcus pyrogenes, and Yersinia enterocolitica. The antimicrobial substance was stable at pH 2-12 and 121℃ for 15 min and insensitive to proteinase K, protease, amylase, and catalase. Purification of the antimicrobial substance was conducted through methanol and acetonitrile/ethylacetate extraction, ultrafiltration with a 500 Da cutoff, thin layer chromatography (TLC) with silicagel 60, and high performance liquid chromatography (HPLC) with a C18 reverse phase column. The λmas of the purified antimicrobial substance was determined as 192 nm by ultra violet (UV) scanning, while the molecular weight was estimated as 453 Da based on the mass spectrum. Accordingly, the current results suggest that the antimicrobial substance from the L. amylovorus ME-1 was not a bacteriocin, but rather a new non-proteinaceous substance distinct from acidophilin, acidolin, diacetyl, and reuterin.

β-Glucans, which were isolated from sangwhang (Phellinus linteus), were subjected to reductive amination and the biological properties of the derivative were investigated. The degree of substitution of the aminated sangwhang β-glucan was calculated by elemental analysis to be 1.13. Bronchoalveolar lavage (BAL) experiments showed that the aminated derivative increased nitric oxide production. In addition, the amination enhanced in vitro cytotoxic activities against HT1080 and SNU-C2A cell lines. Thus, the aminated derivative is shown to enhance immune systems by the incorporation of amino groups into the polymer structure.