Youngwoon Choi

The relation between glycogen, lactate content and muscle fiber type composition, and their influence on postmortem glycolytic rate and pork quality

This study examined the relation between glycogen, lactate content and muscle fiber type composition, and evaluated their influence on postmortem glycolytic rate and meat quality. Muscle samples were classified based on their glycogen and lactate content at 45min postmortem. Muscles with low glycogen and high lactate levels showed low muscle pH(45min) and high R-values. However, muscles with low glycogen and lactate levels showed normal rates of postmortem glycolysis and normal meat quality. On the other hand, muscles with high glycogen and lactate content showed rapid postmortem glycolysis, paler surface color, higher drip loss, and higher extents of protein denaturation than muscles with high glycogen and low lactate content. These results may be partially explained by muscle fiber type composition. Muscles with low glycogen and lactate content at early postmortem are composed of significantly higher fiber type I and lower fiber type IIB as compared to muscles with high glycogen and lactate content.

Comparing the histochemical characteristics and meat quality traits of different pig breeds

The purpose of this study was to compare the muscle histochemical characteristics and meat quality traits between Berkshire, Landrace, Yorkshire, and crossbred pigs. A total of 594 pigs were evaluated. A clear difference between histochemical properties was observed from the results for fiber type composition. In Berkshire pigs, the area percentage of type I fibers was higher (P<0.001) and that of type IIb fibers was lower (P<0.05) than those of other breeds. The muscle pH(45min) and pH(24h) were significantly higher in Berkshire pigs. Drip loss and color parameters were significantly different between the breeds (P<0.001). The Berkshire pigs, which showed the highest muscle pH and lowest drip loss and L(∗) values, contained a significantly higher percentage of type I fibers than the other breeds. By comparing the fiber type compositions of the different breeds, the results imply that the longissimus dorsi muscle of Berkshire pigs is more oxidative than that of other breeds. A high pH value in Berkshire pigs is due to a high percentage of type I fibers and a low percentage of type IIb fibers. Based on these results, we conclude that muscle fiber composition can explain in parts the variation of meat quality across and within breeds.

High-speed synthetic aperture microscopy for live cell imaging

We present a high-speed synthetic aperture microscopy for quantitative phase imaging of live biological cells. We measure 361 complex amplitude images of an object with various directions of illumination covering an NA of 0.8 in less than one-thirteenth of a second and then combine the images with a phase-referencing method to create a synthesized phase image. Because of the increased depth selectivity, artifacts from diffraction that are typically present in coherent imaging are significantly suppressed, and lateral resolution of phase imaging is improved. We use the instrument to demonstrate high-quality phase imaging of live cells, both static and dynamic, and thickness measurements of a nanoscale cholesterol helical ribbon.

Variations in metabolite contents and protein denaturation of the longissimus dorsi muscle in various porcine quality classifications and metabolic rates

The purpose of the present study was to investigate the variations in metabolite contents and muscle protein denaturation in various porcine quality classifications and metabolic rates. A total of 226 crossbred pigs were evaluated. Samples were classified based on muscle pH(45min) and R-value into fast or normal glycolysing group. Drip loss and lightness (L*) were used to assign samples as PSE, RSE, or RFN pork. Normal-glycolysing PSE pork contained an exceptional amount of initial glycogen and the high level of lactate at 24h postmortem (PM). The initial levels of metabolites related closely with muscle pH, R-value and protein solubility at 45min PM. The fast glycolysing group exhibited severe protein denaturation during the early postmortem period, and among them, fast-glycolysing PSE pork exhibited most pronounced protein denaturation. Via examination of each sarcoplasmic protein fraction, it was found that the bands for fructose-6-phosphate kinase, creatine kinase, triosephosphate isomerase, and myokinase were generally more evident as fainter bands in the fast-glycolysing pigs.

Diffraction optical tomography using a quantitative phase imaging unit

A simple and practical method to measure three-dimensional (3-D) refractive index (RI) distributions of biological cells is presented. A common-path self-reference interferometry consisting of a compact set of polarizers is attached to a conventional inverted microscope equipped with a beam scanning unit, which can precisely measure multiple 2-D holograms of a sample with high phase stability for various illumination angles, from which accurate 3-D optical diffraction tomograms of the sample can be reconstructed. 3-D RI tomograms of nonbiological samples such as polystyrene microspheres, as well as biological samples including human red blood cells and breast cancer cells, are presented.

Full-field and single-shot quantitative phase microscopy using dynamic speckle illumination

We developed an off-axis quantitative phase microscopy that works for a light source with an extremely short spatial coherence length in order to reduce the diffraction noise and enhance the spatial resolution. A dynamic speckle wave whose coherence length is 440 nm was used as an illumination source. To implement an off-axis interferometry for a source of low spatial coherence, a diffraction grating was inserted in the reference beam path. In doing so, an oblique illumination was generated without rotation of the wavefront, which leads to a full-field and single-shot phase recording with improved phase sensitivity of more than a factor of 10 in comparison with coherent illumination. The spatial resolution, both laterally and axially, and the depth selectivity are significantly enhanced due to the wide angular spectrum of the speckle wave. We applied our method to image the dynamics of small intracellular particles in live biological cells. With enhanced phase sensitivity and speed, the proposed method will serve as a useful tool to study the dynamics of biological specimens.

Improved modification direction methods

The original exploiting modification direction (EMD) method proposed by Zhang and Wang is a novel data hiding technique which can achieve large embedding capacity with less distortion. The original EMD method can hide (2n+1)-ary numbers by modifying at most one least-significant bit (LSB) of n pixel values. The proposed methods in this paper, 2-EMD and EMD-2, modify at most two pixels of the LSB values. Efficiency of the proposed methods is shown theoretically and through experiments. The 2-EMD and EMD-2 can hide even larger numbers than the EMD with similar distortion under the same conditions. This paper shows that the EMD-2 is much better than the EMD, and slightly better than 2-EMD when n is 3, 4 and 5. The way to generate basis vector can be used for the generalization of the n-EMD and EMD-n where n>1.

Effects of supercritical carbon dioxide treatment against generic Escherichia coli, Listeria monocytogenes, Salmonella typhimurium, and E. coli O157:H7 in marinades and marinated pork

This study was conducted to evaluate the effects of supercritical carbon dioxide (SC-CO(2)) treatment on soy sauce and hot-pepper paste marinades, as well as in marinated pork products, for the inhibition of generic Escherichia coli, Listeria monocytogenes, Salmonella typhimurium, and E. coli O157:H7. SC-CO(2) was more effective at destroying foodborne pathogens when it was applied to the marinades than the marinated products. SC-CO(2) treatment at 14MPa and 45°C for 40min resulted in a greater reduction in soy sauce (2.52-3.47logCFU/cm(2)) than in hot-pepper paste marinade (2.12-2.72log CFU/cm(2)). In the case of the marinated pork, when SC-CO(2) was applied at 14MPa and 45°C for 40min, the reduction levels of L. monocytogenes were 2.49 and 1.92logCFU/cm(2) in soy sauce and hot-pepper paste marinated pork, respectively. The results should be useful in the meat industry to help increase microbial safety and assure the microbial stability of marinades and marinated products.

The influence of pork quality traits and muscle fiber characteristics on the eating quality of pork from various breeds

The purpose of this study was to compare parameters associated with pork quality, muscle fiber, and eating quality among various breeds, and to examine if differences in eating quality were associated to pork quality and muscle fiber characteristics. For carcass and pork quality, although there were significant differences among breeds, the values of parameters in all pigs were assigned a normal quality class, a likely outcome of the similarity in the area percentage of type I and IIB fibers. For eating quality, pork loins from Berkshire pigs were more tender and full of pork flavor than Landrace and Yorkshire pigs. Except juiciness and mouth coating, over 20% of the variability in the eating quality parameters can be explained by pork quality traits and muscle fiber characteristics using multiple regression analysis. Furthermore, differences in muscle pH(24h), cooking loss, shear force, and NPPC marbling score could explain a large proportion of variation in eating quality parameters associated with the texture of pork.

Combined effect of organic acids and supercritical carbon dioxide treatments against nonpathogenic Escherichia coli, Listeria monocytogenes, Salmonella typhimurium and E. coli O157:H7 in fresh pork.

Aims:  To evaluate the effectiveness of organic acids and supercritical carbon dioxide (SC‐CO2) treatments as well as their combined effect for the reduction of nonpathogenic Escherichia coli and three pathogenic bacteria in fresh pork.