Ho Hyun Chun

Effect of tempering methods on quality changes of pork loin frozen by cryogenic immersion

The quality characteristics of pork loin frozen by cryogenic immersion were examined, such as the drip loss, cooking loss, water holding capacity, moisture content, protein solubility, lipid and protein oxidation, color, and microstructure, and compared after different tempering methods: radio frequency (27.12MHz), water immersion, forced-air convection, and microwave tempering. Forced-air tempering was the most time-consuming process, whereas electromagnetic energy methods (radio frequency and microwave) were the shortest. The tempering rate of radio frequency at 400W was 5 and 94 times greater than that obtained with water immersion and forced-air tempering, respectively. The drip loss, water holding capacity, moisture content, color, and microstructure of pork samples all declined as a result of microwave tempering. By contrast, the least degree of changes in the drip loss, microstructure, and color of the pork loin samples was obtained with radio frequency tempering, suggesting its potential application in providing rapid defrosting without quality deterioration in the frozen meat industry.

Changes in Quality of Hanwoo Bottom Round under Different Freezing and Thawing Conditions

This study examined the effects of freezing and thawing conditions on quality of Hanwoo bottom round. The beef samples were frozen by air blast freezing at -20°C or ethanol immersion freezing at -70°C and then stored at -20°C for 10 days. After 10 days of storage, the frozen samples were thawed with air blast thawing at 4°C or water immersion thawing at 4°C and subjected to subsequent analyses of drip loss, water holding capacity, thiobarbituric acid reactive substance (TBARS), volatile basic nitrogen (VBN), total aerobic bacteria, and microstructure. Drip loss significantly increased in samples treated with air blast freezing compared to ethanol immersion freezing, whereas freezing and thawing processes had no significant impact on water holding capacity of the samples. Thawing conditions had a much stronger influence on the TBARS and VBN of the samples than freezing conditions. There was no significant difference in the population of total aerobic bacteria among the four samples subjected to one freeze-thaw cycle. In addition, to analyze the effects of freeze-thaw cycle on the quality of beef, three freeze-thaw cycles were performed during storage. Multiple freeze-thaw cycles increased drip loss, TBARS, and VBN and decreased water holding capacity, accelerating microstructural damage. These data indicate that Hanwoo bottom round can be rapidly frozen and thawed by using ethanol immersion freezing and water immersion thawing methods with minimal impact on meat quality.

Combined Effects of Sanitizer Mixture and Antimicrobial Ice for Improving Microbial Quality of Salted Chinese Cabbage during Low Temperature Storage

The combined effects of a sanitizer mixture solution and antimicrobial ice on the quality of salted Chinese cabbages were examined. Salted Chinese cabbages were treated with a sanitizer mixture (comprised 50 ppm aqueous ClO2 and 0.5% citric acid), packed in 2% brine and antimicrobial ice, and stored for 12 days at 4 and 10°C. Microbiological data on the salted Chinese cabbages after washing with the sanitizer mixture indicated that the pop- ulations of total aerobic bacteria, and yeast and molds decreased by 2.20 and 1.28 log CFU/g after treatment with the sanitizer mixture. In addition, coliforms population of salted Chinese cabbage after 12 days storage at 4°C in the combined mixture of the sanitizer and antimicrobial ice was 3.22 log CFU/g, which was a significantly different from that of control (5.46 log CFU/g). The combined treatment of sanitizer mixture, antimicrobial ice, and low temper- ature at 4°C suppressed reduction of pH and elevation of titratable acidity, resulting in delaying the growth of lactic acid bacteria. Differences in salinity, hardness, and Hunters L * , a * , and b * values among treatments were negligible during storage at 4°C. Therefore, this study suggests that a combination of sanitizer mixture, antimicrobial ice treatment, and low temperature storage could improve the microbial safety and quality of salted Chinese cabbages during storage.

Effects of 27.12 MHz Radio Frequency on the Rapid and Uniform Tempering of Cylindrical Frozen Pork Loin (Longissimus thoracis et lumborum)

Quality characteristics of frozen cylindrical pork loin were evaluated following different tempering methods: 27.12 MHz curved-electrode radio frequency (RF) at 1000 and 1500 W, and forced-air convection (FC) or water immersion (WI) at 4°C and 20°C. The developed RF tempering system with the newly designed curved-electrode achieved relatively uniform tempering compared to a parallel-plate RF system. FC tempering at 4°C was the most time-consuming process, whereas 1500 W RF was the shortest. Pork sample drip loss, water holding capacity, color, and microbiological quality declined after WI tempering at 20°C. Conversely, RF tempering yielded minimal sample changes in drip loss, microstructure, color, and total aerobic bacteria counts, along with relatively uniform internal sample temperature distributions compared to those of the other tempering treatments. These results indicate that curved-electrode RF tempering could be used to provide rapid defrosting with minimal quality deterioration of cylindrical frozen meat block products.

Effects of Freezing and Thawing Treatments on Natural Microflora, Inoculated Listeria monocytogenes and Campylobacter jejuni on Chicken Breast

The effects of freezing and thawing conditions on microbiological quality and microstructure change of inoculated (Listeria monocytogenes and Campylobacter jejuni) and non-inoculated chicken breasts were investigated. Chicken breasts were frozen with air blast freezing (−20, −70, and −150oC), ethanol (−70oC) and liquid nitrogen (−196oC) immersion freezing. There were no significant differences on the populations of L. monocytogenes inoculated with chicken breasts under different freezing conditions. However, air blast freezing (−20oC) resulted in significant reductions for total aerobic bacteria and C. jejuni compared to the control and other freezing treatments. The frozen samples were thawed with (hot or cold) air blast, water immersion, and high pressure thawing at 4oC and 25oC. the populations of total aerobic bacteria, and yeast and mold in the frozen chicken breast increased by 5.78 and 4.05 log CFU/g after water immersion thawing (25oC) treatment. After five freeze-thaw cycles, the populations of total aerobic bacteria, yeast and mold, and C. jejuni were reduced by 0.29~1.40 log cycles, while there were no significant differences (P > 0.05) in the populations of L. monocytogenes depending on the freeze-thaw cycles. In addition, the histological examination of chicken breasts showed an increase in spacing between the muscle fiber and torn muscle fiber bundles as the number of freeze-thaw cycles increased. These results indicate that freezing and thawing processes could affect in the levels of microbial contamination and the histological change of chicken breasts.

Effects of CFSs produced by lactic acid bacteria in combination with grape seed extract on the microbial quality of ready-to-eat baby leaf vegetables

Abstract The effects of the combined use of cell-free supernatant (CFS) and grape seed extract (GSE) in inhibiting the growth of pre-existing and inoculated foodborne bacteria on mixed, ready-to-eat (RTE) baby leaf vegetables were examined. Lactobacillus brevis WK12 and Leuconostoc mesenteroides WK32 produced significantly more acetic and lactic acid than citric, malic, succinic, or fumaric acids after 24 h of fermentation. The inhibition zone sizes observed when Lactobacillus brevis WK12 and Leuconostoc mesenteroides WK32 CFSs and 0.1% GSE were used in combination were much greater than those observed when either of the CFSs alone was used on agar plates. The application of 5% CFS from Lactobacillus brevis WK12 or Leuconostoc mesenteroides WK32 in combination with 0.1% GSE reduced the total counts of aerobic mesophilic bacteria, coliforms, and yeasts/molds in RTE baby leaf vegetable samples by 2.01, 1.74, and 1.87 log CFU/g, respectively, compared with those determined in the control. Combined CFS and GSE treatment reduced Escherichia coli O157:H7 and Listeria monocytogenes counts by 1.72 and 2.89 log CFU/g, respectively. These results suggest that the combined CFS and GSE treatment may act as a natural disinfectant, enhancing the safety of RTE baby leaf vegetables.