Nonthermal sterilization of Listeria monocytogenes in infant foods by intense pulsed-light treatment

The purposes of this study were to determine the inactivation effects of intense pulsed light (IPL) on Listeria monocytogenes and the commercial feasibility of this sterilization method. The inactivation of L. monocytogenes at cultivated plates increased with increasing electric power and treatment time. Approximately 4–5 log reduction of the cell was achieved with IPL treatment for 5000, 600, 300, and 100 μs at 10, 15, 20, and 25 kV of voltage pulse, respectively. In the early stages of IPL treatments at 10, 15, and 20 kV, little inactivation was observed with a critical treatment time (t_c) of 360.6, 95.5, and 32.2 μs, respectively, while an abrupt inactivation without a critical treatment time was observed at 25 kV. The sterilization effects on commercial infant foods inoculated with L. monocytogenes were investigated at 15 kV, which showed higher energy efficiency for the inactivation of L. monocytogenes.     

Microbiological contamination of fresh-cut produce in Korea

Food Science and Biotechnology - This study evaluated the microbiological contamination of fresh-cut produce in Korea. A total of 108 fresh-cut vegetables and fruits were surveyed for the aerobic...     

Effect of package size and temperature on the volume expansion of flexible permeable packages of Kimchi,a Korean fermented vegetable

The effect of package size and temperature on package volume expansion was investigated when P71197, a high CO₂ permeability film of amorphous nylon laminate structure, was applied to packaging kimchi, a Korean ethnic fermented vegetable. The volume expansion, after an initial lag period, rapidly reached a maximum and then either decreased or stayed constant. A higher temperature and a larger package caused greater volume expansion within the experimental time span. Based on the criterion of ≤0.8 ml/g as a tolerable volume change, the appropriate window of package size and temperature has been suggested. The expanded volume was found to consist mainly of CO₂ produced from kimchi, resulting in higher CO₂ concentrations for higher temperatures and larger package sizes. The effect of package size on the volume expansion and gas composition can be explained by the differences in the ratio of surface area to filled weight among the packages. The effect of storage temperature can be explained by the difference in activation energy between CO₂ production from the kimchi and gas permeation through the film. Copyright © 2001 John Wiley & Sons, Ltd.     

Caking characteristics and sensory attributes of ramen soup powder evaluated using a low-resolution proton NMR technique

A low-resolution proton nuclear magnetic resonance (NMR) technique was used to characterize the quality of ramen soup powder during storage. The caking behavior of ramen soup powders was observed during 20 weeks of storage at different temperatures (30, 37, 45, and 55 °C) by monitoring changes in spin-spin relaxation times (T₂) using a CPMG (Carr-Purcell-Meiboom-Gill) pulse sequence. Water in ramen soup powder was classified into two fractions based on two spin-spin relaxation times, T₂₁ and T₂₂, and their respective proton intensities, A₁ and A₂. Increases in T₂₁ and T₂₂ were observed during storage at 37, 45, and 55 °C, which indicated that the molecular mobility of water in ramen soup powder increased. The changes in A₁ and A₂ suggested that there was a redistribution of water from a lesser “bound” water state to more mobile state during storage. T₂₁ and A₁ were critical factors for explaining the caking characteristic of ramen soup powder during storage. Also, the results showed that sensory attributes of ramen soup powder deteriorated during storage, indicating that caking could accompany changes in organoleptic qualities and that these changes could be detected by monitoring changes in NMR parameters.     

Antagonism of Helicobacter pylori by bacteriocins of lactic acid bacteria

Antimicrobial activity of seven bacteriocins produced by lactic acid bacteria against Helicobacter pylori strains (ATCC 43504, Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH [DSM] 4867, DSM 9691, and DSM 10242) was investigated in vitro using a broth microdilution assay. The bacteriocins chosen for the study were nisin A; lacticins A164, BH5, JW3, and NK24; pediocin PO2; and leucocin K. Antimicrobial activity of the bacteriocins varied among the H. pylori strains tested, of which strain ATCC 43504 was the most tolerant. Among the bacteriocins tested, lacticins A164 and BH5 produced by Lactococcus lactis subsp. lactis A164 and L. lactis BH5, respectively, showed the strongest antibacterial activity against H. pylori strains. MICs of the lacticins against H. pylori strains, when assessed by the critical dilution micromethod, ranged from 0.097 to 0.390 mg/liter (DSM strains) or from 12.5 to 25 mg/liter (ATCC 43504), supporting the strain-dependent sensitivity of the pathogen. Pediocin PO2 was less active than the lacticins against four strains of H. pylori, and leucocin K was the least active peptide, with no inhibition toward H. pylori ATCC 43504. Anti-Helicobacter activity of lacticin A164 was dependent on initial inoculum size as well as concentration of the bacteriocin added.     

Enhanced extraction of flavanones hesperidin and narirutin from Citrus unshiu peel using subcritical water

Flavanones including hesperidin and narirutin constitute the majority of the flavonoids that occur naturally in citrus fruits. The main purpose of this study was to extract valuable natural flavanones from agricultural by-products such as citrus peels using subcritical water extraction (SWE). Thus, the application of SWE to extraction of flavanones hesperidin and narirutin from Citrus unshiu peel was evaluated, and the effect of key operating conditions was determined by varying the extraction temperature (110–200 °C) and time (5–20 min) under high pressure (100 ± 10 atm). The maximum yields of hesperidin (72 ± 5 mg/g C. unshiu peel) and narirutin (11.7 ± 0.8 mg/g C. unshiu peel) were obtained at an extraction temperature of 160 °C for an extraction time of only 10 min. These yields accounted for approximately 99% of the total amount of these flavanones in the original material. The SWE was compared with three conventional extraction methods in terms of the extraction time and recovery yields for hesperidin and narirutin. The hesperidin yield by SWE was more than 1.9-, 3.2-, and 34.2-fold higher than those obtained by extraction methods using ethanol, methanol, or hot water, respectively, and the narirutin yield was more than 1.2-, 1.5-, and 3.7-fold higher.     

Biochemical,microbiological, and nutritional aspects of kimchi (Korean fermented vegetable products)

Kimchi is a traditional, fermented Korean food that is prepared through a series of processes, including pretreatment of oriental cabbage (or radish), brining, blending with various spices and other ingredients, and fermentation. The characteristics of kimchi differ depending on the kimchi varieties, raw materials used, process, fermentation, and preservation methods. However, kimchi has typical biochemical, nutritional, and organoleptic properties and health‐related functions. Kimchi fermentation is initiated by various microorganisms originally present in the raw materials, but the fermentation is gradually dominated by lactic acid bacteria. Numerous physicochemical and biological factors influence the fermentation, growth, and sequential appearance of principal microorganisms involved in the fermentation. Complex biochemical changes occur depending on the environmental conditions before, during, and after fermentation. The most important characteristics are the compositional changes of sugars and vitamins (especially ascorbic acid), formation and accumulation of organic acids, and texture degradation and softening. Nutritionally, kimchi is an important source of vitamins, minerals, dietary fiber, and other nutrients. This review covers in some detail the biochemical, microbiological, and nutritional characteristics of kimchi.     

Subcritical water extraction of flavonol quercetin from onion skin

Subcritical water could be an excellent alternative to organic solvent as a medium for extracting flavonol quercetin, due to its temperature-dependent selectivity, safety, efficiency of recovery, and lower cost. This study investigated the application of subcritical water extraction (SWE) of quercetin from onion skin and evaluated the effect of key operation conditions by varying the temperature (100-190 °C), extraction time (5-30 min), and mixture ratio of onion skin and diatomaceous earth (DE) (0.5:3.5-2:2) under high pressure (90-131 bar). The maximum yield of quercetin (16.29 ± 0.75 mg/g onion skin) was obtained at extraction temperature of 165 °C, extraction time of 15 min, mixture ratio of 1.5:2.5 for onion skin and DE. The SWE was compared with three conventional extraction methods in terms of the efficiency. The quercetin yield by SWE was over eight-, six-, and fourfold greater than those obtained using the ethanol, methanol, and water-at-boiling-point extraction methods, respectively.     

Microbial inactivation in fresh and minimally processed foods by intense pulsed light (IPL) treatment

Food Science and Biotechnology - The purposes of this study were to evaluate the inactivation effects of intense pulsed light (IPL) on indigenous and inoculated microorganisms in fresh and...