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Log Colony-forming Units (log + colony-forming_unit)
Selected AbstractsUltrasonication and Fresh Produce (Cos lettuce) PreservationJOURNAL OF FOOD SCIENCE, Issue 2 2006Said Ajlouni ABSTRACT Washing Cos lettuce in various sanitizers at different concentrations with and without ultrasonication (40 KHz) reduced the microbiological counts by 1 to 2.5 log colony-forming units (CFU)/g immediately after washing. Ultrasonication of Cos lettuce in water, chlorinated water, peracetic acid, hydrogen peroxide, and their combinations at various temperatures (4 °C, 20 °C, 35 °C, 47 °C, and 50 °C) had no significant effects (P > 0.05) on the total or the psychrophilic counts during storage at 10 °C. The total count in Cos lettuce reached 9.74 ± 0.035 log CFU/g after ultrasonication (2 min at 50 °C) in chlorinated water (100 mg/L) and storage for 6 d at 10 °C. Extending the ultrasonication (40 kHz) of Cos lettuce for up to 20 min did not improve the bactericidal effect of ultrasonication. However, long-time ultrasonication (20 min) caused significant (P < 0.05) damage to the quality of Cos lettuce tissues. [source] Effectiveness of Some Natural Antimicrobial Compounds in Controlling Pathogen or Spoilage Bacteria in Lightly Fermented Chinese CabbageJOURNAL OF FOOD SCIENCE, Issue 9 2005Yasuhiro Inatsu ABSTRACT: This study was designed to evaluate the bactericidal or bacteriostatic effect of chitosan, an allyl isothiocyanate (AIT) product, and nisin for the artificially inoculated pathogenic bacteria (Escherichia coli, Salmonella Enteritidis, Staphylococcus aureus, and Listeria monocytogenes) or natural microflora of fermented Chinese cabbage. Addition of 0.1% chitosan decreased the population of pathogens from 0.7 to 1.7 log colony-forming units (CFU)/g after 4 d of storage at 10 °C. The bactericidal activity of chitosan was found to be stronger than that of nisin (0.05 mg/g). Addition of 0.2% of the AIT product (containing AIT and hop extract) exhibited a bacteriostatic effect. However, a combination of AIT product and chitosan enhanced bactericidal efficacy against L. monocytogenes. The addition of chitosan or AIT product was observed to suppress the populations of mesophilic and coliform bacteria during storage at 10 °C for 4 d. Moreover, the use of chitosan or the AIT product did not change the sensory quality of the lightly fermented vegetable. Therefore, these results suggest that chitosan or the AIT product could be useful to improve the microbial safety and quality of lightly fermented vegetable. [source] Antimicrobial Effects of Lactoferrin, Lysozyme, and the Lactoperoxidase System and Edible Whey Protein Films Incorporating the Lactoperoxidase System Against Salmonella enterica and Escherichia coli O157:H7JOURNAL OF FOOD SCIENCE, Issue 7 2005Seacheol Min ABSTRACT: Lactoferrin (LF), lysozyme (LZ), the lactoperoxidase system (LPOS), and edible whey protein isolate (WPI) films incorporating LPOS were studied for inhibition of Salmonella enterica and Escherichia coli O157:H7. Antimicrobial effects of LF (5 to 40 mg/mL), LZ (1 to 20 mg/mL), and LPOS (0.5% to 5.0% [w/v] [0.03,.25 g/g, dry basis]) were examined by measuring turbidity of antimicrobial-containing media after inoculation and by examining cell inhibition by WPI films incorporating LPOS (LPOS-WPI films) on an agar recovery medium. Elastic modulus (EM), tensile strength (TS), percent elongation (%E), oxygen permeability (OP), and Hunter L, a and b of WPI films incorporating 0.03 to 0.25 g/g of LPOS were compared with those of plain WPI films without LPOS. The growth of S. enterica and E. coli O157:H7 (4 log colony-forming units [CFU]/mL) in tryptic soy broth (TSB) was not prevented by LF at ,20 and ,40 mg/mL, respectively. S. enterica and E. coli O157:H7 in TSB were not inhibited by LZ at , 6 and , 20 mg/mL, respectively. LPOS at concentrations of 2.75% (w/v) and 1.0% (w/v) reduced S. enterica and E. coli O157:H7 to below the limit of detection (1 CFU/mL) in TSB, respectively. LPOS-WPI films (0.15 g/g) completely inhibited S. enterica and E. coli O157:H7 (4 log CFU/cm2), inoculated either onto agar before placing the film disc or onto top of the film disc. Incorporation of 0.25 g/g of LPOS decreased EM, TS, and %E. The oxygen barrier property of WPI films was improved with the incorporation of LPOS at 0.15 to 0.25 g/g. [source] Hydrogen Peroxide and Calcium Chloride Added to Irrigation Water as a Strategy to Reduce Bacterial Populations and Improve Quality of Fresh MushroomsJOURNAL OF FOOD SCIENCE, Issue 6 2005Naveen Chikthimmah ABSTRACT The quality and value of fresh mushrooms are often diminished by the presence of high bacterial populations that cause a brown, blotchy appearance. The objective of the present research was to evaluate the addition of hydrogen peroxide and/or calcium chloride to irrigation water as a means to reduce total bacterial populations on fresh mushrooms. Crops were grown using commercial mushroom growing practices except for the addition of 0.75% hydrogen peroxide and/or 0.3% calcium chloride irrigation water added to the crop starting 11 d after the casing layer was applied on top of mushroom compost. Irrigation water without the added treatments acted as the control. Mushrooms were aseptically sampled from the production beds for enumerating bacterial counts. Total aerobic bacterial populations were determined by standard microbiological plating procedures. Mushroom whiteness (L -value) and color (delta E) after harvest and postharvest storage were measured using a Minolta chromameter. Harvested mushrooms were separated by treatment and weighed to record yield. Mushrooms irrigated with water (control) had 7.3 log colony-forming units (CFU) of aerobic bacterial populations per gram of fresh mushroom tissue. Compared with the control, irrigation with 0.75% hydrogen peroxide and 0.3% calcium chloride reduced the bacterial populations on fresh mushrooms by 87% (6.4 log CFU/g). Irrigation with hydrogen peroxide and calcium chloride significantly enhanced mushroom whiteness after harvest as well as after 6 d of postharvest storage at 12 °C. The irrigation treatments did not have a significant effect on crop yields; hence, the addition of hydrogen peroxide and calcium chloride to irrigation water was demonstrated to have good potential as a practical strategy to reduce bacterial populations and to improve the quality of fresh mushrooms. [source] Numerical Analysis of Heat Transfer during Surface Pasteurization of Hot Dogs with Vacuum-Steam-Vacuum TechnologyJOURNAL OF FOOD SCIENCE, Issue 9 2004L. Huang ABSTRACT: The objective of this study was to validate the fundamental heat-transfer mechanism governing the process of vacuum-steam-vacuum surface pasteurization of hot dogs. It was hypothesized that the steam could not directly flow into the pores below the surface of hot dogs, and the heat was transferred into these areas by conduction. A numerical analysis program was first developed to estimate the heat-transfer coefficient between steam and hot dogs and was then used to simulate the temperature distribution at different locations below the surface. The hypothesis and computer simulation model were successfully validated using hot dogs surface-inoculated with Listeria innocua. Results showed that the heat from saturated steam must be conducted into the interior to kill L. innocua harboring in the pores and irregularities below the surface of hot dogs. Results of computer simulation and biological validation also suggested that heating must be maintained at 138 °C for at least 25 s to achieve a complete elimination (> 8 log colony-forming units per gram) of L. innocua from hot dogs. [source] Comparison of the performances of different fermentation strategies on cell growth and bacteriocin production by Lactobacillus curvatus CWBI-B28JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 3 2007Hakim Ghalfi Abstract The dynamics of cell growth and bacteriocin production by Lactobacillus curvatus CWBI-B28 in modified De Man/Rogosa/Sharp (mMRS) broth with various concentrations of glucose and complex nitrogen source (CNS; peptone, yeast extract and meat extract) was investigated in flask fermentations and in a laboratory fermentor using batch and fed-batch cultivations. In fed-batch fermentation the rate of feeding of the reactor with the substrates was either maintained constant (0.12 L h,1) or varied exponentially as a function of time. The results showed that both cell growth and bacteriocin activity were influenced by changes in the concentrations of glucose and CNS. Optimal growth and bacteriocin activity were obtained in mMRS broth containing 40 g L,1 glucose and 40 g L,1 CNS (mMRS40/40). A bacteriocin titre of 4266 AU mL,1 and a cell count of 8.7 log colony-forming units (cfu) mL,1 were recorded when this medium was used for cultivation. In batch fermentation using the same medium, a higher cell count (9.5 log cfu mL,1) and twice as much bacteriocin as in flask fermentation were produced. The highest bacteriocin titre (8533 AU mL,1) was obtained with fed-batch fermentation at an exponentially varying rate of feeding. Bacteriocin activity and cell dry mass did not always correlate. Copyright © 2007 Society of Chemical Industry [source] | ||||||||||