Antimicrobial activity of cyclodextrin entrapped allyl isothiocyanate in a model system and packaged fresh-cut onions.

The aim of this work was to determine the antimicrobial effect of allyl isothiocyanate (AIT) entrapped in alpha and beta cyclodextrin inclusion complexes (ICs). In model experiments, AIT formulations were applied to filter paper discs fixed inside the lid of Petri dishes, where the agar surface was inoculated with the target organism (Penicillium expansum, Escherichia coli or Listeria monocytogenes). Solid phase microextraction coupled with gas chromatography was used to determine static headspace concentrations of AIT formulations. The antimicrobial effect of beta IC was determined during aerobic storage of packaged fresh-cut onions at 5 °C for 20 days. AIT entrapped in beta IC exhibited a significantly (p < 0.05) better antimicrobial effect compared to unentrapped AIT. AIT vapour concentrations in the static system were highest for unentrapped AIT followed by beta IC and alpha IC. Application of beta IC (200 µl/l) to packaged fresh-cut onions effectively decreased numbers of L. monocytogenes, which were also decreased at slower rates to undetectable levels on untreated cut onion. After 10 days, total aerobic counts were ca. 4 log CFU/g lower on onions treated with beta IC (100 and 200 µl/l) compared to untreated controls. This work demonstrates the utility of beta IC as an antimicrobial treatment with potential applications in packaged fresh-cut vegetable products.

Evidence of an antilisterial factor induced by wounding of iceberg lettuce tissues.

AIMS: To examine the influence of wound-associated reactions in cut iceberg lettuce (Lactuca sativa L.) tissues on the fate of Listeria monocytogenes. METHODS AND RESULTS: Aqueous extracts prepared from shredded iceberg lettuce before and after storage in high oxygen permeability film were inoculated with L. monocytogenes. Listeria monocytogenes grew in extracts prepared from fresh lettuce. In contrast, inhibition ranging from arrested growth to a decline in cell viability was observed in extracts prepared from samples stored for 1-3 days. Similar behaviour was evident in lettuce shreds inoculated with 10(5) CFU g(-1)L. monocytogenes immediately after processing or after 3 days in storage. Heat treatment of the cut tissues at 47 degrees C for 3 min before storage diminished the inhibitory effect. CONCLUSIONS: The results provided evidence that an antilisterial factor or factors are released by wounded iceberg lettuce tissues. Antilisterial activity was mitigated by heat treatment of the lettuce. SIGNIFICANCE AND IMPACT OF STUDY: This study indicates that intrinsic factors associated with plant metabolism could play a significant role in the ecology of human pathogens in packaged horticultural products.

Disinfection of mung bean seed with gaseous acetic acid.

Mung bean seed inoculated with Salmonella Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes (3 to 5 log CFU/g) was exposed to gaseous acetic acid in an aluminum fumigation chamber. Salmonella Typhimurium and E. coli O157:H7 were not detected by enrichment of seeds treated with 242 microl of acetic acid per liter of air for 12 h at 45 degrees C. L. monocytogenes was recovered by enrichment from two of 10 25-g seed samples treated in this manner. Fumigation with gaseous acetic acid was also lethal to indigenous bacteria and fungi on mung bean seed. The treatment did not significantly reduce seed germination rates, and no differences in surface microstructure were observed between treated and untreated seed viewed by scanning electron microscopy.

Effect of calf feeding regimes and diet EDTA on physico-chemical characteristics of veal stored under modified atmospheres.

Physico-chemical characteristics of veal from 30 calves allotted to five different rations with respect to iron bioavailability were evaluated at packaging and after 2 and 4 weeks of storage under both 100% CO(2) and 100% N(2). The five diets were 'Milk', 'Grain', 'Mix' (combination of Milk and Grain) and 'Mix + EDTA' and 'Grain + EDTA' where 15 mg EDTA were added per mg Fe in the feed concentrate. Diet EDTA was generally more influential on veal quality than storage treatments. The chelator caused an unexpected pH drop in veal stored four weeks irrespective of storage conditions (p ≤ 0.05). However, the colour, texture and flavour of meat from animals fed EDTA in the Grain- and Mix-ration was equivalent to that of Milk-fed veal (p ≤ 0.05). The EDTA treatments also improved the appearance of veal under anoxic atmospheres. Upon storage however, the chelator increased veal drip losses (p ≤ 0.05) and also cooking losses from Grain-fed calves (p ≤ 0.05). Packaging under CO(2) decreased pH (p ≤ 0.05) and increased drip losses (p ≤ 0.05) but did not alter other physico-chemical parameters. Dietary treatments had no effect on shear forces (p > 0.05) which decreased after two weeks in storage (p ≤ 0.05) independent of gas atmospheres. Overall, the quality characteristics of pale veal were obtained following addition of EDTA in Grain- and Mix-fed animals and were maintained in storage. This approach looks promising for the veal industry but warrants further research.

Functionality of high and low voltage electrically stimulated beef chilled under moderate and rapid chilling regimes.

Chuck muscles from 24 beef carcasses electrically stimulated (ES) with either high or low voltage, or a combination of both, and submitted to conventional or rapid chilling regimes were used in a model system study (pH, salt-solubloe protein extraction, emulsifying capacity) and in frank-further fabrication and analysis (yield, color, texture). Glycolytic rates measured in the loin had no effects on the functional parameters or on the quality of frankfurters. The ultimate pH values of unstimulated carcasses remained higher than in any ES carcasses, and led to higher protein extraction (P ≤ 0·05). However, ES had no further influence on the emulsifying capacity or on frankfurter yield and quality parameters independently of the voltage used (P > 0·05). Chilling regimes had no influence on the functional parameters of the model system but slightly influenced the yield and chewiness of the frankfurters (P ≤ 0·05). Therefore, the use of any type of ES in combination with either conventional (Canadian) or more rapid chilling is unlikely to have commercial significance on the yield or quality of frankfurters.

Bacteriology of Hot and Cold Boned Pork Preblends.

Ground pork and preblends containing 2% NaCl or 2% NaCl plus 200 ppm NaNO2 were prepared from hot (HB) and cold (CB) boned pork in a commercial slaughtering plant. Total aerobic mesophiles, psychrotrophs, Enterobacteriaceae , salt tolerant, and lactic acid bacteria were enumerated in freshly ground meat and in preblends stored for 1 week at 2°C. Boning method had no effect on mesophillic, psychrotrophic, and salt tolerant counts in freshly ground meat, but Enterobacteriaceae and lactic acid bacteria were found in higher numbers in CB than HB meat (P < 0.05). Addition of salt plus nitrite led to the inhibition of most bacterial groups, although lactic acid bacteria were found in higher numbers in HB preblends after one week of storage (P < 0.05). The data revealed that HB pork preblends of excellent bacteriological quality and stability can be produced in an industrial context.

Detachment ofPseudomonas fluorescens from biofilms on glass surfaces in response to nutrient stress.

The effects of glucose and nitrogen depletion on the colonization of glass Petri plates byPseudomonas fluorescens were studied in batch culture. Colonization of the surfaces was initiated before colonization of the bulk phase, and biofilm formation was observed. This resulted in an apparent lag in the batch growth curve for the cell suspension. The lag phase was an artifact caused by the partitioning of cells between the bulk and solid phase of the culture and was not due to a reduction in the growth rate of unattached cells. The specific growth rate of the unattached cells (0.331 hour(-1)) was almost twice that determined for the total population (0.171 hour(-1)). Consequently the growth rate of biofilm-forming bacteria cannot be determined in batch culture unless the growth of both attached and unattached cells is monitored, and batch growth curves may contain artifacts due to the formation and dispersion of biofilms. The depletion of either glucose or nitrogen led to the active detachment of cells from the biofilm. An increase in the hydrophobicity of unattached cells was noted on depletion of carbon. This increase was the result of emigration of cells from the surface into the bulk phase.

Behavior ofPseudomonas fluorescens within the hydrodynamic boundary layers of surface microenvironments.

Phase, darkfield, and computer-enhanced microscopy were used to observe the surface microenvironment of flow cells during bacterial colonization. Microbial behavior was consistent with the assumptions used previously to derive surface colonization kinetics and to calculate surface growth and attachment rates from cell number and distribution. Surface microcolonies consisted of closely packed cells. Each colony contained 2(n) cells, where n is the number of cell divisions following attachment. Initially, cells were freely motile while attached, performing circular looping movements within the plane of the solid-liquid interface. Subsequently, cells attached apically, maintained a fixed position on the surface, and rotated. This type of attachment was reversible and did not necessarily lead to the formation of microcolonies. Cells became irreversibly attached by progressing from apical to longitudinal attachment. Longitudinally attached cells increased in length, then divided, separated, moved apart laterally, and slid next to one another. This resulted in tight cell packing and permitted simultaneous growth and adherence. After approximately 4 generations, individual cells emigrated from developing microcolonies to recolonize the surface at new locations. Surface colonization byPseudomonas fluorescens can thus be subdivided into the following sequential colonization phases: motile attachment phase, reversible attachment phase, irreversible attachment phase, growth phase, and recolonization phase.

Microbiological Stability of Pasteurized Ham Subjected to a Secondary Treatment in Retort Pouches.

A ham processing procedure consisting of pasteurizing, packaging in retort pouches, and subjecting the hams to a secondary heat treatment was evaluated as a method of increasing microbial stability. Pasteurized hams reheated at 121°C for 10 min and stored at 1±1°C or 6±1°C showed no microbial growth after 6 or 12 months of storage. The number of microorganisms in pasteurized hams not receiving the secondary heat treatment ranged from 103/g to >108/g and from 102 to >108/cm2 on the surface after 3 to 5 months of storage. Pasteurized hams that had been inoculated with Clostridium sporogenes spores before pasteurization followed by a secondary heat treatment at 121°C for 10 min showed a delay in the occurrence of swollen packages when stored at room temperature compared to hams not receiving the secondary heat treatment. However, the secondary heat treatment did not prevent spoilage of hams. Ham that has not been treated to eliminate spores should be refrigerated.