Debilitation in conidia of the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae and implication with respect to viability determinations and mycopesticide quality assessments.

Germination of Beauveria bassiana (Bb) and Metarhizium anisopliae (Ma) conidia determined from a fast-rehydration (FR) protocol were compared to those obtained when dry conidia were subjected to slow rehydration (SR) by holding under high humidity conditions prior to aqueous suspension. Differences in viability estimates obtained using the FR vs. SR protocols increased markedly after conidia were exposed to various stress factors in storage (high a(w), temperature, and O(2) concentrations), with the SR protocol producing higher estimates of viability in all cases. After Bb conidia were stored under moist conditions for 21 days at 25 degrees C, the SR estimate of viability was >21% greater than the FR estimate. In jars flushed with different O(2) concentrations and stored at 50 degrees C for 34 days, proportional differences between protocols varied, depending on water activity, from 18-44% in jars flushed with 0% O(2) (100% N(2)) to as high as 63-93% when treated with 21-22% O(2). For conidia stored over a broad range of moderate to high temperatures in the absence of O(2), SR-FR differences were

The role of packaging film permselectivity in modified atmosphere packaging.

Modified atmosphere packaging (MAP) is commercially used to increase the shelf life of packaged produce by reducing the produce respiration rate, delaying senescence, and inhibiting the growth of many spoilage organisms, ultimately increasing product shelf life. MAP systems typically optimize O(2) levels to achieve these effects while preventing anaerobic fermentation but fail to optimize CO(2) concentrations. Altering film permselectivity (i.e., beta, which is the ratio of CO(2)/O(2) permeation coefficients) could be utilized to concurrently optimize levels of both CO(2) and O(2) in MAP systems. We investigated the effect of modifying film permselectivity on the equilibrium gas composition of a model MAP produce system packaged in containers incorporating modified poly(ethylene) ionomer films with CO(2)/O(2) permselectivites between 4-5 and 0.8-1.3. To compare empirical to calculated data of the effect of permselectivity on the equilibrium gas composition of the MAP produce system, a mathematical model commonly used to optimize MAP of respiring produce was applied. The calculated gas composition agreed with observed values, using empirical respiration data from fresh cut apples as a test system and permeability data from tested and theoretical films. The results suggest that packaging films with CO(2)/O(2) permselectivities lower than those commercially available (<3) would further optimize O(2) and CO(2) concentration in MAP of respiring produce, particularly highly respiring and minimally processed produce.

Growth and survival of Escherichia coli O157:H7 on fresh-cut apples in modified atmospheres at abusive temperatures.

The effects of reduced-O2 and elevated-CO2 modified atmospheres (MAs) and abusive temperatures on the growth and survival of E. coli O157:H7, yeast, and molds and on changes in the visual quality of fresh-cut apples were evaluated. High-CO1 and low-O2 (> or = 15% and < 1%, respectively) atmospheres inhibited the growth of the pathogen on apple slices at 15 and 20 degrees C. However, the population of the pathogen increased by 1 log cycle after 2 weeks of storage in air. The high-CO2 MA resulted in the inhibition of yeast and mold growth, less browning, and better visual quality than did air and ambient-CO2 atmospheres. The results of this study confirm that E. coli O157:H7 can grow on apple slices in air. These results also show that these organisms survive but are inhibited in MAs with high CO2 levels at abusive temperatures. An MA can increase the shelf life of fresh-cut apples by improving retention of visual quality and inhibiting yeast and molds. Thus, contamination of minimally processed apples with E. coli O157:H7 can be a safety issue for both air- and MA-packaged cut apples.

Nitric oxide inhibition of alcohol dehydrogenase in fresh-cut apples ( Malus domestica Borkh).

The effects of nitric oxide (NO) and nitrite treatment on alcohol dehydrogenase activity and the shelf life of apple tissue were investigated. Fresh-cut apple slices were stored for 2 days at 6 °C in 0.25-1% NO (v/v, balance N2) or 100% N2 atmospheres. Slices were also treated with 1% NO or 2 mM sodium nitrite (NaNO2) for 20 min, stored for 6 weeks in 100% N2 at 6 °C, and analyzed for acetaldehyde, ethanol, and ethyl acetate accumulation, firmness, and color. Compared with N2 or deionized water controls, treatment with 1% NO or 2 mM NaNO2 inhibited ethanol accumulation, whereas that of acetaldehyde increased. Ethyl acetate accumulation was inhibited only by NO. Slice firmness was not affected by NO or NaNO2 treatment, but slices were darker than the untreated controls. NO and nitrite may extend the shelf life of fresh-cut produce with low concentrations of phenolic compounds.

Inhibition of Surface Molds on Cheese by Polyethylene Film Containing the Antimycotic Imazalil.

Imazalil, an antimycotic agent, was incorporated into low density polyethylene (LDPE) film and the resulting films tested for ability to inhibit Penicillium sp., and Aspergillus toxicarius growth by measuring the rate of carbon dioxide (CO2) production in sealed jars containing either inoculated potato dextrose agar (PDA) or Cheddar cheese. Inhibition of surface mold growth on cheese was also determined in open systems. An imazalil concentration of 2000 mg/kg LDPE film delayed A. toxicarius growth on PDA while LDPE film containing 1000 mg/kg imazalil markedly delayed Penicillium sp. growth. Furthermore, LDPE film containing 1000 mg/kg imazalil inhibited both molds growing on Cheddar cheese. These data suggest that incorporation of an antimycotic agent such as imazalil into food contact packaging films would inhibit surface mold growth.

Influence of New Packaging Technologies on the Growth of Microorganisms in Produce.

Several new technologies which are intended to extend the shelf life of respiring fruits and vegetables have been or are being developed. This is in response to the increased consumption of fresh fruits and vegetables and the desire to distribute branded products. The most widely studied and adopted technologies are controlled or modified atmosphere packaging. These packaging methods alter the gases surrounding a respiring product in order to slow the normal senescence or decay of the product. Controlled or modified atmosphere packaging can also affect the types and growth rates of microorganisms associated with produce. This may slow the rate of deterioration of the produce but could also provide sufficient time for human pathogens to develop rendering the product unsafe while still edible. This possibility has not been thoroughly researched and so interest in the safety of these technologies exists. Of primary importance is the relationship between the growth rate of pathogenic microorganisms and the rate of decay of the produce. Produce which has spoiled beyond the point where it is edible is of much less risk than produce which remains edible while becoming infectious or toxic. The relationship between the formation of botulinum toxin and "edibility" of extended shelf-life packaged tomatoes is an example of such concern. Often measures of toxin formation are available but not directly compared to the likelihood that a product is acceptable and would be eaten. This paper discusses one such approach.

Comparative Growth of Spoilage and Pathogenic Organisms on Modified Atmosphere-Packaged Cooked Beef.

The influence of CO2 atmospheres on the growth of spoilage and pathogenic microorganisms on cooked, sliced roast beef was investigated. An atmosphere containing 75% CO2, 15% N2 and 10% O2 was identified as the most effective in the simultaneous inhibition of Pseudomonas fragi , Salmonella typhimurium , Staphylococcus aureus , and Clostridium perfringens . Inoculated roast beef was exposed to two temperature abuse regimes to observe the resultant microbiological changes in air and three modified atmospheres containing 75% CO2 and O, 5 or 10% O2 (balance N2). The modified atmospheres inhibited the growth of S. aureus during abusive storage, and atmospheres containing 5 or 10% O2 inhibited the outgrowth of C. perfringens . The modified atmospheres were less effective in inhibiting the growth of S. typhimurium . However, high Salmonella counts were accompanied by high Pseudomonas counts. The concept of a Safety Index, which compares numbers of spoilage and pathogenic organisms, was developed to aid in the evaluation of modified atmospheres.

The Relationship Between Botulinal Toxin Production and Spoilage of Fresh Tomatoes Held at 13 and 23°C Under Passively Modified and Controlled Atmospheres and Air.

The formation of botulinal toxin relative to spoilage of fresh whole tomatoes was investigated at 13 and 23°C under passively modified (MA) and controlled atmospheres (CA) and air. Tomatoes were subsurface inoculated with a composite of type A and proteolytic and nonproteolytic type B strains of Clostridium botulinum spores. Some were also inoculated with Alternaria mold spores. MA (1.0-2.9% O2) was passively established by a combination of product respiration and package permeability. CA was established by placing tomatoes in continuously flushed (1% O2, 20% CO2, balance N2) Plexiglass plastic containers. Tomatoes were tested for botulinum toxin by the mouse assay at the time when they first became inedible based on predefined stages of decay rather than specific storage times in order to determine the relationship between spoilage and botulinal toxigenesis. All tomatoes became inedible according to the established criteria within 17 to 46 d depending on the storage temperature and atmosphere. Botulinum toxin was not detected in the 24 composite samples of inedible tomatoes (representing 99 tomatoes) which were tested at the time they first became inedible. Toxin was detected in four of five additional composite samples (representing 10 tomatoes) which were held 2 to 9 d beyond the time they were first determined to be inedible. These data indicate that MA-packaged tomatoes can become toxic but only after becoming severely spoiled beyond the point of being organoleptically acceptable. The risk of botulism from consumption of extended shelf life whole tomatoes appears to be insignificant.