Fractoemission from Failure of Metal-GIass Interfaces

Electron and photon emissions accompanying the failure of a metal/glass interface were studied. Experimental evidence is given in support of a previously presented model involving microdischarges accompanying fracture which result from charge separation occurring between the metal and glass surfaces. The role of contact charging at the metal/glass interface in establishing this charge separation is discussed.     

Microbiology of brines used to mature feta cheese

The microfloras of brines from two commercial factories manufacturing traditional feta cheese were examined over a period of 60 days, which is the normal maturation time for Greek feta. Non-starter lactic acid bacteria were the dominant group, and Lactobacillus paracasei ssp. paracasei and Lactobacillus plantarum were the principal species identified. A number of strains of Debaryomyces hansenii were isolated from the brines, and both the yeasts and the lactobacilli possessed enzymes capable of degrading fat or protein. It is suggested that these microfloras play an important role in the maturation of feta cheese. No recognized pathogens were isolated from the brines of' either factory.     

THERMAL RESISTANCE OF BACILLUS STEAROTHERMOPHILUS SPORES IN DRIED PASTA AT DIFFERENT STAGES OF REHYDRATION

The thermal resistance of Bacillus stearothermophilus spores at different stages of rehydration was examined. Inoculation was achieved by rehydrating pasta samples in water containing 1‐mL spore crop (10⁶ spores/mL); the product was heat sealed in sterile pouches and processed in a laboratory retort. Thermal inactivation of spores was carried out using 10 time intervals at 121C for moisture contents, 70, 90, 105, 115, 125 and 145% dry basis. The death curves obtained consisted of two phases, an initial rapid decline (1.5 to 2.6 log reductions) followed by a slower, linear decrease of survivors from which the decimal reduction time (D value) was calculated. D₁₂₁ values were found to decrease with increasing moisture content and ranged from 4.6 to 6.5 min. The thermal resistance constant (z value) was examined to assess the effect of temperature (110–125C) on lethality. z values decreased with increasing moisture content and ranged from 10.7 to 15.6C. The results of this study demonstrate that temperature and moisture content influence the effectiveness of the intended heat process. For products that are rehydrated during heat treatment, the moisture content of the product is a critical factor. Therefore, if complete rehydration is not achieved, this may result in the heat process being less effective for the destruction of microorganisms, which may have implications in regard to food safety.     

EFFECTS OF LACTIC ACID IN PROCESSING WATERS ON THE INCIDENCE OF SALMONELLAE ON BROILERS1

Commercial broilers were inoculated with 10⁵-10⁶/mL Salmonella typhimurium in the drinking water at 14, 10, 7, 4, and 2 days prior to processing. At 49 days of age, broilers were processed in a pilot processing facility. In additional trials, commercially-obtained pre- and post-chill carcasses were subjected to microbiological testing. Lactic acid (LA) (1%) was added to the scald and/or chill waters or to pre- (2%) or post-chill (1%) dips to reduce microbial contamination on ready-to-cook carcasses. In each trial, 12 carcasses per treatment were sampled for the presence of salmonellae (inoculated serotype and/or indigenous organisms) using a whole carcass rinse technique. The dip applications evaluated included 1 and 2% LA at various temperatures and exposure periods. Two control treatments which were not subjected to LA but were processed and handled similar to treated carcasses were evaluated for each trial conducted. Treatments that consistently resulted in reduced levels of salmonellae on carcasses included LA treatment (1%) in the chill water, a pre-chill dip (2% for 2 min at 37 C), 1% LA as a post-chill dip (≥60 s at 1.1 C), and 2% LA as a pre-chill dip (60 s at 37 C). All picked carcasses treated with LA exhibited mild skin discoloration, particularly in the highly pigmented areas.     

OXIDATION OF HYDROCARBONS BY HEMIN1

A model system for cytochrome P-450 comprised of hemin, thiosalicylic acid, and solvent (acetone and water), oxidized cyclohemne and n-hexane at pH 2.7. Oxidation of cyclohexane yielded more cyclohexanol than cyclohexanone under mild reaction conditions, whereas the oxidation of n-hexane generated more 3- and 2-hexanones than 3- and 2-hemnols. Oxygen was a limiting factor in the reaction, and increased oxygen pressures increased the ratio of cyclohexanone to cyclohexanol formed. Lag time for product formation decreased in a linear fashion with an increase in temperature. In addition, cyclohexanone decreased relative to cyclohexanol as the temperature was increased. Antioxidants increased the lag time for product formation, but had little effect on the final quantity or ratios of the oxidative products generated. 1,3 Diphenylisobenzafiran had no effect on the lag time, whereas Tiron and catechol increased the lag time. In contrast to aliphatic thiols, aromatic thiols were capable of driving the oxidative reaction. The model hemin system was approximately 6% as active as natural cytochrome P-450. Hemin immobilized on glass beads effectively catalyzed the oxidation of cyclohexane.     

Region Recognition Using Area Method

Visual aids in the form of graphs and charts are often used in analysis and design procedures. Commonly, a graph is divided into regions of common characteristics, such as in a soil classification scheme in which a set of properties are located on a chart and the soil classification is given. Although these aids are useful in hand calculations, it is often difficult to implement these charts into a computer code. A general technique is described in this paper which can simplify both implementation and the regional coordinate analysis by the use of an area coordinate method. An example and a short Fortran code are also included to show how this technique can be used.     

VARIATION OF LAG TIME AND SPECIFIC GROWTH RATE AMONG 11 STRAINS OF SALMONELLA INOCULATED ONTO STERILE GROUND CHICKEN BREAST BURGERS AND INCUBATED AT 25C1

One strain of 11 serotypes or 11 strains of Salmonella, which were isolated from the ceca of broilers, were surveyed for their growth kinetics on sterile ground chicken breast burgers incubated at 25C to determine the variation of lag time and specific growth rate. Growth curves, four per strain, were fit to a two‐phase linear model to determine lag time (h) and specific growth rate (log₁₀/h). Repeatability of growth kinetics measurements for individual strains had a mean coefficient of variation of 11.7% for lag time (range: 5.8 to 17.3%) and a mean coefficient of variation of 6.7% for specific growth rate (range: 2.7 to 13.3%). Lag time among strains ranged from 2.2 to 3.1 h with a mean of 2.8 h for all strains, whereas specific growth rate among strains ranged from 0.3 to 0.38 log₁₀ per h with a mean of 0.35 log₁₀per h for all strains. One‐way analysis of variance indicated that lag time (P =0.029) and specific growth rate (P =0.025) differed slightly among strains. S. Haardt had a shorter (P < 0.05) lag time than S. Agona and S. Brandenburg, whereas the specific growth rate of S. Enteritidis was less than (P < 0.05) the specific growth rates of S. Typhimurium and S. Brandenburg. All other strains had similar lag times and specific growth rates. The coefficient of variation among strains was 9.4% for lag time and 5.7% for specific growth rate. These results indicate that there were only minor differences in the lag times and specific growth rates among the strains of Salmonella surveyed. Thus, the growth kinetic values obtained with one strain of Salmonella may be useful for predicting the growth of other strains of Salmonella for which data do not currently exist.