CALCOFLUOR AS A FLUORESCENT PROBE TO DETECT BIOFILMS OF FOODBORNE PATHOGENS

Biofilms enable foodborne pathogens to resist removal from surfaces, survive disinfection and elude detection. This study evaluated the use of Calcofluor, which binds to polysaccharides containing β-D-glucans, to detect biofilms produced by Salmonella enterica serovar Berta and Salmonella enterica serovar Typhimurium DT104 (St DT104), Escherichia coli, Aeromonas hydrophila, Vibrio cholerae O139 and Hyphomonas adhaerens. Biofilms produced by St DT104, S. berta and V. cholerae on five types of surfaces (glass, polypropylene, Teflon™, stainless steel and aluminum) were detected by Calcofluor. Results suggest the potential use of Calcofluor as probes of foodborne pathogens in biofilms.     

A Predictive Model for Food Particle interactions with Contact Surfaces

The protein adsorption rate from whole milk onto various surfaces was modeled as a function of contact surface tension, surface temperature, and time. A new kinetic parameter related to the value of contact surface tension which corresponds to a minimal interaction between food components and the solid surface is introduced. This experimentally measurable parameter quantifies the influence of contact surface tension on the activation energy required for irreversible protein adsorption. In spite of its simplicity, the model adequately predicted initial adsorptive behavior under steady flow conditions for a wide range of surface properties.     

Disinfection of Rice Seeds Prior to Sprouting

Different methods of rice seeds disinfection were investigated in order to limit the development of micro-organisms during sprouting. At room temperature, sodium hypochlorite at 1000 ppm or hydrogen peroxide resulted in a 2 to 3 log decrease in aerobic plate counts. Ethanol was found to inhibit germination, thus prohibiting its use. The limited effectiveness of decontaminating solutions could be because they did not access the bacteria, which was supported by the results of washing with benzalkonium chloride. Greater reduction (up to 5 log) was obtained by soaking seeds for 5 min in a sodium hypochlorite solution at 60°C.     

Vitamin B6 In Ready-To-Eat Cereals: Analysis By High Performance Liquid Chromatography

Twenty-four ready-to-eat cereals obtained locally were analyzed for their vitamin B₆ content by a recently developed high performance liquid chromatographic (HPLC) procedure. The method uses sulfo-salicylic acid as an extraction agent with subsequent qualitative and quantitative analysis by anion exchange chromatography. All six forms of vitamin B₆ plus their metabolite, pyridoxic acid, can be identified and quantified. Spot checks of the results obtained with this method and with a radiometric-microbiological assay give agreement to within 5%. On the other hand, disagreements of up to 38% are found on comparison with the standard AOAC microbiological procedure used by a commercial laboratory. The results indicate no significant variations between boxes within the same lot, but in one-third of the cereals tested, significant variations were found from lot to lot.     

Pectolytic Enzymes in Sweet Bell Peppers (Capsicum annuum L.)

Low levels of polygalacturonase (PG) and pectinesterase (PE) activities were quantitated in sweet bell peppers at four stages of maturity based on surface ground color (dark green, light green, turning, and red). The PG activity increased during pepper ripening and was maximal at the turning stage while the PE activity declined during ripening and was maximal at the light green stage. Pepper texture measurements were found to decline concomitantly with the increase in PG activity. Pepper PG showed pH optimum between 4.8 to 5.0 and increased temperature stability with advanced ripening. Compared to tomatoes, pepper PG activity was 116- to 164-fold lower and pepper PE activity was 429- to 1900-fold lower than the corresponding tomato enzymes.     

Vacuum Infiltration of Polyamines Increases Firmness of Strawberry Slices Under Various Storage Conditions

Strawberry slices were vacuum infiltrated with polyamines and changes in firmness during storage were determined. Spermine and spermidine at 10 mM or 100 mM significantly increased firmness, whereas pu-trescine was not as effective at increasing firmness of slices stored at 1°C. The firming effect of the polyamines was similar to that of calcium chloride, and may have been due to their ability to bind to cell walls and membranes. In ripe receptacles of various cultivars which differed in firmness, putrescine (12–38 nmol/g fresh weight) and spermidine (19–33 nmoI/g fresh weight) were the predominant polyamines, while only low levels of spermine (<10 nmol/g fresh weight) were present. There was no discernible relationship between endogenous polyamine levels and fresh fruit firmness for the cultivars studied.     

RHEOLOGICAL AND CHEMICAL PROPERTIES OF MOZZARELLA CHEESE

Dynamic viscoelastic parameters and chemical properties of Mozzarella cheese produced using a "no-brine" cheese making method with 3 different cooking temperatures (38, 41, and 44C) were determined. Samples were stored for 3 weeks at 4C before dynamic mechanical analysis at 22C. G', G" and tan δ were 5.8 – 6.4 × 10⁵ dyne/cm², 1.9 – 2.1 × 10⁵ dyne/cm², and 0.33 – 0.35, respectively, at 1% strain and 10 rad/s. The percentage of intact α_s-casein and β-casein were 38–40% and 33–35% of total protein in the cheese, respectively. The range of cooking temperatures used in this experiment had little effect on dynamic viscoelastic properties or the amount of intact protein for the cheese.