Modeling the Growth Inhibition Kinetics of Baker's Yeast by Potassium Sorbate Using Statistical Approaches

Potassium sorbate is widely used as a preservative in food products. The inhibition kinetics of yeast growth by potassium sorbate was determined in order to predict the inhibition mechanism and develop an antimicrobial activity model. Linear regression resulted in uncompetitive growth inhibition using different concentrations of nutrients in liquid media containing yeast extract, malt extract (YM broth) and potassium sorbate. At 30°C, constant K_s of YM broth to yeast was 0.254%, maximum growth rate (μ_max) of yeast was 0.008 min^-1, and inhibition constant (K_i) of potassium sorbate to yeast growth was 0.324%. This statistical method could reliably determine the growth inhibition mechanism and kinetics.     

EFFECT OF SODIUM LACTATE, CALCIUM LACTATE AND SODIUM ALGINATE ON BACTERIAL GROWTH AND AMINOPEPTIDASE ACTIVITY

The effects of sodium alginate (0.4 and 0.8%), calcium lactate (0.15 and 0.3%) and sodium lactate (60% solution; 1, 2, 3 and 4%) on growth and aminopeptidase activity of Pseudomonas fragi ATCC 4973 and Salmonella typhimurium in trypticase soy broth or autoclaved ground beef were studied for 5 days at 5°C. Sodium alginate and calcium lactate did not change colony counts of P. fragi or S. typhimurium; and had only slight effects on aminopeptidase activity. Sodium lactate (3 and 4%) showed inhibitory activity on growth and aminopeptidase activity of P. fragi. Sodium lactate also decreased aminopeptidase activity of S. typhimurium but had no major influence on colony counts. In general, aminopeptidase activity was inhibited more than cell multiplication by higher levels of alginate and sodium lactate .     

Estimating Solar Irradiance on Inclined Surfaces: A Review and Assessment of Methodologies

A variety of numerical models for calculating the solar irradiance for an inclined surface are described and evaluated using data for Vancouver, B.C., Canada. While all the hourly models have a common approach for calculating the direct component of the solar irradiance there is a variety of methods for calculating the diffuse irradiance based on the portion of the sky hemisphere within the field of view of the surface. A less significant distinction between the models is in the methods used to calculate the amount of radiation received as a result of reflection from adjacent surfaces.

The paper demonstrates that the principal features of the anisotropic distribution of sky radiance must be included in the numerical computations since the use of the unrealistic isotropic model leads to significant short and long term errors. Inclusion of directional reflectance in the slope irradiance calculations will lead to increased accuracy for the estimated values, with greatest improvement being achieved in the winter months due to a zenith angle dependency on the significance of the directional reflectance.

Errors in estimating the slope irradiance with an anisotropic model are shown to compare favourably with the errors associated with a direct measurement of the solar irradiance.     

EFFECT OF FILMS OF DIFFERENT OXYGEN TRANSMISSION RATE ON TOXIN PRODUCTION BY CLOSTRIDIUM BOTULINUM TYPE E IN VACUUM PACKAGED COLD AND HOT SMOKED TROUT FILLETS

Studies were done to determine the effect of film oxygen transmission rate (OTR) on the time to toxicity in vacuum packaged cold and hot smoked rainbow trout fillets challenged with C. botulinum type E (10² spores/g) and stored at refrigerated conditions (4C), and under mild (8C) and moderate (12C) temperature abuse conditions. While no samples were toxic at 4C, toxin was detected within 28 days at 8C for cold smoked trout fillets vacuum packaged in films with high OTR. Toxin was also detected for most vacuum packaged hot smoked trout fillets within 14–28 days at 8C, with the exception of trout fillets packaged in films with an OTR > 10,000 cc/m²/day. In most cases at 8C, spoilage, based on odor/color scores, preceded or occurred simultaneously with toxigenesis. At 12C all cold and hot smoked trout were toxic after 14–21 days and samples packaged in films with an OTR <5000 cc/m²/day became toxic before, or at the same time as, samples became spoiled. This study has shown that vacuum packaging of trout fillets in low gas barrier films, ranging in OTR from approximately 3,000 to approximately 10,000 cc/m²/day at 24C and 0% relative humidity (RH), did not prevent the growth and toxin production by C. botulinum in vacuum packaged cold and hot smoked trout fillets at 12C. Additional barriers, other than the OTR of the packaging film, need to be considered to ensure the safety of vacuum packaged trout fillets, particularly at mild to moderate temperature abuse storage conditions.     

Whey Protein Coating Effect on The Oxygen Uptake of Dry Roasted Peanuts

A procedure was developed to coat peanuts with aqueous whey protein isolate (WPI) solutions based on increasing coating-solution viscosity. Oxygen uptake of WPI-coated nuts and uncoated nuts were compared. WPI coatings delayed oxygen uptake of dry roasted peanuts at intermediate (53%) and low (21%) storage relative humidity. They had similar results at 29°C and 37°C. The effects of coating thickness and storage relative humidity indicate that the mechanism of protection of the coatings was through their oxygen barrier properties.     

ALTERATION OF GLUCOSINOLATE CONTENT, PATTERN, AND MUTAGENICITY OF CABBAGE (BRASSICA OLERACEA) GROWN ON MUNICIPAL SEWAGE SLUDGE—AMENDED SOIL

Cabbage (Brassica oleracea var. capitata) was grown on soil (control) or municipal sewage sludge-treated plots. The cabbage was freeze-dried and analyzed for glucosinolate content and pattern. Results showed that cabbage grown on sludge-amended soil contained only half the glucosinolate content of cabbage grown on the control plot. The pattern of individual glucosinolates present was also altered. The sludge-grown cabbage glucosinolate extract was shown to be mutagenic in the non-activated test system of S. typhimurium TA 100. Extracts of both sludge-grown and control cabbage were shown to enhance the mutagenicity on a dose-response basis of aflatoxin B₁, benzo(a)pyrene, and captan.     

A Cooling System with Water Recycle for Blanched Vegetables

A water conserving cooling system with water recycle for blanched vegetables was designed to complement a previously developed water recycling blancher. The two stage cooler consisted of an evaporative cooling section with forced air and water sprays and a flume cooler with water, which was both refrigerated and recycled. A pilot scale blanching and cooling system was constructed, and broccoli spears were processed. The cooling system was effective at lowering the product temperature rapidly while maintaining the quality of the product at a high level as determined by ascorbic acid concentration, percentage of total solids, percentage of retained chlorophyll, and microbial counts.     

MOLECULAR THERMODYNAMICS OF GAS SOLUBILITY(Ⅰ)HENRY’S CONSTANTS OF GASES IN NONPOLAR SOLVENTS

A molecular thermodynamic model of gas solubility in nonpolar solvents has been established. The Helmholtz energy of liquid mixture is calculated through the following three steps. First, the pure components in standard state are mixed isothermally to form an ideal gas mixture. Then each molecule is inflated into a hard sphere with diameter σ. The corresponding Helmholtz energy change is calculated by using the Mansoori-Carnahan-Starling-Leland equation. Finally, the molecules are charged with LJ 12-6 potential to form the real liquid mixture, where the structure is described by an approximated radial distribution function gij(r)=H(r-r)+βδ(r-rj). Henry's constants are then calculated from residual chemical potential.With the use of the same LJ parameters, this model can predict the computer simulation results of Henry's constant quite well. In this respect, this model is superior to Pierotti's theory. For practical systems, Henry's constants of various gases in C_1—C_(20) alkanes and their isomers, naphthenes, aromatic hydrocarbons and liquified gases can be well correlated over a wide temperature range using only one adjustable parameter. The predictions for △H_(s1), △S(s1) and V_1 are also satisfactory.