Apparent diffusivities of reducing sugars in potato strips blanched in water

The mechanism of reducing sugar losses was investigated in potatoes cut into 9.5 × 9.5 mm and 13 × 13 mm strips and blanched for 300–2400s at different temperatures between 70°C and 100°C. Experiments were carried out using large amounts of well-agitated water. Assuming no chemical reaction and using appropriate solutions of the unsteady state diffusion equation for square parallelpiped geometry, the apparent diffusivities, D_a, of reducing sugars in the potato matrix were determined at different temperatures. the incorporation of the dimensions of the strips in the solution of the diffusion equation was sufficient to explain the effect of size on losses. Values of D_a were found to be in the range 1.2 × 10^-11 1.7 × 10^-11 m²s^-1 and could be correlated with temperature according to the Arrhenius law.     

Moisture Diffusivity in Sponge Cake as Related to Porous Structure Evaluation and Moisture Content

ABSTRACT: Water diffusivity within sponge cake was determined at 5, 20, and 25 °C by identification from a water sorption kinetic and using a mathematical model based on Fick's 2nd law. Water diffusivity at 20 °C within sponge cake varied from 0.5 × 10^-10 m²/s to 7.5 × 10^-10 m²/s as a function of sponge cake moisture content. Influence of temperature on the concentration-dependent diffusivity was investigated. The activation energy was found to vary with sponge cake moisture content from 84 to 128 kj/mole. Effective diffusivity variations were correlated with the changes in microstructure of the material that was observed by using environmental scanning electron microscopy. The level of porosity in the material played a dominant role in determining the effective diffusivity.     

Inactivation of Escherichia coli O157:H7 and Salmonella enteritidis in Liquid Egg White Using Pulsed Electric Field

ABSTRACT: The effects of temperature and pulsed electric field (PEF) intensity on inactivation of pathogens such as Escherichia coli O157:H7 and Salmonella enteritidis in egg white was investigated. Liquid egg white inoculated with 10⁸ colony-forming units (CFU)/mL of each pathogen was treated with up to 60 pulses (each of 2 JAS width) at electric field intensities of 20 and 30 kV/cm. The processing temperatures were 10°C, 20°C, and 30°C. After treatment, uninjured and total viable cells were enumerated in selective and nonselective agars, respectively. Maximum inactivations of 3.7 and 2.9 log units were obtained for S. enteritidis and E. coli O157:H7, respectively, while injured cells accounted for 0.5 and 0.9 logs for E. coli O157:H7 and S. enteritidis , respectively. For both bacteria, increasing treatment temperature tended to increase the inactivation rate. There was synergy between electric field intensity and processing temperature. The inactivation rate constant k _T values for E. coli O157:H7 on both selective and nonselective agars were 8.2 × 10^-3 and 6.6 × 10^-3/μS, whereas the values for S. enteritidis were 16.2 × 10^-3 and 12.6 × 10^-3/μS, respectively. The results suggest that E. coli O157:H7 was more resistant to heat-PEF treatment compared with S. enteritidis.     

EFFECT OF SEVERAL EXPERIMENTAL PARAMETERS ON COMBINATION OF RED KIDNEY BEAN (PHASEOLUS VULGARIS) α-AMYLASE INHIBITOR WITH PORCINE PANCREATIC α-AMYLASE

Purified red kidney bean (Phaseolus vulgaris) amylase inhibitor forms a 1:1 stoichiometric complex with porcine pancreatic α-amylase leading to complete loss of enzyme activity on starch. Rate of complex formation is pH dependent and is maximal at pH 5. The rate constants for complex formation, as measured by loss of amylase activity, were 2.85 × 10⁴ M^-1 sec^-1 at pH 6.9 (ionic strength of 0.918) and 2.55 × 10⁵ M^-1 sec^-1 at pH 5 at 30°C. At pH 6.9, rate of complex formation was 4.8 times faster at 0.918 ionic strength as compared with the rate at 0.138 ionic strength. At 30°C, pH 6.9 and ionic strength of 0.168 the dissociation constant of the enzyme-inhibitor complex was determined to be 3.5 × 10^-11 M. The rate constant for dissociation of the complex was calculated to be 8.7 × 10^-8 sec^-1 under the same conditions. The rate constant for complex formation, at ionic strength of 0.168, was 1.1 × 10⁴ M^-1 sec^-1 at 37⁰ and 9.77 × 10² M^-1 sec^-1 at 25.7°C. The calculated activation energy for complex formation is 39.5 kcal/mole suggesting a rate-controlling conformational change. Oxidation of the carbohydrate moiety of the glycoprotein inhibitor caused complete loss of activity. Maltose, a competitive inhibitor of α-amylase, bound as readily to the enzyme-inhibitor complex as to free α-amylase. Trypsinized α-amylase, although still able to bind to Sephadex, did not bind inhibitor. The experiments with maltose and trypsinized amylase suggest the inhibitor may not bind at the active site of α-amylase.     

Mathematical Evaluation of Effective Moisture Diffusivity in Fresh Japanese Noodles (Udon) by Regular Regime Theory

The effect of moisture content and temperature on the effective moisture diffusivity was investigated to have the optimal drying condition of Japanese noodles (Udon) using regular regime theory. The drying of fresh Udon of different moisture contents was carried out under constant conditions of relative humidity and airflow at 20, 30, and 40 °C. The existence of regular regime periods for fresh noodles was experimentally verified. Effective moisture diffusivity obtained ranged from 2.1 × 10 ^-7 to 3.7 × 10 ^-7 cm² s^-1. The effect of temperature on effective moisture diffusivity was adequately modeled by the Arrhenius relationship, although the effect of moisture content was quite small.     

PRODUCTION OF FLAVOR COMPOUNDS: ALDEHYDES AND ALCOHOLS FROM LEUCINE BY MICROENCAPSULATED CELL-FREE EXTRACTS OF STREPTOCOCCUS LACTIS VAR. MALTIGENES

Cell-free extract (CFE) from Streptococcus lactis var. maltigenes was examined for its ability to catalyze the formation of 3-methyl butanal and 3-methyl butanol from leucine as affected by pH, substrate concentration and gradual addition of NADH. Pseudo K_m and v_max, determined for CFE were 6.5 × 10^-3 M and 7.1 μmol/liter-min when 3-methyl butanal was measured and 9.4 × 10^-3 M and 2.4 μmol/liter-min for 3-methyl butanol. The CFE, leucine and cofactors were encapsulated in milkfat and incubated for 40 h at 22°, Rate of formation and final concentration of 3-methyl butanal and 3-methyl butanol were related to substrate concentration, indicating that flavor intensity can be controlled with encapsulated enzymes by limiting substrate concentration. Diffusion of 3-methyl butanol and acetic acid from microcapsules was affected by concentration and their lipophilic/hydrophilic character. Altering the pH of fluid surrounding microcapsules containing CFE had limited effect on the internal pH, as indicated by enzyme probes, demonstrating that capsules provide an environment isolated from the bulk phase of foods.     

RELEASE OF PROPYL PARABEN FROM A POLYMER COATING INTO WATER AND FOOD SIMULATING SOLVENTS FOR ANTIMICROBIAL PACKAGING APPLICATIONS

The release phenomena of propyl paraben from a polymer coating to water and three food simulating solvents (10% aqueous ethanol, 50% aqueous ethanol, n-heptane) were studied for antimicrobial packaging applications. The effects of food simulating solvent, initial concentration in the coating and temperature on the propyl paraben release were examined. The initial concentration of propyl paraben in the coating ranged from 1.26 × 10⁴ to 10.52 × 10⁴ g/m³ and the temperature from 5.5 to 30C. For water, the release was controlled by Fickian diffusion with constant diffusion coefficient (7±11 × 10^-11 cm²/s at 30C), and independent of the initial concentration. For 10% ethanol, the release followed again the Fickian model with constant diffusion coefficient (30±40 × 10^-11 cm²/s at 30C). For 50% ethanol and n-heptane, the release was instantaneous and not controlled by Fickian diffusion. For the release into water, the activation energy for diffusion from the Arrhenius relationship was around 88 kJ/mole.     

CHARACTERIZATION OF PHYTASE OF BEANS (PHASEOLUS VULGARIS)

Phytase from California Small White beans was extracted, concentrated and enriched by heat treatment and ammonium sulfate fractionation. Crude enzyme fractions tenaciously retained endogenous phytate which could be removed by autolysis at 45°C and pH 5.2. Characterization of the phytase preparation showed: (1) increase in activity with increasing temperature from 37 to 60°C, (2) an activation energy of approximately 9,200 cal/mole for the hydrolysis of inositol hexaphosphate; (3) pH optimum of 5.2; (4) a K_m value of 2.22 × 10^-4M; (5) apparently partial inhibition at high substrate concentrations; (6) fully competitive inhibition by one of the reaction products, inorganic phosphate, with K_i=3.1 × 10⁴M. These properties and kinetic constants are comparable to those reported for phytase preparations from similar sources and they adequately account for in situ autolytic loss of phytic acid from these beans.     

The air drying behaviour of fresh and osmotically dehydrated banana slices

Ripe banana, cut to 10mm thick slabs were osmotically treated in sugar solutions of 35, 50 and 65° Brix for 36h. The initial moisture content fell from a value of 3.13kg H₂O DM to 2.19, 1.63 and 1.16kg H₂O kg⁻¹ for treatment in the three solutions, respectively. These slabs, with Total Soluble Solids (TSS) contents of 26, 34 and 39° Brix, respectively, as well as freshly cut but untreated slabs (15° Brix) were air dried in a cabinet type tray drier to near equilibrium conditions at fixed temperatures from 40 to 80°C and at a constant air speed of 0.62m s⁻¹. Drying was found to occur in the falling rate period only for both banana types and two drying constants K₁ and K₂ were established for a first and second falling rate period of drying. Increasing the drying air temperature significantly enhanced the drying rate and the K-values, except at 80°C when the rates fell, possibly because of case hardening of the slabs. Reducing the slab thickness also improved the drying rate, but increasing the air speed to 1.03m s⁻¹ did not have any profound effect. As the sugar content of the banana slabs increased through the osmotic treatment, drying rates fell. Calculated apparent moisture diffusivities at 60°C ranged from 34.8× 10⁻¹⁰ m² s⁻¹ (fresh slab) to 8.8×10⁻¹⁰ m² s⁻¹ for dried (39° Brix) slabs. The moisture diffusivity was significantly lowered as the moisture content dropped in drying and with increased levels of sugar. Previously osmosed and then air dried banana slabs showed appealing colour and texture compared to the fresh banana.     

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.     

LINKING MICROBIOLOGICAL CRITERIA FOR FOODS WITH QUANTITATIVE RISK ASSESSMENT

The current annual risk of acquiring a foodborne disease in the United States is estimated at 2.7 × 10^-2. The risk of associated death is estimated at 3.7 × 10^-5. These represent a health care burden >$3 billion. Using a risk assessment model one can identify levels of microbial contamination which may be unacceptable in foods and appropriate controls needed to reduce these levels. Salmonella bacteria continue to represent a large percentage of the identifiable infections. A model developed from human dose-response studies predicts the probability of infection for Salmonella at 7.5 × 10^-3 with exposure to a single CFU of the organism. Risks of severity (hospitalization), mortality, reactive arthritides, and mortality in the elderly are estimated at 3.1 × 10^-6, 7.5 × 10^-6, 1.7 × 10^-5, and 2.8 × 10^-4. Exposure to microbial contaminants needs to be evaluated on a single meal basis. For chicken, exposure may range from a single drum stick (38g) to a half broiler (176g) but averages around 80g. For beef between 51 and 85g may be consumed during a single meal. Therefore, methods for monitoring must be able to detect at least 1 CFU/80g. Risks for some pathogenic E. coli are estimated at 1,000 to 10,000 less than Salmonella. Therefore, use of coliforms as indicators needs to be assessed and related to occurrence and survival and regrowth potential of the enteric bacteria of greater public health concern. Because, 20% of the U.S. population may be considered to be in a special population category and at an increased risk of severe outcomes, no more than 20% failure of a standard should be acceptable .     

Isolation and characterization of polygalacturonase and invertase from a yeast Endomycopsis fibuligera (3812) bioconversion of date wastes

Properties of polygalacturonase [E.C. 3.2.1.15] (E₁) and invertase (E.C. 3.2.1.26] (E₂) isolated and purified in powdered form from Endomycopsis fibuligera grown on date wastes were measured.
The molecular weights were estimated to be about 32000 and 69500, and they were highly specific for hydrolysing (1–4) and (1–2) glycosidic links respectively. the K_m value of E₁ was 7.1 × 10^-2M for soluble-pectic acid and that for E₂ was 6.7 × 10^-2M for sucrose at pH4.5, and optimal pHs were 3.5 for E₁ and 4.0 for E₂. the purified enzymes are stable on storage for more than one year at - 20°C.     

Moisture Diffusivity in Tylose Gel (Karlsruhe Test Material)

ABSTRACT: Tylose gel (the Karlsruhe test substance) is a meat analog commonly used for studying heat transfer during freezing and thawing operations. It has thermal properties similar to lean beef, which are well defined in literature; however, moisture diffusivities for Tylose gel are not available in the literature. In this article, the mass transfer properties of Tylose were investigated. This included determining a moisture isotherm for Tylose and measuring effective moisture diffusivity as a function of temperature using 2 different methods: a drying method and a concentration-distance method. The moisture isotherm was fit best using the Guggenheim-Anderson-de Boer (GAB) equation. The resulting moisture diffusivities were fit to an Arrhenius model for temperature dependence from 2.5 °C to 12 °C. The moisture diffusivities measured for Tylose ranged from 4.00 × 10^-11 to 9.75 × 10^-11 m²/ s, depending on temperature. The drying method resulted in moisture diffusivities that were found to have higher dependence on temperature than when the concentration-distance method was used. The concentration-distance method gave much more variation among measurements.     

Inactivation of Listeria monocytogenes on Beef Bologna and Cheddar Cheese Using Polyvinyl-idene Chloride Films Containing Sorbic Acid

ABSTRACT: Polyvinylidene chloride (PVDC, Saran^R F-310) films containing sorbic acid (0%, 1.5%, and 3.0% w/v) were prepared with use of a solvent-casting method and were then placed between slices of commercially produced beef bologna that were previously surface-inoculated with L. monocytogenes at 10³ or 10⁵ CFU/g. In addition, cubes of commercial Cheddar cheese were surface-inoculated to contain 10³ or 10⁵ Listeria monocytogenes colony-forming units (CFU) /g and then wrapped with the sorbic acid-containing films. Films containing 1.5% and 3.0% (w/ v) sorbic acid prevented growth of L. monocytogenes on bologna slices with populations as much as 7.1 logs lower after 28 d of storage at 4 °C compared with the sorbic acid-free controls. In contrast, numbers of Listeria remained relatively stable on Cheddar cheese with populations decreasing < 1.3 logs after 35 d of storage. With use of the sorbic acid-containing films, common spoilage organisms were also inhibited on both products. After 28 d of contact with bologna and Cheddar cheese, these films retained 7% and 60% of their original sorbic acid content, respectively, with the control film retaining 85% of its original sorbic acid content. Given these findings, sorbic acid-containing films may be useful in enhancing the safety and shelf-life of ready-to-eat delicatessen products.     

HYGIENIZATION OF INDIAN CHICKEN MEAT BY IONIZING RADIATION

Both fresh and frozen chicken meat were evaluated for microbiological status by screening for total bacterial counts and for the presence of pathogens like Enterobacteria , Bacillus cereus, coagulase positive Staphylococci and Salmonella spp. Most of the samples exhibited heavy bacterial contamination (1.2 × 10⁵ - 2.6 × 10⁶/g), mainly with Staphylococcus spp. (1.5 × 10⁴ - 2.8 × 10⁵/g). All the chicken samples also showed the presence of Salmonellae (3 × 10¹ - 2.1 × 10²/g). Among the different serotypes observed in chickens . S. typhimurium was common in fresh as well as frozen chicken. Radicidation at 2 kGy at cryogenic conditions (−40°C) was efficient in eliminating the natural pathogenic contamination of the poultry . Salmonella spp. viz. S. seftenberg and S. typhimurium differed in radiation sensitivity, the D₁₀ values in phosphate buffer (pH 7.2) being 0.25 kGy and 0.12 kGy, respectively. Chicken homogenate (10%) offered approximately 2-fold protection to these cells. Chicken samples artificially inoculated with a heavy inoculum (10⁸ cells/g) of these 2 serotypes required higher gamma radiation doses of 4–5 kGy. The findings suggested that a dose of 2 kGy is adequate for normally contaminated chicken samples, but for the heavily contaminated chicken a dose of 4–5 kGy, depending upon the predominating Salmonella serotype present, is required .     

SIMULATING DIFFUSION MODEL AND DETERMINING DIFFUSIVITY OF POTASSIUM SORBATE THROUGH PLASTICS TO DEVELOP ANTIMICROBIAL PACKAGING FILMS

A diffusion model was simulated by computer programming and diffusivities of potassium sorbate through various plastic films were determined by a lag time method. The simulation showed that partition coefficient affected the flux of total penetration but did not affect the lag time. Therefore, the lag time method is appropriate in determining diffusivity, using any value for the partition coefficient. The diffusivities of potassium sorbate were 1.83 × 10⁻⁸ cm²/s, 4.26 × 10⁻¹³ cm²/s, 4.65 × 10⁻¹³ cm²/s, and 5.47 × 10⁻¹³ cm²/s through low density polyethylene (LDPE), high density polyethylene, polypropylene, and polyethylene terephthalate, respectively at 25 C. Arrhenius equation shows very good fit between the diffusivity and the temperature by the linear regression analysis. D₀ and E_a of potassium sorbate through LDPE film resulted in 1.98 × 10⁻⁶ cm²/s, and 11.83 KJ/mole K. The concentration of potassium sorbate was insignificant and did not contribute to the statistical model. This result verifies that the diffusion of potassium sorbate in LDPE film is typical case ofFickian diffusion.     

Fate of Aflatoxin M1 during Manufacture and Storage of Feta Cheese

ABSTRACT:  The effect of feta cheese manufacture on aflatoxin M₁ (AFM₁) content was studied using an enzyme immunoassay technique. Feta cheese was made from milk spiked with 1 and 2 μg AFM₁ per kilogram milk. Pasteurization at 63 °C for 30 min caused <10% destruction of AFM₁. During cheese making, the remaining AFM₁ in milk was partitioned between curd and whey with two-thirds retained in the curd and one-third going into the whey. Cheeses were then stored for 2 mo in 8%, 10%, and 12% brine solutions at 6 and 18 °C. There was a 22% to 27% reduction of AFM₁ during the first 10 d of storage, with slightly more loss as salt concentration increased and when the cheese was stored at 18 °C. Further storage caused only slight decrease in AFM₁ and after 30 d of brining there was no difference in AFM₁ content of the cheese based upon salt concentration of the brine. At 18 °C, no further losses of AFM₁ occurred after 30 d, and at 6 °C, there was continued slight decrease in AFM₁ levels until 50 d. After 60 d of brining, there was a total loss of 25% and 29% of the AFM₁ originally present for cheese brined at 6 and 18 °C, respectively. Thus, the combination of pasteurization, conversion of milk into feta cheese, and at least 50 d storage of cheese in brine caused a total loss of about 50% of the AFM₁ originally present in the raw milk.     

Modelling the deep-fat frying of beef meatballs

Mathematical models describing heat, moisture and fat transfers during deep-fat frying of beef meatballs were developed and validated against experimental data consisting of temperatures at two locations in the product, and average moisture and fat contents. Fat diffusivity in the product was 0.287 × 10^-7m²s^-1 while fat conductivity followed Eyring's model with frequency factor of 0.137 × 10^-6m s^-1 K^-1 and activation energy of 2.70 kJ mol^-1.     

Alginate- and gellan-based edible films for probiotic coatings on fresh-cut fruits

ABSTRACT:  Alginate- (2% w/v) or gellan-based (0.5%) edible films, containing glycerol (0.6% to 2.0%), N-acetylcysteine (1%), and/or ascorbic acid (1%) and citric acid (1%), were formulated and used to coat fresh-cut apple and papaya cylinders. Water vapor permeability (WVP) was significantly higher ( P < 0.05) in alginate films (0.30 to 0.31 × 10⁻⁹g m/Pa s m²) than in the gellan ones (0.26 to 0.27 × 10⁻⁹g m/Pa s m²). Addition of 0.025% (w/v) sunflower oil decreased WVP of gellan films (0.20 to 0.22 × 10⁻⁹ g m/Pa s m²). Water solubility of gellan and alginate films at 25 °C (0.47 to 0.59 and 0.74 to 0.79, respectively) and their swelling ratios (2.3 to 2.6 and 1.6 to 2.0, respectively) indicate their potential for coating high moisture fresh-cut fruits. Fresh-cut apple and papaya cylinders were successfully coated with 2% (w/v) alginate or gellan film-forming solutions containing viable bifidobacteria. WVP in alginate (6.31 and 5.52 × 10⁻⁹g m/Pa s m²) or gellan (3.65 and 4.89 × 10⁻⁹ g m/Pa s m²) probiotic coatings of papaya and apple, respectively, were higher than in the corresponding cast films. The gellan coatings and films exhibited better water vapor properties in comparison with the alginate coatings. Values > 10⁶ CFU/g B. lactis Bb -12 were maintained for 10 d during refrigerated storage of fresh-cut fruits, demonstrating the feasibility of alginate- and gellan-based edible coatings to carry and support viable probiotics on fresh-cut fruit.     

Chemiluminescent determination of hydrogen peroxide in water

A method for determining low concentrations of hydrogen peroxide (H₂O₂) in water, based on the chemiluminescent oxidation of 3-aminophthalhydrazide (luminol) by H₂O₂ in the presence of a copper ion catalyst, is described. Levels of H₂O₂ down to 3 × 10^-8 mol/1 (1 ppb) can be determined. The method may be used to monitor the amount of residual H₂O₂ in aseptically filled packages sterilized with H₂O₂ before filling.