Brian E. Farkas

Modeling heat and mass transfer in immersion frying. I, model development

This paper presents the development of the mathematical equations used for modeling immersion frying of an infinite slab. Immersion frying was viewed as a moving boundary problem similar to that found in freezing and freeze-drying. The infinite slab was divided into two regions, the crust and core, and macroscopic balances were used to develop the governing partial differential equations for heat and mass transfer in each region. Flux relations were proposed for the heat and mass transfer and incorporated into the partial differential equations. The final set of equations consisted of four non-linear partial differential equations and appropriate boundary conditions and initial conditions.

Modeling heat and mass transfer in immersion frying. II, model solution and verification

Abstract A mathematical model of heat and moisture transfer in a infinite slab undergoing immersion frying was solved using a three step procedure: a coordinate transformation of the partial differential equations, application of the finite difference method of Crank-Nicolson to produce a series of nonlinear algebraic equations, and Gauss-Seidel iteration for solution of the equations. Simulation output consisted of temperature profiles, moisture profiles, average moisture content, moisture transfer flux rates, and crust thickness data. The model was verified by comparison of the predicted temperature profiles, average moisture content, and crust thickness with experimental data. A good agreement between the predicted and experimental data was obtained.

IMAGE PROCESSING METHOD TO DETERMINE SURFACE AREA AND VOLUME OF AXI-SYMMETRIC AGRICULTURAL PRODUCTS

ABSTRACT An image processing based method was developed to measure volume and surface area of ellipsoidal agricultural products such as eggs, lemons, limes, and peaches. The method assumes that each product has an axi-symmetric geometry and is a sum of superimposed elementary frustums of right circular cones. The product volume and surface area are calculated as the sum of the volumes and surface areas of individual frustums using Matlab®. The dimensions of individual frustums are determined from a digitized picture of the product acquired by a Charged Coupled Device (CCD) camera and processed in Adobe Photoshop®. The volumes and surface areas computed showed good agreement with analytical and experimental results. The developed method proved to be accurate, precise, and easy to use.

Effects of High-Pressure Processing on Immunoglobulin A and Lysozyme Activity in Human Milk

Banked human milk, processed using low-temperature/long-time or Holder pasteurization, inactivates pathogenic microorganisms but degrades important biochemical components. High-pressure processing kinetics favor inactivation of microorganisms with retention of biochemical activity and nutritional quality of foods. The effects of high-pressure processing (400 MPa) and low-temperature/long-time pasteurization (62.5°C, 30 minutes) on total immunoglobulin A and lysozyme activity in human milk were investigated. Indirect modified enzyme-linked immunosorbent and a Micrococcus lysodeikticus turbidimetric assay were performed to measure immunoglobulin A immunoactivity and lysozyme activity, respectively. Pressure-treated samples retained significantly higher (P < .05) levels of immunoglobulin A and lysozyme activity compared to samples treated with low-temperature/ long-time pasteurization. These data suggest that high-pressure processing is a potential alternative to thermal pasteurization of human milk that can give greater retention of some bioactive components. Further research is needed to determine whether high-pressure processing can inactivate pathogens of concern in donor human milk. J Hum Lact. 23(3):253-261.

Inactivation of bacterial pathogens in human milk by high-pressure processing.

Low-temperature, long-time (LTLT) pasteurization assures the safety of banked human milk; however, heat can destroy important nutritional biomolecules. High-pressure processing (HPP) shows promise as an alternative for pasteurization of breast milk. The purpose of this study was to investigate the efficacy of HPP for inactivation of selected bacterial pathogens in human milk. Human milk was inoculated with one of five pathogens (10(8) to 10(9) CFU/ml), while 0.1% peptone solution solutions with the same levels of each organism were used as controls. The samples were subjected to 400 MPa at 21 to 31 degrees C for 0 to 50 min or to 62.5 degrees C for 0 to 30 min (capillary tube method) to simulate LTLT pasteurization. Tryptic soy agar and selective media were used for enumeration. Traditional thermal pasteurization resulted in inactivation (> 7 log) of all pathogens within 10 min. In human milk and in peptone solution, a 6-log reduction was achieved after 30 min of HPP for Staphylococcus aureus ATCC 6538. After 30 min, S. aureus ATCC 25923 was reduced by 8 log and 6 log in human milk and peptone solution, respectively. Treatments of 4 and 7 min resulted in an 8-log inactivation of Streptococcus agalactiae ATCC 12927 in human milk and peptone solution, respectively, while Listeria monocytogenes ATCC 19115 required 2 min for an 8-log inactivation in human milk. Escherichia coli ATCC 25922 was inactivated by 8 log after 10 min in peptone solution and by 6 log after 30 min in human milk. These data suggest that HPP may be a promising alternative for pasteurization of human milk. Further research should evaluate the efficacy of HPP in the inactivation of relevant viral pathogens.

Thermal and Dielectric Properties of Sweetpotato Puree

Abstract Pureeing of sweetpotato (SP) is carried out to enhance the conversion of the roots into value‐added products. During processing, production and home utilization, the puree is often heated (conventional cooking or microwaved), hence the need to measure the corresponding properties of SP puree. Thermal (specific heat, thermal conductivity, density, and thermal diffusivity) and dielectric properties (dielectric constant and dielectric loss factor) of SP puree were determined within a temperature range of 5 to 80°C. Increase in temperature increased the specific heat (3.70–3.78 kJ/kg K), thermal conductivity (0.52–0.78 W/m K), and thermal diffusivity (1.98 × 10−7–4.25 × 10−7 m2/s) of SP puree. The density (705–485 kg/m3) of the puree decreased with temperature. Both temperature and frequency (900–2500 MHz) significantly affected the dielectric constant (60.5–73.0) and dielectric loss factor (16.5–29.5) of SP puree. At the two frequencies (915 and 2450 MHz) used in industrial food processing, calculations showed that the penetration depth was not significantly affected by temperature at 2450 MHz, while at 915 MHz, the penetration depth decreased with temperature.

The Effect of Feed Solids Concentration and Inlet Temperature on the Flavor of Spray Dried Whey Protein Concentrate

Previous research has demonstrated that unit operations in whey protein manufacture promote off-flavor production in whey protein. The objective of this study was to determine the effects of feed solids concentration in liquid retentate and spray drier inlet temperature on the flavor of dried whey protein concentrate (WPC). Cheddar cheese whey was manufactured, fat-separated, pasteurized, bleached (250 ppm hydrogen peroxide), and ultrafiltered (UF) to obtain WPC80 retentate (25% solids, wt/wt). The liquid retentate was then diluted with deionized water to the following solids concentrations: 25%, 18%, and 10%. Each of the treatments was then spray dried at the following temperatures: 180 °C, 200 °C, and 220 °C. The experiment was replicated 3 times. Flavor of the WPC80 was evaluated by sensory and instrumental analyses. Particle size and surface free fat were also analyzed. Both main effects (solids concentration and inlet temperature) and interactions were investigated. WPC80 spray dried at 10% feed solids concentration had increased surface free fat, increased intensities of overall aroma, cabbage and cardboard flavors and increased concentrations of pentanal, hexanal, heptanal, decanal, (E)2-decenal, DMTS, DMDS, and 2,4-decadienal (P < 0.05) compared to WPC80 spray dried at 25% feed solids. Product spray dried at lower inlet temperature also had increased surface free fat and increased intensity of cardboard flavor and increased concentrations of pentanal, (Z)4-heptenal, nonanal, decanal, 2,4-nonadienal, 2,4-decadienal, and 2- and 3-methyl butanal (P < 0.05) compared to product spray dried at higher inlet temperature. Particle size was higher for powders from increased feed solids concentration and increased inlet temperature (P < 0.05). An increase in feed solids concentration in the liquid retentate and inlet temperature within the parameters evaluated decreased off-flavor intensity in the resulting WPC80.

THERMAL PROPERTIES OF SKIPJACK TUNA (KATSUWONUS PELAMIS

Differential Scanning Calorimetry (DSC) was used to obtain specific heat, heat of fusion, and protein denaturation temperatures of raw skipjack tuna. Thermal conductivity values of raw skipjack tuna over a range of temperatures were determined by the line heat source probe method. Statistical analysis showed that there was no significant difference between the specific heat of loin meat (3.536 kJ/kg K), red meat (3.505 kJ/kg K), and viscera (2.263 kJ/kg K). There were significant differences between the backbone and loin meat, backbone and red meat, and backbone and viscera on specific heat values. The protein denaturation temperature of loin meat was higher than that of red meat. There was no significant difference between thermal conductivity of raw loin meat (0.57 W/m K) and viscera (0.56 W/m K). In general, thermal conductivity increased with temperature.

Detection of discoloration in thermally processed blue crab meat

This study objectively and quantifiably examined the effect of a series of factors on blue crab meat discoloration. Factors explored include heating process, animal harvest location, and position of meat within a container. A Spectrogard colorimeter was used to collect visual reflectance spectra between 380 and 720 nm. Meat degree of coloration was characterised objectively and rapidly by using lightness (L), red–green (a) and yellow–blue (b) colour values. Results showed that meat became darker with increasing heating process; crab harvest location had significant effect on the lightness of the flesh; and meat that is located in the bottom of a can was darker than that in the top. This study will serve as a baseline for the development of a coloration quality control system. © 1999 Society of Chemical Industry

The effect of acidification of liquid whey protein concentrate on the flavor of spray-dried powder

Off-flavors in whey protein negatively influence consumer acceptance of whey protein ingredient applications. Clear acidic beverages are a common application of whey protein, and recent studies have demonstrated that beverage processing steps, including acidification, enhance off-flavor production from whey protein. The objective of this study was to determine the effect of preacidification of liquid ultrafiltered whey protein concentrate (WPC) before spray drying on flavor of dried WPC. Two experiments were performed to achieve the objective. In both experiments, Cheddar cheese whey was manufactured, fat-separated, pasteurized, bleached (250 mg/kg of hydrogen peroxide), and ultrafiltered (UF) to obtain liquid WPC that was 13% solids (wt/wt) and 80% protein on a solids basis. In experiment 1, the liquid retentate was then acidified using a blend of phosphoric and citric acids to the following pH values: no acidification (control; pH 6.5), pH 5.5, or pH 3.5. The UF permeate was used to normalize the protein concentration of each treatment. The retentates were then spray dried. In experiment 2, 150 μg/kg of deuterated hexanal (D₁₂-hexanal) was added to each treatment, followed by acidification and spray drying. Both experiments were replicated 3 times. Flavor properties of the spray-dried WPC were evaluated by sensory and instrumental analyses in experiment 1 and by instrumental analysis in experiment 2. Preacidification to pH 3.5 resulted in decreased cardboard flavor and aroma intensities and an increase in soapy flavor, with decreased concentrations of hexanal, heptanal, nonanal, decanal, dimethyl disulfide, and dimethyl trisulfide compared with spray drying at pH 6.5 or 5.5. Adjustment to pH 5.5 before spray drying increased cabbage flavor and increased concentrations of nonanal at evaluation pH values of 3.5 and 5.5 and dimethyl trisulfide at all evaluation pH values. In general, the flavor effects of preacidification were consistent regardless of the pH to which the solutions were adjusted after spray drying. Preacidification to pH 3.5 increased recovery of D₁₂-hexanal in liquid WPC and decreased recovery of D₁₂-hexanal in the resulting powder when evaluated at pH 6.5 or 5.5. These results demonstrate that acidification of liquid WPC80 to pH 3.5 before spray drying decreases off-flavors in spray-dried WPC and suggest that the mechanism for off-flavor reduction is the decreased protein interactions with volatile compounds at low pH in liquid WPC or the increased interactions between protein and volatile compounds in the resulting powder.