Original article: Apparent thermal diffusivity estimation for the heat transfer modelling of pork loin under air/steam cooking treatments

Apparent thermal diffusivity linear functions vs. product temperature were estimated for pork cooked under two different treatments (forced convection, FC and forced convection/steam combined, FC/S) at 100, 110, 120 and 140 °C by means of experimental time–temperature data and a developed finite‐difference algorithm. Slope and intercept of each function were employed to calculate apparent thermal diffusivity at 40, 55 and 70 °C. Generally, FC/S treatments gave significantly higher apparent thermal diffusivities in comparison with FC conditions. Apparent thermal diffusivities were used to develop a model for cooking time and final core temperature prediction on the basis of oven setting. The model was validated by means of additional cooking tests performed at different temperatures of those employed for model development. Root mean square error values lower than 3.8 °C were obtained comparing predicted and experimental temperature profiles. Percentage errors lower than 3.1% and 3.5% were, respectively, obtained for cooking times and final core temperatures.     

Thermal inactivation ofClostridium perfringensvegetative cells in ground beef and turkey as affected by sodium pyrophosphate

The heat resistance (55–65°C) ofClostridium perfringensvegetative cells in ground beef and turkey that included 0, 0.15 or 0.3% (w/w) sodium pyrophosphate (SPP) was assessed in bags heated using a water bath. The surviving cell population was assayed on tryptose–sulfite– cycloserine agar. The decimal reduction (D)-values in beef that included no SPP were 21.6, 10.2, 5.3, and 1.6min at 55, 57.5, 60, 62.5°C, respectively; the values in turkey ranged from 17.5min at 55°C to 1.3min at 62.5°C. Addition of 0.15% SPP resulted in concomitant decrease in heat resistance as evidenced by reduced bacterialD-values. TheD-values in beef that included 0.15% SPP were 17.9, 9.4, 3.5, and 1.2min at 55, 57.5, 60, and 62.5°C, respectively; the values in turkey ranged from 16.2min at 55°C to 1.1min at 62.5°C. The heat resistance was further decreased when the SPP level in beef and turkey was increased to 0.3%. Heating such products to an internal temperature of 65°C for 1min killed >8log₁₀cfug^-1. The z-values in beef and turkey for all treatments were similar, ranging from 6.22 to 6.77°C. Thermal death time values from this study should assist institutional food service settings in the design of thermal processes that ensure safety againstC. perfringensin cooked beef and turkey.     

Acidulant and oven type affect total anthocyanin content of blue corn cookies

BACKGROUND: Anthocyanins, pink to purple water‐soluble flavonoids, are naturally occurring pigments with claimed health benefits. However, they are sensitive to degradation by high pH, light and temperature. Blue corn (maize) contains high levels of anthocyanins. Cookies are popular snacks and might serve as a vehicle to deliver antioxidants. A cookie formula with a high level of blue corn was developed with added acidulents and baked in ovens with different heat transfer coefficients. RESULTS: The best whole‐grain blue corn flour/wheat pastry flour ratio (80:20 w/w), guar gum level (10 g kg^?1, flour weight basis) and water level (215 g kg^?1, flour weight basis) were determined based on response surface methodology analysis. The interactions of citric and lactic acids and glucono‐δ‐lactone with three oven types having different heat transfer coefficients (impingement oven 179 °C/4 min, reel oven 204 °C/10 min and convection oven 182 °C/4 min) influenced the total anthocyanin content (TAC) remaining in blue corn‐containing cookies after baking. CONCLUSION: Cookies baked with citric acid in the convection oven retained the maximum TAC (227 ± 3 mg kg^?1). By baking rapidly at lower temperatures and adding acidulents, it may be possible to increase residual natural source antioxidants in baked foods. Copyright © 2010 Society of Chemical Industry     

Steam Assisted Hybrid Cooking Behavior of Semitendinosus Muscle: Heterocyclic Amines Formation,Soluble Protein Degradation,Fat Retention,Surface Color,and Cooking Value

Beef (Semitendinosus muscle) was cooked in natural convection, forced convection and steam assisted hybrid oven and saturated steam oven at different oven temperatures until the geometric center of samples reached different end temperatures. Heterocyclic amine (HCA) compounds formation, soluble protein degradation kinetics, cook value, changes in fat content, surface colour and overall acceptance of cooked beef were determined. Soluble protein degradation of beef was considered as first order reaction kinetics and the reaction rate constants, k, were determined in the range of 0.014-0.052 min^?1. In steam assisted hybrid oven had higher reaction rate constants compared to that of the convection ovens. The effect of cooking temperature on soluble protein degradation for natural convection, forced convection and steam assisted hybrid oven followed the Arrhenius type of equation with activation energies of 12.45, 14.57 and 60.16 kJ/mol, respectively. Lower HCAs contents, shorter cooking times, lower cook values and lower fat retention were obtained by steam assisted hybrid oven cooking. Steam assisted hybrid cooking could be considered as an alternative cooking method to obtain a healthier product without compromising the eating habits of conventional methods due to better appearance (moderate burned surface) than saturated steam oven samples and a product retaining the most of the nutritional values.     

TENSILE PROPERTIES OF BEEF SEMITENDINOSUS MUSCLE AS AFFECTED BY HEATING RATE AND END POINT TEMPERATURE

The effects of heating rate and end point temperature on tensile properties of beef semi-tendinosus muscle were studied. Samples of meat heated in glass tubes in a water bath to simulate oven roasting at 93 °C had lower (P < 0.01) shear values than those heated to simulate oven roasting at 149 °C. Samples heated to 60 and 70°C had lower (P < 0.001) shear values than samples heated to 50°C. Instron breaking strength values varied (P < 0.001) with end point temperature, but were not significantly affected by the rate of heating. Significant (P < 0.001) interactions between the end point temperature and heating rate, as well as between the end point temperature and fiber direction suggested that Instron breaking strength measurements may be more sensitive to changes in tenderness than Warner Bratzler shear measurements.     

Effect of Steam-Assisted Hybrid Cooking on Textural Quality Characteristics,Cooking Loss,and Free Moisture Content of Beef

Semitendinosus muscles were cooked in a steam-assisted hybrid oven and also convection ovens at three different oven temperatures (180, 210, and 240°C) until three different end point temperatures [65°C (medium-rare), 72°C (medium), 80°C (medium-well)] were reached. Textural properties of cooked beef were investigated by the Warner Bratzler shear test and texture profile analysis. Cooking loss and free moisture content of muscle tissue was determined for each cooking condition. In addition, sensory analysis was carried out in order to compare with the instrumental results and correlations between instrumental texture parameters and sensory results. Steam-assisted hybrid oven cooking of beef resulted in a tougher texture, higher cooking loss, and lower free moisture content than convection cooking. High correlation coefficients (r² > 0.70) were observed between instrumental texture measurements and sensory results for all ovens, especially in terms of tenderness. The free moisture content and adhesiveness values were also correlated well with juiciness (r² > 0.70) for all oven types.     

Baking of Sponge Cake: Experimental Characterization and Mathematical Modelling

Sponge cake is a sweet bakery product that begins as a fluid batter and, during baking, transforms into a porous solid, presenting an important volume expansion. The aim of this work was, first of all, to study experimentally the influence of operative conditions (natural and forced convection; oven temperature, from 140 to 180 °C; steam addition) on volume expansion and the heat transfer dynamics during baking of sponge cake. It was observed that an increase in oven temperature, airflow and steam injection produces an increase in volume expansion. Secondly, a mathematical model was developed to simulate heat transfer coupled with volume expansion. Both experimental and simulated temperature profiles verified that the last region to achieve a correct degree of baking is the one near the crust around the axial axis. In consequence, the minimal baking time was defined as the average time at which this region reaches 95–98 °C. The baking time was strongly affected by the effective oven temperature, with a slight influence of the convection mode.     

Cooking influences on the palatability of roasts from the beef hip

Two experiments were undertaken to obtain factual information to serve as a basis for guidance to consumers regarding optimal preparation and cooking procedures to be utilized with beef round cuts. Experiment I compared low temperature, dry beef cookery with moist beef cookery with a dry heat finish on five different roast cuts from the beef hip. Experiment II compared four different cookery methods for their influence on palatability attributes and cooking properties of eye of round (semitendinosus) roasts. Based upon results from Experiment I, low temperature, dry heat cookery should be recommended to consumers to improve the palatability of roasts from the beef hip, providing consumers are prepared to expend twice as long to prepare roast cuts. Results from Experiment II clearly indicate method C [high temperature, covered (oven turned on to 260 °C, with 250 ml of water added after 30 min)] should not be the method of choice. Although any of the other three methods could be recommended to provide a relatively palatable product, method D [high temperature initially, subsequently reduced, uncovered (roast brushed with 5 ml of Kitchen Bouquet™, placed into a cold oven turned on to 260 °C, with 250 ml of water added after 30 min and the oven temperature reduced to 140 °C)] appears to provide a more acceptable product based upon tenderness, particularly initial tenderness, than methods A [low temperature, dry heat (140 °C oven, uncovered with no moisture added)] and B [low temperature with moisture added (160 °C oven, uncovered with 250 ml of water added initially and 50 ml of water added every 30 minutes)]. In addition 46.4 min/kg less time was required to prepare roasts with method D than with method A. Consequently, the method of choice for recommendation to consumers is method D.     

Effects of Heat Transfer by Radiation and Convection on Browning of Cookies at Baking

The effects of modes of heat transfer (radiation or convection) on the baking color development of food were studied. An experimental baking oven that could be altered to two heat transfer modes was designed; the ratio of heat by radiative transfer to total heat transferred was about 30% or 70%. The glucose-glutamate solutions were heated at different air temperatures to measure the browning rates to calculate the activation energies. Cookies were baked at 200°C to measure the lightness of color on the surface and the surface temperature. It was clarified that the development of color depended on the temperature only.     

Thermophysical Properties of Extruded Beef/Corn Flour Blends

Thermal properties, specific heat, and thermal conductivity of three beef/corn meal blends extruded to reach end product temperatures of = 91°C and 109°C were analyzed. Density was also measured and used to calculate thermal diffusivity. The extruded products had densities of 1,054 to 1,091 kg/m³; specific heat was 2.944 to 3.055 kJ/ kgK; and thermal conductivity, 0.26 to 0.39 W/mK. Calculated values of thermal diffusivity were 0.831 to 1.200 (xl0^-7m7sec). With the exception of specific heat, extrusion conditions and formulation affected some of the products physical characteristics and thermal properties.     

Baking of muffins: Kinetics of crust color development and optimal baking time

Baking is a decisive stage in the production of bakery products, in general—muffins, in particular—for most of the quality attributes of the final products depend on it. The aim of this work is to model the kinetics of muffin crust color development during baking and to evaluate the feasibility of this kinetic model to predict the baking times. Surface color is represented by the Browning Index, and the effect of baking temperature (from 140 to 220 °C) and process convective characteristics (natural convection, forced convection, and steam-assisted forced convection) are analyzed. Minimal baking times are calculated from experimental core temperature measurements. The modeling of browning kinetics, which incorporates the optimal crust color determined by sensory analysis, allows the estimation of optimal baking times. For all the tested conditions t _op?>?t _min, assuring a product whose inner structure was already totally baked. Finally, minimal, half, and optimal baking times present an exponential dependence with the oven temperature. Besides, there are no significant differences between both forced convection modes.     

Influence of Rapid Cooking Methods on the Survival of Trichinella spiralis in Pork Chops from Experimentally Infected Pigs

Pork chops (1.3, 2.5 or 3.8 cm thick) cooked to an internal temperature of 17 or 77°C by conventional oven, convection oven or flat grill contained no motile trichinae, whereas chops cooked to 66°C sometimes contained motile trichinae. Chops cooked by either charbroil or deep fat fry and pretreated in a microwave oven sometimes had motile trichinae even after cooking to an end point of 77°C. Chops, which had been frozen for 18 hr at -23°C and were thawed by microwave to 0°C then deep fat fried to an end point temperature, sometimes had infectious trichinae as confirmed by tests with rats and mice. Additional research is underway to verify the thermal death times and temperatures for T. spiralis larvae.     

Beef broth flavour: study of flavour development

Of the range of preparation conditions studied here, the beef broths with the most favourable sensory characteristics (P ≤ 0.05) were those manufactured with minced meat in a 7.5 g l⁻¹ NaCl solution in proportions of 1:2 (w/v), heated at 85 °C for 60 min (the beef broth flavour was clean, clear, without any off‐flavour). Our data indicate the importance of accurately determining the heat treatment, since intermediate treatments yielded beef broths of good quality, whereas less intense treatments produced broths with raw meat and bloody and metallic flavours, and intensely heated broths had a warmed‐over or sour and astringent flavour. At higher temperatures the cooking time required to obtain a good‐quality broth decreased. From the analysis of variance of the sensorial data, temperature plays a more important role than cooking time in the development of the sensory properties of beef broths. © 2000 Society of Chemical Industry     

Cholesterol and Selected Attributes of Pork Tenderloin Steaks Heated by Conventional, Convection, and Microwave Ovens to Two Internal Endpoint Temperatures

Six treatment combinations for determination of cholesterol and selected quality attributes of pork tenderloin steaks were studied with three oven types (conventional, convection and microwave) and two internal endpoint temperatures (71°C and 77°C). In general, pork tenderloin steaks heated in the microwave oven had lower evaporative loss and higher drip loss. Cholesterol (wet weight basis) of the pork steaks was not affected by oven type; however, heating to the higher internal endpoint temperature (77°C) increased (concentrated) the cholesterol. On a dry weight basis, microwave-heated steaks contained more cholesterol when compared to conventional and convection-heated samples.     

Effect of Steam Baking on Acrylamide Formation and Browning Kinetics of Cookies

Abstract: Effects of baking method and temperature on surface browning and acrylamide concentration of cookies were investigated. Cookies were baked in natural and forced convection and steam‐assisted hybrid ovens at 165, 180, and 195 °C and at different times. For all oven types, the acrlyamide concentration and surface color of cookies increased with increasing baking temperature. Significant correlation was observed between acrylamide formation and browning index, BI, which was calculated from Hunter L, a, and b color values, and it showed that the BI may be considered as a reliable indicator of acrylamide concentration in cookies. Acrylamide formation and browning index in cookies were considered as the first‐order reaction kinetics and the reaction rate constants, k, were in the range of 0.023 to 0.077 (min^?1) and 0.019 to 0.063 (min^?1), respectively. The effect of baking temperature on surface color and acrylamide concentration followed the Arrhenius type of equation, with activation energies for acrylamide concentration as 6.87 to 27.84 kJ/mol; for BI value as 19.54 to 35.36 kJ/mol, for all oven types. Steam‐assisted baking resulted in lower acrylamide concentration at 165 °C baking temperature and lower surface color for all temperatures. Steam‐assisted baking is recommended as a healthy way of cooking providing the reduction of harmful compounds such as acrylamide for bakery goods, at a minimal level, while keeping the physical quality. Practical Application: The kinetics of acrylamide formation and browning of cookies will possibly allow definition of optimum baking temperatures and times at convectional and steam‐assisted baking ovens. The kinetic model can be used by developing baking programs that can automatically control especially a new home‐scale steam‐assisted hybrid oven producing healthy products, for the use of domestic consumers.     

Enzymatic Conversion of Starch in Twin-Screw HTST-Extruder

Wheat starch was liquefied to DE 25–30 employing heat stable α-amylase and twin-screw Werner & Pfleiderer Continua 58 HTST-extruder. Most significant reduction in batch saccharification time was obtained when starch was liquefied as a slurry containing 60% water at 120°C mass temperature, feed rate 1 500 g min⁻¹, screw rotation rate 250 min⁻¹, and 0.9% (w/w, d.s.) Novo Termamyl 120 L α-amylase was added immediately after initiation of gelatinization in the extruder. Saccharification was carried out at 60°C employing 0.36% (w/w, d.s.) Novo glucoamylase 150 L to reach a DE 96 in 22 h. Best total conversion was, however, obtained when also saccharification was initiated in the extruder by adding glucoamylase just before the die element, after lowering mass temperature to 60°C, and by allowing the saccharification to continue at 60°C after extrusion processing to reach a DE 94 in 5 h and DE 97 in 21 h.     

CONVECTION HEAT TRANSFER COEFFICIENT FOR A RESTRUCTURED PORK/SOY HULL PRODUCT1

Heat transfer coefficients, h, (J/cm²°C min) were determined for a pork/soy hull mixture during heating in a convection oven (142°C) with and without control of the dew point. Data were acquired by heat processing 5 stacked layers of product (10 × 10 × 1 cm) so that heat was only conducted into the top surface. One experiment was designed to determine h when the second layer from the top reached one of 6 temperatures: 20, 32, 44, 56, 68 and 77°C, with no control of the dew point. the second experiment determined h for 60 min of heating for 5 dew point levels: 6, 21, 31, 40 and 50°C. Without the control of humidity, values for h ranged from 0.0170–0.0366 J/cm²°C min. the heat transfer coefficient increased with temperature and heat processing time. Product yield and surface area ratios decreased as h increased. When relative humidity was controlled, values for h ranged from 0.0167–0.0270 J/cm²°C min, decreasing for dew points above 31°C.     

Total Caloric Input of a Thermal Process as an Index of Lethality for Foot-and-Mouth Disease Virus

Because significant quantities of foot-and-mouth disease virus undetectable by cell culture infectivity assay can persist in infected tissues throughout thermal processing, classical methods for measuring virus inactivation are difficult to achieve. This study was undertaken to observe the lethality of a given process rather than determining a constant for process time for a given lethality. Thermal diffusivities (α) and one-dimensional heat flux (Q) were determined for three thermal processes used in processing of beef and pork products. Foot-and-mouth disease virus survived in ground beef cooked in flexible nylon thermal processing tubes to core temperatures of 63°C (892 kcal/ m²) in 1.2 hr and 71.2°C (1004 kcal/m²) in 1.45 hr; however, the virus did not survive after processing to a core temperature of 79.4°C (1363 kcal/m²) in 2.0 hr.     

EFFECT of DIFFERENT TEMPERATURE CONTROL METHODS ON HEATING TIME and CERTAIN QUALITY PARAMETERS of OVEN-ROASTED BEEF

Four different methods of oven roasting beef were studied. Twelve semi-tendinosus muscles were transversely divided, and the 24 subsamples were allocated to 4 cooking methods: High temperature roasting (HTR) with a constant oven temperature of 170C; low temperature roasting (LTR) with a constant oven temperature of 120C; maximum temperature roasting (MTR) with maximally 70C 1 cm below the roast surface and temperature difference roasting (TDR) with constantly 50C between the oven and 1 cm below the roast surface. Quality parameters measured were cooking loss, Warner-Bratzler shear parameters and taste panel ratings. Mean heating times of HTR, LTR, MTR and TDR were 69, 100, 79 and 157 min, respectively. Most of the quality parameters by HTR were significantly poorer as compared with the other methods, while differences between LTR, MTR and TDR were small. Surface heat transfer coefficient was estimated as 14.1 W/m²C. Heating times were predicted with a maximum deviation of 10%.     

DIMENSIONLESS CORRELATIONS FOR MIXED and FORCED CONVECTION HEAT TRANSFER to SPHERICAL and FINITE CYLINDRICAL PARTICLES IN an ASEPTIC PROCESSING HOLDING TUBE SIMULATOR

Dimensionless correlations for estimating heat transfer coefficients for spherical and finite cylinders under mixed and forced convection heat transfer regimes were individually investigated using multiple regression of statistically significant dimensionless groups. Food and model particles were subjected to heat treatments in an aseptic processing holding tube simulator (carrier fluid: 0, 0.5, and 1.0%, carboxymethyl cellulose solutions, w/w basis; temperature: 90 to 110C; flow rate 1.0 to 1.9 × 10⁻⁴ m³/s). the type of test material was found to have a significant effect on the Nusselt number, and hence developed correlations. Introducing a diffusivity ratio defined as the ratio of particle-to-fluid thermal diffusivities was found to consistently improve developed models. Excellent correlations (R²≥ 0.97) were obtained between the Nusselt number and dimensionless groups for all models. Natural convection in heat transfer correlations in situations where forced convection is expected to be the dominant mechanism was accommodated.