Heat Transfer Coefficients on Cakes Baked in a Tunnel Type Industrial Oven

Using an h-monitor, surface heat flux and effective surface heat transfer coefficients were evaluated during baking of two cakes in a tunnel-type multi-zone industrial oven. An average 75–80% of total heat flux was counted as radiation heat. Air-mass temperature outside the boundary layer was determined from the experimental temperature profiles over the h-monitor top plate. In the range of baking temperatures (186–22 5°C), relative air velocities (0.02-0.437 m/s) and absolute humidities (0.0267–0.0428 kg H₂O/kg dry air) heat transfer coefficients were 20 to 48.0 W/m²K. A simple regression model was developed based on experimental data.     

A Quality Comparison of Devil's Food and Yellow Cakes Baked in a Microwave/Convection Versus a Conventional Oven

A quality comparison was made of devil's food and yellow cakes baked in microwave/convection (MW/C) and conventional (CON) ovens as either single or double layers. Single MW/C layers were rated slightly lower than CON layers for crust color, moistness and total sensory score. However, double layers were rated equal or near-equal to CON layers. Although slight differences were found, all MW/C cakes were acceptable. These results indicated that high quality cakes can be baked 15–25% faster in a MW/C than in a CON oven.     

Sensory and Nutritional Properties of Cookies Based on Wheat-Rice-Soybean Flours Baked in a Microwave Oven

Three formulas of cookies prepared from 50:45:5 (I), 50:40:10 (II) and 50:35:15% (III) wheat flour, broken rice flour, and defatted soy flour, respectively, baked in a microwave oven (2450 MHz) for 240 sec, were rated as the best of six formulas for flavor and texture by a trained panel. Cookies of formulas I and II were preferred over formula III by a consumer-type panel. Cookies of all three formulas showed no significant differences in nitrogen balance, apparent biological protein value and apparent net protein utilization. Apparent protein digestibility and protein efficiency ratio were significantly higher in formulas II and III than in formula I.     

对流传热系数的研究

应用量纲分析法和实验测定相结合的方法,通过实验得到了形式较简捷的对流传热系数α的准数关联式.     

Quantifying Enhancement in Heat Transfer Due to Natural Convection During Canned Food Thermal Sterilization in a Still Retort

Thermal sterilization of canned viscous liquid foods using saturated steam is enabled by natural convective heat transfer. However, the governing equations for two-dimensional convective heat transfer may be only rigorously solved by numerical calculations. On the other hand, if conduction is assumed to be the only mode of heat transfer, the thermal sterilization problem has analytical solutions for simple boundary conditions. However, the conduction model may not be appropriate in describing thermal sterilization of even viscous liquid foods and may cause considerable error in the prediction of the important parameters such as slowest heating zone (SHZ) temperature and lethality. The longer time for sterilization recommended by the conduction model may lead to overprocessing and an unacceptable food product. The objective of this work is to quantify the faster temperature rise in the food can due to natural convection when compared to the temperature rise obtained by only conductive heating. The consequent enhancement in lethalities is also reported. In addition, this work’s objective is to investigate how quickly the natural convective heat transfer effects begin to dominate over the solely conduction heating mode. The volume-averaged temperature as well as the SHZ temperature variations with time was calculated for the convection-augmented mode using computational fluid dynamics (CFD) simulations. Lethality values were then calculated based on volume-averaged temperature as well as the SHZ temperature. Food cans of different aspect ratios and food medium thermal conductivities are considered in this analysis. For the food system investigated, the critical Fourier number at which the transition to convection-augmented mode of heat transfer occurred is identified and explained from scaling considerations. In the conduction-dominated mode, it was possible to use analytical solutions to predict the volume-averaged and SHZ temperatures of the liquid food undergoing thermal sterilization. The Nusselt number correlation developed by Kannan and Gourisankar (2008) was used in the lumped parameter transient heat transfer model to predict the volume-averaged temperatures in the convection-dominated region. The volume-averaged temperatures from this approach were found to be in good agreement with the CFD simulation results. The time predicted for the SHZ to reach the minimum sterilization temperature was significantly lower when convective heating was also considered. The volume-averaged temperature and SHZ temperature enabled an estimation of overall sterility levels attained and minimum sterility levels prevalent inside the can, respectively. Even though the volume-averaged temperature increase due to convection was only about 10 K, the resulting accumulated lethality values were higher by an order of magnitude. The increase in SHZ temperatures was much higher in the convection-augmented mode, and consequently greater integrated lethalities were attained. The simple conduction model that is amenable to analytical solution cannot be used to approximate the heat-transfer-related phenomena even for “quick estimation” purposes when convection effects are significant. This precaution is found necessary even for the reasonably high viscous carboxy methyl cellulose system, whose average viscosity values ranged between 13 and 3 Pa s during the course of the sterilization process.     

In Situ Determination of Apparent Thermophysical Properties of a Composite Slab Undergoing Transient State Heat Transfer

A method was developed to determine the thermophysical properties of a two layered composite slab whose one exposed surface was subjected to a known temperature history and whose other surface to convective and radiative heat exchange. The physical properties to be determined were the thermal conductivity and diffusivity of one of the two layers and the contact conductance between the two layers, the coefficient of convective surface heat transfer, and the absorbtivity of thermal radiation energy applicable to one exposed surface of the slab. The developed method was used to determine property values of the insulated wall of a still retort.     

Modeling Heat Transfer During Oven Roasting of Unstuffed Turkeys

A finite element method was used to solve the unsteady state heat transfer equations for heating of turkeys in a conventional electric oven. Breast, and thigh and wing joint temperature in 5.9, 6.8, 8.6, 9.5, and 10.4 kg turkeys were simulated. A surface heat transfer coefficient of 19.252 W/m2K determined by transient temperature measurements in the same oven, was used. Thermal conductivity measured using a line heat source probe from 0 to 80°C was 0.464 W/mK. Simulated temperatures were within 1.33, 1.47, and 1.22°C of experimental values of temperature in the breast, thigh, and wing joint, respectively. Initial temperature 1,2, and 3°C lower than 4°C required additional baking time of 16,22, and 27 min., respectively for the thigh joint to reach the target endpoint temperature.     

Consumer Acceptability and Quality Evaluation of Potato Strips Baked in a Radiant Wall Oven

Instrumental and sensory quality of potato strips baked in a radiant wall oven was evaluated and compared to deep-fat fried and conventional oven baked samples. Even though radiant wall oven baked potato strips had one-fourth the fat content of the deep-fat fried samples, there was no significant difference in chroma, cutting and puncture force of radiant wall oven baked and deep-fat fried samples. Consumer acceptability of radiant wall oven baked potato strips was 65.7 and 85.7% before and after revealing the nutrition facts, respectively. Both were lower than acceptability of deep-fat fried samples. However, 36.5% of consumers were willing to purchase radiant wall oven baked samples.     

Modeling Flow and Heat Transfer During Freezing of Foods in Forced Airstreams

ABSTRACT: Mathematical modeling of food freezing has been limited to the modeling of the internal heat transfer where the external convective heat-transfer coefficients are assumed or empirically estimated. Previous procedures followed to solve the external boundary layer in tandem with the internal heat transfer were constrained by numerical complexities due to the transient nature of the heat transfer, requiring unsteady formulation for the flow. In this article, attempts have been made to decouple the flow and heat transfer equations for the external boundary layer flow over a food product being frozen. The flow equations have been solved as a steady-state problem using Falker-Skan transformations of the boundary layer equation. The heat-transfer equation for fluid flow is solved as an unsteady-state problem in conjunction with the internal heat transfer and phase change inside the product undergoing freezing. The model is validated for a case of air-impingement freezing.     

食品添加剂与配料焙烤食品美味之源

焙烤食品是以谷物、酵母、食盐、糖和水为基本原料,添加适量油脂、乳品、鸡蛋、添加剂(如疏松剂、改良剂、防腐保鲜剂、香料、色素)等,采用焙烤加工工艺定型和熟制的一大类食品.焙烤食品主要包括面包、糕点、饼干三大类产品,此外还有月饼、点心、膨化食品等;除传统的普通烘焙食品外,近几年还出现了一些强化营养、注重保健功能的焙烤食品,如荞麦保健蛋糕、螺旋藻面包、高纤维面包、全麦面包等.     

纳他霉素在焙烤食品中的应用

纳他霉素是由链霉菌经发酵、提取,精制获得的广谱高效的生物防腐剂．可以抑制各种霉菌、酵母的生长和繁殖。1982年6月．美国FDA批准纳他霉素为食品添加剂．WTO和FAO规定其每曰允许摄入量（ADI）为0．3mg／kg。1996年．我国将纳他霉素纳入食品添加剂范畴．并规定食物中纳他霉素的最大残留量为10mg／kg。     

Two Dimensional Simultaneous Heat and Moisture Transfer in Composite Food

A computerized method was developed to predict two dimensional, simultaneous heat and moisture transfer in a composite food with chemical reactions, based on the use of the chemical potential as the mass transfer potential. Thermodynamically interactive heat and mass fluxes were included in the mathematical model. Composite cylindrical samples in three layers prepared from a high amylose starch granule hydrate and a mixture of the same dhydrate and sucrose were dried in a forced air dryer to experimentally verify values predicted by the computerized method. The central temperatures and average moisture contents of the samples determined experimentally, agreed well with those predicted theoretically.     

高温热转移印花纸的纸张性质及印刷适性

通过对国内外几种高温热转移印花纸的纸张性质参数的测试和对比,研究热转移印花纸的基本纸张性质,分析国产纸张的不足之处;通过对进口纸的印刷适性参数的测定,浅析高温热转移印花纸的应用前景。     

Temperature Histories at Critical Points and Recommended Cooking Time for Whole Turkeys Baked in a Conventional Oven

Time-temperature histories and cooking times were determined for turkeys baked at 162.8°C from 4.44°C to an endpoint of 82.2°C in the thigh joint or breast. Turkeys (128) in five weight classes from 5.9 to 10.8 kg (0.9 kg increments) were equally divided into fresh, frozen, stuffed, unstuffed, and cooked shielded or unsheilded groups. The slowest heating point was either the wing joint or stuffing geometric center. Cooking time for unsheilded turkeys was 155 min plus 11 min/kg, unstuffed, and 200 min plus 8.8 min/kg, stuffed. Median cooking loss was 23%. Shielding of breasts prolonged cooking time. The cooking endpoint of 82.2°C in the thigh joint provided adequate lethality against Salmonella in the slowest heating points of both stuffed and unstuffed birds.     

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.     

面团强化剂在冷冻焙烤食品中作用

该文分析冷冻焙烤食品在制作和冷藏过程中存在问题;详细论述面团强化剂与速冻焙烤食品相互作用原理;并探讨面团强化剂对冷冻食品品质特性影响。     

Heat and Mass Transfer Coefficients in Drying of Starch Based Food Systems

Experiments were conducted to measure the temperature and moisture content of starch and starch-fructose samples during drying. A two-dimensional finite element model was developed. An exhaustive parameter estimation technique was applied in conjunction with the model and drying data to estimate the moisture filtration coefficient k_p and the surface heat and mass transfer coefficients, h_q and h_m. Minimization of the deviation between experimental and simulation data resulted in a k_p value of 0.51*10^?7 kg.m/N.h and 0.52*10^?7 kg.m/N.h for the starch and starch-fructose samples. Corresponding values of h_q were 15.8 W/m²K and 21.2 W/m²K and that of h_m were 1.12*10^?6 m/s and 0.94*10^?6 m/s respectively.     

Fluid Flow and Heat Transfer in Air Jet Impingement in Food Processing

ABSTRACT: Air impingement technology is gaining popularity in food-processing operations such as baking, freezing, drying, and toasting. In this article, physical characteristics of impinging jets, such as turbulent mixing in the free jet region, stagnation, boundary-layer formation, recirculation, and their interactions with food products in terms of heat and mass transfer have been reviewed. The discussion includes experimental methods used for measurement of heat and mass transfer for single and multiple slot and circular jets. Procedures used for measurement of heat-transfer coefficient such as lumped sensor method, micro-calorimetric approach, and use of flux sensors are presented. Typical qualitative and quantitative flow-field studies using planar visualization and laser Doppler anemometry have been reviewed. Numerical modeling of air impingement systems is discussed with special consideration of problems arising in food-processing systems.     

抗菌针织物的热湿传导性能研究

抗菌纺织品发展的新重点在于抗菌纤维的开发以及织物抗菌性能与其他功能性的结合，本文就抗菌纤维织造的针织品的热湿传导性能进行了讨论。     

浅谈焙烤食品与酵母

“焙烤食品”可以说是舶来名词,来自英文“baking”,即经烘烤加工的谷类食品,通常被理解为面包等西式糕点。焙烤食品营养非常丰富,且不说添加其中的各种营养配料,仅其主原料小麦粉就有着其他谷物望尘莫及的营养优势：小麦粉所含蛋白质是大米的23倍,