TEMPERATURE DISTRIBUTIONS DURING HEAT/HOLD PROCESSING OF FOOD

The unsteady-state differential equations for conduction heating were solved for the heat/hold process. The heat/hold process consists of heating the food to a certain mass average temperature and then adiabatically holding the piece until the desired reactions are complete. Charts for predicting the center and mass average temperatures for three basic geometries (infinite cylinders, infinite slabs and spheres) are presented along with methods to combine these solutions for other geometries. The use of these charts in blanching situations is shown     

RESIDENCE TIME DISTRIBUTION OF FOOD AND SIMULATED PARTICLES IN A MODEL HORIZONTAL SWEPT SURFACE HEAT EXCHANGER1

The residence time distribution (RTD) of food and inert particles flowing in a swept surface heat exchanger at room temperature was investigated. The effects of selected experimental conditions on RTD include particle shape (cube, cylinder, and sphere), particle concentration (10, 20, and 30% w/v), particle type (potato, carrot, turkey, green peas, and polystyrene), fluid viscosity (water, 0.5% CMC, and 1.0% CMC), bulk flow rate (5.8 × 10^?4, 7.28 × 10^?4, and 8.71 × 10^?4 m3/s) and shaft rotational speed (30, 60, and 90 rpm). Although turkey cubes were denser than other food particles, they moved faster than potato and carrot particles. Mean particle normalized residence time (MNPRT) of food particles (green peas) were found to be significantly higher than that of simulated particles (polystyrene). Cylindrical particles stayed longer than cubic particles in water, but not significantly in CMC solution. MNPRT values were found to be dependent on viscosity. Increasing particle concentration (up to 30%) tended to decrease MNPRT. Both bulk flow rate and shaft rotational speed tend to decrease MNPRT, thus reducing the lethality achieved. The distribution of residence time curves were narrowed by decreasing particle concentration, bulk flow rate, and shaft rotational speed, and by using fluids with high viscosity. In general, particle velocity was found to be higher than the average bulk velocity. The fastest particle velocity was found to be 3.23 times the average bulk velocity while the ratio was 0.382 for the slowest.     

A MODEL OF FOOD SPREADABILITY FROM FLUID MECHANICS

Subjective spreadability was predicted through understanding of psychophysical mechanisms involved during the back and forth spreading action of foods on crackers. Transient complex Theology of food products is incorporated into mass and momentum balances used to model the spreading action. Furthermore, because the consumer is in contact with the food product through a knife, it is assumed that the inverse of the torque needed to generate the deformation is assessed as spreadability. Torque is assumed to be equal to the shear stress on the knife multiplied by the distance the knife traueled across the cracker. Because this distance is constant, the final form for the psychophysical model is:

Using magnitude estimation, subjective spreadability scores ranged from 0.13 for marshmallow cream to 5.23 for squeeze margarine. When these scores were plotted versus the model on log-log coordinates, the best slope was 0.85 with a correlation coefficient of 0.95. The results strongly support the assumption that shear stresses generated on the knife are assessed as spreadability by the consumer.     

LITERATURE DATA OF HEAT TRANSFER COEFFICIENTS IN FOOD PROCESSING

ABSTRACT

Published data on the surface heat transfer coefficients in food processing operations have been selected from the literature, organized into a database, and presented. Useful information concerning the proposed equation, the system geometry, the experimental conditions, the range of application, and the relevant references, are tabulated.     

谷氨酰胺转胺酶在食品加工中的应用

介绍了谷氨酰胺转胺酶的一些功能特性，并对其在食品中的应用进行了综述。     

乳酸链球菌素的特性及其在食品中的应用

乳酸链球菌素是由乳酸链球菌产生的一种高效、无毒、安全、无副作用的天然食品防腐剂.介绍乳酸链球菌素的特性、效用及在食品加工中的应用.表明乳酸链球菌素在食品加工中是理想的食品防腐剂.     

HEAT TRANSFER COEFFICIENT IN FOOD PROCESSING: COMPILATION OF LITERATURE DATA

ABSTRACT

Heat transfer coefficient data in food processing were retrieved from literature and classified per process and material. Most of the data were available in the form of empirical equations using dimensionless numbers. All available empirical equations were transformed in the form of Heat Transfer Factor vs. Reynolds Number (j_H=aReⁿ). In the case when more than one equation reported for the same process and material, a new similar equation was fitted to consolidate the existing literature equations. It is expected that the resulting equations are more representative and predict more accurately the heat transfer coefficients. Average equations for each process are also proposed.     

EFFECTS OF RECOVERY METHODS ON THE FUNCTIONALITY OF PROTEIN CONCENTRATES FROM FOOD PROCESSING WASTES1

The multiple effects of the method of protein recovery on food protein functionality are presented. The results indicate the influence of method of protein coagulation (heat coagulation versus coagulation at room temperature) and type of coagulant (HCl, FeCl₃, Al₂(SO₄)₃, citric acid) on protein solubility, water binding capacity and baking properties. Dehydration conditions such as air inlet/outlet temperature (120-125/42-42° C to 190-195/70-72°C) or pH of the protein coagulate (pH 4 to 8) as well as methods of dehydration (freeze-, spray-, drum-drying) affected the water binding capacity and protein solubility of plant protein concentrates. Insignificant correlations (P < 0.01) existed between solubility values and water binding capacity data. Marked effects of the interactions between method of dehydration, protein source or dehydration temperature and pH of the coagulate on protein functionality were found. Based on the data presented it is proposed to develop processes for the production of protein concentrates with “tailored” functionality by selecting specific protein recovery processes and by mixing differently processed protein concentrates.     

EFFECT OF TEMPERATURE AND WATER CONCENTRATION DURING PROCESSING ON FOOD QUALITY

Water content and temperature during food processing have a pronounced influence on the rates of those changes in food properties which are the object of the process such as reduction in water content or sterilization. However, they also strongly influence adverse side effects such as browning, loss of nutrients or shrinking. When the effects of temperature and water concentration on the process rates of the desired and adverse processes are known, the processes can be optimized. An example of the optimization procedure is given for the spray drying of heat-labile aroma containing liquid foods. Both temperature and moisture content of the droplets change with time in spray-drying. In a second example a new and simple calculation method is introduced for the optimization of quality retention in the sterilization of packed foods.     

食品超高压处理过程中传热模型和相转变的研究进展

食品超高压处理技术是食品领域的一项新技术,在食品工业中的应用越来越广泛.但目前超高压处理过程中食品的温度分布和传热模型仍未研究清楚,采用数学方法对食品超高压处理过程中的传热现象进行模拟可以有效地均匀化和优化超高压处理条件,这对于实际生产具有指导意义.本文综述了食品在超高压处理过程中的传热模型和相转变的研究进展,对超高压低温条件下的冻结和解冻过程也进行了讨论.     

HEAT TRANSFER TO WATER AND SOME HIGHLY VISCOUS FOOD SYSTEMS IN A WATER-COOLED SCRAPED SURFACE HEAT EXCHANGER

Heat transfer in a water-cooled scraped surface heat exchanger has been investigated. The overall heat transfer coefficient in the heat exchanger is composed of three elements: heat transfer coefficient in the coolant jacket, resistance to heat flow in the separation wall and heat transfer coefficient inside the scraped cylinder. A method for assessing the heat transfer coefficient at the coolant side was developed. In contrast with studies published elsewhere, heat transfer was investigated with food systems which are non-newtonian and possess a complicated and unknown flowing behavior at higher shear rates. For water and three starch-based food products (starch content 12–18%) the heat transfer coefficients inside the scraped cylinder were measured for shaft speeds ranging from 1.67 to 10 revolutions/s. The experimental results were compared with heat transfer coefficients calculated with a model based on the penetration theory. For the starch-based products, in general, no consistent interactions between mass flow rates and internal heat transfer coefficients were observed. In the shaft speed range studied heat transfer coefficients at scraped surface varied from 3200 to 7800 W/m² K for water, from 500 to 3150 W/m² K for velouté sauce, from 670 to 1330 W/m² K for roux and from 780 to 1900 W/m² K for ragout.