Heat Penetration Curves Research Articles

Developing an Accurate Heat Transfer Simulation Model of Alaska Pollock Surimi Paste by Estimating the Thermal Diffusivities at Various Moisture and Salt Contents

Abstract Alaska pollock (AP) surimi paste was prepared (0–3% salt and 76–84% moisture). The density, specific heat, and thermal conductivity were measured and modelled in temperatures between 25 and 90 °C (R 2 > 0.92). The thermal diffusivity (α) function showed a strong dependence on the moisture content and a unique salt dependence at 84% of the moisture content and applied to the heat transfer simulation of surimi paste. The simulation model coupled with the empirical thermal properties accurately predicted the heat penetration curves during heating with RMSE values ranging from 0.43 to 1.22 °C. The salt dependence on thermal diffusivity was identified and modeled only at 84% moisture content. With a model for 84% moisture content, the RMSE value of 3% salt content decreased from 1.11 °C to 0.56 °C. This study demonstrated that an accurate prediction of the heat transfer of the surimi paste needs to be coupled with the nonlinear thermal diffusivity functions.

EFECTO DEL CONTENIDO DE HUMEDAD Y TEMPERATURA SOBRE LA DIFUSIVIDAD TÉRMICA EN GRANOS ANDINO

Este estudio muestra un método sencillo para evaluar la difusividad térmica (α) en granos andinos de quinua (Chenopodium quinoa Willd) y cañihua (Chenopodium pallidicaule Aellen). Además, se estudió el efecto de la temperatura de 25 a 35°C y humedad en base húmeda de 10 a 20% sobre el comportamiento de esta propiedad. El método empleado para determinar la difusividad fue el propuesto por Gupta, el cual hace uso de las curvas de penetración de calor en un equipo especialmente armado para este fin. Los resultados obtenidos indican que los valores varían entre 7,5 y 8,9 x 10-8 m2.s-1. La evaluación de los datos indica que existe una fuerte influencia del tipo de grano, la humedad y la temperatura en esta propiedad térmica. Adicionalmente, se usó la metodológica de superficie de respuesta para encontrar un modelo empírico para representar la difusividad térmica en función del contenido de humedad y temperatura.

Mathematical modeling of the heat transfer process and protein denaturation during the thermal treatment of Patagonian marine crabs

Southern Ocean swimming crab Ovalipes trimaculatus and the Patagonian stone crab Platyxanthus patagonicus are fishing resources with commercial value. Thermal treatment of crabs is necessary to denature muscle proteins, facilitating meat detachment from the crab shell (picking procedure). The proximal composition, protein patterns of crab muscle, thermophysical properties and heat transfer coefficients were determined. Heat transfer during thermal processing of body (i.e., cephalothorax) and claws of both crab species was simulated using a finite element computational code; the simulations were experimentally validated. Color changes in crab muscle during the heating process were measured. Thermal denaturation kinetics of myofibrillar proteins was determined using Differential Scanning Calorimetry (DSC) in small samples previously heated in water under controlled conditions. DSC thermograms of raw crab muscle showed two peaks at 49.0±0.4 and 77.5±0.6°C corresponding to myosin and actin respectively. Activation energies for the denaturation of myosin (145.70kJ/mol) and actin (156.42kJ/mol) were calculated from Arrhenius equation. The degree of denaturation achieved by the myofibrillar proteins at the coldest point of the muscle in body and claws during the heating process was established by considering the protein denaturation kinetics determined by DSC, the activation energies and the heat penetration curves. Adequate conditions for the detachment of meat from the crab exoskeleton were established. The obtained results may help in determining the optimal heating times during the industrialization of these crustaceans.

PREDICTION OF HEATING LENGTH TO OBTAIN A DEFINITE F VALUE DURING PASTEURIZATION OF CANNED FOOD

ABSTRACTAn empirical mathematical method to predict the heating length necessary to reach a desired F value during pasteurization treatments of canned food was developed. The method was based on (1) the fitting of heat penetration curve previously subdivided into three subsets of data and (2) the prediction of new heat penetration curves able to obtain the desired F value. The method was validated at laboratory and industrial scales by performing experimental tests on gherkins in vinegar, mushrooms in maize oil and semidried tomatoes in glass pots and tin cans. In all cases, the model well fitted the experimental data, obtaining r and E values lower than 0.990 and 3.66, respectively. The comparison between predicted and experimental heating times stated the accuracy of the method; in fact, at laboratory scale, the relative deviation values ranged between 0.622 and −5.644; instead, in a continuous pasteurizer tunnel, the values were lower than −3.898.PRACTICAL APPLICATIONSPasteurization is the most important technology applied at industrial scale to reach safety of acidified canned foods. Although it is widely used and known, often the small medium enterprises are unable to optimize the process basing the definition of operative conditions on empirical information; for these reasons and with the aim to assure the safety, heating time is often overestimated, leading to several drawbacks such as the increase of the energy consumption, heat degradation and the decrease of productivity. In this way, the mathematical method developed in this work, which is a user‐friendly tool to calculate with high accuracy, and on the basis of few experiments, the heating time necessary to reach the F value desired, is very important to the canned food industry.

A quick method for thermal diffusivity estimation: Application to several foods

A reliable, quick and userfriendly method for thermal diffusivity estimation has been developed. An appropriate software tool, based on least square optimization of a finite difference solution of Fourier’s equation , has been created and an appropriate measuring cell has been designed and made in order to decrease the systematic error in probe positioning. The method has been experimentally validated and its results have been compared with those obtained by three other available methods. Several foods (tomato products, low-acid pasta sauces, olive pate, confectioner’s custard and apricot jam) were tested and in every case the method proved to be effective. The developed software also allowed estimation of thermal diffusivity via heat penetration curves obtained by variable temperature treatments. So it has been also possible to exclude the contribution of container material from the estimation of thermal diffusivity of liquid packed foods. The proposed method turns out to be a useful tool for scientific design of several processes, such as sterilization and pasteurization, and for correct control of transport, storage and distribution of foods.

CHANGES IN APPARENT VISCOSITY AND VITAMIN C RETENTION DURING THERMAL TREATMENT OF BUTTERNUT SQUASH (CUCURBITA MOSCHATA DUCH) PULP: EFFECT OF RIPENING STAGE

ABSTRACT The effects that ripening stage have on the apparent viscosity and ascorbic acid retention in squash pulp exposed at cooking process were analyzed. Total soluble solids contents were taken as indicative of ripening degree. In the raw material, water contents ranged from 79 to 96%, but no significant differences were observed among samples grouped as unripe, ripe and overripe. The ascorbic acid contents of pulp increase with increases in soluble solids contents. Pulp from unripe and ripe squash had similar apparent viscosity values; however, lower viscosity values were obtained in pulp from overripe squash. During heat treatment, significant changes in the apparent viscosity values of pulp from unripe and ripe squash were observed. Heat penetration properties of squash pulp indicate correlation between the inverse slope of the straight portion in the heat penetration curves on a semilog plot (fh) and thermal diffusivity values (α) with dry matter content, but no correlation was found with squash maturity degree. High ascorbic acid retention (82%) in pulp held for 30 min at 95C was found independently of squash maturation degree.PRACTICAL APPLICATIONSKnowing the rheological behaviour and the ascorbic acid retention of butternut squash pulp during cooking process could be used as a valuable information previously to make decisions for use this crop as a food supply.

Safe cooking optimisation by F-value computation in a semi-automatic oven

Cooking represents an important step in food processing for both sensorial and safety aspects. Aim of this study was to optimise the cooking cycles of a semi-automatic oven by definition and settling of minimum thermal conditions to guarantee safety while keeping sensorial quality of cooked foods. To this purpose, the heat penetration curves and the correspondent thermal lethality effect ( F T) of cooking cycles conventionally adopted to prepare some foods and dishes characterised by different microbial risk (high: lasagne pie, meat minced roll, meat filled peppers; standard: spinach and salmon), were determined. On the basis of the microbial quality and the desired safety level, minimum thermal conditions ( F 71.1 = 5 min and T = 75 °C at the slowest heating point of the food) were defined and settled in the electronics of the oven. These conditions were found to determine a sufficient number of log reduction of both total microbial count and coliforms able to guarantee safety as well as sensory quality at consumption. The oven with modified electronics during the heating step of cooking cycles records in real time the temperature in the product by a multipoint thermocouple, detects the slowest heat penetration curve and computes, by an internal computer the correspondent F 71.1. After initial setting of the food category, this semi-automatic oven is able to find automatically the proper process conditions during cooking to obtain the correspondent F T, to let the cooking stop at the end of the recipe or to conduct the thermal treatment till the reaching of the set F T according to the risk category chosen before cooking start.

Thermal diffusivity of soursop ( Annona muricata L.) pulp

The thermal diffusivity ( α) of soursop pulp was evaluated by the use of heat penetration curves in 8Z short cans which were considered as finite cylindrical objects. The pulp was obtained from fruits belonging to the same lot and tested at two different maturity levels (ripe and unripe). The experiments were carried out at three different temperature ranges including freezing ones. The results showed that the thermal diffusivity had values sixteen-times lower at temperatures below 0°C (1–1.53×10 −8 m 2/s). The values for α at temperatures above 0°C are in agreement with the results published by other authors for other vegetable products. There is no difference in the α values for the pulps from ripe and unripe fruits at a level of significance of 5%.

Evaluation of process deviations, consisting of drops in rotational speed, during thermal processing of foods in rotary water cascading retorts

Taking into account the similarities of broken-line heating curves and heat-penetration curves obtained when a product undergoes a drop in rotational speed during thermal processing in a rotary water cascading retort, a semiempirical method used for handling broken-line heating behaviour is suggested as a method of dealing with this type of process deviation. For this purpose, the possibility of extrapolating the empirical heating rate parameter f lv determined on the heat-penetration curve of white beans in brine processed in a still retort, to the ‘still’ conditions associated with a rotational speed drop in a rotary water cascading retort, was investigated. Following this approach, safe product temperature predictions were obtained. The main criterion influencing the quality of the evolution was the determination of the correct empirical parametric value to be used. This means, when determining this parametric value, care is required when selecting the correct temperature interval on the heat-penetration curve.

On the theoretical basis of the asymptotic semilogarithmic heat penetration curves used in food processing

To characterize heat penetration curves in food processing, ‘f’ and ‘j’ values are generally used for conduction as well as convection heating. Such asymptotic semilogarithmic time-temperature relations have been mathematically proven only for the restricted cases of conduction heating in regular geometries and for forced convection heating. This study mathematically justifies and interprets such approximation in the case of conduction heating in arbitrary shapes. In the case of natural convection heating, the complicated nature of the governing equations and the flow instabilities are discussed and it is concluded that such a semilogarithmic time-temperature relation is unlikely from physical as well as mathematical considerations, although, both the theoretical (numerical) solution as well as the experimental data for the natural convection heating can be empirically approximated to such a semilogarithmic form over small ranges of processing time for practical purposes.

Calculation of adequate processing conditions of the Heat Sterilization of Packaged "MOCHI" Rice Cake using General Method

Heat penetration rate to the center of packaged rice cake under the heating at various temperatures was measured. From the results of heatpenetration curves into packaged rice cake and the thermotolerance of the isolated bacteria, adequate processing times at various temperatures were calculated by Bigelow's General Method. The processing conditions for packaged rice cake were 115°C for 19.8 minutes, 120°C for 18.2 minutes, and 125°C for 15.1 minutes, respectively. The browning of rice cake, thus sterilized, was more or less greater than the customarily pastuerized, but the extent of browning was not so serious visually.