Retort Temperature Profiles Research Articles

Variable Retort Temperature Profiles (VRTPs) and Retortable Pouches as Tools to Minimize Furan Formation in Thermally Processed Food.

Furan and its derivates are present in a wide range of thermally processed foods and are of significant concern in jarred baby and toddler foods. Furan formation is attributed to chemical reactions between a variety of precursors and a high processing temperature. Also, some kinetic models to represent its formation in different food materials have been studied and could predict the furan formation under simulated operating conditions. Therefore, this review aims to analyze and visualize how thermally processed foods might be improved based on optimal control of processing temperature and package design (e.g., retort pouches) to diminish furan formation and maximize quality retention. Many strategies have been studied and applied to reduce furan levels. However, an interesting approach that has not been explored is the thermal process design based on optimum variable retort temperature profiles (VRTPs) and the use of retortable pouches considering the microstructural changes of food along the process. The target of process optimization would be developed by minimizing the microstructural damage of the food product. It could be possible to reduce the furan level and simultaneously preserve the nutritional value through process optimization.

Optimal operation of thermal processing of canned tuna under product variability

Thermal processing of canned products is subject to variability among the different items in a batch, which results in differences in terms of food quality and safety. Such variability is mainly caused by heterogeneity in the thermal processing unit as well as differences in the quantity of food, its compaction, and the quantity of packing liquid from item to item. Besides, for a proper design of the process operation strategies, different conflicting objectives, such as maximization of product quality and uniformity or minimization of processing time and energy consumption, must be considered. In this paper, we present a suitable formulation to efficiently address the multi-objective optimization problem of thermal processing of canned food under the presence of product variability. Such variability has been characterized from experimental data provided by an industrial cannery. Our formulation exploits the monotonic and convex behavior of the quality/safety indicators and the product kinetics with respect to the uncertain thermal coefficients, avoiding thus the computationally-expensive stochastic approach via Monte-Carlo simulations. In particular, customizable retort temperature profiles are considered as a beneficial alternative to the standard constant retort temperature practice.

Assessment and outlook of variable retort temperature profiles for the thermal processing of packaged foods: Plant productivity, product quality, and energy consumption

Thermal processing has been used for packaged foods for many years and remains one of the most common and safe processes to preserve foods and extend their shelf life. Advances in thermal processing in the last two decades have helped maintain its relevance in international food trades. In this study, we aimed to gain a better understanding of thermal food processing using variable retort temperature profiles (VRTPs). VRTPs were assessed to optimize processes, either by ensuring high quality level or minimizing the operating process time. Based on the research results, VRTPs could improve quality retention; however, the improvement was not sufficient to be detectable by consumers and to justify implementation of VRTPs at the industrial level. Our general assessment provided a preliminary guide for processors to discover real opportunities for VRTPs, e.g., increased productivity by reducing operating process time and energy consumption.

Optimization of thermal processing of canned mussels

The design and optimization of thermal processing of solid-liquid food mixtures, such as canned mussels, requires the knowledge of the thermal history at the slowest heating point. In general, this point does not coincide with the geometrical center of the can, and the results show that it is located along the axial axis at a height that depends on the brine content. In this study, a mathematical model for the prediction of the temperature at this point was developed using the discrete transfer function approach. Transfer function coefficients were experimentally obtained, and prediction equations fitted to consider other can dimensions and sampling interval. This model was coupled with an optimization routine in order to search for different retort temperature profiles to maximize a quality index. Both constant retort temperature (CRT) and variable retort temperature (VRT; discrete step-wise and exponential) were considered. In the CRT process, the optimal retort temperature was always between 134 °C and 137 °C, and high values of thiamine retention were achieved. A significant improvement in surface quality index was obtained for optimal VRT profiles compared to optimal CRT. The optimization procedure shown in this study produces results that justify its utilization in the industry.

Variable retort temperature optimization using adaptive random search techniques

Global optimization algorithms and software based on adaptive random search techniques show considerable promise as more rapid and efficient approach to process optimization in the food industry. This paper describes use of the method in finding optimum variable retort temperature profiles that would maximize quality retention or minimize process time without compromising target lethality or minimum required quality retention in the case of thermal processing of canned foods. Results agreed well with those previously published by others who used more traditional approaches for similar optimization problems. Results also showed that the method lent itself well to the use of a cubic spline approximation for the dynamic temperature profiles, thereby reducing significantly the number of variables and dimensional space of the problem, in contrast to other methods, while producing superior results.

Computer Simulation of On-Line Control of Thermal Sterilization of Canned Foods Subjected to Arbitrary Retort Temperature Deviations

A computer control logic algorithm has been developed to compensate for the effects of arbitrary retort temperature deviations on lethality. The algorithm is based on calculating the can center temperature for any retort temperature profiles using an alternating direction implicit finite difference method. Lethal rate and corresponding accumulated lethality were calculated during the simulation process. Five types of process deviations were investigated including one with multiple deviations. All the deviations investigated resulted in serious under processing with relative errors in sterilization value ranges from 16.9 % to 43.2 %. A correction measure for process with retort temperature deviations based on targeting the lethal rate of the standard process at the end of the heating phase was proposed. The implementation of this measure resulted in successful correction for all the deviations investigated with a maximum relative error in sterilization value of 9.5 % on the over processing side. This work indicates that the current control algorithm could be incorporated in HACCP guideline, as an online corrective measure for retort temperature deviations during thermal sterilization process.

Multiple Ramp-variable Retort Temperature Control for Optimal Thermal Processing

Variable retort temperature (VRT) thermal processing has been recognized as an innovative method to improve food product quality and save process times. The key to designing a VRT thermal process is to choose a reasonable (optimal) VRT temperature profile for a given food product and package being thermally processed. The selection of optimal retort temperature profiles with a multistage ramp function involving multiple variables is complex and difficult to handle by conventional optimization methods. Newer concepts such as artificial neural networks (ANN) and genetic algorithms (GA) have the potential to deal with such complex situations. The objective of this study was to develop ANN-GA based procedures for the selection of the optimal retort temperature profile under multistage ramp-variable (MRV) retort temperature control for optimizing thermal processing. ANN concepts were used for developing dynamic prediction models for process time, average quality retention and surface cook value, in which the input variables were ramp time (30-70min) and step temperatures (104-134 °C) in four consecutive stages of retort processing. GA-ANN based optimization procedure was then developed using a commercial GA and ANN software, and used for searching the best combination of retort ramp/soak sequence in each of the four stages to give a continuous variable temperature profile that achieves the optimization objective under imposed constraints conditions. The statistical results of modelling performance for all ANN models were: average correlation coefficient r2 = 0.95 and relative error Er = 2.05%. The optimization results and processing efficiency using GA were affected by main GA configuration parameters including initial population number, mutation rate and crossover rate, and the optimal configuration parameters of GA for this study were determined by trials. The optimal retort temperature profiles meeting different optimization objectives for different can sizes were obtained using the GA-ANN optimization method. Compared with the constant retort temperature, the MRV process could improve both process time (up to 43%) and surface quality (up to 24%) significantly. The results suggested that the hybrid artificial intelligence techniques of neural networks and genetic algorithms can be efficiently used for modelling and optimization of the MRV retort temperature control for thermal processing.

Mathematical model development, experimental validation and process optimization: retortable pouches packed with seafood in cone frustum shape

The aim of this research was to develop and validate a mathematical model coupled with an optimization technique for thermal processing of conduction-heated foods in retortable pouches in order to: (a) search for variable retort temperature profiles to minimize process time, and (b) search for variable retort temperature profiles to minimize quality gradient (thiamine) within the product. The model was validated utilizing Jack mackerel ( Trachurus Murphyi) packed in retortable pouches. The conjugated gradient method was utilized as a search technique to find the best variable retort temperature profile to satisfy the specific objectives. The simulation results were in good agreement with the observed temperatures. The prediction errors obtained in the validation study were under 5%. Non-significant differences ( P<0.05) were found between the experimental and predicted values. Simulations showed that significant reduction in process time (20–30%) could be attained utilizing variable retort temperature profiles while maintaining product quality.

Computer simulation of food sterilization using an alternating direction implicit finite difference method

A computer simulation model for food sterilization was developed based on the solution of Fourier’s heat conduction equation for finite cylindrical geometry. The solution is based on the alternating direction finite difference method. Experimental verification of the model was performed using two sets of published data, which shows good agreement with the simulation results. Furthermore, the model performance was tested by subjecting a constant retort temperature profile to an upset condition, the model responded quite well indicting its potential for investigating the influence of constant retort temperature upset conditions on lethality and the effects of variable retort temperature profiles on quality retention and process optimization. In addition, the model can also be used for process control.

THERMAL PROCESS EVALUATION OF RETORTABLE POUCHES FILLED WITH CONDUCTION HEATED FOOD

ABSTRACTTwo models using the finite element technique (FE) and another using an analytical solution to solve the 3‐dimensional heat conduction equation for a finite plate were built. FE models were built considering the actual pouch shape and retort temperature profile. Chi‐square and regression lines were obtained for each set of temperatures generated by the models against experimental data. A mass average sterilizing value of 9.9 min was estimated when a critical point sterilizing value was at 8.7 min using the 3‐Dimensional FE model. Close agreement was found among the three models for heating phase. Using actual retort temperature profile made FE models more accurate than the one using analytical solution, especially for cooling phase.

Retort Temperature Profile for Optimum Quality during Heat Sterilization of Foods in Cans and Retortable Pouches

Retort Temperature Profile for Optimum Quality during Heat Sterilization of Foods in Cans and Retortable Pouches

Determination of the heat transfer coefficient between bulk medium and packed containers in a batch retort

The external heat transfer coefficient in steam retort processing was determined experimentally in a pilot scale retort. The heat transfer equations were solved applying finite elements and using the actual retort temperature profile as boundary condition. The instantaneous values of the heat transfer coefficient were determined, to analyse its time-variability along a retort cycle. It was found that reliable results for the external heat transfer coefficient at time t could be obtained from the derivatives of the average heat transfer coefficient calculated between time zero and time t. The results showed a sharp increase of the heat transfer coefficient in the earlier times of heating (up to 4–5 min of processing), followed by a slightly increasing pattern during the remaining heating period. Using average heat transfer coefficients for the heating phase (and for the cooling phase) also resulted in quite accurate estimates of the temperature at the geometric centre of a can. The influence of the two average heat transfer coefficients, heating and cooling, on the lethality was studied by building a response surface. It was concluded that the variability of the coefficient during heating has a greater impact, especially in the range 150–260 W/m 2 K.

Robust optimal receding horizon control of the thermal sterilization of canned foods

Open loop optimal control strategies for the thermal sterilization of canned foods are computed and analysed. The optimal retort temperature profiles ensure that the required degree of sterilization is met whilst minimising costs. The costs are defined in terms of batch time and retention of nutrient value in the food material. The model is a finite dimensional approximation of the infinite dimensional system. The errors due to the finite dimensional approximation and the uncertainty in the thermal diffusivity parameter of the model are considered. Based on the analysis a closed loop receding horizon optimal controller is designed. Simulation experiments reveal the robustness of the receding horizon optimal controller with respect to uncertainty in the thermal diffusivity parameter. The simulations also reveal that the loss of performance is relatively small and that the batch-time may be reduced significantly.

Inverse Superposition for Calculating Food Product Temperatures during In‐container Thermal Processing

ABSTRACTA procedure was developed for theoretical calculation of internal product temperatures during in‐container sterilization of foods. Experimental product temperatures were determined through traditional heat penetration tests (processing in a retort with come‐up time of increasing temperature and holding time at constant temperature). These were used to produce, through a proposed inverse superposition solution, a “standardized,” normalized, dimensionless product temperature curve corresponding to the response of product temperature to a constant retort temperature profile. This “standardized” curve was then used, through Duhamel's superposition theorem, to calculate product temperatures for time‐varying retort temperature profiles. Limitations associated with the application of Duhamel's theorem were also transferred to the proposed methodology. Theoretical, for perfect mixing, and experimental, for conduction heating, data were used in example calculations.

Simultaneous optimisation of surface quality during the sterilisation of packed foods using constant and variable retort temperature profiles

The differences in temperature dependence between spore inactivation and degradation of quality factors allow the optimisation of thermal processes in terms of maximisation of quality retention by choosing an optimum heating profile. While the maximisation of the retention for a single quality factor has received considerable attention in research, the possibilities of simultaneously maximising the retention of different quality factors have up to now not been addressed. In this article the possibilities of the simultaneous optimisation for more than one quality factor were theoretically assessed. The use of both constant and variable retort temperature profiles was considered. A special emphasis was given to the formulation of appropriate objective functions for the simultaneous optimisation of the surface retention of quality factors. For the simultaneous optimisation of quality factors the objective functions should be formulated in terms of maximising final retention and not, as in the case of single component optimisation, in terms of minimisation of cook values. The use of variable retort temperature profiles was shown to be particularly interesting for the simultaneous optimisation of more than one quality factor, as the final retention calculated compared well with the maximum retention achieved using individual calculated optimum constant retort temperature control for each of the components.

Retort Temperature Profile for Optimum Quality during Conduction‐Heating of Foods in Retortable Pouches

ABSTRACTThe optimal control theory was used to determine the optimum retort temperature profile for quality retention at a given level of sterilizing value in conduction‐heating of foods in retortable pouches. The cook‐value (C‐value) was employed to describe quality changes. Optimization was considered to be a constrained optimal control problem with unspecified terminal time, and it was solved numerically, using the conjugate gradient minimization method. Optimum retort temperature profiles were determined for the volume average and surface C‐values for browning reactions. Final C‐value for volume average decreased by 10% as compared with that for optimum constant retort temperature, and the value for surface decreased by 30%. This method may be applicable to heat sterilization of canned foods as well.

AN EMPIRICAL EQUATION FOR THE DESCRIPTION OF OPTIMUM VARIABLE RETORT TEMPERATURE PROFILES THAT MAXIMIZE SURFACE QUALITY RETENTION IN THERMALLY PROCESSED FOODS

It has been previously shown that, when compared with the traditional constant retort temperature profiles, variable retort temperature profiles allow a modest increase in quality retention during the sterilization of packed foods. When the minimization of the process time with a constraint on the minimum surface quality is considered, variable retort policies show significant reductions on process times when compared to equivalent optimum constant retort temperature profiles. However the results were presented on a case by case basis and no effort was done to try to generalize this principle. In order to allow the generalization of the use of variable profiles we present in this article an empirical formula, developed based on the analysis of calculated optimum variable retort temperature profiles, that allows an accurate description of optimum variable temperature profiles. The use of the proposed equation allows a substantial reduction on the calculation effort necessary for the calculation of optimum variable retort temperature profiles.

VARIABLE CONTROL of A BATCH RETORT and PROCESS SIMULATION FOR OPTIMIZATION STUDIES

A microcomputer was interfaced with a batch retort for digital PI control of the retort temperature. Six retort temperature profiles (three isothermal, sinusoidal, step, and ramp) were examined for processing pea puree to nearly the same lethality values in 211 × 400 cans. Thiamine content and steam consumption were measured. Thiamine retentions in non‐isothermal processes were greater than in the isothermal processes, but there was no significant difference in the steam consumption.Lethality and thiamine retention were also simulated using a finite difference model for the same heating profiles, with good agreement with experimental results. the simulation suggests that differences in thiamine retention due to differing heating regimes are significant only for large lethality values and smaller cans. For F0 values smaller than 10 min, the simulation suggests that the sinusoidal heating regime will provide better thiamine retention. Limitations of the model and suggestions for future improvement are also discussed.

Optimization of Retort Temperature Profile Using Optimal Control Theory.

In the sterilization process for foods packed in cans or retortable pouches, it is of importance to reduce quality deterioration of packed foods, achieving a certain level of sterilization. For this purpose, the optimum retort temperature profile is investigated in this paper. The optimal control theory was used to determine the optimum retort temperature profile for maximizing quality retention for a given final sterility value during the heat sterilization of conduction heating foods in flat containers. This is a constrained optimal control problem with an unspecified terminal time. The conjugate gradient minimization method is applied to this problem. The results show that the best profile can nearly be approximated by a ramp function.

OPTIMIZATION of SURFACE QUALITY RETENTION DURING the THERMAL PROCESSING of CONDUCTION HEATED FOODS USING VARIABLE TEMPERATURE RETORT PROFILES

Optimal variable retort temperature profiles (VRT) for the sterilization of conduction heated foods were calculated using a quasi-Newton multivariable optimization algorithm considering both the maximization of surface quality was the minimization of total process time. When the maximization of surface quality was the objective, an increase up to 20% in quality retention was predicted for optimal VRT profiles as compared to optimal constant retort temperature profiles (CRT). When considering the minimization of total process time, the use of VRT profiles allowed reduction in the total process time of up to 45% while still pro- viding the same surface quality as optimal CRT. Since the results could not be generalized, it was concluded that optimal VRT profiles should be calculated on a case-by-case basis