Holding Tube Length Research Articles

Evaluation of thermal and nonthermal treatment of margarine: Pasteurization process efficiency, kinetics of microbial destruction, and changes in thermophysical characteristics

The objective of this study was the thermophysical characterization and microbial evaluation of the commercial margarine production process. Thermal destruction of Escherichia coli (K-12) was characterized between 60 and 70°C with a decimal reduction time (D value) between 4.44 and 0.22 min and a Z value of 7.72°C. Pulsed light treatment as a nonthermal alternative was used for comparison; however, the effectiveness was very weak with a 90% surface decontamination yield after 20 s of high-intensity pulsed light treatment. Rheological studies showed a two-stage flow behavior due to the melting phenomenon of margarine and the use of the Arrhenius model yielded an activation energy of 186.3 and 15.0 (kJ/mol) before and after a phase transition point at 36.6°C, respectively. The differential scanning calorimetric studies showed three main peaks related to the melting of unsaturated fats (−22.0°C), melting of brine phase (−6.1°C), and melting of saturated fats (31.3°C). The holding tube length was calculated based on the physical properties of margarine and different Reynolds numbers. Practical applications Margarine production is still a growing industry and nowadays many novel approaches are used for pasteurization purposes and hence the evaluation of process efficiency and product characterization is desirable. In this regard, the present work provides helpful data for te margarine production by adjusting a practical approach toward evaluating the thermal pasteurization efficiency. In addition, the evaluated thermophysical characterization of margarine presents a scientific basis for the research and development in terms of product formulation and thermal/nonthermal process adaptations.

Lethality Calculation of Particulate Liquid Foods during Aseptic Processing

In the past two decades, aseptic processing has been implemented in the food industry to sterilize particulate liquid food mixtures. To ensure that particulates in the liquid receive sufficient heating, mathematical modeling is employed to evaluate the temperature and lethality level in the particles. We developed a model for the thermal processing of liquid foods containing cubic particles in a continuous laminar pipe flow system, comprising a tubular heat exchanger. In our simplified approach, heat transfer equations for particulate liquid foods were solved analytically and numerically to evaluate the effect of certain process parameters on the time temperature profiles of particles and the lethality value in the products. A comparison of the particles’ lethality values was made between the experiment and simulation for two different particle residence times in a case study, and the model predictions were in good agreement with experimental data. Based on modeling studies, it was found that within the range of parameters studied, an increase in flow rate and particle size resulted in a decrease in the lethality value of the particles, while an increase in particle concentration and holding tube length resulted in the opposite effect.

LETHALITY CONTRIBUTION FROM THE TUBULAR HEAT EXCHANGER DURING HIGH‐TEMPERATURE SHORT‐TIME PROCESSING OF A MODEL LIQUID FOOD

ABSTRACT Experiments were conducted using Bacillus stearothermophilus spores in 0.5% w/w carboxymethylcellulose suspension to evaluate come‐up contributions from the tubular heat exchanger. A lab‐scale UHT/HTST simulator that allowed samples to be collected at the exit of the heat exchanger and holding tube was used with operating temperatures up to 270F. The bulk mean residence time in the heat exchanger ranged from 30 to 89 sec, while that in the holding tube ranged from 4 to 14 sec. It was observed that between 40% and 51% of the cumulative lethality ( ) at the exit of the holding tube, was contributed by come‐up in the tubular heat exchanger. This come‐up contribution was determined on the basis of having an of 8.5 min in the holding tube alone. It was evident that come‐up lethality will depend on product initial temperature, residence time and temperature history in the heat exchanger, with higher temperatures obviously contributing more lethality. Therefore, the entire aseptic system becomes even more complex since several critical parameters need to be monitored, controlled and documented. Experimental data compared favorably with computer‐simulated data using the AseptiCAL™ software, with the software package giving more conservative results. Ultimately, come‐up credit (CUC) should be tested on a pilot scale or industrial setup by way of reduced residence time (i.e. increased fluid flow rate), reduced holding tube length or temperature in order to determine if CUC can be applied towards the lethality required for the product. Monitoring and control devices become critical to ensure consistency and reproducibility in product residence time and time–temperature history, in the tubular heat exchanger.

Refunctionalization of extruded‐expelled soybean meals

AbstractSoybean meals produced by extruding‐expelling (FF) have poor functional properties due to heat denaturation of the proteins, which limits their utilization in foods. Hydrothermal cooking (HTC), a treatment in which steam (150°C) and high shear are applied to a slurry of soybean meal, was used to refunctionalize EE protein meals. Two EE samples with protein dispersibility indexes (PDI) of 35 and 60 were used, along with solvent‐extracted white flakes and full‐fat whole soy meal as controls. Two HTC methods were explored: One method used a treatment temperature of 154°C and seven different residence times, controlled by varying the holding tube length; the other involved flashing the treated slurry directly into the atmosphere without any back‐pressure regulation or holding. Effects of residence time on functional properties of the samples were investigated. The maximum effect of HTC conducted with the use of holding tubes (with‐holding‐tube HTC) was also compared with that of flash‐out HTC. Solid dispersibility, protein dispersibility, and emulsification capacity of both EE meals were significantly improved by both types of HTC treatments. The flash‐out HTC showed more benefits than the with‐holding‐tube HTC in refunctionalizing heat‐denatured EE protein. For example, the solid dispersibility, protein dispersibility, and emulsification capacity of EE meal with PDI of 35 were improved 2.0, 4.4, and 2.1 times, respectively, by flash‐out HTC treatment. Therefore, the HTC refunctionalization was proved effective in partially restoring the functional properties of the heat‐denatured soy proteins.

Residence Time Distributions of Meat and Carrot Cubes in the Holding Tube of an Aseptic Processing System

Residence time distribution (RTD) of meat and carrot cubes in the holding tube of a commercial pilot scale aseptic processing system was evaluated using a full factorial design of experiments employing holding tube length (4·6, 9·2, 13·8 and 18·4 m), flow rate (10, 15 and 20 kg/min), particle size (10 and 20 mm meat cubes and 6 and 13 mm carrot cubes) and concentration of the carrier fluid (40 and 60 g/100 g starch) as factors. All test factors significantly ( P< 0·05) influenced the fastest particle residence time and its normalized counterpart, the mean particle residence time and standard deviation of RTD. Experimental RTD was well described by a generalized logistic model ( r 2> 0·95). The model parameters were responsive to test factors and could be well described using multiple regression analyses of test factors and their interactions.

Mathematical Characterization of Residence Time Distribution Curves of Carrot Cubes in a Pilot Scale Aseptic Processing System

Residence time distribution (RTD) of food particles and carrier fluid was evaluated in a commercial pilot scale aseptic processing system using o full factorial design of experiments employing flow rate (15 and 20 kg/min), temperature (80 and 100°C), holding tube length (1.5, 17.5 and 26.7m) particle (carrot cubes) size (6 and 13 mm) and starch concentration (30 and 50 g/kg) of the carrier fluid as factors. RTD curves of carrot cubes were characterized in this study using a special case of the logistic model (autocatalytic or inverse exponential model). Three model parameters (an accumulation rate factor, B; a concentration limit factor, U and a half-time factor, M) fully described the RTD curve: F = C/[1 + e -B(n-M)]. The model was used to describe the influence of various process parameters and to obtain E-type RTD curves. All test factors were significant (P < 0.05) in influencing the parameters associated with the logistic model. Using multiple regression, the logistic parameters were related to the experimental factors (R 2 > 0. 78).

A computer simulation program for evaluation of the continuous heat treatment of particulate food products. Part 2: Utilisation

A computer program for calculation of temperatures in a liquid containing particles during continuous heat treatment has been developed at the SIK. The program facilitates the study of the influence of processing on product quality in an aseptic processing system. The calculated F value is related to the safety, and the cook value (C value) is related to the quality of the product. In this paper, results of some calculations using the program are presented. They concentrate on the influence of the processing conditions on the process design. These results indicate that factors such as particle heat transfer coefficient, both in the holding tube and in the scraped surface heat exchangers (SSHEs), flow conditions, particle diameter and sterilisation temperature have consequences for the holding tube length, i.e. the processing time, for a given lethality. For example, for small particle heat transfer coefficients (< 100 W m 2 K), a small change will have a large effect on the required processing time (i.e. the holding tube length). However, at particle heat transfer coefficients > 150–200 W m 2 K a small change does not greatly affect the processing time (i.e. holding tube length). The program can thus be used to examine whether the surface heat transfer coefficient is the rate-limiting factor, or whether the heat conduction inside the particles is more important in the design of the process.

Residence time distribution of carrot cubes in starch solutions in a pilot scale aseptic processing system

Residence time distribution (RTD) of carrot cubes flowing in starch solutions was evaluated in a commercial pilot-scale aseptic processing system using a full factorial design of experiments employing flow rate (15 and 20 kg/min), temperature (80 and 100°C), holding tube length (0, 60 and 100%), particle size (6 and 13 mm) and starch concentration (3 and 5% w/w) as factors. All factors were found to be significant ( p<0·05) in influencing the fastest particle residence time (FPRT), mean particle residence time (MPRT), particle residence time variance (PRTV) and their normalized versions. While particle size, holding tube length and starch concentration increased the FPRT, fluid flow rate and temperature had the opposite effect. The FPRT was lower than the average fluid retention time under all testing conditions.

SENSITIVITY ANALYSIS of ASEPTIC PROCESS SIMULATIONS FOR FOODS CONTAINING PARTICULATES1

ABSTRACTA sensitivity analysis of a computer model, simulating heat transfer into particulate foods processed in a continuous aseptic system was conducted to determine how the model reacts to the variations in selected product and process input parameters depending on simulation types, namely, “Total”, “F0 Hold” and “Hold Only”. Three major output variables, namely, holding tube required to destroy 6 D of Clostridium sporogenes (PA3679), destruction of thiamine and inactivation of peroxidase were selected for the sensitivity analysis. Theoretical results indicated that basically no difference between the “Total” system approach and the “F0 Hold” approach was found on the model prediction. Particle size, particle thermal properties such as density and specific heat were the most sensitive parameters (within the range investigated) among product parameters which influence holding tube length required, thiamine and peroxidase retention while fluid properties such as fluid thermal conductivity and viscosity were less susceptible to affect the model prediction regardless of simulation types. Among process parameters, product flow rate and product initial temperature seemed to be the most critical parameters within the range covered in this study while rotor speed seemed to be one of the least critical parameters to influence the model prediction regardless of simulation types.

PREDICTION OF HOLDING TIMES FOR CONTINUOUS THERMAL PROCESSING OF POWER‐LAW FLUIDS

ABSTRACTCorrelations for predicting fastest element holding times (neglecting diffusion) in smooth tubes from process flow conditions are presented for any time‐independent, nonviscoelastic fluid in laminar or turbulent flow. The results were derived from previously developed semi‐theoretical and empirical relationships for power‐law fluids. However, the pre dictions can be applied with only slight approximation to nonpower‐law fluids. A holding tube length based upon these correlations should provide a safe process since no fluid element should be in the tube for less time than predicted.

Effect of Process Variables on the Holding Time in an Ultrahigh-Temperature Steam Injection System

Holding time was measured by monitoring the conductivity of a salt charge at each end of a holding tube on a strip chart recorder. The effect of pressure and temperature of the heated product on the holding time was studied in 88.7- and 113.7-cm tubes. Holding tube pressure was designated as that pressure in excess of the saturated vapor pressure of water at the holding temperature. Excess pressures of about 1 kg/cm2 were required to ensure reproducible measurement of holding time. At excess pressures below 0.7 kg/cm2 two-phase flow existed. Holding time decreased with pressure until all vapor was condensed. Holding time also decreased as temperature increased because of condensate added to the product and because of the reduced density at higher temperatures. A method for predicting holding tube length for a desired holding time or a holding time for a given holding tube length is presented. The prediction, computed from process and system parameters, ensures a safe process from a public health viewpoint. Calculation is based upon heat and mass balances and velocity distribution in a pipeline.