Aseptic Processing System Research Articles

Inactivation kinetic parameters of hydrogen peroxide application in commercial sterility of aseptic processing systems

Hydrogen peroxide (H2O2) is a commonly used sterilant for aseptic processing and packaging systems. Surrogate bacterial spores are commonly used for the microbiological validation of the sterilization process. However, limited information is available on the resistance of these surrogate spores in liquid H2O2 (LHP) and vapor H2O2 (VHP). This study aims to fill the gaps in understanding of microbial inactivation parameters and the impact of temperature on VHP effectiveness. 35 % LHP experiments were conducted at temperatures ranging from 25 to 70 °C, while VHP tests were performed using vaporized sterilant technology (VST) and temperatures ranging from 43.3 to 60 °C. Exposure times ranged from 1 to 18 s, and VHP concentrations of 2500 and 4450 PPM were used while maintaining a relative humidity of 0.5%. The model performance of the log-linear and Weibull model was assessed using Root Mean Square Error (RMSE), the sum of the square, and Akaike Information Criterion (AIC) scores. The Weibull model outperformed the log-linear model in terms of parameter estimation and statistical indices.

Heat transfer analysis in a heat exchanger with two coaxial tubes for sustainable aseptic processing of foods

Thermal-based approaches in food sterilization techniques principally utilize the heating process until the desired sterilization level of the food can achieved. More specifically, aseptic processing allows for a more cost-effective and time-efficient method for preserving food without degrading the food quality. In this work, we propose a heat transfer analysis of a scraped surface heat exchanger with two coaxial tubes that provides a simplified prototype of a sustainable aseptic processing system. The heat exchanger is installed with scraped blades to allow a stirring mechanism that can only oscillate back and forth at certain angles called oscillating angles. In this simulation, water and solid food particles are put in the system. Moreover, simple regression models are used to find the relation between the mechanical properties of the stirring process with the heat transfer properties. Therefore, experimental data of the temperature and heat transfer coefficient during the heating are used for model fitting. The model fit shows that the angle, frequency, and velocity of the stirring affect the temperature trend and the heat flow rate inside the system. Establishing a comprehensive heat transfer modelling can help to improve the traditional sterilization approach to focus on optimizing energy efficiency and reducing environmental impacts.

Food Hygiene in aseptic processing and packaging system: A survey in the Italian food industry

European legislation requires that processing and packaging of food be done hygienically; moreover many European and International voluntary documents aimed at an easier implementation of Food Hygiene are available. Several sources show that poor hygiene of equipment is one of the most serious problems in the food industry; nevertheless there is still little awareness of possible consequences of equipment that is not hygienically designed. A survey on implementation of Food Hygiene in the Italian food industry was carried out, by using a specifically developed check-list; the case of Aseptic Processing and Packaging Systems was covered. Considering the available literature and with the confirmation of the performed survey, more consideration to Regulations and voluntary documents is needed for safer food.

Optimal shape design of bypass holding tubes configuration in asepting processing

The concept of aseptic processing originated to solve problems associated with conventional ‘in-container’ sterilization of foods such as low rate of heat penetration to the slowest heating point in the container, the long processing times required to deliver the required lethality, destruction of the nutritional and sensory characteristics of the food, low productivity, and high energy costs. Aseptic processing technique has been successfully applied to liquid foods and acid foods containing discrete particulates. However, the extension of aseptic processing to heterogeneous low-acid liquid foods containing discrete particulates has been difficult due to lack of data on critical factors such as interfacial heat transfer coefficient between the liquid and the particle as well as the residence time distribution (RDT) of particles in the holding tube of the aseptic system. Geometry of holding tube represents a primary parameter in determining the residence time distribution of particulate inside an aseptic processing system. Several configuration had been investigate in the past, including curved geometries in order to minimize spreading of RTD. In the following work an experimental bypass holding tube is optimized numerically and experimentally. Numerical optimization was performed by using the Optimal Shape Design, where the essential element respect to classical numerical simulations in fixed geometrical configurations, is to introduce a certain amount of geometrical degrees of freedom as a part of the unknowns, which means that the geometry is not completely defined, but part of it is allowed to move dynamically in order to minimize or maximize the objective function.

Flow diversion in aseptic processing and packaging systems: how guidelines allow avoiding bad design

Flow diversion is a matter of concern for Food Hygiene in Aseptic Processing and Packaging Systems. The relevant standards and guidelines have been examined: since the Aseptic Processing is a widely used and well-established technology, there is quite a lot of available material. The flow diversion topic is also addressed, particularly by EHEDG Guidelines. The correct choice of the temperature probe, also plays an important role in the successful design of a flow diversion system. A procedure, which also includes simple simulation tools, has been developed in order to properly design the flow diversion device. A real case study is also reported. This research reaffirms that it is necessary to have more regard to standards and guidelines and also shows how guidelines allow avoiding bad design.

Sterilization solutions for aseptic processing using a continuous flow microwave system

The conventional method of sterilization of an aseptic processing system by recirculating hot water cannot be applied to a continuous flow microwave heating system. Therefore, a model solution with dielectric and flow properties similar to that of the food product is required as a sterilization solution. Dielectric properties of solutions of table salt, sugar, CMC, and mixtures of these solutes were measured and correlations for the dependence of dielectric properties on concentration of solute and temperature were developed. Sterilization solutions were prepared by matching the dielectric and rheological properties of solutions prepared from table salt, sugar, and CMC to those of the food product to be processed. Dielectric properties of milk and sweet potato puree were compared to those of salt–sugar–CMC mixtures and a model solution that closely matched the properties of each product was prepared and experimentally tested in a 5 kW continuous flow microwave system operating at 915 MHz. The temperature profile at the exit of the heating section during heating of the sterilization solution was compared to the temperature profile during heating of the product. It was observed that the temperatures during transition from sterilization solution to the product did not change appreciably. Thus, these model solutions can be used as sterilization solutions for aseptic processing using a continuous flow microwave system.

Determination of food particle residence time distributions in coiled tube and straight tube with bends at high temperature using correlation analysis

The effects of tube geometry (coiled and straight), particle concentration (0–30% v/v), average product flow rate, and carrier fluid temperature (96–124 °C) on residence time distributions of model food particles in the holding section of an aseptic processing system were investigated by means of correlation analysis. Hold tube geometry and flow rate exerted significant effects on the mean normalized residence time. Minimum normalized residence time was significantly influenced by the fluid temperature and the interaction between hold tube geometry and particle concentration. In the coiled tube, standard deviation of normalized residence time decreased with an increase in particle concentration. The fastest-moving particles in the coiled tube possessed a velocity of 1.96 times the average product velocity, whereas the velocity of fastest-moving particle in the straight tube was 1.8 times the average product velocity. Based on empirical expressions of the residence time parameters as functions of particle concentration and dimensionless groups ( Fr f, Re gp, and Ar f), variable influence of several forces on particle residence time of particulate food suspensions in different settings was deduced.

Fluid-to-particle Heat Transfer Coefficients for Continuous Flow of Suspensions in Coiled Tube and Straight Tube with Bends

Fluid-to-particle heat transfer coefficient (h fp ) for spherical particles in continuously flowing food suspensions (0–30% v/v green peas in 1.5% sodium carboxymethylcellulose solution) in the holding section of an aseptic processing system was determined. The effects of hold tube geometry, temperature, flow rate, and particle concentration were investigated. The h fp values ranged from 538 to 1450 W/m 2·°C in the coiled tube and from 204 to 1220 W/m 2·°C in the straight tube. Significantly, higher h fp value was observed for particles in the coiled tube as compared to that in the straight tube. The h fp value increased with temperature, flow rate, and particle concentration. Dimensionless correlations relating the Nusselt number to Reynolds and Prandtl numbers were developed. Estimation of h fp values based on the particle resistance temperature device (RTD) data and dimensionless correlations indicated a reduction in the degree of overprocessing of average particles when a coiled tube was used instead of a straight tube for the holding section.

USE OF ABLATION TO DETERMINE THE CONVECTIVE HEAT TRANSFER COEFFICIENT IN TWO‐PHASE FLOW

ABSTRACTThe fluid to particle convective heat transfer coefficient (hfp) is an essential design parameter in the development of an aseptic processing system. The convective heat transfer coefficient was determined using a new method based on ablation heat transfer. The amount of solid lost (ablated) was shown to be directly proportional to the energy flux across the fluid‐solid interface with the constant of proportionality being hfp. Change in mass of an ice sphere was used as an ablation probe to study hfp in straight, round conduit. Values of hfp ranged from 1,369 to 2,749 W/m2K over a Reynolds number range of 2,766 to 17,081.

AN ELECTRONIC METHOD TO MONITOR TEMPERATURE INDICATED BY MERCURY–IN–GLASS THERMOMETERS

The U.S. Food and Drug Administration mandates that mercuryinglass thermometers be used as the standardtemperature reference in canning and aseptic processing systems used to sterilize foods. To actively incorporate such devicesinto an automatic control system, an electronic method to monitor the temperature as indicated by a mercuryinglassthermometer was investigated. An indirect temperature measurement device based on the principle of a combination of aparallelplate and a coaxial capacitor in conjunction with a mercuryinglass canners thermometer was developed. Thechange in capacitance with varying levels of mercury was measured from two copper plates attached to the glass sides of thethermometer. The level of the mercury inside the MIG thermometer was reflected in a change of the total capacitance of theexperimental sensor. A linear regression analysis of the experimental data demonstrated the linear relationship between thetotal capacitance and the level of the mercury column. For the temperature range of 71.1 to 93.3
C (160 to 200
F),capacitance of the experimental sensor ranged from 34.9 to 36.9 pF. Precision of the device was determined to be 0.09 pF/
C(0.05 pF/
F).

PHYSICAL PROPERTIES OF RECONSTITUTED CARROT/ALGINATE PARTICLES STABLE FOR ASEPTIC PROCESSING

ABSTRACT Textural and thermophysical properties of reconstituted carrot/alginate particles, subjected to thermal and mechanical stresses during aseptic processing, were investigated. Four levels of sodium alginate (4, 6, 8 and 10%) and calcium chloride (0.2, 0.5, 1.0 and 1.5%) and three levels of water addition (50, 150 and 300 mL) were used for two types of alginate (high in guluronic acid, HGA and low in guluronic acid, LGA). Hardness, water content, density and thermal conductivity of reconstituted carrot/alginate particles were determined using an Instron, an oven drying technique, a pycnometer measurement and a line heat source method, respectively. Moreover, Bacillus subtilis was inoculated in carrot/alginate particles.Reconstituted particles, unlike carrot cubes and other vegetables, were thermally stable. The moisture content increased with a decrease in calcium chloride concentration and an increase in water addition. There was no significant effect of formulation on density and thermal conductivity measurements. Reconstituted carrot/alginate cubes were able to sustain successfully thermal and mechanical stresses encountered in a pilot scale aseptic processing system.

A neuro-computing approach for modeling of residence time distribution (RTD) of carrot cubes in a vertical scraped surface heat exchanger (SSHE)

A neuro-computing approach was used for modeling two residence time distribution (RTD) functions — the time-specific (E-type distribution) and the cumulative particle concentration function (F-type distribution) — of carrot cubes in starch solutions in a vertical scraped surface heat exchanger (SSHE) of a pilot scale aseptic processing system. Experimental data obtained for E ( t) and F( t) under various test conditions were used for both training and evaluation. Multi-layered artificial neural network (ANN) models with four input and two output neurons were trained. The network was optimized by the varying number of hidden layers, number of neurons in each hidden layer and learning runs, and a combination of learning rule and transfer functions, using a back-propagation algorithm. The trained ANN model was validated by a set of independent experimental data. The ANN models were also compared with conventional models developed based on multiple regression techniques. The results indicated that there was better agreement between experimental and ANN model predicted values for both E ( t) and F ( t) functions. The average modeling errors associated with ANN were 5.7 and 3.0%, respectively, for E( t) and F( t), while they were 15.5 and 12.3%, respectively, with the multiple regression models.

Particle Passage Time Distributions in Vertical Pipe Flow of Solid–Liquid Food Mixtures

In sterilizing food particulate systems, knowledge of the residence time of the fastest moving particle in the heating and holding sections of the aseptic processing system is required. It is equally important to determine the mean and maximum particle residence times and ideally the whole distribution of residence times should be known; it is important that the fastest particle is sterilized without overcooking the slowest particle. Whilst a number of studies have reported data on horizontal food flows, few have considered vertical flows although they form a significant part of food plant. This paper reports experimental results on the vertical upflow of almost neutrally-buoyant alginate particles in carboxymethylcellulose (CMC) solutions in a 48 mm diameter pipe. The spherical particles used had 5 and 10 mm diameters, and were conveyed at solids fractions of 16−55% v/v and mean mixture velocities of 77−230 mm −1 s. The mean apparent viscosity of the carrier fluids ranged from 29 to 422 mPas, and the tube Reynolds number varied from 8.7 to 381. Particle passage times were measured by Hall effect sensors or visual tracers. The results show that four different particle passage time distributions can exist depending on the flow pattern present, and the solids concentration has the strongest effect on minimum passage times. For particle Reynolds numbers less than 0.08, an annular particle region existed which caused high values of maximum passage time.

Color Improvement and Metallo‐chlorophyll Complexes in Continuous Flow Aseptically Processed Peas

ABSTRACTFresh and frozen green peas were blanched in zinc solution (50 to 500 mg/L) and thermally processed in a particle cell reactor, which simulates a continuous flow aseptic processing system. The thermal process temperatures ranged from 121 to 145 °C at holding times from 0 to 20 min. The degradation of chlorophyll and the resulting formation of Zn‐pheophytin a and Zn‐pyropheophytin a were monitored. Quantitative analysis of the metallo‐chlorophyll complexes was performed by high‐performance liquid chromatography. Complex formation increased during heat processing and was dependent on the zinc concentration absorbed within the peas during blanching. At 130 to 145 °C, the formation of Zn‐pyropheophytin a increased and processing between 121 to 125 °C promoted the formation of Zn‐pheophytin a. Improvements in color relative to control samples suggested that the process might be applicable to two‐phase continuous aseptic processing of vegetables.

Determination of Lethality During Aseptic Processing of Particulate Foods

Experimental and modelling studies were conducted to ascertain the effect of viscosity, flow rate, particle size, particle concentration on the residence time distribution of particles during non-Newtonian flow in a holding tube. Another program was written to determine the temperature distribution within particles during flow in the heat exchanger, holding tube, and cooling section of an aseptic processing system. Based on this, the lethality of different processes was determined depending on the target microorganism. The extent of nutrient retention and enzyme destruction was also computed. Experimental studies indicated that an increase in viscosity, flow rate or particle concentration decreased the mean and minimum residence time while an increase in particle concentration resulted in the opposite effect. In addition, it was found that an increase in viscosity widened the residence time distribution (RTD), while an increase in flow rate, particle size or particle concentration narrowed the RTD. Process lethality decreased from 8.0 to 2.3 mins when particle size increased from 1.0 to 1.5 cm; decreased from 5.9 to 4.0mins when particle concentration increased from 30 to 50%; and decreased from 6.5 to 3.0 mins when the heat transfer coefficient decreased from 300 to 200W/m2-K.

DETERMINATION OF FLUID‐TO‐PARTICLE HEAT TRANSFER COEFFICIENTS FOR ROTATING PARTICLES1

ABSTRACT Fluid‐to‐particle heat transfer coefficients (hfp) were determined for stationary and rotating potato‐alginate cubes heated by carboxymethylcellulose solutions in an aseptic processing system. Fluid temperature, fluid average velocity, CMC concentration, and particle size were varied. In the stationary particle case, the slip generalized Reynolds numbers (Regs) ranged from 1.3 to 6.7. For the rotating particles, Regs ranged from 0.91 to 5.0 and the generalized rotational Reynolds numbers (Regr) ranged from 6.0 to 33. The hfp ranged from 120 W/m2°C to 2400 W/m2°C and from 360 W/m2°C to 4300 W/m2°C for stationary and rotating particles, respectively. Particle rotation significantly increased hfp. Fluid temperature, particle size, fluid average velocity, and CMC concentration had significant effects on hfp for both stationary and rotating particles. Using Regs in the dimensionless correlation gave a better prediction of hfp for the rotating particles than using Regr.

Distribution of Liquid‐Solid Heat Transfer Coefficient among Suspended Particles in Vertical Holding Tubes of an Aseptic Processing System

ABSTRACTMass transfer coefficients between sucrose coated particles and water as the suspending fluid, were measured to obtain values of the heat transfer coefficient by analogy with mass transfer. In a vertical holding tube configuration, the mass transfer coefficient spanned considerable range for those particles with comparable residence time. At Reynolds number 26100, the average mass transfer Sherwood number expressed in terms of residence time was Sh= ‐110.4t+215.1, and it scattered normally with standard deviation 19.2. The results indicated that heat transfer coefficients vary among particles with different residence times and may be significantly different even for particles with the same residence time.

Residence time distribution of food and simulated particles in a holding tube

Residence time distribution (RTD) was determined for food and simulated particles flowing in a holding tube, as affected by particle shape (cube, cylinder, sphere), particle concentration (10, 20, and 30% w/v), particle type (potato, carrot, turkey, green peas, and polystyrene), fluid viscosity (0.0% CMC, 0.5% CMC, 1.0% CMC), bulk flow rate (5.81, 7.28, and 8.71 × 10 −4 m 3/s) and SSHE shaft speed (30, 60, and 90 rpm). Residence times of tracer particles were recorded by a video camera equipped with a timer. Cylindrical particles remained in the holding tube longer than cubic particles. Increasing particle concentration and bulk flow rate tended to decrease mean normalized particle residence time (MNPRT). Increasing fluid viscosity decreased MNPRT significantly, apparently due to the strong lift action of the fluid on the particles. Although turkey particles were denser than other food particles, they had smaller residence times than the carrot and potato particles. The MNPRT of green peas was found to be significantly higher than that of polystyrene spheres. Swept-surface heat exchanger shaft speed did not influence MNPRT in the holding tube. The residence time distribution curves were narrowed by decreasing particle concentration and increasing bulk flow rate, and by using high viscosity fluids and cubic particles. The longest particle residence time was 5.3 times the average bulk residence time. The fastest particle did not exceed 1.8 times the average bulk velocity. This finding is within the conservative value of 2.0 considered safe in sizing holding tubes in aseptic processing systems.

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.

Residence time distribution of particulate foods at aseptic processing temperatures

Knowledge of experimental residence time distribution of foods containing particles being processed aseptically is crucial to designing safe thermal processes while simultaneously ensuring optimum product quality. Past attempts at designing high-temperature short-time process recommendations depended on conservative estimates for residence time in a holding tube while ignoring the effect of the scraped-surface heat exchangers. This resulted in excessive thermal treatment and a consequent loss of textural and nutritional quality attributes. Experiments were conducted to determine residence time of particles in food being processed in a commercial scale aseptic processing system at 135–140 °C. Residence time data, which included among others, the effect of particle-particle interaction in a viscous fluid product made up of a 6% starch solution containing 15% diced potatoes, were collected and treated statistically. The data show that the methodology developed yields reproducible data, which when treated statistically, allows prediction of fastest particle residence time with a high level of confidence. In addition, data presented for the high-viscosity starch-based product, showed a marked absence of any channeling effects as the product passed through scraped-surface heat exchangers, a holding tube, and interconnecting piping of a commercial processing system.