**1. Introduction**

378 Food Industrial Processes – Methods and Equipment

S.O. Jekayinfa, P.O. Okekunle, I.G. Amole, J.A. Oyelade, (2005) "Evaluation of corrosion

Corrosion Methods and Materials, Vol. 52 Iss: 4, pp.214 - 218

372

cost in some selected food and agro-processing industries in Nigeria", Anti-

Heating process for food is of importance to the consumers since it is considered to be one of food preservation techniques. Under these techniques food can be stored or edible within a long period of time. One of them which require heat treatment is sterilization process. Thermal sterilization of prepackaged canned foods in retort has been the most widely used during the twentieth century. Typically this method consists of heating food containers in pressurized retorts at specified temperatures for prescribed lengths of times (Teixeira and Tucker, 1997).

The process time for canned food is indicated based on the sufficient achievement of bacterial inactivation in each container in order to comply with public health standards or food safety. In addition it will minimize the probability of food spoilage. The traditional methods for thermal process calculations or validation such as Ball and Stumbo methods were developed and widely used ever since. However they required the off-line input of tables and consequently series of calculation steps which might be resulting in too-long or too short heating process. At present there are a lot of commercial software available which could be used either on-line or off-line analysis for sufficient heat treatment or process lethality (Fo) such as CAN-CALC, and CALSoft™ etc. Balaban (1996 cited by Teixeira et al., 1999) described that CAN-CALC software needed to get fh (heating rate factor) and jh (heating lag factor) from heat penetration test prior to be able to predict internal center product temperatures in response to any dynamic boundary temperature for products of any shape and size as shown in figure 1 and 2. Therefore if assumed that the selected can was at the slowest heating point of the retort, simulated system Fo for food products that heated by any combination of conduction or convection heat transfer also could be obtained. However, the software performance was emphasizing with its capability to deal with process deviation such as steam shutting off and back on. The CALSoft™ software (Anonymous, 2011) was designed specifically for conducting heat penetration and temperature distribution testing, evaluating the collected data, calculating a thermal process or vent schedule/come-up time, and evaluating process deviations. It was supposed to use with CALPlex™ data logger and claimed for the most widely used commercial thermal processing software.

Sterilizing Value and Heat Distribution in Retort for Canning Process 381

375

Fig. 2. Graphical display of calculated or predicted and experimented temperature at coldest

Many researchers (Lappo and Povey ,1986; Ryniecki and Jayas, 1993) had employed the accumulated process lethality to design system process control for batch steam retort. A number of thermocouples were connected to the cans. The mean temperature at the center of those cans was used for calculating process lethality in real time. Datta et al. (1986) used the numerical solution of 2 dimensional heat transfers in a finite cylinder as a part of the decisionmaking software in a computer-based retort control system. Actual retort temperature was read directly from sensors located in the retort and it was continually updated with each iteration of the numerical solution. Heating was continued until the accumulated lethality was reached some designated target value and the process would always end with the desired level of sterilization. However their solution of the model has some limitations since purely conduction-heated canned food was simulated for. Later many research works (Bichier et

Visual Basics computer simulation package for thermal process calculation was developed by Chen and Ramaswamy (2007). This graphical user interface (GUI) program was designed for training and testing of artificial neural artwork models and for study of process design or other research purposes. It is applicable to different retort thermal processing with different types of food such as solids, liquids and liquids containing particles in containers of different shapes and size. Temperature in container was solved by using finite difference and a numerical

There have been several attempts to develop control approaches for thermal process operation in food canning. Traditionally it consists of maintaining specified operating conditions that have been predetermined from product or process heat penetration test. The

integration method was used for calculating process lethality and quality retention.

point in CAN-CALC software (Balaban, 2004)

al.,1995 ; Teixeira, 1992) had been done without these limitations.

Accomplished Fo of the coldest point in canned food can be expressed as

$$F\_o = \int\_0^{t\_h} 10^{(T - T\_{nf})/z} \text{ dt} \tag{1}$$

It is calculated in the unit of minutes at reference temperature (*Tref* ) ; *T* is the temperature at coldest point in the container; *Tref* is a standardized reference temperature, usually 121.1oC or 250oF ; *z* is temperature dependency factor from microbial thermal death time curve and expressed as temperature change required for a ten-fold change of destruction time. Usually it is 10 oC for Botulinum cook. Equation (1) can be usually evaluated by numerical integration as general method or computed from the sum of the different sterilizing value ( *Fi* ) accomplished after small time intervals ( *t* ) as temperature change throughout the process (Teixeira and Tucker, 1997).

$$F\_o = \sum\_{i=1}^{n} \Delta F\_i = \sum\_{i=1}^{n} 10^{(T\_i - T\_{ref})/z} \Delta t \tag{2}$$

When comparing to all other methods to calculate Fo, the general method has been accepted to be the most accurate. However, the disadvantage of this method is used to be the clumsiness since it has to obtain the lethal rate in every time step. The smaller time step, the more accurate it will be. But when using computer as a tool to perform all these calculation, Fo determination become rapid and simple.

Fig. 1. Parameters input in CAN-CALC software before simulating for system Fo (Balaban, 2004)

( )/

It is calculated in the unit of minutes at reference temperature (*Tref* ) ; *T* is the temperature at coldest point in the container; *Tref* is a standardized reference temperature, usually 121.1oC or 250oF ; *z* is temperature dependency factor from microbial thermal death time curve and expressed as temperature change required for a ten-fold change of destruction time. Usually it is 10 oC for Botulinum cook. Equation (1) can be usually evaluated by numerical integration as general method or computed from the sum of the different sterilizing value ( *Fi* ) accomplished after small time intervals ( *t* ) as temperature change

*ref <sup>t</sup> TT z Fo*

( )/

10 *i ref n n TT z*

dt (1)

(2)

0 10 *h*

1 1

*FF t*

When comparing to all other methods to calculate Fo, the general method has been accepted to be the most accurate. However, the disadvantage of this method is used to be the clumsiness since it has to obtain the lethal rate in every time step. The smaller time step, the more accurate it will be. But when using computer as a tool to perform all these calculation,

Fig. 1. Parameters input in CAN-CALC software before simulating for system Fo (Balaban,

*o i i i*

Accomplished Fo of the coldest point in canned food can be expressed as

throughout the process (Teixeira and Tucker, 1997).

Fo determination become rapid and simple.

2004)

Fig. 2. Graphical display of calculated or predicted and experimented temperature at coldest point in CAN-CALC software (Balaban, 2004)

Many researchers (Lappo and Povey ,1986; Ryniecki and Jayas, 1993) had employed the accumulated process lethality to design system process control for batch steam retort. A number of thermocouples were connected to the cans. The mean temperature at the center of those cans was used for calculating process lethality in real time. Datta et al. (1986) used the numerical solution of 2 dimensional heat transfers in a finite cylinder as a part of the decisionmaking software in a computer-based retort control system. Actual retort temperature was read directly from sensors located in the retort and it was continually updated with each iteration of the numerical solution. Heating was continued until the accumulated lethality was reached some designated target value and the process would always end with the desired level of sterilization. However their solution of the model has some limitations since purely conduction-heated canned food was simulated for. Later many research works (Bichier et al.,1995 ; Teixeira, 1992) had been done without these limitations.

Visual Basics computer simulation package for thermal process calculation was developed by Chen and Ramaswamy (2007). This graphical user interface (GUI) program was designed for training and testing of artificial neural artwork models and for study of process design or other research purposes. It is applicable to different retort thermal processing with different types of food such as solids, liquids and liquids containing particles in containers of different shapes and size. Temperature in container was solved by using finite difference and a numerical integration method was used for calculating process lethality and quality retention.

There have been several attempts to develop control approaches for thermal process operation in food canning. Traditionally it consists of maintaining specified operating conditions that have been predetermined from product or process heat penetration test. The

Sterilizing Value and Heat Distribution in Retort for Canning Process 383

377

in figure 3. Up to 8 thermocouples could be instrumented to the loaded cans and hard-wired through a retort (figure 4). They were used for sensing the analog inputs of temperatures from different locations in the retort and then they were transformed to digital temperature

Thus time-temperature history data from tested cans and some for temperature in the retort were recorded and displayed graphically in every 4.5 second in the developed program as GUI software coded by Visual Basic 6.0. Prior to the test, all the temperature reading probes were calibrated from the temperature range of ambient to 140oC by comparing to the

The designed computer program is able to access the recorded Quick-Basic data file which provide real-time of time-temperature history in cans and retort, and calculate them for lethal rate in every 4.5 second by Simpson's rule of numerical integration to obtain accomplished Fo dynamically during sterilizing. In order to evaluate the accuracy of this program, time-temperature history data was also tested with F-ADDING which is a computer program for calculating Fo coded by Rouweler (2000). The minimum accomplished Fo among all of them from each probe is obtained as system Fo and it is compared simultaneously with the target Fo needed to end the process in the minimum of process time. The flowchart of the algorithm for on-line Fo assessment is shown in figure 5. This approach was accepted as unquestionably the most effective and most certainly the very safest on-line correction when process deviation occurs (Teixeira and Tucker, 1997; Simpson et al., 2007) since thermocouples were used to on-line measure temperature not

Fig. 3. Enhanced A/D multi-lab card & programmable gain amplifier/multiplexer board

data via the interface PCL-812PG A/D card.

only retort but also the cans.

reading of reliable portable digital thermometer measuring hot oil.

first control strategy was to employ real-time heat penetration data acquisition for intelligent on-line control of thermally processed foods. It was the most effective way to handle process deviation. However prior to start thermal operation, a number of product containers are instrumented with temperature probes then filling and seaming. Connection is made between these containers to data logger through the lead wires. Computer thus have the real-time accessing the data from data logger and perform calculation for accomplished sterilizing value at the coldest spot of container. The calculated accomplished sterilizing value is continually compared with the target value required at the end of heating. This strategy provides very accurate calculation of process lethality and is able to handle the process deviation without operator intervention and without any unnecessary degree of over-processing. The most valuable feature of this control strategy is that it is nearly foolproof since any thing that might have gone wrong earlier in the product preparation is revealed and accounted for. However, the obvious disadvantage for this type of control strategy would be cost prohibitive (Simpson et al., 2007).

Another retort control strategy that many researchers had worked on is about on-line correction of process deviation which is integrating of the real-time data acquisition for retort temperature, on-line correction factor and mathematical heat-transfer model of can temperature (Teixeira and Manson, 1982; Datta et al., 1986; Teixeira and Tucker, 1997). However, the strategy that will be the future trend is microcontroller-based retort control system or simply on-line temperature measurement of retort to lap top computer. When the calculated accomplished lethality reaches the specified target value, computer will automatic shut off or turn on valves (Simpson el al., 2007). Awuah *et al*. (2007) discussed that Can-Calc process simulation software also was tested for its performance and further integrated into a computer-based on-line control system by Noronha et al. (1995) and Teixeira et al. (1999).

As a whole, the purpose of software design and hardware control was based on the fact that foods should not be overheated since it leads to detrimental effect to food quality as well as the waste of energy and water. Thus heat should be minimally applied or applied as necessary as it needs. In order to get the above mentioned process, it is essential to have proper machine or devices associated with analysis method to assess the process efficacy involving heat treatment for any one of canned products and heat distribution in sterilizing device.

However, in Thailand most of the hardware and software available now are imported. They are designed basically on either the post assessment (after completely heating foods) or undergo heating. Up to now more efforts have been carried out for developing the intelligent on-line retort control system which is capable of rapid evaluation, on-line correction and printed documentation. The development of local devices or software for such purposes is still rarely found in Thailand. Thus the objectives of the research are to develop visual basic computer software to integrate the on-line data acquisition. The assessment of sterilizing value or process lethality (Fo) as well as heat distribution in retort was performed while heating. The software also can be used as an education tool for thermal processing study.

#### **2. Materials and method**

#### **2.1 On-line data acquisition and sterilizing value (Fo) assessment**

Quick Basics program was designed and developed to obtain the interfacing data from PCL-812PG card (multifunction data acquisition card) together with PCLD-889 boards (amplifier/multiplexer board with signal conditioning and cold junction sensing circuit) as

first control strategy was to employ real-time heat penetration data acquisition for intelligent on-line control of thermally processed foods. It was the most effective way to handle process deviation. However prior to start thermal operation, a number of product containers are instrumented with temperature probes then filling and seaming. Connection is made between these containers to data logger through the lead wires. Computer thus have the real-time accessing the data from data logger and perform calculation for accomplished sterilizing value at the coldest spot of container. The calculated accomplished sterilizing value is continually compared with the target value required at the end of heating. This strategy provides very accurate calculation of process lethality and is able to handle the process deviation without operator intervention and without any unnecessary degree of over-processing. The most valuable feature of this control strategy is that it is nearly foolproof since any thing that might have gone wrong earlier in the product preparation is revealed and accounted for. However, the obvious disadvantage for this type

Another retort control strategy that many researchers had worked on is about on-line correction of process deviation which is integrating of the real-time data acquisition for retort temperature, on-line correction factor and mathematical heat-transfer model of can temperature (Teixeira and Manson, 1982; Datta et al., 1986; Teixeira and Tucker, 1997). However, the strategy that will be the future trend is microcontroller-based retort control system or simply on-line temperature measurement of retort to lap top computer. When the calculated accomplished lethality reaches the specified target value, computer will automatic shut off or turn on valves (Simpson el al., 2007). Awuah *et al*. (2007) discussed that Can-Calc process simulation software also was tested for its performance and further integrated into a computer-based on-line control system by Noronha et al. (1995) and Teixeira et al. (1999). As a whole, the purpose of software design and hardware control was based on the fact that foods should not be overheated since it leads to detrimental effect to food quality as well as the waste of energy and water. Thus heat should be minimally applied or applied as necessary as it needs. In order to get the above mentioned process, it is essential to have proper machine or devices associated with analysis method to assess the process efficacy involving heat treatment

However, in Thailand most of the hardware and software available now are imported. They are designed basically on either the post assessment (after completely heating foods) or undergo heating. Up to now more efforts have been carried out for developing the intelligent on-line retort control system which is capable of rapid evaluation, on-line correction and printed documentation. The development of local devices or software for such purposes is still rarely found in Thailand. Thus the objectives of the research are to develop visual basic computer software to integrate the on-line data acquisition. The assessment of sterilizing value or process lethality (Fo) as well as heat distribution in retort was performed while heating. The software also can be used as an education tool for

Quick Basics program was designed and developed to obtain the interfacing data from PCL-812PG card (multifunction data acquisition card) together with PCLD-889 boards (amplifier/multiplexer board with signal conditioning and cold junction sensing circuit) as

of control strategy would be cost prohibitive (Simpson et al., 2007).

for any one of canned products and heat distribution in sterilizing device.

**2.1 On-line data acquisition and sterilizing value (Fo) assessment** 

thermal processing study.

**2. Materials and method** 

in figure 3. Up to 8 thermocouples could be instrumented to the loaded cans and hard-wired through a retort (figure 4). They were used for sensing the analog inputs of temperatures from different locations in the retort and then they were transformed to digital temperature data via the interface PCL-812PG A/D card.

Thus time-temperature history data from tested cans and some for temperature in the retort were recorded and displayed graphically in every 4.5 second in the developed program as GUI software coded by Visual Basic 6.0. Prior to the test, all the temperature reading probes were calibrated from the temperature range of ambient to 140oC by comparing to the reading of reliable portable digital thermometer measuring hot oil.

The designed computer program is able to access the recorded Quick-Basic data file which provide real-time of time-temperature history in cans and retort, and calculate them for lethal rate in every 4.5 second by Simpson's rule of numerical integration to obtain accomplished Fo dynamically during sterilizing. In order to evaluate the accuracy of this program, time-temperature history data was also tested with F-ADDING which is a computer program for calculating Fo coded by Rouweler (2000). The minimum accomplished Fo among all of them from each probe is obtained as system Fo and it is compared simultaneously with the target Fo needed to end the process in the minimum of process time. The flowchart of the algorithm for on-line Fo assessment is shown in figure 5. This approach was accepted as unquestionably the most effective and most certainly the very safest on-line correction when process deviation occurs (Teixeira and Tucker, 1997; Simpson et al., 2007) since thermocouples were used to on-line measure temperature not only retort but also the cans.

Fig. 3. Enhanced A/D multi-lab card & programmable gain amplifier/multiplexer board

Sterilizing Value and Heat Distribution in Retort for Canning Process 385

379

Fig. 5. Program algorithm for dynamic accomplished Fo determination

Fig. 4. Computer-based on-line assessment systems

Fig. 4. Computer-based on-line assessment systems

Fig. 5. Program algorithm for dynamic accomplished Fo determination

Sterilizing Value and Heat Distribution in Retort for Canning Process 387

381

A small vertical retort with diameter of 38.8 cm and electric boiler were constructed for the test as shown in figure 4. The interfacing devices was assembled – interface cards, thermocouples, connectors, computer and peripheral equipments- vertical retort and electric boiler. One probe of thermocouples (probe # 1) were connected to the end tip of mercury thermometer in the retort and one (probe # 8) connected to the center of can which was hot filled with distilled water and then seamed. The rest of them (6 probes) were distributed appropriately inside the retort as shown in figure 6. The on-line graphical display of temperature from 8 thermocouple probes was shown while heating. In addition, the probes # which provides minimum and maximum temperature, as well as maximum temperature difference were indicated through out the heating process. The sterilization temperature at

110 and 121oC were chosen to investigate the heat distribution in the retort.

Fig. 6. Positions of thermocouple probes in heat distribution test

**2.3 Process design and minimum heat accumulation in canned products** 

exposed directly to the temperature of the heating medium in the retort.

Heat accumulation in canned products during sterilizing could be investigated either from their heat penetration profiles or accomplished Fo values. Thus three probes of thermocouples were connected to the cans and located those (3 cans) in the basket since these 3 locations tend to be the cold points of system - probes # 3, 4, and 5 attached to the cans located at the positions 1, 3, and 5 in the basket respectively (figure 7) and probe # 6

The cans were hot filled with concentrated pineapple juice then seamed and put into the basket at specific locations in the retort as mentioned above. The retort was full loaded with the rest of the cans. Specify target sterilizing value was chosen according to product

**2.2 Heat distribution performance in retort** 

Fig. 5. Program algorithm for dynamic accomplished Fo determination (continue)
