**2.2 Heat distribution performance in retort**

386 Food Industrial Processes – Methods and Equipment

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

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**

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

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

Sterilizing Value and Heat Distribution in Retort for Canning Process 389

Connected to probe # 5

383

Connected to probe # 4

Fig. 8. The connecting points to validate the coldest spot in a can

Fig. 9. USB A/D board (NI USB-9211A 4 CH, 24 BIT)

**unit** 

computer (figure 10).

**2.5 Portable educational tools for computer-based off-line assessment of sterilizing** 

The objective of this part was to design the computer program for assessing process lethality from interfacing data system via USB-A/D board. Thus the driver and interfacing program for data logger, National Instrument USB-9211A, 4 Channel 24 bit (figure 9) was installed to a note book computer. The commercial interfacing software was sensing voltage signal through 1 to 4 type-T thermocouples and transforming to digital data stored in a note book

characteristics (table 1) in GUI window. The information about target sterilizing value could be added to the file by pressing updated button. Subsequently sterilization was commenced by removing air in retort by replacing it with steam. Start button in Fo determination GUI window was pressed to begin recording time-temperature data via the interfacing devices until the minimum value of accomplished Fo (system Fo) reached specified target Fo. Thus process schedule was recorded automatically and displayed graphically. Even though concentrated pineapple juice is acid food (pH > 4.0), mild sterilizing is usually sufficient and therefore could be applied. Specified target Fo would be chosen as <sup>10</sup> *<sup>F</sup>*121.1 = 0.6-0.8 minutes (Rouweler, 2000) in this case. However in order to demonstrate the process design with this educational tool, the experiments were carried out with the holding temperature during sterilization selected to be at 110oC and 120oC.

Fig. 7. Location of cans which connected to thermocouples in the bask


Table 1. The characteristics of tested product.

#### **2.4 Coldest spot in container**

To validate the capability of program when it was used to find the coldest spot in a container, the interfacing devices were assembled as before. One of the cans was hard-wired with 2 thermocouple probes: probe# 4 at 1/4 of central axis from bottom of can, and probe# 5 at half of central axis as shown in figure 8 while probe# 6 was for measuring temperature of medium in the retort. This can was filled up with baby corns in saline solution which was solids in liquid type of canned food, and then seamed. The position to put this can in the retort was the slowest heating point of this equipment. After the retort was full loaded with cans, sterilization process was carried out at 121oC for some certain period of time as before, minimum accomplished Fo of which could be obtained.

characteristics (table 1) in GUI window. The information about target sterilizing value could be added to the file by pressing updated button. Subsequently sterilization was commenced by removing air in retort by replacing it with steam. Start button in Fo determination GUI window was pressed to begin recording time-temperature data via the interfacing devices until the minimum value of accomplished Fo (system Fo) reached specified target Fo. Thus process schedule was recorded automatically and displayed graphically. Even though concentrated pineapple juice is acid food (pH > 4.0), mild sterilizing is usually sufficient and therefore could be applied. Specified target Fo would be chosen as <sup>10</sup> *<sup>F</sup>*121.1 = 0.6-0.8 minutes (Rouweler, 2000) in this case. However in order to demonstrate the process design with this educational tool, the experiments were carried out with the holding temperature during

sterilization selected to be at 110oC and 120oC.

Concentrated pineapple

**2.4 Coldest spot in container** 

Table 1. The characteristics of tested product.

minimum accomplished Fo of which could be obtained.

Fig. 7. Location of cans which connected to thermocouples in the bask

Product Can size pH oBrix Sterilizing Temp.(oC)

120

juice 200 x 202 4.06 60.4 <sup>110</sup>

To validate the capability of program when it was used to find the coldest spot in a container, the interfacing devices were assembled as before. One of the cans was hard-wired with 2 thermocouple probes: probe# 4 at 1/4 of central axis from bottom of can, and probe# 5 at half of central axis as shown in figure 8 while probe# 6 was for measuring temperature of medium in the retort. This can was filled up with baby corns in saline solution which was solids in liquid type of canned food, and then seamed. The position to put this can in the retort was the slowest heating point of this equipment. After the retort was full loaded with cans, sterilization process was carried out at 121oC for some certain period of time as before,

Fig. 8. The connecting points to validate the coldest spot in a can

#### **2.5 Portable educational tools for computer-based off-line assessment of sterilizing unit**

The objective of this part was to design the computer program for assessing process lethality from interfacing data system via USB-A/D board. Thus the driver and interfacing program for data logger, National Instrument USB-9211A, 4 Channel 24 bit (figure 9) was installed to a note book computer. The commercial interfacing software was sensing voltage signal through 1 to 4 type-T thermocouples and transforming to digital data stored in a note book computer (figure 10).

Fig. 9. USB A/D board (NI USB-9211A 4 CH, 24 BIT)

Sterilizing Value and Heat Distribution in Retort for Canning Process 391

385

located in the basket at the center of bottom layer as the most probably slowest heating point. However one thermocouple (probe # 1) was exposed in the autoclave indicating medium temperature measurement during sterilizing. Temperature of 121 oC for 15 min was chosen for demonstrating sterilizing condition. Temperatures from 4 channels was recorded and stored in text file (\*.txt) for every 2 seconds after running autoclave until finishing cooling process. QuickCalFo (Chamchong et al., 2008) was software designed to perform the off-line process lethality assessment by using Visual Basic 6.0 program. Input data of temperature and time during sterilization was retrieved from stored text file (figure 12) while target Fo for each product with specific can size was pre-entered and saved into the program or selected from the list of available data before starting analysis for system Fo. The result could display the temperature and time record in a spread sheet as well as heat penetrating curves and lethal rate profiles. Fo values from each temperature-time profile were calculated by Simpson's rule general method and the minimum value was shown in the combo box nearby as system Fo or accomplished Fo. The accuracy of Fo calculation from this software was validated as before by comparing it with that obtained from F-ADDING

program coded by Rouweler (2000).

Fig. 12. Visual Basics form to specified target sterilizing value (Fo)

Fig. 10. Hardware installed for the off-line assessment of sterilizing unit

Fig. 11. The locations of cans connected to thermocouple probes # 2-4 in the autoclave

Tab water samples in 300\*407 size cans were prepared to be full loaded in vertical commercial autoclave (HA-240MII/-300MII, Japan). Three cans were hard-wired to the thermocouple probes # 2-4 at the coldest point of cans (figure 11) and located at possibly slowest heating point in the autoclave. Therefore one of the can attached to probe # 3 was

Fig. 10. Hardware installed for the off-line assessment of sterilizing unit

4

Autoclave

Notebook

2

Fig. 11. The locations of cans connected to thermocouple probes # 2-4 in the autoclave

Tab water samples in 300\*407 size cans were prepared to be full loaded in vertical commercial autoclave (HA-240MII/-300MII, Japan). Three cans were hard-wired to the thermocouple probes # 2-4 at the coldest point of cans (figure 11) and located at possibly slowest heating point in the autoclave. Therefore one of the can attached to probe # 3 was

Upper layer of cans Lower layers of cans

3

USB-A/D Board

located in the basket at the center of bottom layer as the most probably slowest heating point. However one thermocouple (probe # 1) was exposed in the autoclave indicating medium temperature measurement during sterilizing. Temperature of 121 oC for 15 min was chosen for demonstrating sterilizing condition. Temperatures from 4 channels was recorded and stored in text file (\*.txt) for every 2 seconds after running autoclave until finishing cooling process. QuickCalFo (Chamchong et al., 2008) was software designed to perform the off-line process lethality assessment by using Visual Basic 6.0 program. Input data of temperature and time during sterilization was retrieved from stored text file (figure 12) while target Fo for each product with specific can size was pre-entered and saved into the program or selected from the list of available data before starting analysis for system Fo. The result could display the temperature and time record in a spread sheet as well as heat penetrating curves and lethal rate profiles. Fo values from each temperature-time profile were calculated by Simpson's rule general method and the minimum value was shown in the combo box nearby as system Fo or accomplished Fo. The accuracy of Fo calculation from this software was validated as before by comparing it with that obtained from F-ADDING program coded by Rouweler (2000).


Fig. 12. Visual Basics form to specified target sterilizing value (Fo)

Sterilizing Value and Heat Distribution in Retort for Canning Process 393

387

The software package for process design was divided into 3 parts: (1) the main window of the GUI to receive the input parameter which is target sterilizing value. The user can choose this value from pull down combo box or add/delete and update to have more choices for later use (figure 12). (2) Graphical window of temperature and time profiles with 8 corresponded text boxes to display accomplished sterilizing values from maximum 8 probes (figure 13). There is one text box at the bottom to display system sterilizing value which is the minimum value among all of accomplished sterilizing values from each probe. System sterilizing value increases while the process is underway heating and cooling and ultimately reaches the designated target sterilizing value. Program then displays text message at the bottom of GUI for the operator to stop steaming and total process time during heating is shown in upper right corner text box. The temperature and time record can be used for process design or as documentation in quality assurance system. (3) The spread sheet of temperature-time recorded from 8 thermocouple probes which could display minimum and maximum temperature, as well as maximum temperature difference (max-min) at each time

Fig. 14. Real-time heat distributions in retort, record from 8 thermocouple probes

Practically heat distribution in a retort should be carried out before performing the assessment of sterilizing value of the process in order to validate the slowest heating point. Therefore heat distribution in a retort (as in part 3 from mentioned above) was observed from on-line temperature record obtained from different locations of this equipment. For sterilizing at 110oC in a small retort unit distributed heat could be indicated by temperature values at positions 1-8 in the retort corresponding to probe # 1-8 (figure 6). In addition minimum heating reading from thermocouple probe which was connected to the can located at the slowest heating point was able to be quantified as the accomplished Fo for the

**3.1 Computer-based on-line assessment of sterilizing value** 

interval through out the heating process (figure 14).

**3. Results and discussion** 

**3.2 Heat distribution in retort** 

Fig. 13. Real-time heat penetration curve and Fo of concentrated pineapple juice when sterilizing at (a) 110 C (b) 120C
