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

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 interval through out the heating process (figure 14).


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

#### **3.2 Heat distribution in retort**

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

Sterilizing Value and Heat Distribution in Retort for Canning Process 395

1.29, 1.91 and 2.29 minutes, respectively, while the one outside the can was 3.53 minutes. Thus this was assuring that the coldest point was from the position 1 or at the bottom layer of cans and at the center of the basket. To get enough heat treatment for the products, heat distribution test must be carried out once the machine was installed or process/product was

sterilizing at 110C (min)

Table 2. Process design or schedule obtained from heat penetration curve of concentrated

From heat penetration curve, Fo of the system represents the minimum accumulated heat at coldest point of can in the retort. As in figure 13 (a) and (b), system Fo was obtained from different probes or positions of cans i.e. probe # 3 (position 1) from figure 13 (a) and probe # 5 (position 5) from figure 13 (b), the Fo of which were 1.29 and 0.94 minutes respectively. According to the steam flow pattern of this retort shown in figure 15, the cans located at positions 1 and 5 were supposed to be at the stagnation points and had minimum convective heat accumulation in each run. However the minimum accumulated heating

Come-up time 2.5 2.5 Holding period 7.5 2.0 Cooling period 7.0 1.5 Total process time 10.0 4.5 Calculated system Fo 1.29 0.94 Remark: Calculated system Fo is including come-up time, holding and cooling period.

Time used during sterilizing at 120C (min)

389

Sterilizing period Time used during

Total process time does not include cooling period.

pineapple juice when target Fo = 0.7 minutes

Fig. 15. Configuration of steam flow pattern in retort

modified.

system. Then it could be used as an indicator for stopping steaming. Therefore the display was able to assure the minimum heat distribution occurring while heating. The coldest point of the system should be coming from the can which had the thermocouple connected with and was located at position 8 or at the upper layer of cans and at the center of the basket. To get enough heat treatment for the products, heat distribution test must be carried out once the machine was installed or process/product was modified.

For the same retort, it was found that when holding temperature of sterilization was moderate at 110oC heat distribution was more uniform than that at 121oC. Temperature difference from max and min at any holding time or temperature deviation was between 1.8 to 3.1oC (1.6-2.8%) when sterilizing temperature was at 110oC but it was between 5-14oC (4.1-11.6%) at 121oC sterilizing temperature. This was possible since heating at 121oC required higher heating rate. However more of stagnant point or dead legs would appear. According to the steam flow pattern in this retort, the probe located at positions 3 (on top of the can which was at the center of basket) and 6 (upper layer and in between cans) were found to be the stagnation points and shown minimum convective heat transfer in each run at higher sterilizing temperature. However the minimum heating point for lower sterilizing temperature was found to get changed to be either position 5 or 2 (top of the retort) at the early stage of holding temperature in sterilizing period and then changed to location 3 for the rest of holding time. This was possible because the more amount of steam used during heating at 121oC, the narrower the stagnation area would be. In addition, when lower amount of steam used at 110 oC sterilizing temperature, the probes at position 5 and 2 in the top layer of cans initially would get contacted with steam slower than any other locations. After heating at this temperature for a while, heating was up to the top of retort. Temperature at position 5 and 2 would be no longer the minimum.

However the exit point of coming steaming was from the bottom. Whenever steam valve was not fully opened the thermocouples in the lower layer would be affected or heated first. Therefore accomplished Fo obtained from the can at the center upper layer of the basket was suitable to be system Fo because the temperature from the probe nearby (probe 3) had demonstrated minimum heat received.

#### **3.3 Process design or schedule and minimum heat accumulation in canned products**

The process design or schedule of acid food like concentrated pineapple juice was shown in table 2. The obtained process time of sterilizing acid food at 110 and 120oC was 10 and 4.5 minutes excluding cooling period respectively. At higher sterilizing temperature (120oC), it was shorter than that at lower temperature (110oC) since both were calculated based on the same specified target Fo (0.7 minutes) or having the same area under the heat penetration curve before stopping steaming. Although the specified target sterilizing value for such a product was chosen to be 0.7 minutes but Fo of the system obtained was 1.29 and 0.94 minutes for sterilizing at 110 and 120oC, respectively. This was because the calculation was including come-up time, holding and cooling period. Thus a little over-process could occur in each run since there was slow removal of heat during cooling. Improved and proper design of cooling system in the retort would provide better product quality in terms of organoleptic properties.

Heat accumulation in canned products can be observed from all accomplished Fo values obtained from different locations in retort. For sterilizing at 110oC in figure 13 (a), accumulated heat which could be indicated by accomplished Fo at positions 1, 3, and 5 were

system. Then it could be used as an indicator for stopping steaming. Therefore the display was able to assure the minimum heat distribution occurring while heating. The coldest point of the system should be coming from the can which had the thermocouple connected with and was located at position 8 or at the upper layer of cans and at the center of the basket. To get enough heat treatment for the products, heat distribution test must be carried out once

For the same retort, it was found that when holding temperature of sterilization was moderate at 110oC heat distribution was more uniform than that at 121oC. Temperature difference from max and min at any holding time or temperature deviation was between 1.8 to 3.1oC (1.6-2.8%) when sterilizing temperature was at 110oC but it was between 5-14oC (4.1-11.6%) at 121oC sterilizing temperature. This was possible since heating at 121oC required higher heating rate. However more of stagnant point or dead legs would appear. According to the steam flow pattern in this retort, the probe located at positions 3 (on top of the can which was at the center of basket) and 6 (upper layer and in between cans) were found to be the stagnation points and shown minimum convective heat transfer in each run at higher sterilizing temperature. However the minimum heating point for lower sterilizing temperature was found to get changed to be either position 5 or 2 (top of the retort) at the early stage of holding temperature in sterilizing period and then changed to location 3 for the rest of holding time. This was possible because the more amount of steam used during heating at 121oC, the narrower the stagnation area would be. In addition, when lower amount of steam used at 110 oC sterilizing temperature, the probes at position 5 and 2 in the top layer of cans initially would get contacted with steam slower than any other locations. After heating at this temperature for a while, heating was up to the top of retort.

However the exit point of coming steaming was from the bottom. Whenever steam valve was not fully opened the thermocouples in the lower layer would be affected or heated first. Therefore accomplished Fo obtained from the can at the center upper layer of the basket was suitable to be system Fo because the temperature from the probe nearby (probe 3) had

**3.3 Process design or schedule and minimum heat accumulation in canned products**  The process design or schedule of acid food like concentrated pineapple juice was shown in table 2. The obtained process time of sterilizing acid food at 110 and 120oC was 10 and 4.5 minutes excluding cooling period respectively. At higher sterilizing temperature (120oC), it was shorter than that at lower temperature (110oC) since both were calculated based on the same specified target Fo (0.7 minutes) or having the same area under the heat penetration curve before stopping steaming. Although the specified target sterilizing value for such a product was chosen to be 0.7 minutes but Fo of the system obtained was 1.29 and 0.94 minutes for sterilizing at 110 and 120oC, respectively. This was because the calculation was including come-up time, holding and cooling period. Thus a little over-process could occur in each run since there was slow removal of heat during cooling. Improved and proper design of cooling system in the retort would provide better product quality in terms of

Heat accumulation in canned products can be observed from all accomplished Fo values obtained from different locations in retort. For sterilizing at 110oC in figure 13 (a), accumulated heat which could be indicated by accomplished Fo at positions 1, 3, and 5 were

the machine was installed or process/product was modified.

Temperature at position 5 and 2 would be no longer the minimum.

demonstrated minimum heat received.

organoleptic properties.

1.29, 1.91 and 2.29 minutes, respectively, while the one outside the can was 3.53 minutes. Thus this was assuring that the coldest point was from the position 1 or at the bottom layer of cans and at the center of the basket. To get enough heat treatment for the products, heat distribution test must be carried out once the machine was installed or process/product was modified.


Remark: Calculated system Fo is including come-up time, holding and cooling period. Total process time does not include cooling period.

Table 2. Process design or schedule obtained from heat penetration curve of concentrated pineapple juice when target Fo = 0.7 minutes

Fig. 15. Configuration of steam flow pattern in retort

From heat penetration curve, Fo of the system represents the minimum accumulated heat at coldest point of can in the retort. As in figure 13 (a) and (b), system Fo was obtained from different probes or positions of cans i.e. probe # 3 (position 1) from figure 13 (a) and probe # 5 (position 5) from figure 13 (b), the Fo of which were 1.29 and 0.94 minutes respectively. According to the steam flow pattern of this retort shown in figure 15, the cans located at positions 1 and 5 were supposed to be at the stagnation points and had minimum convective heat accumulation in each run. However the minimum accumulated heating

Sterilizing Value and Heat Distribution in Retort for Canning Process 397

391

Fig. 16. Temperature and time display in real time recording via USB-A/D board

Fig. 17. Recorded data obtain via USB-A/D board

point was found to get changed from position 1 located at the bottom center of the basket to position 5 located at the upper center of the basket while sterilizing at higher temperature. This was possible because the more amount of steam used during heating at 120oC, the narrower the stagnation area would be. In addition, while cooling, the can at position 5 (top layer of cans) would get contacted with blowing air into retort during balancing pressure right after stop steaming. Therefore system Fo would be obtained from the can at the center upper layer of the basket due to smaller heat accumulation. However cold water could significantly enhance heat removal when it was leveled up to that position in retort.

#### **3.4 Coldest spot in a container**

The sterilizing values at 2 different points could be used as indicated tool to validate the coldest spot in a container while undergo sterilizing process. As shown in figure 8 the can was instrumented with 2 thermocouple probes and hard-wired through a retort. Probe# 4 was at 1/4 of central axis from bottom of can, and probe# 5 was at the half of central axis while probe# 6 was for measuring temperature in the retort. It was found that temperature rising and dropping from probes #4 and 5 were almost identical and hard to distinguish. In addition, during sterilizing there were 3 main different periods of operations – come-up time, holding at sterilizing temperature and cooling periods. Heating rate at different period through the can and different spot in the can could be varied. Thus practically coldest spot in the can may not be the same point at all the time. However minimum accumulated heat in the can need to be known since it was used as critical point to evaluate for enough heat treatment of the process. Thus minimum sterilizing value was useful and reliable to represent the minimum accumulated heating point in the can. From table 3, the sterilizing values corresponding to probes # 4, 5 and 6 were 3.69, 2.85 and 9.54 minutes respectively. According to the meaning of accomplished sterilizing value of the process, the coldest spot was found from the minimum value (2.85). So for this type of food, baby corns in saline solution, heat transfer was the slowest at half of central axis of container.


Table 3. Validation of coldest spot in the can by sterilizing value

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

The temperature and time logging on-line was displayed as in figure 16 but they were retrieved off-line as a text file shown in figure 17. Then Fo was calculated from these data which were coming from thermocouple probes connected to 3 cans and one exposed to heating medium in the autoclave. From QuickCalFo as shown in figure 18, it showed that the slowest heating point in the retort was from thermocouple probe # 3 which was attached to the can located at the center bottom layer of the basket in the autoclave. Thus the accomplished sterilizing value or system Fo was chosen from the minimum of 12.81 minutes among all from 4 thermocouple probes. In analysis Fo frame box at the bottom right corner, the message after

point was found to get changed from position 1 located at the bottom center of the basket to position 5 located at the upper center of the basket while sterilizing at higher temperature. This was possible because the more amount of steam used during heating at 120oC, the narrower the stagnation area would be. In addition, while cooling, the can at position 5 (top layer of cans) would get contacted with blowing air into retort during balancing pressure right after stop steaming. Therefore system Fo would be obtained from the can at the center upper layer of the basket due to smaller heat accumulation. However cold water could

The sterilizing values at 2 different points could be used as indicated tool to validate the coldest spot in a container while undergo sterilizing process. As shown in figure 8 the can was instrumented with 2 thermocouple probes and hard-wired through a retort. Probe# 4 was at 1/4 of central axis from bottom of can, and probe# 5 was at the half of central axis while probe# 6 was for measuring temperature in the retort. It was found that temperature rising and dropping from probes #4 and 5 were almost identical and hard to distinguish. In addition, during sterilizing there were 3 main different periods of operations – come-up time, holding at sterilizing temperature and cooling periods. Heating rate at different period through the can and different spot in the can could be varied. Thus practically coldest spot in the can may not be the same point at all the time. However minimum accumulated heat in the can need to be known since it was used as critical point to evaluate for enough heat treatment of the process. Thus minimum sterilizing value was useful and reliable to represent the minimum accumulated heating point in the can. From table 3, the sterilizing values corresponding to probes # 4, 5 and 6 were 3.69, 2.85 and 9.54 minutes respectively. According to the meaning of accomplished sterilizing value of the process, the coldest spot was found from the minimum value (2.85). So for this type of food, baby corns in saline

Probe # Connecting point Sterilizing value at 121<sup>C</sup>

4 1/4 of central axis from bottom of can 3.69 5 the half of central axis of can 2.85 6 Exposed to heating medium in retort 9.54

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

The temperature and time logging on-line was displayed as in figure 16 but they were retrieved off-line as a text file shown in figure 17. Then Fo was calculated from these data which were coming from thermocouple probes connected to 3 cans and one exposed to heating medium in the autoclave. From QuickCalFo as shown in figure 18, it showed that the slowest heating point in the retort was from thermocouple probe # 3 which was attached to the can located at the center bottom layer of the basket in the autoclave. Thus the accomplished sterilizing value or system Fo was chosen from the minimum of 12.81 minutes among all from 4 thermocouple probes. In analysis Fo frame box at the bottom right corner,

(min)

significantly enhance heat removal when it was leveled up to that position in retort.

solution, heat transfer was the slowest at half of central axis of container.

Table 3. Validation of coldest spot in the can by sterilizing value

**3.4 Coldest spot in a container** 

**unit** 

the message after

Fig. 16. Temperature and time display in real time recording via USB-A/D board


Fig. 17. Recorded data obtain via USB-A/D board

Sterilizing Value and Heat Distribution in Retort for Canning Process 399

393

Coldest spot in a container during sterilization process can be verified by employing sterilizing value (Fo). The minimum of these values is corresponding to the point in the can which has the lowest accumulated heat. The coldest spot in the can of baby corns in saline solution while undergo sterilizing was confirmed to be at half of central axis of can by

Portable or handy educational tools for sterilizing process was necessary to be available since most of the processes may routinely carry out for the same process schedule. The

This study was supported by faculty of Engineering at Kamphaengsaen, Kasetsart

Anonymous. (January 2011). TechniCAL. Consulting Services and Products for Food

Awuah, G. B., H. S. Ramaswamy and A. Economides. 2007. Thermal Processing and Quality : Principles and Overview. *Chemical Engineering and Processing*, 46 , pp. 584-602. Balaban, M. O. (March 2004). Software for Food Engineering. Thermal Processing. 15 January 2008, Available from http://mob.ifas.ufl.edu/SOFTWARE.HTM Bichier, J. G., A. A. Teixeira, M. O. Balaban and T. L. Heyliger. 1995. Thermal Process

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Datta, A. K., A. A. Teixeira and J. E. Manson. 1986. Computer-based Retort Control Logic for On-line Correction of Process Deviations. Journal of Food Science, 51, pp. 480-483. Lappo, B. P. and M. J. W. Povey. 1986. Microprocessor Control system for Thermal

Noronha, J., M. Hendricks, A. van Loey and P. Tobback. 1995. New Semi-empirical

Non-conductive Heating Foods. *Journal of Food Engineering*, 24, pp. 249-268. Rouweler, J. 2000. Main Unit Operations in Food Processing. Material handout in 10th

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Sterilization Operations. *Journal of Food Engineering*, 5, pp. 31-53.

Simulation of Canned Foods under Mechanical Agitation*. Journal of Food Process* 

Process Lethality (Fo) Assessment from Interfacing Data System via USB-A/D Board. Engineering Project. Department of Food Engineering. Faculty of Engineering at Kamphaengsaen. Kasetsart University. Nakhon Pathom, Thailand. Chen, C. R. and H. S. Ramaswamy. 2007. Visual Basics Computer Simulation Package for

Thermal Process Calculations. Chemical Engineering and Processing, 46 ,pp. 603-

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International Course on Food Processing. International Agricultural Centre.

computer Control of Canned Food Sterilization. *Journal of Food Engineering*, Vol. 19,

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http://www.tcal.com/CALSoftSoftware.php

*Engineering*, Vol. 18, No.1, pp. 17-40.

Wageningen, The Netherlands.

No. 1, pp. 75-94.

committing minimum value of Fo.

**5. Acknowledgement** 

**6. References** 

613.

result could be used to assure food safety control.

University, Nakhon Pathom 73140 Thailand.

analyzing indicated whether the product had enough heat treatment or not. To display temperature and time as a spread sheet on the left side of this figure, time interval of data was selected first at the bottom between in every 1, 2 or 5 minutes. Then the temperature and time only at this specific interval was shown in the spread sheet of GUI. Heat penetration and lethal rate profiles from all 4 probes were also displayed graphically. The x and y range of these 2 graphs were adjusted automatically according to process temperature and time span used. In addition, this visual basic form could be printed out for food safety documents.

Fig. 18. The result displayed by QuickCalFo
