University of Houston • University of Houston-Clear Lake • ISSO Annual Report Y2002—pp. 101-104

Monitor and Control of Microbial Growth in a Food Processor Prototype

Clint L. Rappole (UH) and Stephen J. French (NASA)

Abstract
Researchers of the Advanced Food System (AFS) at Johnson Space Center are developing technologies to process raw crops into palatable food items. The Soymilk, Tofu, Okara, and Whey processor (STOW) prototype is the first technology to be evaluated for its ability to make soy related food items. The use of ultra-violet light may assist the AFS in reducing its need for traditional sanitizing agents. The STOW was rebuilt into a stainless steel version and the effects of different ultraviolet light treatments on microbial growth were measured. Results indicate that ultraviolet light would be a significant asset to the AFS in reducing microbial loads. It would also reduce the strain on water recovery systems.

DEVELOPMENT OF EQUIPMENT FOR USE ON LONG DURATION SPACE missions will need to address the issue of sanitation. Reasons for this research extend beyond the typical concerns of earth-based technologies. Equipment will not only need to produce a safe and acceptable product but will also need to conform to limitations on water and energy use. Failure to do so could disrupt balances within a closed environment life support system (CELSS). The Advanced Food System (AFS) is investigating ways of reducing water use and removing chemical cleaner use during the sanitizing of equipment. One of the technologies being considered is ultraviolet (UV) light. UV light renders materials microbiologically safe by disrupting microbe DNA.

The Soymilk, Tofu, Okara, and Whey processor (STOW) prototype is the first piece of equipment to be developed by the AFS for use in CELSS testing. Engineering aspects correlated with production methodologies and Equivalent System Mass (ESM) values are being assessed for the STOW processor prototype. Collection of data analyzing UV light efficacy when incorporated in the STOW will add to the knowledge base regarding the overall suitability of the STOW for CELSS testing.

Research objectives were (1) to determine aerobic bacterial counts in the STOW processor prototype and (2) to gain knowledge concerning the use of alternative sanitation practices.

Methods
In earlier operation, the STOW processor prototype was rendered inoperable through the destruction of heating elements crucial for tofu manufacture. Initially, efforts were diverted in order to reestablish operational ability. In this regard the contribution of funds from ISSO to the Advanced Food System efforts was efficacious and valuable. Funds provided by ISSO enabled a complete rebuilding of the operational hardware and the purchasing of supplies for conducting work in line with the original intent of the project. The rebuild of the STOW converted the operational hardware to a stainless steel form thought to be more durable for purposes of conducting long-term research. An illustration of the initial and current hardware is seen in Fig. 1.

Figure 1. The STOW processor prototype in its initial form (l.) and in its streamlined form (r.)

The resulting STOW prototype represented a smaller and lighter technology in comparison to the initial prototype. Using this equipment, work was conducted on investigating UV light use for sanitation purposes.

Soymilk was made using dried, whole soybeans in water at a 4:1 ratio. The resulting milk was sprayed on the inner surface of one of the tanks used for soymilk manufacture. Researchers applied UV light treatment (24, 1, 0.5, 0.25 or 0 hours) and followed the effort by surface sampling the inner tank using sterile swabs. The inoculated swabs were transported from NASA-JSC to the University of Houston for microbiological processing. The swabs were diluted in 3 mL of peptone broth and vortexed. Samples of 0.1 mL and 0.001 mL were removed and plated on a tryptic soy agar petri plate for enumeration of aerobic microbes. The plates were incubated at 30°C for 24-48 hours and the resulting colonies were counted using a standard colony-counting unit. Results were reported as colony-forming units (CFU). Counts above 250 were reported as too numerous to count (TNTC).

Results and Discussion
Results indicated that relatively little exposure to UV light succeeded in sanitizing the STOW. After observing high microbial counts in a control group, there was a sharp decline after 15 minutes of UV light exposure (Table 1). Randomization of treatment times show that sanitation was significant with any treatment performed and that exposure for longer than 15 minutes did not significantly increase microbial kill. Acomplete listing of results can be seen in Table 2. Based upon this study, a treatment of 15 minutes UV light would be recommended after processing to assist in sanitizing the STOW processor and minimally affect ESM impact.

Table 1. Data samples from three locations (Z1-Z3) within tank using control (C) and fifteen minutes of UV exposure (UV15) at time zero

While sanitizing with UV light was shown to be effective in this study, the approach to the assessment of sanitation using this technology must also be addressed. In this study, soymilk was sprayed on the surfaces of the tank to mimic conditions of microbial distribution. Aspects of this approach are not practical to real world processing techniques but were used for need of an adequate control. First, the application of heating temperatures typical to soymilk production will result in the destruction of microorganisms within the tank. This would aid in reducing the overall microbial load present in the STOW following soymilk production. This load would also be influenced by ubiquitous microorganisms in the equipment (perhaps present from a previous run or from human contact) and within the soybeans provided. The amount present from soybeans may be heavily influenced by growth conditions employed.

Grinding and heating of soybeans/soymilk will inevitably produce particulate matter and foam. Particulate and foam formation will increase the penetration required from the UV source to reach any microorganisms present. Survival of any microorganism through this mechanism would increase the likelihood of growth following production. Therefore, it is recommended that a process for removing physical contamination be implemented in coordination with UV technology to ensure equipment sanitation following a production run. Use of water streams of sufficient strength and/or sonification should be considered for this purpose.

Changes made to the STOW Processor Prototype
Software redesign will incorporate the following features:

• Immediate control of STOW functions upon software initiation.

• Addition of an automation sequence and data logging capability.

• Addition of future hardware add-on capability.

• Increased safety by adding feedback control over heater element.

• Increased safety by removal of electronics from immediate vicinity of liquids.

• Decreased size and weight of control hardware.

Hardware redesign will include the following features:

• Removal of heater elements from grinder head and incorporation into process tank.

• Removal of temperature probe from grinder head and incorporation into process tank.

• Construction of a detachable motor.

• Incorporation of UV lamp into grinder head.

• Incorporation of spray nozzles into coagulation tank inlets.

• Removal of filtration apparatus.

• Removal of the heat exchanger unit.

• Reduction in water inputs (3 to 1) and various supply lines.

• Decrease in overall system mass from 126Kg to 35Kg.

Post-Doctoral Fellows
Dr. Stephen J. French earned his doctorate at the Ohio State University. On March 1, 2003 he accepted a position with a contractor for NASA (Lockheed) in their Space Food Systems Laboratory as a Senior Research Scientist at NASA.

Dr. Elena Vittadini received her doctorate degree from the University of Massachusetts. She is currently a visiting scholar at the Ohio State University. In March, 2003, she accepted a position as a contract professor within the "Brain Drain" program of the Italian Ministry of University Research. This program was created to provide an incentive to return to Italy highly educated (Ph.D.) Italian citizens who had been working and living abroad for at least three years. Her research in Italy will focus on: "Development of Functional Food Products for Space Use." Italy is a member of the European Space Agency (ESA).

Dr. Yael Vodovotz received her doctorate degree from the University of Massachusetts. Dr. Vodovotz is an Assistant Professor at the Ohio State University in the Department of Food Science and Technology. She continues to be an Affiliate Faculty Member with the Commercial Space Center in Ames, Iowa, which has provided funding for research equipment within the laboratory.

Publications
Clubbs, E., E. Vittadini, T. H. Shellhammer, and Y. Vodovotz. "Extending the Shelf-Life of Corn Tortillas: Effects of High Pressure Processing and Added Glycerol," 33rd International Conference on Environmental Systems (ICES), Vancouver, B.C., 2003.
French, S. J. "Standard Operating Procedure Manual for the Soymilk, Tofu, Okara and Whey (STOW) Processor Prototype," NASA document. (In process.)
French, S. J. and M. H. Perchonok. "Bread Making for Long Duration Space Missions: Bran and Protein Content Effects on Loaf Characteristics." (In process.)
French, S. J. and M. H. Perchonok. "Bread Making for Long Duration Space Missions: Equipment Assessment." (In process.)
French, S. J., M. H. Perchonok, and J. L. Greene. "Bread Making for Long Duration Space Missions: Soy Product Incorporation." (In process.)
Vittadini, E. and Y. Vodovotz. "Comparison of Physio-Chemical Properties of Wheat and Soy Containing Breads during Storage as Studied by Thermal Analyses," J. Food Science. (Submitted.)
Vittadini, E., E. Clubbs, J. Sachleben, and Y. Vodovotz. "Effects of High Pressure Treatment and Glycerol on the Physio-Chemical Properties of Corn Tortillas," J. Cereal Science. (In preparation.)

Presentations
Clubbs, E., T. Shellhammer, and Y. Vodovotz. "Effects of Glycerol and Salt on the Physio-Chemical Properties of Corn Tortillas," poster presentation, Institute of Food Technology, Anaheim, CA, June 17, 2002.
Clubbs, E., E. Vittadini, T. H. Shellhammer, and Y. Vodovotz. "Extending the Shelf-Life of Corn Tortillas: Effects of High Pressure Processing and Added Glycerol,’’ 33rd International Conference on Environmental Systems (ICES), Vancouver, B.C., 2003. (Accepted.)
French, S. J. "Bread Making for Long Duration Space Missions," 33rd International Conference on Environmental Systems (ICES), Vancouver, B.C., 2003.
French, S. J. "Current Food-Related NASA Funded Research Projects," Annual Institute of Food Technologists Meeting and Food Expo, Chicago, IL, 2003.
French, S. J. "Soy in the NASA Space Program to Planet Mars," National Soy Research Laboratory, Champaign, IL, 2003.
Vittadini, E., E. Clubbs, J. Sachleben, and Y. Vodovotz. "Effect of High Pressure Treatment and Glycerol on the Physio-Chemical Properties of Corn Tortillas," Symposium of Nuclear Magnetic Resonance in Food Science, Parigi, Sept. 2002.
Vittadini, E., E. Clubbs, J. Sachleben, and Y. Vodovotz. "Effects of High Pressure and Glycerol on the Physico-Chemical Properties of Corn Tortillas," 6th International Conference on Applications of Magnetic Resonance in Food Science, Paris, 2002.
Vodovotz, Y. "Effects of Soy on Bread’s Physio-Chemical Properties during Storage," Institute of Food Technology Annual Conference, Anaheim, CA, June 17, 2002.
Zhang, Y. C., E. Vittadini, J. R. Sachleben, and Y. Vodovotz. "Changes in Water State and Distribution in Soy Containing Bread during Storage," IFTAnnual Meeting, 2003. (Accepted.)

Funding
French, S., M. Perchonok, and C. Rappole. A continuation of the project "Prediction of Processing Parameters of Wheat- Based Food Products with Varying Composition." Center Director’s Discretionary Fund Program, FY 2002, $50,000.
Vodovotz, Y. (Ohio State University) "Model System for Functional Foods: Tomato Products Containing Soy." Co-PI: S. J. Schwartz, M. Failla, S. K. Clinton, J. Bomser, N. H. Hooker, D. Francis, J. Delwiche; USDAInitiative for Future Agriculture and Food Systems Program, 2001-2003, $1,275,000.

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Institute for Space Systems Operations - Y2002 Annual Report
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