High Pressure Processing of Low Acid Foods

NON-TECHNICAL SUMMARY: Canning has been the technology of choice for commercial sterilization of shelf-stable low-acid foods. The harsher thermal treatment often significantly deteriorates product quality and heat sensitive ingredients. Pressure assisted thermal processing (PATP), is an emerging sterilization technology that utilize combination of intense pressure (500-700 MPa) and heat (90-120oC) to preserve shelf-stable low-acid foods. Soups, egg products, coffee, tea, vegetables, meat, sauces, and mashed potatoes are examples of products that can be preserved using this technology. The overall objective of the research is to document PATP process conditions would ensure commercial sterility of PATP low-acid shelf stable food products. The least treated zones inside a a pilot scale high pressure sterilization unit will be investigated. Combined pressure-thermal B. amyloliquefaciens spore inactivation data will be fitted using traditional linear and nonlinear (example-Weibull's model) models. The model is expected to be useful in obtaining microbial lethality at varying pressure-heat conditions and potentially can be used as an aid for industry process validation filing with regulatory agencies. Studies will investigate the influence of food matrix, pH, water activity on PATP spore lethality. Bactericidal, and sporostatic effect of selected antimicrobial compounds will be investigated. Flow cytometry will be used to detect, enumerate and study spore germination during PATP. Structural and biochemical changes occurring during thermal and PATP treatments will be monitored by evaluating the IR spectra. The impact of transient pH shift under pressure on spore inactivation will be considered. The influence of vegetable tissue structure on process uniformity will be evaluated. Investigator will seek industrial and regulatory authority guidance and feedback on research each year through Center for Advanced Processing and Packaging Studies, IFT Nonthermal Processing Division and other industrial interactions. Improved knowledge on mechanism of spore inactivation during PATP, will help identify process conditions that may lead to enhanced spore lethality. Process nonuniformity studies could help minimize the presence of least processed zone within pressure vessel. The results of the study would further help to define optimum combination of pressure-heat treatment needed to achieve commercial sterility and the maximum retention of product quality attributes. <P>
APPROACH: The temperature non-uniformity within a pilot scale high pressure processor will be investigated. A chemical marker based technique, which utilize a browning reaction between a simple sugar and an amino acid (Maillard reaction), will be used for evaluating PATP process uniformity. Combined pressure-thermal B. amyloliquefaciens spore inactivation data will be fitted using traditional linear and nonlinear models. Studies will investigate the influence of food matrix, pH, and water activity on PATP spore lethality. Bactericidal and sporostatic effect of selected antimicrobial compounds will be investigated. Inoculated studies will evaluate the storage stability of PATP processed samples. Flow cytometry will be used to detect, enumerate and study spore germination process and can be an effective technique to study the physiological changes of spores treated by PATP. Structural and biochemical changes occurring during thermal and PATP treatments will be monitored by evaluating the IR spectra. The impact of transient pH shift under pressure on spore inactivation will be considered. The influence of vegetable tissue structure on process uniformity will be evaluated. Investigator will seek industrial and regulatory authority guidance and feedback on research output each year through Center for Advanced Processing and Packaging Studies,IFT Nonthermal Processing Division and other similar industrial interactions. <P>PROGRESS: 2007/01 TO 2007/12 <BR>
OUTPUTS: Pressure-assisted thermal processing (PATP) is a promising emerging technology for production of commercially sterile low-acid shelf-stable foods with minimal thermal impact on product quality. The inactivation and recovery of PATP-treated Bacillus amyloliquefaciens spores in selected low-acid foods (egg patty mince and green pea puree) during extended product storage was studied. Mechanism of spore inactivation during PATP was studied by studying infrared absorption bands. In-situ properties (thermal conductivity, reaction volume,pH and density) of food materials under pressure were studied. The efficacy of pressure treatment in preserving selected instrumental quality attributes of carrots was investigated. Microscopic examination of the product was carried out to investigate extend of thermal damage in PATP samples. Raghupathy Ramaswamy (PhD) and Maria Villacis (MS) completed research on high pressure processing and completed their degrees. Dr. Ramaswamy is currently employed by Auvre Technologies, Kent, WA. Ms. Villacis is employed by Nestle. Technology transfer occurred in the form of pilot plant demonstrations as well as one-on-one meetings with interested food processors. Research was disseminated in the form of nine peer-reviewed journal articles. Results of the study was further disseminated to the food industry through 2007 IFT short course on nonthermal processing and 2008 Nonthermal workshop held at Portland, OR. <BR> PARTICIPANTS: PI: Balasubramaniam VM Faculty Collaborators: Sastry, SK; Yousef, AY; Rodriguez-Saona, L. E Researchers: Rastogi, NK; Ahn, J; Nguyen, L.; Stephen Min; Maria Villacis. <BR> TARGET AUDIENCES: Spore inactivation research will help the industry and regulators in establishing criteria for safe processing of low-acid shelf-stable food products by high pressure sterilization. Insitu property study under pressure contributed to database on properties of complex food materials under pressure and improved our knowledge on thermal distributions during high-pressure sterilization. Food quality research will help the food industry in evaluating the quality of low-acid shelf stable food products treated by high pressure sterilization. <BR> PROJECT MODIFICATIONS: Not relevant to this project.
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IMPACT: 2007/01 TO 2007/12 <BR>
Pressure (700 MPa) treatment in combination with heat (105-121C) beyond selected pressure holding times decreased B. amyloliquefaciens populations to undetectable levels by the enrichment procedure. An FTIR spectroscopy analysis revealed that during PATP, changes in á-helix and â-sheets of secondary protein were evident in specific spectral regions. Thermal conductivity and density of all samples increased as a function of pressure. Among the products tested, carrot had the highest thermal conductivity at 700 MPa and 75C, while chicken fat had the lowest k under similar conditions. pH change from 0.1 to 400 MPa was -0.48 for citric acid, -1.09 for phosphoric acid, 0.28 for MES, and -0.01 for sulfanilic acid. In comparison to thermal processing (TP), PATP better retained color of carrot samples. During TP, carotene content decreased from 17.7 to 13.2 mg/100g, however, in case of PATP (700 MPa-105C) carotene content decreased from 17.7 to 14.1 mg/100g. Both PATP and TP completely inactivated natural flora present in the samples. Under comparable process temperatures (up to 105C), PATP protected carrot quality attributes better than TP samples. The results of the study will help the regulators and the food industry scientists to evaluate the microbial efficacy of pressure-sterilized products. The study helped to document the role of thermal gradient on PATP process non-uniformity. The study provided insight on extend of tissue softening and quality degradation after PATP treatment.
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PROGRESS: 2006/01/01 TO 2006/12/31 <BR>
The combined pressure-thermal inactivation kinetics of spores from three strains of anaerobic (Clostridium sporogenes, C. tyrobutylicum, and Thermoanaerobacterium thermosaccharolyticum), and six strains of aerobic (Bacillus amyloliquefaciens and B. sphaericus) bacteria were studied. Survivor data were modeled using log-linear and Weibull models to obtain relevant kinetic parameters. In comparison to thermal treatment alone, the combined pressure-thermal conditions accelerated the inactivation of the spores tested. A measurable fraction of spore populations was inactivated during the pressure come-up time. Pressure-assisted thermal processing (PATP) at 700 MPa and 121C for 1 min inactivated up to 7-8 log for some of spores tested. Among bacteria evaluated, based on survivor curve data T. thermosaccharolyticum, B. amyloliquefaciens Fad 82, and Fad 11/2 were found to produce the most PATP-resistant spores. Thermal conductivity (k) and density of selected food materials were estimated under combined pressure-temperature conditions using a line heat source probe (for thermal conductivity measurements) and variable volume piezometer (for density measurements). Combined pressure-temperature treatment increased k values of tested food materials. At 700 MPa, food samples reduced in volume by 14-16%. Density of all samples at 25C increased as a function of pressure and was characterized by a second order polynomial. A study was conducted to evaluate the efficacy of pressure treatment (500 to 700 MPa) in preserving selected instrumental quality attributes of carrots under comparable process temperature (95-121C). In comparison to TP, PATP better retained color of carrot samples. Combined pressure-thermal treatment resulted in decrease in carotene content; however, the reduction was lower as compared to TP. Natural flora present in carrot samples were completely inactivated for both PATP and TP treatments. Under comparable process temperatures (up to 105C), PATP protected carrot quality attributes better than TP samples. At 121C, process and pre-process thermal history greatly influenced carrot textural change and pressure protective effects were less pronounced. PATP is a potential alternative for producing superior quality shelf-stable low-acid foods.
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IMPACT: 2006/01/01 TO 2006/12/31 <BR>
Pressure-assisted thermal processing can inactivate harmful bacterial spores, at temperatures less than those needed for retorting, and potentially without the use of chemical preservatives. The realization of this potential can benefit consumers by providing safe and better tasting shelf-stable foods such as soups and meat entrees in lighter containers. In-situ property measurement studies will provide an improved body of knowledge on thermal distributions during high-pressure processing, physico-chemical changes in foods under pressure, and facilitate development of database on properties of complex food materials under pressure.
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PROGRESS: 2005/01/01 TO 2005/12/31 <BR>
The combined pressure-thermal inactivation kinetics of spores from three strains of anaerobic (Clostridium sporogenes, C. tyrobutylicum, and Thermoanaerobacterium thermosaccharolyticum), and six strains of aerobic (Bacillus amyloliquefaciens and B. sphaericus) bacteria were studied. Spores of these bacteria were prepared in deionized water or minced egg patty and treated in a custom-made kinetic tester over various pressure (0.1 and 700 MPa) and thermal (105 and 121C) combinations. Survivor data were modeled using log-linear and Weibull models to obtain relevant kinetic parameters. In comparison to thermal treatment alone, the combined pressure-thermal conditions accelerated the inactivation of the spores tested. Spores became less sensitive to pressure changes at higher temperatures. A measurable fraction of spore populations was inactivated during the pressure come-up time. Pressure-assisted thermal processing (PATP) at 700 MPa and 121C for 1 min inactivated up to 7-8 log for some of spores tested. Among bacteria evaluated, T. thermosaccharolyticum, B. amyloliquefaciens Fad 82, and Fad 11/2 were found to produce the most PATP resistant organisms. PATP inactivation plots showed characteristic upward curvature, which is indicative of the tailing behavior. The developed kinetic model parameters for various aerobic and anaerobic spores under well-defined pressure-thermal conditions could be used for the evaluation of various critical PATP parameters. Experiments underway for in-situ measurement of thermal conductivity, compression heating, and electrical conductivity of selected liquid foods under elevated pressure. Experiments were conducted using custom fabricated high-pressure equipment. Thermal conductivity of the tested food materials increased linearly with increase in pressure. Compression heating values of polar liquids exhibited a linear trend with increase in pressure and a non-linear trend was observed with non-polar liquids and fatty acids. Among the liquids with varying polarity, compression-heating values decreased with increasing polarity index during high pressure processing. For 0.1m NaCl at 25C, electrical conductivity increased as a function of pressure from 1.13 S/m at 0.1MPa to 1.35 S/m at 400 MPa and 1.18 S/m at 800 MPa. Studies are in progress to evaluate thermal and electrical conductivity values of liquid foods.
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IMPACT: 2005/01/01 TO 2005/12/31 <BR>
Pressure-assisted thermal processing can inactivate harmful bacterial spores, at temperatures less than those needed for retorting, and potentially without the use of chemical preservatives. The realization of this potential can benefit consumers by providing safe and better tasting shelf-stable foods such as soups and meat entrees in lighter containers. In-situ property measurement studies will provide an improved body of knowledge on thermal distributions during high-pressure processing, physico-chemical changes in foods under pressure, and facilitate development of database on properties of complex food materials under pressure.

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PROGRESS: 2004/01/01 TO 2004/12/31 <BR>
Resistance of selected Bacillus spores to pressure assisted thermal processing (PATP) was studied. Spores suspended in de-ionized water or food matrix were preheated to a predetermined temperature and pressure processed using a high-pressure food processor at 700 MPa to 105C, 90C, and 70C. Pressure holding times ranged from 0-5 minutes. Thermal spore inactivation studies were also conducted for at 121.1C, 100C, and 70C. Viable spores in processed samples in all cases were enumerated after 48 h using plate count agar with incubation temperatures of 37C for B. polymyxa and B. subtilis; and 55C for B. stearothermophilus. Transmission Electron microscopy (TEM) images of treated spores were obtained to compare the nature of damage caused by different treatments. PATP accelerated the inactivation for all Bacillus (B. stearothermophilus, B. polymyxa, B. subtilis) spores when compared to the thermal treatment alone. Among the Bacilli spp. tested, B. stearothermophilus seems to be the most PATP resistance. It had a decimal reduction time of 0.29 min at 105C/700MPa. Heat shocking did not seem to contribute to the lethality of PATP, with the exception of B. polymyxa where heat shocking caused an additional one-log reduction. TEM images showed more profound damage to the core of certain spores due to PATP treatment. While thermal inactivation of spores followed first- order kinetics, PATP inactivation exhibited non-linear death behavior. Among the models (Modified Gompertz equation, Weibull and Log-logistic equation) tested Weibull model described best PATP inactivation of B. stearothermophilus spores in egg. Experiments are in progress to estimate the combined pressure-thermal resistance of non-pathogenic surrogate Clostridium spores.
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IMPACT: 2004/01/01 TO 2004/12/31 <BR>
Pressure-assisted thermal processing can inactivate harmful bacterial spores, at temperatures less than those needed for retorting, and potentially without the use of chemical preservatives. The realization of this potential can benefit consumers by providing safe and better tasting shelf-stable foods such as soups and meat entrees in lighter containers.
<BR> <BR> PROGRESS: 2003/01/01 TO 2003/12/31 <BR>
A custom designed mini-high pressure sterilization tester is being fabricated. The unit can precisely control the pressure-temperature during process treatment. Chamber volume is about 20 ml. Maximum pressure limit of the unit is 700 MPa and can process food samples up to a process temperature of 125C. Studies are in progress to evaluate the feasibility of producing shelf-stable egg products using a pilot scale QFP-6 high pressure food processor. Experiments were conducted to evaluate two different pre-heat techniques on quality of pressure processed eggs. Screening studies with various Bacillus and Clostridium spores for combined pressure-temperature resistance in model and food substances is also under progress.
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IMPACT: 2003/01/01 TO 2003/12/31 <BR>
Pressure-assisted thermal processing can inactivate harmful bacterial spores, at temperatures less than those needed for retorting, and potentially without the use of chemical preservatives. The realization of this potential can benefit consumers by providing safe and better tasting shelf-stable foods such as soups and meat entrees in lighter containers.