Progress 01/01/14 to 12/31/18
Outputs
Target Audience:Manufacturers of low-moisture foods, Radiofrequency equipment manufacturers Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The graduate student was trained in interdisciplinary research that involves engineering (novel radiofrequency processing), microbiology (safety), and chemistry (quality). How have the results been disseminated to communities of interest?In addition to publishing and presenting results, we have disseminated the results to Henningsen Foods, manufacturer of egg white powders. Henningsen Food is intrigued by improvement in gelling properties of egg white powder and is currently considering funding further studies to identify RF process parameters and scaling-up to industry. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Traditional thermal processing has limitations in pasteurizing low-moistureproducts because of low thermal conductivity and high thermal resistance of the foodborne pathogens. Radio frequency (RF) waves heat these products rapidly and volumetrically, and thereforeit is feasible to develop high-temperature short-time processes. Even though, few studies have demonstrated benefits of RF processing in lab-scale batch processing, heating non-uniformity and arcing have been the major issues limiting the successful deployment of this technology. In the past, several feasibility studies have been focused on batch processes and therefore seldom addressed industrial feasibility.This project focusedon developing continuous processing of egg white powder (EWP) and cumin seeds for imporving microbiological safety with minimal deterioration in food quality. A. Continuous radio-frequency pasteurization of egg white powder: Traditionally, EWP is pasteurized by placingpackaged productin a hot room at 58°C to 60°C for 10 to 14 days. This long process is energy intensive. RF-assisted thermal processing was investigatewd to develop high-temperature and short-time pasteurization method. 1) Major activities completed / experiments conducted; Continuous RF processing was evaluated for pasteurization of EWP. EWP samples were inoculated with five different strains of Salmonella cocktail or Enterococcus faecium NRRL B-2354 for the microbial challenge studies. A cardboard box (140 x 103 x 132 mm3) was used to package the EWP sample (550 ± 0.1 g) which was approximately 1/20 scale of the commercial package size to simulate the industrial hot room pasteurization package conditions of EWP. RF heating was conducted in a 6 kW, 27.12 MHz pilot-scale parallel-plate RF heating system (Model SO-6B, Monga Strayfield Pvt. Ltd., Pune, India). To evaluate the inoculation method, stability and homogeneity tests were conducted for 15 days for both Salmonella and E. faecium in EWP. 2) Data collected; Stability and homogeneity of microbial inoculation wastested for 15 days. On day 0, 1, 2, 3, 6, 9, 12, 15, three aliquots of the EWP samples (3.0 ± 0.1 g) on each tray were randomly picked and packed by Whirl-Pak bags. Then, the sample was diluted by adding 27 mL 0.1% BPW, stomached for 1 min in a stomacher (Neutec Group Inc, NY, USA), duplicate-plated onto TSAYE supplemented with 0.05% (w/v) ammonium iron citrate, and 0.03% (w/v) sodium thiosulfate(mTSA) for Salmonella or TSAYE supplemented with 0.05% (w/v) ammonium iron citrate, and 0.025% (w/v) esculin hydrate (eTSA) for E. faecium, and incubated for 24 h at 37°C. After incubation, colonies with a black center on mTSA were counted as Salmonella while black colonies on eTSA were counted as E. faecium NRRL B-2354. High initial population level of both bacteria, 8.7 and 7.9 log CFU/g of Salmonella and E. faecium, were achieved by this inoculation method. The packaged EWP with inoculated packs was placed in a conveyor belt moving at 0.8 m/h inside the RF chamber andheated to 80°C. It was then immediately transferred to a mechanical convection oven (GCA Precision Scientific Group, Chicago, IL) which was preheated to 80°C and then held for 0, 2, 8, and 16 h. After holding in the oven, the inoculated packs were taken out from the box and immersed into ice water bath to quickly cool the samples. Next, the packed samples were transferred to sterile Whirl-Pak bags, 10-fold diluted using BPW and then stomached for 1 min in a stomacher (Neutec Group Inc., Farmingdale, NY). The stomached samples were then serially diluted in 9 mL of 0.1% BPW, spread plated onto mTSA for Salmonella or eTSA for E. faecium and incubated for 24 h at 37°C for enumeration. 3) Summary statistics and discussion of results. After 15 days of equilibration in the chamber, there were less than 1 log CFU/g reduction for Salmonella and less than 0.5 log CFU/g reduction for E. faecium which indicated that this inoculation method is suitable for microbial challenge studies.After holding the samples for 1 h in the convection oven, more than 5 log reduction of Salmonella was achieved at most of the locations except the cold spot. After 2 h of holding in the oven, more than 6.69 log CFU/g reduction of Salmonella was achieved at all locations. Traditional method of pasteurization takes up to 2 weeks at 58-60°C. RF-assisted thermal processing reduced the pasteurization time to 2 hours, after preheatingEWP in RF. At both 0 and 1 h holding time, reduction of E. faecium was lower than Salmonella at each location which indicated that E. faecium has a higher thermal resistance than Salmonella during RF heating. Therefore, E. faecium can be considered as a suitable surrogate for Salmonella during RF heating of EWP. 4) Key outcomes or other accomplishments realized. Compared to the traditional hot-room method, RF heating considerably reduced the process time for EWP pasteurization. A proper surrogate has been identified for the validation of industrial-scale thermal pasteurization and RF processes. The inoculation method has been shown to provide a stable inoculated samples with high microbial load for microbial challenge studies. B. Radiofrequency processing of cumin seeds: 1. Major activities completed / experiments conducted; Microbial validation of continuous radiofrequency (RF) pasteurization of cumin seeds was investigated. Either a 5-strain Salmonella enterica cocktail or Enterococcus faecium was inoculated into cumin seeds for microbial challenge studies in continuous RF heating. A plastic pack consisting of inoculated cumin seeds (20 g) was placed at the cold spot (top center) in a tray containing 430 g of uninoculated cumin seeds in the same tray. The whole tray was subjected to RF heating in a 6 kW 27.12 MHz RF system until the cold spot temperature reached 100 ?. Based on study on batch processing of cumin seeds, it took 108 s to achieve 5-log reduction of Salmonella. The treatment time in continuous processing was adjusted by settingthe conveyor belt speeds to33.2 m/h. Data collected; When counting plates, colonies with a black center on mTSA were deemed to be Salmonella, while black colonies on eTSA were counted as E. faecium. To enumerate surviving cells after continuous RF treatment, the inoculated sample in the small bag (20 g) was transferred to a sterile Whirl-Pak and tenfold diluted by adding 180 mL of 0.1% BPW and then homogenized for 1 min in a stomacher (Neutec Group Inc, NY, USA). Blended samples werediluted in 9 mL of 0.1% BPW and all samples were plated in duplicate onto mTSA for Salmonella and eTSA for E. faecium and incubated for 24±2 h at 37°C. Summary statistics and discussion of results and After 108 s of continuous RF heating at the belt speed of 33.2 m/h, there were more than 5 log reduction for both Salmonella and E. faecium and the microbial population reached below thedetection limit (< 10 CFU/g). Key outcomes or other accomplishments realized. This study demonstrated that continuous RF processing is suitable process forpasteurization of cumin seeds andE. faecium is a suitable surrogate for Salmonella.
Publications
- Type:
Other
Status:
Awaiting Publication
Year Published:
2019
Citation:
Chen L., and Subbiah J. (2019). Radiofrequency Pasteurization of Low-moisture Foods: Critical Process Control Parameters. Food Safety Magazine.
- Type:
Journal Articles
Status:
Submitted
Year Published:
2019
Citation:
Chen L., Wei X., Irmak S., Chaves B., Subbiah J. (2019). Inactivation of Salmonella enterica and Enterococcus faecium NRRL B-2354 in cumin seeds by radiofrequency heating. Food Control, Submitted.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2018
Citation:
Chen, L., & Subbiah, J. (2018). Radiofrequency Inactivation of Salmonella spp. in Cumin Seeds. American Society of Agricultural and Biological Engineers (ASABE) Annual Meeting, July 29- August 1, Detroit, MI.
- Type:
Other
Status:
Published
Year Published:
2018
Citation:
Subbiah, J., Birla, S.L., Thippareddi, H., 2018. Radiofrequency Heating of Egg White Powder Moving on a Conveyor Belt. USDA Project Directors Meeting, International Association for Food Protection (IAFP) Annual Meeting, July 8-11, Salt Lake City, UT.
|
Progress 01/01/17 to 12/31/17
Outputs
Target Audience:Food industry, equipment manufacturers. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?Published a perr-reviewed Journal article and presented results at scientific meetings. What do you plan to do during the next reporting period to accomplish the goals?Perform microbial validation of radiofrequency processing of low-moisture foods.
Impacts
What was accomplished under these goals?
Radiofrequency (RF) processing is a novel thermal processing method, that volumetrically heat the food products. Due to shorter come-up time, RF can be designed as a high-temperature and short-time processing to achieve desired microbial safety with minimal deterioration in food quality. Obj. 1. Develop a continuous RF processing system for in-package powder and pumpable food pastes. a. Major activities completed / experiments conducted; During RF treatment, the wheat sample (8.7% wet basis moisture content) was placed in a rectangular container.A 6 kW, 27.12 MHz parallel plate RF heating system with a free-running oscillatorwas used in this study. A commercial finite element method based software COMSOL Multiphysics was used to simulate the RF heating process with the movement of food product. The food product was placed on a conveyor belt with a moving speed, u = 14.23mh−1. 2) Data collected; About 3.39 kg of wheat filled in a rectangular polypropylene container was placed on the conveyor belt with a moving speedof 14.23mh−1. The sample was heated in a RF system for 287 s to validate the model. After the RF heating process, the spatial temperature profiles in top, middle, and bottom layers (60, 40, and 20mm from the bottom of the container, respectively) were recorded by an infrared camera with an accuracy of ±2 ?C. 3) Summary statistics and discussion of results and A discrete moving step approach was used in the simulation. The predicted spatial temperatures in top, middle, and bottom layers showed less than 3.5 °C lower prediction than the experimental result. The measured anode current showed a good linear correlation with the predicted total power absorption. The movement of food product could help improve the heating uniformity of RF heating process. The optimum number of discrete moving steps was determined to be nine for accurate temperature prediction with total conveyor belt movement distance of 1.13 m which is equivalent to optimize step size of 0.1256 m/step (0.3 m for entry and exit, respectively, and 0.53 m for fully covered by electrodes) at speed of 14.23 m h−1. 4) Key outcomes or other accomplishments realized. This model can be used to understand the industrial continuous RF heating of food products to enhance uniform heating. Obj. 2. Determine RF process parameters based on microbial inactivation kinetics and product quality deterioration kinetics 1) Major activities completed / experiments conducted; RF processing is evaluated for heating of black peppers.The whole black peppercorn has an initial moisture level of 11.61 ± 0.29% (wb). The moisture content of the samples was determined before and after RF heating. Whole black peppercorns were adjusted to a moisture content of 12.7% (wet basis), prior to RF treatment. 2) Data collected; RF heating was conducted in a 6 kW, 27.12 MHz pilot-scale parallel-plate RF heating system (Model SO-6B, Monga Strayfield Pvt. Ltd., Pune, India). The electrode gap was adjusted by moving the top electrode which regulated the RF power. A total of 400 ± 0.1 g of sample was placed uniformly in a laminated paper trayand placed inside the RF heater at the center of the bottom electrode. Subsequently, the tray was sealed by using polyethylene filmto minimize heat and moisture loss from the surface and a vented nut was fixed onto the center of the film for controlled release of water vapor. An infrared camerawith an accuracy of ± 2°C was used to obtain temperature profiles of the top surface of RF treated samples immediately after RF heating, after removing the film. Three fiber optic temperature probeswith an accuracy of ± 0.6°C were inserted at the geometric center of the top, middle and bottom layer to acquire temperature data during RF heating. 3) Summary statistics and discussion of results and Heat treatment of the inoculated samples was conducted using RF conditions that gave the fastest heating rate at an electrode gap of 10.5 cm to prevent too much quality deterioration. The RF heating times were determined to be 120 s, 150 s and 180 s which give a final average surface temperature around 80 °C, 95 °C and 105 °C, respectively. The temperature of the bottom layer increased faster than the other layers and the top layer was the slowest. The temperature profile shows that the central area heated up slower than the peripheral area, with the hot spots located around the edge. 4) Key outcomes or other accomplishments realized. The cold spot of RF treated whole black peppercorn was located at the center of the top surface. Thus, microbial challenge studies can be performed by placing the innoculated pack at the cold spot. Obj. 3. Validate process design with microbial challenge study with the selected low-moisture food products. 1. Major activities completed / experiments conducted; A small polyethylene bag (6 cm x 8 cm) was used to pack 20 g of inoculated sample and placed in the cold spot, which was the center of the top surface. Five different strains of Salmonella enterica were selected to conduct the microbiological studies andEnterococcus faecium NRRL B2354 was selected as the non-pathogenic surrogate for validations. The inoculated samples were aseptically transferred to an equilibration chamber to reach a target water activity. 2) Data collected; Upon inoculation, the bacteria require some time to adjust to the low aw environment and antimicrobial compounds in the whole black peppercorn. Immediately after the RF treatment, a thermal image of the top surface was taken by the infrared camera to confirm that the sample achieved the expected temperature before transferring the sample to a sterile bag. To enumerate surviving colonies after RF treatment, the sample in the small bag (~20 g) and the remaining sample were enumerated separately. 4) Summary statistics and discussion of results and Based on stability and homogeneity tests, the samples were equilibrated for 5 days before RF testing. After 2 min of RF heating, a reduction of 2.94 log CFU/g was achieved for the whole sample while only 1.08 log CFU/g reduction was obtained for the sample in the bag, indicating a significant difference (P < 0.05). Upon applying a 2.5 min RF heating treatment to the inoculated sample, the levels of Salmonella were reduced by 5.31 and 5.08 log CFU/g in the whole sample and sample in the bag, respectively, resulting in an insignificant difference (P > 0.05). Extending the RF heating to 3 min resulted in no recovery from the plates (< 10 CFU/g), suggesting that more than 6 log reduction was obtained. Therefore, the RF heating treatment of 2.5 min was chosen for the surrogate studies. The population of E. faecium reduced by 5.26 and 4.80 log CFU/g at 2.5 min treatment time in whole sample and sample in the bag, respectively. Less log reduction was attained for E. faecium than Salmonella in both whole sample and sample in the bag. 4) Key outcomes or other accomplishments realized. RF heating is a promising technology for inactivation of Salmonella spp. in whole black peppercorn. A 2.5-min RF heating treatment provides more than 5 log reduction for Salmonella spp. without causing quality deterioration. E. faecium was found to be a good surrogate for Salmonella spp. for RF heating of whole black peppercorn.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2017
Citation:
Chen, J., S. Lau, L. Chen, S. Wang, J. Subbiah. 2017. Modeling radio frequency heating of food moving on a conveyor belt. Food and Bioproducts Processing. 102, 307-319. 10.1016/j.fbp.2017.01.009
- Type:
Other
Status:
Published
Year Published:
2017
Citation:
Subbiah J., Birla S., Thippareddi H. 2017. Continuous RF Processing of Food Products. Presented at the USDA NIFA Project Directors Meeting, Jul 8, Tampa, FL.
- Type:
Theses/Dissertations
Status:
Published
Year Published:
2017
Citation:
Wei, X. 2017. Radiofrequency processing for inactivation of Salmonella spp. and Enterococcus faecium NRRL B-2354 in whole black peppercorn and ground black pepper. M.S. Thesis. University of Nebraska-Lincoln. Available at: https://digitalcommons.unl.edu/foodscidiss/88/
|
Progress 01/01/16 to 12/31/16
Outputs
Target Audience:Manufacturers of low-moisture foods. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?Continuous radiofrequency processing of wheat flour is being conducted.
Impacts
What was accomplished under these goals?
Come-up time for thermal processing of low-moisture foods such as wheat flour for enhancing microbiological safety is long due to their lower thermal conductivity. In the present study, a novel radiofrequency (RF)-assisted thermal processing for reducing the come-up time and for improving the safety of soft wheat flour (SWF) was investigated. 1) Major activities completed / experiments conducted: In our earlier work, RF-assisted thermal processing has been demonstrated to reduce the come-up time of egg white powder, which is a low-moisture food ingredient. Therefore, novel RF-assisted thermal processing is a promising method for pasteurizing wheat flour without compromising quality and functionality. Hence, the overall objective of thisstudy was to determine the optimum temperature and time combinations for RF-assisted thermal processing of SWF. The specific objectives were to: 1) investigate the effect of RF-assisted thermal processing on quality and functionality of the SWF, 2) compare the quality and functionality of RF-assisted thermally processed SWF with that of the unpasteurized SWF, and 3) evaluate the functionality of RF-assisted thermally processed SWF in the end product (sugar-snap cookies). 2) Data collected; SWF samples from three different production lots were procured locally (Omaha, Nebraska, USA) immediately after milling. The commercially pasteurized SWF samples from the same production lots were also procured after thermal processing by the miller. The moisture content of the SWF was measured following a hot air oven method at 105°C for 24 h. The protein content (total nitrogen) was determined with the LECO protein analyzer (Model: Leco FP-528, Leco Corporation, MI). The crude fat was measured using a Soxtec system (Model: Soxtec System HT 1043 Extraction Unit, Tecator, Sweden). The ash content and pH of SWF were measured following the AACC methods 08-01 and 02-52, respectively. Based on the reported D and z values of Salmonella spp. in SWF, the temperature and time combinations for RF-assisted thermal processing were selected. The selected temperature and time combinations were, RF heating to 80°C followed by holding in a hot air oven at 80°C for 7 h and 10 h; RF heating to 90°C followed by holding in a hot air oven at 90°C for 2 h and 3 h; and RF heating to 100°C followed by holding in a hot air oven at 100°C for 0.75 h and 1 h. The above selected treatment conditions were estimated to achieve minimum of 7- log reductions of Salmonella spp. in SWF of 0.18 water activity. SWF samples were treated in a 6-kW parallel plates (electrodes) RF heating system (Model: SO-6B, Monga Stray field Pvt. Ltd., Pune, India) operating at 27.12 MHz. SWF sample of 415 g was taken into a cylindrical polypropylene container (190 mm diameter and 23 mm height) and flattened the top surface. The cylindrical container with the sample was placed at the center of the bottom electrode. A fiber optic temperature probe (Neoptix, Inc., Quebec City, Quebec, Canada) was placed into the SWF sample at the geometric center. The minimum spacing of 90 mm was maintained to achieve maximum RF power coupling for high heating rate without any arcing. With this electrode spacing average heating time of 189 ±19 s and 350±52 s were taken to heat the SWF samples to 80°C and 100°C, respectively. The SWF samples were heated to the treatment temperatures of 80°C, 90°C and 100°C with RF power and then maintained at those temperatures for different time periods in a hot air oven. The quality and functional properties of RF-assisted thermally processed SWF was evaluated through the chemical methods i.e., solvent retention capacity (SRC), swelling power, and sodium dodecyl sulfate (SDS) sedimentation tests and flour functionality by evaluating the quality of sugar-snap cookies. The GLIMMIX procedure of SAS software 9.3 (SAS Institute Inc., Cary, NC, USA) was used to analyze the data. Dunnett's multiple comparison tests with adjustment was used to determine significant difference of each property at different RF-treatment levels in comparison with unpasteurized SWF as a control. The adjusted p-values (Adj. P) were tested at α = 0.05. 3) Summary statistics and discussion of results: ?The final moisture content of processed SWF at 90°C for 3 h and 100°C for 0.75 h and 1 h were significantly lower than that of the unpasteurized SWF. The color of RF-assisted thermally processed SWF was not significantly affected by the process when compared to that of the unpasteurized SWF. All the SRC attributes except water SRC and 50% Sucrose SRC at 80°C for 10 h and 90°C for 3 h, and SDS sedimentation volumes except at 90°C for 3 h of RF-assisted thermally processed SWF were not significantly different from that of the unpasteurized SWF. The processing conditions of 80°C for 7 h, 90°C for 2 h, and 100°C for 0.75 h favorably increased the final and trough viscosity values of RVA. Most of other RVA parameters for RF-assisted thermally processed SWF at severe processing conditions (80°C for 10 h, 90°C for 3 h, and 100°C for 1 h) were significantly different from that of the unpasteurized SWF. The swelling power and peak viscosity values together indicate the slight modification of starch property by the RF-assisted thermal processing. The width of the sugar-snap cookies for all the RF-assisted thermally processed SWF was not significantly different from that of the unpasteurized SWF. The cookie height for all the RF-assisted thermally processed conditions except at 80°C for 7 h was significantly higher than that of the unpasteurized condition. However, the color, hardness and fracturability values of sugar-snap cookies were not significantly different at all the RF-assisted thermally processed conditions when compared with that of the unpasteurized condition. 4) Key outcomes or other accomplishments realized. The quality and functional properties of RF-assisted thermally processed SWF and quality of the sugar-snap cookies indicate that the selected RF-assisted thermal processing temperatures and time combinations of 80°C for 7 h, 90°C for 2 h, and 100°C for 0.75 h did not influence the quality and functionality of the SWF significantly. However, the severe RF-assisted thermal processing conditions of 80°C for 10 h, 90°C for 3 h, and 100°C for 1h significantly influenced the quality and functionality of the SWF. Hence, it may be concluded that the RF-assisted thermal processing of the SWF at 80°C for 7 h, 90°C for 2 h, and 100°C for 0.75 h with an objective of achieving a minimum of 7 log reductions of Salmonella spp. can be designed without compromising the quality and functionality.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Huang, Z., Marra, F., Subbiah, J., Wang, S. (2016). Computer simulation for improving radio frequency (RF) heating uniformity of food products: a review. Critical reviews in food science and nutrition, DOI:10.1080/10408398.2016.1253000
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Boreddy, S.R., H. Thippareddi, G. Froning, and J. Subbiah. 2016. Novel Radiofrequency-Assisted Thermal Processing Improves the Gelling Properties of Standard Egg White Powder. Journal of Food Science, 81 (3): E665-E671.
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Boreddy, S.R. and J. Subbiah. 2016. Temperature and moisture dependent dielectric properties of egg white powder. Journal of Food Engineering, 168: 6067.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2016
Citation:
Boreddy, S., Froning, G., Thippareddi, H., Subbiah, J. 2016. Radiofrequency-assisted thermal processing for improving microbiological safety and functionalities of egg white powders. CoFE 2016, Conference on Food Engineering, Columbus, OH.
|
Progress 01/01/15 to 12/31/15
Outputs
Target Audience:Manufacturers of low-moisture food products. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?In addiotion to publishing results in peer-reviewed Journal articles and scientific presentations, we have shared the results with few food industries, who are manufacturers of low-moisture foods. What do you plan to do during the next reporting period to accomplish the goals?We are currently focussing on wheat flour, another low-moisture food product which has been implicated in foodborne illness outbrteak. The results will be reported in the next period.
Impacts
What was accomplished under these goals?
Low-moisture foods are traditionally considered as microbiologically safe foods. However, recent foodborne illnesses associated with consumption of low-moisture foods have heightened the concern of their microbiological safety. Thus, there is a critical need to pasteurize low-moisture foods. Traditional thermal processing methods are not suitable for pasteurizing these foods because of low thermal conductivity and high thermal resistance of the foodborne pathogens. In this study, a novel radiofrequency (RF)-assisted thermal processing method for pasteurization of egg white powder (EWP) is developed at both batch and continuous processing. Both quality and safety of products were evaluated. Obj. 1: Develop a continuous RF processing system for in-package powder and pumpable food pastes. Major activities completed / experiments conducted; Major activity include development of a novel radiofrequency (RF)-assisted thermal processing method for pasteurization of egg white powder (EWP) at both batch and continuous processing. Traditionally, egg white powder (EWP) is stored in a hot room maintained at 58°C to 60°C for 10 to 14 days for pasteurization and to improve functional properties. This long and energy-intensive process limits plant production capacity. In this study, radiofrequency (RF) assisted thermal processing was evaluated for pasteurization of EWP with the objective of reducing the storage period in a hot room, thereby reducing the energy requirement, while minimizing loss of functional properties. After demonstrating that RF-assisted thermal processing is feasible at batch scale, the continuous radiofrequency (RF)-assisted thermal processing of packaged EWP was investigated with an objective of reducing the processing time without compromising functionality. Data collected; Spray-dried EWP (pH ~9.5) was RF heated to 60°C, 70°C, 80°C, or 90°C and maintained at the same temperature for different storage periods ranging from 1 h at 90°C to 3 days at 60°C in a hot air oven. The quality and functional properties of the RF-treated EWP, including color, foaming capacity (overrun), foam stability, solubility, gel firmness, and gel elasticity, were evaluated. The come-up time at the center of the packaged EWP under RF heating and hot air oven heating was determined. Summary statistics and discussion of results and RF pretreatment of EWP at 90°C followed by holding in a hot air oven for 8 to 24 h provided optimal functional properties. RF-assisted thermal treatment at all levels did not significantly reduce the color lightness (L* values), solubility (Haenni value), and moisture content when compared to traditionally processed EWP. However, RF-pretreated EWP had a significantly lower foaming capacity (overrun) when compared to traditionally processed EWP. It was found that RF pretreatment at 90°C and holding in a hot air oven for 8 h or longer resulted in similar foam stability, water holding capacity, gel firmness, and gel elasticity. Therefore, we recommend RF heating of EWP to 90°C followed by holding in a hot air oven for 8 h or longer to produce similar or better functional properties compared to traditionally processed EWP. This treatment process is estimated to achieve ³7 log reduction of Salmonella spp. Thus, RF-assisted thermal treatment can be used to reduce the pasteurization duration from the current 10 to 14 days to less than 24 h. The maximum temperature difference among the measured locations within a package during both the stationary and conveyor movement conditions was 15°C. The geometric center of the package was the hottest location during RF heating with the conveyor movement. The continuous RF-assisted thermally processed packaged EWP at 80°C for 16 h exhibited excellent functionality than that of the EWP processed on batch mode. However, the EWP processed at 90°C for 16 h was lost foaming functionality due to protein aggregation. Further studies are needed to minimize aggregation resulting from non-uniform heating in packaged EWP. 4) Key outcomes or other accomplishments realized. We demonstrated the feasibility of designing a high-temperature short-time pasteurization process for EWP using RF-assisted thermal processing at both batch and continuous scale. The continuous RF-assisted thermally processed packaged EWP at 80°C for 16 h exhibited excellent functionality, while assuring food safety. Obj. 2. Determine RF process parameters based on microbial inactivation kinetics and product quality deterioration kinetics 1) Major activities completed / experiments conducted; The thermal destruction of Enterococcus faecium ATTC 8459 and Salmonella spp. was determined at 3 water activity levels (0.11, 0.18 and 0.33) at 80ºC, 85ºC and 90ºC in a low-moisture food product, wheat flour. 2) Data collected; Aerobic plates counts petrifilms were used as non-selective medium for both bacteria, Enterobacteriaceae petrifilms were used as selective medium for Salmonella spp., and peptone water modified with sodium azide as a selective medium for Enterococcus faecium. 3) Summary statistics and discussion of results and Significant differences were observed for both organisms between the two media with higher D-values on the non-selective medium (p <0.05). Lower D-values were observed for both organisms at higher water activities (p <0.05). The D-values of Salmonella spp. were 112.87 min, 61.01 min and 32.36 min at 80ºC, 85ºC and 90ºC, respectively in wheat flour at water activity of 0.11. At water activity of 0.18, the D-values of Salmonella spp. were 59.05 min, 30.90 min and 18.78 min at 80ºC, 85ºC and 90ºC, respectively. The D-values of Salmonella spp. were 25.10 min, 13.25 min and 6.22 min at 80ºC, 85ºC and 90ºC, respectively at aw 0.33. Higher D-values were observed for Enterococcus faecium ATTC 8459 compared to Salmonella spp., at all the conditions of the study, with no significant differences (p≥0.05), except at the water activity of 0.18 at 85ºC (p<0.05). The D-values of Enterococcus faecium ATTC 8459 were 117.97 min, 64.31 min and 38.24 min at 80ºC, 85ºC and 90ºC, respectively in wheat flour at water activity of 0.11. At water activity of 0.18, the D-values of Enterococcus faecium ATTC 8459 were 65.26 min, 50.49 min and 19.17 min at 80ºC, 85ºC and 90ºC, respectively. The D-values of Enterococcus faecium ATTC 8459 were 29.01 min, 15.09 min and 9.71 min at 80ºC, 85ºC and 90ºC, respectively at water activity of 0.33. The z-values were determined at each water activity, and there were no significant differences between the three (3) water activities (p≥0.05). Salmonella spp. and Enterococcus faecium had approximately the same z-values. The z-values of Salmonella spp. ranged from 16.53 to 18.50ºC, while the z-values of Enterococcus faecium ranged from 18.80 to 21.61ºC. 4) Key outcomes or other accomplishments realized. These results suggest that Enterococcus faecium ATTC 8459 can be used as a surrogate for Salmonella spp. in wheat flour at the three levels of water activity used in the study. Thermal inacvtivation kinetics data can be incorporated in the design of RF system for pasteurizing wheat flour. Obj.3. Validate process design with microbial challenge study with the selected low-moisture food products. None.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2015
Citation:
Boreddy, S.R. and J. Subbiah. 2015. Physical and thermal properties of spray dried egg white powder. Transactions of the ASABE, 58(5): 1409-1416.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2015
Citation:
Boreddy, S.R. and J. Subbiah. 2015. Effect of Radio Frequency Assisted Thermal Processing on Functional Properties of High Gel and Standard Egg White Powders. Proceedings of the 49th Annual Microwave Power Symposium (IMPI 49), June 16-18, San Diego, CA, pp: 32-33.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2015
Citation:
Boreddy, S.R. and J. Subbiah. 2015. Temperature and moisture dependent dielectric properties of egg white powder. Proceedings of the 49th Annual Microwave Power Symposium (IMPI 49), June 16-18, San Diego, CA, pp: 34-35.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2015
Citation:
Boreddy, S.R. and J. Subbiah. 2015. Physical and Thermal Properties of Spray Dried Egg White Powder. Presented at the 2015 ASABE Annual International Meeting, June 26-29, New Orleans, Louisiana.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2015
Citation:
Lau S.K., S. Irmak, and J. Subbiah. 2015. Quality Analysis of Peanut Butter Treated by Radio Frequency Heating. Presented at the 49th Annual Microwave Power Symposium (IMPI 49), June 16-18, San Diego, CA.
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Progress 01/01/14 to 12/31/14
Outputs
Target Audience: Manufacturers of low-moisture food products. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest? The results have been presented at the International Microwave Power Symposium annual meeting. What do you plan to do during the next reporting period to accomplish the goals? We will focus on conitnuous radiofrequency processing of peanut butter and other low-moisture food products.
Impacts
What was accomplished under these goals?
We are focusing on radiofrequency (RF)processing of peanut butter, a low-moisture food that has been implicated in recent foodborne illness outbreaks. The goal is to design a continuous RF processing system for peanut butter. The first step in understanding the interactions of radiofrequency waves with peanut butter is to measure temperature-dependent thermal and dielectric properties of peanut butter. We also finalized the quality analyses protocols Obj 1. Develop a continuous RF processing system for in-package powder and pumpable food pastes. 1) Major activities completed / experiments conducted; We measured the temperature-dependent dielectric properties of peanut butter. We also finalized the protocols for quality analysis of peanut butter. 2) Data collected; We used a network analyzer connected with a high-temperature probe to measure temperature-dependent peanut butter from 20°C to 100°C. 3) Summary statistics and discussion of results Its dielectric properties were found to be dependent upon frequency and temperature while its thermal conductivity remained almost constant (0.2 W m-1 K-1) throughout the temperature range. The low value of the latter indicates that the come-up time in the traditional thermal pasteurization method will be long resulting in more non-uniform heating making it ineffective. RF heating may prove to be a suitable pasteurization method. The dielectric properties were relatively constant throughout the measured frequencies below 50°C, and then began to peak in the frequency range of 250 to 350 MHz above 50°C. This suggests that if electromagnetic heating was performed within the aforementioned range of frequencies (250 to 350 MHz), the heating rate will increase with temperature, leading to runaway heating at regions that are already hot. Therefore, electromagnetic heating should be performed at other frequencies where the dielectric properties do not vary much with temperature. 4) Key outcomes or other accomplishments realized. The measured temperature-dependent properties of peanut butter can be used as inputs to multiphysics model for designing continuous RF processing of peanut butter. Obj 2: Determine RF process parameters based on microbial inactivation kinetics and product quality deterioration kinetics 1) Major activities completed / experiments conducted; Microbial inactivation kinetics in peanut butter were collected from the literature. Based on the microbial inactivation kinetics, different time-temperature combinations to achieve five log reductions were determined. On those conditions, peanut butter quality was determined. 2) Data collected; Based on published thermal inactivation kinetics, the time required for 5 log reductions of Salmonella spp. at 83 and 90°C were determined to be 110 and 49 minutes, respectively. Samples of peanut butter were treated at the chosen time-temperature conditions using RF heating, with the samples being placed in containers designed based on heat transfer model simulation results. On those conditions, quality analysis were performed to identify the best process conditions for RF pasteurization without significant quality degradation. The quality analyses were performed immediately after treatment, after 1 month of storage at room temperature, and at accelerated storage conditions (1 month of storage at 40°C). Peanut butter oils were extracted using soxhlet extraction unit and hexane solvent for 4 hours. Fatty acid profiles (Fatty acid methyl esters) were collected using GC following AOCS Method Ce 1b-89. Fatty acid concentration was determined based on peak areas. Lipid oxidation, which is also called auto-oxidation, occurs in lipid material by way of a free-radical mechanism. Peroxide value quantifies the lipid oxidation and was determined by titration with sodium thiosulfate. The compositions of peanut butter oils was determined by a Thermo Scientific GC-MS (Trace 1310 GC and ISQ QD MS) using TG-5MS 30m x 0.25mm x 0.25um capillary column. The compositions of the samples were identified using NIST mass spectral library. The volatile compositions of peanut butter was determined by the GC-MS system using headspace injection unit. Two grams of peanut butter in head space vial with magnetic screw cap was heated up to 70 °C. The volatile compounds formed were separated using TG-5MS 30m x 0.25mm x 0.25um capillary column and identified in MS detector using NIST mass spectral library. Oil separation was measured by storing peanut butter in 20 mL cylinders and measuring the amount of oil separated from the peanut butter. Spreadability was considered as a combination of the peak and trough forces exerted by the peanut butter on a 60° conical probe lowered into and pulled from the peanut butter in a textural analyzer. Water activity was determined using a vapor sorption analyzer. Color values (L*, a* and b*) were determined using a Minolta colorimeter. 3) Summary statistics and discussion of results Preliminary results indicate that as temperature increases, fatty acids with double bonds tend to degrade into breakdown compounds. In addition, the amount of breakdown compounds increased further after one month of storage. In contrast, the degradation was not found on control (untreated) samples. 4) Key outcomes or other accomplishments realized. Quality analysis indicates that milder RF processing may be necessary. The microbial load in the peanut butter is very low that the five log reductions may not be necessary to achieve an acceptable level of risk. Further investigations are being conducted. Obj 3: Validate process design with microbial challenge study with the selected low-moisture food products. Not yet started.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Lau S.K., Subbiah J. 2014. Dielectric Properties and Thermal Conductivity of Peanut Butter. Proceedings of 2014 IMPI 48th Annual Microwave Power Symposium June 18-20, 2014 New Orleans, LA.
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