Performing Department
College of Engineering
Non Technical Summary
In the 1920's, Clarence Birdseye introduced the flash freezing technology for food. This marks the birth of the retail frozen food industry, an industry that has changed the global food economy. The global frozen food market exceeds $250 billion annually, including $53B annually in the U.S. The low temperatures associated with freezing reduce the rate of chemical reactions and thereby reduce spoilage and inhibit the growth of undesirable bacteria in the food. However, while of great economical value, the current food freezing technologies suffer from major drawbacks. Not all food products can be frozen, and the quality of frozen food products is often less than that of fresh foods. Biological matter is made primarily of water, and the main reason freezing has detrimental effects is the formation of damaging ice crystals throughout the frozen product. In addition, while freezing inhibits the growth of the pathogens (microbes and parasites), it does not destroy them. Therefore, frozen foods must be cooked immediately after thawing to ensure safety.Our project will develop a new food freezing technology, isochoric (constant volume) freezing, that has the potential to revolutionize the frozen food industry. It is based on the unique fundamental relationship between temperature and pressure. Imagine leaving a soda can in the freezer--after a while, the can bursts, because the internal contents expand as they freeze. But what happens if, instead of a fragile aluminum can, the soda was stored in a stout steel vessel that could resist the expansion?Our group has been studying the answer to that question. Essentially, when ice begins to expand, it creates a pressure inside the container. In our soda can example, the pressure then bursts the can. But if the pressure cannot break the container and escape, it will continue to build. And as it happens, ice is less likely to form as pressure builds. This means that in an isochoric container (the stout steel vessel in our example), only a fraction of the liquid inside will freeze, leaving the rest in a liquid state at high pressure. This ice-liquid balance provides the foundation for our technology. Using isochoric principles, we are able to store food in the liquid portion of a container and hold it at temperatures well below freezing, without any ice forming and damaging the food. Imagine if food still looked, felt, and tasted fresh when you pulled it from the freezer--in addition to myriad other benefits, this is possible with isochoric freezing.The goal of this proposal is to advance the field of isochoric freezing, from a preliminary laboratory concept, to a prototype industrial technology that will serve the frozen food industry in the U.S. and around the world. To this end we will develop optimal isochoric freezing protocols for sample products such as leafy greens, berries, tomatoes and tuna, evaluating both the quality and nutrition of the foods and the capacity of isochoric storage to kill foodborne pathogens. Additionally, our group will design and fabricate larger-scale isochoric devices both for industry and home-use. Picture removing food from the freezer and not having to wait for it to thaw!This proposal represents a joint effort between researchers from the BioThermal Laboratory in the UC Berkeley Department of Mechanical Engineering (which has operated in Berkeley for 27 years) and the USDA, Agricultural Research Service, Western Regional Research Center (WRRC) in Albany, CA (who was designated a National Historic Chemical Landmark by the American Chemical Society in recognition of their pioneering research on frozen foods).
Animal Health Component
0%
Research Effort Categories
Basic
50%
Applied
30%
Developmental
20%
Goals / Objectives
The primary goal of the proposed study is to develop a new technology for preservation of food products by isochoric (constant volume) freezing - from basic engineering and food technology first-principles to a commercial prototype. This novel technology has the potential to substantially improve the quality, nutrition, and safety of frozen food products, and to reduce energy usage in the food industry. This approach represents a radical departure from conventional food freezing technologies, which use isobaric (constant pressure) freezing.Preservation of food products by isochoric freezing, a technique which we have pioneered, presents an entirely new field of research for the food industry. Therefore, our secondary goals are to introduce and educate users in the food industry as to the attributes and advantages of isochoric freezing and ultimately to transfer the technology into commercialization.Our goals will be achieved via completion of the following four objectives:Study of isochoric frozen food quality and nutritionTo demonstrate the value of this new freezing technology, we have chosen to study the quality and nutrition of four model food products which to date have not been preserved satisfactorily by freezing, specifically spinach, raspberries, tomatoes, and tuna fish.Food specimens will be frozen in both an isochoric freezing chamber and an isobaric (conventional) freezing chamber to a range of temperatures from 0 C to - 60 C in 5C increments, with preservation periods of 3h, 6h, 24h, 7d and 1 m. A variety of final product quality parameters will be evaluated, including color, texture, moisture content, drip loss, nutrients (vitamin C, vitamin B1 and total soluble phenolics), and sensory analyses, and by each parameter the quality of isochoric preservation vs. isobaric (conventional) preservation will be compared.To accomplish this objective, we will initially use a prototype isochoric freezing chamber already in operation in the Rubinsky Lab at UC Berkeley and described in several publications. Food quality and nutrition will be evaluated at the USDA Western Regional Research Center (WRRC), Healthy Processed Foods Research Unit, which has all of the equipment and personnel required for these tests. In parallel, we will design and construct industrial-grade prototype isochoric chambers in which products will be tested throughout the duration of the project.These milestones will be reached through a partnership between Professor Rubinsky and his graduate student Matt Powell-Palm from the UC Berkeley Dept. of Mechanical Engineering, The Berkeley Food Initiative, and Drs. Tara McHugh and Cristina Bilbao from the USDA WRRC, Healthy Processed Foods Research Unit.Study of isochoric frozen food safetyFrom a food safety perspective, conventional isobaric freezing is used primarily because low temperatures reduce the metabolism of living organisms, and therefore inhibit the growth of pathogens. Conventional freezing also has a limited ability to destroy pathogens. There is evidence however that the combination of low temperature and high pressure that occurs during isochoric freezing has not only the ability to reduce metabolism, as in conventional freezing, but to also actively destroy pathogens.This objective thus aims to evaluate the capacity of isochoric freezing to control foodborne pathogens as a function of temperature, pressure and storage time. The same food products tested in objective a) for quality and nutrition will be evaluated for safety. We will use foodborne pathogens from our strain collection associated with contaminated foods. These include: three strains of E. coli O157:H7, isolated from human feces associated with consumption of contaminated apple juice; Listeria monocytogenes, isolated from contaminated cheese; Salmonella enterica serovar Hadar, isolated from contaminated turkey; and Salmonella paratyphi B, isolated from frozen raw tuna. Standard microbiology tests available at the WRRC facilities will be employed.In addition to the participants listed for the first objective, to reach these milestones we will use the BSL-2 food safety laboratories and the expertise of the Produce Safety and Microbiology Research Unit under Dr. Vivian Wu at the WRRC.c) Engineering design and fabrication of scalable isochoric freezing systemsThis objective aims to support the scientific research detailed in Objectives a) and b) with engineering research. The engineering group, comprised primarily of members of the UC Berkeley Department of Mechanical Engineering, will continuously design, fabricate, and maintain the isochoric chambers used in this project.To facilitate the transition from laboratory prototype to industrial prototype, the engineering group will employ heat transfer, thermodynamics, solid mechanics, and material selection techniques to design larger isochoric chambers for use with increased sample sizes. The primary design goal is to reduce cost and weight while maintaining structural integrity and pressure tolerance. Furthermore, working with stakeholders from Objective d), we will produce prototypes for tailored applications in industrial and home-use settings and transfer the technology into commercialization.d) Education and outreach on isochoric freezing of food technologiesPreservation of food by isochoric freezing does not represent an incremental advance in food preservation-- it is a completely new technology for the industry. Therefore, education and outreach to potential stakeholders is a primary aim. The PIs of this proposal are well-recognized scientists and firmly established in their fields, and thus positioned well to effectively introduce the technology to the broader food industry and scientific community.A first step towards this end will be to form a technical advisory board consisting of members from the frozen food industry as well as the American Frozen Food Institute (AFFI), with established backgrounds in food freezing. The technical advisory board will be in continuous contact with our research group to ensure that success is achieved. Through partnerships with members of the technical advisory board the technology of isochoric freezing will be transferred into the food industry.Education about isochoric freezing will be achieved through publication in peer-reviewed scientific journals, lectures, attendance everywhere from conferences to farmers markets to 4-H events, and through distribution of research reports to stakeholders in the frozen food industry, commodity organizations, and government regulatory agencies (as well as to consumers). We will also maintain a website dedicated to isochoric freezing, and hold industry workshops on isochoric technology.Additionally, we will educate via the Fung School of Engineering Leadership at U.C. Berkeley, through which Dr. Rubinsky supervises between six and nine MSc students annually. This one-year program prepares graduate students for all aspects of industrial product development, from market research to mass manufacturing, and we anticipate that these students will contribute to the development of isochoric technologies and become valuable education and outreach resources as they transition into industry work.
Project Methods
Study of isochoric frozen food quality and nutritionFour model foods will be evaluated: spinach, raspberries, tomatoes, and tuna fish. These foods were chosen because they suffer from substantial loss of quality during conventional freezing and food safety issues.Specimens will be frozen in isochoric freezing chamber and an isobaric (conventional) freezing chamber to a range of temperatures from 0 C to - 60 C in 5C increments, with preservation periods from 3h to 1 m. A variety of final product quality parameters will be evaluated, including color, texture, moisture content, drip loss, nutrients (vitamin C, vitamin B1 and total soluble phenolics), and sensory analyses, using standard, widely accepted methodologies and by each parameter the quality of isochoric preservation vs. isobaric (conventional) preservation will be compared.Statistical analysis used will be appropriate to the type of variable and the goal of the experiment. For measurable variables, t-test, analyses of variance and logistic regression methods will be used. For the proposed experiments, data will be analyzed with available statistical software such as (Statview 4.5 for Windows). The ultimate outcome of this part of the study is characterization of the quality of the food samples as a function of various isochoric freezing protocols. We will identify the optimal temperature of preservation by isochoric freezing and allowable time of preservation.This portion of the project will be considered successful when parameters for optimal isochoric freezing of these foods have been identified and results have been published in peer-reviewed journals.Study of isochoric frozen food safetyThis objective will evaluate the capacity of isochoric freezing to control foodborne pathogens as a function of temperature, pressure and storage time. The same food products tested for quality and nutrition will be evaluated for safety. We will use foodborne pathogens from our strain collection associated with contaminated foods. These include: three strains of E. coli O157:H7, from human feces associated with consumption of contaminated apple juice; Listeria monocytogenes, from contaminated cheese; Salmonella enterica serovar Hadar, from contaminated ground turkey; and Salmonella paratyphi B, from frozen raw tuna.Prior to each experiment, frozen stock cultures of each pathogen will be activated at 37 °C for 24 h in tryptic soy broth (TSB). Overnight cultures will be streaked on MacConkey sorbitol agar (MSA), xylose lysine deoxycholate agar (XLD), or PALCOM agar for E. coli O157:H7, Salmonella, and Listeria strains respectively. Isolated colonies will be cultured in TSB and incubated for two 24 h intervals. Overnight cultures will be collected and suspended in 0.1% peptone water. Individual strains from each species will be combined to make an intraspecific cocktail. Each 2 cm cube or slab of food will be inoculated with the prepared pathogen containing cocktail. Spinach will be inoculated with E. coli 0157:H7; Raspberries with L. monocytogenes; Tomatoes with S. enterica and tuna fish with S. paratyphi. Following inoculation both the inoculums alone and food samples will be treated under control or isochoric freezing conditions as outlined in Specific Aim 1. The samples will be exposed to temperatures in the range of from 0 C to - 60 C, in increments of 5 C for various periods of time. The periods of time are 3h, 6 h, 24h, 7d and 1 m. The preserved sample will be examined in comparison with fresh controls and controls frozen under similar conditions in the isochoric device - but at atmospheric pressure (this is possible by not closing the cap on the device). Following treatment samples will be thawed and storage studies will be performed on products stored under refrigeration conditions for 0 days, 3 days, 7 and 14 days for all foods.Microbial enumeration after processing and storage. For microbial colony counts following treatment and storage, food samples will be homogenized for 2 min in a stomacher with 90 mL of 0.1% peptone water. After the homogenate is serially diluted with 0.1% peptone water, 0.1 mL aliquots of dilutes will be spread plated on the pathogenic specific selective media as described previously. Each plate will be incubated overnight at 37 °C and microbial reduction (log CFU/g) will be determined by comparison of treated samples to the control. To aid in the recovery of injured bacteria, a thin TSA layer will be overlaid on each selective agar plate before plating (thin agar layer method).Statistical analysis. Experiments will be performed three times separately. The statistical analysis used will be appropriate to the type of variable and the goal of the experiment. For measurable variables, t-test, analyses of variance (ANOVA, with multiple comparisons using Bonferroni or Sheffe adjustment of a-error) and logistic regression methods will be used. For the proposed experiments, data will be analyzed with available statistical software (Statview 4.5 for Windows, Abacus Concepts, Berkeley, CA or GraphPad Prism v4. San Diego CA.).We anticipate that the ultimate outcome of this part of the study will be the characterization of the sterilization capabilities of isochoric freezing as a function of the various protocols to which they were exposed. We should identify the optimum temperature and storage conditions required for sterilization.This portion of the study will be considered successful when it will provide the freezing parameters for the sterilization of the pathogens studied.c) Engineering design and construction of isochoric freezing systemsThis objective aims to support the preceding scientific research with engineering research, and to provide tools for industrial implementation of the technology. The research has three main elements: a) material selection, b) mathematical modeling and c) design and fabrication of devices.Material search - The principal design objective is to reduce the cost and weight of isochoric chambers. To this end we will perform a thorough search of light-weight materials that can withstand the requisite temperatures and pressures. These types of materials have been studied extensively by NASA and the Armed Services, and are of increasing scientific interest. An important challenge may also be to find materials that additionally have a high thermal conductivity, which will likely require investigation of novel composites. In particular, we will examine the use of various composite structures that can withstand high hydrostatic pressure and have low weight, such as carbon fiber reinforced titanium sheets or carbon-carbon with unidirectional reinforcement fibers, whose strength is up to 700 MPa.Mathematical modeling - We will use industry-standard computational software such as COMSOL and ANSYS to model: a) the heat transfer during isochoric freezing and b) stress-strain relations in the isochoric chamber as a function of the materials used and the shape and dimensions of the chamber.Design and fabrication of devices - the Department of Mechanical Engineering at UC Berkeley has a state of the art machine shop with reduced-cost fabrication services for faculty and graduate research. The UC Berkeley team will work continuously both to maintain current isochoric devices for laboratory research and to develop larger-scale devices for industry use.The study will be considered successful when devices capable of facilitating the research described in Objectives A and B have been fabricated and maintained, and when a scalable device for industrial applications has been fabricated and tested in context.d) Education and outreach on isochoric freezing of food technologies - Methods for accomplishment of this section of the study are provided in other sections of this write-up.