Recipient Organization
LINCOLN UNIVERSITY
820 CHESTNUT ST
JEFFERSON CITY,MO 651023537
Performing Department
Agriculture
Non Technical Summary
Sous vide, a method of cooking vacuum packaged products in a heated water bath (typically below the boiling point of water), has seen significant increases in interest over the past decade, in many cases driven by guides, testimonials, and equipment manufacturers primarily situated on the internet. This has lead to a mass of collected "wisdom" distributed over the same channels regardingthe best ways to perform the process, many of which do not always appear safe from a scientific stand point. At the same time, we do know that long-time, low-temperature processes can be designed to create safe products, and in fact many such processes are used for diverse products in the meat, poultry, dairy and egg industries.But in order to develop those processes, robust scientific test must be performed, and that is the corner stone of this project. In this work, three simple questions will need to be answered for a variety of whole and ground muscle foods (Beef, Pork, and either poultry or small ruminants like goats or sheep)-•Can the USDA tables, developed for cooking large roasts via conventional means, be extrapolated to lower temperature, longer time cooking methods like sous vide while maintaining consumer safety as it relates to dangerous pathogens?•If not, what are the time temperature combinations necessary to ensure consumer safety?•How will such treatments affect consumer perceptions of quality?In order to answer those questions, several techniques are needed- Cooking via immersion circulator, monitoring of internal temperature via automated system, inoculation of meat samples, determination of bacterial counts before and during cooking, and testing of the color, texture and sensory attributes of non-innoculated samples. In order to properly model the technique as used in restaurants and homes, commercially available immersion circulators will be used along with insulated containers. All meat samples will be fabricated from primal or sub primal cuts to a uniform thickness and vacuum sealed in pouches. Prior to trials for bacterial inactivation or effect on quality, a series of tests will be needed to determine average come-up time for cuts of various thickness. That is, how long must a given cut of meat be subjected to heating before the centermost part of the product reaches a target temperature. To determine this, the come-up time trials will make use of pouches that have been fitted with watertight thermocouple ports and the related thermocouples inserted into the midpoint of the sample. Then they will be subjected to sous-vide cooking while the temperatures are monitored using an automated system.After come up time for various thicknesses of the has been determined, bacterial inactivation trials can be started, which will require multiple techniques, including propagation of inoculum, inoculation of meats using methods that ensure inoculum reaches the inside of the meats, sampling over cooking time, and enumeration of samples using established techniques. These trials will utilize either actual pathogens, or non-pathogenic surrogates with equal or greater thermal resistance. Strains will be chosen which have the ability to grow on selective media (typically via resistance to certain anti-microbial compounds) in order to prevent native microflora from skewing the results.Once time-temperature combinations capable of reducing bacterial contamination below the target goal have been established for a given type of muscle food, testing on quality can begin. Internal and external color before and after both minimal (as established in the microbial experiments) and extended cooking, as will measures of texture by means of a universal testing machine (Texture analyzer), including shearing force, chewiness, firmness, etc. These measurements will aid in the understanding of how the process can affect the quality of the meat, as many internet sources suggest that longer processes can result in a tenderizing effect without having any scientific measure of when during the cook those changes occur, and at what point the changes become less desirable.The final tests will be sensory in nature, using human panelists. Samples will be prepared in food-grade spaces, based upon the parameters developed in the previous 2 studies to ensure both safety and quality. In addition to the sous-vide cooking, samples for sensory analysis will be subjected to surface searing using either radiant or conductive heat methods in order to present a more traditional appearance, and evaluated for flavor, texture and appearance using an established sensory method such as the 9-point hedonic scale, or the JAR scale.The data generated by this study will greatly increase our understanding of the technique, and allow for the development of consumer/ industry resources such as tables of temperature/ time setting for a given degree of doneness, extension pamphlets outlining best practices, and scientific publications to further interest and inquiry among fellow scientists.
Animal Health Component
100%
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Goals / Objectives
This project seeks to do the following:Determine whether USDA appendix A can be utilized for sous vide cooking. The lowest temperature in Appendix A is 130°F (54.4 °C) with a hold time of 121 minutes. This temperature is typically described as somewhere between Rare and medium, depending on the author. If a beef steak, in vacuum packaging, is submerged in circulating 55 ° water for 121 minutes, plus an experimentally determined come up time (the time for the center to reach 54.4 °C) will it show a 7-log reduction in Salmonella? If so, then it can reasonably be assumed that the table can be relied upon. If not, then additional work will need to be done.Determine whether lower temperature treatments can be extrapolated from Appendix A. Careful examination of the table shows that the USDA is using a z-value of 10°F. That is, for each increase in temperature of 10 °F, the required cooking time is decreased by a factor of 10. Likewise, decreasing the temperature by the same amount results in a ten-fold increase in required hold time. This simple logarithmic relationship for thermal death times should mean that one can determine the required cook time for lower temperatures. So for a 125 °F temperature, it should require a 173.1 minute cook (plus come up time). This would result in a steak described as rare, and should the process be sufficient to inactivate the Salmonella at the 7-log level, that would suggest the table values can be extrapolated across the range of common doneness levels.If temperature/ time combinations cannot be either directly gleaned from Appendix A, extrapolated from Appendix A, or both, then what time/temperature combinations will effect the required inactivation? Can this data be developed into a predictive model, and if so, what are the terms/ relationships? As an example, if the 54.4 °C/ 121 minute sous vide cook is insufficient, how long of a cook (if any) would effect the required inactivation.If one or more sufficient time/ temperature combinations are suitable for producing safe products (as determined by the levels of inactivation in previous experiments), then how do these combinations affect consumer opinions of desirable flavor, texture, and acceptability? Do treatments in excess of the minimum increase or decrease consumer scores? Sous vide has often been described as a means to improve texture vs traditional cooking methods due to increased holding at low temperatures, but does this hold true when the processes are of sufficient rigor to eliminate pathogens?
Project Methods
Meat fabrication: Intact meats: Individual steaks/ chops of approximately 2 cm thickness will be fabricated from common primal cuts. (e.g. for beef, either top round or strip loin primals). For microbial tests, each steak/ chop will be further broken down into regular rectangular shapes prior to inoculation. For ground products, grinding will be performed on a selected sample either on site, or at the place of purchase to limit co-mingling.Determination of come-up time: Whole steaks/chops or patties of ground meat will be placed in flexible pouches fitted with water tight packing glands. These glands will then be used to pass thermocouple wires through the pouch and into the geometric center of the samples, before sealing the pouches under vacuum and placing into preheated circulating water baths. Periodic temperature measurements will be recorded in order to determine how long a steak must sit in the circulating bath before the entire sample is in equilibrium with the water temperature.Microbial inoculation: An internal inoculation method will be utilized on fabricated steak/chop pieces (e.g. the "pin pad" inoculation method described by Sun et al. (2017) whereby a "bacterial lawn" will be propagated on appropriate solid media using a cocktail of either E. coli or Salmonella spp, with individual strains selected based on prevalence and thermal resistance. This lawn will then be gently suspended using a small amount of peptone water, then collected via scraping and transferred to the wells of a microplate. A corresponding long-pin pinpad will then be used to transfer inoculum from the wells into the inside of the steak pieces, with inoculation occurring from each side.) Ground samples will be directly inoculated with suspensions of bacteria and mixed to disperse.Microbial enumeration: Samples will be enumerated for E. coli and Salmonella (or appropriate surrogates) using appropriate techniques described in the FDA Bacteriological Analytical Manual. This will typically entail blending or stomaching of samples to extract viable microbes, serial dilutions and growth on appropriate selective solid media during a 24-48 hr. incubation at 35-37 °C, followed by manual or automated colony counting.Instrumental measures of color and tenderness: Appropriate instruments will be used to determine both color and texture of sous vide cooked samples. Specifically, a properly calibrated colorimeter will be used to determine surface and center color, while a universal testing machine fitted with a Warner-Bratzler shear probe and base will be used to determine shearing force of cylindrical cores excised from the steaks. In addition, a "two-bite" TPA (texture profile analysis) will be conducted on cubes excised from the steaks to determine chewiness, hardness and cohesiveness, using the methods described by Caine, Aalhus, Best, Dugan, and Jeremiah (2003).Sensory analysis: Consumer acceptability and ranked preference tests will be carried out at two discreet locations: Jefferson City, MO and either Lincoln, NE or Athens, GA in order to limit geographic bias. A total minimum of 150 total panelist will be recruited and presented with samples of sous vide cooked beef steaks from each primal independently and asked to evaluate the quality characteristics of the samples. All samples will be cooked via Sous vide and finished by surface searing using a direct radiant heat source. Sensory panels will be conducted according to ASTM guidelines, and will have oversight from the Institutional Review Board with jurisdiction over the specific site.