INVESTIGATING THE EFFECT OF VACUUM DRYING TECHNIQUES ON FLAVOR AND AROMA COMPOUND RETENTION AND RECOVERY USING HOPS AS A MODEL SYSTEM

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: AFRI COMPETITIVE GRANT
• Reporting Frequency: Annual
• Accession No.: 1023022
• Grant No.: 2020-67034-31725
• Cumulative Award Amt.: $180,000.00
• Proposal No.: 2019-07153
• Project Start Date: Jul 1, 2020
• Project End Date: Jun 30, 2023
• Grant Year: 2020
• Program Code: [A7101]- AFRI Predoctoral Fellowships

Recipient Organization
PENNSYLVANIA STATE UNIVERSITY
408 Old Main
UNIVERSITY PARK,PA 16802-1505

Performing Department
Food Science

Non Technical Summary
Food products that are valued for their flavor and aroma, such as herbs and hops, are often dried convectively (using hot air) to preserve them for safe long-term storage. However, many flavor and aroma compounds are sensitive to high temperatures, and convective drying causes many of these compounds to be lost. Vacuum drying, on the other hand, uses lower temperatures than traditional convective drying. By drying these food products using lower temperatures, it may be possible to retain these flavor and aroma compounds while still preserving the food products for long-term use. Using hops as a model system, we will vacuum dry wet hops in a laboratory at a variety of temperatures and pressures in order to determine which conditions result in the most flavor and aroma compounds left in the hops at a reasonable time scale. Also, we will monitor the flavor and aroma compounds that are lost during vacuum drying. Using solid phase media, we will recover the compounds that would otherwise be waste products during vacuum drying and evaluate their performance as a value-added product that small-scale growers can also sell to beer manufacturers. We will build a low-cost commercial-scale vacuum drying oast and provide the schematics to small scale hop growers.Vacuum drying is an expensive technology and is not feasible for large growers, who would oversaturate the market with more expensive premium hops. However, small scale growers may be able to take advantage of this technology due to their smaller agricultural output. Due to the retention of these flavor and aroma compounds, growers of high value agricultural products will have a higher quality product that will be more economically valuable but will not saturate the market. Additionally, recovering some of the flavor and aroma compounds lost during drying would open the possibility from growers to sell them as a value-added product.

Animal Health Component

100%

Research Effort Categories

Basic

0%

Applied

100%

Developmental

0%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
501	5010	2000	60%
501	5010	2020	40%

Knowledge Area
501 - New and Improved Food Processing Technologies;

Subject Of Investigation
5010 - Food;

Field Of Science
2020 - Engineering; 2000 - Chemistry;

Keywords

flavor compounds

aroma compounds

aroma recovery

drying kinetics

plant products

vacuum drying

Goals / Objectives
The major goal of this project is to evaluate the effect of vacuum drying on the retention and recovery of flavor and aroma compounds in agricultural products, using hops (Humulus lupulus L.) as a model system.Objective 1: Determine the effect of vacuum and temperature on the drying kinetics of hops. Hops at approximately 80% moisture content will be dried to 8-10% moisture content in a bench-scale vacuum oven at various temperatures (40°C, 50°C, 60°C) and pressures (between 0 atm and 1 atm gauge pressure). The drying kinetics of hops will be determined at constant and varied drying rates by modeling the data (moisture content vs time at various temperatures and pressures) in a program such as MATLAB. This will suggest if increasing drying temperature or decreasing pressure towards the end of the drying process can shorten the overall drying time significantly. Finally, hops will be dried using the fastest drying conditions, as determined in the above experiments, with various bed depths (e.g. a single vs double layer of hops) to determine if hops can be efficiently dried using a deeper bed.Objective 2: Measure the flavor and aroma compounds (alpha/beta acids, volatile organic compounds (VOCs)) of hops after vacuum drying and apply the vacuum drying to a commercial scale. Hops at approximately 80% moisture content will be dried to 8-10% moisture content in a bench-scale vacuum oven at various temperatures (40°C, 50°C, 60°C) and pressures (between 0 atm and 1 atm gauge pressure). The dried hops will be analyzed for their alpha/beta acid and VOC content. The optimal temperature and pressure for drying hops in terms of these chemical markers will be determined. A commercial scale vacuum drying oast will be constructed from a Corten steel shipping fitted with vacuum pumps, heaters, and humidity sensors. The optimal temperature and pressure as determined by the bench-scale vacuum drying experiments will be used in the commercial-scale vacuum drying oast. The overall performance of the commercial drier and its impact on the hop quality will be determined.Objective 3: Recover VOCs lost during vacuum drying of hops using an in-line solid phase media and evaluate their use in beer. A solid phase microextraction bar (SPME) bar will be placed in-line before the vacuum pump to collect the VOCs lost during vacuum drying. These VOCs will be identified and quantified using a GC-MS and compared to those collected during steam distillation of hops. These experiments will be scaled up using in-line solid phase media to trap the VOCs during vacuum drying, and food grade solvents will be used to recover the VOCs. Finally, the performance of these VOCs will be determined in finished beer. Beer will be brewed in the Pennsylvania State University's wet pilot plant and the aroma profile will be altered in one of four ways: using recovered VOCs from vacuum drying; using recovered VOCs from steam distillation; dry hopping using vacuum dried hops; dry hopping using traditionally dried hops. The aroma profiles of these beers will be determined on a GC-MS using headspace-SPME to determine how vacuum dried hops or VOCs recovered from vacuum dried hops affect beer.

Project Methods
Efforts:-Scientific conferences such as American Chemical Society and Institute of Food Technologists annual meetings-Farm Scale Hops Processing Workshop, hosted by the Pennsylvania State University-Extension and outreach through the publishing of the commercial-scale vacuum drying hop oast schematics and equipmentEvaluation:Determining the drying kinetics of hops will be done by collecting and graphing moisture content vs. time data, and fitting an experimental model that describes the drying kinetics. This experimental model will be compared to other models of drying kinetics of comparable products (such as rosemary and spearmint) in order to determine other agricultural products that could benefit from vacuum drying.The alpha/beta acids in the hops will be measured using the American Society of Brewing Chemists (ASBC) Hops-14 official method. Successful drying conditions will be evaluated by determining which drying condition resulted in a statistically significant retention of the alpha and beta acids.The volatile organic compounds in the hops will be using the GC-MS method described in Vazquez-Araujo et al, 2013. Successful drying conditions will be evaluated by determining which drying condition resulted in a statistically significant retention of aroma compounds.The VOCs lost during drying will be measured by placing a 50/30 micrometer DVB/CAR/PDMS solid phase microextraction (SPME) bar in-line between the vacuum oven and the vacuum pump. VOCs will be identified and quantified using the GC-MS method described in Vazquez-Araujo et al, 2013. The appropriate drying conditions will be determined by comparing the VOCs recovered during vacuum drying to the VOCs recovered during steam distillation.?Collecting and recovering VOCs lost during drying will be done by placing solid phase media in-line between the vacuum oven and the vacuum pump, as described in Samuelsson et al, 2006. The VOCs will be recovered using a food grade solvent and will be identified using the ASBC Hops-17 official method. The appropriate food grade solvent will be determined by how closely the VOCs recovered with the scaled up solid phase material correlate to the VOCs recovered with SPME.Evaluating the performance of recovered VOCs from vacuum drying, recovered VOCs from steam distillation, vacuum dried hops, and commercially dried hops in finished beer will be done by adding the above into finished beer and evaluating the aroma profile using GC-MS and headspace SPME. The performance of recovered VOCs and vacuum dried hops in finished beer will be determined by comparing those aroma profiles to their non-vacuum dried counterparts.

Progress 07/01/20 to 01/22/23

Outputs
Target Audience:This research is targeted to both hop growers and beer brewers. The targeted hop growers aresmaller scale hop growers who do not dry their hops on a large scale and could thus benefit from vacuum drying to retain flavor and aroma compounds. The targeted beer brewers are those interested in retaining thiols,potent aroma compounds favored by the current trend of hoppy beers, during drying and during the brewing process. This information is useful for hop growers when deciding on fungicides and hop drying conditions, and it is useful for brewers in order to increase the stability of their product. Changes/Problems:The project has shifted focus from researching vacuum drying as a method to preserve the aroma and flavor of hops, to researching copper binding as a method to preserve the same characteristics. The initial results from the vacuum drying study were promising, as hops dried in a vacuum oven at various temperatures with and without the application of a vacuum showed significant differences in hop aroma retention. However, when the most promising vacuum drying condition was compared to a traditional hop drying condition carried out in an incubator, the vacuum drying conditions did not retain more aroma compounds. Additionally, the traditional hop drying conditions resulted in hops that were dried faster than under vacuum conditions. This left us questioning the efficacy of vacuum drying as a method to preserve aroma and flavor compounds, and its benefit for the hop and brewing industry. Due to the development of the in-house thiol analysis, we decided to shift the focus of the project to protecting thiol compounds from being oxidized by endogenous copper found in beer. This still fulfills our initial goals of supporting hop growers and craft brewers because a more thorough exploration of copper-thiol interactions can lead to more informed decisions about the use of copper-based fungicides during hop growing, a better understanding of thiol stability within the beer, and a more optimized plan for dry-hopping beers, which is currently an important method of imparting hop flavor and aroma due to the rise of India Pale Ale style beers. What opportunities for training and professional development has the project provided?The PI has met with the primary (Elias) and secondary (Anantheswaran) mentors on a weekly basis to discuss current research, future directions, and technical planning required to continue with both. The PI attended the American Chemical Society Fall Meeting and presented a poster based on the research funded by this grant.The PI has attended panels and workshops, both virtual and in-person, to meet with industry professionals and academics on how to best manage projects, improve leadership skills, and improve communications with mentors. This project has also allowed the PI to work closely with an expert in chromatography and develop skills on how to summarize and report data to various individuals, from technical details to big-picture trends. How have the results been disseminated to communities of interest?The PI presented a poster at the American Chemical Society Fall 2021 meeting (Naziemiec, Kwasniewski, Anantheswaran, Elias. Effect of vacuum drying on flavor and aroma compound retention and stability in hops (Humulus lupulus)). The PI also presented this research in the public doctoral seminar and has written a doctoral dissertation. Papers are in development. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? All of Objective 1 was accomplished, with the exception of the bed depth study. The bench scale portion of Objective 2 has also been completed, but the experiments with the commercial scale oast were not carried out due to the inability to seal the Corten shipping container to withstand vacuum pressures. Due to developments of an in-house thiol analysis method, Objective 3 was instead shifted tostudying the stability of thiol compounds both during drying and during the brewing process. Due to this shift in focus, it was observed that certain highly valued thiol compounds were protected from being oxidized by copper by dipeptides that are found in beer. These observations have culminated in a study suggesting what dry hopping practices brewers can undertake in order to protect thiols from oxidation and increase the desired thiols in their beers.

Publications

Progress 07/01/21 to 06/30/22

Outputs
Target Audience:This research is targeted to both hop growers and beer brewers. In this reporting period, a specific direction that was pursued was the stability of thiols, potent aroma compounds favored by the current trend of hoppy beers, during drying and during the brewing process. This information is useful for hop growers when deciding on fungicides and hop drying conditions, and it is useful for brewers in order to increase the stability of their product. Changes/Problems:The project has shifted focus from researching vacuum drying as a method to preserve the aroma and flavor of hops, to researching copper binding as a method to preserve the same characteristics. The initial results from the vacuum drying study were promising, as hops dried in a vacuum oven at various temperatures with and without the application of a vacuum showed significant differences in hop aroma retention. However, when the most promising vacuum drying condition was compared to a traditional hop drying condition carried out in an incubator, the vacuum drying conditions did not retain more aroma compounds. Additionally, the traditional hop drying conditions resulted in hops that were dried faster than under vacuum conditions. This left us questioning the efficacy of vacuum drying as a method to preserve aroma and flavor compounds, and its benefit for the hop and brewing industry. Due to the development of the in-house thiol analysis, we decided to shift the focus of the project to protecting thiol compounds from being oxidized by endogenous copper found in beer. This still fulfills our initial goals of supporting hop growers and craft brewers because a more thorough exploration of copper-thiol interactions can lead to more informed decisions about the use of copper-based fungicides during hop growing, a better understanding of thiol stability within the beer, and a more optimized plan for dry-hopping beers, which is currently an important method of imparting hop flavor and aroma due to the rise of India Pale Ale style beers. What opportunities for training and professional development has the project provided?The PI has met with the primary (Elias) and secondary (Anantheswaran) mentors on a weekly basis to discuss current research, future directions, and technical planning required to continue with both. The PI has attended panels and workshops, both virtual and in-person, to meet with industry professionals and academics on how to best manage projects, improve leadership skills, and improve communications with mentors. This project has also allowed the PI to work closely with an expert in chromatography and develop skills on how to summarize and report data to various individuals, from technical details to big-picture trends. How have the results been disseminated to communities of interest?The PI presented a poster at the American Chemical Society Fall 2021 meeting (Naziemiec, Kwasniewski, Anantheswaran, Elias. Effect of vacuum drying on flavor and aroma compound retention and stability in hops (Humulus lupulus)). Papers are in development. What do you plan to do during the next reporting period to accomplish the goals?The PI is planning on defending her dissertation in the fall and is focusing on finishing the aforementioned dry-hopping experiments.

Impacts
What was accomplished under these goals? No further progress was made under these goals. While initial results were promising, there were no significant advantages when vacuum drying was compared to conventional hop drying. However, due to the development of an in-house thiol analysis method, the project shifted to studying the stability of thiol compounds both during drying and during the brewing process. Due to this shift in focus, it was observed that certain highly valued thiol compounds were protected from being oxidized by copper by dipeptides that are found in beer. These observations have culminated in a study suggesting what dry hopping practices brewers can undertake in order to protect thiols from oxidation and increase the desired thiols in their beers.

Publications

Progress 07/01/20 to 06/30/21

Outputs
Target Audience:This research is targeted towards hop growers, specifically smaller scale hop growers who do not dry their hops on a large scale. In this project, we are using hops as a model system because of their high content ofaroma and flavor compounds. At this point in the project, initial findings have not been shared publically, however the project director has been accepted to present a poster at the American Chemical Society in August 2021. The American Chemical Society presentation will allow these findings to be shared with agricultural scientists. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The PI has met with the primary (Elias) and secondary (Anantheswaran) mentors on a weekly-to-biweekly basis to discuss current research,future directions, and the technical planning required to continue with both. The PI attended leadership workshops (Student Leadership Practices Inventory Workshop) virtually to understand herleadership style and develop the leadership areas she is lacking in. The PI will attend the American Chemical Society Fall Meeting and will present a poster based on the research funded by this grant. How have the results been disseminated to communities of interest?Due to the COVID-19 pandemic and the limitations on in-person research, the planned dissemination of the research has been modified. The PI has not published a paper or presented at a conference, however, the PI will present a poster on the current findings of this project at the American Chemical Society Fall Meeting in August 2021. A paper will follow this presentation. What do you plan to do during the next reporting period to accomplish the goals?The focus of the next reporting period will be on Objective 3. For initial experiments, a system for easily inserting the SPME and other solid phase media will need to be built; initial designs are underway. A list of relevant aroma compounds has been compiled due to experiments in Objective 2.During the scale up experiments in Objective 3, different food grade solvents will be tested to determine which gives the highest recovery of these aroma compounds. Finally, a sensory experiment will need to be designed and implemented to assess the performance of VOCs in finished beer, but this is dependent on the state of sensory research and the COVID-19 pandemic.

Impacts
What was accomplished under these goals? All of Objective 1, apart from the bed depth study, has been completed. The bench scale portion of Objective 2 has also been completed, but the vacuum drying experiments with acommercial scaleoast havenot been completed. Theresults from the completed experiments in Objective 1 and Objective 2 have been accepted for a poster presentation at the American Chemical Society Fall Meeting in August 2021. A publication of the results is to follow. The design of the capture system required for Objective 3 is underway.

Publications