Source: UNIV OF MINNESOTA submitted to
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
Funding Source
Reporting Frequency
Accession No.
Grant No.
Project No.
Proposal No.
Multistate No.
Program Code
Project Start Date
Sep 1, 2007
Project End Date
Aug 30, 2009
Grant Year
Project Director
Labuza, T. P.
Recipient Organization
ST PAUL,MN 55108
Performing Department
Non Technical Summary
Moisture-induced protein aggregation in the dry and intermediate moisture foods results in changes in the structure/texture of the food matrix as well as changes in the biological value during storage. Identify the molecular mechanisms and controlling factors for moisture-induced protein aggregation in low and intermediate-moisture food matrices, and evaluate the changes in structure, texture and nutritional value with the goal of determining ways to inhibit such reactions and improve the stability and nutritional quality of such foods.
Animal Health Component
Research Effort Categories

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
Goals / Objectives
(1) Evaluate the mechanism of moisture-induced protein aggregation and related changes in nutritional and physical properties of simple protein powder based systems (the simple model system) during storage as a function of water content and temperature so as to set the basis for understanding the greater complexity in intermediate-moisture food bar systems, which can contain different sugars, glycols and sugar alcohols. (2) Identify the moisture-induced protein aggregation and the related changes in microstructure, texture and nutritional quality of protein bar model systems (the complex model system) with increased complexity of ingredients (sugars, glycols, sugar alcohols, etc.).
Project Methods
1. Specific objective 1 (A) Determine the moisture sorption isotherms for dry protein powder food matrices, and measure the glass transition temperature of the protein matrix as a function of moisture content. (B) Investigate the occurrence of moisture-induced protein aggregation in dry protein powder food matrices, as a function of storage conditions (relative humidity, temperature) and elucidate the molecular mechanisms involved in aggregation. (C) Influence of matrix pH on protein aggregation. 2. Specific objective 2 (A) Investigate the moisture-induced protein aggregation and their mechanisms in the protein bar dough model system, and elucidate the variations among different protein sources. (B) Investigate the effect of protein aggregation on the structure and texture of matrix, and elucidate the variation among different protein sources. (C) Distinguish the critical factors controlling protein aggregation, and elucidate their effects on aggregation rate, mechanisms and resulted changes in structure/texture.

Progress 09/01/07 to 08/30/09

OUTPUTS: The project focused on investigating the ability of polyols and cysteine to improve the stability of whey proteins in both pure whey model systems and then in an intermediate-moisture protein/energy bar model system. The stability problem caused by both Maillard browning and disulfide interactions. This research began in 2002 with Midwest Dairy Center support. It morphed into this USDA NRI 3 year grant. In 2010, it was further supported with a 2-year grant from the American Egg Board. It has funded 4 post docs and 3 MS degrees and supported 6 undergrads. Three post docs got faculty or research appointments at Jiangnan University and the Univisity of Wisconsin. One was selected as the outstanding young research food scientist in the world by the International Union of Food Science and Technology(IUFOST) in 2010 for the work done basically for this protein aggregation project. An MS grad was hired by the Irish Dairy Board to continue this same work at University College Cork, Ireland. The work has produced 6 refereed publications with 3 more submitted and 1 in preparation, 5 of them are in the J. Agric. Food Chem, the top refereed research journal for food chemistry. There are a total of 32 citations for 4 of the papers (15,9,6,2), a good accomplishment in a short time (Google Scholar). The results of this work have been presented: 1) nationally at the IFT (3 venues: '08,'09,'10) including an invitation to review our results at one meeting sponsored by the Dairy Foods Division; 2) at the Jiangnan University US Alumni Association special meeting held at the 2010 IFT meeting; and 3) internationally at a meeting on water in foods held in Germany, at the IUFOST 15th bi-annual meeting in Cape Town and at the international Whey Symposium held in Paris. In each case there were 200 or more professionals attending the sessions. PARTICIPANTS: Former/present Post Docs: Peng Zhou, Assoc. Prof., State Key Laborartory for Food Science, Jiangnan U, Wuxi, PRC; Xaouming Liu, Asst. Prof. School of Food Sc. & Tech., Jiangnan U, Wuxi, PRC; Michael Uzzan, Technion University, Haifa, Israel and Qinchun Rao U of Minnesota. Former MS food science students: Amy Tran,U College, Cork, Ireland, Heather Taterka, Fulbright Scholarship winner who did post MS work at the Norwegian National Research Center in Trondheim, Norway is now pursuing a PhD in US; Na Wang, Schroder Cheese, Milwaukee, WI; Food Science Undergrads: Sarah Gutkowski Rachel Kyllo, Brian Folger, Kristen Ruud, Ian Ronnigen and Neal Fredrickson. Chemical Engineering Undergrads Aaron Hutt, Cherry Lam, Katlin Sautner, Tim Blaisius, Brian Blonigan, Zac Metz. Chemistry major at St. Scholastica, Duluth, MN - Kenny Smith. Industrial Partners: Davisco Foods, LeSuer, MN, Glanbia, ID and NGOs: MN Dairy Association, Dairy Marketing Inc. International Dairy Export Council. TARGET AUDIENCES: The food industry as a whole. PROJECT MODIFICATIONS: Nothing to report as project has been comleted

This research was prompted by the findings in the pharmaceutics industry related to protein aggregation in the dry and semi-moist state of a dry inhalation insulin drug, as well as bovine somatatropin. The latter work was done at Parke Davis by one of my PhD graduates. The insulin drug was designed for diabetics and removed the need to inject into the blood stream. Unfortunately the insulin became insoluble and caused granulomas to form in the lungs of users prompting an Adverse Event report to the FDA. Eventually the FDA recalled the drug for the 10 USA manufacturers. In 2001, our lab was consulted by a number of protein bar manufacturers. They needed help finding the cause of bar hardening without moisture loss. We had been working on this on another project related to soft cookie hardening and postulated 3 modes: (1)inter protein aggregation through disulfide bond formation; (2) Maillard browning aggregation since most companies used high fructose corn syrup (HFCS) as the sweetener and (3) HFCS crystallization leading to loss of plasticizer. Initial work on whey/water systems indicated significant hardening and loss of solubility when stored at 35 and 45C: 1 month at 45C is equivalent to 1 year at 23C. We found that 85-95% of the aggregation was disrupted by adding dithiothrietol an S-S bond breaker. In testing these findings in model intermediate moisture protein/energy bars (IMF), the 1st significant outcome was that replacing HFCS with a polyol like glycerol or maltitol eliminated most of the non-enzymatic browning and kept the bar softer for at least one year while maintaining protein nutritional quality as measured by the OPA method. Since maltitol contributes sweetness, it was a better polyol to use. Propylene glycol (PG), although an excellent plasticizer, reacted with the protein causing insolubilization. This is similar to the findings in IMF cat food in the 1980's that the PG, when ingested reacted with blood hemoglobin (called Heinz body formation), causing it to reduce oxygen transport leading to anemia of the cats. The FDA eventually banned PG in pet foods. Second, replacing 25% of the whey isolate in the bar with a medium degree (5 to 7%) whey hydrolysate, lowered the glass transition temperature thereby making the bar softer. Third, adding an optimum amount of cysteine inhibited the disulfide aggregation and preserved protein quality. Thus a combination of all 3 approaches can be used by protein/energy bar makers to get an acceptable shelf life and ensure consumers that the bar actually delivers high quality protein. Thus there is a change in both knowledge and actions, especially by the manufacturers of protein bars. These concepts are being used by the International Dairy Export Council (IDEC) for the manufacture of bars for countries like Ethiopia where starvation and Kwashiorkor remain prevalent. This research has also led the American Egg Board to fund us in this area as the use of egg proteins has been low by the bar industry because of it's tendency to harden during storage due to the high -SH group content. Hopefully we will find that the same mechanisms will prevail.


  • Zhou, P. and Labuza T.P. 2007. Effect of moisture content on the glass transition and protein aggregation of solid-state whey proteins and their hydrolysates. J. Food Biophysics 3:108-116
  • Zhou, P., Liu, X. and Labuza, T.P. 2008. Moisture induced aggregation of whey proteins in a protein/buffer model system. J. Agric. Food Chem. 56:2048-2054
  • Zhou, P., Liu, X. and Labuza, T.P. 2008. Effects of moisture-induced whey protein aggregation on protein conformation, the state of water molecules, and the microstructure and texture of high-protein-containing matrix. J. Agric. Food Chem. 56:4534-4540
  • Liu, X., Zhou, P., Tran, A. and Labuza, T.P. 2009. Effects of polyols on stability of Whey Proteins in Intermediate Moisture Model Systems. J. Agric. Food Chem. 57(6):2339-2345 http://DOI10.1021/jf802789y
  • Zhou, P. and Labuza, T.P. 2009. Moisture-introduced aggregation of whey proteins. International J. of Science & Marketing for Nutraceutical Actives, Raw Materials, Finished Products 8(4):29-32
  • Zhu, D. and Labuza T.P. 2010. Effect of cysteine on protein bar hardening in Whey Protein Isolate(WPI)protein bars in WPI/buffer model systems. J. Agric. Food Chem. 58(13):7970-7979 DOI: 10.1021/jf100743z
  • Submitted: Yu, Y., Zhou, P., Liu, X. and Labuza, T.P. 2011. Glycation of major whey proteins inintermediate moisture food systems containing fructose. Submitted to J. of Agric. Food Chem.
  • Labuza, T.P. and Zhou, P. 2010. Collaborative research on mechanisms of protein bar aggregation and hardening. US Jiangnan Alumni Assoc. Special Program on Joint US/PRC Research on functional foods, Chicago, IL
  • Zhou, P., Tran, A. and Labuza, T.P. 2010. Effects of Maillard Reaction on the Quality of Whey-based Nutritional Protein Bars. IUFOST 15th Bi-annual Meeting, Cape Town, South Africa
  • Guo, M.F., Zhou, P., Liu, D.S., Liu, X.M. and Labuza, T.P. 2011. Effect of Maillard reaction-induced modification and aggregation of whey proteins on the hardening of protein bar model system. Submitted to J. of Agric. Food Chem.
  • Liu, D.S., Zhou. P., Liu, X.M. and Labuza, T.P. 2011. Moisture-induced aggregation of alpha lactalbumin Effects of temperature, cations and pH. Submitted to J. of Agric. Food Chem.
  • In preparation: Tran, A., Zhou,P., Zhu, D. and Labuza, T.P. 2011. The chemistry of degradation of intermediate Moisture Protein Bars.
  • Abstract: Zhu, D. and Labuza, T.P. 2009. Effect of cysteine on lowering protein aggregation and subsequent hardening of WPI protein bars (Poster paper 09-A-3192). IFT Annual Meeting, Anaheim, CA
  • Zhu, D. and Labuza, T.P. 2009. Effect of cysteine on lowering protein aggregation and subsequent hardening of WPI bars (Poster paper 06/06/09) USDA NRI PI Meeting, Anaheim, CA
  • Tran, A., Taterka, H. and Labuza, T.P. 2009. Quality Changes during storage of a whey based protein nutrition bar (Poster paper). IFT Annual Meeting, Anaheim, CA
  • Tran, A., Taterka, H. and Labuza, T.P. 2009. Quality Changes during storage of a whey based protein nutrition bar (Poster paper), USDA NRI PI Meeting, Anaheim, CA
  • Labuza, T., Zhou, P., Zhu, D., Taterka, H. Tran, A. 2010. Influence of moisture content and humectant type on aggregation of protein, hardening and nutritional quality loss during storage of protein nutritional bars. EURO Foods Water 7th Biannual Meeting, Stutgart, Germany.
  • Zhu, D., Folger, B., Gutkowski, S., Sautner, K., Fredrickson, N.R. and Labuza, T.P. 2010. Reducing loss of protein bar quality during storage by delaying protein aggregation and inhibiting non-enzymatic browning (NEB). Poster Abstract # 184-1. IFT Annual Meeting, Chicago, IL

Progress 09/01/07 to 08/31/08

OUTPUTS: After being funded by DMI to get preliminary work done in 2007 we then got a USDA NRI grant to further work on the problem of the hardening of protein bars. Early work showed that whey protein based bars hardened much faster that did soy based bars. At the end of last year we also got funding from Davisco, a producer of the whey proteins we are using. The work is at 2 levels: (1) the very basic chemistry of the hardening process and (2) finding practical solutions to the problem. In the basic chemistry area we are looking at three mechanisms that can occur: (a) simple water diffusion into the protein particles causing loss of plasticizer volume between the particles; (2) inter-protein disulfide bond formation; and (3) protein interactions that occur through the Maillard browning reaction which not only makes them hard but also causes loss of protein quality. An additional finding was that there is also a direct action of a commonly used humectant, namely propylene glycol (PG), with the whey protein causing it to aggregate and become totally insoluble. Several years ago the FDA banned the use of PG in intermediate moisture pet foods as it caused an interaction with the hemoglobin in the blood cells of cats, (Heinz body formation) causing anemia. The results of these studies were presented at 2 dairy protein advisory committee meetings at the DMI headquarters in Chicago, at the International Dairy meeting in San Francisco (> 300 attendees), at the International Whey Conference (invited) in Paris (> 250 attendees). A poster paper and an oral invited presentation for the Dairy Division of IFT (> 200 attendees), along with a poster at the USDA NI PIs in New Orleans, a poster at the IUFOST meeting in Shanghi China, and a invited oral presentation at the Euro Foods Water Congress in Stuttgart GR ((200 attendees). We also transferred our results to the Am. Dairy Export Council (ADEC) who are making protein bars to help stave off malnutrition in Ethiopia. We have also presented at Davisco, a sponsor of the research. PARTICIPANTS: Dr. Peng Zhou (Post-doc) PhD at Cornell Univ. with Joe Regenstein on protein matricies. 1st 2 years on the DMI project then 6 months on the NRI followed by becoming a Professor at Jiangnan Univ. (Wuxi, PRC) in the State Laboratory in the Food Science and Technology Dept. He and Dr. Xiaoming Lui, his wife both have appointments at Jiangnan Univ., the largest Food Science program in China. While at Minnesota, he trained 4 other researchers in the use of the DSC, TAXT-Extra, and FTIR Dr. Xiaoming Lui (Post-doc) Prior PhD with Barry Swanson at Washington State Univ. with a focus on protein chemistry and then Post-doc with Dr Lloyd Metzger at the Univ. of Minnesota working on protein aggregation during thermal processing of fluid whey systems. Dr. Dan Zhu (Post-doc). Prior Post-docs in China and Japan and at the Diary Research Center Univ. of Wisconsin. She not only carries out the basic part of the research but also does training of others. Amy Tran, MS student who will graduate in February, is doing research on evaluating the loss of protein nutritional quality in the bars under ASLT conditions. Heather Taterka, MS student, is evaluating the influence of different humectants on quality changes during storage. She will finish in August and has a Fulbright Fellowship to work at the Norwegian Technical Laboratories beginning in October. Tim Blasius is an Junior in Chemical Engineering who did an Undergraduate Research Opportunities Program study in our labs in the 2008 spring semester and continued on as a lab helper this past fall working with all the graduate students in my lab. He will have a summer internship at Malt O-Meal (Northfield, MN) during the summer of 2009 working on cereal chemistry problems. Katlin Sautner is a sophomore chemical engineering student who we hired as a lab assistant and will continue helping the graduate students on this project. Laurie Nelson-Davis She is the Director of Product Development at Davisco International Foods (Egan MN) who has supported our research. She did the seminal work for her MS thesis on proteins bar hardening in our labs which lead to support from DMI and then USDA. Matt Davis of Davisco has supported this work from the start. TARGET AUDIENCES: Our audiences are food scientists interested in the chemistry of protein quality change, the protein industry interested in selling quality proteins and the nutritional bar manufacturers (a $1 billion market) PROJECT MODIFICATIONS: None

As noted above in the last year we have given talks or poster presentations about our work at 2 international meetings in the US and 3 foreign countries. We have sent information to at least 20 companies who have heard the presentations, 3 of whom are the major manufacturers of whey proteins. They are translating the findings to their clients who are making protein bars. Our work with ADEC will insure that the children getting the protein bars will be of high enough quality to be consumed, ie not hard and of high nutritional value. Because of funding other than the USDA we were able to travel outside the USA to present to a more global audience. The response at the whey conference in Paris was exceptionally good as many foreign companies that are involved with bars were present and requested further material. A recent visit to the grocery store shows that one of our findings, i.e. the negative reaction of PG with whey protein, may have lead to many bar makers switching over to maltitol despite its high cost.


  • Refereed Journal Articles Zhou, P., Liu, X., and Labuza, T.P. 2008. Effects of moisture-induced whey protein aggregation on protein conformation, the state of water molecules, and the microstructure and texture of high-protein-containing matrix, Journal of Agricultural and Food Chemistry, 56: 4534-4540
  • Zhou, P., Liu, X. and Labuza, T.P. 2008. Moisture induced aggregation of whey proteins in a protein- buffer model system. Journal of Agricultural and Food Chemistry, 56: 2048-2054
  • Conference Proceedings Labuza, T.P., Zhou, P., Liu, X., Davis,L., and Tran, A. 2008 Protein aggregation and hardening of whey based protein bars during storage. 5th International Whey Conference Paris, France Proceedings
  • Abstracts Labuza, T.P. 2008. Influence of moisture on aggregation of protein during storage. 5th Euro Foods Water Conference, Stuttgart, Germany.
  • Labuza, T.P., Tran, A., Taterka, H., and Zhou P. 2008. Mechanisms for Whey Protein aggregation during storage. Abstract Book of the 5th International Whey Congress (IWC), Paris, France.
  • Zhou, P., Liu, X., Tran, A., and Labuza, T.P. 2008. Aggregation of whey protein in nutritional bars. Abstract Book IFT Dairy division for IFT Annual Meeting, New Orleans, LA.
  • Labuza, T., Zhu, D., Taterka, H., and Tran, A. 2008. Influence of moisture on aggregation of protein during storage. Abstract book Annual Meeting of USDA CREEES PIs NRI Grants. New Orleans, LA.
  • Zhou, P., Liu, X., Tran, A., and Labuza, T.P. 2008. Effect of Polyols on Functionality and Stability of Whey Protein Based Nutritional Bars. Abstract book of IFT Annual Meeting, New Orleans, LA.