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, 2002
Project End Date
Aug 31, 2006
Grant Year
Project Director
McCarthy, K.
Recipient Organization
DAVIS,CA 95616-8671
Performing Department
Non Technical Summary
Shelf-stable foods are becoming increasingly important as value added products for the U.S. food industry. Two of the most important factors relating to loss of quality in these products are the internal redistribution of moisture and fat. Redistribution of these components will be characterized experimentally and theoretically during storage. The objectives of this project include methodologies to follow internal moisture and lipid migration, mathematical modeling techniques to characterize the migration and physical parameters to use in the models for predicting component migration rates.
Animal Health Component
Research Effort Categories

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
Knowledge Area
502 - New and Improved Food Products;

Subject Of Investigation
5010 - Food;

Field Of Science
2020 - Engineering;
Goals / Objectives
The objectives of this work are: methodologies to follow internal moisture and lipid redistribution in food products during their shelf-life using magnetic resonance imaging (MRI), mathematical modeling techniques to determine diffusivity values, and compilation of mass diffusivity values, on time scales relevant to both processing and product shelf life.
Project Methods
Shelf-stable homogeneous and multi-layer food products are becoming increasingly important as value-added products for the U.S. food industry. These types of foods may be processed or formulated such that different regions have different moisture saturations and/or different water activity levels. These different levels of water activity provide a driving force for moisture migration that can reduce product quality and/or decrease stability. Traditionally moisture saturation levels in foods have been measured gravimetrically. However, for packaged shelf-stable foods for which there is no net gain or loss of moisture, gravimetric analysis provides no information. To gain insight into moisture migration in these products, new experimental techniques are needed. Magnetic resonance imaging has been chosen as the primary experimental method in this study because the samples can be rapidly and noninvasively characterized. While other methods could be used to measure moisture and lipid content MRI will provide the best combination of spatial and temporal resolution. Food systems will fall into the following categories: (1) moisture migration, (2) lipid migration, and (3) simultaneous moisture and lipid migration. The transport of moisture and/or lipid in food during processing and storage is primarily characterized as unsteady state diffusion. In the past, this diffusion process was typically characterized by moisture loss from the food product to the surroundings using models that reflect on overall moisture loss (vs. redistribution) over time, and experimental data that has no spatial information. This work provides significant advantages over this approach. Using MRI experimental data, the changes in moisture and lipid distribution can be modeled by Fick's second law with both spatial and temporal resolution and the diffusion coefficient as the adjustable parameter.

Progress 09/01/02 to 08/31/06

The objective of the NRI award was to develop methodologies to follow internal moisture and lipid redistribution during the shelf-life of food products using magnetic resonance imaging (MRI) and to quantify those changes. Three potential food systems were identified: pasta (moisture migration), brownies (simultaneous moisture and lipid migration) and filled confectionery (oil migration). Work began with the brownie system. In those experiments, we used MRI to evaluate the migration of water and lipid in a brownie/cream cheese system. In all the brownie/cream cheese formulations, we expected oil and water to migrate from a region of higher concentration to a region of lower concentration, with differences due to formulation. Our conclusions from those studies were that water spin-spin relaxation times change dramatically during storage. These changes indicate that the mechanisms responsible for spin-spin relaxation of the protons in the water molecules were sensitive to the staling process. There was not any evidence of significant water migration during storage. Water loss did not occur based on gravimetric analysis. Oil migration was very slight during the storage time and at most a minor contributor to quality changes. At that point, research focused on the third system, oil migration in filled chocolates. Oil migration in filled chocolates limits shelf life due to texture changes and loss of visual appeal. Spatial and temporal oil concentration changes of a two-layer chocolate and peanut butter filling system, which models a filled chocolate, were monitored using magnetic resonance imaging (MRI). During this project, we collaborated with researchers in the chocolate industry, specifically Hershey Foods Corporation researchers (Hershey, PA) and Guittard Chocolate Company researchers (Burlingame, CA). These companies provided in-house training to researchers supported by the NRI award, equipment loan, and commercially produced chocolate and peanut butter filling formulations. Chocolate formulations differed in manufacturer, particle size, anhydrous milk fat content, emulsifier type (soy lecithin and polyglyceryl polycinoleate) and emulsifier level. An MRI spin echo imaging pulse sequence was optimized for the model system and 4 distinct storage studies were performed to monitor the spatial distribution of liquid oil in the model system. The studies ranged from 3 months to a year in duration. Mathematical models were used to evaluate diffusivity values as appropriate; the diffusivities were on the order of 1e-12 m2/s and are consistent with diffusivities reported in the literature for similar systems. At storage temperatures higher than 20C (e.g., 25C and 30C), additional migration mechanisms were recognized. Two manuscripts are in preparation to report this aspect of the research.

A Fickian-based diffusion model alone is not capable of qualitatively or quantitatively predicting liquid oil spatial profiles in filled chocolate confectionary products. Typically, industrial processing/storage strategies for these chocolate products are based on diffusion as the controlling mechanism for oil migration, these strategies are being reevaluated. With respect to long term impact of this work, two graduate students, who were financially supported by this award, completed their Master of Science degrees and currently have positions with international food companies. The post doctoral researcher, supported by this award, obtained a tenure-track faculty position at a research university. These researchers presented NRI-funded research results at national and international meetings. In addition to peer-reviewed publications, research reports were prepared for industry collaborators in order to enhance communication and maintain the industrial relevance of the work.


  • M.J. McCarthy, P.N. Gambhir, A.G. Goloshevsky. 2005. NMR for Food Quality Control. Chapter 4.7 pp 471-488. IN:S. Staph and S.I. Han (eds.) NMR Imaging in Chemical Engineering. Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany.
  • McCarthy, M.J., D.S. Reid and Daijing Wei. 2003. Fat bloom in chocolate. Manufacturing-Confectioner 83(9):89-93.

Progress 01/01/05 to 12/31/05

Objective 1: Migration of oil from high oil content centers into chocolate coatings results in product quality changes. These include loss of texture in the chocolate and filling and fat bloom on the chocolate surface. The objective of the current study was to examine oil migration in systems of increasing solid phase complexity. Three systems were prepared: peanut oil/cocoa butter; peanut butter filling/cocoa butter; and peanut butter filling/chocolate. The bottom layer, either cocoa butter or chocolate, was one cm in height. The top layer, either peanut oil or peanut butter filling, was one cm in height. Magnetic resonance imaging (MRI) was used to measure liquid oil signal as a function of vertical position over a storage time of six months. A calibration curve was prepared to convert signal intensity into mass of peanut oil per volume of sample. During the six months of storage, peanut oil, from either pure oil or the peanut butter filling, penetrated the lower layer. When the lower layer was cocoa butter, peanut oil penetrated throughout the entire bottom layer. There was a gradient from higher to lower signal intensity from the interface between the two components to the bottom. The increase in oil concentration relative to the distance from the original interface varied between samples. For peanut oil/cocoa butter, the oil concentration increased 0.26 g/cm3 at 25% distance from the interface and 0.23 g/cm3 at 50% distance from the interface. For peanut butter filling/cocoa butter, there was an increase of 0.17 g/cm3 at 25% and 0.10 g/cm3 at 50%. For peanut butter filling/chocolate, there was an increase of 0.12 g/cm3 at 25% and 0.04 g/cm3 at 50%. The addition of nonfat solids to cocoa butter significantly influenced oil migration through the cocoa butter liquid phase. This provides additional evidence for the importance of a capillary transport mechanism. Objective 2: The transport mechanisms will be modeled using the data obtained under Objective 1.

Oil migration in high value foods, like filled chocolates, leads to unwanted changes in texture, color and flavor. The work provides insight to manufacturers regarding key factors that affect quality; results will be used to increase economic benefits due to higher quality products and longer shelf life.


  • Choi, Y.J., McCarthy, K.L., McCarthy, M.J. 2005. Oil migration in a chocolate confectionery system evaluated by magnetic resonance imaging. J Food Science 70(5):E312-E317.

Progress 01/01/04 to 12/31/04

A magnetic resonance imaging (MRI) methodology was developed to follow oil migration in food products that have two or more oil-containing components in contact. Specifically, work has been performed to evaluate oil migration in chocolate products. Oil migration is a common problem in composite chocolate confectionery products resulting in softening of chocolate and hardening of the filling. Spatial and temporal changes in the liquid oil content of a two-layer peanut butter and chocolate model system were evaluated using an MRI technique. The experimental factors were: chocolate particle size, milk fat content, emulsifier concentration, degree of temper, and storage temperature. The responses were migration rate and overall change in signal intensity, which characterized the amount of migration. Based on analysis of variance (ANOVA), particle size, milk fat content and storage temperature were significant factors for oil migration rates. Milk fat content and temperature were significant factors for overall change in signal intensity. This research is submitted for publication.

Oil migration in composite foods, like filled chocolates, leads to unwanted changes in texture, color and flavor. The work provides insight to manufacturers regarding key factors that affect quality; results will be used to increase economic benefits due to higher quality products.


  • No publications reported this period

Progress 01/01/03 to 12/31/03

The time-dependent internal moisture and lipid distributions in prepared foods are being evaluated experimentally and mathematically as a function of composition and storage conditions. During storage the internal component distributions are being measured using magnetic resonance imaging. Primary emphasis has been placed on monitoring the mutual diffusion of peanut oil and cocoa butter in a peanut butter cup system. Preliminary changes in lipid distribution are similar to those observed in a model chocolate hazelnut system.

Many quality issues relate to lipid/moisture loss or redistribution within food products. The characterization and understanding of lipid/moisture composition changes will guide product formulation and processing choices to improve/maintain product quality. The information provided will yield economic benefits to manufacturers, retailers and consumers.


  • No publications reported this period

Progress 01/01/02 to 12/31/02

The time-dependent internal moisture distributions in cooked spaghetti are being evaluated and mathematically modeled as a function of composition (recipe) and holding time after cooking. During the holding time, changes in the moisture distribution will be followed using a magnetic resonance imaging (MRI) spin-echo based pulse sequence. Immediately after cooking the moisture distribution is expected to be nonuniform for all samples, with moisture content high at the surface of the pasta and lower at the center. This gradient will equilibrate over time as the moisture redistributes. The moisture redistribution will be modeled using a one-dimensional Fickian diffusion model and characterized by diffusivity values.

Many quality issues relate to moisture loss or redistribution within food products. This characterization of moisture within foods is needed by the industry to guide reformulating and processing to maintain product quality. The information will provide economic benefits to manufacturers and retailers, especially in the future as more foods are formulated for specific functional benefits.


  • No publications reported this period