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3D micro X-ray images help answer questions about fried foods’ internal structure

3D solid network image of pores formed in a potato during frying. Image courtesy of Pawan Takhar.

URBANA, Ill. – What happens to food and its microstructure when it is fried is a complicated process, both scientifically and mathematically speaking. While consumers want a product that is crispy and tasty, food scientists seek to get a closer glimpse into what exactly is going on inside the food during frying in order to improve products.

Particularly, Pawan Takhar, a University of Illinois food scientist, is interested in the food’s uptake of oil during frying and how that oil gets distributed throughout the food. “Through conventional lab techniques we can already see how much oil content is in food material, but we didn’t know how it gets distributed throughout the material,” he says.

To understand the distribution of oil better, Takhar and his lab recently conducted a study using X-ray micro-computed tomography (micro-CT) to gain 3D images of the microstructure of fried potato disks after they had been fried for various lengths of time.

During deep frying, as food is immersed in hot oil, water in that food quickly evaporates and steam pressure builds. This pressure affects the microstructure, including the porosity—the number and size of pores in the food—as well as the twistiness of the pathways between those pores (tortuosity). This determines how and how much oil gets taken up into the food.

For the study, russet potatoes cut into disks that were 45-mm in diameter and 1.65 mm thick were fried at 190 degrees Celsius for 20, 40, 60, or 80 seconds, freeze dried, and scanned.

Takhar says about 986 2D images of the potato samples were collected and then combined to produce 3D images. Using the 3D images, they were able to gain more information about the pores and pore networks in the material.

The researchers observed that as frying time increased, pore size increased, allowing for greater uptake of oil. They also saw a correlation between oil content and how the network of pathways between the pores changed throughout the frying time. These pathways act like channels for water and vapor flow and oil penetration in the food.

“As you fry the material, you can see how those pore structures are forming,” Takhar says. “We found that in the beginning of frying, the pore network is very complicated. The waviness in the pathway, the tortuosity, is very complex in the beginning so the material resists oil penetration. But as the frying progresses, those pathways become simpler. Pores open up and are easily accessible from the outside and oil can be taken up.”

Takhar also explains that oil was observed distributed across the full thickness of the potato disks. In thicker materials with lots of moisture (like chicken nuggets and French fries), they have observed the oil to remain near the surface as continuous evaporation helps to resist oil penetration.

“It is not easy to make a product that has no oil and still provides taste, flavor and texture that consumers enjoy,” he says. “People like that fried flavor and the texture of crispiness outside and softness inside. At the same time you want to reduce the oil content to make the food healthier. With this network study we wanted to see how those networks are formed, because networks are also related to texture.” It’s a combination of the oil content and air pockets in the pore structure that provide the desired crispy texture.

The findings from the potato disks in the study can also be applied to other fried foods, Takhar says. His lab has done previous research on frying using chicken nuggets and French fries.

While Takhar and his lab have done mathematical modeling of what happens during frying—just one previous paper outlines over 100 mathematical equations involved in the process—he says this study provides some experimental validation as to what is happening inside the food material.

“I would say we still only understand about 10 percent of what is taking place during frying,” says Takhar. He and his lab have studied the effects of frying for 10 years. “For an engineer or a food scientist, it’s the ultimate problem because it’s so complicated.

“Our aim is to make these products healthier, so that they have the same taste and texture but, at the same time, have lower fat content. That is our long-term goal with our research,” Takhar says.

“Microstructural characterization of fried potato disks using X-Ray micro computed tomography,” is published in the Journal of Food Science and can be found online athttp://dx.doi.org/10.1111/1750-3841.13219 Co-authors are Tanjila Alam, formerly a graduate student at the University of Illinois, and Pawan S. Takhar of the University of Illinois.

Funding was provided by USDA-NIFA.

The researchers acknowledge Beckman Institute at University of Illinois for providing assistance with the micro CT scanning experiments.

News Source:

Pawan Takhar, 217-300-0486

Original story posted here:

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Scientists tackle our addiction to salt and fat by altering foods’ pore size, number

URBANA, Ill. – Two University of Illinois food scientists have learned that understanding and manipulating porosity during food manufacturing can affect a food’s health benefits.

Youngsoo Lee reports that controlling the number and size of pores in processed foods allows manufacturers to use less salt while satisfying consumers’ taste buds. Pawan Takhar has found that meticulously managing pore pressure in foods during frying reduces oil uptake, which results in lower-fat snacks without sacrificing our predilection for fried foods’ texture and taste.

Both scientists are experts in food engineering and professors in the College of Agricultural, Consumer and Environmental Sciences’ Department of Food Science and Human Nutrition.

Regarding salt, Lee said, “Six in 10 American adults either have high blood pressure or are on the borderline of this diagnosis largely because they eat too much salt. Overconsuming salt is also associated with the development and severity of cardiovascular and bone diseases, kidney stones, gastric cancer, and asthma.”

Because 70 percent of the salt Americans consume comes from processed foods, Lee began to study the relationship between the microstructural properties of these foods and the way salt is released when it is chewed.

“Much of the salt that is added to these foods is not released in our mouths where we can taste it, and that means the rest of the salt is wasted,” he said. “We wanted to alter porosity in processed food, targeting a certain fat–protein emulsion structure, to see if we could get more of the salt released during chewing. Then food manufacturers won’t have to add as much salt as before, but the consumer will taste almost the same amount of saltiness.”

Increasing porosity also changed the way the foods broke apart when they were chewed, exposing more surface area and increasing saltiness, he said.

“When foods crumble easily, we further reduce the amount of salt that is needed. Changing the number or size of pores in the food’s surface can help us to accomplish this,” he said.

Takhar said that his porous media approach to understanding the behavior of water, oil, and gas during frying will help create strategies that optimize the frying process, reduce oil uptake, and produce lower-fat foods.

The articles Takhar publishes in academic journals feature page after page of complex mathematical equations that describe the physics involved in the transport of fluids and in textural changes in foods. These equations then guide the simulations that he performs in his laboratory.

“Frying is such a complicated process involving more than 100 equations. In a matter of seconds, when you put the food in the fryer, water starts evaporating, vapors form and escape the surface, oil penetration starts, and heat begins to rise while at the same time there’s evaporative cooling off at different points in the food. Some polymers in the food matrix may also change their state, and chemical reactions can occur. It’s not an easy set of changes to describe,” he said.

Within 40 seconds of frying, the texture of gently fried processed foods like crackers is fully developed, the scientist said. “That’s the cracker’s peak texture. Any longer and you’re just allowing more oil to penetrate the food.

“A lot of frying research has focused on capillary pressure in the oil phase of the process, but we have found that capillary pressure in the water phase also critically affects oil uptake,” Takhar said.

Capillary pressure makes overall pore pressure negative, and that negative pressure tends to suck oil from inside. His simulations show when that pressure is becoming more negative.

“The trick is to stop when pore pressure is still positive (or less negative)—that is, when oil has had less penetration. Of course, other variables such as moisture level, texture, taste, and structure formation, must be monitored as well. It’s an optimization problem,” he noted.

When this exquisite balance is achieved, lower-fat, healthier fried foods are the result, he added.

“Temporal Sodium Release Related to Gel Microstructural Properties—Implications for Sodium Reduction” was published in a recent issue of Journal of Food Science. Lee and Wan-Yuan Kuo are co-authors of the study, which will continue to be funded by USDA. “Modeling Multiscale Transport Mechanisms, Phase Changes, and Thermomechanics during Frying” was published in a recent issue of Food Research International. Co-authors are Takhar and Harkirat S. Bansal of the U of I and Jirawan Maneerote of Kasetsart University in Bangkok, Thailand. The Takhar study was funded by USDA and the Royal Thai Government.


News Sources:
Youngsoo Lee, 217-333-9335
Pawan Takhar
, 217-300-0486

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Food Dehydration Reduction of Postharvest Losses – Prof. Hao Feng, February 10, 2015

“Food DehydrationReduction of Postharvest Losses,” Hao Feng, Ph.D, Professor, Department of Food Science and Human Nutrition (fshn.illinois.edu), University of Illinois at Urbana-Champaign. 

Lecture slides:
http://intlprograms.aces.illinois.edu…

Event: Food Systems for Food Security Symposium
February 10, 2015, ACES Library, Information and Alumni Center, Urbana, Illinois
http://intlprograms.aces.illinois.edu…
http://intlprograms.aces.illinois.edu/content/food-systems-food-security-symposium

Sponsor: International Food Security at Illinois
College of Agriculture, Consumer and Environmental Sciences
University of Illinois at Urbana Champaign

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Hao Feng

Power ultrasound as a new food and bioprocessing modality, novel chemical and physical treatments for improving the quality and safety of fresh and fresh-cut produce, conversion of biomass for production of biofuel and value-added products, food dehydration, heat and mass transfer analysis, and determination of physical and transport properties of food and biological materials.


Professor; haofeng@illinois.edu; more detail here.


 

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Nicki Jene Engeseth

Dr. Nicki J. Engeseth

Dr. Engeseth’s research focus is on the study of chemical and biochemical reactions in food products with the eventual goal of manipulation of these pathways for enhancement of food quality. Highlights include the impact of growing conditions, processing and storage on quality and nutritional value of fruits and vegetables. This includes the study of oxidative reactions and antioxidant action with the eventual goal of manipulating such reactions for enhanced food stability and nutritional quality. Also being studied are the physical properties of food lipids, such as cocoa butter and the impact of changes through storage and processing on consumer perception of product quality.

Oilseed lipid/fatty acid biosynthesis pathways; manipulation of oilseeds to alter fatty acid composition and total oil content; chemistry and modes of action of natural antioxidants.Vegetable oils are one of the most valuable components of oilseeds and are an important constituent of both human and animal diets. Oil quality is dependent upon the fatty acid composition. Our laboratory studies the pathways for fatty acid biosynthesis in oilseeds, with particular emphasis on acyl carrier protein’s role in determination of plant fatty acid composition and oil content. We have developed a series of transgenic plants to investigate the impact of altered acyl carrier protein levels on oilseed quality. Some of this research also extends into the study of pathways for unusual fatty acid biosynthesis so that we may be able to produce unusual fatty acids desirable for nutritional applications in common oilseeds. Additionally, we study the impact of altered environmental atmospheric levels of CO2 and ozone on soybean quality through a multi-investigator project (SOYFACE), including major storage components of carbohydrate, lipid and protein and other key compounds with potential biological activity such as isoflavones, other phenolics and saponins. The impact of ozone on oxidative stress issues on soybeans will be addressed as will the impact of altered environmental atmospheres on gene regulation of key pathways influencing soybean quality.Other research in our laboratory has been focused on natural antioxidants, with a particular emphasis thus far on honey. Projects related to this include the study of honey as a protective agent against oxidative deterioration reactions in foods and the mechanisms by which honey imparts this protection, including detailed characterization of antioxidant components of honeys. Other projects include the investigation of honey and other food components as sources of dietary antioxidants and the ability of these natural sources to protect against oxidative stress in human/animal systems.


Professor of Food Chemistry; engeseth@illinois.edu; more detail here.


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Keith R. Cadwallader

Dr. Keith R. Cadwallader

Food quality depends largely on the sensory properties of a food, including flavor (taste and aroma), color, texture and overall appearance. Among these, flavor is often the most important determinant of food acceptance by the consumer. Aroma is an important element of flavor and is attributed to the perception of volatiles (aroma compounds) present in the dynamic headspace (mouth and nasal cavities) of the food during consumption. Dr. Cadwallader’s research revolves around the study of food flavor as it relates to overall food quality. He is interested in both the basic and applied aspects of the flavor chemistry of foods. His fundamental (foundation) research includes the development of improved methods for the chemical/sensory characterization of food flavor systems. These studies have led to the identification of the character-impact aroma compounds of various foods, including seafood, meat, dairy, vegetable and beverage products as well as food ingredients such as herbs and spices. Dr. Cadwallader’s applied studies are mainly the result of his collaboration with food industry partners. Research in this area includes the development of technology for the creation/recovery of natural flavorings, study of the impact of food processing, packaging and storage on flavor quality and identification of off-flavors and taints. In addition to the above, Dr. Cadwallader is also interested in the physical chemistry of flavor-food matrix (binding) and flavor-flavor interactions flavor release and flavor stability.


Professor of Food Chemistry; cadwlldr@illinois.edu; more detail here.


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Munir Cheryan

Dr. Munir Cheryan

Membrane separations; Bioprocessing; Fermentation; Dairy Technology; Corn Refining; Soybean Processing; Vegetable Oil Processing.


Professor Emeritus; mcheryan@illinois.edu; more detail here.


 

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Pawan Takhar

Dr. Pawan Takhar

Dr. Takhar uses porous media physics to study food and bioprocessing applications via mathematical modeling and experimental validation. He focuses on making further improvements in the multiscale hybrid mixture theory (HMT) with applications in swelling biopolymers. His research group has applied the theory for predicting fluid transport and stress-crack initiation in foods; performing macroscale and microstructural experiments (using NMR imaging, X-ray tomography and scanning electron microscopy) for obtaining further insight into transport mechanisms; solving unsaturated transport problems such as frying and starch expansion during extrusion; designing controlled release applications; and adapting the concepts from transport theories to work with food safety problems (fractional differential equations based new application in this field). Numerous bioprocesses such as drying, sorption, solvent transport, controlled release, conditioning, cooking, storage etc. can be addressed using his general approach on transport mechanisms. His team has also performed validation experiments on continuous and intermittent drying, and sorption to develop strategies for obtaining foods with reduced fractures and fried foods with lower fat content.


Associate Professor; ptakhar@illinois.edu; more detail here.


 

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Shelly J. Schmidt

Dr. Shelly J. Schmidt

Dr. Schmidt’s food materials science research program uses multi-level analytical techniques, such as Nuclear Magnetic Resonance (NMR) spectroscopy, Magnetic Resonance Imaging (MRI), Differential Scanning Calorimetry (DSC), Dynamic Vapor Sorption (DVS), Dynamic Dewpoint Isotherms (DDI), and Thermogravimetric Analysis (TGA) to elucidate the relationship between water and solids dynamics (mobility) and the physical, chemical, and microbiological stability and quality characteristics of food systems.


Professor; sjs@illinois.edu; more detail here.


 

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Scott A. Morris

Dr. Scott A. Morris

Dr. Morris’ research focuses on devising and developing new engineering technologies for the food production and packaging industries: Defect Imaging: In conjunction with the Beckman Center for Advanced Research, using ultrasound and optically computed tomography, the University of Illinois Packaging Laboratory has developed experimental technologies that are being used to evaluate defects in package seals and structures for use in preventing post-processing contamination. Process Optimization: Using simulation modeling of packaging lines, the University of Illinois Packaging Laboratory has demonstrated that it is both feasible and profitable to implement operational modifications to increase productivity. In a major food company’s packaging plant, analysis and restructuring of machine operation protocols resulted in a $1.6 million per year increase in production, with no additional capital investment. Security: Using cryptographic techniques as well as advanced optical information technologies, preliminary investigations are being conducted into the feasibility of providing high security verification markings for structures such as food and pharmaceutical packages. This research is directed at determining whether or not it is both possible and practical to include information verifying shipment source and contents during distribution. Informatics: Work is underway to determine the nature and extent of impact of information systems associated with the manufacture, distribution and use of both consumer and industrial products and materials.


Associate Professor; smorris@illinois.edu; more detail here.


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