Director of Graduate Studies, Professor
Biological Engineering and Food Science
Extrusion of foods and feeds, processing of grain-based foods, new uses of agricultural materials and biomechanics.
Glass transition temperatures of cereal-based foods
Background: Crispness is important to many cereal-based foods, such as breakfast cereals and cereal-based snacks. It has been reported that the crispness of foods is highly sensitive to moisture change. It is also suggested that the glass transition theory may provide a clearer approach to understanding the texture changes of crisp snacks as the water content increases. The purpose of this study was to investigate the crispness of cereal-based foods as a function of glass transition and moisture content using corn cake as a model system.
Recent Results: Effects of water plasticization on corn cakes were predicted by the Gordon-Taylor's equation. Moisture sorption isotherms were established using the BET and GAB equations. The relationships among glass transition, moisture and texture were explored. The BET monolayer moisture contents were good indicators of the initial loss of crispness of the corn cakes. Glass transition results indicate that the loss of crispness of corn cakes took place within their glassy state. Water plasticization effects of the corn cakes were well predicted by the Gordon and Taylor equation and may be responsible for the texture change within the glassy state.
High-moisture vegetable protein texturization by twin-screw extrusion
Background: Extrusion technology has been used to produce texturized soy protein products for many years, primarily as meat extenders for human consumption. The market and consumer acceptability of this type of products is still limited, mainly due to less than desirable textural characteristics of the texturized soy products. High moisture texturization by twin-screw extrusion can greatly improve the textural properties of the products. This research will lead to expanded utilization of soybeans and wheat as value-enhanced food. The objectives of this project were to develop high quality meat analogs using vegetable proteins (e.g. soy protein and wheat gluten) with high moisture extrusion technology and to conduct fundamental research related to high moisture extrusion.
Recent Results: Different from products extruded at a moisture level of <30% wet basis, the extrudates produced at high moisture levels were dense and fibrous in nature possessing elasticity and chewiness values similar to real meat such as beef. The extrudates rehydrated well; rehydrated samples were tender, retaining their integrity upon heating.
Viscoelastic properties of soy protein isolate and wheat starch systems
Background: Twin screw extrusion texturization of vegetable proteins under high moisture conditions has a great potential in novel food product developments. During high moisture texturization, food proteins undergo thermal gelation, which causes structural changes. The extent of denaturation and the exposure of functional groups during such processes may affect the rheological properties of gels and the texture of the final products. The objective of this study was to investigate the viscoelastic behavior of soy protein isolate and wheat starch systems as a function of temperature and protein content.
Recent Results: The results of this study suggest strong relationships between viscoelastic properties and gel structure formations, and can provide important information on texture formation during high moisture texturization of vegetable proteins. Below 90°C, the viscoelastic properties of soy protein isolate and wheat starch systems were less affected by temperature and angular velocity. Around 90°C, the viscoelastic properties of the soy protein isolate system showed strong and non-linear dependency of the angular velocity. The elastic modulus of the systems increased with increasing wheat starch content. Adding wheat starch to the soy protein systems also reduced the non-linearity of the elastic and viscous moduli, especially at 90°C.
Partial list of instruments
RheoStress RS100 (Haake, Paramus, NJ). A sophisticate rheometer which allows rheological measurements under controlled stress (CS), controlled rate (CR) and oscillation (OSC) test modes.
Exstar 6100 Dynamic Mechanical Thermal Analyzer (Seiko nstruments, Chiba, Japan). This instrument has four modes of sample deformation including compression, tension, shear and bending, and is able to operate from -150 to 600C at 0.01 to 20C/min heating and cooling rate from 0.01 to 100Hz. Italsohas Fourier transform technology in the noise reduction, and is able to handle a wide range of materials from solid films to melts.
PyrisTM 1 Differential Scanning Calorimetry with TAC 7/PC Thermal Analysis Controller (Perkin-Elmer Corp., Norwalk, CT) is a state-of-the-art computer controlled laboratory instrument that operates with Perkin-Elmer's unique power compensation design. TA.XT2, TA.HDi Texture Analyzers with XTRA Dimension software (Texture Technologies, Corp., Scarsdale, NY). It provides force or distance measurements in compression or tension mode with a wide variety of available probes.
The Fox 200 heat flow meter instrument (LaserComp, Wakefield, MA). A complete system with thermal conductivity instrument for testing in accordance with ASTM C518 and ISO 8301 specifications.
HAAKE Viscotester VT550.