Principles and Guidelines for In-Line Viscometry in Cereal Extrusion

Area of Science:

• Food Science and Engineering
• Rheology of Biopolymers
• Extrusion Technology

Background:

• Extrusion cooking is vital in the food industry, particularly for cereal-based products, due to its efficiency and nutrient preservation.
• Rheological properties (viscosity, elasticity) are critical for optimizing extrusion processes, but conventional off-line methods fail to capture the in-process conditions.
• In-line viscometers offer a solution for real-time analysis, though their application to heat- and shear-sensitive biopolymers requires specialized designs.

Purpose of the Study:

• To review the application of in-line viscometers in food extrusion, focusing on biopolymer analysis.
• To discuss the challenges and adaptations needed for measuring rheological properties of sensitive food materials.
• To introduce methodologies for assessing steady shear viscosity, extensional viscosity, and normal stress differences in food extrusion.

Main Methods:

• Review of existing literature on in-line viscometer designs for food applications.
• Analysis of methodologies for measuring key rheological parameters (steady shear viscosity, extensional viscosity, first normal stress difference).
• Discussion of biopolymer sensitivity to thermomechanical degradation during extrusion.

Main Results:

• Conventional rheometers are inadequate for replicating the thermomechanical history of food during extrusion.
• In-line viscometers, primarily tested with polymers, need adaptation for biopolymers like starch due to their sensitivity.
• Specific methodologies exist for measuring various rheological properties in-line, crucial for process control.

Conclusions:

• In-line viscometry is an emerging and essential tool for optimizing food extrusion processes, especially for biopolymers.
• Adapting viscometer design is critical to account for the unique properties and sensitivities of food materials.
• This review provides a foundational understanding for researchers in biopolymer and food engineering regarding in-line rheological measurements.