Temperature Dependent Dielectric and Thermal Properties of Whey Protein Gel

Transcription

1 Temperature Dependent Dielectric and Thermal Properties of Whey Protein Gel J. Chen, K. Pitchai, J. Raj, S. Birla, R. Gonzalez, D. Jones, J. Subbiah 46 th Annual Microwave Power Symposium Las Vegas, NV 21 June 2012 Session : Dielectric Properties University of Nebraska Lincoln ConAgra Foods, Inc.

2 Microwaveable foods - convenient Growing Billion dollar industry

3 Domestic ovens non-uniform heating Temperature dependent properties Standing wave pattern

4 Food quality and safety issues Vision, Taste, Smell, Nutrition Outbreaks

5 Microwave model can be used for Food product design Designing food products that respond well to microwave cooking is a mixture of art and science, with heavy emphasis on the science.

6 Microwave heating modeling Multiphysics Equations Electromagnetic & Temperature Fields Material Properties Dielectric properties Thermal properties 6

7 Properties are important Dielectric properties ε * = ε'-jε", Dielectric constant (ε ): capacitance of material and its ability to store electric energy Dielectric loss factor (ε"): ability of material to dissipate electric energy as heat Thermal properties Thermal conductivity (k):property of material's ability to conduct heat Specific heat capacity (Cp):amount of heat required to change material s temperature

8 Properties are needed For modeling of frozen food, dielectric and thermal properties from frozen to thawed state are needed. Dielectric and thermal properties data in frozen state are limited. 8

9 Objective Temperature Dependent, Frozen to Thawed Dielectric properties dielectric constant dielectric loss factor Thermal properties thermal conductivity specific heat capacity 9

10 Whey protein gel Widely used as model food to emulate the real food Easily created as different shapes and sizes Easily formulated to match the real food in dielectric properties and thermal properties 10

11 Sample preparation 20% Whey Protein Powder, 0.56% CaCl 2, 0.5% guar gum Whey protein powder, 80% CaCl 2 Guar gum Whey protein mixture 11

12 Sample preparation Heat the WPG mixture at 95 oven for 90 min Core the sample with a cylindrical tube, and freeze in -20 freezer for overnight 12

13 Dielectric properties system setup Programmable water bath Test cell Network analyzer 13

14 Dielectric test cell 14

15 Dielectric measurement Frequency range: MHz, interval 5 MHz Calibration: Air, Short, 25 deionized water Debye relaxation: ε ω = ε + ε 1 + iωτ where ε is the permittivity at the high frequency limit, where ε =ε s -ε is the static, ε s is low frequency permittivity, and τ is the characteristic relaxation time of the medium.

16 Dielectric properties Validation of calibration 40 Dielectric properties of methanol at DC_theory DC_measure LF_theory LF_measure Frequency, MHz

17 Dielectric Constant Frequency dependence of dielectric constant of WPG Temperature, Frequency, MHz 17

18 Dielectric Constant Temperature dependence of dielectric constant of WPG at 915 and 2450 MHz MHz 2450 MHz Temperature, 18

19 Dielectric Loss Factor Frequency dependence of dielectric loss factor of WPG Temperature, Frequency, MHz 19

20 Dielectric Loss Factor Temperature dependence of dielectric loss factor of WPG at 915 and 2450 MHz MHz 2450 MHz Temperature, 20

21 KD-2 Pro thermal properties analyzer 21

22 Thermal properties Thermal Conductivity Frozen sample: W m-1 K-1 Thawed sample: W m-1 K-1 22

23 Differential scanning calorimetry setup DSC Liquid N 2 Cylinder 23

24 Specific heat capacity, KJ/(Kg K) Specific heat capacity measurement Heating rate: Temperature range Heating rate /min Temperature,

25 Cp, KJ/(Kg K) Specific heat capacity of WPG Heating rate: 2 /min Temperature, 25

26 Conclusion Dielectric and thermal properties of whey protein gel were determined and reported as a function of temperature and frequency. These properties are critical input parameters to a microwave heat transfer model. 26

27 Dielectric properties Dielectric properties Dielectric properties Dielectric properties Future Work: Calibration at multiple temperature water DC_theory LF_theory DC_measure LF_measure water DC_theory LF_theory DC_measure LF_measure Frequency, MHz Frequency, MHz water DC_theory LF_theory DC_measure LF_measure water DC_theory LF_theory DC_measure LF_measure Frequency, MHz Frequency, MHz

28 Acknowledgements Dr. Jeyamkondan Subbiah Dr. David Jones Dr. Sohan Birla Krishnamoorthy Pitchai John Diamond Raj Ricardo Gonzalez This study was primarily sponsored by ConAgra Foods, Inc. Partial support for this study was provided by the USDA CSREES NIFSI grant (Project number: )

29 Questions? 29

30 Thank you 30 30