Abstract

The objective of this study was to monitor and model the texture changes of foxtail millet extrudates with different structural properties as a function of water activity (a_w). Four extrudates, after equilibrated at a_w of 0.113-0.97, were compressed using a TA.XT2 Texture Analyzer. Two force-related texture parameters, Peak Force (PF) and Total Work (TW) and two jaggedness-related, Number of Spatial Ruptures (NSR) and Specific Ling Length (SLL), were extracted from their force-displacement curves. Water sorption led to loss of jaggedness of their force-displacement curves. All the four texture parameters decreased when a a_w increased to a certain value. Before the decrease occurring, TW and PF increased for all the extrudates with a a_w increase, while SLL increase was observed only for two extrudates and no NSR increase was observed for all extrudates. The critical water activity (a_wc) where texture parameters decreased rapidly ranged between 0.42 and 0.83 depending mainly on the kinds of the extrudates and to some extent on the texture parameters studied. The extrudates with coarse structure exhibited lower force-related values, while the extrudates with fine structure exhibited lower jaggedness-related values. Crispness index, a combination of force- and jaggedness-related texture criteria, decreased almost linearly as a a_w increase up to 0.61~0.66 for all the extrudtes. The Peleg-Fermi equation can satisfactorily model the changes in jaggedness-related texture parameters as a function of a_w. A modified form of the Peleg-Fermi equation, proposed in this study, was needed to model the changes of force-related parameters better.

Keywords:

Extrusion, foxtail millet, hydrosorption, modeling, Peleg-Fermi model, texture,

References

1. Arimi, J.M., E. Duggan, M. O'Sullivan, J.G. Lyng and E.D. O'Riordan, 2010. Effect of water activity on the crispiness of a biscuit (Crackerbread): Mechanical and acoustic evaluation. Food Res. Int., 43: 1650-1655.
   CrossRef    
2. Barret, A.H. and G. Kaletunc, 1998. Quantitative description of fracturability changes in puffed corn extrudates affected by sorption of low levels of moisture. Cereal Chem., 75(5): 695-698.
   CrossRef    
3. Braga, L.L.M. and R.L. Cunhn, 2004. Plasticization and antiplasticization of small molecule in cellular foods: TMDSC and mechhanical properties. Int. J. Food Prop., 7(1): 105-120.
   CrossRef    
4. Chang, Y.P., P.B. Cheah and C.C. Seow, 2000. Variations in flexural and compressive fracture behavior of a brittle cellular food (dried bread) in response to moisture sorption. J. Texture Stud., 31: 525-540.
   CrossRef    
5. Chauvin, M.A., F. Younce, C. Ross and B. Swanson, 2008. Standard scales for crispness, crackliness and crunchiness in dry and wet foods: Relationship with acoustical determinations. J. Texture Stud., 39: 345-368.
   CrossRef    
6. Colonna, P., J.L. Doublier, J.P. Melcion, F. de Monredon and C. Mercier, 1984. Extrusion cooking and drum drying of wheat starch. I. Physical and macromolecular modifications. Cereal Chem., 61(6): 538-541.
   
7. George, W., S.W. Halek and K.L.B. Chang, 1989. The effect of moisture content on mechanical properties and texture profile parameters of corn meal extrudates. J. Texture Stud., 20: 43-55.
   CrossRef    
8. Gibson, L.J. and M.F. Ashby, 1999. Cellular Solids: Structure and Properties. 2nd Edn., Pergamon Press, Oxford, U.K.
   
9. Goerlitz, C.D., W.J. Harper and J.F. Delwiche, 2007. Relationship of water activity to cone crispness as assessed by positional relative rating. J. Sens. Stud., 22: 687-694.
   CrossRef    
10. Gondek, E. and P.P. Lewicki, 2006. Antiplasticization of cereal-based products by water. Part II: Breakfast cereals. J. Food Eng., 77: 644-652.
    CrossRef    
11. Greenspan, L., 1977. Humidity fixed points of binary saturated aqueous solutions. J. Res. Natl. Bur. Stand., 81: 89-96.
    CrossRef    
12. Guo, X.E. and L.J. Gibson, 1999. Behavior of intact and damaged honeycombs: A finite element study. Int. J. Mech. Sci., 41: 85-105.
    CrossRef    
13. Harris, M. and M. Peleg, 1996. Patterns of textural changes in brittle cellular cereal foods caused by moisture sorption. Cereal Chem., 73(2): 225-231.
    
14. Heidenreich, S., D. Jaros, H. Rohm and A. Ziems, 2004. Relationship between water activity and crispness of extruded rice crisps. J. Texture Stud., 35: 621-633.
    CrossRef    
15. Katz, E.E. and T.P. Labuza, 1981. Effect of water activity on the sensory crispness and mechanical deformation of snack food products. J. Food Sci., 46: 403-409.
    CrossRef    
16. Kulchan, R., P. Suppakul and W. Boonsupthip, 2010. 54 Texture of Glassy Tapioca-flour-based Baked Product as a Function of Moisture Content. In: Reid, D.S., T. Sajjaanantakul, P.J. Lillford and S. Charoenrein (Eds.), Water Properties in Food, Health, Pharmaceutical and Biological Systems: ISOPOW 10. Wiley-Blackwell, Ames, Iowa, pp: 591-598.
    CrossRef    
17. Lane, R.H., 1998. Cereal Foods. In: Official Methods Analysis of the Association of Official Analytical Chemists. 16th Edn., AOAC International, Gaithersburg, MD, pp: 1-37.
    PMCid:PMC124796    
18. Lewicki, P., E. Jakubczyk, A. Marzec, M.C. Cabral and P.M. Pereira, 2004. Effect of water activity on mechanical properties of dry cereal products. Acta Agrophysica, 4(2): 381-391.
    
19. Li, Y., K.M. Kloeppel and F. Hsieh, 1998. Texture of glassy corn cakes as a function of moisture content. J. Food Sci., 63(5): 1-4.
    CrossRef    
20. Martinez-Navarrete, N., G. Moraga, P, Talens and A. Chiralt, 2004. Water sorption and the plasticization effect in wafers. Int. J. Food Sci. Tech., 39: 555-562.
    CrossRef    
21. Marzec, A. and P.P. Lewicki, 2006. Antiplasticization of cereal-based products by water. Part I. Extruded flat bread. J. Food Eng., 73(1): 1-8.
    CrossRef    
22. Nicholls, R.J., I.A.M. Appelqvist, A.P. Davies, S.J. Ingman and P.L. Lillford, 1995. Glass transition and fracture behaviour of gluten and starches within the glassy state. J. Cereal Sci., 21(1): 25-36.
    CrossRef    
23. Norton, C.R.T., J.R. Mitchell and J.M.V. Blanshard, 1998. Fractal determination of crispy or crackly textures. J. Texture Stud., 29: 239-253.
    CrossRef    
24. Pamies, V.B., G. Roudaut, C. Dacremont, L. Meste and J.R. Mitchell, 2000. Understanding the texture of low moisture cereal products: Mechanical and sensory measurements of crispness. J. Sci. Food Agr., 80: 1679-1685.
    CrossRef    
25. Roos, Y.H., K. Roininen, K. Jouppila and H. Tuorila, 1998. Glass transition and water plasticization effects on crispness of a snack food extrudate. Int. J. Food Prop., 1(2): 163-180.
    CrossRef    
26. Roudaut, G. and D. Champion, 2011. Low-moisture food: A physicochemical approach to investigate the origin of their physical instability versus water or sucrose. Food Biophys., 6: 313-320.
    CrossRef    
27. Roudaut, G., C. Dacremont and M.L. Meste, 1998. Influence of water on the crispness of cereal-based foods: Acoustic, mechanical and sensory studies. J. Texture Stud., 29: 199-213.
    CrossRef    
28. Roudaut, G., F. Poirier, D. Simatos and M.L. Meste, 2004. Can dynamical mechanical measurements predict brittle fracture behaviour? Rheol. Acta, 44: 104-111.
    CrossRef    
29. Saeleaw, M., K. Dürrschmid and G. Schleining, 2012. The effect of extrusion conditions on mechanical-sound and sensory evaluation of rye expanded snack. J. Food Eng., 110: 532-540.
    CrossRef    
30. Sauvageot, F. and G. Blond, 1991. Effect of water activity on crispness of breakfast cereals. J. Texture Stud., 22: 423-442.
    CrossRef    
31. Surówka, K., 2002. Food texture and methods of its study (In Polish). Przemysl SpoSywczy, 10: 12-17.
    
32. Suwonsichon, T. and M. Peleg, 1998. Instrumental and sensory detection of simultaneous brittleness loss and moisture toughening in three puffed cereals. J. Texture Stud., 29: 255-274.
    CrossRef    
33. Wollny, M. and M. Peleg, 1994. A model of moisture-induced plasticization of crunchy snacks based on Fermi's distribution function. J. Sci. Food Agr., 64: 467-473.
    CrossRef    
34. Zhao, X.W., 2006. Extrusion characteristics of foxtail millet. Ph.D. Thesis, Northwest Science and Technology University for Agricultural Forestry, Yangling, Shaanxi.
    

Competing interests

The authors have no competing interests.

Open Access Policy

This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Copyright

The authors have no competing interests.