نوع مقاله : مقاله پژوهشی

نویسنده

استادیار پژوهش موسسه تحقیقات فنی و مهندسی کشاورزی

چکیده

در این تحقیق، دمای انتقال شیشه­ای (Tg)  و دمای ذوب (Tm)  ژلاتین با رطوبت­های 7، 11، و 14 درصد به کمک تکنیک گرماسنجی پویشی تفاضلی (DSC) اندازه­گیری شد.  با افزودن آب به ژلاتین، مقادیر gTو Tm کاهش یافت.  Tg ژلاتین نیمه­بلوری بیش از مقدار Tgدر ژلاتین با ساختار بی­شکل یا آمورف بود که با سردکردن سریع از حالت مذاب به دست می­آید.  تغییر انتالپی (∆H) حاصل از پدیده زمانمندی فیزیکی در حالت شیشه­ایدر ژلاتین با ساختمان­های مولکولی مختلف (نیمه­بلوری یا بی­شکل) و در رطوبت­ها و دماهای نگهداری متفاوت مطالعه شد.  مشخص شد که مقدار و میزان تغییر انتالپی، با افزایش پارامتر دمای جابه­جایی (Ta-Tg) افزایش می­یابد.  این پارامتر قادر است اثرهای ویژگی ساختمانی، میزان آب، و دمای نگهداری را توضیح دهد.

عنوان مقاله [English]

Enthalpy Relaxation of Gelatin in the Glassy State

چکیده [English]

The glass transition temperature (Tg) and the melting temperature (Tm) of gelatin at water contents between 7 and 14% were measured using differential scanning calorimetry.  The plasticisation of the polymer by water led to a decrease in Tg and Tm. The Tg of partially crystalline gelatin was higher than that of the amorphous one obtained by quenching from the melt. The enthalpy relaxation occuring during the ageing of gelatin in the glassy state was studied for different structures (partially crystalline or amorphous), water contents and ageing temperature (Ta). The extent and rate of this relaxation associated with physical ageing were found to increase when the shifted temperature parameter (Ta-Tg) increased.  This parameter was able to account for the effects of structure, water content and ageing temperature.

کلیدواژه‌ها [English]

  • Enthalpy Relaxation
  • gelatin
  • Glass Transition Temperature
  • Melting Temperature
  • Physical Ageing
Chung, H. J. and Lim, S. T. 2003. Physical ageing of glassy normal and waxy rice starches: effect of ageing temperature on glass transition and enthalpy relaxation. Carbohydrate Polymers. 53, 205-211.
Farhat, I. A., Mousia, Z. and Mitchell, J. R. 2001. Water redistribution during the recrystallisation of amylopectin in extruded amylopectin-gelatin blends. Polymer. 42, 4763-4766.
Ferrari, C. and Johari, G. P. 1997. Thermodynamic behaviour of gliadins mixture and the glass-forming transition of its dried state. Int. J. biological Macromolecules. 21, 231-241.
Kalichevsky, M. T., Blanshard, J. M. V. and Tokarczuk, P. F. 1993.  Effect of water content and sugares on the glass transition of casein and sodium caseinate. Int. J. Food Sci. Tech. 28, 139-151.
Lawrence, W. E., Seferis, J. C. and Gillespie, J. W. 1992. Material response of a semicrystalline thermoplastic polymer and composite in relation to process cooling history. Polymer Composites. 13, 86-96.
Lawton, J. W. and Wu, Y. V. 1993. Thermal behavior of annealed acetic acid-soluble wheat gluten. Cereal Chem. 70, 471-475.
Lourdin, D., Colonna, P., Brownsey, G. J., Noel, T. R. and Ring, S. G. 2002. Structural relaxation and physical ageing of starchy materials. Carbohydrate Res. 337, 827-833.
Marshall, A. S. and Petrie, S. E. B. 1980. Thermal transition in gelatin and aqeous gelatin solutions. J. Photographic Sci. 28, 128-134.
Mousia, Z., Farhat, I. A., Blachot, J. F. and Mitchell, J. R. 2000. Effect of water partitioning on the glass-transition behaviour of phase separated amylopectin-gelatin mixtures. Polymer. 41, 1841-1848.
Moynihan, C. T., Macedo, P. B., Montrose, C. J., Gupta, P. K., DeBolt, M. A., Dill, J. F., Dom, B. E., Drake, P. W., Easteal, A. J., Elterman, P. B., Moeller, R. P., Sasabe, H. and Wilder, J. A. 1976. Structural relaxation in vitreous materials. Annals N. Y. Academy Sci. 279, 15-35.
Noel, T. R., Parker, R., Ring, S. M. and Ring, S. G. 1999. A calorimetric study of structural relaxation in a maltose glass. Carbohydrate Res. 319, 166-171.
Nyquist, H. 1983. Saturated solutions for maintaining specified relative humidities. Int. J. Pharm. Tech. Proc. 4, 47-48.
Pinhas, M. F., Blanshard, J. M. V., Derbyshire, W. and Mitchell, J. R. 1996. The effect of water on the physicochemical and mechanical properties gelatin. J. Thermal Analysis. 47, 1499-1511.
Shogren, R. L. 1992. Effect of moisture content on the melting and subsequent physical aging of cornstarch. Carbohydrate Polymers. 19, 83-90.
Slade, L. and Levine, H. The Glassy State in Foods. In: Blanshard, J. M. V. and Lillford, P. J. (Eds). 1993. Nottingham University Press. UK.
Sobral, P. J. A. and Habitante, A. M. Q. B. 2001. Phase transitions of pigskin gelatin. Food Hydrocolloids. 15, 377-382.
Sperling, L. H. 1986. Introduction to Physical Polymer Science. J. Wiley and Sons Inc. New York.
Struik, L. C. E. 1980. Physical ageing of dry elastin. Biopolymers. 19, 1667-1673.
Struik, L. C. E. 1978. Physical Ageing in Amorphous Polymers and Other Materials. Elsevier. UK.
Thiews, J. T. and Steeneken, A. M. 1997. The glass transition and sub-Tg endotherm of amorphous and native potato starch at low moisture content. Carbohydrate Polymers. 32, 123-130.
Ward, A. G. and Courts, A. 1977. The Science and Technology of Gelatin. Academic Press.
Williams, L. M., Landel, R. F. and Ferry, J. D. 1955. The temperature dependence of relaxation mechanisms in amorphous polymer and other glass forming liquids. J. Am. Chem. Soc. 77, 3701.
Wungtanagorn, R. and Schmidt, S. J. 2001. Thermodynamic properties and kinetics of the physical ageing of amorphous glucose, fructose and their mixture. J. Thermal Analysis Calorimetry. 65, 9-35