The Relationship between Glass Transition and Quality in Foods (Turkish with English Abstract)

Year 2006, Volume: 31 Issue: 5, - , 01.10.2006

Meral Kılıç E. Özgül Evranuz

Abstract

Glass transition is a state change that is defined as the transition of an amorphous solid from a rubbery and viscous structure to a glassy and hard structure. This state transition takes place at a characteristic temperature range for the solid. State changes in amorphous solids are dependent on temperature and water content. Carbohydrates and proteins in foods exhibit glass transition. When water activity is high in foods, deterioration reactions can be explained by water activity. However, in foods at low water activity containing amorphous components, glass transition temperature (Tg) becomes a factor determining stability. When these types of foods are stored at temperatures lower than the Tg, rates of deterioration reactions can be minimized and by this way the stability can be maximized. Glass transition has been related with physical and some chemical deterioration reactions in foods. Microbial deteriorations have not been completely related to glass transition as they occur at high water activity values. Critical water content/water activity values that depress the Tg value to storage temperature can be determined for foods and stability can be increased by considering these values during processing and storage.

Keywords

Glass transition, quality, stability

Gıdalarda Camsılığa Geçiş ve Kalite İlişkisi

Abstract

Camsılığa geçiş amorf bir katının kauçuğumsu ve viskoz bir yapıdan camsı ve sert bir yapıya geçişi olarak ifade edilen bir hal değişimidir. Bu hal değişimi katı için karakteristik bir sıcaklık aralığında meydana gelir. Amorf katılardaki hal değişimleri sıcaklık ve su içeriğine bağlıdır. Gıdalarda karbonhidratlar ve proteinler camsılığa geçiş göstermektedirler. Gıdadaki su aktivitesi yüksek olduğunda bozulma reaksiyonları su aktivitesi ile açıklanabilmektedir. Ancak su aktivitesinin düşük olduğu ve amorf katı bileşen içeren gıdalarda camsılığa geçiş sıcaklığı (Tg) dayanıklılığı belirleyen bir faktör olabilmektedir. Bu tip gıdalar Tg'nın altındaki sıcaklıklarda depolandıklarında bozulma reaksiyonlarının hızı minimize edilmekte ve bu şekilde dayanıklılık maksimize edilebilmektedir. Camsılığa geçiş ile gıdalardaki fiziksel ve bazı kimyasal bozulmalar ilişkilendirilmiştir. Mikrobiyal bozulmalar yüksek su aktivitelerinde meydana geldiği için camsılığa geçiş ile tam olarak ilişkilendirilememektedir. Gıdalar için Tg değerini depolama sıcaklığına düşüren kritik su içeriği/su aktivitesi değerleri belirlenebilmekte ve işleme ve depolama sırasında bu değerler göz önünde bulundurularak dayanıklılık artırılabilmektedir.

Keywords

Camsılığa geçiş, kalite, dayanıklılık  

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