Thin Layer Drying Models in Food Systems

Abstract

Drying is one of the most complicated food processes which include simultaneous heat and masstransfer. It is generally defined as the removal of moisture from food. The microbial and enzyme activity indry food products are quite low due to reduced water activity. Therefore, drying is widely preferred inlong term storage of foods. The drying mechanism, common drying techniques used in industry andthin layer drying models were summarized in this review. Thin layer drying models can be classified astheoretical, semi-theoretical and empirical. Theoretical models can be applied to all process conditions.However, due to their practical inconvenience, semi-theoretical and empirical models are widelypreferred in drying studies. Among the models studied in food drying, semi-theoretical models, Pageand Midilli, were found to be the best fitting models. In addition, the effective diffusion coefficientcalculated from Fick’s Second Law and the activation energy, which is determined using Arrheniusequation, give valuable information regarding drying. The effective diffusivities and activation energyvalues in foods were reported in the range of 10-7-10-11m2/s and 10-80 kJ/mol, respectively

Keywords

• Food drying methods, drying mechanism, thin layer drying models, diffusion coefficient,activation energy

Gıdalarda İnce Tabaka Kurutma Modelleri

Abstract

Kurutma, ısı ve kütle aktarımıyla geçekleflen en karmaflık proseslerden biridir. En genel tanımı ilekurutma, gıdadan suyun uzaklafltırılmasıdır. Kurutma ifllemi ile su aktivitesi azalan gıda ürünlerinde,mikrobiyel aktivite ve enzim aktivitesi oldukça düflük seviyededir. Bu sebeple gıdaların kurutulması,uzun süreli depolamalarda ço¤unlukla tercih edilir. Bu derlemede kurutma iflleminin mekanizması,endüstride sıklıkla kullanılan kurutma yöntemleri ve ince tabaka kurutma modelleri özetlenmifltir. ‹ncetabaka eflitlikleri teorik, yarı teorik ve ampirik modeller olarak sınıflandırılabilir. Her ne kadar teorikmodeller tüm proses koflulları için kullanılabilir olsa da, pratik olmayıflları sebebiyle gıdalarda yapılankurutma çalıflmalarında genellikle yarı teorik ve ampirik modeller tercih edilmektedir. Bu modellerincelendi¤inde, gıdaların kurutma verilerine en iyi uyum sa¤layanların, yarı teorik modellerden Page veMidilli oldu¤u görülmüfltür. Ayrıca, Fick’in ikinci yasasından elde edilen efektif difüzyon katsayısı veArrhenius ba¤ıntısı kullanılarak hesaplanan aktivasyon enerjisi, kurutma ifllemi hakkında önemli bilgilersa¤lamaktadır. Literatürdeki farklı çalıflmalarda efektif difüzyon katsayısının ve aktivasyon enerjisininsırasıyla 10-7-10-11m2/s ve 10-80 kJ/mol aralı¤ında de¤iflti¤i bildirilmifltir

Keywords

• Gıdalarda kurutma yöntemleri, kurutma mekanizması, ince tabaka kurutmamodelleri, difüzyon katsayısı, aktivasyon enerjisi

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