第八章第八章干燥干燥解析.pdfVIP

第八章 干燥 第八章 干燥 Chapter 8 Chapter 8 第一节 基本概念 第一节 基本概念 Basic Concepts Basic Concepts 8— 1 Importance and 8— 1 Importance and Purpose of drying Purpose of drying （重要性和目的） （重要性和目的） • Significance of Drying Process as an Unit Operation – It is widely used in every walk of life. E.g. Food stuff, wood processing, plastics industry, paper making etc. • It is one of the oldest methods of preserving food. – Primitive societies practiced the drying of meat and fish in the sun long before recorded history. – Today the drying of foods is still important as a method of preservation. Dried foods can be stored for long periods without deterioration occurring. • The principal reasons for this are that The microorganisms which cause food spoilage and decay are unable to grow and multiply in the absence of sufficient water . Many of the enzymes which promote undesired changes in the chemical composition of the food cannot function without water. (Without moisture or water, the enzyme activity is inactivated) The Purpose of Drying The Purpose of Drying • Easy for preservation or store • Easy for preservation or store – Drying makes food or raw food materials have long – Drying makes food or raw food materials have long shelf life. ( in terms of microorganism and enzyme shelf life. ( in terms of microorganism and enzyme action). action). – Need small space of storehouse – Need small space of storehouse • Convenient for transportation • Convenient for transportation – Weight and volume are greatly reduced,improves – Weight and volume are greatly reduced,improves significantly the efficiency of transportation In terms significantly the efficiency of transportation