Microstructure analysis of dried yogurt: Effect of different drying methods

Processing of food involves many structural changes in their macroscopic and microscopic levels (≅ below 100 micron). Most food contains protein, fat, carbohydrate (sugar, polysaccharides) and water which form the food microstructure. Processing methods like drying, homogenization, crystallization, powder production, gelatinization of starch etc change the microscopic structure of the food material. These microscopic changes have strong influence on properties like rheology, glass transition, stickiness, dispersibility, hygroscopicity, moisture sorption of final processed materials. Therefore it is important to study the food microstructure during processing to enhance the quality of processed food or to change the processing operations/conditions. In this study, plain yogurt was selected as a model food to analyze the microscopic structural changes after drying using different drying methods. Plain yogurt was dried at four different drying methods viz., air, vacuum, freeze and microwave vacuum drying. The microscopic structural changes of dried yogurt were analyzed using scanning electron microscope and X-ray diffraction pattern. Moisture sorption characteristic of the yogurt was also studied.