Food Science: Courses: FS 532

14. Dehydration Evaluation

Introduction

This lab is done in conjunction with the drum drying (Lab 11) and freeze drying (Lab 12) lab exercises. The tables in these lab exercises are needed for the drying evaluation.

Procedure
  1. Product appearance. Note appearance of all dried samples. Complete portions of the tables in the freeze drying and drum drying lab exercises that pertain to dehydrated product appearance. Also note the difference between freeze dried and air dried carrots.
  2. Bulk density. Determine bulk density of freeze dried and air dried carrots, as well as of freeze dried peas. Weigh dried product and place in graduated cylinder to estimate volume. Bulk density is g product per ml occupied by product.
  3. Yield and Shrinkage. Calculate % yield and % shrinkage of freeze dried carrots and peas. Definitions are given in the table from the freeze drying lab exercise. Record yield and shrinkage values in table. Do not calculate yield and shrinkage for freeze dried milk and coffee.
  4. Powder rehydration. Determine powder rehydration time by adding 0.1 g powder to 100 ml water and estimating the time required for the powder to disperse. Also note whether powder has a tendency to sediment or float. Do this test on all the drum dried milk powders, the freeze dried milk, and a commercial spray dried milk powder. Record the information on the tables from the drum drying and freeze drying lab exercises.
  5. Non-powder rehydration. Subsequent to measuring bulk density, rehydrate freeze dried peas and both freeze dried and air dried carrots by adding 2 g product to 100 ml distilled water and boiling for 15 min. Decant water and reweigh sample. Calculate rehydration ratio (See table from freeze dried lab exercise for definition.). Compare rehydration ratio for freeze dried carrots to air dried carrots. Note characteristics of all rehydrated samples.
  6. Solubility index. Determine the solubility index of all milk samples (drum dried, freeze dried, spray dried) as follows:
    1. Add 5 g powder to 50 ml water.
    2. Mix in blender for 90 s.
    3. Transfer sample to 250 ml beaker and remove foam with spatula or spoon.
    4. Transfer sample to 50 ml centrifuge tube and centrifuge 5 min at setting 5.
    5. Decant to within ca. 5 ml of sediment.
    6. Add 25 ml water and mix.
    7. Add water to 50 ml mark.
    8. Recentrifuge 5 min. at setting 5.
    9. Record ml sediment in centrifuge tube.
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Copyright © 2003, Department of Food Science,
University of Wisconsin-Madison. 		Updated April 15, 2003.
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