Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Food Science and Technology

Committee Chair(s)

D. K. Salunkhe


D. K. Salunkhe


Ethelwyn B. Wilcox


Delbert A. Greenwood


Lynn H. Davis


Leonard E. Olsen


Chang Y. Lee


Many innovations have been attempted to shorten drying time or improve dehydration techniques for foods. Despite the recent advances in science and technology the bulk of dried fruit production throughout the world, over 1 1/2 billion tons (dry basis), is prepared by the energy of the sun (Copley and Van Arsdel, 1964). However, other techniques and processes for food dehydration and preservation are occupying more prominent positions in the overall production of dehydrated foods, particularly in the more advanced countries. Economics notwithstanding, it is readily apparent that dehydration as compared to sun-drying offers at least two main advantages. It is more sanitary and it is independent of inclement weather and thus of geographics. These two reasons are perhaps among the chief ones for the increasing technical developments in dehydration by procedures such as cabinet drying (Beavens, 1944), vacuum drying (Schroeder and Schwarz, 1949), freeze drying (Lawler, 1963) and foam-mat drying (Morgan and Ginnette, 1960). They are perhaps also the reason for continuing research on new and improved dehydration processes which may be adaptable to certain types of products. In this continuing search, electromagnetic waves, which are similar to the more familiar light or radiowaves but differ in frequency and wavelength, have received little attention.

Dielectric heating has been utilized in various applications (Shaw and Calvin, 1949; Sherman, 1944). Microwave, another family of electromagnetic waves, has also been studied, for example, by Cotterill and Delaney (1959) for moisture determination in liquid eggs, by Losche and Mucke (1950) for reduction in germ counts in milk, by Copson (1953, 1962) for processing of orange juice, and by others (Jeppson, 1964), but this technique has not been employed to any extent as a tool for regular dehydration or preservation of fruits and thus its effect, if any, on biochemical and physical changes in foods is not known.

It is believed that an exploratory investigation on the use of microwave radiation for fruit dehydration either alone or in combination with hot air drying, along with a study of its effects on selected biochemical and physical changes in the dried produce as compared with freeze-dried and hot-air dried products would provide valuable information to the food industry.

The aims of this study are (a) to explore the utility of microwave radiation for dehydration of apples (dried to about 5 percent moisture), either alone or in combination with hot air drying when necessary, (b) compare the products so obtained with straight dehydrated and freeze-dried apples, (c) to assess the effect of microwave exposure on chemical, biochemical, organoleptic, and physical changes in apples and thus evaluate the potential of microwave radiation either alone or in combination with other principal drying methods, as a process for fruit dehydration, and (d) to determine the effectiveness of microwave energy for enzyme inactivation and sulfur-free cut dried fruit production.