Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Food Science and Technology

Major Professor

Melvin R. Johnston

Committee Members

Ivon E. McCarty, Thomas B. Harrison


The objective of this study was to compare the freeze-dried banana puree slices treated by firming agents with untreated banana puree slices to see if any particular levels of firming agents would produce a more desirable product texture.

In this study, an air-blast freezer (-30°F.) was used to freeze the rope of banana puree. Firming agents were selected to prevent damage from freezing, dehydration, and furthermore, to improve firmness of freeze-dried banana after rehydration. The frozen weiner casings with filled puree were removed from the air-blast freezer, and all subsequent work prior to freeze-drying was done inside a CF. still air freezer. The filled casings were removed with a sharp knife. When The trays of banana samples for freeze-drying were placed in the chamber(Del-Vac Freeze-Dryer, Model 11212 RVM), the platen temperature was approximately 10°F. while the samples were -20°F. The trays were placed on the shelf, a vacuum was applied, and the thermostat was turned to 150°F.After 4.5 hours the thermostat was adjusted (platen temperature) to 125°F.for the remainder of the drying time.

Both subjective and objective quality measurements were employed for evaluating the freeze-dried banana product. Randomized complete-block design was used for measuring the effect of kind and level of firming agents by taste panel test (both texture scoring and hedonic rating).Chi-square test was used for interpretation of difference-preference paired comparison test for selection of type of puree sample). A 4 x6 factorial design for computing the Shear-Press measurement was employed. Color measurement was carried out by the Color-Eye, interpretation of measurement was made on C.I.E. basis. An Allo-Kramer Shear-Press and recorder indicator was used to determine the texture of the banana product. In statistical analysis, BMD02S IBM Model 7040 Digital Computer was used to compute Chi-squares. ANOVAR, with usage of theFortran Library Input Subroutine and some Fortran IV subroutine subprograms, were used to perform the analysis of variance calculations.Duncan's Multiple Range test DUNMRT subroutine on the IBM Model 1640Digital computer was used to perform this test; and it was used to determine which product mean scores were significantly different.

The following conclusions may be drawn from this study:1. The freeze-drying cycle used in this study was found promising for the ultimate freeze-dried product.2. Stability of color of freeze-dried banana slices which contained less than 5 per cent moisture was high.3. Rehydration test showed the lower the pH of the medium the "slower the water reabsorbed by freeze-dried bananas.4. The four firming agents selected (MC, CMC, Kraystay, andGuar Gum) provided a higher finishing temperature in the freeze-drying operation with little or no damage of product quality. They improve the firmness of the product after rehydration.5. Freeze-dried banana slices treated with firming agents rated significantly higher than the untreated freeze-dried banana product for both texture and preference tests.6. Results of Duncan's Multiple Range test for the effect of levels of firming agents as measured by Shear-Press were all significantly different at 0.05 level of probability.7. The effect of kinds of firming agents on the texture of freeze-dried banana as measured by the taste panel test showed that there were significant differences between each pair of mean score — MC having the highest mean score, followed by CMC, Kraystay, and Guar Gum.8. Results of Duncan's Multiple Range test on agents by level interactions showed that 5 per cent CMC had the highest mean shear value,5 per cent MC the next, followed by 4 per cent CMC, and 4 per cent MC.9. The taste panel test score (both mean texture score and mean hedonic rating) revealed that firming agent levels from 1 to 3 per steadily increased mean score while higher levels decreased them. Thus The lower levels may be considered promising from the standpoint of the overall quality of the freeze-dried banana product. Conversely, the shear value of the product rose consistently with increased levels of the firming agents except for the Kraystay, in which case the value dropped sharply at levels exceeding 3 per cent.

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