The effect of surface water removal on selected quality factors of minimally processed lettuce

Author

Amy Christine Loewus

Date of Award

8-1996

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

John Mount

Committee Members

David Golden, Carl Sams

Abstract

Spin drying (1, 15, and 30 min) and tunnel drying (5, 10, and 15 min) were used to study the effects of surface moisture removal on the quality of minimally processed and modified atmosphere packaged lettuce over a 16-day storage period. A control sample was used to test the effects of no surface moisture removal on the quality of lettuce over the 16-day storage period. Lettuce was inoculated with indigenous lettuce spoilage flora at a level of 5x10⁵ cfu/g. The parameters used to test the quality of the stored lettuce were percent moisture, color, package atmosphere, and microbial counts. Moisture analysis results indicated that spin drying for 1, 15, or 30 min or tunnel drying for 10 and 15 min, were less dry than the lettuce with no surface moisture removal (P<0.5). Tunnel drying for 15 minutes and spin drying for 30 minutes were the most effective surface moisture removal treatments, removing 0.9 and 0.8% moisture from the lettuce surface respectively. A correlation of r = 0.996 was found between the aerobic plate counts (30°C) and the psychrotrophic counts (7°C) in the microbial study (P<0.05). Spin drying produced lower microbial counts compared to the control (P<0.5). Tunnel drying had no significant effect on the microbial counts (P>0.05). The most effective treatments were spin drying for 15 or 30 min, removing approximately 0.5 log₁₀ cfu/g from the lettuce (P<0.05). Lettuce that was tunnel dried for 10 or 15 min or spin dried for 30 min had a higher hue angle, indicating less browning, than the control (P<0.1). The total change in Color (ΔE) results were similar. The analysis of the percent carbon dioxide in the package atmosphere revealed that spin drying the lettuce significantly reduced the amount of carbon dioxide inside the package (P<0.05). However, tunnel drying the lettuce had no effect on the amount of carbon dioxide inside the package (P>0.05). Results from a consumer sensory panel indicated that after 4 days of storage, only 15% of the panelists would purchase the control lettuce while 40% would purchase the lettuce spin dried for 15 or 30 min or tunnel dried for 15 min. The results of this study illustrated that technique of moisture removal does make a difference in the number of microorganisms and the amount of carbon dioxide produced inside the package with only spin drying being effective. However, tunnel drying (10 and 15 min) was equally as effective as spin drying (30 min) for controlling change in color of the lettuce over storage time.

Recommended Citation

Loewus, Amy Christine, "The effect of surface water removal on selected quality factors of minimally processed lettuce. " Master's Thesis, University of Tennessee, 1996.
https://trace.tennessee.edu/utk_gradthes/6826