Date of Award

8-2022

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Food, Nutrition, and Culinary Science

Committee Chair/Advisor

Paul Dawson

Committee Member

Julie Northcutt

Committee Member

Michelle Parisi

Abstract

The effects of oxygen transmission rate of packaging material on the shelf life of aquaponically-grown Finstar lettuce was studied. Parameters of packaging headspace gas composition (oxygen and carbon dioxide concentrations) and lettuce pH, percentage weight loss, total aerobic microorganisms, and color were analyzed every ten days for sixty days. Finstar lettuce was stored at 4○C in four different types of packages (treatments), including a clamshell package and three film bags with oxygen transmission rates (OTR) of 3.0-6.0 cc/(m2/24 hr/1 atm), 80-90 cc/(m2/24 hr/1 atm), and >225 cc/(m2/24 hr/1 atm). Lettuce stored in clamshell packages (20.9-24.1% O2) or bags with >225 OTR (11.8-23.3% O2) had higher levels of oxygen in the headspace than the 3.0-6.0 OTR (0.034-23.1% O2) or 80-90 OTR (0.7-23.3% O2) packages while carbon dioxide levels in the headspace of both the 3.0-6.0 OTR (0-20.5% CO2) and 80-90 OTR (0-10.9% CO2) packages were significantly higher than the clamshell packages (0-0.5% CO2) and >225 OTR bags (0-3.9% CO2). The pH values of the clamshell packaged lettuce (6.00-6.82) were significantly lower than 3.0-6.0 OTR (6.34-7.37) and 80-90 OTR (6.40-6.95) but not the >225 OTR (6.25-6.79) packaged lettuce. The percentage weight loss of the 3.0-6.0 OTR package (-0.76-1.05%) was significantly lowest while the percentage weight loss of the clamshell package was significantly highest (0.81-7.72%). The packages with lower carbon dioxide headspace percentages and higher oxygen headspace percentages had lower pH values. Shelf-life ratings by a panel (1=eat as is, 2=trim then eat or 3=discard) of the 80-90 OTR packaged lettuce were significantly lower than the shelf-life ratings of lettuce packaged in all the other treatments while shelf-life ratings of the >225 OTR packaged lettuce were significantly higher than the lettuce packaged in all the other packaging treatments. There were no differences in the color of lettuce (lightness, greenness, yellowness) stored in the different packaging treatments. However, the hue angles of lettuce packaged in the 80-90 OTR bags were significantly higher than the lettuce packaged in the >225 OTR bags. There were no significant differences in numbers of total aerobic microorganisms recovered from lettuce packaged in the different treatments (CFU/g or log CFU/g). Finstar lettuce displayed a long shelf-life compared to previous studies on other varieties of lettuce regardless of the package atmosphere. The long shelf-life may be attributed to Finstar having resilient genetic properties along with being greenhouse-grown which lessens the possibility of contamination compared to field-grown lettuces.

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