Date of Award:

1971

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Food Science and Industries

Advisor/Chair:

B. Singh

Co-Advisor/Chair:

D. K. Salunkhe

Abstract

Lettuce heads (Cultivar "Great Lakes") were stored in different concentrations of O2 and CO2, including l percent O2 and l percent CO2, 2.5 percent O2 and 2.5 percent CO2, 5 percent O2 and 0 percent CO2, and 5 percent O2 and 5 percent CO2; temperatures of 35 and 70 F; and with or without microbe- and senescence-inhibiting chemicals and packaging. The samples were taken on the twentieth and fortieth days in the first series of experiments; and in the subsequent experiments, on the fifteenth, thirtieth, forty-fifth, sixtieth, and seventy-fifth days of storage for quality evaluation, determination of rate of respiration, and chemical analyses.

The results indicated that lettuce could be stored at 35 F for at least 2 to 3 weeks. At this temperature, lettuce heads were still field fresh and bright green, without apparent sign of quality deterioration. At 70 F, none of the treatments could prolong the shelf-life of the lettuce more than l week.

Lettuce heads maintained the best marketing quality when stored in atmospheres of 2.5 percent O2 and 2.5 percent CO2 at 35 F for 60 days. Microbe- and senescence-inhibiting chemicals (Captan, Phaltan, Mycostatin, and N6-benzyladenine) had detrimental effects on the quality of lettuce stored in controlled atmosphere.

The reduction in russet spotting was the major benefit in controlled atmosphere storage at 35 F. In addition, the incidence of pink rib and butt discoloration was less than for those lettuce heads held in the conventional refrigerator. However, the hearts of the lettuce were sensitive to low O2 injury in controlled atmospheres consisting of 1 percent O2 and l percent CO2.

Controlled atmosphere (2.5 percent O2, 2.5 percent CO2) and controlled atmosphere combined with polyethylene packaging reduced the CO2 production, degradation of chlorophyll, loss of total sugar, and starch. Phaltan (microbe inhibitor, 1,000 ppm) or Phaltan in combination with polyethylene packaging under controlled atmosphere storage had an adverse effect on the lettuce held in the conventional refrigerator. In every case, the rate of respiration was in direct correlation with the sugar retention data.

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