Abstract
A pc-controlled, fiber-optic oxygen meter was tested to determine the potential of measuring endogenous oxygen levels in fresh fruits. Cucumber (Cucumis sativus L.) and tomato (Solanum lycopersicum L.) fruit were selected for this study. Endogenous oxygen level of cucumber fruit was measured using several methods; however, obtaining results without damaging the sensor was difficult due to the firm structure of the mesocarp tissue. Method 1 involved creating a small hole (perpendicular to the fruit surface), for sensor placement, by inserting a 23-gauge needle (0.6-mm diameter and 25-mm length) to a depth of 25 mm. Method 2 was developed to avoid damaging sensors, which involved creating a larger cavity for sensor placement by removing a 5-mm diameter, 34-mm length directly under the epidermis, starting at the blossom end. Oxygen content of cucumber fruit was approximately 19% when measured at 6-mm or 12-mm depth (using Method 1). Cucumber fruit treated with a commercial vegetable coating had lower oxygen content (11%) compared to untreated (18%) using Method 2. Endogenous oxygen level of tomato was also determined in locule and blossom-end tissues (10-mm depth). Fruit at pink and light red ripeness stages were measured initially and after 3 d at 24 °C. The oxygen level was lower in the locule (5%) than in the blossom end or columella tissue (15%). There was no difference in oxygen level for either ripeness stage. Real-time measurement of endogenous oxygen is feasible using this microsensor, although its fragile construction requires precise positioning and use of soft-textured fruits and vegetables.
