Recovery of flavors and savory compounds from food wastewaters has long been contemplated; however, it was not economically and technically possible (with few exceptions) until the advent of membrane-based technologies. Today, pervaporation technology has been used successfully for recovering flavor products from fermentation broth in bioreactors and for aroma recovery (Trifunovic and Tragardh, 2002; Peng and Liu, 2003). Wastewaters from fruit and vegetable processing operations, in particular, are good candidates for flavor recovery. For example, blanching waters from vegetable processing contain aroma compounds that could be harvested for used in a number of food and nonfood applications. Blanching is the process of heating vegetables to a temperature high enough to destroy enzymes (and possibly some microorganisms) present in the tissue. It stops the enzyme action that causes loss of color and flavor during storage. In water blanching, the vegetables are submerged in boiling water. In steam blanching, the vegetables are suspended above the boiling water and heated only by the steam. Water blanching usually results in a greater loss of nutrients through leaching, but it takes less time than steam blanching. The blanched foods are usually submerged in cooling water immediately after blanching. The combined wastewater from blanching and cooling contains a certain amount of soluble solids, coarse debris, fine particles, and small molecules such as odorous (aroma) compounds. Aroma compounds in blanching water are varied depending on the vegetable being blanched. For example, more than 33 aroma compounds have been found in cooked cauliflower, cabbage, Brussels sprouts, and runner beans (MacLeod and MacLeod, 1970). Some of the aroma compounds that could be present in the blanching water of several common vegetables are listed in Table 8.3. The flavors listed in Table 8.3 are either characteristic in cooked (blanched) vegetables or relatively abundant in terms of approximate percentage relative abundance. These compounds can all be recovered with pervaporation technology; however, separation or fractionation of these molecules is difficult at present.
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