Ozone Aided Corn Steeping Process
In corn wet milling, sulfur dioxide (SO₂) is used traditionally in the steeping process as a key step in ensuring high starch yields. SO₂ has two major functions: first, it prevents the growth of putrefactive microorganisms, and second, it helps break down disulfide bonds so that starch can be easily separated from its encompassing protein matrix (Blanchard, 1992). Typically, 0.1-0.2% sulfur dioxide is added to the water for steeping. Although most of the added SO₂ leaves the process at some point during wet milling, some remains in the final products (Committee on Food Chemicals Codex, 1997). SO₂ in the wastewater or emitted to the air is hazardous both to the environment and to human health. SO₂ is a primary component of acid rain, as its chemical reaction with water produces sulfuric acid. Human exposure to SO₂ can cause impairment of respiratory function, aggravation of existing respiratory disease (especially bronchitis), and a decrease in the ability of the lungs to clear foreign particles (Office of Air Quality Planning and Standards, 1994). Manufacturers often must devote additional resources to reducing residual SO₂ in final products to approved levels. In recent years, demand for organic starch products has been rising and residual SO₂ in the final products will certainly jeopardize manufacturers' "organic" claim for their products. Therefore, manufacturers must find alternative steeping processes.

Ozone (O₃) is an alternative to SO₂ because ozone is a disinfectant and an oxidant, and thus has the ability to suppress the growth of putrefactive organisms and break down the protein matrix. The benefits of using an ozone-aided steeping (OAS) process are three-fold: (1) no residual ozone will remain in the products, and thus manufacturers need not be concerned with residual O₃ or SO₂ levels in the final products, and the products can be labeled as "organic"; (2) ozone reverts to oxygen after use, and thus does not pose a threat to the environment; and (3) production costs required for the OAS process may be lower than those associated with SO₂ processing.

Despite these potential advantages, no reports describing the use of ozone in corn steeping can be found in the published literature. The objectives of this study were to investigate the feasibility of using ozone to replace SO₂, and to determine the effects of some processing variables on the performance of an OAS process.

Our results demonstrated that ozone-aided steeping (OAS) process was as good as conventional SO₂ steeping process in terms of starch yield. The study also shows that OAS process can be conducted at a lower temperature (e.g., 20C) for a shorter time (e.g., 36 hr) compared with the conventional processes using SO₂, suggesting a significant energy saving and productivity increase. It was found that when and how long ozone is applied to the steeping system is of great importance to the performance of OAS process.

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