Heat Transfer Effects of Phytic Acid Concentration and Phytase Addition on Fouling Behavior of Steepwater
Ju Tian1, David B. Johnston2, Nicki J. Engeseth1, Vijay Singh1, M. E. Tumbleson1 and Kent D. Rausch1,*
1Univeristy of Illinois at Urbana-Champaign, Urbana, IL
2Eastern Regional Research Center, ARS, USDA, Wyndmoor, PA
Heat transfer fouling describes the phenomenon of unwanted materials forming and accumulating on heat transfer surfaces. This can lead to a decrease in process efficiency, as fouling of heat transfer equipment increases energy consumption and maintenance costs. In the corn wet milling industry, evaporator fouling takes place when steepwater is concentrated. Steepwater is the solution resulting from the corn steeping process and is composed of solubilized kernel compounds, microbes (principally lactobacilli) and solid from recycled process streams.
Research on corn processing fouling has focused on the effects of steepwater solid, corn oil, pH, Reynolds number, solids concentration and carbohydrates (Agbisit et al 2003, Singh et al 1999, Wilkins et al 2006ab, Arora et al 2010, Challa et al 2014). However, effects of phytic acid concentration or phytase addition on the fouling characteristics is not known. There are reports from industry suggesting phytic acid content is positively correlated with fouling rate, and adding phytase to the process stream may help reduce fouling. Research also has shown the solubility of certain phytic acid metal complexes, the product of chelation reaction between metal ions available in corn process streams (Mg, Ca, K) and phytic acid, can be influenced by adding phytase (Ekholm et al 2003). A study on one of these phytic acid metal complexes (Ca) concluded the concentration was positively correlated with fouling in the dairy industry at high temperatures (Bansal et al 2006). The purpose of this study was to evaluate effects of phytic acid concentration and phytase addition on steepwater fouling behavior. Experiments were conducted using commercial steepwater with different phytic acid concentrations. With phytic acid addition, the phytic acid concentrations of the samples were adjusted to vary from 25 mg/g sample to 75 mg/g sample. Fouling resistances were measured using an annular probe with a 7 L batch system. Mean fouling rate, maximum fouling resistance and induction period characterized fouling behavior. The results will provide a better understanding of phytic acid effects on wet milling fouling and provide possible solutions to fouling mitigation in the wet milling process.
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