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Introductiond-Psicose (d-ribo-2-hexulose) is a C-3 epimer of d-fructose that is found in fairly small quantities in nature. Because of the small amount of d-psicose present in natural products, few studies have investigated this sugar. Recently, Izumori and his co-workers developed a new method for the large-scale production of d-psicose (Takeshita et al., 2000). The ability to produce large amounts of d-psicose has made it possible to conduct various studies on its use in food. Safety testing of the sugar has verified that d-psicose causes no mutagenesis or acute toxicity (Matsuo et al., 2002). The sweetness of d-psicose is approximately 70% that of sucrose, and little of the sugar is converted to energy in humans . Additionally, d-psicose suppresses blood glucose elevation after eating Iida et al., 2008) and reduces body fat accumulation (Matsuo et al., 2001). Moreover, food products incorporating proteins glycated with d-psicose exhibit excellent antioxidant activity and good rheological properties (Puangmanee et al., 2008;Sun et al., 2006). Hence, the addition of d-psicose as a substitute for alimentary sugars in foodstuffs might be a strategy for developing new functional foods. A syrup containing this sugar is currently on the market.The commercialization of d-psicose as the functional sugar in a food requires that the factors affecting d-psicose formation in food products be clarified, because foods containing a large amount of d-psicose are expected, so the function of the foods must be accurately estimated. Previously (Oshima et al., 2006) we reported that psicose is found in various food products and suggested that the sugar was produced from fructose or sucrose under ordinary heating conditions. Moreover, based on the psicose concentration in food products, we expected that the sugar concentration, heating time, and temperature during the manufacturing process influence the concentration of psicose in food products. Binkley (1963) Agriculture, Kagawa University, 2393 Ikenobe, Miki-cho, Kita-gun, Kagawa 761-0795, Japan Received August 11, 2013 Accepted December 14, 2013 Factors affecting the formation of psicose in food products during cooking were investigated based on psicose formation from fructose in various food products and during the caramelization process. Psicose was produced upon heating not only in fructose meringue that had a high fructose content and was alkaline, but also in dried apple that was weakly acidic. Optimized conditions for psicose formation were determined by experiments on fructose caramelization. From the results, we concluded that the following factors affect psicose formation in food products during cooking: high temperatures, high pH, high fructose concentration, and extended cooking time. Of these, the pH of the food was the most important factor for psicose formation in food products.Keywords: psicose, fructose, food products, caramelization, cooking conditions H. Oshima et al. 424 known reaction for the isomerization of sugar. Many investigators (Beveridg et...