| Summary: | Infusion is the process defined as filling in the pores of starch-based food materials by partially wetting liquid foods so as to obtain a relatively higher calorie food product in a lower bulk volume. The main objective of this research was to investigate the effects of the physical properties of the liquid (surface tension, angle of contact, and viscosity) and the pore structure of the starch-based solid (porosity, and pore size distribution) on the infusion process. Chessmen Butter Cookies (Pepperidge Farms) and Wonder White Sandwich Bread (ITT Continental Baking Co.) were selected as the starch-based porous solid food materials. Bread is a highly expanded product (porosity = 0.92), while cookies are relatively dense products (porosity = 0.58). Safflower oil (surface tension = 32dyn/cm; viscosity = 47centipoises) and silicone oil (surface tension = 20dyn/cm) of the same viscosity were selected to study the effect of surface tension. Silicone oils of 47 and 490 centipoises viscosity were chosen to study the effect of viscosity. Chocolate syrup was selected to assess the effect of nonNewtonian behavior. Both bread and cookies contain pores larger than 200$\mu$m pores which do not offer resistance to flow. Pore diameters measured from SEM micrographs proved the existence of pores with diameters up to 650$\mu$m for bread. The smallest pore size for both bread and cookies was found as 6$\mu$m by mercury porosimetry. Therefore, in order to achieve uniform infusion of liquid food materials containing particulate solids, it is necessary to use starch-based porous food materials with a controlled minimum pore size which is greater than the particle size of the particulate solids integrated with the infusing liquid. Infusion of oils into starch-based food materials is a very efficient process which occurs between vacuum and 200,000dyn/cm$\sp2$, since surface tension of oil-based liquid foods are low. Moreover, the process is aided by the oil absorption capacity of starch-based foods indicated by partial wetting behavior. Contact angles of oils on bread and cookies were found as 45 degrees (partially wetting), while the contact angle of chocolate syrup was measured as 65 degrees on cookies (partially wetting) and 126 degrees on bread (nonwetting).
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