WHEN FOODS ARE SPECIAL For the growth of a baby it is very important that feeding integrates any possible nutritional principle deficiencies, depending on the different local conditions. Raw materials can be often found on site and a technology capable of exploiting them is enough Due to the demographic growth, demand for baby foods is strong. They must meet nutritional and hygienic requirements an be economically convenient. The demand for the utilisation of local crops such as sorghum, millet, soybeans, cassava, and many others still continues especially in the developing countries. Extrusion-cooking is one of the favourite technologies used to transform this local raw materials. The Research & Development Centre of Pavan has been very successful in the development of extruded products using its single screw G-model extruder and thanks to TT-model twin screw extruders the processing is even more versatile. In the production of baby foods, it is very important to gelatinize the starchy component of the cereal base material, otherwise children consuming them will have digestive problems. The term 'gelatinization of starch' indicates the process whereby starch, in granular and crystalline structure, swells and transforms, in a continuous amorphous phase, in the presence of heat and water. Therefore, when we speak of pregelatinized starch or flours, we refer to the starch components which have undergone the process of gelatinization and have been dried and subsequently ground. The principal properties of these types of product include:

- absence of birifringence in singular starch granules; - rapid and high rehydration capacity when mixed with cold water;high cold paste

viscosity; - higher susceptibility to enzymatic digestion, and therefore, improved digestibility.

Drum drying is the most commonly used equipment for pregelatinizing flours and starches. The process is delicate considering both its management and maintenance, and it has high energy costs as feed slurries are normally reported to include only about 44% solids. This means that drying to an assumed moisture content of 6% involves the evaporation of 1 of water per 1 kg of product. Extrusion cooking has long been considered the best alternative to drum-drying. Energy costs are relatively lower since the feed includes up to 70% solids which means that drying to a final moisture content of about 6% would involve the evaporation of only about 0.350 Kg of water per Kg of product. However, this process has had up until now the disadvantage of a higher mechanical shear which could damage the molecular structure of the starch, reduce the cold paste viscosity and the water absorption. Pavan has developed an extrusion-cooking process which, preserving its intrinsic advantages, eliminates the quality defects of the finished product (see fig. 1). The twin-screw extruder has been designed taking into consideration again the requirements of cereal flours and starches such an accurate moisturising/conditioning along with the problems connected with the excessive shearing of the swollen starch granules. The process starts with the dosing of the flourmix and the water in a very high speed pre-mixer to guarantee a very uniform hydration of the dry solids of the flourmix (processed with a 33% humidity content). The moisturised dough then rests in the mixing vessel as long as it is required for the water to diffuse evenly with the flour/starch and to start the swelling process of the starch granules. The forced feeding screw guarantees a constant feeding of the main screw thus a constant degree of fill. The speed of the screw is variable to enable the control of different raw materials/mix cooking times. For this process a low

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shear screw elements in the screw configuration and low screw speed of about 150 rpm is used. The temperature profile can be carefully controlled and adjusted to different raw materials needs since the heat generation by internal shear is lower than in high shear extruders. Furthermore, each section of the barrel is provided with autonomous thermoregulation system. Using this process a series of studies and investigations have been conducted at the Pavans R&D Centre using different kinds of materials ranging from common starches such as wheat, maize and rice to a wide range of flours such as sorghum, millet, rice-soy mixture, banana and even cassava. Microbial destruction as well as the deactivation of antinutritional enzymes such as urease and trypsin inhibitors gave excellent results. The nutritional aspect, particularly the amino acid profile modifications and available lysine were also analyzed and gave very acceptable results (see fig. 2). A final baby food formulation based on maize-rice-soybean flour was extruded using Pavans technology for the pregelatinization and subsequently mixed with sugar, milk powder, oil, minerals and vitamins was tested using in-vitro and as well as in-vivo analysis obtaining very satisfactory results. The possibility to use the same technology for the production of breakfast cereals and snack foods, allow to consider this extrusion process as ideal to obtain products in line with hygienic and nutritional rules. By Luciano Mondardini - Pavan R&D Director

Luisito Virtucio - Pavan New Products Development Manager