Dardo Mario De Greef

Effects of extrusion conditions on physical and nutritional properties of extruded whole grain red sorghum (sorghum spp)

Abstract In order to analyze the effects of extrusion temperature (T: 164, 182, 200 °C) and grits moisture content (g/100 g sample) (%M: 14, 16.5, 19) on textural and physicochemical properties of red sorghum extrudates, whole grain flour was extruded according to a factorial experimental design. The higher values for specific mechanical energy consumption (1006.98 J/g) and expansion (3.36) were obtained at 164 °C–14%M and for sensorial hardness at 164 °C–19%M. While for specific volume, the highest value (10.41 cm3/g) was obtained at 200 °C–14%M. Water solubility and water absorption were directly related with T and inversely with M. Microscopic observation of the samples indicates that the greatest cooking degree was obtained at 200 °C–4%M and the lowest at 164 °C–19%M. Extrusion at 182 °C–14%M allows obtaining an expanded product with good properties. Proximal composition did not show statistically significant differences with raw sample. Extruded sample showed a 25.4% reduction of available lysine and a 31% increase in protein digestibility.

Iron and zinc availability and some physical characteristics from extruded products with added concentrate and hydrolysates from bovine hemoglobin.

Abstract Four hydrolysates were obtained from bovine hemoglobin concentrate (BHC) and used to fortify extruded maize products. Extrusion was carried out with a Brabender single-screw extruder. Physicochemical properties from extruded products were measured. The iron availability was estimated by the dializability method, which measures the mineral dialyzed after a double digestion simulating physiological processes. The physicochemical properties of the extruded products were not affected by fortification, with the exception of total soluble solids. The enzymic hydrolysis increased the iron dializability with respect to the substrate. The highest value of iron dializability corresponded to the more hydrolysated sample. Extruded products fortified with BHC hydrolysates showed higher iron dializability than those fortified with BHC. However, iron dializability corresponding to BHC is lower than that expected from heme iron. Therefore, heme-iron availability is low when it is determined in the absence of meat proteins, and hydrolysis could increase potential iron availability.

Extrusion Conditions and Amylose Content Affect Physicochemical Properties of Extrudates Obtained from Brown Rice Grains

The utilization of whole grains in food formulations is nowadays recommended. Extrusion cooking allows obtaining precooked cereal products and a wide range of ready-to-eat foods. Two rice varieties having different amylose content (Fortuna 16% and Paso 144, 27%) were extruded using a Brabender single screw extruder. Factorial experimental design was used to study the effects of extrusion temperature (160, 175, and 190°C) and grits moisture content (14%, 16.5%, and 19%) on extrudate properties. Specific mechanical energy consumption (SMEC), radial expansion (E), specific volume (SV), water absorption (WA), and solubility (S) were determined on each extrudate sample. In general, Fortuna variety showed higher values of SMEC and S (703–409 versus 637–407 J/g; 33.0–21.0 versus 20.1–11.0%, resp.) than those of Paso 144; on the contrary SV (8.64–3.47 versus 8.27–4.53 mL/g) and WA tended to be lower (7.7–5.1 versus 8.4–6.6 mL/g). Both varieties showed similar values of expansion rate (3.60–2.18). Physical characteristics depended on extrusion conditions and rice variety used. The degree of cooking reached by Paso rice samples was lower than that obtained for Fortuna. It is suggested that the presence of germ and bran interfered with the cooking process, decreasing friction level and broadening residence time distribution.

Application of an ideal model to the scaling up of a laboratory extruder

Abstract The application of an ideal model to the scaling up of a laboratory single screw food extruder is analysed. The method proposed by Harper (case 3) with a scale up factor of 2.25 was used. Experiments were carried out using a commercial corn grits sample. To compare the extruders performance, the following parameters were measured in each experiment: output (Q), measured as the solids (at feeding moisture level basis) coming out from the extruder; the die pressure (P), measured at the cylindrical head which supports the die and degree of cooking (DC), which is taken as product characteristic. DC was estimated by two parameters, the water solubility (S) and the amylographic retrogradation (R). Two grits feeding moisture levels were selected for the extrusion (15% and 30 %) in order to produce products having two different degrees of cooking levels, high and low, respectively. Three screw speeds for each extruder and two different die l/d ratio: l/d=10 and l/d=20. were used in the experiments. The results show that the scaled up extruder (SE) gives lower Q values than the predicted by the model. This is due, mainly because a higher DC is obtained with the SE. The differences in DC are more significant in the case of 15% moisture and even more noticeable for the longer die and higher rpm. We conclude that, considering the simplicity of the model used, it could be applied to the scaling up of a single food extruder providing that a new set of processing condition are found for the SE so as to obtain the same DC as that of the small one. Among the different alternatives used (change of the die l/d ratio or adjusting moisture level or the change of rpm), the decrease in the die l/d ratio seems to be the best, because the higher cooking capacity of the SE allows to increase the output by reducing the die flow restriction (l/d).