Extrusion of soy protein with gelatin and sugars at low moisture content

Soy protein-based materials modified with gelatin, lactose and sucrose were prepared by extrusion at low moisture content. The effect of composition on the extrusion parameters was investigated and specific mechanical energy (SME) was measured as an indication of extrusion processability, thus providing good characterization of the extrusion process in order to make it highly energy efficient and cost effective. Water content was the most important factor on the extrusion parameters and product properties. The incorporation of gelatin increased SME and the product obtained at the extruder die was not continuous. However, when lactose was added, SME decreased and the color of the product changed due to Maillard reaction. This reaction could be analyzed by Fourier transformed infrared spectroscopy (FTIR) where the changes of the amide I and amide II bands reflected that hydroxyl groups in sugars and amino groups in soy protein isolate (SPI) were consumed during extrusion. These results are in good agreement with total soluble matter (TSM) values, which were lower for mixtures with lactose than sucrose due to a higher degree of Maillard reaction. Moreover, X-ray diffraction (XRD) and scanning electron microscopy (SEM) results also showed the influence of Maillard reaction, which lead to more ordered and compact structures, respectively.

► The water content was the most important factor on the extrusion parameters.
► The incorporation of gelatin increased friction in the extruder barrel.
► The color of the product changed depending on the sugar employed.
► Lactose is a reducer disaccharide which can react with protein through Maillard reaction.
► Lactose caused a more compact and ordered structure.