Extrusion of rice grits with lingonberry pomace hydrolysate: moisture content and characteristics of the extrudate

Fruit and berry pomaces are promising sources of biologically active compounds: dietary fibers, phenolic compounds, pectins, carotenoids, and natural antioxidants that have preventive and therapeutic effects in metabolic, cardiovascular, gastrointestinal and neurodegenerative diseases. The active inclusion of pomaces as by-products in the food technologies contributes to the transition to more sustainable industrial processes. The study was conducted to investigate the influence of the moisture content of the mixture during the processing of rice with hydrolysate of lingonberry pomace on the operating parameters of extrusion, technological and physicochemical characteristics of the extrudates. Lingonberry pomace hydrolysate was obtained by an enzymatic method using a complex of biocatalysts, including pectinase, cellulase, protease and lipase. The hydrolysate was dried, added in an amount of 5 % to rice and extruded varying the moisture content in the range of 15–21 %. Control samples were rice extrudates obtained with a moisture content of 15 and 21%. An increase in the moisture of the extruded mixture led to a decrease the extrusion temperature from 160 to 152 °C, the torque from 80 to 52 %, the pressure from 4.0 to 2.4 MPa, and the specific mechanical energy from 0.152 to 0.099 kW h/kg. In terms of structural and mechanical properties, an increase in moisture of mixture with hydrolyzed lingonberry pomace leads to a decrease in the quadratic expansion coefficient from 7.3 to 3.5. The bulk density increases from 89.5 to 243.2 g/dm3 , the hardness of the extrudates – from 7.5 to 39.0 N, the average crushing force – from 3.4 to 16.1 N. The frequency of microfractures during puncture and deformation as a characteristic of porosity decreases from 3.5 to 2.0 mm-1 . The dynamic viscosity of suspensions of extrudates with lingonberry pomace hydrolyzate increases significantly with increasing moisture content during extrusion from 2.0 to 4.0 Pa s. The trends in changes in thermomechanical processing modes determined by the amount of water in the system, technological and structuralmechanical properties for the control and experimental mixtures were identical without significant differences. It was established that the maximum content of phenolic compounds of 679. 6 mg/kg corresponds to extrudates with hydrolyzed lingonberry pomace produced at minimum moisture of 15 %, by moisture of 21 % the content of phenolic compounds is only 223.1 mg/kg