CHEMICAL INTERACTIONS BETWEEN ISOLATED SOY PROTEIN AND VITAL GLUTEN IN MEAT ANALOGUE OBTAINED BY THERMOPLASTIC EXTRUSION AT HIGH MOISTURE

The thermoplastic extrusion at high moisture of vegetable proteins results in the formation of meat analogue with fibril structure similar to animal meat (mainly beef). The aim of this study was to evaluate the type of chemical bonds and/or interactions comprised in the meat analogues structure formation, on isolated soy protein (ISP) basis with partial replacement by vital gluten, obtained by thermoplastic extrusion at high moisture. The meat analogues were evaluated by using Surface Response Methodology in a Composite Central Rotational Design of three independent variables, where: X1 – vital gluten (0-30 %), X2 – moisture content (50-70 %) e X3 – 3rd zone temperature (60-120 ºC). The extrusion process was carried out in a co-rotational intermeshing twin screw extruder, with temperature set at 50, 70 and 90 ºC for the 1st, 2nd and 4th zones, respectively, feed rate set at 12 kg.h-1, screw speed set at 300 rpm and a rectangular die of 7.5, 33.5 and 450 mm of dimension. For the protein extraction of the raw materials and the trials were used seven different solvents, as follow: PB (phosphate buffer 40 mM and pH 7.5); SDS (sodium dodecil sulphate 2 %); Triton (Triton 100X 3 %); Urea (urea 8 M); 2ME (β mercaptoethanol 2 %); SDS+U (sodium dodecil sulphate 2 % + urea 8 M); and 2ME+U (β-mercaptoethanol 2 % + urea 8 M). The results of the trials ranged between 9.34 and 13.42 % (PB), 23.45 and 38.25 % (SDS), 12.96 % and 24.70 % (Triton), 25.14 and 53.22 % (urea), 10.99 and 15.10 % (2ME), 45.35 and 61.68 % (2ME+U) and 27.97 and 41.85 % (SDS+U). The independent variables showed significant influence (P≤0.10) in the protein solubility for PB, Triton, 2ME, 2ME+U and SDS+U solvents. The ANOVA results showed values of R2 ≥0.8783, Fcalculated¬ greater as Ftabulated and p-value <0.001. The greater influence on the protein solubility was found in the addition of vital gluten, followed by moisture content and 3rd zone temperature. The results showed that there was a good protein denaturation due the low solubility obtained in the PB, thus favoring the formation of protein aggregates. The main interactions between proteins were verified by 2ME solvent, which is responsible for breaking the disulfide bonds, and 2ME + U solvent, due to the synergy between the disulfide bond formation, hydrophobic interactions, and hydrogen bonds. Thus, the formation of fibril structure of the meat analogue showed better conditions using 10-12 % of vital gluten, 55-60 % of moisture content and 90-100 °C of 3rd zone temperature.