Soybean straw nanocellulose produced by enzymatic or acid treatment as a reinforcing filler in soy protein isolate films

•Enzymatic and acid hydrolysis were used to produce soybean straw nanocellulose.•SPI films were reinforced with nanocellulose produced by enzymatic/acid hydrolysis.•CNFs presented a greater aspect ratio and thermal stability and lower crystallinity.•CNFs as reinforcing filler yielded more elongable nanocomposites with lower WVP.•Both CNFs and CNCs improved the mechanical resistance of SPI films. This work is a comparative study of the application of mercerized soybean straw (MSS) and nanocellulose produced by acid (CNCs) or enzymatic hydrolysis (CNFs) as reinforcing fillers in soy protein isolate (SPI) films. CNCs presented average dimensions of about 10 nm-thick and 300 nm-long with a crystallinity index of 57%, whereas CNFs have similar diameters, though with greater lengths (>1 μm), lower crystallinity index (50%) and greater thermal stability. Incorporation of 5% of CNCs and CNFs (g/100 g of SPI) improved the SPI film tensile strength by 38 and 48% respectively, and decreased the SPI film elongation at break when compared to control films. The SPI-CNC films showed the lowest values for solubility, probably due to their higher crystallinity (63%). On the other hand, the water vapor permeability was solely reduced with CNF addition, which can be attributed to their higher aspect ratio (length/diameter) and a better incorporation into the protein matrix.