Influence of nanocellulose with different particle size on pasting and rheological properties of wheat starch

The aim of this study was to evaluate the effect of nanocellulose with different particle sizes on pasting and rheological properties of wheat starch during short-term storage (<4 h) after gelatinisation. Cellulose nanocrystals (CNC) and bacterial cellulose (BC) at concentrations up to 10%w/w were incorporated into wheat starch suspensions. Rheological characterization included pasting properties assessed by Rapid-Visco-Analysis, amplitude-frequency-time sweeps and in-shear recovery tests. Atomic force microscopy (AFM) and dynamic light scattering were used to determine particle size and charge of nanocellulose. In addition, morphology analysis of the starch-nanocellulose gels was analyzed by optical and polarised microscopy and by AFM.Our results showed that addition of nanocellulose significantly altered the pasting properties of starch, with the effects largely dictated by particle size (∼100 nm CNC, ∼3900 nm BC). Nanocellulose caused a significant increase in G′, which was proportional to nanocellulose concentration. However, loss factor values showed significant structural differences, presumably due to nanocellulose size. Starch-CNC blends showed a rapid decrease in loss factor, indicating strong gel formation, whereas starch-BC blends showed a loss factor indicating weak gel formation. Morphology analysis showed large differences in structure between systems. BC tends to form clusters of gelatinized granules surrounded by BC, whereas CNC tends to form starch-CNC aggregates. In-shear recovery data showed that strong gels had lower recovery capacities, while the weaker gels had higher recovery values.In conclusion, nanocellulose particle size induced significant structural changes in wheat starch during short-range retrogradation, likely driven by the organization adopted by the starch in the presence of nanocellulose.