Development of a novel pressure vessel system for the simulation of starch expansion – Methylated and regular waxy corn behave significantly different with and without cellulose inlcusion

Authors: RICHTER, JANA - Washington State University; SAUNDERS, STEVEN - Washington State University; IKUSE, MARINA - Washington State University; Finnie, Sean; GANJYAL, GIRISH - Washington State University

Submitted to: Starch
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: To increase the nutritional value of expanded snack products, much effort has been made to include more dietary fiber into direct expanded snack products using extrusion processing. This study aimed to investigate the molecular interaction between starch and cellulose in a simulated expansion processing setup. Comparison of the expansion performance of unmethylated and methylated material will help to understand the importance of hydrogen bonds during the extrusion process of pure starch as well as starch-fiber blends. A pressure vessel setup for a simulated expansion process as it occurs during extrusion processing has been developed successfully. Because the expansion of starch-cellulose blends using the designed tool was similar to the expansion of such blends when extruded, the setup has been proven to be suitable for the underlying question of interest. The obtained data show that methylated starch behaved significantly differently than non-methylated starch with and without the inclusion of cellulose, with the methylated starch expanding much less. This decreased expansion ability might be due to the lower amount of hydrogen groups and the consequential lower potential to form hydrogen bonds but could also be due to the higher viscosity profile that methylated starch exhibited. Yet, the higher viscosity of the methylated starch might be beneficial for the structure integrity when including cellulose. Further research is needed to fully conclude the importance of hydrogen bonding during the expansion process of starch-fiber blends. It is suggested that such investigations include the use of ionized compounds that could potentially intensify intermolecular interactions.

Technical Abstract: Fortification of direct-expanded products with insoluble fiber generally leads to a decrease in expansion. To be able to include higher percentages of the health beneficial compounds in puffed products, it is essential to understand the molecular interactions between starches and fibers. A pressure vessel setup was developed to allow for a small-scale simulated expansion process testing. Testing of methylated waxy corn starch, which is commercially unavailable and hence, only available in small quantities when produced in the laboratory helps to understand the importance of hydrogen bonding during the expansion phenomenon. Waxy corn starch was methylated, and both, non-methylated and methylated starch, were tested for their expansion ability at cellulose inclusion levels of 0, 5, and 20%. The specific volume of pure non-methylated starch was 16.3 ± 1.8 cm2/g, almost three times higher than the one of pure methylated starch, which showed a specific volume of around 6.0 cm2/g. Possible reasons for this decrease might be the elimination of hydroxyl groups capable of forming hydrogen bonds or the significantly higher viscosity of the methylated starch. While fortification with 5% cellulose did not have significant effects on the expansion, 20% cellulose significantly reduced the specific volume for both. Scanning electron microscopy (SEM) images of the expanded structure showed a smaller cell size with the inclusion of high cellulose levels but further suggested the higher viscosities to be beneficial for expanded starch-fiber products.