Mechanism of casein improving 3D printing accuracy of cassava starch gel

In July 2022, Lu Boyi, a scientist on the quality safety and nutrition quality assessment post of the national cassava industry technology system, and the team of the School of Biosystem Engineering and Food Science of Zhejiang University, published a research paper entitled "Investigation of the mechanism of casein protein to enhance 3D printing accuracy of cassava starch gel" in the international journal Carbohydrate Polymers (Top of Zone 1, IF: 10.723). Zhejiang University is the first authorship unit of the article, Ji Shengyang is the first author, and Professor Lu Baiyi is the corresponding author. This study was supported by the National Key R&D Project (2021YFD1600105-03), the National Agricultural Industry Technology System Post Scientist Project (CARS-11), and the Ministry of Agriculture and Rural Affairs' Agricultural Product Quality and Safety Financial Special Project (GJFP202043).

Starch is widely distributed in nature and is one of the most important carbohydrates in human diet. It is often used as a gelling agent and thickener in various food formulas. In view of the shear thinning pseudoplastic behavior of starch, its application in 3D printing as a typical gel and viscoelastic material has been widely reported. The purpose of this study is to explain the mechanism of the addition of casein to improve the printing accuracy of cassava starch gel from the perspective of the multi-scale structure of starch (fine structure, short-range ordered structure) and gel properties (rheology, water distribution and submicroscopic properties), so as to clarify the relationship between structure, property and printing accuracy. It was found that the addition of casein increased the average molecular weight of cassava starch, reduced the swelling potential of starch, resulting in a decrease in line width and an increase in center layer height of 3D printed products, ultimately improving the printing performance of 3D printed products. In addition, the increase of casein reduces the short-range ordered structure of cassava starch, reduces the relaxation time of gel system and increases the free water content, further improves the elastic modulus of gel system, and ultimately improves the printing accuracy of 3D printing products. This study provides valuable information for the application of starch protein complexes in 3D printing.

Research Highlights:

1. It was found for the first time that casein can be used to improve the printing accuracy of starch gel materials;

2. From the perspective of multi-scale structure and gel properties of starch, the relationship between structure, properties and printing accuracy is systematically expounded.

Research conclusion:

1. The high concentration of casein reduces the viscosity of the gel system, which is conducive to the smooth extrusion of materials in the 3D printing process;

2. The addition of casein increases the yield stress (τ y) of the gel system, thus improving the mechanical properties of 3D printing products;

The addition of casein increases the molecular weight of starch, reduces the swelling potential of starch, thereby reducing the printing line width and ultimately improving the printing accuracy of the product;

4. The addition of casein reduces the short-range ordered structure of starch, thus changing the water distribution of the gel system, further improving the rigidity of the gel system, and ultimately improving the printing performance of the product;

5. An increase in casein content promotes cross-linking with starch molecules, transforming printed products from a sponge like porous structure to a layered structure.