A paper recently published in the Journal of Food Engineering demonstrated the feasibility of using defatted soybean flour (DSF) in a 3D food printer (3DFP) to print food with desired quality and shape.
Study: Applicability of defatted soybean flours to 3D food printer: Effect of milling methods on printability and quality of 3D-printed foods. Image Credit: nnattalli/Shutterstock.com
3DFPs represent an innovative technology that can print food products with detailed and complex shapes, which is difficult to achieve using other fabrication techniques. Food products fabricated using 3DFPs can be customized in terms of nutritional value, taste, texture, and appearance depending on individual health conditions and preferences.
Extrusion-based printing has been investigated extensively to prepare food products using 3DFPs. In this technique, food materials are extruded through computer-controlled nozzles to print food products of various shapes. Different types of food products in the form of semi-solid states or paste can be used as inks in extrusion-based printers.
A 3D computer-aided design (CAD) is used to design the food shapes in advance, which are then converted into Geometric code (G-code) using slicer software to control the nozzle movements, dispensing speeds, and travel speeds, and finally loaded into printers.
Defatted soybeans are produced in substantial quantities across the world. Although defatted soybeans act as an excellent source of high dietary fiber and other nutrients as they contain 25-30% carbohydrates and 50% protein, their use as a food ingredient has remained limited.
DSF is considered suitable as raw material for 3DFPs as it is inexpensive and has a high nutritional value. However, studies investigating the feasibility of using DSF in 3DFPs have not been performed until now.
Moreover, the printability of food materials such as DSF paste in extrusion-based 3DFPs depends on their capacity to form 3D models and maintain their shape for a specific duration after printing. Printer parameters and rheological properties of food materials critically influence printability.
For instance, the food materials must demonstrate shear-thinning behavior with adequate flowability to extrude through a printer nozzle with ease and necessary mechanical strength to support their weight and the weight of the top layer.
The physicochemical properties of DSFs differ with their production methods and related variations to the particle size. However, no studies have not been conducted to evaluate the relationship between the printability and particle size of DSF.
In this study, researchers milled defatted soybeans using a hammer mill and a jet mill to produce DSF with various particle sizes and investigated the effects of different particle sizes on the printability and physicochemical properties of the DSF paste and the surface structures and textures of the printed food products.
Defatted soybeans in granular form with a short and long diameter of two mm and four mm, respectively, were used as the primary starting material for this study. A hammer mill containing 12 movable hammers and a jet mill was utilized to obtain DSF with coarse and fine particles, respectively.
DSF was mixed with distilled water manually for five min to prepare DSF pastes that were used as inks in the food printer. The water content in the prepared pastes was maintained at 74, 72, 70, and 68% w.b. to ensure the printability of the paste.
Researchers performed particle size distribution measurements of the milled powder and rheological measurements of DSF pastes and evaluated the applicability of a screw-extruder-based 3DFP for 3D printing food using the DSF pastes. Cumulative volumes of 90% (D90), 50% (D50), and 10% (D10) particle size were obtained using the dry powder system module.
A 3D model of a hollow cylinder with 10 mm height, 10 mm inner diameter, and 20 mm outer diameter was created using the free 3DCAD software. Printability was determined by evaluating the appearance and measuring the diameter and height of the printed structures using a caliper and comparing them with the originally designed model.
The loss modulus, storage modulus, and complex viscosity were measured as a function of frequency. Researchers also analyzed the surface structure and texture profile of the 3D-printed foods.
Food products were 3D-printed successfully using the screw-type 3DFP and DSF paste as raw material/printer ink. The particle size distribution shape after milling the defatted soybeans was close to a normal distribution. However, a higher share of fine particles was observed in the DSF prepared using the jet mill compared to the DSF using the hammer mill.
The moisture content of the defatted soybeans decreased after milling. D50 of the DSF prepared using a hammer mill and jet mill was 93.3 μm and 6.1 μm, respectively. Additionally, a more uniform particle size was observed in the DSF produced using a jet mill. Thus, jet mills were more suitable for preparing powders with finer particles with higher uniformity.
The DSF pastes were composed of elastic gel-like structures that allowed them to retain their shape after 3D printing. The loss and storage modulus of the pastes decreased with the rising moisture content, leading to a reduction in the viscosity and strength of the DSF pastes.
A higher loss and storage modulus were observed in the DSF pastes produced from coarser DSF when the moisture content was 68–74% w.b. compared to the pastes obtained from finer DSF. Additionally, the complex viscosity of the DSF pastes decreased linearly with the rising frequency.
These results demonstrated the shear thinning behavior of the DSF pastes, which was necessary for the extrusion of the paste from the 3DFP nozzle. Moreover, the complex viscosity was higher in coarse DSF compared to finer DSF, and the difference increased with the increased moisture content. These differences in rheological properties affected the printing performance.
The DSF pastes with 70–74% w.b. moisture content were extruded successfully from the nozzle of the 3D printer. DSF pastes with 68% w.b. moisture content were not dispensed from the printer nozzle irrespective of the DSF particle size. The pastes were not able to support their own weight at 74% moisture content, and the lower part of the printed hollow cylinder became wider, specifically when coarser DSF with 93.3 μm D50 value was used to produce the DSF paste.
The appearance of the printed specimen/hollow cylinder was similar to that of the original design when finer DSF paste with 70–72% w.b. moisture content and 6.1 μm D50 value and coarser DSF with 70% w.b. moisture content and 93.3 D50 value was used as the 3DFP ink. The holes of the cylinder collapsed at higher moisture contents for both coarser and finer DSF.
The diameters of the printed specimens were close to that of the original design value when DSF pastes with 70–72% w.b. moisture content were used as ink. However, the diameter increased when the moisture content reached 74% w.b., specifically when coarser DSF was used as ink, due to the broader bottom layer of the printed specimens.
Thus, the printability of the DSF pastes with finer particles and 70-74% moisture content was higher compared to the pastes with coarser particles, making them suitable for use to improve the appearance of printed foods in practical applications.
No notable difference was observed in the hardness of the pastes when the moisture content was below 70%. However, the hardness varied at a moisture content above 70%, with the finer DSF displaying higher hardness compared to the coarser DSF at 72% moisture content. These variations were also observed in textural properties, with higher values for gumminess, cohesiveness, and adhesiveness observed in coarser DSF at 70% w.b. moisture content.
Moreover, the surface structure of the printed specimens differed based on the DSF particle size due to the variations in texture profiles between particle sizes, with specimens printed with finer DSF possessing less bumpy and smooth surface structures.
To summarize, the findings of this study effectively demonstrated that finer DSF could be used effectively in 3DFPs to print food products with the desired shape, quality, and appearance.
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Sasaki, T., Nei, D. Applicability of defatted soybean flours to 3D food printer: Effect of milling methods on printability and quality of 3D-printed foods. Journal of Food Engineering 2022. https://www.sciencedirect.com/science/article/abs/pii/S0260877422002916?via%3Dihub
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