3D Printing Progress in Gluten-Free Food—Clustering Analysis of Advantages and Obstacles

Abstract

Gluten-free food is a huge group of products whose common characteristics are recipes containing non-gluten flour or starches. Most of them are bakery-related products which initially were manufactured based on the recipe containing wheat/wheat flour. Nowadays, the growth of the gluten-free food sector is mainly powered more by trends and personal choices of consumers following the “healthy choice” diet than patients with real medical conditions, who need to follow the strict gluten-free diet. 3D printing is considered a disruptive technology, and being an additive manufacturing technique contributes directly to structure/texture creation. Food 3D printing as a manufacturing technology is struggling with repeatability and precision but is still very promising as a potential problem solver, especially in texture creation, which is the main technological problem for the gluten-free bakery. The article aims to analyze, using clustering analysis, the main obstacles so far identified for gluten-free 3D printing. Meanwhile, the prospects of producing personalized food products using 3D printing and its relationship with the UN Sustainable Development Goals 2030 as the advantages of this technology were discussed. The up-to-date exploitations of 3D printing techniques in gluten-free food manufacturing were discussed.

1. Introduction

Currently, 3D food printing is becoming more popular and widespread due to the increasing consumer demand for innovative and personalized food products. This is facilitated by additive manufacturing potential capabilities, including the production of three-dimensional products with complex geometric structures, special textures, and specified and personalized nutritional content. The ability to print food products depends on multiple aspects of the 3D food printing technique, such as the type of printer, the printing material, its rheological properties, post-processing, etc. [1]. The fast development of 3D printing has led to a change in the way we think about food design, providing unexpected solutions like the development of 3D printing technology of orange skin using orange concentrate [2].

The number of publications on this topic is growing every year. Research shows that the rheology of the printed raw material is crucial for the design, development, and application of food printing. In addition to 3D food printing as a technique, new edible food ink technologies are being developed for 2D and 4D printing. An interesting fact is that 4D food printing provides self-transformation of color/texture/taste and other properties of the printed object as a function of time, pH, or temperature, which results in a unique character and visual appreciation during meals [3].

The development of appropriate rheology models for raw materials with different properties indicates the ability to further explore the relationship between ink structure and the performance of printing for multifunctional food products [4]. However, to date, 3D-printed food systems have been studied with a limited number of food systems, the most common being chocolate, fruit and vegetable mixtures and powders, flake-based cereal snacks, hydrocolloids, egg yolk, cheese, and minced meat. This limited number of materials used for 3D printing is explained by the physical characteristics of food systems, the so-called 3D printing suitability, as well as the ability to maintain the dimensions of the printed form. According to some studies, the main prospects of 3D food printing are personalized food production [5,6], on-demand production, reduction of food waste, and co-development for the needs of food consumers. Personalized food production through this technique has the potential to create food not only with designed shapes and sizes but also with planned nutritional and functional properties that match the specific needs of individuals [7].

New technologies can be valuable for improving food security and overcoming global hunger. There are a number of countries suffering from hunger today. The 3D printing can be used to develop food products with maximized nutritional value from a variety of sources, such as meat, seeds, insects, and algae [8]. These products can be produced in ways that are visually appealing, with improved nutritional profiles, and in different shapes and colors. Considering circular economy strategies, the reduction of food waste could be achieved by using agro-industrial by-products in printed food products [9]. Biologically active compounds contained in food industry by-products can be used as innovative ingredients for functional foods produced by 3D printing, improving the nutritional profile and the overall design of food, as well as addressing food waste management in a sustainable approach [10].

Many studies were conducted to evaluate the feasibility of 3D printing of different food matrices using various structure-forming components. For example, egg white was found to be suitable for printing mixed with gelatin, starch, and sucrose [11], and the possibility of printing brown rice was optimized [12]. The main 3D applications for printing flour-based food products are still based on extrusion technology and relate to raw materials that can be printed natively, such as cereal products and chocolate. A special feature of this technique is the possibility of using it as a method of producing dietary products with modified texture, which requires further research. Both protein and vegetable products have already been 3D printed via extrusion devices, providing the texture categories defined by the International Dysphagia Dietary Standardization Initiative. In that particular case, 4D food printing can offer more benefits by creating forms that are more appealing through color change and flavor release after extrusion [13].

Physically, extrusion-based 3D printing is achieved by depositing viscoelastic raw material through a printer nozzle to create three-dimensional food structures layer by layer. Currently, progress has been made by studying the feasibility of printing food materials, the formulation of printing materials, and the optimization of printing parameters to produce personalized food in the future [14].

For the 3D printing of flour products, an important role is played by the components that are structure formers, such as protein and gluten, which give food a viscoelastic structure. Rice flour, for example, is widely used to make gluten-free products; however, being low in protein and gluten-free is not used natively in 3D printing technologies [15]. Many gluten-free product formulations are based on the use of rice flour, but due to its low protein content, rice flour requires additional components to improve its 3D printing capability. It has been proposed to mix rice flour with Jagerry to improve the viscoelastic properties of the 3D printing mass, as well as an alternative to using sugar, for the production of gluten-free products using 3D printing [16].

The sustainable perception of gluten-free food consumption is also growing. Gluten-free products based on naturally gluten-free flours became perceived as a healthier and, sometimes, more sustainable solution for today’s consumers. Producing gluten-free foods can be more environmentally friendly if done properly [17]. The production of gluten-free products, as well as the use of 3D printing for dietary products, has its own peculiarities. In particular, gluten-free complex powder mixtures have great potential for 3D printing personalized nutritious snacks. It was found that the quality of printing gluten-free products was strongly influenced by the particle size of the raw material, the diameter of the nozzle, and the amount of water [5]. Thus, understanding the interplay among all those parameters, as well as their impact on the printing process, can be crucial to achieving the best print accuracy and quality of 3D-printed snacks.

During 3D printing, natural or other food additives that function as binding agents are commonly added to achieve the desired viscosity and rheological properties, supporting ease of extrusion and printed structure after deposition [18]. However, this does not mean that printing other materials without a binding mechanism is impossible; examples of such food formulas include a combined high-fiber flour paste, rice dough, and wheat dough enriched with alternative types of insect-derived proteins [19]. Thus, it is relevant to note that the suitability of food materials for 3D printing can largely depend on the components/composition of the food material and the corresponding dynamic viscosity and rheological properties, which do not necessarily require systematic modifications to determine sufficient fluidity, plasticity and mechanical properties of the ink. As the following example shows, 3D printing can often require a purely experimental approach. While increasing the content of skim milk and sugar in cookie dough that does not contain stabilizers or gum resulted in increased deformation of dough samples (rice, tapioca, and wheat) and greater collapse of 3D structures after baking, respectively [20], tapioca dough with reduced sugar and milk content has better viscoelastic properties, supporting structurally stable 3D printed cookies.

Numerous studies have established that the printability of food system formulations, especially gluten-free formulations, can be determined based on computed rheological data [21,22,23,24]. Pavičić et al. (2021) investigated the influence of different types of flour and fat on dough rheology and the technological characteristics of 3D-printed cookies [25]. The study aimed to relate the printing quality and physical properties of the cookies to the dough rheology and dietary fiber content. The results showed that the choice of flour and fat type had an impact on the flow properties and dynamic moduli of the dough, which in turn affected the 3D printing performance. Another study by Lille et al. (2020) focused on the structural and textural characteristics of 3D-printed protein- and dietary fiber-rich snacks made of milk powder and wholegrain rye flour [26]. The study highlighted the importance of wholegrain rye flour as a source of dietary fiber in 3D printing formulations due to its low gluten content. The presence of dietary fiber in the flour can influence the rheological properties of the dough and ultimately affect the performance of the 3D printing process. Furthermore, the study by Carrillo-Navas et al. (2016) examined the effect of the gelatinized flour (GF) fraction on the thermal and rheological properties of wheat-based dough and bread [27]. The study found that the addition of the gelatinized flour fraction influenced the rheology of the dough, indicating that the composition of the flour can impact the flow properties of the dough and, consequently, the 3D printing performance [27]. Overall, these studies suggest that the natural constituents of GF flour, such as proteins and dietary fibers, can affect the rheological properties of the dough, including its flow properties and dynamic moduli. These rheological properties, in turn, can influence the performance of the 3D printing process. Therefore, understanding the relationship between GF flour constituents, dough rheology, and 3D printing performance is crucial for optimizing the formulation and processing parameters in GF flour-based 3D printing applications. The high correlation established and known between the structure forming capacity and particular constituents will facilitate the application of suitable raw material in the printing process, will lower the technology implementation costs, and will speed up the popularization of 3D printing manufacturing in food processing.

Previous consumer research shows that all consumers of gluten-free dietary products can be divided into three segments: convenience-oriented consumers, health-oriented consumers, and environment-oriented consumers [28]. In this regard, further developments of gluten-free products should focus on the above groups of interested consumers. The development prospect of 3D food printing is to make personalized and attractive food designs available based on personal nutrition to meet specific requirements of healthy lifestyles, in particular, the production of gluten-free products. Although there is a lot of research on the 3D printing of food products, the technology of 3D printing gluten-free food products based on flour is still under active development and needs more research.

The main purpose of this review is to discuss using 3D printing in the production of gluten-free food and to summarize the advantages and obstacles of using 3D printing for the production of gluten-free products.

2. Methods

The bibliometric analysis used in this study was based on a literature review, which is a tool for clustering and displaying information from scientific documents, using keywords, citations, etc., to outline the characteristics of the scientific field, namely gluten-free products and to identify new features and networks of connections with 3D printing of food products. As reported by Waltman, L.; Van Eck, N.J., and Noyons, E.C.M. (2010), bibliometrics allows us to see how research topics are related to each other and to outline how scientific topics develop over time [29]. In addition, bibliometric analysis makes visible the invisible connections between highly cited papers and research frontiers [30], paving the way for innovative ideas.

The present study is based on a bibliometric literature analysis using a thematic approach [31,32,33], as the search for information on the application of 3D printing to food production includes a wide range of sources, and then the search is narrowed to the production of gluten-free products. In this study, a bibliometric analysis of specific terms related to the application of 3D printing for sustainable food production for gluten-free nutrition was conducted in Scopus, a well-known scientific database of peer-reviewed academic documents containing more than 5000 journals and 24,000 publications.

The data collection began in October 2022. The method of bibliometric mapping was used to analyze the publications of 2019–2022 (N = 752). The results indicate the existence of several relatively independent research areas with seven major clusters. This clearly shows that the process of gluten-free food development, especially 3D printing of gluten-free food products, touches on many issues and is, in fact, a cross-subject study.

The research was carried out using VOS Viewer 1.6.17 (CWTS, Leiden, The Netherlands) [34], and the shared use of terms was chosen to explore the research streams that researchers discussed in the context of 3D food printing and gluten-free food production. The results of the analysis are presented in the following section in a network graph (figure in Section 3.1), with the diameter of the circle indicating the frequency of occurrence of a particular term, while the width of the link indicates the strength of the relationship between the two terms. Terms that are frequently mentioned in collaborative research will be associated with one cluster.

This study analyses the key publications identified through bibliometric analysis on the possibility of developing sustainable gluten-free flour food production using 3D printing. The selection of these case studies was made in order to overcome some of the limitations of bibliometric analysis and to select leading publications that are directly relevant to the aims of this study. Although the bibliography of 3D food printing has been growing in recent years, and there are also a large number of reviews aimed at outlining the most important features of 3D food printing, the segment of 3D printing of gluten-free products requires analysis.

The connection between gluten-free (GF) flour and its natural constituents, such as proteins and dietary fibers, dough rheological properties, and 3D printing performance, has been explored in several studies.

3. Results and Discussion

3.1. Using 3D Printing of Gluten-Free Products

As a result of the bibliometric analysis, several clusters (Figure 1) were obtained to assess the current research situation and identify the advantages and obstacles to the use of 3D printing of gluten-free products.

It is obvious (Figure 1) that the rheological properties of printed gluten-free food products are key, as indicated by the repeated use of keywords such as “rheological properties”, “rheology”, “texture”, and “viscosity” (C1, C2, C3). This fact also proves that food products, including gluten-free ones used for 3D printing, must have constant rheology and texture to obtain a high-quality final product. Therefore, this highlights the need to analyze the suitability of the proposed printable mixtures, rheological properties, and specific chemical composition of the raw materials when developing gluten-free food material for 3D printing.

As illustrated in Figure 1, there are several key factors that affect the quality of the final product produced using 3D food printing. The first and most important is the material’s properties, i.e., the chemical composition and the presence of the necessary components that give the dough system the required rheological parameters. This is evident from the following—the diagram shows that the circles of the largest diameter in different clusters relate to the rheological properties of the mass, as well as the composition of the food mass (C1, C2, C3, and C7). This shows the importance of balancing the rheological properties of printed materials to facilitate printing and maintain sufficient mechanical properties to resist curling during printing and post-processing to fully retain the printed complex shape.

Another factor is the process parameters, which are evident from the large number of smaller rings that indicate printing speed, pressure, thermal properties of the raw material, moisture content, pH, etc. The third factor is post-processing after 3D printing, which is also highlighted by the large number of small rings in different clusters, such as baking, frying, steam treatment, etc.

The use of bibliographic analysis allowed us to highlight the role of the components that make up the food mass for 3D printing. The sensory properties, texture, and structure of 3D printed foods play an important role in the acceptance of 3D food products, so their connection with the main technologies used and possible improvements in quality properties by incorporating enriching components into the final food product are shown. In different clusters, a large number of small rings can be seen, indicating substances that provide the structure of the design—starch, pectin, gluten, etc. In order to ensure the desired sensory performance, coloring agents are used, in particular, to ensure the overall acceptability of the final product (C6), as well as enrichment agents that provide the appropriate nutritional value to the printed food (C2, C4, and C7).

Most currently used 3D food printing methods are based on material extrusion. Such techniques can realize continuous printing and are particularly suitable for preparing food using liquid or low-viscosity materials, such as gluten-free dough, mashed potatoes, etc., with a variety of complex and unique structures. As the results show, most often, the study of extrusion-based 3D printing of food products is carried out in the plane of dependence of the formulation and rheological properties, as well as the stability of the structure after post-processing (C1, C2, C3, C4, and C7).

The importance of optimizing the dough formula for 3D printing and subsequent baking to obtain a stable designed geometry is emphasized (C1). In 3D printing, yield strength, i.e., rheological properties, is commonly used to assess the extrusion ability of a food mass. The influence of sucrose, butter, and different types of flour on the extrusion and 3D printing ability of the dough that is later baked was also investigated. This is related to the mechanical strength of the food mass, as a higher extrusion force corresponds to a higher mechanical strength of the food mass [20].

It is important to balance the rheological properties of the mass and maintain sufficient mechanical properties to facilitate 3D printing to resist curdling during printing and subsequent processing to fully retain the printed complex shape. A key role in this is played by changing the amount or ratio of ingredients, which can improve thermomechanical properties and control the ability of food products made in this way to retain their shape. For example, the use of sodium alginate in concentrations of (0, 0.25%, 0.50%, 0.75%, 1.00%, wt %) was proposed as a structure enhancer for 3D printed rice flour products. The results of the physicochemical properties showed that the rice paste mixed with sodium alginate exhibits shear liquefaction so that it can be used as an ideal material for 3D printing (C4 and C5). The viscosity, degree of bound water, and mechanical strength of rice paste increased with the addition of sodium alginate [15].

All the analyzed studies on 3D food printing provide valuable information about the ability of flour dough to be printed and further processed. However, methods for developing structurally stable gluten-free flour dough formulation still need to be improved to maintain the three-dimensional complex shapes after baking and support the trend away from additives and yield enhancers, especially for gluten-free mixes and dough [20].

A bibliometric analysis shows that there is still a lack of research, reflected in scientific articles, that directly links the production of gluten-free products to 3D printing (Figure 2). However, it illustrates the connection of gluten-free production with rheological properties, texture, rheology, thermal, structural and physical properties, and some formulation components.

The creation of 3D-printed food with programmed texture aims to obtain personalized properties, improving the competitiveness of the industry through new perceptions of texture, functional or nutritional focus of food, and helping to mitigate swallowing or chewing problems in vulnerable people. Therefore, the rheological properties of the flour mass must be taken into account, as well as the close relationship between 3D printing movements and food texture, morphology, and pore distribution (Figure 3).

It has been shown that 3D printing of food material depends on many factors, including temperature, raw material composition, humidity, and the use of additives, which have a significant impact on the process and quality of the 3D printing itself and the quality of the final product (Figure 2 and Figure 3), which is also consistent with the results obtained by other researchers [5].

Thus, understanding the rheological properties of gluten-free raw materials and the possibility of printing complex food formulations is crucial for 3D printing. The analysis also shows that in order to customize the texture of a gluten-free mass, it is necessary not only to investigate the rheological properties of the mass and its suitability for 3D printing but also whether and how the 3D printing process itself affects the mechanical characteristics of the used mixture, as well as to choose the optimal post-processing after 3D printing.

3.2. Advantages and Obstacles of Gluten-Free Food Production Using 3D printing

As shown above, today, most of the research on 3D printing of gluten-free products is carried out in terms of studying the technological features of the process selecting ingredients to obtain the best characteristics of finished products made using this method. However, 3D printing still remains the technology of food production, which is fundamentally important for ensuring the health and well-being of consumers. Since the production of gluten-free products involves the exclusion of white refined wheat flour and the use of non-traditional types of flour milling, meals, etc., it can be argued that an increase in the production and consumption of such food products will prevent the formation of chronic diseases associated with excessive consumption of white refined flour products.

One of the most important benefits of 3D printing gluten-free products is their possible important contribution to the achievement of the Sustainable Development Goals (SDGs) by 2030.

Table 1. The possible relation between 3D printing of gluten-free products for personalized nutrition and the UN SDGs (https://unstats.un.org/sdgs/metadata/. Accessed on 14 May 2023).

SDGs UN	Specific SDG Indicator	Brief Explanation of the Correlation with the Production of Gluten-Free Food Products Using 3D Printing
SDG 1	SDG 1.5 is designed to help build the resilience of the poor and vulnerable against extreme events and disasters.	The first SDG is related to humanity’s efforts to end poverty in all its possible forms, which also includes food security and sustainable access to food. Experience has shown that the most vulnerable segments of the population (the poorest, least developed countries in Africa) suffered from food shortages, primarily due to the lack of cereals (wheat, corn) caused by the military conflict in Ukraine [35]. Therefore, the production of food products with the planned nutritional content through 3D printing using non-traditional gluten-free raw materials is a promising method of ensuring the sustainability of food chains, which will increase the resilience of the poor and those in vulnerable environments and reduce their vulnerability to extreme events.
SDG 2	SDG 2.1–2.5 is directly related to the achievement of food security, designed to help improve nutrition, which is possible through the development of gluten-free food products with the prescribed nutritional content through 3D printing.	Achieving this goal implies equal access to safe, sufficient, and nutritious food for all people, including those in vulnerable situations, the poor, infants, and people with special needs. The production of food with the intended nutritional content through 3D printing using non-traditional gluten-free raw materials will contribute to sustainable food production systems. Such production can use food waste from other food production as non-traditional gluten-free raw materials, which will also contribute to increasing the added value of food, gradually improving land and soil quality, and helping maintain ecosystems.
SDG 3	SDG 3 is directly related to the topic under study because ensuring a healthy lifestyle and promoting the well-being of people at any age cannot be achieved without ensuring sustainable food chains.	Reducing the global maternal mortality ratio, mortality of newborns and children under 5 years of age, as well as reducing premature mortality from non-communicable diseases and diseases associated with air, water, and soil pollution—the achievement of these goals and positive changes in the relevant indicators will be facilitated by the production of enriched functional gluten-free products with adjustable composition, manufactured by 3D printing, which does not create additional food waste and is designed to meet the shortage of specific foods.
SDG 9	SDG 9.4–9.5 are indirectly related to the 3D printing of gluten-free products—improving technological capabilities, supporting local technologies, research, and innovation.	This SDG 9 aims to promote the modernization of various industries for sustainability in order to increase resource efficiency in the development of gluten-free products through 3D printing—this can be achieved through the introduction of local clean and environmentally friendly raw materials. It also includes encouraging innovation and increasing research; in developing countries, this could include researching and incorporating locally available ingredients, including gluten-free raw materials, into the technology.
SDG 12	SDG 12.3, 12.5, 12.7, and 12 a are about developing models of sustainable consumption and production, replacing wheat flour with other plant-based ingredients, and creating food products with adjustable composition by 3D printing, which directly contributes to this goal.	To ensure the efficient use of natural resources, this area of research on the use of local, environmentally friendly, available resources as raw materials for the production of gluten-free products by 3D printing requires further development. In addition, the use of food waste from one food production facility for use in the technology of gluten-free products with a controlled composition will reduce food losses along the production chain. The proposed method of 3D printing gluten-free food products with a predetermined composition contributes to the prevention, reduction, and reuse of food waste.

shows the possible benefits of the ongoing research and development of 3D printing of gluten-free products and the optional connection to the achievement of the UN’s 2030 SDGs.

The 17 United Nations Sustainable Development Goals (SDGs) were developed to create a vision for achieving a sustainable future. One of the key objectives of writing the UN 2030 SDGs was to “leave no one behind”, and to recognize the power of science and the interconnectedness between social, environmental, and economic development goals. This study aims to help illustrate the importance of further development of this technology, which will help accelerate action and overcome obstacles to progress in sustainable development by offering simple solutions, one of which is the use of 3D printing of gluten-free products with a predetermined composition using unconventional raw materials.

The analysis revealed (

Table 2. Analysis of key publications.

Promising Materials Proposed for 3D Printing	The Scientific Manuscript Short-Cuts	Ref.
Programmable texture properties of cereal-based snacks mediated by 3D printing technology
.	The paper shows the possibility of producing cereal snacks with different texture properties using 3D printing technology. 3D printing of food products can be used to create controlled pores in cereal-based snacks in order to create new foods with different structural properties	[5]
Applicability of Rice Doughs as Promising Food Materials in Extrusion-Based 3D Printing
Flour from waxy rice, indica rice, and japonica rice.	This study has shown that the use of high-amylose rice for 3D printing of food products has a high potential and can be used as a basis for the production of fortified food products by 3D printing.	[15]
3D printing of cereal-based food structures containing probiotics
Wheat dough, calcium caseinate, the probiotic strain of Lactobacillus plantarum.	The possibility of 3D printing of wheat dough enriched with probiotic cultures that were well preserved during baking was shown.	[36]
Application of 3D Printing in the Design of Functional Gluten-Free Dough
Gluten-free flour preparation was supplied from Sinblat (Sinblat Alimentación Saludable S.L., Foios, Spain), Rosehip (Rosa canina).	The possibility of 3D printing of gluten-free products enriched with rose hips is shown. This study has shown the prospect of 3D printing of bread dough as a method of personalizing food products, which opens up wide opportunities for enrichment.	[37]
Study the correlation between the instrumental and sensory evaluation of 3D-printed protein-fortified potato puree
Dehydrated potato puree, Protein acid hydrolysate soy, Cricket protein powder 70% protein (Acheta domesticus), Egg albumin 75% protein.	This study aims to develop 3D printed products for people with swallowing problems, i.e., to show the possibility of developing individualized nutrition with simultaneous enrichment with protein components. In general, the usefulness of using the instrumental method to characterize food products with modified texture was demonstrated with statistical correlation.	[38]
Texture Design and Its Effect on Soft Foods Suitable for Nursing Foods Using Macroscopic 3D Structures Printed by 3D Food Printer
Protein, Egg white, Milk, Gelling agent, Gelling agent mixture, Auxiliary Ingredient, Powdered oils, Wheat fiber, sucrose.	The research is concerned with studying the effect of macroscopic 3D structures of soft food products printed on a 3D printer on the texture of soft food products for baby food. The possibility of reproducing the texture of printed objects, even for soft foods, is shown. It is established that the texture of soft foods can be controlled by a macroscopic three-dimensional structure created using a 3D food printer.	[39]
Rheological properties, dispensing force, and printing fidelity of starchy gels modulated by concentration, temperature, and resting time
A starchy-gel system.	This study demonstrates the flexibility of 3D-printed food structures, the properties of which can be adjusted by changing the composition of the starch gel food ink. This research on 3D printing starch gels can serve as a basis for the development of food matrices for 3D printing gluten-free food products.	[40]
3D printing properties of Flammulina velutipes polysaccharide-soy protein complex hydrogels
Soy protein isolate hydrogels, Flammulina velutipes polysaccharide	The research is aimed at improving the 3D printing technology based on soy protein isolate for special consumer groups. The study of food matrices for 3D printing based on polysaccharide-soy protein hydrogels has the potential to be used in the creation of gluten-free food products by 3D printing.	[34]
Hot extrusion 3D printing technologies based on starchy food: A review, Carbohydrate Polymers
Native Starch, Acetylated Starch, Cationic Starch, OSA Starch, Distarch Phosphate, Oxidised Starch	The review aims to show the potential and capabilities of 3D printing starch-based food products and the impact of various additives, design features, and 3D printing process parameters. The study of the rheology, microstructure, and interaction of components and processing methods and 3D printing process parameters helps in the further development and adjustment of the composition and process parameters of gluten-free food products.	[41]
Powder properties, rheology, and 3D printing quality of gluten-free blends
Corn, millet, buckwheat, chia, flaxseed, sweet potato flour, rice protein	The proposed method of cryo-milling, which has not been used before for the preparation of powders for 3D printing, has achieved the best results in 3D printing gluten-free products. The prospects for the development of gluten-free food products by 3D printing and the dependence of the quality of the finished product on the properties and size of raw material powders and the amount of water are shown.	[42]
Effect of rheological properties of potato, rice, and corn starches on their hot-extrusion 3D printing behaviors
Rice starch (RS), potato starch (PS) and corn starch (CS)	This study focuses on the HE-3D printing of starch, and the relationship between rheological properties and printability was established. The results showed that concentrated starches exhibit shear liquefaction and strain sensitivity, which could be printed as HE-3D printing materials. In addition, the parameters τ y and G′ of all the studied samples, which are crucial for maintaining the deposited layers and preserving the printed forms, increased with increasing starch concentration. The correlation between rheological properties and printability of several types of starch was established, which can serve as a basis for the development of gluten-free food products by 3D printing.	[43]
3D extrusion printing and post-processing of fibre-rich snack from indigenous composite flour
A fiber- and protein-rich composite flour made from local ingredients (millet, roasted gram, green gram, and ajwain seeds)	The mixtures were developed and 3D printed as snacks with the best resolution and stability under optimized printing parameters. Appropriate pretreatment methods were used to optimize the food matrix component without adding additives as structure improvers. The development of gluten-free snacks by 3D printing using a composite flour rich in fiber and protein and without the use of structure enhancers serves as a basis for further research.	[44]
Trends in functional food development with three-dimensional (3D) food printing technology: prospects for value-added traditionally processed food products
This review of the 3D printing process discusses key factors, including the suitability of edible inks for 3D printing purposes, printing parameters, and additional post-printing treatments, that influence the process of developing successful edible 3D structures with the potential to develop structures for dietary/functional foods.		[45]

) that nowadays, food chemical additives are often used in formulations, but there is a gradual shift towards additives obtained from natural sources. Mixing additives to create a printable product can be a significant barrier to scaling up the production of functional foods via 3D printing due to concerns about additives and the demand for products with minimal chemical enhancements. Thus, the prospect may lie in finding and using suitable pretreatment methods, optimizing food matrix components without adding additives, or adding natural raw materials that tend to maintain proper flow behavior and function as food additives.

According to the results of the bibliometric analysis, the leading countries in terms of the number of citations and the number of scientific publications on this topic are China, India, Australia, the USA, and the Republic of Korea (

Table 3. Affiliation of the selected publications by keywords according to the results of the bibliometric analysis to the country and territory.

Countries and Territories	Scholarly Output	Views Count	Field-Weighted Citation Impact (Excl. Self-Citation)	Citation Count (Excl. Self-Citation)
China	208	9770	2.84	5433
India	71	3311	2.20	923
Australia	70	4748	3.70	3455
United States	48	2478	2.66	796
Republic of Korea	37	1272	1.54	370
Canada	32	1275	2.22	382
The   Netherlands	23	1455	2.16	376
Singapore	21	1455	2.87	633
Italy	20	1937	2.68	482
Spain	19	1158	1.74	473

). Furthermore, many studies have argued that the rheological properties of the material, structure accuracy and shape stability, compatibility with conventional food processing techniques (e.g., baking and cooking), or post-processing resistance are important factors for successful extrusion 3D printing of gluten-free food products.

4. Conclusions and Future Remarks

Consequently, the use of gluten-free products is becoming increasingly popular, especially when it comes to nutrition for people with special needs. In addition, 3D printing technology for personalized food products helps to reduce food waste and develop food products for specific consumer needs. In fact, the SDGs have the same driving forces as those that drive progress in the development of new foods for dietary or special purposes with new techniques like 3D printing: public health and well-being, environmentally sound production, sustainable use of valuable resources, and newer ones like climate change prevention, promoting inclusivity and food accessibility.

The benefits of 3D food printing include the possibility of using this technology in personalized or targeted nutrition, such as infant gluten-free or elderly diets, and the possibility of enriching with active ingredients to prevent specific disorders. The 3D printing of food products offers several advantages, such as process flexibility, reduced risk for innovative products, lower costs, on-demand production, and reduced waste and environmental impact. In addition, 3D printing involves end users in the production process, which contributes to the sustainable production of essential food products. Understanding the rheological characteristics of gluten-free raw materials and the ability to print various food formulations is crucial for 3D printing and requires further study.

The hardest challenge for the wide spreading of this technique is that the number of raw materials suitable for printing is extremely limited [46], especially for gluten-free food products. Other major challenges are the retention of the printed structure and the complexity of developing multicomponent food recipes. Also, most current 3D food printing technologies cannot directly convert raw materials into final food with just one processing step, which is also true for gluten-free foods [47]. Thus, printed gluten-free products should have been easily treatable with traditional food production processes, i.e., baking, boiling, steaming, etc., which is crucial for the further development of 3D printing technology and is a promising research direction.