due to the instability of fat globules when subjected to heat treatment. Further, textural properties of the printed beef were greatly influenced by the presence of lard fat at interlayers, as the fat content proportionally decreases the hardness and chewiness of the cooked samples. This study describes the significance of fat in assisting the printing of meat fibrils and its effect on end‐product quality (Dick et al. 2019; Wood et al. 2008).
In another study, the effect of the addition of oil on flexibility and flowability of material supply was investigated (Liu et al. 2019). A composite dough was prepared from wheat flour, mango powder, olive oil along with water and the change in viscosity of dough was studied in correlation with total solids content. The addition of 2% (w/w) of olive oil into the material supply enhanced the 3D printing performance of dough that resulted in a better surface finish of the 3D printed samples. This was due to the presence of the higher amount of unsaturated fatty acids of olive oil that imparts lubrication and plasticizing behaviour of the material supply. In general, unsaturated fats have more spreading power than saturated ones, thus the addition of olive oil had a significant impact on the final baking quality of 3D printed samples such as tenderness, mouthfeel, appearance, and colour of the product (Liu et al. 2019). Fats and oils are considered to be the most prominent ingredients in tuning the physiochemical attributes of the material supply towards 3D printing. Along with other food constituents, lipids impart a creamy texture to the printing mixture thereby enhances dough formation. This was due to the presence of β′ crystal of the fatty acids that remains to be more stable than α and β forms. Although the portion of lipids was taken in smaller proportions in the material supply, these are the key component in tailoring the printability of the whole printing mixture.
Figure 3.4 Multi‐material 3D printed meat (a) Raw and cooked samples, (b) 3D printed meat paste and lard interlayers.
Source: From Dick et al. (2019), Figure 03 [p. 13] / With permission of Elsevier. DOI‐https://doi.org/10.1016/j.meatsci.2019.02.024.
3.4.4 Dietary Fibre
Dietary fibres are a group of indigestible roughage portion of a meal comprised of carbohydrate components that are not hydrolysed by the intestinal enzymes. This class of macromolecules possess a vital functionality in regulating the normal physiology of the human body (Zinina et al. 2019). A considerable portion of dietary fibres in a regular diet helps in maintaining gut health with reduced incidence of diseases related to sedentary workstyle such as cardiovascular disease (CVD), diabetes, and obesity. Based on solubility, these portion of indigestible carbohydrate polymers is categorised as soluble and insoluble. The former class of soluble dietary fibre (SDF) includes pectin, gum, and mucilage while the latter group of insoluble dietary fibre (IDF) includes cellulose, hemicellulose, and lignin (Dai and Chau 2017). With increasing awareness, the dietary concepts are changing from refined food towards whole food for accomplishing the potential benefits of dietary fibres. Sources of fibre‐rich foods include cereal grains (wheat, oats, barley, psyllium husk), pulses (soy, peas and beans) and legumes, fruits, and vegetables (Mehta et al. 2019). In this regard, printing foods that are rich in fibres are quite interesting as other than providing the nutritional benefits it also possesses organoleptic value as it imparts texture and flavour to the foods and remains to be an active ingredient in personalizing the diet. In this regard, a study on the printability of fibre‐rich foods is quite adequate as it provides a way for the customization of foods and hence personalized nutrition.
Only a few studies were reported on revealing the complexity involved in the 3D printing of fibres. Lille et al. (2018) conducted a study on correlating the material supply for the development of novel 3D structures with a food formula rich in fibre and protein with reduced‐fat and sugars. The ingredients of the printing mixture composed of starch, nanocellulose fibres and milk powder. These ingredients were tested individually as well as in combination for obtaining stable 3D structures after printing. Considering the printability of fibres, the gel matrix was reinforced with cellulose nanofibers (CNF). Printing of fibres showed that there was a discontinuous material flow of the CNF gel system that seems to block the printing nozzle due to its larger fibre particles, causing phase separation and material flocculation (Lille et al. 2018). This study provides a comparative assessment of ingredients and showed that 3D printing of fibres was quite difficult than that of starch and protein‐based food systems. Further, the study highlights a key challenge associated with the printing of fibre‐rich food systems providing an overall idea of the applicability of diverse food materials for 3D printing.
In another study, a fibrous cellular material freeze‐dried spinach was characterized for microstructural composition and the suitability of which as food ink was assessed for 3D printing (Lee et al. 2019). The effect of particle size on printing performance was investigated and the addition of 10% (w/w) xanthan gum showed a promising result in retarding the swelling effects of spinach powder by increasing its water holding capacity. Here, printability was demonstrated by the shear modulus and the extrudability. Results showed that the mechanical stability of the printed structures was improved with the higher particle size of spinach powder (Figure 3.5). Further, this study emphasized particle size as an important variable in assessing the printability of the food ink. However, the study was not focused on revealing the science behind the printing of fibrous material. In another study, researchers have made successful attempts in the printing of fibre and protein‐rich indigenous composite flour (Krishnaraj et al. 2019). Here, natively printable composite flour composed of barnyard millet, green gram, fried gram, and ajwain seeds were subjected for 3D printing to develop a nutritious snack for personalized nutrition. The formulated composite flour contains a concoction of macronutrients with 11% and 18% of fibre and protein, respectively. The physicochemical composition of the indigenous native flour was responsible for its printability. The presence of a small fraction of lipid in the millets was adequate for aiding the smooth flow of printing material supply as it results in the plasticizing effect that eases the material flowability through the printing nozzle (Krishnaraj et al. 2019). Further, the ingredient composition of the formulated material supply well assists in overcoming other undesirable effects of agglomeration and flocculation of fibre during printing.
Except for handful of works, there is only less information available on printing characteristics of fibre‐rich material supply. With the available literature, it was evident that the printability of the dense nature of fibrous material could be correlated with physical attributes such as particle size, surface corrugation, and material density (Nachal et al. 2019). Certain pre‐processing was adequate for fibre‐rich material in order to make it suitable for 3D printing applications. This includes size reduction and particle breakdown with the regulation of total solids content that in turn determines the printing quality of fibre‐rich material supply. Still, the biophysics underlying the printability of fibres has not yet been well explored. More studies must be taken forward for exploring the inherent potential benefits of 3D printing of fibre‐rich material supplies.
Figure 3.5 Effect of particle size on 3D printing of fibrous spinach powder (a) 307 μm, (b) 259 μm, (c) 172 μm, (d) 50 μm.
Source: From Lee et al. (2019), Figure 03 [p. 05] / With permission of Elsevier. DOI‐https://doi.org/10.1016/j.jfoodeng.2019.03.014.
