Valorisation of vegetable food waste utilising three-dimensional food printing

ABSTRACT Food waste utilisation and zero waste approach are among the many ways of building a sustainable economy. Food waste as authentic edible food being accepted by the consumers still has many barriers to overcome. One tool to help in the valorisation of food waste to value-added products is three-dimensional food printing (3DFP). These products can lead to easier and greater acceptance of food waste by consumers, having familiar nature with respect to taste, texture and appearance as other consumables. In the present study, food ink recipes were formulated from spinach stems and kale stalks, the common green leafy vegetable wastes. These spinach and kale inks were then characterised on their rheological properties of shear thinning and yield stress. The inks were subjected to IDDSI tests meant for standardisation of soft foods for dysphagia patients. This paper demonstrates ways of converting vegetable wastes into edible diets that are aesthetically pleasing through 3DFP.


Introduction
Food wastage has become a topic that is highly discussed as countries move towards a sustainable future and securing food for future generations (Leroy et al. 2015).The accumulation of food waste has affected the environment detrimentally due to the constant consumption of resources and the endless release of greenhouse gas emissions.Food waste is often produced along the food supply chain resulting in a third being disposed of globally (Stuart 2009).Food waste generation is much more prominent at the consumer level in the developed countries (FAO 2011).Due to the scarcity of land resources, Singapore is highly dependent on imports, and at least 40% of these imports are lost as food waste.From farm to market, a total of $2.54 billion worth of food was wasted annually, with $342 million lost from households.One in three residents in Singapore would dispose of 10% of purchased food weekly.This food waste contaminates recyclables and also creates stench and vector breeding problems that disrupt people's way of life (SEC 2019).These food wastes added up to one of the top five largest waste stream produced (NEA 2019).
In a bid to reduce the amount of food waste and to strengthen food security, Singapore employed multiple approaches to avoid overreliance on imported food.One of the proposed strategies was to deploy new technologies and innovations to convert food waste into value-added products (SEC 2019).Therefore, food upcycling can be one of the strategies employed to improve self-sufficiency.Numerous food upcycling projects are introduced with the aim of reducing industrial food waste as the characteristics of food industry waste makes it highly suitable for upcycling (Zhang et al. 2007).Thus, there is more economic value in recycling industry food waste.However, food waste generated in household is greater than industry food waste especially in developed countries (FAO 2011;Mirabella, Castellani, and Sala 2014).Recycling of these food waste is highly laborious and costly due to the complex nature of food wastes and its distribution in the landscape.Furthermore, incineration of food waste to recover energy has the lowest priority.The most preferred approach towards reducing food waste was through upcycling where consumers are advised to reduce food waste at its source and donate unused food (NEA 2022).
Recent breakthroughs in additive manufacturing (AM) have brought a new perspective on using additive technologies to ensure food security and sustainability.Innovative techniques based on AM like plant bioprinting (Ghosh and Yi 2022) and three-dimensional food printing (3DFP) are being employed.3DFP generates dishes by adding food layer-by-layer, extrusion printing being the most often utilised technique.3DFP allows for the optimisation of nutrition to cater to the specific needs of certain target groups requiring soft diets or specific nutritional demands like athletes, pregnant women, etc.This innovative technology provides for the creation of aesthetically pleasing dishes with precision (Chua 2020).3DFP technologies have been employed to print natively extrudable inks (Voon et al. 2019) such as chocolate, cheese (Karyappa and Hashimoto 2019;Lee, Karyappa, and Hashimoto 2020) and hydrogels, and non-natively extrudable food such as vegetables and meat (Dick et al. 2020).Non-natively extrudable food has been used together with food hydrocolloids (HCs) to print food for groups with specific nutritional needs like dysphagia patients (Pant et al. 2021;Zhang et al. 2022).
Vegetables are a great source of vitamins, minerals, dietary fibre, antioxidants and water (Slavin and Lloyd 2012).Therefore, vegetables are often included in most dishes and diets.However, vegetables are one of the highly wasted commodities (FAO 2011).This is due to strict industry standards and short shelf life of the vegetables which leads to the disposal of vegetable wastes.Keeping this in mind, some of the common vegetable wastes are the stalks of vegetables despite their nutritional value (Storck et al. 2013;Yuan et al. 2015).These vegetable stalks like kale and spinach stems are usually discarded during the industry processes (Mauro, da Silva, and Freitas 2010).At a household level, vegetable stalks are usually disposed due to its tough composition.3DFP can be offered as an alternative to fully utilise the whole vegetable and ensure zero wastage.However, the highly fibrous vegetable stalks tend to affect the printability of the food inks formulated, which can be improved by sieving the mixture and incorporating ingredients to bind the fibres.One research study utilised the incorporation of kale and spinach stalk flours to formulate three different types of cookies (Mauro, da Silva, and Freitas 2010).
3DFP is valuable in providing nutritionally sufficient, safe and visually stimulating food for people who have dysphagia.Dysphagia is a condition in which people experience difficulty in swallowing due to an irregular delay in moving food (Alagiakrishnan, Bhanji, and Kurian 2013).The slow movement of food induces coughing and choking due to the food residue being trapped.This event results in patients suffering from weight loss, dehydration and a lack of nutrition.With 3DFP, pureed food which is recommended for dysphagia patients can be created aesthetically.This can prevent malnutrition and dehydration (Lee, Pant, et al. 2021).Further customisation of the food can be done by adjusting the textural properties of the food (Tokifuji et al. 2013;Yoshioka et al. 2016) or by adjusting the viscoelastic characteristics of the fluids for better adoption (Kouzani et al. 2017;Tan et al. 2018).
This paper examined whether different food processing methods can render the vegetable food wastes, spinach stems and kale stalks printable.The effect that different formulations of vegetable waste have on the rheological properties of food inks was also studied while ensuring that the texture of these food inks met the standards of dysphagic diets set by the International Dysphagia Diet Standardization Initiative (IDDSI 2019).

Origins of formulations of food inks
The formulations of the food inks discussed in this paper originated from the contestants who participated in a local (Singapore) 3D printing competition named SUTD X Armstrong 3D Printing Design & Innovation: Digital Gastronomy.The competition was organised to encourage the use of AM technologies in the food industry.In addition, sustainability was also actively promoted throughout the competition as contestants were tasked to incorporate food waste (specifically spinach stems and kale stalks) in their food ink formulations.These recipes underwent further modifications to create food inks for further analysis.

Formulation of food inks
The materials used to develop the food inks were sourced from the local grocery stores in Singapore.The vegetables (kale and spinach) were stripped of their leafy components to obtain the stems and stalks.These were chilled at 4 °C for a maximum of two days until use.The stems and stalks were rinsed and manually chopped.These were then boiled till tender for ∼15 min (spinach) and ∼45 min (kale).Excess water from the boiled vegetable wastes was squeezed and drained off.A food processor blended the boiled stems and stalks separately for 5 min until a puree-like consistency was acquired.Nine food inks were thus created with the vegetable purees.Five inks were prepared with spinach puree (S1, S2, S3, S4 and S5), and three inks consisted of kale puree (K1, K2 and K3).The remaining ink was made using a mixture of spinach and kale, designated as ink SK.Pure spinach and kale purees were denoted as ink S and ink K, respectively, without any further ingredient addition.The final food inks were sieved using a ≤ 2 mm sieve to prevent the printer nozzle from clogging.
Following is a generalised description of the ingredients used in the ink formulations which was modified from the contestants' recipes.Vegetables (spinach stems, kale stalks, pumpkin, potatoes, sweet potatoes) were either boiled or steamed till tender.
Ink S1: 50 g spinach puree was mixed with 50 g mashed sweet potato, 5 g of lemon zest was added.
Ink K1: 50 g kale puree mixed with 22 g mashed potatoes and 10 g of bread slurry.15 g herbs cream cheese was added along with 3 g of cincalok chili.
Ink S2: 50 g spinach puree was mixed with 20 g potato, 20 g pumpkin, 4 g honey.Spinach was dried using paper towels to prevent excess water in the ink.
Ink K2: 50 g kale puree was mixed with 30 g potato and 10 g stir-fried tom yum paste after removing the chilli from the paste.
Ink S3: Mushrooms and onions were sautéed in oil at a 1:1 ratio till mushrooms were cooked well.Salt, pepper and garlic paste was added.Spinach and the mushroom paste were mixed in a 2:1 ratio, ground and sieved to get the ink.
Ink K3: Kale puree and potatoes were mixed and blended in a 2:1 ratio along with two tablespoons of garlic spread.
Ink S4: Boiled spinach was mixed with mashed potatoes in a 7:3 ratio, Maggi tastemaker was added to this mix.
Ink S5: Boiled spinach was mixed with charcoal pills to darken the paste and agar and gelatin hydrocolloids (HCs) were added at a 5:1 ratio to get a paste like consistency.
Ink SK: Boiled spinach, kale and potatoes were mixed with corn-starch slurry with spices like nutmeg, cloves, ginger, cinnamon and sugar and heated till boiling.The ink was cooled and blended before printing.

3D-printing of the food inks
An extrusion-based 3D food printer, FOODINI (Natural machines, Spain), was employed to print 3D models.A nozzle size of 1.5 mm was utilised to print a hexagonal prism with a height of 9 mm with 6 layers.Following is the table of print parameters selected for the standard hexagonal prism design: Printability of the food inks was assessed based on the ability to maintain the structure for 30 min and the syneresis of the food inks.Printing parameters such as print speed and extrusion rate were optimised and fixed before printing.The design of a hexagonal prism was pre-stored in the FOODINI database.

Syneresis of the food inks
Syneresis was examined using a modified filter paper blotting method for hydrogels' syneresis (Ferrero, Martino, and Zaritzky 1994) described in our previous papers (Zhang et al. 2022).Syneresis experiments were conducted thrice by spreading 1 g of food ink within a circle radius of 1 cm on a grade 4 Whatman filter paper.The food inks and filter papers were left undisturbed under room conditions for 30 min.Images of the filter papers were captured together with a 1 × 1 cm red square, which was used as a reference for image evaluation.The area wetted by liquid was measured and examined using ImageJ software to determine the circumference of the water ring.

Rheological characterisation
An oscillatory rheometer (Discovery Hybrid Rheometer DHR-2, TA Instruments, Delaware, USA) was used to investigate the rheological properties of the food inks.ETC aluminium parallel plates of 25 mm diameter were utilised with a truncation gap of 1000 µm.The instrument was lowered to squeeze out the excess food inks which was scraped carefully to prevent the edge effect.A series of experiments were conducted in triplicates at 25 0.1 °C.The first experiment conducted was the viscosity shear thinning experiment by applying a stepwise shear rate ramp from 0.001 to 1000 s −1 on the vegetable waste inks.In addition, oscillation amplitude sweep experiments were performed to study the viscoelastic properties of the inks.Stresses were applied varying from 0.1 to 1000 Pa with a constant frequency of 1 Hz.

International Dysphagia Diet Standardization Initiative (IDDSI) tests
The IDDSI provides a framework which classifies food and drinks into eight levels and suggests a series of tests to define the level of the texturally modified foods (IDDSI 2019).The fork pressure test was performed where pressure was applied on the printed models until the thumb nail blanches (Pant et al. 2021).The spoon tilt test was conducted to examine the adhesiveness and cohesiveness of the food inks (Atherton et al. 2007)

3D printed shapes
In total there were nine different ink formulations that were tested on 3D printability by printing a hexagon of 9 mm height and six layers.The inks were classified as spinach inks designated as S1, S2, S3, S4 and S5 and kale inks names as K1, K2, K3.Ink SK denoted the recipe had mixed spinach and kale purees.Spinach puree and kale puree were represented by ink S and ink K, respectively.The printed 3D structures were evaluated based on structural integrity and shape fidelity.3D-printed hexagons of various inks that maintained their shape for at least 30 min were deemed printable.All the inks were printed using a 1.5 mm FOODINI nozzle.Spinach and kale inks used to formulate dishes were printed separately.All the inks were printable (Figure 1).Kale inks printed well with uniform and smooth extrusion of inks (Figure 1, top panel) and showed little water spread (Figure 4).Among the spinach inks, inks S1, S3 and S5 printed well, whereas the rest of the inks though printable were not extruding properly (Figure 1, bottom panel).There were some missing sections and gaps among few layers of these inks.Kale inks were able to form stable self-supporting structures without requiring any additional hydrocolloids (HCs) apart from starch source.This may be due to the reasons that the kale stalks had relatively low water content on boiling/steaming as compared to spinach stems and most of the kale ink formulations had potato (boiled or steamed) as a source of starch in them (Section 2.2.).One of the ink formulations (ink SK) also had corn starch in addition to potato which is a known food thickener.Starch has long been used as a thickener which accounts for the good printing outcome in kale inks without HC addition.Thickening of starch granules is due to their swelling up on heating, followed by rupturing near boiling (Saha and Bhattacharya 2010).
Spinach inks were relatively difficult to formulate as compared to kale inks due to the high water content after boiling the spinach stems.Even after sieving the spinach puree was very watery hence ink formulation was challenging despite using potato as a thickener.Only one spinach ink, S5 made use of two gelling HCs, agar and gelatin without any starch source, hence that ink was quite stable to extrude.Food HCs like xanthan gum, kappa carrageenan, agar, gelatin, locust been gum, etc. are used for their thickening or gelling action, known to bind the water molecules well and change the viscoelastic properties (Saha and Bhattacharya 2010).
Rest of the spinach inks had potato or sweet potato (ink S1), the natural starch source as a thickener to help printing apart from ink S3 which used mushrooms and onions instead of potato.Ink S2 had pumpkin added to the spinach puree which turned it waterier (Figure 4) and hence difficulties were encountered to print it.Ink S4 also had less of potato and hence starch mixed in watery spinach puree, and it reflected on its poorly printed shapes (Figure 1, bottom panel.Figure 2).However, all the prints were stable for 30 min and could be extruded into hexagonal shapes.
Figure 2 depicts the dishes printed in the SUTD X Armstrong 3D Printing Design & Innovation: Digital Gastronomy competition held in Singapore in 2022.The competition served the purpose of creating awareness of 3DFP as well as food sustainability.One of the rounds focussed on vegetable waste of spinach stems and kale stalks.Participants were to formulate recipes utilising these two waste sources and then 3D print various designs.Teams came up with unique formulations and designs that were judged on various metrics.3D-printing of food waste serves two purposes, one to reduce food wastage and another to reduce or overcome the consumers' hesitancy towards adopting food waste as legitimate food choice.Mixing with different ingredients may mask the unpalatable flavours of the stems and stalks of the vegetables and presenting them as eye pleasing 3D-printed dishes may stimulate interest for wider adoption.High end restaurants can work with utilising 3DFP as an innovative tool to serve visually appealing meals (Baiano 2020).

Rheological characterisation of food waste inks
Food waste inks were tested for their rheological properties (Figure 3).Studies were conducted on shear thinning and yield stress of the inks.Only one spinach ink, S5 had gelling HCs like agar and gelatin added to the ink while being formulated.HCs like agar and gelatin primarily work as gelling agents rather than thickeners.They form thermo-reversible gels on cooling and are extensively used in the food industry (Milani and Maleki 2012).Agar is commonly used in bakery products and jellies (StanleyNF 2006).Gelatin gels are slow setting, melting at low temperature making them the choice HC for yogurt products and low fat spreads (Saha and Bhattacharya 2010).Shear thinning and yield stress are crucial for extrusion printing as the inks can flow and get extruded owing to decreased viscosity on applying high shear rates (Lee, Hoo, and Hashimoto 2021).Yield stress is indicative of the maintenance of the printed shape parts.It has been clearly demonstrated that for extrusion 3D printing, the viscosity and yield stress of the inks determine the printing behaviour and self-supporting ability of the inks, respectively (Jiang et al. 2019).Shear thinning figures are represented in Figure 3(i) (spinach inks) and Figure 3(ii) (kale stalks).All the food waste inks had the required and necessary shear thinning behaviour.As presented in Figure 3(i), the highest viscosity amongst the spinach inks was observed for ink S5 and the lowest was for ink S3 formulation.Ink S5 owing to the addition of agar powder and gelatin powder in combination with charcoal might have given this ink the highest mechanical strength.Gelatin acts as a gelling agent giving low viscosity solutions forming soft elastic gels on cooling.Agar, a strong gelling HC combined with gelatin imparted ink S5 its high viscosity (Milani and Maleki 2012).Ink S3 with the combination of spinach, mushrooms and onions, might have led to the formulation having more water content as compared to the rest of the inks as all the three vegetables have high amount of water in them.This resulted in the ink having the lowest viscosity which thins out on applying pressure.Spinach stem puree by itself had the second highest viscosity owing to the fibrous nature of the stems.Rest of the ink formulations based on spinach stems had lower viscosities than spinach.However, all the inks were printable (Figure 1).Ink S5 had viscosity ⍰10,000 Pa s which helped with the printability of this ink formulation (Figure 3(i)).With kale inks (K, K1, K2, K3, SK) similar thinning out of inks was observed on applying pressure (Figure 3(ii)).Ink K2 exhibited highest viscosity followed by K3 and SK inks.There was not much difference in the viscosity profiles of the kale inks, and all of them printed well (Figure 1).
Oscillatory amplitude sweep tests were used to determine the yield stress of the inks (Figure 3(iii, iv)).Linear viscoelasticity region (LVR) was observed on the application of a low sinusoidal oscillatory stress with the storage modulus (G ′ , black line) being constant and greater than the loss modulus (G ′′ , green line Figure 3 (v, vi)).This property is essential to form selfsupporting structures (Jiang et al. 2019).Solid like behaviour of the inks is indicated by G ′ , which imparts high mechanical strength to the inks to withstand deformation on pressure (Liu et al. 2019).On reaching respective yield stresses, the inks began to flow, i.e. demonstrating elastic or liquid like behaviour.Here, G ′′ became greater than G ′ (Figure 3(v, vi)).On reaching mean yield stress, the inks break their microstructure and begin to flow, a property needed for extrusion printing.Figure 3(iii, iv) depicts the mean yield stresses of spinach and kale inks, respectively.Even though higher yield stresses may mean better self-supporting ability upon extrusion, very high values may put abnormal pressure on the extruder, which again is not desirable.On observing spinach inks graph, ink S5 had significantly higher yield stress (p ≤ 0.01) as compared to the spinach puree (ink S).This corelated as the formulation had the highest viscosity due to the addition of two HCs.A combination of agar and gelatin render the ink quite viscous, modifying its viscoelastic property and hence higher yield stress.Rest of the spinach inks do not have much significant difference as compared to spinach puree in their yield stresses.Ink S4 had low yield stress hence it extruded easily, but the printed structure was slightly compromised as compared to the rest of inks.Printability of these inks indicated that the values were adequate to uphold the shapes on printing.Yield stresses of inks between 100 and 1000 Pa are reported to have good shape fidelity (Lille et al. 2018).
For kale inks, pure kale puree (ink K) had yield stress significantly higher than the rest of the kale inks (p ≤ 0.05).This could be explained due to the fibrous nature of the kale stalks.Even on boiling, grinding and sieving the puree, to get rid of the fibres for smooth extrusion, enough fibres remained to impart such high mechanical strength to the puree.On combination with potato and other ingredients upon sieving, the viscosities of the kale inks (inks K1, K2, K3 and SK) may be modified to make them printable.Ink SK showed slightly higher yield stress as compared to inks K1, K2 and K3 which can be explained to the addition of corn starch which again thickened to give it strength (Xu et al. 2012).All the inks displayed self-stabilising structures owing to adequate yield stresses.Yield stress needs to be optimised so that it is not too high to affect the extrusion ability of the printer yet enough to attain the needed mechanical stability of the printed structures.Hence kale puree (ink K) had very high yield stress however it may not print well owing to the printer limitation.

Syneresis (water spreading) of food inks
Excess water leaking from foods is referred to as syneresis, which is not desirable (Mizrahi 2010).Syneresis is a problem in the food industry as it leads to non-appealing visuals of foods (Figure 4, ink S2).In the 3DFP context, it is a major problem as excess water in the food inks leads to decreased overall integrity of the printed shapes causing them to be less stable.Inks with high water content have difficulty in printing and they can collapse easily on addition of layers.In the present study, water spread was measured quantitatively by measuring the area wetted by water on a piece of Whatman filter paper as depicted in Figure 4 (Pant et al. 2021;Zhang et al. 2022).
Figure 4 denotes syneresis of spinach and kale inks and the results were analysed and compared within these two subgroups.Spinach inks S2 and S4 had significantly higher water spread as compared to the rest of the spinach inks.This is due to the fact that these inks' formulations had other ingredients with high water content.Both ink S2 (comprising of honey, pumpkin) and S4 (spinach and potato) had higher water content and that led to less optimal prints also (Figures 1 and  2).Rest of the spinach inks had enough starch to hold the excess water of boiled spinach puree or had HCs added to them (ink S5).Kale inks had much less water seepage compared to spinach inks owing to the fibrous nature and low water content of boiled and pureed kale stalks.Among the kale inks, inks K1 and SK showed some water spread, with ink SK having significantly higher syneresis as compared to ink K1.This could be explained by the combination of spinach stems in kale ink which caused excess water content of this ink.

International Dysphagia Diet Standardization Initiative (IDDSI)
Foods are classified into 8 levels (0-7) with levels 0-3 for thickened drinks and levels 4-7 representing pureed, minced and moist, soft-bite-size and easy-to-chew foods.The formulated spinach and kale inks were tested on IDDSI fork pressure and spoon tilt tests as these inks resembled how purees behave with respect to their flow properties.3D printed structures also resemble soft foods ready for chewing, Representative results are shown in Figure 5 (kale inks) and Figure 6 (spinach inks).Fork pressure tests were used to assess if on using thumb pressure (equivalent to tongue pressure in the mouth during swallowing), whether the shapes deformed adequately and did not regain the shape.This is to ensure the safety of the people on soft diets to prevent accidental choking.All the inks deformed enough on the application of fork pressure.With spoon tilt test, adhesiveness (the stickiness of foods) and cohesiveness (the ability to hold together) of the food inks were examined.Even though for kale inks, inks K3 and SK had some shape deformation on fork pressure application, both the inks were quite sticky.Hence may not be appropriate as soft diets for people with swallowing difficulties.For spinach inks, similar observation was made for inks S1 and S5, both disintegrating on fork pressure tests yet were sticky enough to not have the inks slide off well during spoon tilt tests.Rest of the inks from S2-S4 were soft to deform and slid off the spoon.Both these tests, helped to distinguish that some of the food inks are transitional foods (IDDSI 2019).This was due to the nature of these inks as starting as solid 3D-printed shapes yet deforming on pressure application.These foods may melt on contact with water/saliva mimicking mouth conditions, hence labelled as transitional foods   (Dick et al. 2020).Further tests may be conducted on these inks to suitably and classify as dysphagia friendly.

Discussion
Our previous studies have focused on 3DFP of fresh and frozen vegetables and alternative proteins with the use of certain HCs like xanthan gum, locust bean gum and kappa carrageenan (Pant et al. 2021;Zhang et al. 2022).With this study, we have attempted printing of vegetable food waste for food upcycling.Food waste was the theme of one of the rounds of the first 3DFP competition (SUTD X Armstrong 3D Printing Design & Innovation: Digital Gastronomy) held in Singapore, 2022, combining 3DFP and sustainability themes.Spinach stems and kale stocks were chosen as the vegetable wastes that get discarded quite often.Students at local junior colleges and polytechnics were tasked to innovate dishes based on these two wastes that looked good and were tasteful.A total of six dishes were featured (Figure 2).The recipes were modified for better waste utilisation and to lessen the quantity of HCs used in the original recipes.This paper then explored the printability of the modified inks using commercial food printer, FOODINI and their rheological properties along with determining their suitability as dysphagia diets.With our previous studies (Pant et al. 2021) it was determined that the vegetables like peas with higher starch content (Singh et al. 2005) printed nicely.Their structural integrity was better as compared to green leafy vegetables like bok choy.This was due to higher starch content for peas and negligible starch content for leafy greens in addition to higher water content in them.No additional starch source was added to these vegetable food inks.Hence the use of vegetables that incorporate starch as a base to the food matrix was chosen.For the present work, recipes based on food waste had the addition of starch mostly in the form of potatoes and sweet potatoes, which are the common testing ingredients for extrusion printing (Liu, Bhandari, Prakash, & Zhang, 2018;Liu, Zhang, et al. 2018).Also, because the use excess HCs was not very viable to preserve the taste.Only one team recipe was made using HCs (ink S5 had agar and gelatin) and ink SK had corn starch, source of commercial starch (Abotbina et al. 2020) as the binding agent making the inks viscous and thick enough to print.The food industry utilises starch to thicken and stabilise fluid foods owing to its high viscosity and bland flavour (Xu et al. 2012).We were able to print using less amounts of HCs as compared to the contestants' recipes, at times completely eliminating the need of HCs.Though HCs are used to reduce syneresis and act as stabilising, thickening, gelling agents and viscosity modifiers, they may impart some undesirable properties.This was done with the understanding that higher HCs usage may adversely affect the texture and taste of food inks (Lee, Takahashi, Arai, Lee, & Hashimoto, 2021).Studies have indicated aroma and taste perception may get reduced with higher concentration of HCs (Awwad 2019).Firmer gels require more time for establishing taste and have lower taste perception as compared to softer gels (Guinard and Marty 1995).All the printable inks (9) were shear thinning and had adequate mechanical strength to be able to hold their shapes.Syneresis was observed more for spinach inks due to higher water content after boiling as compared to kale inks.The addition of starch and HCs inhibited the water spread.Ink S5 with agar and gelatin mixture had low syneresis level even though agar gels have pronounced syneresis, it was countered by gelatin addition known for preventing syneresis (Milani and Maleki 2012).Hence, the choice of HCs also become important in formulating inks.Food inks which had less incorporated starch (inks S2, S4) had marked syneresis.While being subjected to IDDSI fork and spoon tests, few of the inks qualified as soft diets presumably suitable for dysphagia patients.
3DFP is an innovative technology that can produce end products from unconventional and mostly discarded food sources like peels, stems, stalks, seeds, etc. to take the form and shape based on 3D models.Orange peel waste known for a variety of nutrients and vitamins is produced in copious amounts by the food industry.One paper looked at 3D-printing of orange peels with the aim of food upcycling into snacks (Leo et al. 2022).Another research article examined okara (a waste byproduct of soybean generated during soymilk and bean curd production) 3D-printing behaviour with respect to its particle size (Lee, Takahashi, et al. 2021).With this tool, aesthetically pleasing and appetising forms of these unwanted food produce can be created with simple cooking techniques.This can lead to greater consumer awareness and acceptance of the previous underutilised resources, thereby promoting sustainable choices.Product familiarity for the consumers can be attempted by designing models for common place snacks and desserts like chips, wafers, cookies, etc. and then use food waste from different sources for recipe formulation.

Figure 1 .
Figure 1.3D-Prints.Representative images of 3D-printed hexagons of vegetable food waste inks, top panel depicts kale inks and bottom panel depicts spinach inks.

Figure 6 .
Figure 6.IDDSI (International Dysphagia Diet Standardization Initiative 2019) tests: spinach inks.Fork pressure test on soft and bite sized 3D printed samples, Spoon tilt tests.