The effect of hydrocolloids on GFB quality has been the subject of numerous investigations. Significant hydrocolloids used in food processing, including agarose, xanthan gum, carboxymethylcellulose (CMC), hydroxypropyl methylcellulose (HPMC), locust bean gum, guar gum, β-glucan, pectin, and carrageenan, have been taken into consideration for this purpose [91, 92].

Hydrocolloids are a crucial ingredient in GF baking, enhancing the cohesive and viscoelastic behavior of the batter by forming gels. They stabilize gas cells, act as water binders, and delay retrogradation. The effect on batter properties depends on the amount and type of hydrocolloid used, their interaction with other food components, and process parameters like temperature, shearing, and pH. The addition of hydrocolloids significantly influences pasting properties, gelatinization, swelling, and staling of starch in GFB [93].

Research has indicated that HPMC is the most effective and is the recommended ingredient in commercial GF products. According to Foschia et al. [87], hydrocolloids were discovered in 27 bread samples from well-known GF firms, with psyllium being the most common at 74.1%. The most popular items were also discovered to be millet and rice bran extract.

The most popular hydrocolloid, HPMC, was also found to be included in 64% of bread compositions [77], followed by xanthan gum (53%), guar gum (37%), and psyllium (34%). A mixture of hydrocolloids was employed in over 80% of GFBs, improving the bread’s characteristics. For the purpose of enhancing crumb texture, HPMC is frequently mixed with other hydrocolloids. Because of its thermo-reversible gel qualities, breads baked exclusively with HPMC have a drier, crumblier texture.

Fiber falls under the water-binding and film-forming ingredients category. Alternatives to hydrocolloids have been investigated as potential food additives, including arabinoxylans (AXs) and oat ß-glucan. Aside from their potential health benefits, especially the prebiotic effect, their application can influence the texture and viscosity of food [94]. This is crucial because a lot of GF goods are processed flour-based and low in nutritional fiber. To achieve correct crumb structure development and thorough gelatinization of starch during baking, fiber addition to GFB should be accompanied by enough water. Because of their gelling, water-holding, and structure-building qualities, fibers increase the viscosity of the batter, improve gas retention, and boost bread volume.

Starches also act as water-binding and film-forming ingredients. Due to their affordability, hypoallergenic qualities, and white hue, GF flours and starches such as rice and maize are frequently utilized in the industry. However, because of how poorly these starches interact with functional proteins, they have certain technical constraints [95]. Rice flour is combined with starches such as GF wheat starch, corn starch, tapioca starch, potato starch, cassava starch, and sorghum starch to get better results.

The morphology, viscosity, and gelatinization behavior of these starches vary greatly, which affects the specific volume, hardness, elasticity, and chewiness of bread crumbs [96–98]. The viscosity parameters, color, homogeneous air cells, delayed starch retrogradation, and overall sensory acceptance are all improved by adding 20–30% potato starch. According to Onyango et al. [99], dough air bubbles are maintained with the aid of cassava starch, which develops better crumb characteristics.

Unlike starches and fibers, whey protein is a structure-forming, volume-filling, taste-giving ingredient. As a functional ingredient, it is added to bread in order to improve its absorption of water and to supply nutrients. It possesses some of the strain-hardening and elastic qualities of gluten when combined with starch, but the increased internal crosslinking that occurs during kneading makes the particles more stable. The quality of the particle network is affected by the capacity to form disulfide bonds, which may lead to stiff dough and subpar bread qualities. According to Storck et al. [100], 6% whey protein powder increases the amount of protein in GFB without affecting the amount of dietary fiber. Additionally, the properties of GFB tissue, like volume, size, and kneading capacity, are enhanced by whey protein.

Pseudocereals have the potential to operate within all the categories; their starches are water-binding and film-forming, and their proteins are structure-forming and volume-filling.

Pseudocereals such as buckwheat, amaranth, quinoa, and teff have been the subject of extensive research, revealing their high fiber, mineral, and vitamin content [101–103]. A study conducted by Kim et al. [104] showed some health benefits of amaranth in diabetic rats, which helped to reduce hyperglycemia by lowering glucose levels and raising insulin levels. Buckwheat protein concentrates and amaranth can also improve cholesterol and triglyceride levels. With a softer crumb and a larger loaf capacity, pseudocereals can add to the nutritional content of food.

Experiments based on rice flour showed good rheology with as much as 40–50% buckwheat fiber. Lemos et al. [41] suggest that a 10% addition of amaranth flour is recommended, while the addition of 10% of quinoa flour can enhance the rheology and appearance by 7.4% without sacrificing flavor. In general, there are several health advantages that are linked to the exploitation of pseudocereals [105].

Although quinoa, amaranth, buckwheat, and teff are good grains for GFB because of their nutritional and technological advantages, their usage is limited because of how much they affect taste, color, aroma, and cost. When these grains are used in large amounts in bread recipes, the sensory qualities such as a thick crust, black crumb, powerful flavor, and taste, are affected. According to studies, adding 10–30% unhusked buckwheat reduces flavor and acceptability of taste, but husked buckwheat delivers higher acceptability, volume, and superior texture. Proteins in buckwheat can lead to allergic reactions and have been linked to 3–3.5% of cases of anaphylaxis in Japan and South Korea [106].

Protein additives from milk, soy, lupine, egg, and pea protein are frequently used in GFB formulations to enhance the dough’s characteristics. These supplements have higher water absorption, viscoelastic qualities, anti-staling, and structure-forming actions. Protein from eggs makes the crumb more elastic and aids in the formation of a finer cell texture [32]. Preparations made from peas and lupines provide more palatable color and scent, improving sensory characteristics, while consumer assessments decline when soy protein is used. Also, adding protein to bread raises the enthalpy of retrograded amylopectin and hardens it during storage [107, 108]. Proteins have a significant impact on the color and textural characteristics of bread crumb and loaf. Even at low dosages, dairy proteins can improve the color and Maillard’s response. Soy protein-containing GFB samples have noticeably darker crust and crumb [52].

It is important to remember that proteins from milk, eggs, soy, and lupines are allergenic, even with their technological advantages. This makes handling allergens during food manufacturing more difficult for those with CD who also have combined allergies to lupine, milk, eggs, or soy products.

For non-thermal preservation, HHP is a contemporary processing technique. The product’s rheology may be impacted by changes to the functional characteristics of proteins and starch. HHP causes a change in viscoelastic behavior in starch by altering its microstructure without sacrificing granule integrity. Depending on the type of starch, the constituents of the food, and the water content of the sample, full gelatinization happens above a critical pressure. Quaternary and tertiary structures in proteins are altered by HHP, which makes SH groups more reactive. With a few exceptions, most research has been conducted on doughs containing gluten. Using buckwheat, white rice, and teff as ingredients, Vallons et al. [109] discovered that starch gelatinization and protein crosslinking enhanced the viscoelastic qualities of the GFB batters. High pressure was also found to enhance the elasticity, volume, and texture of the batter in oat bread [110].

In order to enhance the qualities of bread, the baking business is progressively utilizing non-traditional heating methods, including microwave, infrared (IR), jet-impingement, or hybrid heating. These methods can affect the development of flavor, color, and crumb and crust formation [111]. While IR baking and microwave baking are time and money-efficient methods, IR has a low penetration power but can enhance sensory experience. A unique kind of forced convection heating called “jet-impinging” causes hot air to impinge on the bread’s surface, increasing heat transfer but also resulting in a thick crust and higher energy consumption. These methods have not yet, however, been thoroughly examined or taken into account for making GFB. In general, the application of these methods in the baking industry holds potential for enhancing the texture and quality of bread.

It has been discovered that hybrid heating, an unconventional baking technique, works best for lowering processing expenses, boosting energy effectiveness, and improving bread quality [111]. Nevertheless, less has been discovered about how these approaches work in conjunction, and their full potential has not yet been realized. The only hybrid technique employed in GF baking is IR-microwave baking (see Table 3). Studies have shown that during baking, the use of GFB results in rapid heat generation and a lack of crust, higher crumb texture, moisture loss, reduced starch granule breakdown, poor gelatinization or digestibility, and increased flavour loss. The necessary bread quality may be achieved by combining microwave baking technology with additional rapid surface heating techniques, such as IR radiation.

The necessity for alternative methods to manufacture high-quality, additive-free GFBs and customer demand for clean labels have brought sourdough, an age-old method, to the attention of “novel” technology. Studies have indicated that sourdough is both economical and ecologically benign, and it can solve most of the issues associated with the manufacturing of poor-quality GFB [56, 117]. During fermentation, the presence of lactic acid bacteria (LAB) by-products, such as lactic acid, exopolysaccharides (EPS), and volatile and antibacterial chemicals, can be advantageous. The primary source of the dough’s acidification is the lactic and acetic acid produced by LAB, which changes the dough’s structure-building ingredients and increases the solubility of proteins, giving the dough a softer crumb texture. Bread’s texture and aroma are greatly influenced by the lactic to acetic acid ratio. Additionally, by inhibiting starch retrogradation, organic acids prolong the shelf life of bread by preventing staling. However, proteases and amylases are examples of natural enzymes that may be activated by acidification, compromising the bread crumb. Preservation can be aided by additional metabolites.

Research has shown that choosing the right starter cultures is crucial when making GF sourdough since different microorganisms react differently to the same starting material. The availability of carbohydrates, nitrogen sources, lipids, free fatty acid concentration, enzymatic activity, buffer capacity, and growth factors in the substrate can all have an impact on microbial development [118, 119]. The final composition of the sourdough can also be affected by process variables such as temperature, dough yield, fermentation period, and number of refreshment steps. The microorganisms Lactobacillus fermentum, Lactobacillus plantarum, and Lactobacillus paralimentarius are typically isolated from GF sourdoughs prepared from rice, amaranth, teff, and maize. When it comes to GF sourdoughs manufactured from rice, quinoa, teff, buckwheat, and amaranth, Lactobacillus plantarum has been the most frequently reported strain [120]. This strain yields cyclic dipeptides and antifungal organic acids that slow down the rate of spoilage and enhance the crumb texture and staling rate of GFB produced with a composite flour. Similar to pure wheat flour, sourdough can improve the textural qualities of GF recipes [121]. Depending on how much sourdough is used and which LAB strain is utilized for fermentation, it also affects the viscoelastic qualities of amaranth batters. Macheke [122] found that sorghum sourdough fermented with Lactobacillus plantarum, Lactobacillus casei, Lactobacillus fermentum, or Lactobacillus reuteri can increase its nutritional content by causing the breakdown of polyphenols. Some LAB strains produce EPS that enhance bread’s texture, rheology, and shelf life. Due to their potential health advantages in bread, their water-binding capacity has generated attention. EPS that are frequently encountered include fructan, glucan, and dextran.

One of the novel and recent heating techniques being researched for baking is called OH. In OH, a material’s electrical resistance causes heat to be produced when an alternating electrical current is sent across it. Unlike traditional heat transfer techniques, this technology provides a quick and even spread of heat [123]. Applications of OH in food processing are growing at the moment, although they are still minimal in baking. Very few studies have concentrated on GFBs (see Table 4); the majority have characterized wheat bread. OH has few applications in baking, despite its potential, basically due to the high cost of operations [123].

Utilizing OH in hybrid heating to produce bread has not been the subject of any research to this day. As was previously indicated, IR, jet impingement, and microwave baking have already been used in hybrid heating. Similar to OH, heating occurs volumetrically during microwave-assisted baking; however, baking in the microwave causes significant quality flaws in breads that have not been observed in OH. Thus, combining OH with other surface heating methods could prove to be a viable strategy in the future for producing high-quality GFBs.

Natural substitutes like AXs, hemicelluloses present in cereal cell walls, are becoming more and more popular as a result of consumer desire for clean-label products. As baking resources, AXs have drawn attention for enhancing bread qualities like crumb texture, loaf volume, and staling. The majority of research has been done on breads that contain gluten, but not many of them have examined how to utilize such functionality in GF formulations. Bender et al. [129] proposed a novel approach by introducing AXs to artificially induce the formation of a hemicellulose network in GF batters. AXs have functional capabilities that enable them to crosslink, developing a stable hemicellulose network under oxidizing conditions, which is crucial for stabilizing and defining the bread structure. Naturally, during the leavening process of dough, rye-specific enzymes oxidize ferulic acid (FA), creating covalent di or tri FA connections between AXs molecules. By purifying several extracted rye AXs, combining them with oxidative enzymes in the batter, and adding sourdough to the recipe to establish the ideal circumstances for AX crosslinking, Bender et al. [129] separated AXs for use in GF formulations. According to these authors, bread qualities were often enhanced by water-extracted AXs more so than by alkaline-extracted AXs. It was demonstrated that other elements used in bread-making, such as the source of flour, significantly influenced the stability of the AX-AX interactions in the batter, in addition to the structural and chemical characteristics of the AXs.

Additionally, in related studies, it was found that adding excessive AXs significantly increased the GF batter’s stiffness and consistency and had negative impacts. Ayala-Soto et al. [130] highlighted that an overabundance of AX addition results in weakened gas cell wall integrity, decreased bread volume, and a dough that is generally more collapsed. The characteristics of flour and the molecular weight of AXs dictate the ideal addition.

About one-third of all enzymes are employed in baking, making them necessary for food products. In order to stabilize the batter and enhance handling and rheological qualities, crosslinking enzymes are frequently used in GFB because they act as conditioners. A gluten-like protein network is formed by transglutaminases through the catalysis of an acyl transfer reaction between the side chains of glutamine and lysine residues. Bread volume, elasticity, consistency, and crumb softness are just a few of the qualities that can be improved with an ideal protein network [124]. The enhanced ability to gas-hole during batter proofing can be attributed to the protein network that has been constructed.

To enhance rheological characteristics, handling, and bread quality, oxidases such as laccase and glucose oxidase are frequently added to GFB. Dimerizing the FA molecules bonded to the polymer, laccase catalyzes the oxidative gelation of AXs in bread dough. On GFB, though, its impact is not quite evident. According to Ayala-Soto et al. [130], adding laccase with maize fiber AXs improves the volume and crumb structure of GF oat bread but does not influence the GF batter or bread quality. It is still required to determine exactly how well this enzyme works in GF baking. Glucose oxidase increases the density and volume of the crumb by encouraging the creation of disulfide and AX cross-links between proteins. According to studies by Renzetti et al. [131, 132], the creation of protein crosslinks is primarily responsible for the dough’s increased viscoelastic qualities. GFB produced with sorghum and corn showed additional benefits; buckwheat, teff, or oat flour did not significantly improve the recipe.

Pyranose 2-oxidase (POx) has been proven to be more advantageous than glucose oxidase because of its greater specificity for glucose. The rheological qualities of GF batters are greatly improved when POx is added alone [133, 134]. AX type, concentration, and flour characteristics all affect how AXs and POx behave in the batter. For GF baking, less frequently utilized enzymes that hydrolyze starch, slow down retrogradation, and extend shelf life are α-amylase and cyclodextrin glycosyltransferase.

Proteases are frequently employed in baking; in wheat bread, they are primarily utilized to mildly hydrolyze gluten and enhance dough extensibility and machinability. Additionally, they have the ability to partially break down large protein complexes, which improves starch swelling and raises the batter’s viscosity.