Study reviews the latest approaches towards improved gluten-free bread properties

Gluten is the three-dimensional protein-starch network that gives bread dough its unique viscoelasticity and baking quality. Without it, dough lacks cohesiveness and elasticity, resembling a liquid cake batter.

Due to the increased prevalence for coeliac disease (CD) and gluten-sensitivity – a 2014 study published in the Journal of Pediatric and Gastroenterology and Nutrition found the incidence of CD has increased fivefold in the last 25 years – there is high demand for premium GF products.

Extensive research has been published on new and innovative methods and technologies for gluten-free baking, specifically focusing on a wide range of ingredients and functional additives – such as pseudocereals, proteins, emulsifiers and other hydrocolloids – to replace the gluten network, aid processing and enhance nutritional quality.

However, it has been seen that technological approaches provide better solutions for enhancing GF bread properties, especially when non-conventional baking alternatives are applied.

The study published in the Journal of Cereal Science summarises a comprehensive evaluation the latest advances in gluten-free baking that would be beneficial for further research, as well as for commercial application.

Novel ingredients to replace the gluten network

These can be classified into three major groups:

Water-binding and film-forming ingredients: Hydrocolloids or thickening agents (locust bean gum, guar gum, pentosans, xanthan, pre-gelatinized native or modified starches and cellulose derivates).
Structure-forming, volume-filling, taste-giving ingredients: Proteins (plant and animal), fats and carbohydrates.
Surface-active substances (emulsifiers): a hydrocolloid-emulsifier-protein system (egg, soybean or milk protein) and enzymes (amylase, cyclodextrin glycosyltransferases, transglutaminase, glucose oxidase, laccase and proteases).

Hydrocolloids

Hydrocolloids have emerged as one of the most crucial ingredients in GF baking, improving the batter expansion by stabilising gas cells and acting as water binders. Pasting properties, gelatinisation, swelling and staling of starch are also significantly influenced.

According to the Austrian scientists, among all hydrocolloids, the application of hydroxypropyl methylcellulose (HPMC) has been found to be most successful for GF breads and therefore favoured by commercial GF bread producers. Breads made solely with HPMC are characterised by a drier, crumblier texture, however, this can be improved with the combination of other hydrocolloids, such as locus bean gum, guar gum or fibres.

Arabinoxylan network

Due to increasing consumer demand for clean label products, a higher focus has been given to replace chemical additives with more natural alternatives. Arabinoxylans (AXs) – a type of cellulose obtained from the outer shell of many cereals – meets that demand, while still fulfilling their purpose as baking aids to improve crumb texture, loaf volume and staling properties in GF breads.

Enzyme technology

Enzymes are widely used in food products, from which approximately one-third is applied in the baking industry. In GF bread-making, enzymes serve as conditioners to improve handling and rheological batter properties, as well as bread quality. Depending on the enzyme’s characteristics, it can stabilise the batter, increase crumb softness, bread volume, crust browning and maintain freshness.

However, their effect is affected by the other dough components, such as the source of flour, presence and type of AX, protein as well as additives that modify the availability of water in the batter (hydrocolloids). Even the batter pH or temperature can significantly affect their activity.

Furthermore, noted the study, the right enzyme concentration must be carefully chosen, since overdosing could decrease bread quality.

Innovative technological approaches

Recently, several technological approaches have been successfully applied to improve bread property, batter consistency and stability. Ohmic heating resulted the most promising approach to overcome bread quality issues, while remaining time and energy-efficient, but sourdough fermentation has peaked interest as it offers textural, sensorial and nutritional advantages.

Sourdough technology

Sourdough – an ancient technique that has been used for centuries – is experiencing a revival, thanks to the demand for clean label and finding alternative technologies that allow high quality of breads without the need of additives.

Recent studies found that sourdough can address most of the problems related to low-quality GF breads, while being cost-effective and environmentally friendly.

While yeasts actively produce CO₂ during sourdough fermentation, the main acidification of the dough is attributed to the lactic and acetic acid generated by LAB.

The positive effects are associated with the presence of LAB byproducts, such as volatile and antimicrobial compounds, lactic acid and exopolysaccharides (EPS) that are produced during fermentation. While yeasts actively produce CO₂during fermentation, the main acidification of the dough is attributed to the lactic and acetic acid generated by LAB. These byproducts modify the dough properties by affecting the main structure-building components and increasing protein solubility, leading to a softer crumb texture.

Lactobacillus plantarum has been the most reported strain in sourdoughs made from rice, quinoa, teff, buckwheat and amaranth, while Lactobacillus fermentum, L. plantarum and L. paralimentarius have also been isolated in sourdoughs made from amaranth, teff, rice and maize. The former produces antifungal organic acids and cyclic dipeptides that improves the crumb firmness and staling rate of GF bread made with a composite flour.

Non-conventional baking technologies

The scientists also reviewed high hydrostatic pressure (HHP) – which exhibits potential for structure formation – as well as a number of non-conventional baking technologies that, although increasingly pursued by the baking industry, have scarcely been considered for GF baking. These include microwave, infrared, jet-impingement or a combination of them, all of which can influence and define properties such as crumb and crust formation, colour and flavour development.

Ohmic heating (OH) is an emerging technology for food processing in which an alternating electrical current is passed through a material, which generates heat by dissipation of the electrical energy as a result of the material’s own electrical resistance. While the application of OH is currently still low in the baking sector, Japan has implemented it on an industrial scale for more than half of the production of panko breadcrumbs.

A recent study looked into using this approach to improve GF bread. GF batters typically have a poor gas-holding ability, the rapid heating of OH stabilises the crumb structure at an early stage of baking, before CO₂ is released during heating. This resulted in a much higher loaf volume and a finer pore structure compared to conventionally baked breads. The researchers also found starch digestibility of the breads was slightly reduced, as more resistant starch was found after the baking process.

They concluded the potential of combining OH with other surface heating technologies might be a promising future approach for the development of high quality GF breads.