In recent years, the use of sprouted flours has significantly increased, and the promotion of these flours is seen on the packaging of products such as bread, cookies, and others. It’s a trend that originated in the United States and, like many others, is gaining momentum in Europe and other parts of the world. Generally, this trend is based on the nutritional benefits of sprouted grains, but it’s necessary to consider some aspects to effectively incorporate the use of sprouted flours.

Introduction

Germination is the process by which a grain gives rise to a new plant. This process is triggered in the germ when the grain has germination capacity and is moistened at the appropriate temperature. The germ contains the embryonic axis that will give rise to the new plant, along with the scutellum. The scutellum contains the first substances that will nourish the plant when this phenomenon occurs. If we compare this process with the development of a baby, we can say that the substances in the scutellum would be equivalent to breast milk. Therefore, the scutellum contains highly digestible nutrients necessary for development in these early stages. Thus, the scutellum is rich in simple sugars, lipids, amino acids and polypeptides, minerals, and vitamins, mainly from groups B and E.

For the plant to continue to develop, and before having roots, the embryonic axis must be nourished from the rest of the grain (mainly from the endosperm). But the substances found in the endosperm, unlike those in the scutellum, are not easily digestible and have a much higher molecular weight. To facilitate digestion, a large number of enzymes are generated in the grain, whose mission is to hydrolyze these components and create pathways for nutrients to reach the new plant. Among these enzymes, amylases and proteases stand out, but there are also beta-glucanases, phytases, and others.

If the process continues, the new plant will be nourished from the grain, causing it to decrease in size while the acrospire (length of the new plant) increases. In general, to produce flours from germinated grains, the process is stopped at this point. Thus, the enzymes have been generated and have begun to act, but the starch and protein content has not been significantly reduced.

After this process, the sprouted grains are moist. They must be dried before milling. The drying process will significantly influence the properties of these flours. More severe heat treatments will reduce microbial load but also inactivate enzymes, darken the flours, and impart aromas and flavours.

The milling process will also influence the properties of the flours. In general, sprouted flours are whole grain flours, as this enhances their nutritional benefits. However, grains can also undergo a process where the outer parts of the grain are removed, either in stone mill systems or roller mills. In this case, the organoleptic quality of the flours can be improved, but their nutritional quality is significantly reduced.

Nutritional Changes in Sprouted Flours

Firstly, it should be noted that most sprouted flours are marketed as whole grain flours, hence they contain higher levels of fibre, minerals, vitamins, and bioactive components compared to any white flour, in addition to a greater antioxidant capacity. Secondly, as the germination process progresses, a series of changes occur in the grain components that can be beneficial to health.

During germination, amylase enzymes (α-amylases and amyloglucosidase) are generated, and others already present in the grain (β-amylases) are activated. As a result of the action of these enzymes, the sugar content increases, such as glucose and maltose, and dextrins, while the starch content decreases. As a consequence of the germination processes, the starch in the grain becomes more digestible, and the glycaemic index increases, although some studies have found contradictory results. This increased digestibility makes these grains very suitable for the production of infant foods and for the elderly.

In the germination process, proteases are also generated, which hydrolyse the proteins present in the grain. As a result of this process, the molecular weight of the proteins is reduced, and polypeptides and free amino acids are generated. The content of essential amino acids also significantly increases, as well as the solubility and digestibility of the proteins.

The enzymes capable of hydrolysing fibres, which are generated in the germination process, allow an increase in soluble fibre at the expense of a decrease in insoluble fibre. In addition, in this process, hydrolysis of arabinoxylans and β-glucans occurs. The consumption of these fibres, present in oats and barley (β-glucans) and in wheat and rye (arabinoxylans) in appreciable quantities, has been associated with a reduction in cholesterol, a reduction in the glycaemic index, and a lower incidence of cardiovascular diseases. However, the effectiveness of these fibres is greater the higher their molecular weight. Therefore, the hydrolysis of these fibres may reduce their effectiveness against these ailments. However, in the case of arabinoxylans, enzymatic hydrolysis increases the content of arabinoxylans of lower molecular weight, with a greater prebiotic effect.

Most of the phosphorus present in cereals is in the form of phytic acid. Phytic acid binds to certain cations, such as iron, manganese, magnesium, calcium, or zinc, forming phytates, and reducing their bioavailability. Therefore, these cannot be utilised by humans. During germination, phytases are generated, enzymes capable of hydrolysing phytates and increasing the bioavailability of mineral substances. These phytases can also act during fermentation, improving the availability of minerals in the flours used in the baking process.

The vitamin content also increases in the germination process due to biosynthesis processes. Among the vitamins that increase their content are vitamin E, folates, and B-group vitamins. However, for this increase to occur, germination must be prolonged. It should also be noted that vitamins can be lost in the soaking process, so it is advisable to use minimal water to reduce losses, and in the drying process, which can reduce the content of heat-labile vitamins if done intensely. It is also important to know that some of the vitamins move to the acrospire, so if this is removed before milling, the vitamin content will be reduced.

A significant increase in the content of polyphenols and antioxidant capacity has also been observed in the flours of sprouted grains compared to non-germinated ones.

Changes in Flour Properties

In the event that germination is prolonged, both the starch and proteins in the flour will be considerably hydrolyzed. In this case, the flours will turn out sweet due to the higher concentration of sugars (maltose and glucose). These sugars will be available for yeast action (fermentation) or to react during baking (Maillard reactions or sugar caramelization). Additionally, starch hydrolysis will affect the thickening capacity of the flours, which will decrease as the germination process progresses. Protein hydrolysis is particularly concerning in the case of wheat flours, as the proteins present in these flours form the gluten network, essential for the production of products such as bread. The breakdown of these proteins impairs the action of the gluten network by weakening it, complicating the production of these types of products. In the case of products where the gluten network is not important, or in other cereals, protein hydrolysis will result in a lower water absorption capacity of the flours, but the consequences will not be severe for flour functionality.

It should be noted that if the drying of the sprouted grains is not too intense and does not inactivate the enzymes present in the grain, these enzymes can act on all the components of the dough into which the sprouted flours are incorporated. In cases of higher enzymatic activity, the effects of proteases can be quite negative, as they break the gluten network, whenever the development of this network is desirable.

Strategies for Using Sprouted Flours

There are three main reasons for using sprouted flours:

1. Responding to consumer demand as a trend. In this case, some producers want to incorporate the claim of the presence of sprouted flours, but without much noticeable difference in their process and final product. For this, small amounts of sprouted flours with low levels of germination are usually added. In these cases, the germination process is shorter (cheaper) and can be carried out at higher temperatures (20-30ºC) that accelerate the process. However, due to the low amounts of sprouted flour, low levels of germination, and minimal enzymatic action on grain components, the nutritional improvements in these products will be very limited.
2. Using sprouted flours to achieve a real impact on the healthy properties of products. In this case, it is advisable to increase the content of sprouted flours in the final formulation and the degree of germination of the flours. However, this can significantly change the characteristics of the dough, so it will be necessary to adapt the formulations and processes. It may be necessary to use stronger flours, or a lower amount of water, or the use of improvers to strengthen the dough. In products where the gluten network is not formed, such as some cookies, this may not be a problem.
3. Using sprouted flours to replace additives. In this case, the incorporation of sprouted flours with enzymatic activity eliminates the need to incorporate amylases for the production of sugars necessary for fermentation and improves the final colour of bread. In these cases, small amounts, less than 5%, are incorporated, and in some cases, white flours are used, although not necessary, unlike cases where nutritional advantages are prioritised, where wholemeal flours are preferred.

Issues in Germinated Production

One of the main problems in germinated production is the high humidity necessary for this process. This humidity, besides favouring germination, also favours the development of microorganisms and therefore the presence of mycotoxins in the final product. Therefore, it is necessary to control the hydration conditions of the grains, as well as the temperatures during germination. Although with rapid germination, of barely 24 hours, which ends just as the acrospire begins to emerge, the development of microorganisms is not usually so critical, neither are high nutritional benefits nor high enzymatic activation obtained. On the contrary, if we want to obtain flours with clear nutritional benefits or a high enzymatic content, longer germination periods are necessary. In these cases, to prevent microbial development, germination must be carried out at low temperatures and with regular aeration of the grain as a whole.

For further information:

Benincasa et al (2019) Sprouted Grains: A Comprehensive Review. Nutrients, 11, 421.

Feng et al (2019) Sprouted Grains Nutritional Value, Production, and Applications. AACC. St Paul, MN (USA)

Hubner y Arendt (2013) Germination of Cereal Grains as a Way to Improve the Nutritional Value: A Review. Critical Reviews in Food Science and Nutrition, 53:8, 853-861.

Lemmens et al (2018) Impact of Cereal Seed Sprouting on Its Nutritional and Technological Properties: A Critical Review. Comprehensive Reviews in Food Science and Food Safety

Singh et al (2015) Enhancement of Attributes of Cereals by Germination and Fermentation: A Review. Critical Reviews in Food Science and Nutrition, 55:11, 1575-1589.