Creating new potential for an old grain – milling hulless barley for fibre-rich fractions and baking healthy bread with barley
Revived interest in barley for food uses
Barley has a long history of food use and in the ancient world was grown mostly to provide food staples for human nutrition. In modern times, consumption of barley-based foods decreased, except for barley used in the production of alcoholic beverages, especially beer. Recently, however, interest in barley as a food grain is reviving due to heightened consumer awareness of good nutrition and increased interest in foods and food ingredients enriched in dietary fibre (DF) (Izydorczyk and Dexter, 2008). Barley grain is an excellent source of soluble and insoluble DF and other bioactive constituents, such as vitamin E (including tocotrienols), B-complex vitamins, minerals, and phenolic compounds. Beta-glucans (β-glucans), the major fibre constituents of barley, have been implicated in lowering plasma cholesterol, improving lipid metabolism, and reducing glycaemic index. The United States Food and Drug Administration (FDA) has recently allowed whole grain barley and barley-containing products to carry a claim that they reduce the risk of coronary heart disease (FDA News Release, 2005). The nutritional values of other fibre components in barley, most notably arabinoxylans, have not been investigated to the same extent as those of β-glucans. However, recent studies revealed positive effects of water soluble maize, wheat and rye arabinoxylans on cecal fermentation, production of short-chain fatty acids, reduction of serum cholesterol and improved adsorption of calcium and magnesium.
In the past decade, many new Canadian barley genotypes including hulless genotypes with waxy starch such as CDC Alamo, CDC Fibar, and CDC Rattan (Canadian Food Inspection Agency) as well as hulless high amylose lines were bred specifically for food uses rather than for malting and brewing and contained higher amounts of β-glucans than traditional malting barley varieties.
High fibre fraction from hulless barley
The distribution of nutrients and functional constituents in the barley kernel is not uniform; therefore, fractionation of barley by physical means allows obtaining products enriched in different constituents. Barley can be roller milled (using wheat milling equipment) into barley flour and a coarse fraction which would be designated as ‘shorts’ (fine bran from reduction system) in wheat milling. Barley flour is rich in starch, whereas the coarse fraction which originates mainly from the endosperm cell walls contains large amounts of β-glucans, other bioactives and dietary fibre constituents. This fraction is, therefore, more accurately designated as a fibre-rich fraction (FRF) in barley milling. The FRF is potentially of more value as a functional food ingredient than barley flour, and the primary goal of barley roller milling for food purposes would more logically be to maximize the yield of fibre-rich products.
Simplified roller milling process to obtain high fibre fraction
The high fibre fraction can be obtained from whole barley grain according to the relatively simple roller milling flow (Figure 1), developed and optimized recently by collaborative efforts of the Basic Barley Research and Milling sections at the Grain Research Laboratory (Izydorczyk et la., 2003). The flow is comprised of break passages through four sets of corrugated rolls with increasing number of corrugations. Following fourth break (B4), the ground product is sieved through two sieves with different apertures; the material that passes through both sieves is the ‘break flour’, whereas the coarse (>600μ) and intermediate (180μ) particles that are retained on the sieves are directed to a shorts duster (SD) and processed separately.
In the shorts duster (also known as bran finisher in wheat milling), the rotating beaters agitate the material in a spiral motion, propelling it against a perforated screen and toward the outlet. Floury material is encouraged to fall through the screen while bigger fibre particles overtail to a secondary outlet. The SD effectively cleans the fibre by releasing starch granules from the fibre particles.
The shorts duster passages generate the ‘SD flour’ and fibre particles (>183μ) that are collected and further refined. The last stages of fibre refinement include a single passage through sizing rolls, sieving, and another shorts duster passage. The ‘shorts’ collected in the final step are designated as barley ‘fiber-rich fraction’.
Power consumption during grinding and yield of barley ‘fiber-rich fraction’ are positively related to β-glucan content in the whole grain. The yield of the fibre fraction obtained by milling hulless waxy barley cultivar, CDC Fibar, was 38%. The fiber-rich fraction is comprised primarily of fragments of the endosperm cell walls and the outer bran particles, so is highly enriched in dietary fibre and β-glucan specifically. As shown in Table 1, the FRF obtained from CDC Fibar contained significantly higher contents of β-glucans, total and soluble dietary fibre, proteins, ash, and vitamins B and E than whole grain flour.
Further enrichment of barley fibre fraction (optional)
Further increases in the concentration of total dietary fibre and of β-glucans in the barley fibre preparation are possible by adding a few refinement steps to the original roller milling process. This can be achieved by pin milling, sieving and another shorts duster passage of the original barley fibre fraction (Figure 2). Indeed, these additional steps significantly increased the content of total dietary fibre and β-glucans in the preparations as well as improved their brightness (Table 1, Figure 3). As seen in Figure 4, the original FRF consists of grain fragments containing primarily the endosperm cell walls and portions of the outer grain layers (pericarp, aleurone, and subaleurone tissues). Some of the larger endosperm fragments also contain starch granules entrapped in the endosperm cells. The additional refinement steps reduced the particle size of the FRF as well as effectively removed the majority of the entrapped starch granules. As a consequence, the enriched FRF resembles small pieces of netting made up of the endosperm and/or aleurone cell walls (Figure 4).
The enriched FRF from cultivar CDC Fibar contained significantly higher amounts of β-glucans, soluble and total dietary fire than the original FRF (Table 1). Also, the amounts of Fe, Zn, Mg, and P, and vitamin B3 were higher in the enriched than in the original FRF. The enriched FRF are also slightly brighter and contain fewer dark specs (due to pericarp fragments) than their original counterparts. The amounts of Ca, Mn, and vitamins B2, B6, and E were slightly lower in the enriched FRF than in the original preparations, but still considerably higher that in the whole grain.
A few commercial β-glucan isolates, with β-glucan content ranging from 5-70%, are currently available, but they are usually obtained through complex chemical processes. Some of the advantages of the barley roller milled fibre preparation include the fact that the FRF is obtained via a chemical-free process that involves only physical grain fractionation and that FRFs offer more nutritional value than β-glucan isolates because they also contain other dietary fibre constituents, minerals, phenolics and vitamins as shown in Table 1.
|Composition/Physical properties||Whole barley||Original fibre-rich fraction||Enriched fibre-rich fraction|
|β-glucan (%, dwb)||9.2||17.4||27.0|
|Arabinoxylans (%, dwb)||5.0||7.1||8.1|
|Total Dietary Fibre (%, dwb)||17.5||35.0||49.0|
|Soluble Dietary Fibre (%, dwb)||not determined||19.8||32.0|
|Proteins (%, dwb)||15.8||17.8||15.7|
|Ash (g/kg, dwb)||22.4||32.2||36.6|
|Vitamins B (mg/100g, dwb)|
|Vitamin E (mg/100g, dwb)||0.96||1.32||0.98|
|Brightness (L*)||not determined||82.8||85.7|
Better bread with barley
Using just a small amount of barley FRF in bread can improve the nutritional quality of a loaf of bread. The Basic Barley Research group together with the Bread Wheat Research group has found that adding barley fibre fractions to wheat flour makes bread that looks and tastes good and has the added benefit of high levels of beta-glucan. Bread with barley FRF was baked using the Canadian short process (CPS) and formula that included flour, whey, shortening, yeast, sugar, salt, and ascorbic acid. To obtain the FDA recommended dosage of 0.75 grams of β-glucan per two-slice serving, it was determined that only 10% of white flour milled from wheat needed to be replaced with the FRF obtained from hulless barley cultivar CDC Fibar according to the original milling process. Because of the higher concentration of β-glucans in the enriched FRF (Table 1), the supplementation level could be reduced to 6% when using the enriched FRF from cultivar CDC Fibar. The water absorption of the barley FRF-supplemented doughs was higher than that of 100% white flour and comparable to the 100% whole wheat flour (Table 2). As a consequence of higher baking absorption, the barley FRF-supplemented loaves and the 100% whole wheat loaves were heavier than the white flour controls. The loaf volume of 10% FRF-supplemented bread was reduced by ~20% compared to the white flour bread and was only 7% lower compared to the 100% whole wheat flour bread. The crumb structure of the FRF-supplemented bread scored higher (by visual evaluation) than that of 100% whole wheat flour, had fewer large holes, and generally finer crumb structure than both wheat flour control breads (Table 2). The 10% FRF-supplemented bread was slightly darker than the white flour bread but substantially brighter than the whole wheat bread. Replacement of white flour with the enriched FRF preparations significantly improved the overall quality of the supplemented bread. The most striking improvements were in the loaf volume, appearance and colour of the bread. The loaf volume of bread supplemented with 6% of enriched FRF was superior to that of 100% whole wheat flour and when compared to white flour bread the volume was reduced by only ~6%. The appearance, crumb texture and colour were better for the 6% enriched FRF-supplemented bread than for the whole wheat flour. The bread supplemented with 6% of enriched FRF had excellent appearance, attractive colour, uniform and slightly finer crumb structure than the control white flour bread (Figure 5 and Figure 6).
The results of this study are very promising for consumers who are looking for healthy food items, but are not willing to compromise the sensory attributes of food products.
|Bread||Baking absorption (%)||Loaf volume (cm3)||Loaf weight (g)||Visual assessment||Brightness (L*)|
|100% white flour||65||2210||286||7.5||6.5||85.0|
|100% whole wheat flour||73||1910||304||6.0||5.5||72.9|
|Loaves with barley fibre|
|+ 10% Fibar FRF (original FRF)||74||1770||300||5.5||5.8||77.5|
|+ 6% Fibar FRF (enriched FRF)||74||2060||302||7.5||5.8||81.7|
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The authors would like to thank Eugene Gawalko (Grain Research Laboratory, Canadian Grain Commission) for mineral analysis, Franca Beraldin (Food and Nutrition Laboratory, Health Canada) for Vitamin B analysis and Sun West Food Laboratory (Saskatoon, Saskatchewan) for Vitamin E analysis.