Home >> Resources/Information >> Extrusion, Food Education
Extrusion Processing Improves Waxy Barley Flour for Bread Making
Report On Research
Research supported by the Alberta Barley Commission: Farmers’ $ at Work
Recognizing the current limitations of incorporating barley flour into bread, Dr. Thava Vasanthan experiments with an extrusion process that results in a well-risen, soft loaf with the nutritional benefit of increased dietary fibre.
Extrusion Processing Improves Waxy Barley Flour for Bread Making
By
T. Vasanthan1,3, S. Gill1, B. Ooraikul1 and B. Rossnagel2
Introduction
Nutritional studies have clearly shown that barley beta-glucan (a dietary fibre component) benefits human health. Consumer awareness about high-fibre diets has shifted food manufacturing towards dietary fibre enriched products, including high fibre baked goods. Little success has been achieved with the addition of barley flour to yeast leavened bread products. Substitution of barley flour above 5% (w/w) produced unacceptable quality breads (low loaf volume and high crumb hardness). The 5% (w/w) addition level is too low to bring beta-glucan to a level necessary to provide the proven health benefits. The use of waxy barley flour with higher beta-glucan content (up to 8%, w/w) or pretreatments (e.g., extrusion cooking) that may change the properties of barley flour and enable higher addition levels are some of the options to produce barley breads with appreciable beta-glucan content.
Extrusion cooking is a highly adaptable, cost-effective, and energy efficient technology commonly used in cereal processing. It can lead to changes in the properties of barley flour components such as starch and beta-glucan and may enhance its suitability for bread making. The objective of this study was to replace a portion of wheat flour with waxy or regular barley flour, in their native or extruded states, and to examine the effect on bread quality characteristics such as loaf volume, crumb firmness and crumb/crust colour.
Materials and Methods
Hulless barley grains (waxy starch variety CDC Candle and regular starch variety Phoenix) were obtained from Agricore United (Calgary, AB). Grains were pearled to 32% and pin-milled into flour. Analyses of flour and breads were performed according to standard methods of American Association of Cereal Chemists (AACC).
Extrusion of barley flour was carried out in a Brabender lab scale co-rotating, conical twin-screw extruder. Barley flour (waxy and regular) was extruded at different temperature-moisture combinations. These combinations were: low temperature (100oC) low moisture (30%), LTLM; low temperature (100oC) high moisture (50%), LTHM; high temperature (130oC) low moisture (30%), HTLM; and high temperature (130oC) high moisture (50%), HTHM.
Breads were prepared and baked using 100 g of flour for each sample. Control bread contained 100% all-purpose wheat flour. Test breads were prepared by replacing all-purpose wheat flour with barley flour at 5, 10 and 15% levels. Barley flour from the two different varieties was used – regular variety Phoenix and the waxy variety CDC Candle. Barley flour was added in the native as well as extrusion cooked states. Bread formula included flour, water, sugar, non-fat dry milk, shortening, salt, active dry yeast and calcium propionate. Besides flour, all the ingredients and their amounts were the same for control as well as test breads.
Bread quality characteristics such as loaf volume, colour and crumb firmness were measured by standard techniques. All experiments were carried out in triplicate and analyses were done in duplicate.
Results and Discussion
The substitution of wheat flour with barley flour (i.e. native or extruded) reduced the loaf volume (Figure 1A&B) and increased the crumb firmness. Depending on the barley variety (CDC Candle or Phoenix) and extrusion conditions (LTLM, LTHM, HTLM or HTHM), the loaf volume, firmness/texture and colour of the bread loaves were altered. Amongst the barley breads prepared from native flours (at 15% barley flour substitution level), Phoenix had higher loaf volume (Figure 1A) and lower crumb firmness than CDC Candle. However, amongst the barley breads prepared from extruded (HTHM) flours, CDC Candle had higher loaf volume (Figure 2B,) and lower crumb firmness than Phoenix.
The lower loaf volume and firmer crumb texture of barley breads as compared with wheat bread may be attributed to gluten dilution. In addition, the physicochemical properties of barley flour components, especially that of beta-glucan and starch, can affect bread volume and texture. Beta-glucan in barley flour could tightly bind to appreciable amounts of water in the dough and suppress the availability of water for the development of the gluten network. An underdeveloped gluten network can lead to reduced loaf volume and increased bread firmness. Furthermore, in yeast-leavened bread systems, in addition to CO2, steam is an important leavening agent. Due to its high affinity for water, beta-glucan could suppress the amount of steam generated, resulting in reduced loaf volume and greater firmness. One of our previous studies has shown that extrusion cooking of barley flour caused fragmentation to beta-glucan molecules. Such fragmentation would likely reduce the water binding capacity of beta-glucan, resulting in improved gluten net formation and steam generation during baking.
The properties of barley starch can also play an important role. Waxy starches usually show a very high affinity to water during gelatinization (cooking in water) than regular starches. Thus, during baking, flour from CDC Candle (that contains waxy starch) will bind excess water and would suppress steam generation, resulting in reduced loaf volume and increased crumb firmness. However, when HTHM-extruded barley flours were used in bread making, better breads were obtained. This may be attributed to the fact that extrusion cooking would have already gelatinized the starch, and thus during bread making the starch would not absorb excessive water.
In the present study, breads made with 15% HTHM CDC Candle flour had highly acceptable properties (loaf volume, firmness and colour). A trial baking with 20% HTHM CDC Candle also yielded a highly acceptable barley bread.
Conclusion
Flour produced from waxy starch barley had higher beta-glucan content but showed poor bread making qualities when compared to regular barley flour. However, extrusion processing (HTHM) appreciably enhanced the suitability of waxy barley flour for bread making. The study indicates that the use of extruded (HTHM) waxy barley flours would be an effective way to produce barley breads (a functional food) with appreciable amounts of beta-glucan. Further research on the functionality of the beta-glucan is required.
1 Dept. of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Canada, T6G 2P5
2Crop Development Centre, University of Saskatchewan, Saskatoon, Canada, S7N 5A8
3Author of correspondence, Ph 780 492-2898; Fax 780 492-8914; e-mail tvasanthan@afns.ualberta.ca
