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Background and Objectives:
Barley is the second top-ranking cereal in Canada; over the last three years the
average annual barley production on prairies has been over 11 million tonnes. The
principal end-users of barley are the feed, and malting and brewing industries. The food
industry, too, has the potential to become an important user of barley, but it needs more
information on the functionality of barley and barley components to ensure their effective
utilization. Barley contains very attractive components. The non-starch polysaccharides of
barley (ß-glucans in particular) are associated with health benefits of dietary
fiber and appear to have cholesterol lowering properties. Barley can also be an excellent
source of starches; several genotypes of barley containing large and small starch
granules, and various amylose-amylopectin ratios (waxy, normal, high-amylose barley) have
been developed and are awaiting greater uses in the food and other industries.
Incorporation of barley starch into blends with other starches and/or non-starch
polysaccharides may provide the food industry with attractive ingredients having unique,
desirable functional properties. Barley components might, therefore, be excellent
value-added products and would increase significantly the value of barley as a crop and
diversify its utilization. Even though, barley is one of the major crops on prairies, very
little effort has been made so far to develop imaginative uses of this valuable renewable
resource. The potential is huge and the prospects are exciting, but their realization
depends on determining, in a sound and rigorous manner, the functional properties of
barley starch and starch blends that would be appropriate for the food industry.
The main objective of the proposed project was to perform strategic research on starch
and non-starch carbohydrates from barley with a view to adding value, improving, and
diversifying utilization of this major Canadian crop.
These studies were designed to investigate the functional properties of barley
constituents which could make them attractive ingredients for the food industry, one of
the largest processor of agricultural crops, and thereby increase the value of barley as a
crop, expand the pool of its users, and diversify its utilization. The project was
undertaken to determine the molecular basis of barley carbohydrate functionality, and
thereby enable formulation of new, cost-effective ingredients with quality enhancing
characteristics, as well as practical applications of barley starch and starch blends in
value-added processing by the food industry. The fundamental insights into the molecular
origin and genetic basis of barley carbohydrate functionality will also enable
recommendation to the molecular biologists and plant breeders which molecular
characteristics of barley polysaccharides should be altered for specific applications.
Procedure, Project Activities, Results and Discussion:
Variation in Total and Soluble ß-Glucan Content in Hulless
Barley: Effects of Thermal, Physical, and Enzymic Treatments
Four types of hulless barley (normal, high amylose, waxy, and zero amylose waxy) from
29 registered and experimental genotypes were analyzed. For each, we have established
moisture, protein, amylose, 100 kernel wt., starch, beta-glucan (total and soluble),
beta-glucanase activity, and slurry viscosity. The various types of barley showed
significant differences in total beta-glucan with average values of 7.5, 6.9, 6.3 and 4.4%
for high amylose, waxy, zero amylose waxy, and normal barley, respectively. The
differences in extractability of beta-glucan (i.e. solubility in water) were quite large.
The solubility of beta-glucans in high amylose barley was relatively low (21-30%) compared
to that in normal (30-45%), zero amylose waxy (34-53%) and waxy (37-53%) barley genotypes.
Viscosity of barley flour slurries was affected by the content of soluble beta-glucans,
beta-glucanase activity, and mol. wt. of beta-glucans. The extractability and physical
characteristics of barley beta-glucans can be modified by thermal, enzymic and physical
treatments of barley. Hydrothermal treatments (autoclaving and steaming) of barley had no
effect on extractability of beta-glucans, but prevented enzymic hydrolysis of
beta-glucans, and thereby substantially improved their viscosity. These treatments,
therefore, might have a potential to positively affect the physiological responses to
barley beta-glucans in human diet. On the other hand, the enzymic and physical treatments
were more important in accounting for the increased extractability of beta-glucans.
Considering that it is soluble dietary fiber that is responsible for desirable
physiological effects in humans, it is essential to investigate, in greater detail,
potential strategies for improving the ratio of soluble to insoluble dietary fiber in
barley.
Isolation and Characterization of Barley Starches
The granular and molecular characteristics of four types of hulless barley starches
(normal, high amylose, waxy and zero amylose) were investigated by particle size analysis
and size exclusion chromatography with light scattering detection. Significant differences
in the granule size distribution and molecular characteristics of amylose and amylopectin
were found in barley starches with variable amylose content. Although bimodal size
distribution of granules was observed for normal, waxy and zero amylose starches, the
proportion of large to small granules for each type of starch differed substantially. The
granular size distribution of high amylose starches was unimodal, showing the highest
proportion of small granule (3 µm). For the intact starch molecules, molecular
weights of high (amylopectin) and low (amylose) Mw fractions were in the range
from 136x106 to 305x106 and from 2.73x106 to 5.67x106,
respectively. The retrogradation kinetics of the four barley starches, as measured by
differential scanning calorimetry, differed significantly. Waxy and zero amylose starches
exhibited very slow retrogradation rates, up to 7 days of storage, compared to those of
normal and high amylose starches. Slow retrogradation of barley waxy starches was also
confirmed by rheological evaluations. Increases in the rigidity of waxy gels were minimal
compared to those of normal and high amylose barley starches as well as of wheat and waxy
maize starches.
These properties of barley waxy starches may be especially
attractive when barley is added to bread flour to prevent staling of bread and extent its
shelf life.
Pearling and Milling of Barley
Processing of barley grain by pearling and milling is an effective way of obtaining
several fractions of barley differing in composition, i.e. starch, protein and dietary
fiber content and, therefore, suitable for various food uses. Pearling of hulless barley
reduces the yield of flour obtained by roller milling, but significantly improves the
flour color. Pearling between 15 and 20% is most likely the best compromise between flour
yield and flour color. Hulless barley genotypes with altered starch composition (i.e. high
amylose or waxy barley) require more grinding energy and yield lower flour yield than
hulless barley genotypes with normal starch characteristics. Pearling from 0 to 40%
increased the content of ß-glucan by 1.2-1.8% in barley and by 0.6-1.3% in flour
depending on the type of barley. Changing the moisture content of barley before milling
from 10-15% reduces the flour yield, but improves the flour color. The yield of
ß-glucan-rich shorts and the content of ß-glucans in shorts increase with
increasing the moisture content of barley before milling. Pearling between 15 and 20% and
adjusting the moisture content between 12.5 and 14.5% appear to be the best compromise
among such parameters as flour yield, flour brightness, short yield, and ß-glucan
content in shorts.
Incorporation of Barley and Barley Components into Food Systems
Barley has not yet been used as the main ingredient in such common food commodities as
pasta, noodles, or yeast leavened baked products. However, partial replacement of wheat
with whole barley or barley components may result in development of acceptable and
functional products. The admixture of barley will undoubtedly affect the unique
dough-producing properties of wheat and consequently the final food product, but its
effects need not be detrimental. Wheats differ in the quantity and quality of gluten, and
various wheat flours may, in fact, tolerate the addition of barley to varying degrees.
The effects of addition of whole barley and
barley components (starch,
ß-glucans and arabinoxylans) on rheological properties of dough prepared from wheat
flours with variable gluten quality (cv. Glenlea, extra-strong; cv. Katepwa, very strong;
cv. AC Karma, strong; and cv. AC Reed, weak) were investigated using mixograph and dynamic
rheological measurements. Whole barley meal, starch and non-starch polysaccharides from
hulless barley with variable starch characteristics (normal, high amylose, waxy, and zero
amylose waxy) were tested. Determining the effects of barley and its components on the
mechanical properties of wheat flour dough is crucial for determining both the handling
properties and the quality of the finished food products. The addition of either
ß-glucans or arabinoxylans appeared to strengthen the wheat dough. The addition of
starch to various wheat flours reduced the strength of the respective flour-water doughs.
However, the overall effect of different starches is dependent on their properties, such
as granular size and water absorption, as well as on the quality characteristics of wheat
flours to which the starches are added. A combination of high amounts of non-starch
polysaccharides and unusual starch characteristics in barley seems to balance the negative
effects associated with gluten dilution typically caused by addition of barley into wheat
flour. Further studies are needed to evaluate the effects of barley on the overall baking
performance of wheat/barley blends.
In the last stage of our research, we have evaluated the addition of barley milling
products, flour and shorts, on the quality of Asian noodles. We used AC Vista, a Canada
Prairie Spring White wheat as the base wheat flour for noodles. The addition of three
different types of barley with variable amylose content (normal, high amylose, and waxy)
was investigated. The hulless barley grains were tempered to 14.5% moisture content prior
to being pearled to 20% and milled. Two milling fractions were considered in our studies,
namely straight grade flour and shorts. The shorts were significantly enriched in both
polysaccharides, arabinoxylans and ß-glucans, compared to the straight grade flours;
they also had significantly higher protein and ash content.
The noodles were made by mixing the ingredients in a Hobart mixer and rolling and
sheeting the crumb using the Ohtake laboratory noodle machine. Both white salted and
yellow alkaline noodles were made at a 20 and 40% barley flour addition level and 25%
shorts addition. Sodium chloride was used in white salted noodles whereas kansui, an
alkali reagent, was used in the production of yellow alkaline noodles to obtain the
characteristic flavour and yellow colour of this type of noodles.
The addition of barley flour to either white salted (WSN) or yellow alkaline noodles
(YAN) resulted in a decrease of brightness and yellowness of the noodles and an increase
in redness. The color of WSN was affected relatively little whereas the color of YAN was
changed to a greater extent. Among the different types of barley, the high amylose samples
exerted the greater effects on color than the other barley types. Barley shorts changed
the color of both types of noodles to a greater extent than barley flour.
Generally, addition of hulless barley flour to noodles decreased the cooking time,
water uptake and solid losses upon cooking. These phenomena were observed for both barley
flour and barley shorts. Addition of waxy barley flour produced softer, less chewy WSN,
whereas the addition of high amylose barley flour produced firmer and chewier WSN. Starch
composition, more specifically the amylose content, had a significant effect on the
texture of WSN. Incorporation of barley flour to YAN, regardless of starch composition,
resulted in firmer, and chewier cooked noodle texture. It appears, therefore, that the
observed differences in texture between the control wheat noodles and those with the
addition of barley cannot be explained solely by the differences in starch composition.
Other components in barley, such as non starch polysaccharides might also affect the
overall noodle texture especially under the alkaline conditions of YAN.
The findings of our studies indicate that hulless barley flour can be successfully
incorporated into noodles and results in products with acceptable appearance and slightly
modified textural parameters. Moreover, incorporation of barley shorts into noodles
results in a functional product with a very high content of dietary fiber (2.3-3.0 gram of
soluble ß-glucan per 150 grams of fresh noodles).
With the growing awareness of beneficial effects of healthy diet on the quality of life
and on cost-effectiveness of health care, hulless barley may become an attractive grain
grown on the prairies.
Hulless barley contains many beneficial constituents with both functional and
nutritional properties. These studies indicated that the amount of these components vary
depending on the genetic factors. At the present time, it is possible to identify several
barley varieties with increased content of beta-glucans and/or unique starch properties.
Some properties of barley components such as solubility of beta-glucans can be modified by
appropriate treatments of barley grain prior to utilization.
Milling of hulless barley may be an effective way of obtaining barley fractions
enriched in particular components. These studies indicated also that barley and/or barley
components may be incorporated into many food products. Wider adoption of barley by food
processors will increase the demand for barley and create opportunities for increased
production of this grain.
Barley is a good source of beta-glucans and starch, and has a potential to replace the
current sources of these ingredients, i.e. oats and corn.
Acknowledgment:
This project was made possible due to funding from the Government of Manitoba and
Canada through the Canada-Manitoba Agri-Food Research and Development Initiative (ARDI).
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