Effects of wheat starch content and structure on the availability of fermentable sugars to optimize

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Effects of wheat starch content and structure on
the availability of fermentable sugars to
optimize ethanol production

• Jessica Saunders, MSc Candidate and David B.
  Levin, PhD
• Department of Biosystems Engineering
• University of Manitoba

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Presentation Overview

• Background
• Ethanol in Western Canada
• Role of starch properties in a-amylolysis
• Research Objectives
• Proposed Methodology
• Findings to date
• Recommendations

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Background Ethanol as an Alternative Energy

• Ethanol industry in Western Canada is rapidly
  developing
• Growing need for a sustainable supply of wheat
  tailored to the demands of the industry
• Industry prefers not to scavenge wheat destined
  for human consumption (low starch, high protein)
• Ethanol quality varietals (high starch, low
  protein)
• Wheat/Corn (Canada) 1.7 Billion Liters, 3.1
  Billion Liters by 2010

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Background Ethanol as an Alternative Energy
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Background Starch

• 83 of kernel is endosperm
• Endosperm contains starches, lipids and proteins
  in a complex matrix
• Wheat kernel is 65 starch

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Background Amylose vs. Amylopectin

• Starch is a food storage polysaccharide used by
  plants to organize glucose polymers
• Two unique patterns of linear organization
• AMYLOPECTIN (75) AMYLOSE (25)

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Background Amylose vs. Amylopectin

• Starch linear structural pattern confers unique
  tertiary structure
• AMYLOPECTIN (75) AMYLOSE (25)

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Background Amylose vs. Amylopectin

• Literature suggests that amylopectin is more
  readily digested by a-amylase
• Genetically modified maize, rice and barley
  containing 100 amylopectin starch are digested
  faster than normal counterparts (Noda et al.
  2002)
• Resistant starches (low GI starches) exhibit
  slow release of glucose into intestinal lumen,
  non-resistant starches (high GI starches) exhibit
  rapid release of glucose into lumen (Bird et al.
  2007)
• Resistant starches high amylose content
• Non-resistant starches high amylopectin content

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Background Starch Granule Polymorph Distribution

• Wheat endosperms consist of three distinct starch
  granules (Raeker et al., 1998)
• A-granules large, disc shaped
• B-granules small, spherical shape
• C-granules not well defined

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Background Starch Granule Polymorph Distribution

• Riffkin et al. (1990) and Brosnan et al. (1999)
• Contributary role of starch granule size
  distribution to ethanol yield

• A vs. B-granule Structural Distinctions
• Amylose content
• Lipid content
• Size
• Crystallinity

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Research Goals

• What structural features of wheat starch make
  high ethanol producing varietals?
• Characterize various classes of wheat (spring,
  winter and waxy) to establish their potential as
  feedstock for bioethanol production.
• Characterizing starch content and structure
  within classes and varietals of wheat to
  establish inherent variation in chemical
  constitution.
• Correlate starch content and structure with
  production of fermentable sugars during
  liquefaction.
• Resultant ethanol yield from profile of
  fermentable sugars.

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Proposed Methodology Wheat Characterization

• Six classes of spring and winter wheats, as well
  as triticale, are under investigation
• Chemical Constitution Percentage Protein,
  Starch, Ash, and Arabinoxylan
• Starch Granule Organization Amylose/Amylopectin
  ratios, Degree of Amylopectin Branching, Starch
  Granule Polymorph Distribution

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Proposed Methodology Oligosaccharide Profiling
After Liquefaction

• Protocols being established in conjuncture with
  collaborators at the Canadian Grain Research
  Laboratory
• Whole grain milled to 0.5 mm
• Whole grain cooked to mash
• Liquefaction carried out at 83.5 C using
  a-amylase for batch runs that exhaust starch
  substrate
• Liquefied mash samples withdrawn, centrifuged and
  supernatant analyzed for fermentable sugars
  (glucose, maltose, maltotriose, maltotetrose )
  using HPAEC with pulsed-amperometic detection

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Proposed Methodology Oligosaccharide Profiling
After Liquefaction
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Results Chemical Constituents of Whole Grain

• Elevated protein appears to decrease starch
  content
• CPSR 61 starch, 13 protein
• CWRW 64 starch, 10 protein
• Constant Ash and Arabinoxylan content across
  classes
• Ash 1.6
  Arabinoxylan 5

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Results Starch Structural Properties
Amylose content appears to be consistent across
classes Average Amylose 28.2 /- 1.28

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Recommendations Chemical characteristics of
wheat starch ideal for use as bioethanol feedstock

• The bioavailability of starch may differ among
  grain cultivars and may affect the conversion
  rate and final yield of ethanol (Moorthy 2002).
• starch content and kernel size are not the only
  critical features
• starch susceptibility to enzymatic hydrolysis
  appears to be paramount

Table I Ideal parameters for Western Canadian
wheat destined for use as bioethanol feedstock
Average values possessed by conventional
cultivars of wheat destined for use as foodstuffs
as reported by The American Association of
Cereal Chemists (2007).
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Acknowledgments

• This work was supported by funds provided by the
  Natural Sciences and Engineering Research Council
  of Canada (NSERC) and Husky Energy.
• Special thanks are extended to Dr. David Levin,
  Dr. Richard Sparling, Dr. Nazim Cicek, and Dr.
  Marta Izyadorcyk for their guidance and support.