Pulse Starch Content

Starch represents the major component of pulse seeds, ranging from 40-50% of the dry seed weight. Starches naturally occur as granules that are composed of chains of glucose units linked together to form the two building blocks of starch: amylose and amylopectin. The ratio of amylose:amylopectin plays an important role in starch functionality. 

Compared to many other naturally occurring starches, pulse starches contain high levels of amylose (29 – 50%) and contain low concentrations (<1%) of minor components such as lipids or proteins (Hoover et al, 2010). As a result of their high amylose content, pulse starches display increased enzymatic resistance which makes them less susceptible to digestion within the body and is attributed to a lower glycemic index upon consumption.  

Starch content of pulses
PulseStarch (%db)Amylose (%starch)
Pea45.7 - 51.231 – 49
Lentil44.5 - 50.129 – 29
Faba Bean40.8 - 47.231 – 40

Adapted from Ren et al. 2021. Publication Pending.

Formats

Starches can either be isolated from pulses using wet processing techniques, or concentrated during air classification to produce a coarse, starch rich product. Wet methods to isolate starch are able to achieve much higher levels of purity (>90%) compared to air classified products which will typically range from 65-80% and contain anywhere from 8-20% of the remaining seed constituents such as protein and fibres. 

Modifications can be applied to pulse starch to alter the functionality, including:

  • Chemical modifications:
    • Acid thinning
    • Oxidation
    • Cross linking
    • Substitution
  • Physical modifications:
    • High hydrostatic pressure treatment
    • Hydrothermal treatments
    • Irradiation
    • Ultrasonication
  • Enzymatic modification

Functionality

Amylose content has a significant effect on the pasting properties of starches, where higher concentrations, such as in pulses, restricts granular swelling. The result is a lower peak viscosity under typical pasting conditions. The reassociation of amylose upon cooling allows for the formation of a strong gel network, pulse starches display characteristically higher gel viscosities.