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
|Pulse||Starch (%db)||Amylose (%starch)|
|Pea||45.7 - 51.2||31 – 49|
|Lentil||44.5 - 50.1||29 – 29|
|Faba Bean||40.8 - 47.2||31 – 40|
Adapted from Ren et al. 2021. Publication Pending.
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
- Cross linking
- Physical modifications:
- High hydrostatic pressure treatment
- Hydrothermal treatments
- Enzymatic modification
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.