Skip navigation to main content

You are here: UNE Home / PIIC / Jenny Wood - Mechanisms of seed coat and cotyledon adhesion influencing dehulling and splitting quality of chickpea seeds

Jenny Wood - Mechanisms of seed coat and cotyledon adhesion influencing the dehulling and splitting quality of chickpea seeds

Jenny Wood

PIIC Postgraduate Student Jenny Wood

The dehulling and splitting process, aims to isolate the two cotyledons (dhal) without chipping/abrasion of the cotyledons or contamination by the seed coat. The ease of separating the seed coat from the cotyledon, and the ease of splitting the cotyledons impact on dhal yields. This dissociation between botanical parts of the seed is influenced by both environmental factors and varietal characteristics.

An estimated 70-90 % of desi type chickpeas are dehulled and split before consumption. Australia produces 300,000 tonnes of desi chickpea annually, yet only value adds by dehulling/splitting around 5% of the crop due to the high cost and difficulties of local processing. The ability to breed desi chickpea cultivars that are easier to dehull/split would benefit Australian processors greatly. On the other hand, such easy-to-dehull/split cultivars would exacerbate unwanted splitting of seed during harvest and handling. Farmers and grain handlers currently have trouble with some cultivars splitting during harvest and handling (especially after pre-harvest rainfall on mature crops) leading to high percentages of split seed and price penalties.

The ideal chickpea would, therefore, be one that withstands harvest/handling, maybe even pre-harvest rainfall, but would dehull and split easily during processing. Such a cultivar would be highly sought after by growers, handlers, millers and exporters alike. The challenge is to achieve both benefits from the same cultivar – obviously breeding alone cannot achieve both of these mutually exclusive outcomes. The identification of the underlying mechanism(s) of seed coat and cotyledon adhesion may enable the development of an effective process to artificially break this adhesion during processing. This would enable the breeding program to focus on chickpea that withstands harvest/handling, and the adhesion-breaking method could be used during processing to optimise dhal yields and quality.

The results of this PhD project are summarised:

  1. Milling quality is a genetically controlled trait that may be manipulated in a breeding program.
  2. Other factors that influence the ease of milling chickpea include seed size, seed shape and weather damage. However, seed coat/cotyledon ratio and seed coat thickness did not significantly affect dhal yields, despite affecting the theoretical maximum dhal yields obtainable.
  3. The physical and chemical properties of chickpea seeds were examined using various microscopy and analytical chemistry techniques that identified potential underlying mechanism(s) responsible for the differing strength of seed coat and cotyledon adhesion in chickpea genotypes.
  4. Six new methods of breaking the adhesive mechanism(s) were proposed from these results, and their effectiveness tested on a difficult-to-mill genotype. Visual quality and taste of the resulting dhal were also considered. Commercially significant improvements in dhal yield were achieved whilst retaining acceptable dhal quality, and are potentially patentable (hence commercial-in-confidence).

The thesis is due for submission in September 2011.