What a wonderful pulse! The amazing wrinkled pea

We've launched an exciting range of wrinkled pea wholefoods - whole and split dried peas, alongside wrinkled pea flour - perhaps the first time mature dried peas of a wrinkled variety have been available. Named for their distinctively wrinkly appearance, there's much that's special about these peas.

What are wrinkled peas?

Austrian monk Gregor Mendel, the father of genetics, reported in 1866 a "difference in the form of the ripe seeds" of different pea plants of the common or garden pea species Pisum sativum. The pods of some plants contained smooth and round peas, others wrinkled and shrunken peas. Wrinkled peas are simply the fully mature and dry peas of varieties whose seeds are wrinkly rather than the more common round peas.

Mendel's early experiments in the heredity of traits involved crossing parent pea plants exhibiting seven contrasting and independent traits, including the wrinkled and round pea shape. Meticulously recording how these traits were passed from the parent generation to successive generations of offspring, Mendel found all seven of his chosen characteristics to exhibit similar mathematical patterns, pointing the way to his theory of dominant and recessive traits.

Wrinkled but sweet

Plant breeders later noted that fresh immature peas of wrinkled varieties were sweeter than those of round types. This sweetness turns out to go hand-in-hand with the wrinkliness of the seeds: wrinkled peas contain more sucrose and draw in more water by osmosis when young, swelling up to plump green peas. Left to mature and dry, the peas shrink down, leaving the stretched skin to wrinkle around the remaining dry matter.

Mendel's results suggested to later scientists that a single genetic locus was responsible for the wrinkled or smooth trait, named rugosus in 1917, with R indicating the dominant smooth and r the recessive wrinkled type. In 1988 Professor Alison Smith, of pioneering pea research institute the John Innes Centre in Norwich, identified the sweet and wrinkled characteristics to be the result of a particular missing enzyme, "starch-branching enzyme (SBE1)". The specific single gene responsible for this enzyme was later identified by Professor Cathie Martin, also of the John Innes Centre.

Favoured for freezing

The appealing plumpness and sweetness of the fresh green immature peas led to these wrinkled types being favoured for production of fresh, and later frozen, peas.

Known by farmers as vining peas (pdf), many wrinkled varieties of pea are now grown within easy reach of the UK's eight freezing factories, located on the eastern coast of the UK between East Anglia and Montrose in Scotland, where growing conditions are favourable. To ensure optimum quality peas must be harvested, delivered and frozen within 2 to 2½ hours.

Timing the harvest of peas for freezing is critical and determined by use of a pea tenderometer. Specialist pea harvester machines mostly serve many farms through the season and are used to pick, thresh and clean the peas, ready for swift delivery to the freezers.

Saving by-passed peas

But if the timing isn't right and the peas can't be harvested at their best, they're no good for freezing and "by-passed", meaning their left in the field. They might be grown on to maturity and harvested dry for animal feed but often the cost is too high and the peas are just ploughed back into the field.

We've worked with Great Glemham Farms in Suffolk to rescue their crop of by-passed peas, harvesting them as dried peas at full maturity and cleaning them up for human consumption.

Resistant starch, perfect food for beneficial gut flora

More recent research at the John Innes Centre, led by Professor Claire Domoney, has explored the potential health benefits of wrinkled peas' high resistant starch content.

The mutation responsible for the wrinkliness and sweetness of wrinkled peas also results in the peas having a significantly higher proportion of resistant amylose starch as opposed to amylopectin.

All starch is comprised of granules containing a mixture of two polymers, amylose and amylopectin, in varying proportions. Amylose is a simple and tight linear chain of linked glucose molecules, while amylopectin is a much larger molecule with many shorter chains branching off the main long chain. Amylopectin's larger surface area facilitates digestion whereas the tightly packed amylose is more resistant.

More amylose - the resistant starch - passes through the digestive tract intact and reaches the colon. Here it is fermented by bacteria, producing short-chain fatty acids with potential health benefits. As resistant starch is more slowly digested it causes less rapid increase in blood sugar and creates a longer feeling of fullness after eating.

The John Innes Centre, in collaboration with the Quadram Institute and Imperial College London, is continuing to investigate the features of wrinkled peas' resistant starch, the effect of cooking, and the health benefits of their use as food.

So wrinkled peas may not only be a delicious way to avoid potential waste when peas for freezing are by-passed, but also a thoroughly nutritious, healthy and satisfying food.

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