Feeding a growing world Potato variations

A new food Four hundred years ago, explorers brought a novel food to Europe from the Americas. It took another 150 years for people across the UK to make this food a central part of their diet - but you have probably eaten it more times than you can remember.

A new food This new plant was so exciting that John Gerard, a celebrity plant collector, showed himself holding a sprig on the front page of his encylopaedia The Herball, or General Historie of Plantes. Photo: Wellcome Library, London

If you know what deadly nightshade looks like, you will see that potato flowers are similar. Potatoes can bear fruit, which look like tomatoes but, like nightshade berries, are poisonous. A new food: the potato Photo: Wellcome Library, London

A new food: the potato Photo: Nattika/Shutterstock.com

Classification and genetics The potato is a starchy, tuberous crop, Solanum tuberosum. The family Solanum also contains tomatoes, aubergines and deadly nightshade. Domesticated potatoes come from the wild species Solanum brevicaule by centuries of selective breeding.

Classification and genetics Most cultivated potato varieties are tetraploid (they have four of each chromosome) and have 48 chromosomes in the nucleus of each cell. There are four diploid species of potato, two triploid species, one pentaploid species and one hexaploid species (Solanum bulbocastanum).

Potato plants Reducing sugars are translocated from leaves to stolon tubers underground. The sugar is converted to starch for storage. At temperatures below 4°C starch is converted to sugar. Photo: Madlen/Shutterstock.com

Potato plants Photo: Rothamsted Research

Diseases of potatoes Late blight caused by Phytophthora infestans (a fungus- like microorganism) Viral diseases carried by insects such as aphids and Colorado beetles Nematode worm (1 mm roundworms) Photo: hsagencia/Fotolia.com

Uses of potatoes Staple crop for humans Animal feed Source of starch for:  thickeners in processed food (e.g. soups)  glue  paper and board manufacture  textiles

Potatoes as a food source The potato is globally important because we can use it to produce high yields of nutritionally valuable food. Potatoes have culinary versatility. They can be roasted, boiled, baked, mashed, fried, riced, made into crisps, dumplings, gnocchi, chips, rösti, bread or pancakes and used in stews, curries, soups, … can you think of anything else?

Potatoes as a food source Photo: Dr Nikolai Windbichler

Potatoes to plastics Waste from potatoes can be used as a source of the polymer polylactic acid (PLA), to meet the growing demand for sustainable materials. PLA is used to make biodegradable packaging. C C O H3CH3CH3CH3C O n

Potatoes are also used to make vodka and poteen (poitín, a strong alcoholic spirit from Ireland). The starch is broken down into sugar, which is fermented to alcohol. Potatoes to ethanol

The starch in potatoes consists of amylose and amylopectin, which have different physical properties. Potatoes with more amylose are better for making mash. Potatoes with more amylopectin are better for boiled potatoes, as it helps them to retain their shape. Starch in potatoes

Acrylamide In 2002 a research team in Sweden discovered that acrylamide and related compounds form when potatoes are heated above 120°C. The longer the cooking time, the more acrylamide forms. Acrylamide is found in crisps, chips and bread (from the same reaction, but with wheat flour). Acrylamide does not form in boiled or microwaved potatoes.

Acrylamide Acrylamide is a compound with the formula C 3 H 5 NO that is thought to cause cancer in humans. H C H OH C C NH 2

Acrylamide Photo: volff/Fotolia.com

The Maillard reaction The Maillard reaction gives food cooked at high temperatures its characteristic brown colour and roasted flavour. Photo: Lilyana Vynogradova/Fotolia.com

The Maillard reaction The reaction takes place between amino acids and reducing sugars such as glucose. When the amino acid asparagine undergoes the Maillard reaction, acrylamide is produced. asparagineacrylamide + reducing sugar > 120°C H C H OH C C NH 2 H2NH2N C HOOC O H C C H H

The health effects of acrylamide Scientific research is ongoing to determine the effects acrylamide has on our bodies. Potential serious effects it may have include:  neurotoxicity (nerve damage)  fertility issues  carcinogenicity (cause of cancer). Currently, food standards agencies do not advise that you avoid related foods altogether, but that you limit your acrylamide intake through a healthy, balanced diet.

Dietary acrylamide exposure Health organisations in several countries regard the levels of acrylamide in foods as a concern and have stated that more research is needed to determine the risks of consuming large quantities of acrylamide. In 2005 a lawsuit was brought in California against several food-processing companies. It was settled in 2008 when they agreed to lower levels of acrylamide in their potato products to 275 parts per billion.

Dietary acrylamide exposure The same food-processing companies have refused to use the genetically modified (GM) low-sugar variety of potato, although this variety would reduce the levels of acrylamides in chips and crisps. Suggest why these companies refused to use low-sugar GM potatoes.

How to reduce your acrylamide intake Eat microwaved baked potatoes or boiled/mashed potatoes rather than chips and crisps. Blanch chips before frying, or make chips from boiled potatoes before frying to reduce the frying time. Don’t fry new potatoes. Dry chips in the oven before eating them.

How to reduce your acrylamide intake Don’t use sprouting potatoes. Don’t eat green potatoes. Avoid dark brown toast and fried bread. Avoid frozen chips. Store potatoes in the dark and not below 4°C (so not in the fridge).

Testing potatoes for sugar content You already know how to test for reducing sugars in foodstuffs. In this activity, you will test different varieties of potato to find out how their levels of reducing sugars vary. When you have your results, compare them all and decide which varieties of potato are likely to be safest for making chips.

Links to video Potatoes – research and the biotechnology of genetic modification