- Baking Europe
- 2 days ago
- 6 min read
Despite not being as well known in Europe, yams are root and tuber crops which are popular in many parts of Africa, the Caribbean and Asia. Nigeria is the largest producer of yam in West Africa (Figure 1), where it serves as a source of income to smallholders and commercial farmers.¹
The savannah region of West Africa contributes 92% (66.8 million tons) of the world’s yam production, making the region the primary yam producer in the world.² Yams are a staple food with economic, cultural and nutritional importance. They belong to the Dioscorea genus with approximately 600 species around the world, however, only 10 species have been domesticated for food and income generation across Africa, Asia and Latin America.
In terms of human consumption, yam is a nutritious food, being a rich source of carbohydrate (dietary energy), vitamins and minerals.³ On a dry weight basis, they (D. rotundata) contain approximately 74% starch, 5% protein, 5% minerals, 3% fibre and 1.9% fat.⁴ They are also proven to have antioxidant activity, meaning they are useful for maintaining gut health.⁵ Popular methods of consuming yams include, boiling, frying or as a dough: ‘Amala’ dough is made by reconstituting yam flour in hot water and it is consumed with various soups and sauces.
Yam as a source of dietary energy and fibre
As the tubers are mostly composed of complex carbohydrates, starch and soluble dietary fibre, yam is a rich source of energy providing 200 dietary calories per person per day to 300 million people across the tropics.⁶ The beneficial effects of sufficient levels of fibre are well documented, aiding the digestive system, increasing water holding capacity and reducing intestinal transit time, lowering the risk of colon cancer.⁷ The fibre content in yam also promotes other positive physiological effects, such as: reduction of blood glucose; reduction of total and LDL (low density lipoprotein) cholesterol; binding of toxins; and encourages the growth of natural gut microbiota.⁷
Yam as a source of vitamins, minerals and antioxidants
Primarily, the tuber is a source of the B-complex group of vitamins providing thiamine (vitamin B1), riboflavin (vitamin B2), and niacin (vitamin B3), which perform various metabolic functions in the body.⁴ ⁸ Secondly, fresh yam tubers also contain good amounts of antioxidants. Small amounts of vitamin A and β-carotene are also present, the carotenes being converted to vitamin A inside the body.⁴ These compounds are powerful antioxidants, with Vitamin A having many functions, such as maintaining healthy skin and defending against illnesses and infection.⁹
Finally, the tubers are a good source of minerals, such as potassium, calcium, sodium, magnesium and phosphorus.¹⁰
Production of yam flour
To reduce post-harvest losses in yam production, fresh yams are processed into yam flours and other composite flours. The utilisation of yam to produce a variety of products with improved nutritional value is one of the great advantages of using it in food products. The flour is produced to make these value-added products by peeling and washing the tubers, then slicing them into thin slices, drying them in hot air ovens and then milling into flour.
In developing countries, sunlight is used as a drying method by spreading out the freshly sliced yams to reduce moisture content. Other forms of drying, such as freeze and flash drying can also be applied.
Use of yam flour in baked products
As baked products are generally made from gluten-based wheat flour, they are avoided by people with
a gluten intolerance. This has led to an increase in the need and therefore the supply of alternative flours such as yam. This is also a good solution in Africa, where cereals like wheat are not produced in sufficient quantities to meet local needs. This problem is therefore alleviated by the production of yam-based flours as a substitute for at least part of the wheat flour needed, or in some cases total substitution.
Yam flour in bread making
In terms of baking characteristics yam flour adds fluffiness and lightness to baked products. Inclusion of the flour in bread recipes will sufficiently maintain the airy, light texture of bread loaves. However, bread made from wheat-yam composite flour containing 25% yam flour (D. purpurea, steamed and freeze dried) and dough improver, has been demonstrated to have a decreased loaf volume (45%) versus the wheat control. The sensory acceptability of the bread from composite flour is not altered at 20% yam flour inclusion, despite the purple colour, which has been attributed to cultural differences: this trial was conducted in Taiwan where colourful foods are deemed as perfectly acceptable by consumers.¹¹
Similarly, a Nigerian study recommended substituting yam flour (D. alata) for 20% of the wheat flour for bread production, as it resulted in a comparable quality (loaf weight) and sensory acceptability when compared to bread made from wheat flour alone. Although this study did not include a dough improver in the recipe, so loaf volume decreased by 28% versus the wheat control.¹²
Yam flours can be substituted for part of the wheat flour in American-style bread, which includes a dough conditioner to control the loaf volume. Inclusion of 20% yam flour makes a satisfactory bread, while bread made with 40% or 50% yam flour is not considered acceptable: the dough tends to rise slowly, which may be due to the large starch granules in yam.¹³
Yam flour (D. japonica) has also been used to make bread in Japan, with a recipe composed of yam flour (10g) and wheat starch (30g). In this study it was found that the yam flour and wheat starch combination was suitable for bread making (bread height, 68.4 mm; specific volume, 3.95 cm³/g) as a substitute for wheat flour (bread height, 69.4 mm; specific volume, 3.45 cm³/g).¹⁴
Yam flour in cake production
Yam flours are used in the production of some Japanese cakes, such as manjyu and karukan, and the flour has also been used for the production of pancakes and cupcakes.¹³ The colour of the flour reflects the colour of the flesh of the yam variety used (e.g. white, orange, or purple) which can add a beneficial colour to the final product, depending on cultural preferences.¹³ Testing reports that cupcakes made from 100% yam flour (Forastero variety of Dioscorea alata) were at least as satisfactory as the wheat control in terms of the sensory characteristics; the doughs even rose more than the wheat control.¹³
In conclusion
Yam, although not as extensively used in Europe as other parts of the world, is rich in fibre, meaning it is very beneficial in supporting a healthy digestive system and reducing instances of disease associated with a low fibre diet.
It is gluten free and helps the body regulate blood sugar levels, making it suitable for those who have to avoid certain foods for health reasons, e.g. coeliac disease or diabetes. For bakers looking to benefit from the ongoing trend in healthy snacking, along with the continued customisation of products for consumers demanding more choice, the use of yam or yam flour in baking is worthy of investigation.
Previously published in Baking Europe Autumn 2023
References
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