Researchers create nutritious gluten-free flour with sweet potato

14 Feb 2023 --- Boasting high vitamin B levels, sweet potatoes are known as a healthy alternative to comfort food favorites such as fries, crisps or wedges. However, the full nutritional benefits of the spud may not yet have been extracted. A recent study has shown that it can be dried into a visually stunning gluten-free flour.

The researchers say the findings could help expand orange sweet potato flour uses for home cooks and the packaged food industry. If the technique were refined and commercialized, sweet potatoes could be used in more applications, including bakery applications, after being ground into flour. 

However, before sweet potato can be used as a common ingredient in baked goods, best practices for processing need to be established. Several studies have investigated specific parameters, including how sweet potatoes are dried and milled.

What has yet to be achieved before the American Chemical Society (ACS) study is determining how the different steps could interact to produce flours best suited for specific products.

Drying before frying
Several gluten-free options are either already available or in development, including those made from banana peels, almonds and various grains. Sweet potato is a strong contender as the hearty tuber is packed with antioxidants, has a slightly sweet flavor and is ideal for thickening or baking.

This study, published in ACS Food Science and Technology, aimed to evaluate the effect of drying temperature and grinding pattern on the physicochemical, hydration, thermal, and pasting properties of orange sweet potato flour (OSPF) and to define its potential application in functional food products.Sweet potatoes are rich in antioxidants and can be used as a thickener and in baking applications. 

The researchers set out to investigate how two drying temperatures and grinding processes affected the properties of orange sweet potato flour.

Air convection drying temperatures (50 and 80 °C) and grinding patterns (shear and consecutive shear–impact) were evaluated. The two factors and their interaction influenced hydration and pasting properties. Particle size and damaged starch content are significantly related to technological properties. 

Wheat flour is the most used flour and has been around since ancient times. Still, it does not cater to gluten-intolerant people or those with celiac disease since the gluten proteins in wheat flour cause stomach pain, nausea and – in extreme cases – even intestinal damage. 

Sampling the sweet potato
The research team prepared samples of orange sweet potatoes (Ipomoea batatas) dried at either 122 or 176 F and then ground them once or twice. They investigated many parameters for each sample, comparing them to store-bought sweet potato flour and traditional wheat. 

Grinding the sweet potato once damaged just enough of the starch to make it ideal for fermented products, regardless of the drying temperature.

Grinding twice further disrupted the starch’s crystallinity, producing thickening agents ideal for porridges or sauces. When baked into a loaf of bread, the high-temperature-dried, single-ground sample featured higher antioxidant capacity than the store-bought version and the wheat flour. 

The results indicated that drying at 80 °C and consecutive shear–impact grinding can produce thickening flours while drying at 50 or 80 °C and shear grinding can produce flours with water retention suitable for gluten-free bread-type products with good antioxidant capacity. Additional knowledge provided by these findings is the importance of the combination of drying temperature and grinding pattern in the technological properties of OSPF.

Edited by Inga de Jong