The breakfast cereal giant filed the international patent to cover the dry-mix of ingredients used and the extrusion processing parameters.
Nestlé said it overcame challenges relating to texture, shape and size as previous attempts to extrude sweet potatoes lacked crunch and were limited to larger, hollow pillow or potato crisp shapes.
“It would be beneficial to provide crispy sweet potato products with a size and shape suitable for being added as inclusions in a breakfast cereal, used as a crispy decoration or included in a cereal bar,” it wrote in its patent filing.
The problem, it said, was extruding a sweet potato product with sufficiently low density to achieve a crispy texture.
Achieving high expansion without burning
Sweet potatoes are not well-suited to frying, Nestlé said, because the product can become rubbery due to relatively high levels of reducing sugars. For this reason, it said temperatures need to be far higher, but this can cause the product to burn, spoiling the flavor.
These reducing sugars – that are more present in purple sweet potato varieties – can also be problematic during the extrusion process, Nestlé said, but added that it had determined the optimal processing parameters for sweet potatoes.
“The inventors surprisingly found that by maintaining the extruder barrel temperature below 150⁰C and the moisture content of the ingredients in the extruder below 20% they were able to obtain a high expansion of sweet potato materials and avoid burning, despite the high levels of sugar in sweet potato.”
The method resulted in low-density expanded sweet potato pieces with a crispy texture, it said.
In addition, Nestlé said the smaller size (between 15mm and 30mm dimension) enabled the product to be easily incorporated into a breakfast cereal. Shapes can also be adjusted by changing the die on the extruder, it said, which can make the food puffs “more fun to eat, especially for children”. Shape options can include circles, ovals, crescents, hearts, stars, cartoon characters of alphabet letters.
Sweet potatoes hit on health
All varieties of sweet potato are low in fat and cholesterol, Nestlé said, as well as a good source of vitamins C, B2 (riboflavin), B6 and E, dietary fiber, potassium, copper, manganese and iron. Purple potatoes also have a higher content of anthocyanins which have antioxidant effects, it said.
The company said the extruded sweet potato inclusions would be useful in the development of healthier cereals or cereal bars that appeal to weight-conscious consumers.
“The expanded low density structure fills the mouth, giving an impression of having plenty to eat, while in fact delivering only a few calories. This is beneficial for people who do not want to eat too much, for example those who do not wish to gain body weight.”
Nestlé added that the use of purple sweet potato in particular has further advantages as it is perceived by consumers, particularly Chinese consumers, to be good for digestion.
The dry basis mix can be made up of sweet potato flour, flakes or mixtures but should contain between 20 and 95% sweet potato, preferably 40-95%, Nestlé said, as a higher level ensures better nutritional value.
Nestlé said the puffs could also be used in confectionery, ice cream, bakery and pastry products.