The nature of the amino acid was found to strongly influence the resulting properties of the amino acid, and perhaps allowing for tailored starches for different food applications, suggests the research in the Journal of Food Science.
Both lysine, a positively-charged amino acid, and lysine, aspartic acid, a negatively charged amino acid, decreased the viscosity of starch paste made from orange-fleshed sweet potatoes
"The decrease in pasting viscosity shows that this starch was modified into a thinner pasting starch. The decrease of both the pasting time and the minimum viscosity for this starch could translate into a faster cooking time and a product that is easier to cook," wrote the researchers from Louisiana State University.
The research appears to support the growing potential of sweet potato starch for use in various food applications as a thickener, an emulsion stabiliser, suspending agent, gelling agent, fibre source, mouthfeel improver, and fat replacer - all of which come under the umbrella of hydrocolloids. This market has grown significantly in the past 20 years in parallel to an increasingly complex food processing industry.
The food industry's most frequently used hydrocolloids include: agar, alginates, arabic, carrageenan, Carboxy Methyl Cellulose (CMC), gelatin, konjac flour, locust bean gum (LBG), Methyl Cellulose and hydroxypropyl Methyl Cellulose (MC/HPMC), microcrystalline cellulose (MCC), pectin, starch and Xanthan.
A potential new member of this team, if further research backs up the promising early studies, could be sweet potato powder, suggest the Louisiana State researchers.
Joan King and co-workers studied the effects of charged (aspartic acid and lysine) and neutral (leucine and methionine) amino acids on the pasting and thermal characteristics of Beauregard sweet potato starches
They report that starch from the orange-fleshed variety was easier to cook, had a lower potential for retrogradation, but was less stable during heating than starches from the white-fleshed variety.
Moreover, this decrease in retrogradation was enhanced by aspartic acid.
"This decrease in the retrogradation of the starch upon cooling may make the starch more suitable for use in some products, such as bakery goods, that could be negatively affected by staling," they said.
Increasing the stability of the starch during cooking was achieved by lysine, as evidenced by a decrease in the breakdown value of the orange-fleshed sweet potato starch.
The neutral amino acids were found to have no significant effects on the characteristics of the starch, compared to control.
"This study showed that pasting properties of sweet potato starches can be altered by the addition of amino acids," they concluded.
Cheap sourcing of a value-adding ingredient?
The researchers also indicate that cost may not be too much of a limiting factor for applying the starches to food.
"Approximately 600,000 tons of sweet potatoes are produced annually in the United States," said the researchers. "Up to 33 per cent of the raw potato brought into processing facilities can end up as waste… At present, there is not much use for this waste and it must be discarded, but much of this waste could be used to produce sweet potato starch in a very cost-effective manner and would also eliminate the unnecessary waste of so many sweet potato pieces."
Clean label drivers
The market for potato starch is growing. According to Market manager Paul Sheldrake from Dutch potato co-operative Avebe, one of the key benefits is that the potato starch-derived ingredient can be labelled as 'starch' rather than 'modified starch', meeting clean label requirements that are being put in place by manufacturers and retailers.
This, he told FoodNavigator.com recently, is an important consumer driver, as there is a general shift away from food additives and ingredients that are seen to be of artificial origin.
Source: Journal of Food Science
Published online ahead of print, 13 May 2008, doi: 10.1111/j.1750-3841.2008.00755.x
"Altering Pasting Characteristics of Sweet Potato Starches through Amino Acid Additives"
Authors: S. Lockwood, J.M. King, D.R. Labonte