According to Erhan, who leads the center's food and industrial oils research unit, the company needed a flavourless, food-grade adhesive that it could use for an assembly line operation that inserts drinking straws into beverage cans, cartons and bottles. Specifically, the company needed a strong, fast-curing adhesive that could bond the straws to a special holder that's lowered into the containers before they're filled and sealed.
At that point, the adhesive was supposed to dissolve in an even, controlled manner. Otherwise, the straws would remain fixed to the holders instead of rising freely out of the containers when consumers opened them.
Of the possible ingredients for the edible adhesive, Erhan his and colleagues chose sugar because of its availability, familiarity to consumers, and widespread use in beverages. Sugar alone isn't a strong adhesive, so the researchers mixed it with water and various organic acids. They then boiled the mixture until the sugar and acids bonded, or cross-linked, forming a dark-yellow adhesive. Over 10 different sugars were trialled, including sucrose, lactose and maltose, and 12 organic acids, including citric acid, malic acid and tartaric acid. Tests show the resulting adhesives bond to wood, metal, cloth, leather, glass, plastic, paper and other materials. Exposed to liquids, the adhesives dissolve and lose their grip in 20 to 60 minutes, depending on the sugar/acid combination used to make them.
ARS has patented the sugar-based edible adhesives on behalf of the US department of agriculture. Besides holding the straws, the adhesives have potential applications in binding food items, food and utensil packaging, and drug capsule layers.