The effect of spent coffee grounds from different brewing cycles on the quality and antioxidant properties of butter cookies

One way to use spent coffee grounds in restaurants and cafes is to develop recipes for cookies, muffins, and biscuits that include them. These products have a grainy structure. This article presents the results of using spent coffee grounds after two brewing cycles to reduce the pronounced graininess of butter cookies and the effect on the quality and antioxidant properties. Spent coffee grounds were obtained after the first (SCG1) and second (SCG2) brewing cycles in a capsule coffee machine, using Robusta coffee, Vietnam, medium roast (7 g per 100 ml of water), after which the spent coffee grounds were dried to a layer thickness of 0.5–0.7 cm using the convective method at a temperature of +60 °C. Dry spent coffee grounds were further ground into powder using an electric coffee grinder and added in quantities of 5; 10; 15% to the recipe for butter cookies. After the second brewing, SCG2 increased its bulk density, water- holding capacity, and oil-holding capacity, while its biologically active compound content and antioxidant activity decreased slightly. Cookie quality parameters depended on the amount and type of SCG. Increasing the amount of SCG did not affect cookie thickness or diameter, but they became darker and crumblier, containing TPC and TFC of 74.5–157.4 and 33.0–79.8 mg/100 g, respectively, exceeding the control by 3.5 times or more. Compared to SCG1, cookies with SCG2 were lighter and crumblier, with a slightly noticeable graininess. Cookies with 15% SCG had the highest antioxidant activity, while sensory acceptance revealed that cookie formulations with 5 and 10% SCG1 and SCG2 were more accepted by the panellists.