Physicochemical Properties, Antioxidant Activity, and Sorption Behavior of Bulgarian Quince Powder (Cydonia oblonga Mill.)

(1) Background: Exploring regional foods can help consumers expand their options for consuming diverse food products in various forms. This could enhance human health in local populations. (2) Methods: The present study evaluated the physicochemical composition of quince powder using standard analytical methods. Color parameters were determined using a PCE-CSM colorimeter equipped with a xenon lamp; the antioxidant activity via DPPH, ABTS, FRAP, and CUPRAC methods; the sorption capacity (at 10 °C, 25 °C, 40 °C and aw from 0.1 to 0.9) through the static gravimetric method; and monolayer moisture content (MMC) with the BET model. The isotherms were fitted via modified Chung–Pfost, Halsey, Henderson and Oswin models. (3) Results: The approximate physico-chemical composition of laboratory-produced quince powder (dried at 45 °C for 10 h) was: proteins—1.27 g, carbohydrates—75.80 g, fats—0.49 g, fibers—21.50 g, ash—2.31 g, and nutritional value—355.65 kcal. The color analysis indicated limited non-enzymatic browning. Antioxidant activity was confirmed by all four methods. The three-parametric Halsey model is recommended to describe the representative S-shaped isotherms from type II. The MMC for the adsorption process ranged from 14.41% d.b. to 7.09% d.b., and for the desorption process, it ranged from 13.11% d.b. to 7.80% d.b.; (4) Conclusions: This study presents a quince powder as a convenient form for both storage and consumption, emphasizing its value as a rich source of bioactive compounds and its suitability for home production and regular inclusion in a healthy daily diet.