Nutritional Composition of Processed Onion: S-Alk(en)yl-L-cysteine Sulfoxides, Organic Acids, Sugars, Minerals, and Vitamin C

The aim of this work was to study the effect of onion high-pressure processing (HPP) and HPP combined with freeze-drying and pulverization, focusing on onion nutritional attributes in terms of S-alk(en)yl-l-cysteine sulfoxides, organic acid, sugar, mineral, and vitamin C contents. Allium cepa L. var. cepa, 'Recas' was treated at T1 (200 MPa/25 A degrees C/5 min), T2 (400 MPa/25 A degrees C/5 min), and T3 (600 MPa/25 A degrees C/5 min). After treatment, high-pressure (HP)-treated (T1, T2, and T3) and untreated or non-HP-treated (T0) samples were frozen (diced onion). Subsequently, part of the diced samples was freeze-dried and pulverized (pulverized onion). In general, the freeze-drying process of fresh onion maintained the concentration of S-alk(en)yl-l-cysteine sulfoxides (ACSOs), organic acids, total sugars, total protein, and minerals, and significantly increased vitamin C concentration. Regarding HPP, the concentration of ACSOs, total sugars, and vitamin C of fresh onion was preserved at the three HPP assayed (200, 400, 600 MPa for 5 min at 25 A degrees C); however, for some organic acids and minerals, small decreases were found. In HP-treated onion (especially for treatment at 400 MPa), freeze-drying retained the levels of the major organic acids, total sugars, total protein, and minerals (Ca, Fe, Mg, K, Na, Zn, Mn, and Se), and increased the content of ascorbic acid and total vitamin C.