**Rachel Levy, Zoya Okun and Avi Shpigelman \***

Faculty of Biotechnology & Food Engineering, Russell Berrie Nanotechnology Institute, Technion, Israel Institute of Technology, Haifa 3200003, Israel; rachel447@campus.technion.ac.il (R.L.); zoya@bfe.technion.ac.il (Z.O.) **\*** Correspondence: avis@bfe.technion.ac.il; Tel.: +97-27-7887-1867

Received: 24 May 2019; Accepted: 10 June 2019; Published: 12 June 2019

**Abstract:** The loss of color pigment is an important quality factor of food products. This work aimed to systematically study, in purified model systems, the influence of anthocyanins' structure (by increasing the size of the conjugated sugar) and the presence of ascorbic acid on their stability and spectral properties during storage at two pH levels relevant to medium and high acid foods (6.5 and 4.5, respectively). Anthocyanins (cyanidin (Cy), cyanidin 3-O-β-glucoside (Cy3G) and cyanidin 3-O-β-rutinoside (Cy3R)) displayed first-order degradation rates, presenting higher stability in acidic medium and enhanced stability with increasing size of conjugated sugar. The addition of ascorbic acid resulted in significantly enhanced degradation. Changes in ultra violet visible (UV-VIS) spectral properties presented a decrease in typical color intensity and pointed towards formation of degradation products. Identification and kinetics of formation for cyanidin degradation products were obtained by high performance liquid chromatography system-mass spectrometry (HPLC-MS).

**Keywords:** anthocyanins; ascorbic acid; UV-Vis; HPLC-MS; kinetics; shelf life
