title: Stability of anthocyanins in frozen and freeze-dried raspberries during long-term storage: in relation to glass transition.
abstract: Anthocyanins, natural plant pigments in the flavonoid group, are responsible for the red color and some of the nutraceutical benefits of raspberries. This study explores anthocyanin degradation in frozen and freeze-dried raspberries during storage in relation to glass transition temperatures. Frozen raspberries were stored at -80, -35, and -20 °C, while freeze-dried raspberries were stored at selected water activity (a(w)) values ranging from 0.05 to 0.75 at room temperature (23 °C) for more than a year. The characteristic glass transition temperatures (T'(g)) of raspberries with high water content and glass transition temperature (T(g)) of raspberries with small water content were determined using a differential scanning calorimeter. The pH differential method was used to determine the quantity of anthocyanins in frozen and freeze-dried raspberries at selected time intervals. The total anthocyanins in raspberries fluctuated during 378 d of storage at -20 and -35, and -80 °C. Anthocyanin degradation in freeze-dried raspberries ranged from 27% to 32% and 78% to 89% at a(w) values of 0.05 to 0.07 and 0.11 to 0.43, respectively, after 1 y. Anthocyanins were not detectable in freeze-dried raspberries stored at a(w) values of 0.53 to 0.75 after 270 d. First order and Weibull equations were used to fit the anthocyanin degradation in freeze-dried raspberries. The 1(st)-order rate constant (k) of anthocyanin degradation ranged from 0.003 to 0.023 days⁻¹ at the selected water activities. Significant anthocyanin degradation occurred in both the glassy and rubbery states of freeze-dried raspberries during long-term storage. However, the rate of anthocyanin degradation in freeze-dried raspberries stored in the glassy state was significantly smaller than the rate of anthocyanin degradation in the rubbery state.
authors.affiliation: Biological Systems Engineering Dept., Washington State Univ., P.O Box 646120, Pullman, WA 99164-6120, USA.
authors.forename: Roopesh M
authors.initials: RM
authors.lastname: Syamaladevi
authors.forename: Shyam S
authors.initials: SS
authors.lastname: Sablani
authors.forename: Juming
authors.initials: J
authors.lastname: Tang
authors.forename: Joseph
authors.initials: J
authors.lastname: Powers
authors.forename: Barry G
authors.initials: BG
authors.lastname: Swanson
mesh_terms: D000872:Anthocyanins / Q000032:analysis / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D061353:Food Storage; D057141:Food, Preserved / Q000032:analysis*; D005612:Freeze Drying; D005628:Frozen Foods / Q000032:analysis; D005638:Fruit / Q000737:chemistry*; D055951:Functional Food / Q000032:analysis*; D006207:Half-Life; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D010858:Pigmentation; D027824:Rosaceae / Q000737:chemistry*; D044366:Transition Temperature; D014861:Washington; D014867:Water / Q000032:analysis
chemical_list: D000872:Anthocyanins; D014867:Water