THERMAL STABILITY OF BLACK CARROT ANTHOCYANINS IN BLOND ORANGE JUICE

Abstract Blond orange juice was colored with black carrot concentrate as an alternative to blood orange juice. Thermal stability of anthocyanins from black carrots in orange juice was determined at 70, 80 and 90C. Anthocyanin degradation in colored blond orange juice followed to first-order reaction kinetics. As expected, the degradation rate was dependent on temperature, being faster at higher temperatures. Half-lives for anthocyanin degradation were 12.5, 6.3 and 3.1 h at 70, 80 and 90C, respectively. Between 70–90C, activation energy was 72.03 kJ mol^-1. Results showed that coloring blond orange juice with black carrot concentrate resulted in a much more stable product as compared with blood orange juice.     

STORAGE STABILITY OF STRAWBERRY JAM COLOR ENHANCED WITH BLACK CARROT JUICE CONCENTRATE

Black carrot juice concentrate was added to enhance the color of strawberry jams prepared from two locally grown cultivars, Osmanl? and Kara. Compared to other cultivars processed to jams, these two cultivars are lightly colored but very aromatic. Color and pigment stability of colored and noncolored (control) strawberry jams were studied during storage. The use of black carrot concentrate as a source of natural colorant stabilized the color of strawberry jam. The stabilization was more noticeable for jams prepared from Osmanl? cultivar. Monomeric anthocyanin degradation was fitted to a first‐order reaction model. Storage temperature had a strong influence on anthocyanin degradation. As the storage temperature increased, the stability of anthocyanins decreased significantly in both colored and noncolored jams. Parallel to decrease in monomeric anthocyanins, hue (h°) values of all jam samples increased throughout the storage. However, increase in h° values was much smaller in colored samples than in noncolored samples. High correlation was found between h° value and anthocyanin concentration at 22C (r = 0.910–0.978) and 37C (r = 0.931–0.981).     

Heat Inactivation Kinetics of Apple Polyphenoloxidase and Activation of its Latent Form

Heat inactivation kinetics of crude polyphenoloxidase (PPO) from six apple cultivars (Golden Delicious, Starking Delicious, Granny Smith; Gloster, Starcrimson and Amasya) were studied at three temperatures (68°, 73° and 78°C). PPO activity initially increased and then decreased with heat, following a first order kinetic model. Increase in activity indicated presence of latent PPO. Regression coefficients for the linear portions of inactivation curves were computed to determine inactivation parameters. Reaction data at 78°C revealed that PPO in Amasya was the least and Starking Delicious the most heat-stable. Rate constants for heat inactivation at 78°C ranged from 15.99–28.27. 10^?2 min^?1. Activation energies varied between 54.7–77.2 kcal. mol^?1 with z values of 7.1–10.0C°.PPO in apples was generally more heat-stable than PPO in most fruits.     

EFFECT OF HYDROGEN PEROXIDE ON SOUR CHERRY ANTHOCYANINS

Degradation of sour cherry anthocyanins was studied at different H₂O₂ concentrations (0.233‐11.63 mmol.L^?1) over the temperature range of 20‐55C. Degradation reaction fitted to a first order kinetic model progressed very rapidly even at low H₂O₂ concentrations. Thus, the t_1/2 values at 20C varied between 111‐20 h in the concentration range of 0.233‐2.327 mmol.L^?1 H₂O₂. The degradation of anthocyanins occurred at a faster rate with increasing temperature at 5.82 and 11.63 mmol.L^?1 H₂O₂ concentrations. Between 25‐55C, activation energies (E_a) were 9.53 and 10.60 kcal.mol^?1 for 5.82 and 11.63 mmol.L^?1 H₂O₂ concentrations, respectively. Higher E_a value at 11.63 mmol.L^?1 H₂O₂ concentration indicated that the effect of temperature increased at higher H₂O₂ concentrations. A quadratic relationship (y = ‐0.0031x²+ 0.0218x + 0.0008, R²= 0.996) was found between the degradation rates at 20C and H₂O₂ concentrations of 0.233‐2.327 mmol.L^?1. According to this equation, k of 1.12 × 10^?3 h^?1 and t_1/2 of 26 days at 20C may be expected at 0.5 ppm (0.0147 mmol.L^?1) H₂O₂ concentration, i.e., the max. allowable H₂O₂ level by FDA in the finished food packages.     

Degradation Kinetics of Anthocyanins in Sour Cherry Juice and Concentrate

The effects of temperature and soluble solids on degradation of anthocyanins in sour cherry concentrate were determined over temperature ranges (-18 to 37)°and 50 to 80°C. Anthocyanin degradation could be modeled as a first-order rate reaction, with rates of 33.97 × 10^minus;3. hr^minus;1 (15°CBrix), 59.19 × 10^minus;3. hr^minus;1 (45°CBrix) and 97.14 × 10^minus;3. hr^minus;1 (71°CBrix) at 80°C. Temperature dependence of reaction was described by the Arrhenius relationship. Activation energy for a solids content of 15-71°C Brix ranged from 16.37-19.14 kcal.mole^minus;1 with an average of 17.45 kcal.mole^minus;1