Mass transfer modeling of the antioxidant extraction of roselle flower (Hibiscus sabdariffa).

The aim of this study was to analyze the equilibrium and dynamic periods for mass transfer during the antioxidant solid-liquid extraction of dry roselle flower (Hibiscus sabdariffa). Extraction kinetics for total phenolic compounds (TPC), total flavonoids (TFL) and total antioxidant capacity (TAC) were obtained at different temperatures (50, 60, 70 or 80 °C) and solvent-to-product mass ratios (100:1, 200:1 or 300:1 g/g) under stirring (220-230 rpm). An analytical solution for unsteady-state mass transfer based on Fick's second law of diffusion was used to mathematically describe solid-liquid extraction curves and for the simultaneous estimation of diffusion coefficients and the final amount of extracted bioactive compounds, which were further related to experimental conditions by a second order model. The amount of extracted bioactive compounds at equilibrium were in the ranges of 30.8-89.8 g GAE/kg d.m. for TPC (0.154-0.373 g GAE/L extract), 40.0-131.6 g catechin/kg d.m. for TFC (0.269-0.559 g catechin/L extract) and 37.5-227.0 g trolox/kg d.m. for TAC (0.346-0.865 g trolox/L extract). On the other hand, diffusion coefficients for TPC, TFC and TAC were in the ranges of 0.72-2.66 × 10-11, 0.25-2.37 × 10-11 and 1.19-5.79 × 10-11 m2/s, respectively.

Use of microbial models to evaluate the effect of UV-C light and trans-cinnamaldehyde on the native microbial load of grapefruit (Citrus × paradisi) juice.

The aim of this research was to evaluate the storage stability (5 °C), and microbial modeling, of Rubi red grapefruit (Citrus × paradisi) juice treated with ultraviolet-C (UV-C) light (0, 10 and 20 min), alone or in combination with trans-cinnamaldehyde (trans-CAH) (0, 25 and 50 µg/mL). A 32 factorial design was used and data modeled with the Weibull, Modified Gompertz and Logistic models. A response surface model was used to evaluate the effect of modeling parameters for suggesting the optimum treatment conditions. Treated and some untreated juice lasted up to 9 days without physicochemical and microbial changes. At the higher combination of UV-C light and trans-CAH, the microbial load of grapefruit juice was maintained below 100 CFU/mL up to 15 days. For mesophiles, the three predictive models indicated that the parameters n and Nmax decreased and the parameters λ and tc increased as the combination of UV-C light and trans-CAH increased. The response surface modeling of the parameters obtained by the predictive models showed acceptable correlation for mesophiles (R2 = 0.815-0.977) but not for yeasts (R2 = 0.618-0.815). The three predictive models showed that, the concentration of trans-CAH had more effect on stopping the microbial growth than the UV-C light treatment.

Antioxidant characteristics of extracts of Hibiscus sabdariffa calyces encapsulated with mesquite gum.

This study compared the stability of extracts of H. sabdariffa calyces microencapsulated with different concentrations of mesquite gum during storage. Dry Roselle calyces were mixed with 50:50 (v/v) ethanol:water solution to obtain 18°Bx concentrate. This Roselle extract concentrate was mixed with purified mesquite gum (100:1-100:5 v/w). The Roselle extract concentrate-gum (RECG) was spray dried at inlet and outlet temperatures of 180 ± 2 and 104 ± 2.3 °C, respectively, at an air flow rate of 38 m3/h. Encapsulated Roselle powders (ERP) were analyzed for moisture content, total monomeric anthocyanins (differential pH), phenolic compounds (Folin and Ciocalteu method), antioxidant capacity (ABTS), and color parameters ([Formula: see text], and [Formula: see text]) after 5 weeks and 1 year of storage. Sorption properties (isotherms) and micrographs of powders were also obtained. The average yield of RECG powders was 15.27 ± 0.81 g/100 mL. During storage, ERP showed average values of phenolic compounds, antioxidant capacity, and anthocyanins of 3.43 ± 0.25 g gallic acid equivalents/100 g, 9.34 ± 1.4 g Trolox equivalents/100 g, and 318.7 ± 20.6 mg cyanidin-O-glycoside/100 g, respectively. Color parameters remained constant along the storage time.