Prior to dilution, the pulp had a pH of 3.18 ± 0.01, total solids content of 17.86 ± 0.1 g/100 g and soluble solids content (Brix) of 13.0 ± 0.5 g/100 g ( Mercali, Sarkis, Jaeschke, Tessaro, & Marczak, 2011). Standards of cyanidin, delphinidin, peonidin, petunidin, malvidin and pelargonidin
were purchased from Sigma Aldrich (St. Louis, USA). HPLC-grade solvents including acetonitrile, methanol, o-phosphoric acid, acetic acid, and hydrochloric acid were obtained from Vetec (Duque de Caxias, Brazil). Experiments were performed in a batch stirred INCB024360 order reactor with ohmic heating at 60 Hz. The ohmic heating apparatus consists of: a manual transformer (0–240 V); a data acquisition system that recorded temperature, current and voltage data (data logger); and an ohmic heating cell containing platinum electrodes and a water jacket. The cell was built in a Pyrex glass shape with a diameter of 8 cm. The set-up used is selleckchem shown in Fig. 1 where VT and A represent
the voltage and current transducers, respectively, and T the temperature sensors. To homogenize the pulp, the ohmic cell was placed above a magnetic stirrer, and to ensure a uniform temperature profile, the temperature was monitored in two different locations inside the ohmic cell, near the electrode and near the cell wall. For these measurements, stainless steel Pt-100 m coated with a nickel–phosphorous alloy were used. For the ohmic heating treatments, the pulp temperature was raised applying the voltage determined by the experimental design until a temperature of 90 °C was reached. The voltage was then lowered to maintain the pulp at this temperature for 2 min. This time/temperature condition was chosen because it is suggested in literature to inactivate anthocyanin-degrading enzymes over (Fennema, 2010). When the thermal treatment was complete, the product was rapidly cooled by passing cold water
(4 °C) through the jacket. The rotatable central composite design was applied to identify the influence of two variables, the applied voltage (V) and the total solids content of the blueberry pulp (g/100 g), on the percentage of anthocyanin degradation (response variable). The coded and uncoded independent variables used in the experimental design are listed in Table 1. Voltage ranges (X1) were selected based on the limitations of the ohmic heating system, and the range of the solids content (X2) was chosen based on the characteristics of the fruit and the stability of the diluted suspension. To determine the influence of the selected parameters on the response variable, experiments were planned according to the central composite design (CCD) using a 22 full factorial and star design with three central points, as shown in Table 2. For the ohmic heating experiments, the error between independent experiments was determined using the central points of the rotatable central composite design.