Kinetics of thermal modifications in a grape seed extract

Area of Science:

• Food Chemistry
• Chemical Kinetics
• Nutraceutical Science

Background:

• Grape seed extract (GSE) is rich in bioactive compounds with health benefits.
• Thermal processing can alter the chemical composition and functional properties of GSE.
• Understanding the kinetics of thermal modification is crucial for optimizing processing and preserving quality.

Purpose of the Study:

• To investigate the thermal modification kinetics of a commercial grape seed extract (GSE).
• To quantify changes in antioxidant activity (AA) and specific phenolic compounds under varying temperatures and times.
• To determine the activation energy (Ea) for observed chemical transformations using kinetic models.

Main Methods:

• Exposed GSE to temperatures of 60, 90, and 120 °C for durations ranging from 5 to 60 minutes.
• Measured antioxidant activity (AA) and absorbance at 420 nm (A420) to assess browning.
• Quantified key compounds: (+)-catechin, (-)-epicatechin, procyanidins B1 and B2, and gallic acid.
• Applied modified Weibull and zero-/first-order models with Arrhenius equation to determine activation energy (Ea).

Main Results:

• Antioxidant activity (AA) remained statistically unchanged (p > 0.05) after thermal treatments.
• Browning (A420), procyanidins, and gallic acid levels increased with heat exposure.
• (+)-Catechin and (-)-epicatechin concentrations decreased significantly.
• The modified Weibull model proved more accurate for describing the kinetic changes.
• Activation energy (Ea) values varied for different components, with browning at 170 kJ/mol and (+)-catechin at 286 kJ/mol.

Conclusions:

• Grape seed extract exhibits thermal stability in terms of overall antioxidant activity.
• Specific phenolic compounds undergo degradation and transformation during heating, leading to browning.
• Kinetic modeling, particularly the Weibull model, effectively describes these thermal degradation and formation processes.
• The determined activation energies provide valuable data for predicting the stability of GSE under different thermal conditions.