Optimization of vacuum-thermal concentration of grapefruit juice: energy consumption, processing time, and selected bioactive compounds

A vacuum-thermal concentrator was constructed to optimize and model the grapefruit juice concentration process by investigating vacuum pressure (5–25 kPa) and temperature (40–60°C). Grapefruit juice with an initial soluble solids content of 10.4 °Brix was concentrated to 65 °Brix. The optimal condition was identified at 10 kPa and 45°C, with a desirability value of 0.972. Experimental validation at this condition resulted in a lycopene content of 17.34 mg 100 g⁻¹, vitamin C content of 63.21 mg 100 g⁻¹, concentration time of 316.1 min, and energy consumption of 1.233 kWh. Quadratic models adequately described all responses, with R² values greater than 0.96. Based on the initial and final sample masses of 1070 and 171 g, respectively, the total retention of lycopene and vitamin C at the validated condition was 28.22% and 25.88%, respectively. These results identify a laboratory-scale operating condition that balances energy consumption, processing time, and measured lycopene and vitamin C concentrations within the investigated process range.