Valorization of apple pomace by-products from the juice processing industry using pressurized liquid technology

Abstract

Bagasse is a by-product of the juice processing industry with a high water content, high acidity, and rapid deterioration. Considering apple pomace, approximately 21 million tons are produced annually, rich in dietary fiber, vitamins, reducing sugars, and phenolic compounds. In this sense, conventional extraction (CE) and pressurized liquid extraction (PLE) were compared in terms of pectin yield, total phenolic compounds, and Ferric ion Reducing Antioxidant Power (FRAP) using a Box-Behnken factorial design considering the variables temperature, pressure, and Solvent/Feed (S/F) ratio. CE occurred with citric acid solution 6.5% (w/v) under stirring for 2 h. PLE occurred continuously with a flow rate of 5 mL min−1 with citric acid solution 6.5% (w/v) for 40 min. The highest pectin yield was 20.05% at 110 °C, 20 MPa, and S/F 10. Further optimized conditions led to a total phenolic compounds yield of 16.3 ± 0.3 mg GAE g−1 and FRAP of 137 ± 5 µmol TE g−1. Although pectin yield was higher for EC (25.27 ± 1.78%), total phenolic compounds content and FRAP were higher for PLE. High contents of glucose and fructose were found in all extracts. However, only high temperatures facilitated the hydrolysis and release of ellagic acid. Furthermore, a kinetic study demonstrated that 91.94% of total pectin was extracted with 11.30 min by PLE. Statistical analysis indicated that the effect of the linear and quadratic terms of the variable S/F ratio was significant for all responses evaluated. Therefore, the design approach efficiently obtained high pectin yields, providing information that allows expansion to pilot and industrial scales.