Scaling-up effects on supercritical CO_2 extraction kinetics of pelletized tomato

摘要

Tomato is a natural source of carotenoids, mainly lycopene, that contribute colour (yellow-to-red) and functional properties (antioxidant) to foods. Supercritical CO_2 extraction is an interesting alternative to recover lycopene from tomato because CO_2 is highly selective and harmless, and leaves no traces in extracts or treated substrates. Because scale-up is important for process design purposes, we set the objective of quantifying the effect of a change in scale, from a one-pass, 50-cm~3 laboratory unit to a 4-dm~3 pilot plant with solvent recycling capabilities, on the extraction rate and yield of oleoresin from pelletized tomato using supercritical CO_2 as the solvent. Screening experiments in the laboratory unit were carried out at 40 or 60 °C and 30 or 50 MPa. Extraction appeared to be a diffusion-controlled process, with yields (percentage of total available oleoresin recovered) increasing more than twice with an increase in temperature from 40 to 60 °C, and increasing in excess of 5 times with an increase in pressure from 30 to 50 MPa. Highest oleoresin yield was 25.1% of all available oleoresin following 7-h extraction at 60 °C and 50 MPa, and unexpectedly, decreased to 17.6% in a 500-cm~3 pilot plant, and increased to 30.7% in 4-dm~3 pilot plant. Because experiments used different substrates, differences between the 500-cm~3 and 4-dm~3 plants were possible due to differences in initial moisture (18 versus 3.7%, respectively) and bulk density (550 versus 760 kg/m~3, respectively) between the substrates. Packing high-moisture pellets densely possible results in agglomeration of the substrate and undesirable channelling in the packed bed.