Extraction kinetics of pre-pelletized Jalapeٌo peppers with supercritical CO2

The aim of this work was to assess and model supercritical carbon dioxide (ScCO2) extraction kinetics of pre-pelletized Jalapeño peppers (Capsicum annuum L.). Pepper flakes were conditioned to low moisture, ground finely and pelletized at high pressure, and pellets were subsequently ground and size classified. The effects of average sample particle size (Dp=0.28–3.19 mm) and superficial solvent velocity (Us=0.14–2.62 mm s−1) were evaluated at 40 °C and 120 or 320 bar. Extraction rate increased as a result of a decrease in Dp. It also increased as a result of an increase in Us at 120 bar, but the effect was almost negligible at 320 bar. Integral extraction yields of capsicum oleoresin and capsaicinoids were ≈0.102 g g−1 and ≈240 mg kg−1, respectively, independent of extraction conditions. External mass transfer coefficients (kf) increased with Us, but this effect was less pronounced than commonly reported in the literature. Values of kf increased as Dp or process pressure decreased, due respectively to increments in specific area and improvements in transport properties. Internal mass transfer coefficients, on the other hand, were 5.3×10−8 m s−1 at 40 °C and 120 bar, and 34.7×10−8 m s−1 at 40 °C and 320 bar. Solutes were effectively liberated from the original matrix with our multistage pretreatment, so that the fraction of free solute did not depend on Dp (α=0.46). Pseudosolubilities for capsicum oleoresin in ScCO2 (≈2100 mg l−1 at 40 °C and 120 bar; ≈13,700 mg l−1 solute/CO2 at 40 °C and 320 bar) were of the same order of magnitude as corresponding true solubilities of capsaicin (5600 and 11,800 mg l−1, respectively). Estimated true solubilities of chlorophyll-a in ScCO2 (2 mg l−1 at 40 °C and 120 bar; 18 mg l−1 at 40 °C and 320 bar), on the other hand, were orders of magnitude smaller, which justifies a much slower extraction rate for green pigments than pungent compounds. Thus, oleoresin obtained after 4 h at 40 °C and 120 bar had a very attractive light yellow tinge.