A non-conventional method to extract D-limonene from waste lemon peels and comparison with traditional Soxhlet extraction

• High-pressure high-temperature extraction of D-limonene from lemon peels was tested.
• Effect of extraction time, temperature and matrix/solvent ratio on yield was studied.
• Influence of particle size distribution and pre-treatment was evaluated too.
• Three-way ANOVA, one-way ANOVA and response surface methodology were performed.
• Non-conventional HTPE was compared with traditional Soxhlet extraction.

Waste citrus peels can be used as source of several bioactive compounds. Among these, D-limonene is the major constituent in lemon essential oil and is of great interest in several fields. With the aim of optimizing D-limonene extraction from lemon peels after citrus processing, a non-conventional solvent extraction was studied. Hexane was used as solvent at high pressure and temperature and influence of extraction time, temperature–pressure and matrix/solvent ratio (M) on yield of D-limonene was analyzed by a statistical approach applied to a three-level full factorial design (33). The highest yield was reached when extraction was performed with M = 1:15 at 150 °C for 30 min (3.56%). Furthermore, a response surface methodology (RSM) was used and experimental results were fitted by a second-order polynomial equation. The effects of drying pre-treatment and particle size were also evaluated in this work. The effectiveness of this innovative method in extraction of citrus essential oils – and, in particular, of D-limonene – has been evaluated and compared to conventional Soxhlet extraction. High pressure – high temperature extraction (HPTE) of D-limonene from lemon peels was better than Soxhlet extraction even with low matrix/solvent extraction (1:4) in terms of energy saving (0.6 kW h vs 2.5 kW h), extraction time (30 min vs 4 h) and product yield (2.97% vs 0.95%).

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