Development and optimization of a two-step co-extraction process for the recovery of pumpkin seed oil and in-situ enrichment with β-carotene compounds from pumpkin peel

Abstract

Vegetable oil industries are interested in producing healthy, high-quality, and cost-effective edible oils. This necessitates greener sources and effective oil enrichment strategies involving non-toxic and natural antioxidants. Thus, this study developed a novel one-pot vegetable oil natural pigmentation strategy to enable the in-situ cold press extraction and pigmentation of the vegetable oils while enhancing yields. The study co-pressed microwave pretreated pumpkin seeds and peels (PSP), 3 3 PSP: Pumpkin seeds and peel producing pumpkin seed oil (PSO) 4 4 PSO: Pumpkin seed oil which facilitated the co-extraction of lipophilic β-carotene compounds from the peels in a structured bed. The processing conditions were optimised for yields through Box-Behnken Design experiments, which varied seed-to-peel ratio (50 – 90 % w/w), microwave power (200 – 600 Watts), irradiation time (180 – 240 sec), and pressure (10 – 20 MPa). Optimal conditions (80 % w/w seeds, 5 5 % w/w seed: mass fraction of seeds (% w/w) in the seed-peel mixture (g) 600 Watts, 240 sec, 20 MPa) recovered 73.58 % oil and 5.48 ± 0.33 mg β-carotene /100 g biomass. PSP oils with natural β-carotene (0.75±0.02 mg β-carotene/100 g oil) pigmentation was more oxidative stable (based on unsaturated fatty acids content) at elevated temperatures (180 °C, 6 h), outperforming unpigmented seed oils (0.47±0.01 mg/100 g oil) despite the reduced yield. Therefore, microwave pretreatment and one-pot co-extraction have the potential to produce high-quality edible oil from vegetable residues with reduced processing steps. Thus, promoting material circularity in food processing. The utilization of a microwave-assisted mechanical processing scheme comprising a mixture of pumpkin seeds and peel provides a potential multi-product pathway for obtaining maximum value from pumpkin residues. This approach offers notable industrial benefits and applications: I. Microwave heating shows promising potential in enhancing the extractability of pumpkin seed oil and β-carotene compounds from the peel. Thus, rendering it a viable pre-treatment method for vegetable oil production and in-situ recovery of natural antioxidants. II. The layered structured-bed presents a co-extraction technique (for pumpkin seed oil and β-carotene) with fewer extraction steps compared to the multi-step, energy-intensive conventional oil enrichment processes. • A two-step process for pumpkin seed oil & β-carotene co-extraction in one pot was designed. • A structured bed of pumpkin seeds and peels is a novel technique for in-situ oil recovery and enrichment. • Extraction of β-carotene from pumpkin peel was facilitated by the co-extracted oil. • β-carotene improved the oxidation stability of pumpkin seed oil. • Microwave pre-treatment enhanced both oil and β-carotene extractability.