Valorization of Agro-Industrial Wastes by Ultrasound-Assisted Extraction as a Source of Proteins, Antioxidants and Cutin: A Cascade Approach

Abstract

The use of agro-industrial wastes to obtain compounds with a high added-value is increasing in the last few years in accordance with the circular economy concept. In this work, a cascade extraction approach was developed based on ultrasound-assisted extraction (UAE) for tomato, watermelon, and apple peel wastes. The protein and antioxidant compounds were obtained during the first extraction step (NaOH 3 wt.%, 98.6 W, 100% amplitude, 6.48 W/cm2, 6 min). The watermelon peels (WP) showed higher proteins and total phenolic contents (857 ± 1 mg BSA/g extract and 107.2 ± 0.2 mg GAE/100 g dm, respectively), whereas the highest antioxidant activity was obtained for apple peels (1559 ± 20 µmol TE/100 g dm, 1767 ± 5 µmol TE/100 g dm, and 902 ± 16 µmol TE/100 g dm for ABTS, FRAP and DPPH assays, respectively). The remaining residue obtained from the first extraction was subsequently extracted to obtain cutin (ethanol 40 wt.%, 58 W, 100% amplitude, 2 W/cm2, 17 min, 1/80 g/mL, pH 2.5). The morphological studies confirmed the great efficiency of UAE in damaging the vegetal cell walls. WP showed a higher non-hydrolysable cutin content (55 wt.% of the initial cutin). A different monomers’ profile was obtained for the cutin composition by GC-MS, with the cutin from tomato and apple peels being rich in polyhydroxy fatty acids whereas the cutin extracted from WP was mainly based on unsaturated fatty acids. All of the cutin samples showed an initial degradation temperature higher than 200 °C, presenting an excellent thermal stability. The strategy followed in this work has proved to be an effective valorization methodology with a high scaling-up potential for applications in the food, pharmaceutical, nutraceutical, cosmetics and biopolymer sectors.

Application of ultrasound technology for the effective management of waste from fruit and vegetable

“…After the first extraction, the remaining residues were subjected to cutin extraction at the following conditions (ethanol 40 wt%, 58 W, 100 % amplitude, 2 W/cm 2 , 17 min, 1/80 g/mL, pH 2.5). Watermelon showed the highest cutin level (55 %), while tomato and apple had 25 and 40 %, respectively [54] . The UAE was applied for 5-, 10-, and 15-min extraction time, amplitude 40, 70, and 100 % with pulse cycle 0.4, 0.7, and 1 s for polyphenolic compounds extraction from seed, pulp, and columella of soursop fruit.…”

“… [53] Tomato, watermelon,& apple peel wastes Proteins, Antioxidants, Cutin 98.6 W, amplitude 100 %, UI 6.48 W/cm 2 , 6 min Maximum proteins 857 ± 1 mg BSA/g extract, TPC 107.2 ± 0.2 mg GAE/100 g DM in watermelon peel, Highest ABTS 1559 ± 20 μmol TE/100 g dm, FRAP 1767 ± 5 μmol TE/100 g dm, DDPH 902 ± 16 μmol in apple peel, tomato 42 % cutin, watermelon 55 %, cutin, apple 40 % cutin. [54] Grapefruit peel Pectin UI 12.56 W/cm 2 , 66.71 °C, 27.95 min, 800 W, 20 kHz Yield 37.78 %. [55] Pomegranate peel Pectin 20 kHz, 130 W, 29 min, 62 °C, LS 1:17.52 g/mL Total yield 23.87 ± 0.28 %.…”

Emerging trends in the appliance of ultrasonic technology for valorization of agricultural residue into versatile products

“…Ultrasound treatment has shown superior owing to its advantages over conventional methods including being simple, adaptable, sustainable, effective, and fast. In addition, this method has also evidenced to be scalable to be adopted in industrial applications [74] , [75] .…”

Formulated hydroxy fatty acids from fruit pomaces reduce apple scab development caused by Venturia inaequalis through a dual mode of action

“…Tomato fruit is one of the most produced crops and concentrates a high amount of cutin (70% w/w) ( Osman et al., 1999 ), whose monomer composition is strikingly homogenous with about 80% by weight consisting of 9(10),16-dihydroxy hexadecanoic acid ( Benítez et al., 2018 ; Marc et al., 2021 ; Escórcio et al., 2022 ). Apple pomaces also contain a substantial amount of cutin (14% w/w) ( Mellinas et al., 2022 ), and could therefore constitute another industrial source of hydroxy fatty acids. Besides, tomato and apple cutin monomer compositions are different ( Kosma et al., 2010 ; Lara et al., 2014 ; Leide et al., 2018 ) which could impact their biological activity ( Schweizer et al., 1996 ; Escórcio et al., 2022 ).…”