Analytical Characterization of Water-Soluble Constituents in Olive-Derived By-Products
Abstract
:1. Introduction
- OTP is the leftover biomass resulting from the pruning of olive trees during cultivation for an average production of 1.3 t/ha/y, and it is made up of approximately 30% leaves, 50% thin branches, and 20% olive wood [4]. It is a lignocellulosic material with a high content of carbohydrates (cellulose and hemicellulose, up to 55% of the total content) and thus holds great potential for use as a raw material within a biorefinery context for the production of biofuels and bioproducts. This by-product has attracted high research attention in recent years and has been investigated as a starting point for its conversion into bioethanol [5,6], cellulose nanofibers [7], xylitol, and antioxidants [4], or oligosaccharides with prebiotic potential [8], among many others;
- OL are originated in olive mills from cleaning operations of collected olives before entering the olive oil extraction process. They are typically disposed of through burning or used as animal feed; however, they are a great source of valuable organic substances like oleanoic acid, mannitol, and oleuropein [9]. The structural composition of OL is made up mostly of extractives (36%) and lignin (40%), with small contents of structural carbohydrates (6% cellulose and 4% hemicellulose) [10]. The high content of these extractable compounds in OL has focused the research on their extraction rather than on the use of OL as a substrate in biorefineries [11];
- OS are separated in olive mills or in olive pomace oil extracting industries before oil extraction and represent up to 15% of the total olive weight [9]. With a high calorific potential, OS is one of the most utilized residual biomasses for the self-generation of heat in agroindustries; up to 78% of all companies in Spain using solid biomass as fuel use OS [12]. Their structural composition consists of up to 50% sugar in the form of cellulose and hemicellulose and 25%–27% lignin [10]. This also grants them a potential use as a raw material in a biorefinery, as the research in this field focuses on its fractionation in order to maximize sugars liberation for further bioconversion [13];
- EOP is the leftover biomass obtained after the oil extraction of olive pomace, making up a 20% of the total dry mass of the pomace, which in turn constitutes 70%–80% of the total weight of the olive itself [14]. Pomace can be reused for further olive oil extraction by means of a solvent extraction process and a refining process and has been reported to be a source of high-value-added compounds such as phenols and polyphenols, vitamins, fatty acids, and other relevant antioxidants [10]. EOP is used as a solid biofuel for self-supply at small plants, though this application comes with high environmental impact due to the emission of hazardous particles and gases through combustion [14].
2. Materials and Methods
2.1. Olive By-Products Sample Preparation
2.2. Analytical Procedures for By-Products Chemical Composition and Extractives Quantification
2.3. Compositional Analysis of Aqueous Extracts
2.3.1. Sugars and Related Alditols
2.3.2. Carboxylic Acids
2.3.3. Inorganic Anions and Cations
2.3.4. Determination of Total Phenolic Content
2.3.5. Phenols by High-Performance Liquid Chromatography (HPLC)
2.3.6. Proteins
3. Results and Discussion
3.1. Structural Composition of Olive By-Products
3.2. Sugars and Alditols
3.3. Organic Acids
3.4. Inorganic Compounds
3.5. Phenolic Compounds
3.6. Overall Extractives Composition
4. Conclusions
Supplementary Materials
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Component | OTP (%dwb) | OL (%dwb) | OS (%dwb) | EOP (%dwb) |
---|---|---|---|---|
Total extractives | 27.8 ± 0.0 | 35.0 ± 0.0 | 6.3 ± 0.5 | 42.0 ± 1.2 |
Aqueous | 23.7 ± 0.0 | 21.9 ± 0.2 | 3.9 ± 0.4 | 37.5 ± 1.5 |
Organic | 4.1 ± 0.2 | 13.2 ± 0.6 | 2.4 ± 0.2 | 4.5 ± 0.4 |
Cellulose | 20.8 ± 0.9 | 9.7 ± 0.1 | 20.9 ± 0.22 | 10.9 ± 1.0 |
Hemicellulose | 14.5 ± 0.4 | 8.4 ± 0.1 | 26.0 ± 0.1 | 11.7 ± 0.6 |
Xylan | 9.2 ± 0.4 | 3.3 ± 0.1 | 23.5 ± 0.1 | 9.4 ± 0.4 |
Galactan | 1.9 ± 0.0 | 1.9 ± 0.0 | 1.2 ± 0.0 | 1.0 ± 0.1 |
Arabinan | 2.6 ± 0.1 | 2.8 ± 0.0 | 1.2 ± 0.0 | 1.0 ± 0.0 |
Mannan | 0.8 ± 0.1 | 0.4 ± 0.0 | 0.1 ± 0.0 | 0.3 ± 0.0 |
Lignin | 22.6 ± 0.5 | 25.7 ± 0.0 | 35.6 ± 0.6 | 23.1 ± 0.5 |
Acid-insoluble | 19.7 ± 0.5 | 23.2 ± 0.0 | 33.9 ± 0.4 | 21.5 ± 0.4 |
Acid-soluble | 2.9 ± 0.1 | 2.5 ± 0.0 | 1.7 ± 0.1 | 1.6 ± 0.1 |
Ash | 2.7 ± 0.2 | 9.1 ± 0.1 | 0.6 ± 0.0 | 9.0 ± 0.4 |
Acetyl groups | 3.3 ± 0.1 | 1.6 ± 0.0 | 5.9 ± 0.1 | 2.1 ± 0.0 |
Proteins | 3.4 ± 0.2 | 7.8 ± 0.0 | 0.7 ± 0.0 | 9.1 ± 0.2 |
Component in Aqueous Extractives | OTP (% w/w) | OL (% w/w) | OS (% w/w) | EOP (% w/w) |
---|---|---|---|---|
Sugars (monomers) | 20.8 | 8.8 | 3.6 | 19.1 |
Glucose | 13.4 ± 0.8 | 5.5 ± 0.5 | 0.8 ± 0.2 | 10.4 ± 1.2 |
Xylose | 0.5 ± 0.1 | 0.5 ± 0.2 | 0.8 ± 0.1 | 0.45 ± 0.0 |
Galactose | 0.5 ± 0.2 | 0.5 ± 0.1 | 0.3 ± 0.1 | 1.0 ± 0.2 |
Arabinose | 0.5 ± 0.1 | 0.6 ± 0.2 | 1.1 ± 0.2 | 0.5 ± 0.1 |
Mannose | 0.4 ± 0.2 | 0.3 ± 0.1 | 0.1 ± 0.1 | 1.6 ± 0.1 |
Fructose | 5.6 ± 0.5 | 1.4 ± 0.2 | 0.5 ± 0.0 | 5.2 ± 1.0 |
Sugars (oligomers determined as) | 20.1 | 16.8 | 16.2 | 14.1 |
Glucose | 15.6 ± 3.3 | 10.4 ± 1.5 | 1.3 ± 0.2 | 7.6 ± 1.8 |
Xylose | 0.2 ± 0.1 | 0.8 ± 0.4 | 10.1 ± 1.8 | 0.2 ± 0.1 |
Galactose | 1.8 ± 0.5 | 2.7 ± 0.7 | 1.9 ± 0.1 | 2.4 ± 0.4 |
Arabinose | 2.4 ± 0.6 | 2.5 ± 0.6 | 2.6 ± 0.3 | 3.6 ± 0.6 |
Mannose | n.d. | 0.3 ± 0.2 | 0.3 ± 0.2 | 0.3 ± 0.3 |
Alditols | ||||
Mannitol | 13.9 ± 0.4 | 4.4 ± 0.4 | 0.4 ± 0.2 | 9.6 ± 1.6 |
Component in Aqueous Extractive | OTP (% w/w) | OL (% w/w) | OS (% w/w) | EOP (% w/w) |
---|---|---|---|---|
Organic acids | 2.0 | 3.2 | 16.3 | 1.7 |
Acetic acid | 0.3 ± 0.1 | 1.0 ± 0.2 | 8.4 ± 0.5 | 1.0 ± 0.0 |
Other acids | 1.6 ± 0.1 | 2.2 ± 0.7 | 7.9 ± 1.2 | 0.7 ± 0.0 |
Component in Aqueous Extractives | OTP (% w/w) | OL (% w/w) | OS (% w/w) | EOP (% w/w) |
---|---|---|---|---|
Total Cations | 1.16 | 3.24 | 4.60 | 6.07 |
K+ | 0.71 ± 0.02 | 1.58 ± 0.07 | 2.96 ± 0.09 | 5.36 ± 0.10 |
Ca2+ | 0.12 ± 0.01 | 0.70 ± 0.01 | 0.22 ± 0.01 | 0.34 ± 0.01 |
Na+ | 0.25 ± 0.01 | 0.49 ± 0.01 | 0.65 ± 0.01 | 0.16 ± 0.00 |
Mg2+ | 0.08 ± 0.00 | 0.46 ± 0.01 | 0.09 ± 0.00 | 0.16 ± 0.01 |
NH4+ | n.d. | 0.01 ± 0.00 | 0.69 ± 0.01 | 0.04 ± 0.00 |
Total Anions | 0.62 | 0.95 | 0.39 | 0.93 |
Cl− | 0.08 ± 0.01 | 0.13 ± 0.01 | 0.32 ± 0.01 | 0.52 ± 0.03 |
NO3− | 0.01 ± 0.00 | n.d. | 0.01 ± 0.00 | n.d. |
SO42− | 0.53 ± 0.06 | 0.81 ± 0.02 | 0.06 ± 0.00 | 0.41 ± 0.02 |
Other Inorganic Compounds | 0.91 | 2.19 | 2.49 | 7.64 |
Component in Aqueous Extractives | OTP (% w/w) | OL (% w/w) | OS (% w/w) | EOP (% w/w) |
---|---|---|---|---|
Total Phenolic Alcohols | 2.02 | 1.33 | 1.58 | 1.31 |
Tyr | 0.06 ± 0.01 | n.d. | 1.10 ± 0.10 | 0.21 ± 0.08 |
OH-Tyr | 0.80 ± 0.11 | 0.28 ± 0.03 | 0.31 ± 0.01 | 1.10 ± 0.32 |
DHPG | 1.14 ± 0.03 | 1.04 ± 0.07 | n.d. | n.d. |
Vanillin | 0.01 ± 0.00 | 0.01 ± 0.00 | 0.17 ± 0.17 | n.d. |
Total Phenolic Acids | 0.01 | n.d. | 0.31 | n.d. |
Vanillic acid | n.d. | n.d. | 0.21 ± 0.01 | n.d. |
Syringaldehyde | 0.01 ± 0.00 | n.d. | 0.10 ± 0.01 | n.d. |
Other Phenols | 0.71 | 0.83 | 2.70 | 1.93 |
Total Phenols (HPLC) * | 2.74 | 2.17 | 4.59 | 3.24 |
Total Polyphenols (FC) | 14.9 ± 0.4 | 12.5 ± 0.2 | 15.6 ± 1.6 | 17.5 ± 0.9 |
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Doménech, P.; Duque, A.; Higueras, I.; Fernández, J.L.; Manzanares, P. Analytical Characterization of Water-Soluble Constituents in Olive-Derived By-Products. Foods 2021, 10, 1299. https://doi.org/10.3390/foods10061299
Doménech P, Duque A, Higueras I, Fernández JL, Manzanares P. Analytical Characterization of Water-Soluble Constituents in Olive-Derived By-Products. Foods. 2021; 10(6):1299. https://doi.org/10.3390/foods10061299
Chicago/Turabian StyleDoménech, Pablo, Aleta Duque, Isabel Higueras, José Luis Fernández, and Paloma Manzanares. 2021. "Analytical Characterization of Water-Soluble Constituents in Olive-Derived By-Products" Foods 10, no. 6: 1299. https://doi.org/10.3390/foods10061299