# Oil Press-Cakes and Meals Valorization through Circular Economy Approaches: A Review
## 5 Possible Ways to Capitalize the by-Products Obtained from the Oil Industry
### Extraction of Bioactive Compounds
#### Antioxidants  
Oil cakes/meals contains free, esterified or condensed form of phenolic acids, flavonoids and lignans that help in reducing oxidative stress and thus preventing various types of cancer. They can be extracted with solvent (it can be used organic solvents, alone or mixed together or non-toxic solvents such as water, but these need to be combined with other mild extraction techniques), high pressure, microwave, and supercritical fluid. Antioxidants extracted in this way can be used in the preparation of foods (beverages, energy bars, bakery, and extruded products) [22; 118]. The major antioxidants in oil cakes are presented in Table 3. The antioxidative activity in soybean cake/meal is due to isoflav and cinnamic acid derivative and for groundnut cake/meal, phenolics, caffe, and chlorogenic acids. Phenolic compounds are the principal antioxidants in rapeseed, coconut, sunflower, mustard, sesame and cotton cakes/meals [22]. Fermentation helps to improve the nutrient levels of oil cake, because during the process a microbial synthesis of biomolecules takes place. Following this idea, [PERSON] et al. [132] observed that in flaxseed oil cake fermented for 48 h with _Rhizopus oligosporus_ DSM 1964 and/or ATTC 6403 there was an increase of 13-85% in phenolic levels and a decrease in scavenging activity by 20-30%. The same results were obtained when peanut oil cake was fermented for 120 h with _Aspergillus auamori_[133]. Another treatment useful in enhancing antioxidant capacity involves the use of ultrasound. Maximum polyphenol content was obtained when the treatment time was 20 min and with the temperature at 70 \({}^{\circ}\)C. The high heat is able to break the bonding between the phenolic compounds and matrix, modifying the structure of plant membranes and causing lipoproteins coagulation. Furthermore, prolongation of exposure means that the ultrasonic wave divided the phenolic extract in longer periods [134]. Cold-pressed cake from walnut is a source of natural antioxidants. [PERSON] [135] extracted phenolic compound from walnut pressed cake. This extract was added in different concentrations(50, 100, and 200 mg/kg) to increase the oxidative stability of walnut oil. The highest result was obtained with the addition of 200 mg/Kg. When oilcake is added directly to oil (1:100) through ultrasonic maceration the oxidative stability decreases although the amount of total phenolic compounds increased. This may be caused by free fatty acids (created in sonification) with a pro-oxidative effect. The cake obtained from sesame oil contained bioactive compounds such as phytochemicals with numerous benefits (phenolic compounds, flavonoids, tocopherols, vitamins, pigments, steroids, carotenoids, and lignans) for health. Lignans such sesamin, sesamolin, sesamol, and sesaminol glucosides have the following effect: anticarcinogenic, antiproliferative, antioxidant, antimicrobial, anti-inflammatory, antidepressant, neuroprotective, and hypocholesterolem activities [136]. Sesame meal introduced in concentrations ranging from 5 to 200 ppm acts as a stabilizer for sunflower and soybean oil, by inhibiting double bond conjugation, thermal deterioration, and losses of polyunsaturated fatty acids. Furthermore, in high concentrations, the efficiency is equivalent to butylated hydroxy anisole and butylated hydroxy toluene. Products were introduced to an oven temperature of 70 \({}^{\circ}\)C for 72 h and subjected to oxidation in the dark, and a protective effect was observed during the initial and final steps. This activity is attributed to the phenolic compounds and their redox properties (extinguish singlet and triplet oxygen, decompose peroxides, adsorb, and neutralize free radicals) [61; 137]. [PERSON] [74] analyzed the potential of using defatted sesame cake to inhibit two digestive enzymes (\(\alpha\)-amylase, \(\alpha\)-glucosidase). The result exhibits a strong inhibitory potential for \(\alpha\)-amylase and mild for \(\alpha\)-glucosidase, due to the presence of phenolic compounds and flavonoids.