Extraction of phenolic compounds from olive-waste cake using ultrasonic process

Exploring the Variability in Phenolic Compounds and Antioxidant Capacity in Olive Oil By-Products: A Path to Sustainable Valorization

The olive oil industry generates large volumes of by-products, creating notable environmental and economic concerns. Among these, olive cake (OC)-a primary by-product of olive oil extraction-stands out due to its high content of bioactive compounds and potential for value-added recycling. This study focused on characterizing six OC samples from the Trás-os-Montes and Alto Douro regions, collected at different processing times and mills. The samples included two derived from pressing (COC), two from two-phase centrifugation (TPOC; one partially pitted and one dehydrated), and two exhausted OC (EOC) samples. Fundamental analyses assessed total phenols, ortho-diphenols, flavonoids, antioxidant capacity, and tannin content. Results revealed significant variation (p < 0.05) in phenolic composition, namely ortho-diphenols and flavonoid levels among the samples. EOC 2 exhibited the highest concentrations (19.61, 21.82, and 20.12 mg CAT/g, respectively), while COC 2 had the lowest (5.08, 5.08, and 2.76 mg GA/g, respectively). This correlated with elevated antioxidant activity in EOC 2, as measured by FRAP, DPPH, and ABTS assays (129.98, 78.00, and 56.65 μmol Trolox/g). In contrast, COC 1 and COC 2 displayed the lowest antioxidant activities (32.61 μmol Trolox/g in FRAP and 17.24 and 18.98 μmol Trolox/g in DPPH). Tannin analysis showed the highest total tannin content in the dehydrated and pitted OC samples (250.31 and 240.89 mg CAT/100 g), with COC 2 showing the lowest (88.17 mg CAT/100 g). Condensed tannin content varied significantly, with EOC 2 presenting the highest level (328.17 mg CAT/100 g) and COC 2 the lowest one (20.56 mg CAT/100 g). Through HPLC-PDA-MS, 22 compounds were identified, with luteolin and verbascoside being particularly prevalent. This in-depth characterization supports the potential valorization of olive by-products, advancing sustainability and promoting a circular economy in the olive oil sector.

Impact of ultrasonication applications on color profile of foods

Food color is a feature that provides preliminary information about their preference or consumption. There are dominant pigments that determine the color of each food; the most important pigments are anthocyanins (red-purple color), chlorophylls (green color), carotenoids (yellow-orange color), and betalains (red color). These pigments can be easily affected by temperature, light, oxygen, or pH, thereby altering their properties. Therefore, while processing, it is necessary to prevent the deterioration of these pigments to the maximum possible extent. Ultrasonication, which is one of the emerging non-thermal methods, has multidimensional applications in the food industry. The present review collates information on various aspects of ultrasonication technology, its mechanism of action, influencing factors, and the competence of different ultrasonication applications (drying, irradiation, extraction, pasteurization, cooking, tempering, etc.) in preserving the color of food. It was concluded that ultrasonication treatments provide low-temperature processing at a short time, which positively influences the color properties. However, selecting optimum ultrasonic processing conditions (frequency, power, time, etc.) is crucial for each food to obtain the best color. The key challenges and limitations of the technique and possible future applications are also covered in the paper, serving as a touchstone for further research in this area.

Hairy Root Cultures as a Source of Polyphenolic Antioxidants: Flavonoids, Stilbenoids and Hydrolyzable Tannins

Due to their chemical properties and biological activity, antioxidants of plant origin have gained interest as valuable components of the human diet, potential food preservatives and additives, ingredients of cosmetics and factors implicated in tolerance mechanisms against environmental stress. Plant polyphenols are the most prominent and extensively studied, albeit not only group of, secondary plant (specialized) metabolites manifesting antioxidative activity. Because of their potential economic importance, the productive and renewable sources of the compounds are desirable. Over thirty years of research on hairy root cultures, as both producers of secondary plant metabolites and experimental systems to investigate plant biosynthetic pathways, brought about several spectacular achievements. The present review focuses on the Rhizobium rhizogenes-transformed roots that either may be efficient sources of plant-derived antioxidants or were used to elucidate some regulatory mechanisms responsible for the enhanced accumulation of antioxidants in plant tissues.

New insights on the utilization of ultrasonicated mustard seed cake: chemical composition and antagonistic potential for root-knot nematode, Meloidogyne javanica

This study focused, for the first time, on the effect of ultrasonic features on the extraction efficiency of secondary metabolites in mustard seed cake (MSC). The nematostatic potential of sonicated seed cake was examined against the second-stage juveniles (J2s) of root-knot nematode, Meloidogyne javanica. The results show that a 35 ppm (parts per million) concentration of a sonicated extract (SE) sample of MSC caused 65% J2s mortality at 18 h exposure period in vitro. It also significantly suppressed the root-knot index (RKI=0.94) in tomato roots. The lethal concentration values for SE were 51.76, 29.79, and 13.34 ppm, respectively, at 6, 12, and 18 h of the exposure period, and the lethal concentration values for the non-sonicated extract (NSE) sample were 116.95, 76.38, and 55.59 ppm, respectively, at similar exposure time. Sinapine and gluconapin were identified as the major compounds in ultrasonic-assisted MSC. Because of the high extraction efficiency of metabolites in the SE, all treatments of SE were shown to be antagonistic to J2s. Thus, this study of ultrasonication activity-based profiling of MSC may help generate target-based compounds at a scale relevant to the control of disease caused by nematodes in economic crops.

Exploitation of Agro-Industrial Waste as Potential Source of Bioactive Compounds for Aquaculture

The agroindustry generates a large amount of waste. In postharvest, food losses can reach up to 50%. This waste represents a source of contamination of soil, air, and bodies of water. This represents a problem for the environment as well as for public health. However, this waste is an important source of bioactive compounds, such as phenolic compounds, terpenes, and β-glucans, among others. Several biological activities have been attributed to these compounds; for example, antioxidant, antimicrobial, gut microbiota, and immune system modulators. These properties have been associated with improvements in health. Recently, the approach of using these bioactive compounds as food additives for aquaculture have been addressed, where it is sought that organisms, in addition to growing, preserve their health and become disease resistant. The exploitation of agro-industrial waste as a source of bioactive compounds for aquaculture has a triple objective-to provide added value to production chains, reduce pollution, and improve the well-being of organisms through nutrition. However, to make use of the waste, it is necessary to revalue them, mainly by determining their biological effects in aquaculture organisms. The composition of bioactive compounds of agro-industrial wastes, their biological properties, and their application in aquaculture will be addressed here.

Humoral and skin mucosal immune parameters, intestinal immune related genes expression and antioxidant defense in rainbow trout (Oncorhynchus mykiss) fed olive (Olea europea L.) waste

A six-week feeding trial was carried out to evaluate the effects of inclusion of dietary olive waste cake (OWC, 0, 0.5, 2.5 and 5 g kg^-1 diet) on performance, antioxidant condition and immune responses of rainbow trout (Oncorhynchus mykiss) (2.5 ± 0.1 g). Supplementing diet with 2.5 and 5 g OWC kg^-1 diet significantly enhanced serum and mucosal lysozyme activity in fish. Regarding mucosal immunity, fish fed 2.5 and 5 g OWC kg^-1 diets had higher skin mucus total Ig concentrations than other groups. In relation to antioxidant status, those in 2.5 g OWC kg^-1 and the control groups exhibited the highest and the least liver superoxide dismutase and glutathione peroxidase activities, respectively. Furthermore, the activity of liver glutathione S transferase in fish fed 2.5 and 5 g OWC kg^-1 diets was higher than the other treatments. In respect to gut cytokines gene expression, our findings demonstrated dietary OWC did not influence interlukines-1β and 10 genes expression, but relative expression of IL8 gene gradually up-regulated with increasing dietary OWC level. Moreover, fish fed 0.5 g OWC kg^-1 and the control diets had the highest and the lowest gut tumor necrosis factor-α gene expression values, respectively. The relative expression of transforming growth factor-β significantly down-regulated in gut of fish fed 2.5 and 5 g OWC kg^-1 diets compared to other groups. Supplementing diet with OWC pronouncedly improved growth and feed conversion ratio in fish compared to the control. Overall, the findings of this study suggested that inclusion of 2.5 g OWC kg^-1 diet can improve growth rate, oxidative stress status, humoral and skin mucosal immune responses in O. mykiss fingerlings and it can be considered as a functional feed additive for this species.

Recovering Metals from Aqueous Solutions by Biosorption onto Hydrolyzed Olive Cake

Olive cake obtained as a by-product from the olive oil industry has been evaluated as biosorbent of heavy metals from aqueous solutions in batch and continuous systems (fixed-bed columns). First, a complete study of effect of hydrothermal treatment with water on biosorption capacity of resulting solid was performed. Results showed that the values of biosorption capacity increased when the particle size of material decreased and the temperature of treatment increased. Then, hydrolyzed olive cake was treated by common chemicals (hot water, nitric acid, and sodium hydroxide) and the impact of chemical treatment was analyzed. The results were well reproduced by Langmuir and Freundlich isotherm models, getting maximum experimental biosorption capacities that changed between 42.34 mg/g obtained for the solid material modified by NaOH and 14.27 mg/g obtained for the solid material modified by nitric acid. Finally, laboratory tests in fixed-bed columns were performed with four different heavy metals and at three different inlet concentrations. The biosorption capacity increased from 2.83 mg/g (Cr), 4.51 mg/g (Cu), 12.30 mg/g (Pb), and 4.10 mg/g (Zn) to 3.08 mg/g (Cr), 5.17 mg/g (Cu), 13.21 mg/g (Pb), and 5.51 mg/g (Zn) when the concentration of metal ions increased, from 50 mg/L to 200 mg/L, respectively. Also, the experimental data obtained was successfully correlated with the Thomas, Yoon–Nelson, and dose–response models.