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The in-line coupling of the pressurized liquid extraction with a solid-phase adsorbent and a UV–Vis detector for the simultaneous extraction and separation of bioactive compounds from yerba mate (PLE-SPE-UV) was carried out in two stages. In the first stage, water was used as a solvent, while in the second stage, ethanol was used. For the optimization of the method, different adsorbents (Sepra C18-E, Isolute C18-EC, and Strata-X C18), temperatures (40–80 °C), solvent flow-rate (1–3 mL/min), and pH (4.0 and 8.0) were evaluated. By using a UV–Vis detector on-line, it is possible to monitor the process in real-time. The developed method allowed obtaining similar or higher recoveries of all the compounds classes than other methods, such as ultrasound-assisted extraction, stirring, maceration, and pressurized liquid extraction alone, in addition to separating them into fractions. The developed method could be used as sample preparation for the analysis of different compounds classes from mate.

Highlights • Apple by-products are a source of phenolic compounds associated with bioactivities. • Apple processing industries generate by-products that could be better used. • This work provides an up-to-date literature overview on extraction techniques. • Gaps and future trends related to apple by-products are critically presented., Apple is one of the most consumed fruits worldwide and has recognized nutritional properties. Besides being consumed fresh, it is the raw material for several food products, whose production chain generates a considerable amount of by-products that currently have an underestimated use. These by-products are a rich source of chemical compounds with several potential applications. Therefore, new ambitious platforms focused on reusing are needed, targeting a process chain that achieves well-defined products and mitigates waste generation. This review covers an essential part of the apple by-products reuse chain. The apple composition regarding phenolic compounds subclasses is addressed and related to biological activities. The extraction processes to recover apple biocompounds have been revised, and an up-to-date overview of the scientific literature on conventional and emerging extraction techniques adopted over the past decade is reported. Finally, gaps and future trends related to the management of apple by-products are critically presented.

The comprehensive analysis of phenolic compounds from natural products comprises critical steps, including quantitative extraction, extract preparation, and chromatographic procedure. Performing these steps off-line requires a long time to obtain results, besides being laborious and more error-prone. This work discusses the concept and presents the details of assembling and validating a new system to comprehensively analyze phenolic compounds in natural products. The system is based on a bidimensional separation through the combination of pressurized liquid extraction with in-line solid-phase extraction coupled online with HPLC-PDA. The system proved to be able to perform a bidimensional separation to characterize the sample and ensure quantitative extraction of all detected components using the most appropriate extraction solvent gradient depending on the raw sample analyzed. The 1st dimension separation is achieved by PLE-SPE with a solvent gradient and differential interactions of extracted compounds with the adsorbent. The 2nd dimension presents the HPLC-PDA separation. The extraction/separation process can be monitored in real-time, and kinetic extraction curves for individual compounds can also be obtained to ensure quantitative extraction. Thus, the 2D PLE-SPE × HPLC-PDA may provide fast and precise comprehensive analyses of a large plethora of phenolic compounds, finding relevant applications in the chemical, food, pharmaceutical, and agricultural fields.

The objective of this work was the development of an on-line extraction/fractionation method based on the coupling of pressurized liquid extraction and solid-phase extraction for the separation of phenolic compounds from apple pomace. Several variables of the process were evaluated, including the amount of water of the first stage (0–120 mL), temperature (60–80 °C), solid-phase extraction adsorbent (Sepra, Isolute, Strata X and Oasis) and activation/elution solvent (methanol and ethanol). The best results were observed with the adsorbent Sepra. The temperature had a small effect on recovery, but significant differences were observed for phlorizin and a quercetin derivative. Results indicate that ethanol can be used to replace methanol as an activation, extraction/elution solvent. While using mostly green solvents (water, ethanol, and a small amount of methanol that could be reused), the developed method produced higher or similar yields of acids (2.85 ± 0.19 mg/g) and flavonoids (0.97 ± 0.11 mg/g) than conventional methods.

In this study it is proposed the introduction of an expansion gas in high pressure water to maximize the cavitation caused by the application of ultrasound to improve the extraction of phenolic compounds from pomegranate peel. Different combinations of ultrasound power (US-Pwr), expansion gas initial pressure (N2-Pi), system pressure (SP) and particle size of sample were evaluated using water as solvent. The use of US-Pwr and N2-Pi individually or combined improved the extraction process proving higher yields. SP was an important parameter affecting extraction yield, showing an inverse relation between its increase and extraction yield. Although higher yields were produced with samples with smaller particles, the combination of ultrasound and expansion gas had a positive effect on the process independently of particle size, promoting an increase of 20-26% in yield. These results suggest an enormous potential to be explored with the introduction of an expansion gas in pressurized liquids in processes assisted by ultrasound for the extraction of phenolic compounds from natural products using green solvents.

The objective of this work was to evaluate the on-line coupling of pressurized liquid extraction with an adsorbent for the simultaneous extraction and separation of flavonols of black tea, producing a concentrated extract that could be used as ingredient for the production of functional bakery products. After the evaluation of different adsorbents, extraction temperatures and solvents, a two-stage process was developed which was capable of producing three extracts: one with high concentration of gallic acid (78.97 ± 5.49 mg/L), another one with high concentration of caffeine (109.72 ± 3.15 mg/L) and a highly concentrated flavonol extract (322.0 ± 4.50 mg/L). The developed method uses greener solvents (water and ethanol) and is capable of producing higher flavonol (~50%) yields than conventional methods. The introduction of the flavonol extract in the dough can be used for the development of functional bakery since compounds were stable under processing conditions.

The combination of ultrasound and pressurized liquid extraction (UAPLE) was evaluated for the extraction of phenolic compounds from pomegranate peels (Punica granatum L.). The influence of several variables of the process on extraction yield, including solvent type (water, ethanol + water 30, 50 and 70% v:v), temperature (50–100 °C), ultrasound power (0–800 W at the generator, or 0–38.5 W at the tip of the probe), mean particle size (0.68 and 1.05 mm), and number of cycles (1–5), were analyzed according to the yield of 20 different phenolic compounds. The most suitable temperatures for the extraction of phenolic compounds using water were from 70 to 80 °C. In general, 100 °C was not adequate since the lowest extraction yields were observed. Results suggested that ultrasound had a greater impact on extraction yields using large particles and that intermediate ultrasound power (480–640 W at the generator, or 23.1–30.8 W at the tip of the probe) produced the best results. Using small particles (0.68 mm) or large particles (1.05 mm), extraction with ultrasound was 1 cycle faster. Ultrasound may have offset the negative effect of the use of large particles, however, did not increase the yield of phenolic compounds in any of the cases studied after five cycles. Additionally, the continuous clogging problems observed with small particles were avoided with the use of large particles, which combined with ultrasound allowed consistent operation with good intra and inter-day reproducibility (>95%). Using samples with large particle size, the best extraction conditions were achieved with water extraction solvent, 70 °C extraction temperature, ultrasound power at 480 W, and 3 cycles, yielding 61.72 ± 7.70 mg/g. UAPLE demonstrated to be a clean, efficient and a green alternative for the extraction of phenolic compounds from pomegranate peels. These findings indicate that UAPLE has a great potential to improve the extraction of bioactive compounds from natural products.