Green Extraction Processes for Complex Samples from Vegetable Matrices Coupled with On-Line Detection System: A Critical Review.

The detection of analytes in complex organic matrices requires a series of analytical steps to obtain a reliable analysis. Sample preparation can be the most time-consuming, prolonged, and error-prone step, reducing the reliability of the investigation. This review aims to discuss the advantages and limitations of extracting bioactive compounds, sample preparation techniques, automation, and coupling with on-line detection. This review also evaluates all publications on this topic through a longitudinal bibliometric analysis, applying statistical and mathematical methods to analyze the trends, perspectives, and hot topics of this research area. Furthermore, state-of-the-art green extraction techniques for complex samples from vegetable matrices coupled with analysis systems are presented. Among the extraction techniques for liquid samples, solid-phase extraction was the most common for combined systems in the scientific literature. In contrast, for on-line extraction systems applied for solid samples, supercritical fluid extraction, ultrasound-assisted extraction, microwave-assisted extraction, and pressurized liquid extraction were the most frequent green extraction techniques.

Pressurized liquid extraction coupled in-line with SPE and on-line with HPLC (PLE-SPExHPLC) for the recovery and purification of anthocyanins from SC-CO2 semi-defatted Açaí (Euterpe oleracea).

This study aimed to extract anthocyanins from dried and semi-defatted açaí pulp using green technologies based on the coupling of pressurized liquid extraction (PLE) with in-line purification through solid-phase extraction (SPE) and on-line analysis by high-performance liquid chromatography (HPLC). Critical parameters that affect the extraction efficiency and purification were investigated and optimized by response surface methodology (RSM). PLE was performed with acidified water at different pH (2.0, 4.5, and 7.0) and temperatures (40, 80, and 120 °C) at 15 MPa, 2 mL/min, and solvent-to-feed mass ratio equal to 40. SPE was optimized in a column packed with the adsorbent PoraPak™ Rxn. Different ethanol concentrations (50, 75, and 100 %) and temperatures (30, 40, and 50 °C) were evaluated for the anthocyanin's elution. The optimal conditions of the two experimental designs were determined by the RSM, firstly for PLE: 71 °C and pH 2; then using this PLE condition, the optimization of the SPE was obtained: 30 °C and 50 % ethanol. The developed PLE method provided similar anthocyanin yield to other techniques, and the coupling with SPE in-line produced an extract 5-fold more concentrated than PLE alone. Therefore, the system (PLE-SPE × HPLC-PDA) proved to be a powerful tool for monitoring the extraction process in real-time.

Semi-continuous flow-through hydrothermal pretreatment for the recovery of bioproducts from jabuticaba (Myrciaria cauliflora) agro-industrial by-product.

The valorization of the by-product of the agro-industrial processing of jabuticaba (Myrciaria cauliflora) was studied by hydrothermal pretreatment. Experiments were carried out in a semi-continuous flow-through process for 45 min, at 15 MPa, a water flow rate of 5 mL min-1, and at different temperatures (60 - 210 °C). The results demonstrate that fructose and glucose were the sugars with the highest concentration in all analyzed treatments. Arabinose and cellobiose were obtained only at higher temperatures (above 130 °C), demonstrating that they were released from the hydrolysis of polysaccharides. The highest cyanidin-3-glucoside yield (1.88 mg g-1) was achieved at 60 °C. The treatments at 135 and 210 °C promoted the degradation of cyanidin-3-glucoside, leading to yields lower than 0.05 mg g-1. At 60 °C, it was possible to recover 74.18 mg g-1 of glucose, 103.77 mg g-1 of fructose, 30.75 mg g-1 of citric acid, and 1.88 mg g-1 of cyanidin-3-glucoside, without the presence of furfural and 5-hydroxymethylfurfural. The results suggest that hydrothermal pretreatment is a promising eco-friendly technology to recover sugars, organic acids, and anthocyanins from jabuticaba by-products in a circular economy framework.

Recovery of sugars and amino acids from brewers' spent grains using subcritical water hydrolysis in a single and two sequential semi-continuous flow-through reactors.

This study evaluated the subcritical water hydrolysis (SWH) of brewer's spent grains (BSG) to obtain sugars and amino acids. The experimental conditions investigated the hydrolysis of BSG in a single flow-through reactor and in two sequential reactors operated in semi-continuous mode. The hydrolysis experiments were carried out for 120 min at 15 MPa, 5 mL water min-1, at different temperatures (80 - 180 °C) and using an S/F of 20 and 10 g solvent g-1 BSG, for the single and two sequential reactors, respectively. The highest monosaccharide yields were obtained at 180 °C in a single reactor (47.76 mg g-1 carbohydrates). With these operational conditions, the hydrolysate presented xylose (0.477 mg mL-1) and arabinose (1.039 mg mL-1) as main sugars, while low contents of furfural (310.7 µg mL-1), 5-hydroxymethylfurfural (<1 mg L-1), and organic acids (0.343 mg mL-1) were obtained. The yield of proteins at 180 °C in a process with a single reactor was 43.62 mg amino acids g-1 proteins, where tryptophan (215.55 µg mL-1), aspartic acid (123.35 µg mL-1), valine (64.35 µg mL-1), lysine (16.55 µg mL-1), and glycine (16.1 µg mL-1) were the main amino acids recovered in the hydrolysate. In conclusion, SWH pretreatment is a promising technology to recover bio-based compounds from BSG; however, further studies are still needed to increase the yield of bioproducts from lignocellulosic biomass to explore two sequential reactors.