Effect of Subcritical Water on the Extraction of Bioactive Compounds from Carrot Leaves

Does Daucus carota L. leaf provide a high potential as a source of bioactive constituents: A case study about the influences of process/storage conditions

The current study focused on the valorization of carrot leaves, Daucus carota L. because of their high amount of ascorbic acid (AA), phenolic compounds, and the related antioxidant activity. In this study, the changes in carrot leaves caused by different drying techniques (freeze, vacuum, microwave-assisted infrared, oven) and different storage conditions (room temperature and refrigerator) were investigated. AA contents of fresh, dried, and stored carrot leaf samples were chromatographically determined. Additionally, analysis of TPA (total phenolic content), TAC (total antioxidant capacity), total chlorophyll, carotenoid, and color were carried out. Additionally, fresh leaves were analyzed to compare their results with the corresponding values of processed or stored samples. TPA, TAC, AA, total chlorophyll, and carotenoid values of the samples stored in the refrigerator were 889 ± 63 mg/100 g d.b., 504 mg/100 g d.b., 269 A.A./100 g d.b., 253 mg/100 g d.b., and 2497 mg/100 g d.b., respectively, while the values of the samples dried at room temperature 620 ± 35 mg/100 g d.b., 303 ± 15 mg/100 g d.b., 110 ± 21 mg A.A./100 g d.b., 44 ± 3 mg/100 g d.b., 641 ± 16 mg/100 g d.b., respectively. Consequently, fresh carrot leaves have a higher vitamin C content than many leafy vegetables and even its own family, parsley. Fresh samples stored at room temperature and in the refrigerator for 7 days provided high ascorbic acid retention. Dried leaves with the MW + IR combined system provided better protection than others in terms of bioactive components. However, OD treatment at 40°C provided better protection and was one step ahead in terms of AA content.

Efficient Recovery Strategy of Luteolin from Agricultural Waste Peanut Shells and Activity Evaluation of Its Functional Biomolecules

Peanut shells (PSs) generated from agricultural waste contain valuable compounds with bioactive properties such as anti-aging, antimicrobial, and antioxidant properties, making it desirable to recycle them as a sustainable resource. The aim of this study is to design an effective luteolin recovery process as the first step of an integrated biorefinery utilizing PSs as raw material. The major extraction variables and their ranges for luteolin recovery from PSs were determined (0-60 °C, 1-5 h, 0-100% MeOH concentration) and a predictive model was derived through a response surface methodology (RSM). Based on the predictive model, the equation determined for the maximal extraction of luteolin at 1 h was as follows: y = -1.8475x + 159.57, and the significant range of variables was as follows: 33.8 °C ≤ temperature (x) ≤ 48.5 °C and 70.0% ≤ MeOH concentration (y) ≤ 97.5%, respectively. High antioxidant and elastase inhibitory activities of PS extracts were confirmed, and these results support their potential to be used as functional materials. In addition, 39.2% of the solid residue after extraction was carbohydrate, which has potential as a carbon source for fermentation. This study provides a useful direction on an integrated biorefinery approach for sustainable agricultural waste valorization.

Subcritical Water Extraction of Natural Products

Subcritical water refers to high-temperature and high-pressure water. A unique and useful characteristic of subcritical water is that its polarity can be dramatically decreased with increasing temperature. Therefore, subcritical water can behave similar to methanol or ethanol. This makes subcritical water a green extraction fluid used for a variety of organic species. This review focuses on the subcritical water extraction (SBWE) of natural products. The extracted materials include medicinal and seasoning herbs, vegetables, fruits, food by-products, algae, shrubs, tea leaves, grains, and seeds. A wide range of natural products such as alkaloids, carbohydrates, essential oil, flavonoids, glycosides, lignans, organic acids, polyphenolics, quinones, steroids, and terpenes have been extracted using subcritical water. Various SBWE systems and their advantages and drawbacks have also been discussed in this review. In addition, we have reviewed co-solvents including ethanol, methanol, salts, and ionic liquids used to assist SBWE. Other extraction techniques such as microwave and sonication combined with SBWE are also covered in this review. It is very clear that temperature has the most significant effect on SBWE efficiency, and thus, it can be optimized. The optimal temperature ranges from 130 to 240 °C for extracting the natural products mentioned above. This review can help readers learn more about the SBWE technology, especially for readers with an interest in the field of green extraction of natural products. The major advantage of SBWE of natural products is that water is nontoxic, and therefore, it is more suitable for the extraction of herbs, vegetables, and fruits. Another advantage is that no liquid waste disposal is required after SBWE. Compared with organic solvents, subcritical water not only has advantages in ecology, economy, and safety, but also its density, ion product, and dielectric constant can be adjusted by temperature. These tunable properties allow subcritical water to carry out class selective extractions such as extracting polar compounds at lower temperatures and less polar ingredients at higher temperatures. SBWE can mimic the traditional herbal decoction for preparing herbal medication and with higher extraction efficiency. Since SBWE employs high-temperature and high-pressure, great caution is needed for safe operation. Another challenge for application of SBWE is potential organic degradation under high temperature conditions. We highly recommend conducting analyte stability checks when carrying out SBWE. For analytes with poor SBWE efficiency, a small number of organic modifiers such as ethanol, surfactants, or ionic liquids may be added.

Subcritical Water Extraction of Antioxidants from Curculigo latifolia Root

This study aims to extract antioxidant compounds from Curculigo latifolia root by subcritical water extraction (SWE). The influence of extraction temperature and time on the antioxidant activity of C. latifolia root extract was investigated in terms of extraction yield, total phenolic content (TPC), total flavonoid content (TFC), 2, 2′-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS), and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. The highest extraction yield (36.5%), TPC (92.55 mg GAE/g), TFC (13.26 mg RE/g), and antioxidant activities by ABTS (66.8 mg trolox equivalent/g sample) and DPPH (128.7 mg trolox equivalent/g sample) were detected at 180°C and 30 minutes extraction time. Based on the results, the optimum condition was selected at 180°C and 30 minutes of extraction. The sample was screened by using liquid chromatography-mass spectrometry (LC-MS) analysis where the phenolic compounds detected were structured based on their [M-H]-peak. The detected phenolic compounds were monobenzone, hydroquinone, phloridzin, pomiferin, mundulone, scandenin, and dimethyl caffeic acid. According to these findings, SWE is a promising, environmentally friendly, and efficient technology in the exploitation of natural products for the development of food and nutraceutical commodities.