Phenolic compounds are well-known phytochemicals found in all plants. They consist of simple phenols, benzoic and cinnamic acid, coumarins, tannins, lignins, lignans and flavonoids. Substantial developments in research focused on the extraction, identification and quantification of phenolic compounds as medicinal and/or dietary molecules have occurred over the last 25 years. Organic solvent extraction is the main method used to extract phenolics. Chemical procedures are used to detect the presence of total phenolics, while spectrophotometric and chromatographic techniques are utilized to identify and quantify individual phenolic compounds. This review addresses the application of different methodologies utilized in the analysis of phenolic compounds in plant-based products, including recent technical developments in the quantification of phenolics.

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Techniques for analysis of plant phenolic compounds.

Flavonoids are major bioactive compounds known to be beneficial against many chronic diseases such as cancer, cardiovascular disorders, and inflammation. Food products obtained from plants are key sources of flavonoids for humans. However, during different food-processing steps, flavonoids are lost in remarkable amounts. Supplementation of flavonoids as a food additive will help in retaining the required health-beneficial amount of flavonoids in the diet, and extraction is an important step in the preparation of food additives. Microwave extraction is one of the most advanced extraction methods, which has the potential of playing a major role in flavonoid extraction and analytical quantification. The present paper reviews the potential application of microwave extraction for flavonoids and the advantage of microwave-assisted process over the other extraction processes generally employed for extraction.

Microwave-Assisted Extraction of Flavonoids: A Review

BACKGROUND: Sorghum possesses phenolic compounds that are health-promoting constituents of the grain. There are approximately40000sorghumaccessions, manyofwhichhavenotbeenevaluatedforthegrain’shealth-promotingpotential. Conventional methods for measuring total phenolic content, flavonoid content and 2,2-diphenyl-1-picrylhydrazyl (DPPH)scavenging capacity are time-consuming and labour-intensive, resulting in low overall throughput. The objective of this study was to develop a high-throughput screening assay for large sorghum sample sets to determineflavonoid and phenolic content and to modify existing DPPH and total phenolic assays. RESULTS: The 96-well assays exhibited a correlation of >0.9 with the conventional assays. The 96-well assays allowed for up to 64 samples to be run per day compared with 20‐24 samples (depending on the test) for the conventional methods. The 96-well assays had excellent accuracy (97.65‐106.16% recovery), precision (1.06‐8.28% coefficient of variation (CV)) and reproducibility (1.32‐2.13% CV inter-day and 1.36‐2.09% CV intra-day).

High‐throughput micro plate assays for screening flavonoid content and DPPH‐scavenging activity in sorghum bran and flour

Portulaca oleracea L., belonging to the Portulacaceae family, is commonly known as purslane in English and Ma-Chi-Xian in Chinese. It is a warm-climate, herbaceous succulent annual plant with a cosmopolitan distribution. It is eaten extensively as a potherb and added in soups and salads around the Mediterranean and tropical Asian countries and has been used as a folk medicine in many countries. Diverse compounds have been isolated from Portulaca oleracea, such as flavonoids, alkaloids, polysaccharides, fatty acids, terpenoids, sterols, proteins vitamins and minerals. Portulaca oleracea possesses a wide spectrum of pharmacological properties such as neuroprotective, antimicrobial, antidiabetic, antioxidant, anti-inflammatory, antiulcerogenic, and anticancer activities. However, few molecular mechanisms of action are known. This review provides a summary of phytochemistry and pharmacological effects of this plant.

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Portulaca oleracea L.: A Review of Phytochemistry and Pharmacological Effects

A review of traditional uses, phytochemistry and pharmacology of Portulaca oleracea L

Portulaca oleracea L. is a traditional edible and medicinal plant in China. Flavonoids are one of the main active ingredients of this plant. Five extraction technologies of flavonoids from P. oleracea L. were investigated and compared, including microwave-assisted extraction, ultrasonic extraction, reflux extraction, Soxhlet extraction, and marinated extraction. The results showed that microwave-assisted extraction was most suitable for the extraction of flavonoids from P. oleracea L. because of its high effect and short extraction time. The found optimum extraction conditions were that the ethanol concentration was 70% (v/v), solid–liquid ratio was 1:50, extracting temperature was 50 °C and irradiation time was 9 min. Quantification was performed by means of UV–Vis spectrophotometry with chromogenic system of NaNO2–Al (NO3)3–NaOH. Under the optimum conditions, the calibration curve for the analyte was linear with the correlation coefficients greater than 0.9999. The average recovery was 102.6%, and its RSD was 1.13%(n = 5). Eight types of P. oleracea L. according to different habits were investigated. The total content of flavonoids was 7.16, 7.10, 9.38, 6.82, 6.78, 11.36, 5.12, and 1.76 mg g−1, respectively.

Yuxuan Liu

Papers

Analysis of Flavonoids in Portulaca oleracea L. by UV–Vis Spectrophotometry with Comparative Study on Different Extraction Technologies