Phytopharmaceuticals. Группа авторов

phenolic compounds [116].

      The extraction yields and the antioxidant and antiviral capacity of green seaweeds extracts significantly increased employing a mixture of glycosyl-hydrolases and exo-glucanases [117].

      UAE combined with EAE improved the extraction of polysaccharides from a freshwater bivalve mollusk, considered to display hypocholesterolemic, hepato-protective, anti-hypertensive properties [118].

      MAE extraction process is based on the effects of the microwave energy absorption by the food matrix. This results in a sudden temperature increase inside the material and high pressures within the vegetable cells, causing their expansion and rupture, releasing bioactive compounds in the extraction medium [119]. The efficiency depends on the conversion of microwave energy into heat by the water molecules. The frequencies allowed for industrial, scientific, and medical uses (ISM frequencies), being the most used the range from 0.915 to 2.45 GHz.

      MAE advantages over conventional methods include: extraction time reduction, environmental friendly, low cost and automation or online coupling to other analytical procedures. In the dynamic microwave assisted extraction (DMAE), the extraction performance improves, decreasing the possible degradation of labile compounds. This continuous, fast and automatic method was successfully employed for flavonoids extraction from different sources [120].

      Enzyme-based ultrasonic/microwave-assisted extraction, (EUMAE) improved the extraction of several natural products, such as orcinol glucoside (with antidepressant activity) from the rhizomes of herbals, more efficiently than conventional techniques [121].

      A very important aspect in UAE and MAE is the selection of the extraction solvent. Organic solvents increase the extraction yield, but they promote environmental risks [122]. In this regard, cyclodextrins (CDs) serve as green extracting agents since they allow the aqueous extraction of both polar and non-polar compounds from natural sources in a safely and in a non-contaminating technique. CDs are cyclic oligosaccharides, containing six, seven or eight glucose units that may host many types of compounds [123]. Molecular encapsulation of bioactive compounds in inclusion complexes, improves their aqueous solubility, stability and/or bioavailability [124] and facilitates their extraction from the natural matrices efficiently and eco-friendly [125].

      2.3.2 In Vitro Tests for Assessing Antioxidant and Antiglycant Activities

Once the bioactive sources have been extracted, the functionality of active extracts has to be measured quantitatively in order to rank candidate species. Much effort is devoted to the search of plants and fruits with antioxidant or antiglycant properties. Thus, a great part of the search efficiency lays in the availability of fast and efficient methods to evaluate the functionality of the extracts and also of their stability during storage.

      Given the worldwide trend towards the reduction of the use of synthetic additives in foods, and of the incorporation of health promoting components, there is a special interest in adding value to plant resources (undervalued subproducts or unexploided vegetable sources), from which extracts with antiglycant or antioxidant activity can be obtained for technological applications [126]. Besides, there is much interest in using natural antiglycating compounds for alleviating diabetic complications. Many studies have revealed a vital role for protein glycation in the pathogenesis of age-related diseases, such as diabetes, atherosclerosis, end-stage renal disease, and neurodegenerative diseases. Protein glycation is related to the reactions between reducing sugars, oxidized products from lipids or sugars, and protein amino groups, resulting in irreversible loss of protein functionality. Thus, antioxidants may also display antiglycant activities [126].

       2.3.2.1 Antioxidant Activity

      Besides the high complexity of vegetable matrices, it is important to consider the multifaceted and plurality of antioxidant mechanisms (hydrogen transfer or simple electron transfer or both) and the variety of assays conditions (pH, temperature, solvent, ionic strength). Moreover, the effectiveness of an antioxidant compound depends on many parameters: medium polarity, temperature, type of substrate and physical condition. As a result, there is no single antioxidant quantification universal test. Consequently, many authors recommend to determine antioxidant ability by several tests, varying the conditions of extraction and quantification as much as possible to estimate the antioxidant capacity in a better way [127].

      Some assays, such as DPPH and ABTS, extensively described, measure the ability of antioxidants to destroy the DPPH_• (diphenyl picryl hydrazyl) radical or the pre-formed radical monocation ABTS+ (2,2-azinobis 3-ethyl-benzothiazoline-6-sulfonic), respectively. The radicals scavenge is determined spectrophotometrically at 515 or 734 nm, respectively, after reaction with the test extract, and related to the amount of antiradical compounds [127–129].

      Phenolic compounds develop anti-radical antioxidant capacity through their hydroxyl groups, and it may correlate or not with total phenolic content [130].

Figure 2.6 shows the total phenols (TP) content and the antioxidant activity (AA) as Trolox (an analog of tocopherol used as standard) equivalents of infusions made with rose petals of different varieties or with two commercial teas, selected for their high antioxidant activity. Kardinal (K) and Gran Gala (GG) rose varieties presented the highest TP contents (P <0.05), even higher than green tea. King’s Ransom (KR) and Cristóbal Colón (CC) showed lower TP content similar to that of black tea (p >0.05). The high content of total phenols in red petal varieties is associated with a higher concentration of the phenolic compounds anthocyanins. On the other hand, the yellow and orange petals are generally linked to the content of non-phenolic antioxidant compounds as carotenoids. For example, marigold flower is a very good source of carotenoids, mainly lutein [131].

The infusions made with the GG and K rose petals presented greater AA (p <0.05) than Green and black teas. Bella Epoca (BE) and CC also showed higher values than Black Tea. KR was the only variety in which a lower AA (p <0.05) was observed than commercial teas [132].

Figure 2.6 Antioxidant activity (AA) and total phenols content (TP) of infusions of rose petals of different varieties and two commercial teas: black and green (results expressed in mg TROLOX acid/g solids for AA and mg chlorogenic acid/g solids for TP).

Figure 2.7a shows the correlation between the TP content and the AA of the evaluated petal infusions. When comparing all the samples, a low correlation was found between the evaluated parameters (R² = 0.5876), which improved when excluding the yellow and orange varieties (R² = 0.7543) [133], indicating that in yellow and orange roses the antioxidant activity is associated with non-phenolic compounds.

Figure 2.7 Correlation between the antiradical activity (%AA) and total polyphenol content (expressed as trolox/gallic acid equivalents) in rose petals and tea infusions (a), and in nine aqueous extracts of wild herbal species from Argentina (b).

      Infusions made with edible flowers have a nutritional advantage over teas because they do not contain caffeine, the latter representing a factor that promotes a transient increase in blood pressure [134]. In turn, infusions made with rose petals are of high AA compared to other medicinal plants.

      Nine herbal species native from Argentina were extracted in boiling