Enhanced extraction of flavanones hesperidin and narirutin from Citrus unshiu peel using subcritical water

Flavanones including hesperidin and narirutin constitute the majority of the flavonoids that occur naturally in citrus fruits. The main purpose of this study was to extract valuable natural flavanones from agricultural by-products such as citrus peels using subcritical water extraction (SWE). Thus, the application of SWE to extraction of flavanones hesperidin and narirutin from Citrus unshiu peel was evaluated, and the effect of key operating conditions was determined by varying the extraction temperature (110–200 °C) and time (5–20 min) under high pressure (100 ± 10 atm). The maximum yields of hesperidin (72 ± 5 mg/g C. unshiu peel) and narirutin (11.7 ± 0.8 mg/g C. unshiu peel) were obtained at an extraction temperature of 160 °C for an extraction time of only 10 min. These yields accounted for approximately 99% of the total amount of these flavanones in the original material. The SWE was compared with three conventional extraction methods in terms of the extraction time and recovery yields for hesperidin and narirutin. The hesperidin yield by SWE was more than 1.9-, 3.2-, and 34.2-fold higher than those obtained by extraction methods using ethanol, methanol, or hot water, respectively, and the narirutin yield was more than 1.2-, 1.5-, and 3.7-fold higher.     

Extraction of active ingredients from green tea (Camellia sinensis): Extraction efficiency of major catechins and caffeine

The effect of different extraction set-ups that influence the extraction efficiency of catechins and caffeine from green tea leaves (variety Fanning Belas, China) were studied using different aqueous and pure solvents (acetone, ethanol, methanol, acetonitrile, water), different temperatures (60, 80, 95 and 100 °C) and times (5–240 min). Raw extracts were analysed for contents of major catechins (EC, EGC, ECG, EGCG), caffeine, proanthocyanidins and flavonols (myricetin, caempherol, quercetin). Starting material was found to contain 191 g major catechins/kg material, 36 g caffeine/kg material and 5.2 g flavonols/kg material on a dry mass basis. The content of major catechins in green tea extracts varied from approximately 280–580 g/kg dry extract, with extraction efficiencies of major catechins varying from 61% to almost 100%. Content of caffeine in extract was in the range of 75 g/kg, where its extraction efficiency varied from 62% to 76%. Average extraction yield was 30% with exceptions when using pure acetone and acetonitrile, where extraction yield was about 3%. Contents of flavonols and proanthocyanidins were in the ranges 6–20 and 12–19 g/kg, respectively. Different extraction procedures with water were also investigated and optimal conditions determined: maximum achieved extraction efficiency of catechins with water was obtained at 80 °C after 20 min (97%) and at 95 °C after 10 min of extraction (90%). Degradation of catechins was observed at higher extraction temperatures and with prolonged extraction times. Using a lower ratio of solvent to material, extraction efficiencies were increased by applying a multi-step extraction procedure. Optimal extraction procedure was then performed using decaffeinated green tea leaves, which were obtained by high-pressure extraction with CO₂, when 98% of caffeine was selectively isolated without significant impact on valuable catechins.     

Solubility and solution thermodynamic properties of quercetin and quercetin dihydrate in subcritical water

Fundamental physicochemical data is required for the design and optimization of food engineering processes, such as extraction. Flavonoids are present in natural products such as grapes and have numerous health benefits particularly with respect to their reported antioxidant properties. Such flavonoid compounds can be extracted from these natural products using a variety of solvents, among them water. In this study, the aqueous solubilities of 3,3′,4′,5,7-pentahydroxyflavone (quercetin) and its dihydrate were measured at temperatures between 25 and 140 °C using a continuous flow type apparatus. The flow rate of subcritical water was studied at 0.1, 0.2 and 0.5 mL/min to study its effect on quercetin solubility and thermal degradation at temperatures greater than 100 °C. The aqueous solubility of anhydrous quercetin varied from 0.00215 g/L at 25 °C to 0.665 g/L at 140 °C and that of quercetin dihydrate varied from 0.00263 g/L at 25 °C to 1.49 g/L at 140 °C. The aqueous solubility of quercetin dihydrate was similar to that of anhydrous quercetin until 80 °C. At temperatures above or equal to 100 °C, the aqueous solubility of quercetin dihydrate was 1.5–2.5 times higher than that of anhydrous quercetin. The aqueous solubility of quercetin anhydrate and dihydrate at different temperatures was correlated using a modified Apelblat equation. The thermodynamic properties of the solution of quercetin and its dihydrate in water were than estimated from their solubility values. A flow rate effect on the aqueous solubility of quercetin and its dihydrate was not observed until above 100 °C where higher solvent (water) flow rates (>0.1 mL/min) were required to maintain a constant solubility in the saturation cell and with minimal thermal degradation of the solute (quercetin dihydrate). The study of its particle morphology under SEM indicated an aggregation of the crystals of quercetin dihydrate at subcritical water temperatures and at lower flow rates (<0.5 mL/min), thereby inhibiting stable solubility measurements and solvent flow through the saturation cell.     

A novel idea in food extraction field: Study of vacuum microwave hydrodiffusion technique for by-products extraction

Vacuum microwave hydrodiffusion and gravity (VMHG), a modified form of solvent free microwave hydrodiffusion and gravity (MHG) technique, was used for extraction of onion by-products. A detailed study concerning about optimisation of different parameters like irradiation power, degree of vacuum and extraction time was performed. Subsequently, the temperature difference in different parts of matrix and also in the reactor was evaluated both in case of MHG and VMHG. Extracts obtained by VMHG, MHG and also conventional solvent extraction method (CSE) were analyzed for quantification of flavonoids by HPLC, along with studying the distribution of flavonoids in different intervals of time at optimised conditions. Two different methods were selected for evaluating the antioxidant capacity of these extracts along with determination of their phenolic content by the Folin-Ciocalteu method: the reduction of the stable DPPH (2,2-diphenyl-1-picrylhydrazyl) radical and the inhibition of the AAPH-induced peroxidation of linoleic acid in SDS micelles. Reduction of pressure up to 0.7 bar at microwave power of 500 W helped to increase the antioxidant activity of onion extracts with 57% increase in total quercetin contents against those obtained at atmospheric pressure. VMHG proved itself an efficient and environment-friendly technique allowing the extraction of flavonols at lower reactor temperature (81 °C ± 1), with improved alterations of tissues observed by microscopic studies, from onion by-products just in 26 ± 1 min, in the absence of any solvent.     

Pressurised hot water extraction with on-line particle formation by supercritical fluid technology

In this work, an on-line process for pressurised hot water extraction (PHWE) of antioxidants from plants as well as drying of the extract in one step by particle formation based on the use of supercritical carbon dioxide (SC-CO₂) has been developed. This process has been called WEPO®, water extraction and particle formation on-line. With this process, dried extracts from onion with the same composition of quercetin derivatives as non-dried extracts have been obtained as a fine powder with spherical particles from 250 nm to 4 μm in diameter. The major compounds present in the extract were quercetin-3,4′-diglucoside, quercetin-4′-glucoside and quercetin. An auxiliary inert gas (hot N₂) was used to enhance the drying process. Parameters such as temperature (120 °C), SC-CO₂ and N₂ pressures (80 and 12.5 bar, respectively) and flow rate of SC-CO₂ (10 ml/min), have been settled by trial-and-error in order to achieve a fine and constant spray formation. Water content, size and morphology, antioxidant capacity and quercetin content of the particles were studied to evaluate the efficiency of the WEPO process. Results were compared with the ones from extracts obtained by continuous flow PHWE followed by freeze-drying. Results showed that both processes gave similar results in terms of antioxidant capacity, concentration of quercetin derivatives and water content, while only WEPO was able to produce defined spherical particles smaller than 4 μm.     

Onion high-pressure processing: Flavonol content and antioxidant activity

Onion flavonol content and antioxidant activity have been related to human health promoting effects. Quercetin and quercetin glucosides (quercetin-4′-glucoside and quercetin-3,4′-diglucoside) have been reported the main onion flavonols in recent literature. Impact of combined treatments of high-pressure processing (HPP) and temperature on onion nutritional attributes has been scarcely studied.Our study aimed to investigate the impact of HPP technology combined with temperature on onion (Allium cepa L. var. cepa, ‘Grano de Oro’) total phenol content, flavonol content, and antioxidant capacity. The experimental design comprised a response surface methodology according to a central composite face-centred design. The variable ranges were 100-400 MPa (pressure) and 5-50 °C (temperature), time was set up constant to 5 min.Response surfaces of onion total quercetin, quercetin-4′-glucoside, and quercetin-3,4′-diglucoside content showed a similar pattern. The application of low temperature (5 °C) combined with pressures of 100 and 400 MPa triggered to a better extraction of these flavonols among the treatments analysed. Response surface of the EC₅₀ antioxidant parameter as a function of pressure and temperature showed a clear trend towards an increase in onion antioxidant activity when applying pressures from 100 to 400 MPa. Four hundred megapascals/5 °C-processed onion showed an approximately 33% higher quercetin-4′-glucoside content compared with the untreated onion, and maintained the antioxidant activity of the untreated onion.     

Aqueous extraction of anthocyanins from Hibiscus sabdariffa: Experimental kinetics and modeling

Solid-liquid extraction of anthocyanins from calyces of Hibiscus sabdariffa L. was studied to evaluate the influence of the operating parameters. Solid-to-solvent ratio and particle size had the main impact on anthocyanin extraction efficiency. Maximum yield of anthocyanins (88%) was obtained at 25 °C with the highest solid-to-solvent ratio (1/25). The decrease in the particle size of the calyces from 2 cm to 150 μm drastically reduced the extraction time. The increase of temperature reduced the extraction time by increasing the diffusion coefficient (3.9 × 10⁻¹¹-1.35 × 10⁻¹⁰ m² s⁻¹ between 25 and 90 °C) but did not modify the extraction yield. A simple extraction model that integrated anthocyanin thermo-degradation kinetic was proposed. A good agreement between the predicted results of the models and experimental data was demonstrated. From a solid-to-solvent ratio of 1/5, an extraction yield of 63% and an anthocyanin concentration of 0.3 g L⁻¹ could be obtained in less than 10 min.     

Laws of flaxseed mucilage extraction

This study examined the application of few-stages aqueous extraction of mucilage from whole flaxseed. Key processing conditions included temperature (40-100 °C), duration (0-60 min), seed to water ratio (1 to 5-30) and mixer rotational speed (0-240 revolutions per minute). It was found, that mucilage extraction from flaxseed is appropriate to carry out without swelling. The maximum yield of flaxseed mucilage was obtained at 80 ± 2 °C with seed to water ratio of 1 to 25. The equation, which described equilibrium solid yield during the extraction depending on the phases’ ratio and the temperature, was found. The equation of solid yield depending on duration and mixer rotational speed under the temperature of 80 ± 2 °C and the seed to water ratio of 1 to 25 was determined. It was showed, that the use of stirring is not expedient for the intensifying the process. The rational duration of extraction under the selected parameters was 30 ± 1 min. To increase the solid content in the extract the few-stages extraction was applied. The three-stage countercurrent extraction of flaxseed mucilage from whole seeds under the temperature of 80 ± 2 °C, the seed to water ratio of 1 to 25, the duration of each stage of 30 ± 1 min was established to receive flaxseed mucilage extract with content of solids from 0.70 to 0.72%, i.e. to extract from 98.3 to 99.1% of mucilage from flaxseed.     

Extraction and deglycosylation of flavonoids from sumac fruits using steam explosion

The effects of steam explosion on the extraction and conversion of flavonoids from sumac fruits were studied. Steam explosion caused the reduction of particle size and led to the formation of large fissures and micropores on the sumac fruit coat. However, there was little change in total flavonoid content. A study of the process kinetics showed that the flavonoid yield of sumac fruits steam-exploded at 200 °C for 5 min reached the maximum of 19.65 mg/g dry weight at 20 min, which was about 8-fold higher than that of the raw sample. In addition, quercitrin (quercetin-3-O-rhamnoside), the dominant flavonoid in sumac fruits, was deglycosylated and converted into quercetin by steam explosion. The conversion ratio was 84.51% under the steam explosion condition of 200 °C for 5 min. It can be concluded that steam explosion is a promising process for application in flavonoid extraction and conversion in the food industry.     

Response surface methodology for protein extraction optimization of red pepper seed (Capsicum frutescens)

Response surface methodology was used to determine optimum conditions for extraction of protein from red pepper seed meal. A central composite design including independent variables such as temperature (30, 35, 40, 45 and 50 °C), pH (7.0, 7.5, 8.0, 8.5 and 9.0), extraction time (20, 30, 40, 50 and 60 min) and solvent/meal ratio (10:1, 15:1, 20:1, 25:1 and 30:1 v/w) was used. Selected response (dependent variable) which evaluates the extraction process was protein yield and the second-order model obtained for protein yield revealed coefficient of determination of 96.7%. Protein yield was primarily affected by pH and solvent/meal ratio. Maximum yield was obtained when temperature, pH, mixing time and solvent/meal ratio were 31 °C, 8.8, 20 min, 21:1 (v/w), respectively. These conditions resulted in protein yield of 12.24 g of soluble protein from extract/100 g defatted red pepper seed flour. The adequacy of the model was confirmed by extracting the protein under optimum values given by the model. These results help in designing the process of optimal protein extraction from red pepper seeds.     

Extraction optimization of watermelon seed protein using response surface methodology

Extraction conditions for maximum protein recovery from watermelon (Citrullus vulgaris Cv Sugar baby) seed meal were investigated using response surface methodology. A central composite design with four independent variables: temperature (40, 45, 50, 55 and 60 °C); NaOH concentration (0.03, 0.06, 0.09, 0.12 and 0.15 g/L); extraction time (5, 10, 15, 20 and 25 min) and solvent/meal ratio (30:1, 40:1, 50:1, 60:1 and 70:1, v/w) was used to study the response variable (protein yield). The experimental values of protein yield ranged between 72.03 and 81.52 g/100 g seed meal. A second-degree equation for independent and response variables was computed and used to create the contour plots graphs. The predicted values obtained for protein yield revealed that coefficient of determination and standard error was 0.80 and 0.906, respectively. Optimum protein extraction was obtained with 0.12 g/L alkali concentration, 15 min extraction time and 70:1 (v/w) solvent/meal ratio at 50 °C. Confirmatory studies revealed that the protein yield under optimum conditions was 80.71 g/100 g seed meal.     

Optimisation of aqueous extraction of gum from durian (Durio zibethinus) seed: A potential, low cost source of hydrocolloid

The main goal of the present study was to investigate the effect of aqueous extraction conditions on the extraction yield and physicochemical properties of the durian seed gum. The studied aqueous extraction variables were water/seed (W/S) ratio (20:1-60:1, w/w), temperature (25.0-85.0 °C), and pH (4.0-10.0). The results indicated that the aqueous extraction variables exhibited the least significant (p < 0.05) effect on oil-holding capacity (OHC). Conversely, they had the most significant (p < 0.05) effect on the span and extraction yield. The current study revealed that the interaction effect of aqueous extraction variables showed the least significant (p < 0.05) effect on the solubility and OHC of durian seed gum. The optimum extraction condition led to the production of durian seed gum with a relatively high extraction yield (56.4%), solubility (27.9%), volume-weighted mean (98.7 μm), span (3.8), water-holding capacity (WHC) (270.6 g water/100 g gum), and OHC (146.5 g oil/100 g gum).     

响应曲面法优化亚临界水提取葡萄籽原花青素的工艺研究

采用自行设计的适合工业化应用的2L 亚临界水提取装置对葡萄籽中原花青素的亚临界水提取工艺进行优化,并与其他提取方法进行对比。结果表明：亚临界水提取原花青素的最佳工艺参数为提取温度151℃、提取时间21min 和提取压力12MPa,在此条件下,原花青素得率为3.88%;与传统索氏提取法和乙醇回流提取法相比,亚临界水提取法具有提取时间短、效率高等优点;所设计的2L 亚临界水提取装置自动化程度高、操作简便。     

Quercetin content in some food and herbal samples

Quercetin is a typical flavonoid ubiquitously present in vegetables and fruits, and its antioxidant effect is implied to be helpful for human health. The efficiency of extraction process and acidic hydrolysis parameters for HPLC analysis of quercetin present in glycosides and aglycone forms was investigated. Hydrolysis for 5 min in the presence of 2.8 M HCl as well as for 10 min with 1.1 M HCl efficiently released quercetin from rutin. The method developed in this study was applied for quantitative determination of quercetin in some food (onion, apple) and herbal (Hypericum perforatum and Sambucus nigra) products.     

Chia seeds: Microstructure, mucilage extraction and hydration

Microstructural features of the chia seeds (Salvia hispanica L.) were studied by light and scanning electron microscopy. The study reports the effect of temperature (4-80 °C), pH (4-8) and seed:water ratio (1:20 and 1:40) on extraction of the mucilage of chia seeds and the effect of temperature (20-80 °C), pH (3-9) and ionic strength (0-1%) on hydration of the extracted mucilage. The mucilage was localized in cellular structures in the first three layers of the seed coat and upon full hydration filaments (mucilage fibers) became apparent and conformed to a transparent “capsule” attached to the seed. During extraction, temperature and seed:water ratio were found to have a significant effect on yield. Hydration of the extracted mucilage was significantly increased at high pH values, and was higher when salt concentration decreased, being maximal when the temperature reached values close to 80 °C.     

Enzymatic water extraction of taxifolin from wood sawdust of Larix gmelini (Rupr.) Rupr. and evaluation of its antioxidant activity

An enzyme incubation–water extraction (EI–WE) method was developed and optimised for the extraction of the natural antioxidant taxifolin and of the total flavonoids from wood sawdust of Larixgmelini (Rupr.) Rupr. A factorial design and a central composite design approach were used for method optimisation. Optimal conditions were 0.5 mg/ml cellulase and 0.5 mg/ml pectinase, a pH of 5.0, a temperature of 32 °C and 18 h incubation time. The flavonoids and taxifolin were extracted in hot water at 50 °C for 30 min, with a solid to liquid ratio of 1:20. Under optimised conditions, the yields of taxifolin and total flavonoids increased from 1.06 ± 0.08 to 1.35 ± 0.04 mg/g and 4.13 ± 0.17 to 4.96 ± 0.29 mg/g, respectively. DPPH and BHT assays revealed that the EI–WE samples had 1.8- and 1.68-fold higher antioxidant activities than the controls. SEM results revealed the structural disruption of wood sawdust with enzyme incubation.     

The effect of microwave assisted extraction on the isolation of anthocyanins and phenolic acids from sour cherry Marasca (Prunus cerasus var. Marasca)

The aim of this study was to evaluate the influence of microwave assisted extraction on the isolation of anthocyanins and phenolic acids from sour cherry Marasca. A general factorial design was used to study the effect of temperature (from 50 to 70 °C), irradiation time (5–12 min) and microwave power (350–500 W) on individual, total anthocyanins and individual and total phenolic acids. Optimal microwave assisted extraction conditions differed for anthocyanins and phenolic acids, especially in terms of temperature and irradiation time, so lower temperature (60 °C) and shorter time (6–9 min) was more convenient for anthocyanins extraction, while phenolic acids gave higher extraction yield at higher temperatures (70 °C) and longer irradiation time (10 min). The optimal microwave power did not differ significantly for studied compounds, ranging about 400 W. Compared to conventional extraction, microwave assisted one showed higher efficiency for all studied compounds.     

Flavonol glucosides in Allium species: A comparative study by means of HPLC–DAD–ESI-MS–MS

Cultivars and consumption typologies of some Allium species can significantly vary from a chemical point of view and even small differences can be important for their characterization and differentiation. Bulbs of three varieties and four consumption typologies of onion (Allium cepa L.) and two varieties of shallot (Allium ascalonicum Hort.) were subjected to HPLC–DAD–ESI-MS–MS analysis. Seven flavonol glucosides were identified in all the samples, two of which, quercetin 3,4′-diglucoside and quercetin 4′-glucoside, represent about the 90% of the overall contents. Cultivars and consumption typologies of the Allium species under study show significant differences in flavonol contents, from the very low quantity of antioxidant compounds in white onion, about 7 mg/kg against 600–700 mg/kg that were found in red and gold varieties, to the enormous content of flavonols that are present in onions of prompt consumption, where quercetin 4′-glucoside exceeds 1 g/kg and quercetin 3-glucoside is present in a ratio higher then 10:1 with respect to its value in the other onion typologies. Shallots are very rich in the two major flavonols.     

Soybean and rice bran oil extraction in a continuous microwave system: From laboratory- to pilot-scale

The performance of a custom-designed, multimode 2450 MHz laboratory-scale, batch type-converted to continuous microwave-assisted extraction (CMAE) system was investigated and the optimization results obtained were used to develop and test a pilot-scale 5 kW, 915 MHz focused cavity CMAE system. Oil was extracted from soy flour and rice bran at various time-temperature combinations with an ethanol: feedstock ratio of 3:1. Both processes were optimized to minimize extraction time while maximizing the quantity of oil extracted. Extraction yields were compared to conventional (CE) and Soxhlet extraction. Yields in the laboratory-scale system for soybean oil were highest at the highest temperature (73 °C) and longest exposure time (21 min), while for rice bran oil, the highest yields were obtained at 73 °C and 17 min. Using the pilot-scale extraction system, greater than 93.0% of total recoverable oil was extracted from both feedstock at all tested flow rates and extraction times, more than the oil recovered by the laboratory-scale unit. Time of extraction and flow rate did not have a significant influence on extraction yield at tested temperatures for the pilot-scale process for soybeans. For rice bran, extraction yield decreased slightly with increasing flow rate (from 0.6 to 1.0 l/min) and extraction time also influenced oil yields. Analysis of oil quality indices (IV, AV, FFA content, wax and phospholipids) extracted by both CMAE processes indicate that the oil meets prescribed biodiesel feedstock quality standards, further justifying use of microwaves as a rapid tool for oil extraction.