The metabolic fate of red wine and grape juice polyphenols in humans assessed by metabolomics

The metabolic impact of polyphenol‐rich red wine and grape juice consumption in humans was studied using a metabolomics approach. Fifty‐eight men and women participated in a placebo‐controlled, double‐crossover study in which they consumed during a period of 4 wk, either a polyphenol‐rich 2:1 dry mix of red wine and red grape juice extracts (MIX) or only a grape juice extract (GJX). Twenty‐four‐hour urine samples were collected after each intervention. ¹H NMR spectroscopy was applied for global metabolite profiling, while GC‐MS was used for focused profiling of urinary phenolic acids. Urine metabolic profiles after intake of both polyphenol‐rich extracts were significantly differentiated from placebo using multilevel partial least squares discriminant analysis. A significant 35% increase in hippuric acid excretion (p<0.001) in urine was measured after the MIX consumption as) or only a red grape juice dry extract (GJX). 24‐h urine samples were collected after each intervention. 1H‐NMR spectroscopy was applied for global metabolite profiling, while gas chromatography‐mass spectrometry (GC‐MS) was used for focused profiling of urinary phenolic acids. Urine metabolic profiles after intake of both polyphenol‐rich extracts were significantly differentiated from placebo using multilevel partial least squares discriminant analysis (ML‐PLS‐DA). A significant 35% increase in hippuric acid excretion (p<0.001) in urine was measured after the MIX consumption compared with placebo, whereas no change was found after GJX consumption. GC‐MS‐based metabolomics of urine allowed identification of 18 different phenolic acids, which were significantly elevated following intake of either extract. Syringic acid, 3‐ and 4‐hydroxyhippuric acid and 4‐hydroxymandelic acid were the strongest urinary markers for both extracts. MIX and GJX consumption had a slightly different effect on the excreted phenolic acid profile and on endogenous metabolite excretion, possibly reflecting their different polyphenol composition.     

Release of phenolic acids from defatted rice bran by subcritical water treatment

BACKGROUND: Oil production from rice bran, an undervalued by‐product of rice milling, produces defatted rice bran (DRB) as a waste material. Although it is considered a less valuable product, DRB still contains useful substances such as phenolic compounds with antioxidant, UV‐B‐protecting and anti‐tumour activities. In this study the phenolic acids in DRB were extracted with subcritical water at temperatures of 125, 150, 175 and 200 °C. RESULTS: Analysis of total phenolics using Folin–Ciocalteu reagent showed about 2–20 g gallic acid equivalent kg^?1 bran in the extracts. High‐performance liquid chromatography analysis showed low contents of phenolic acids (about 0.4–2 g kg^?1 bran). Ferulic, p‐coumaric, gallic and caffeic acids were the major phenolic acids identified in the extracts. Thermal analysis of the phenolic acids was also done. The thermogravimetric curves showed that p‐coumaric, caffeic and ferulic acids started to decompose at about 170 °C, while gallic acid did not start to decompose until about 200 °C. CONCLUSION: Subcritical water can be used to hydrolyse rice bran and release phenolic compounds, but the high temperatures used in the extraction can also cause the decomposition of phenolic acids. Copyright © 2010 Society of Chemical Industry     

Urinary Excretion of Niacin Metabolites in Humans After Coffee Consumption

Scope

Coffee is a major natural source of niacin in the human diet, as it is formed during coffee roasting from the alkaloid trigonelline. The intention of our study was to monitor the urinary excretion of niacin metabolites after coffee consumption under controlled diet.

Methods and results

We performed a 4‐day human intervention study on the excretion of major niacin metabolites in the urine of volunteers after ingestion of 500 mL regular coffee containing 34.8 μmol nicotinic acid (NA) and 0.58 μmol nicotinamide (NAM). In addition to NA and NAM, the metabolites N¹‐methylnicotinamide (NMNAM), N¹‐methyl‐2‐pyridone‐5‐carboxamide (2‐Py), and nicotinuric acid (NUA) were identified and quantified in the collected urine samples by stable isotope dilution analysis (SIVA) using HPLC‐ESI‐MS/MS. Rapid urinary excretion was observed for the main metabolites (NA, NAM, NMNAM, and 2‐Py), with t_max values within the first hour after ingestion. NUA appeared in traces even more rapidly. In sum, 972 nmol h^?1 of NA, NAM, NMNAM, and 2‐Py were excreted within 12 h after coffee consumption, corresponding to 6% of the ingested NA and NAM.

Conclusion

The results indicate regular coffee consumption to be a source of niacin in human diet.

     

Absorption,metabolism, and excretion of green tea flavan‐3‐ols in humans with an ileostomy

Green tea containing 634 μmol of flavan‐3‐ols was ingested by human subjects with an ileostomy. Ileal fluid, plasma, and urine collected 0–24 h after ingestion were analysed by HPLC‐MS. The ileal fluid contained 70% of the ingested flavan‐3‐ols in the form of parent compounds (33%) and 23 metabolites (37%). The main metabolites effluxed back into the lumen of the small intestine were O‐linked sulphates and methyl‐sulphates of (epi)catechin and (epi)gallocatechin. Thus, in subjects with a functioning colon substantial quantities of flavan‐3‐ols would pass from the small to the large intestine. Plasma contained 16 metabolites, principally methylated, sulphated, and glucuronidated conjugates of (epi)catechin and (epi)gallocatechin, exhibiting 101–256 nM peak plasma concentration and the time to reach peak plasma concentration ranging from 0.8 to 2.2 h. Plasma pharmacokinetic profiles were similar to those obtained with healthy subjects, indicating that flavan‐3‐ol absorption occurs in the small intestine. Ileostomists had earlier plasma time to reach peak plasma concentration values than subjects with an intact colon, indicating the absence of an ileal brake. Urine contained 18 metabolites of (epi)catechin and (epi)gallocatechin in amounts corresponding to 6.8±0.6% of total flavan‐3‐ol intake. However, excretion of (epi)catechin metabolites was equivalent to 27% of the ingested (?)‐epicatechin and (+)‐catechin.     

Oil matrix effects on plasma exposure and urinary excretion of phenolic compounds from tomato sauces: Evidence from a human pilot study

The health-promoting effects attributable to dietary phenolic compounds strongly depend on their bioaccesibility from the food matrix and their consequent bioavailability. We carried out a pilot randomized controlled cross-over study to evaluate the effect of addition of an oil matrix during tomato sauce processing, on the bioavailability of tomato phenolics. Healthy subjects consumed a single dose of tomato sauce elaborated without oil (OO-F) and with the addition of 5% virgin olive oil (VOO-E) or refined olive oil (ROO-E). Plasma and urine samples were subjected to solid-phase extraction, followed by HPLC–MS/MS analysis. Six phenolic compounds, three aglycones (naringenin, ferulic and caffeic acids) and their corresponding glucuronide metabolites, were identified and quantified in urine after the ingestion of the tomato sauces. Two of the six phenolic urinary metabolites were also quantified in plasma samples. Only after ingestion of the oil-enriched tomato sauces, did the glucuronide metabolites of naringenin show a bi-phasic profile of absorption in plasma, suggesting that the lipid matrix added to the sauce may stimulate the occurrence of re-absorption events by enterohepatic circulation, potentially enhancing the apparent plasma half-life of the flavanone prior to excretion. The interindividual response variability observed underlies the need for further large-scale investigations.     

Triticale bran and straw: Potential new sources of phenolic acids,proanthocyanidins, and lignans

The distribution of phenolic acids (free and bound), proanthocyanidins, and lignans in defatted triticale bran and straw was determined. For comparison, wheat, rye and oat brans as well as triticale flakes and leaves were also assayed. Most phenolic acids were present in the bound form (89–98%), and released under alkaline extraction conditions. The content of phenolic acids ranged from 65.2 to 252.5 mg/100 g in samples in which ferulic acid predominanted. Triticale straw was the richest source of proanthocyanidins, containing 862.5 mg/100 g (catechin equivalents) of tissue. Triticale straw contained 0.27 mg/100 g of lignan secoisolariciresinol diglucoside (SDG), whereas the bran had only 0.01 mg/100 g. The oxygen radical absorbance capacity (ORAC, μM Trolox equivalents/g defatted material) showed that antioxidant activity of bound phenolics was higher than those of free phenolics. This is the first report on phenolic acids, proanthocyanidin, and lignans content of Canadian triticale by-products, indicating that they may have the potential for use as nutraceuticals and/or functional food ingredients.     

Isolation and Identification of Phenolic Antioxidants in Black Rice Bran

Black rice bran contains phenolic compounds of a high antioxidant activity. In this study, the 40% acetone extract of black rice bran was sequentially fractionated to obtain 5 fractions. Out of the 5 fractions, ethyl acetate fraction was subfractionated using the Sephadex LH‐20 chromatography. The antioxidant activity of phenolic compounds in the extracts was investigated by 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical assay, 2,2‐azino‐bis‐(3‐ethylenebenzothiozoline‐6‐sulfonic acid) (ABTS) radical cation assay, reducing power. The subfraction 2 from ethyl acetate fraction had the highest total phenolic contents (TPC) (816.0 μg/mg) and the lowest EC₅₀ values (47.8 μg/mL for DPPH radical assay, 112.8 μg/mL for ABTS radical cation assay, and 49.2 μg/mL for reducing power). These results were 3.1, 1.3, and 2.6 times lower than those of butylated hydroxytoluene (BHT), respectively. At a concentration of 100 μg/mL, the antioxidant activity and TPC of various extracts was closely correlated, with correlation coefficients (R²) higher than 0.86. The major phenolic acid in subfraction 2 was identified as ferulic acid (178.3 μg/mg) by HPLC and LC‐ESI/MS/MS analyses. Our finding identified ferulic acid as a major phenolic compound in black rice bran, and supports the potential use of black rice bran as a natural source of antioxidant.     

Comparative study of primary and secondary metabolites in apricot (Prunus armeniaca L.) cultivars

BACKGROUND: Apricot is one of the most popular Prunus species grown in the temperate zone and great variation in the contents of primary and secondary metabolites has been reported in its fruit. However, little is known on the phenolic profiles and antioxidant potential of important local cultivars. The objective of the study was to identify valuable parental lines for breeding of cultivars with high health‐promoting effects. RESULTS: Primary metabolites (sugars, organic acids) and secondary metabolites (phenolics) were quantified by high‐performance liquid chromatography–mass spectrometry (HPLC/MS) in fruit of 13 apricot cultivars: total sugars ranged from 59.2 to 212.5 g kg^?1 fresh weight (FW) and total organic acids from 4.2 to 20.8 g kg^?1 FW. Four hydroxycinnamic acids and three flavonols were quantified; their content was significantly higher in skin compared to pulp. Similarly, antioxidative potential was significantly higher in skin and ranged from 125.4 to 726.5 mg ascorbic acid equivalents kg^?1 FW. A positive correlation between total phenolic content and antioxidant potential was determined. Multivariate analysis subdivided the cultivars into five major groups, mostly influenced by the content of individual and total phenolics as well as the antioxidant potential of apricot skin and pulp. CONCLUSION: In regard to high phenolic content in connection with antioxidant potential, three cultivars stand out as the richest in analyzed quality parameters: ‘Mula Sadik’, ‘Bergeron’ and ‘Chuan Zhi Hong’. They also contained high amounts of primary metabolites and should be promoted for further planting and included in apricot breeding programs. Copyright © 2010 Society of Chemical Industry     

Short-chain fatty acid content and pH in caecum of rats given various sources of carbohydrates

The caecal content of short-chain fatty acids (SCFA; acetic, propionic and butyric acid), caecal pH, fermentability and dry matter digestibility (DMD) were examined through balance experiments in rats fed 11 various indigestible carbohydrates. The following carbohydrate sources were incorporated into test diets: cellulose, oat husk, wheat bran, oat bran, pea fibre, linseed fibre, low methoxylated (LM)-pectin, guargum, β-glucans, neosugar and raffinose. The indigestible carbohydrates, except for those in wheat bran, oat husk and cellulose, were highly fermented, ie > 90%. Caecal pH varied between 5·6 and 7·8, with neosugar and raffinose causing the lowest pH and the fibre-free diet and the diet with oat husk the highest. The caecal pool sizes of SCFA were highest with raffinose, β-glucans, LM-pectin, guargum and linseed fibre (335-400 μmol) while pea fibre, wheat bran, oat bran and neosugar gave intermediate levels (137–227 μmol). The pool size with oat husk and cellulose was similar as with the basal diet (45–64 μmol). A high proportion of propionic acid was obtained with guargum and linseed fibre, whereas acetic acid was the predominant product in case of LM-pectin. On the other hand, linseed fibre gave a remarkably low proportion of butyric acid. The quantity fermented and caecal pH correlated well to the amount of SCFA with most materials (r = 0·96 and r = ?0·87, respectively), an exception was neosugar and in case of fermentability also oat bran. DMD values with most of the easily fermented carbohydrates were high (>96%). Exceptions were diets with β-glucans and oat bran which caused low DMD values, about 93%. It is concluded that indigestible carbohydrates may differ in ability to lower caecal pH and to form SCFA during fermentation.     

Activated Carbon and Ion Exchange Treatments for Removing Phenolics and Phytate from Peanut Protein Products

Commercial defatted peanut flour and laboratory defatted peanut meal contained 1.5 and 1.7% phytate, 1756 and 2033 μg g^?1 total phenolic acids and 50 and 120 μg g^?1 neutral phenolics, respectively. Laboratory peanut protein isolate contained undetectable amounts of neutral phenolics, 810 μg g^?1 total phenolic acids and about 1% phytate. The ion exchange treatment removed ≥85% of the phytate and the ion exchange and activated carbon treatments removed 92 and 82%, respectively, of the total phenolic acids from peanut protein isolate. p-Coumaric acid was the major phenolic acid, accounting for 40–68% of the total phenolic acids in all peanut protein products.     

Effects of Various Heat Treatments on Phenolic Profiles and Antioxidant Activities of Pleurotus eryngii Extracts

Free (FP) and bound phenolics (BP) were extracted from freeze dried (FD), oven dried (OD), as well as boiling treated (BT) Pleurotus eryngii samples. Free, bound, total phenolics were quantified using Folin–Ciocalteau assay. Qualitative and quantitative analysis of phenolic compounds were carried out using high‐performance liquid chromatography (HPLC) coupled with diode array detector (DAD), and a total of 8 phenolic compounds were detected. Free phenolic contents followed the order: Freeze‐dried free phenolics (FDFP) > Oven‐dried free phenolics (ODFP) > Boiling‐treated free phenolics (BTFP), and ranged from 95.42 (BTFP) to 442.50 (ODPF) μg gallic acid equivalents (GAE)/g dry weight (DW). Bound and total phenolic contents followed the order: FD > OD > BT, and ranged from 218.33 (BTBP) to 774.17 (FDBP) and 313.75 (BT total phenolics) to 1090.42 (FD total phenolics) μg GAE/g DW. Bound phenolics contributed 49.76% (OD), 69.59% (BT), and 71% (FD) of the total phenolic contents. All free and bound phenolic extracts were investigated for their antioxidant activities by 3 different assays, 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical scavenging activity, reducing power, and superoxide anion radical scavenging activity. FDFP showed strongest DPPH radical scavenging activity (IC₅₀ at 32.61 μg/mL), ODFP showed strongest reducing power (IC₅₀ at 26.31 μg/mL), and BTBP showed strongest superoxide anion radical scavenging activity (IC₅₀ at 14.07 μg/mL).     

Rice kernel phenolic content and its relationship with antiradical efficiency

Plant phenolics exert beneficial effects on human health and may also prevent oxidative deterioration of food. Two field experiments were carried out for characterising phenolics in rice. The first assay was conducted in 1999 and 2000 in Beaumont, TX and included five light‐brown, two purple and 10 red pericarp coloured cultivars. ‘Bran colour’ was highly statistically significant for both bran phenolic concentration and antiradical efficiency (p < 0.001). ‘Year’ and its interaction with bran colour were not significant for the analysed traits, suggesting that seasonal differences and their interactions may not affect phenolic content or antiradical efficiency. The accessions ranged from 3.1 to 45.4 mg gallic acid equivalents (GAE) g^?1 bran and from 10.0 to 345.3 µM trolox equivalents (TE) g^?1 bran for total phenolic content and antiradical efficiency respectively. The light‐brown bran genotypes exhibited the lowest values for phenolic content and antiradical efficiency, whereas red bran ones displayed ca 10 times higher total phenolic content and more than 50 times higher tannin content than light‐brown ones. The two purple lines showed either low or high values for the studied traits. Antiradical efficiency of rice bran extracts was highly positively correlated with total phenolic content (r = 0.99***), suggesting that phenolics are the main compounds responsible for the free radical‐scavenging activity in rice bran extracts. In the second field experiment (Stuttgart, AR, 2001 and Beaumont, TX, 2000), 133 coloured rice cultivars were analysed for total phenolic content in whole grain. The accessions showed a large variation for total phenolics, ranging from 0.69 to 2.74 mg GAE g^?1 grain. The data confirmed previous results suggesting bran colour as the main factor affecting phenolic concentration in rice kernel and seasonal effects and their interactions as not significant. The results also confirm that within red and purple bran groups can be found the highest phenolic concentrations in rice kernel. Published in 2004 for SCI by John Wiley & Sons, Ltd.     

Effect of storage period on physiochemical,total phenolic content and antioxidant properties of bran enriched snacks

The objective of this investigation was to compare total phenolic content and antioxidant activities of various types of cereal brans enriched snack as affected by storage conditions. Extruded snacks were prepared by the addition of cereal brans (wheat, oat and rice) singly and in combination (w:r:o::2:1.5:1.5) to rice flour at 10, 20 and 30 % bran supplementation. The content of total phenolics in the extracts (conventional and microwave assisted extraction) was determined spectrometrically according to the Folin–Ciocalteu procedure and calculated as gallic acid equivalents. Radical scavenging capacity measured by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) methods was studied. The effect of the storage on antioxidant content and capacity showed that total phenolic content and antioxidant activities of bran enriched snacks decreased during storage at ambient temperature. However, a little increase in moisture content, water activity and free fatty acid was observed in six of month’s storage period.     

Phenolic acid composition and antioxidant capacity of acid and alkali hydrolysed wheat bran fractions

Phenolic acid concentrations, profiles and antioxidant capacity of acid and alkali hydrolysates from the bran of six wheat cultivars representing six Canadian market classes were determined. Aqueous ethanol was used to extract the free phenolics (FP) and diethyl ether to extract the insoluble bound phenolics released after acid and alkaline hydrolysis of the bran. Folin–Ciocalteu (FC) reagent was used to estimate the total phenolic content and HPLC-UV to detect and quantitate 14 phenolic acids and one lignan. trans-Ferulic acid was the dominant acid in the bran extracts but mass spectrometric analysis showed tryptophan to be dominant in the FP extracts. The antioxidant capacity of individual phenolic acids and extracts was assessed using 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) equivalent antioxidant assays. The FP extracts had the lowest average antioxidant capacity and the hydrolysates the highest. Based on the concentration of each phenolic acid in the extracts, and the antioxidant capability of each phenolic standard, trans-ferulic acid was the dominant contributor (66.4–95.5%) to antioxidant capacity of the wheat bran extract.     

Phenolic Profile and Antioxidant Activity of Extracts Prepared from Fermented Heat‐Stabilized Defatted Rice Bran

Heat‐stabilized, defatted rice bran (HDRB) serves as a potential source of phenolic compounds which have numerous purported health benefits. An estimated 70% of phenolics present in rice bran are esterified to the arabinoxylan residues of the cell walls. Release of such compounds could provide a value‐added application for HDRB. The objective of this study was to extract and quantify phenolics from HDRB using fermentation technology. Out of 8 organisms selected for rice bran fermentation, Bacillus subtilis subspecies subtilis had the maximum phenolic release of 26.8 mg ferulic acid equivalents (FAE) per gram HDRB. Response surface methodology was used to further optimize the release of rice bran phenolics. An optimum of 28.6 mg FAE/g rice bran was predicted at 168 h, 0.01% inoculation level, and 100 mg HDRB/mL. Fermentation of HDRB for 96 h with B. subtilis subspecies subtilis resulted in a significant increase in phenolic yield, phenolic concentration, and radical scavenging capacity. Fermented rice bran had 4.86 mg gentistic acid, 1.38 mg caffeic acid, 6.03 mg syringic acid, 19.02 mg (‐)‐epicatechin, 4.08 mg p‐courmaric acid, 4.64 mg ferulic acid, 10.04 mg sinapic acid, and 17.59 mg benzoic acid per 100 g fermented extract compared to 0.65 mg p‐courmaric acid and 0.36 mg ferulic acid per 100 g nonfermented extract. The high phenolic content and antioxidant activity of fermented HDRB extract indicates that rice bran fermentation under optimized condition is a potential means of meeting the demand for an effective and affordable antioxidant.     

Phenols in spikelets and leaves of field‐grown oats (Avena sativa) with different inherent resistance to crown rust (Puccinia coronata f. sp. avenae)

BACKGROUND: Avenanthramides, health‐beneficial phenols in oats, are produced in response to incompatible races of the crown rust fungus, Puccinia coronata, in seedlings of greenhouse‐grown oats. This study aimed to elucidate whether avenanthramides and/or other phenolic compounds, together with the activities of phenylalanine ammonia lyase (PAL), phenoloxidase (PO) and the avenanthramide biosynthetic enzyme hydroxycinnamoyl‐CoA:hydroxyanthranilate‐N‐hydroxycinnamoyl transferase (HHT), are associated with crown rust infection in mature field‐grown oats. Nine oat (Avena sativa L.) genotypes with wide variation in crown rust resistance were exposed to naturally occurring fungal spores during the growth period. RESULTS: In the spikelets avenanthramides as well as HHT activities were more abundant in the crown rust resistant genotypes, whereas p‐coumaric and caffeic acids were more abundant in the susceptible ones. In the leaves avenanthramides were not associated with resistance. Instead two unknown compounds correlated negatively with the rust score. Phenols released by alkaline hydrolysis and PAL and PO activities were not related to rust infection, either in spikelets or in the leaves. CONCLUSION: Because grains of crown rust‐resistant oat genotypes seemed to have higher endogenous levels of health‐promoting avenanthramides, use of resistant oats may contribute to a food raw material with health‐beneficial effects. Copyright © 2009 Society of Chemical Industry     

Gamma-oryzanol content,phenolic acid profiles and antioxidant activity of rice milling fractions

This study was aimed to determine γ-oryzanol content and total phenolics, individual phenolic acid profile and the antioxidant activity of the free and bound extracts of rice milling fractions namely, brown rice, unpolished rice, white rice, chalky rice, raw seed and rice bran. Gamma-oryzanol content of milling fractions which is designated with a simple chromatographic method was in the range of 12.19–3,296.5 mg/kg. The whitening and polishing steps reduced approximately 94% of γ-oryzanol of the brown rice when becoming the white rice. The contribution of bound phenolics to the total phenolic content was approximately 40%. Ferulic and p-coumaric acids were the most abundant phenolic acids in bound phenolic extracts and their amounts were 119.98 and 18.10 μg/g, respectively, in rice bran. The best source of γ-oryzanol, phenolics and antioxidants was clearly rice bran and followed by raw seed and brown rice.     

七种谷物麸皮中酚酸类成分分析

利用反相高效液相色谱法(RP-HPLC)测定7 种不同种类及品种的谷物麸皮中8 种酚酸类成分的含量,并利用数学统计的方法对不同种类谷物、各类酚酸及总酚酸含量间的差异性进行分析。分析结果表明：所分析谷物种类所含酚酸的含量顺序为玉米>小麦>荞麦>燕麦,谷物麸皮中酚酸主要以束缚型酚酸形式存在,且肉桂酸类酚酸含量明显大于苯甲酸类酚酸,游离型及可溶共价结合型酚酸中4- 羟基苯甲酸、香草酸含量较高;而在束缚型酚酸中阿魏酸的含量在各类谷物中均最高,玉米品种中可达到6527.86μg/g 麸皮。     

小麦麸皮中酚酸提取方法的研究

研究了酸种类、酸碱浓度、水解时间、水解顺序对小麦麸皮中束缚型酚酸释放量的影响。结果表明,酚酸在小麦麸皮中主要以束缚型形式存在,且肉桂酸类酚酸含量明显高于苯甲酸类酚酸,其中以阿魏酸的含量最高。水解方法对酚酸释放量的影响存在显著差异。采用超声波辅助有机溶剂（甲醇：丙酮：水=7：7：6）提取,酚酸释放量最高的水解条件为：先用2mol／L氢氧化钠室温水解4h,再用2mol／L盐酸于85℃下水解1h,束缚型酚酸总释放量达4719μg／g麸皮。     

Effect of Different Solvents on the Measurement of Phenolics and the Antioxidant Activity of Mulberry (Morus atropurpurea Roxb.) with Accelerated Solvent Extraction

The effects of 9 different solvents on the measurement of the total phenolics and antioxidant activities of mulberry fruits were studied using accelerated solvent extraction (ASE). Sixteen to 22 types of phenolics (flavonols, flavan‐3‐ols, flavanol, hydroxycinnamic acids, hydroxybenzoic acids, and stilbenes) from different mulberry extracts were characterized and quantified using HPLC‐MS/MS. The principal component analysis (PCA) was used to determine the suitable solvents to distinguish between different classes of phenolics. Additionally, the phenolic extraction abilities of ASE and ultrasound‐assisted extraction (UAE) were compared. The highest extraction efficiency could be achieved by using 50% acidified methanol (50MA) as ASE solvents with 15.14 mg/gallic acid equivalents g dry weight of mulberry fruit. The PCA results revealed that the 50MA followed by 50% acidified acetone (50AA) was the most efficient solvent for the extraction of phenolics, particularly flavonols (627.12 and 510.31 μg/g dry weight, respectively), while water (W) was not beneficial to the extraction of all categories of phenolics. Besides, the results of 3 antioxidant capability assays (DPPH, ABTS free radical‐scavenging assay, and ferric‐reducing antioxidant power assay) showed that water‐based organic solvents increased the antioxidant capabilities of the extracts compared with water or pure organic solvents. ASE was more suitable for the extraction of phenolics than UAE.