Phenolic compounds in strawberry (Fragaria x ananassa Duch.) fruits: Composition in 27 cultivars and changes during ripening

Phenolic compounds in fruits of 27 cultivars of strawberry (Fragaria x ananassa Duch.) grown in Norway were characterised and quantified by HPLC-DAD-MSⁿ. Total phenolic content, calculated as the sum of the individual compounds, varied 2.3-fold among cultivars, i.e., from 57 to 133 mg/100 g of fw. There were significant differences among cultivars in concentration of all phenolic compounds. The highest variation between cultivars was found for cinnamoyl glucose (0.6-24.9 mg/100 g of fw). Concentration of anthocyanins, the most abundant class of phenolic compounds in the majority of the cultivars, varied from 8.5 to 65.9 mg/100 g of fw. Flavan-3-ols (11-45 mg/100 g of fw) and ellagitannins (7.7-18.2 mg/100 g of fw) contributed on average 28% and 14% to total phenolic contents in the strawberry cultivars, respectively. In three cultivars harvested at three stages of ripeness, anthocyanins and cinnamic acid conjugates were the compounds most affected by ripening. The anthocyanin profile for the individual cultivars was only slightly affected by ripening and growing conditions.     

CHEMICAL AND ANTIOXIDANT PROPERTIES OF CULTIVATED AND WILD FRAGARIA AND RUBUS BERRIES

ABSTRACT

Content of individual sugars, organic acids, total phenolics (TPH), some important phenolic compounds (kaempferol, myricetin, quercetin, and ellagic acid) and total antioxidant capacity (TAC) in the fruits of strawberry, raspberry and blackberry were studied. A comparison was made between cultivars and wild relatives of each species (Fragaria vesca L., Rubus idaeus L. and Rubus fruticosus L.). The main sugars found were fructose and glucose both in the fruits of wild species and the studied cultivars. Citric acid was determined to be the major organic acid in most of tested berries with the exception of blackberry cultivars, where malic acid was dominant. The content of individual phenolic compounds varied among the wild species, as well as among the studied cultivars. Ellagic acid content was higher in F. vesca, R. idaeus and R. fruticosus (122.5 µg/g FW, 12.71 µg/g FW and 61.7 µg/g FW, respectively) than that obtained in analyzed cultivars. Overall, TPH expressed higher values in the wild strawberry and blackberry species in comparison to the studied cultivars, and consequently, the highest levels of TAC were recorded in F. vesca (5.78 mg asc/g FW), followed by R. fruticosus (4.95 mg asc/g FW).

PRACTICAL APPLICATIONS

In recent years, both wild and cultivated berries have become very attractive for consumers because of potentially beneficial phytochemicals contained in these fruits. Fruit nutritional quality can be described by standard quality parameters (sugars and organic acids), and the analysis of antioxidant capacity influenced by specific related compounds. The importance of flavonoids and other phenolics have been suggested to play a preventive role in the development of cancer and heart disease. A significant positive correlation observed in this study between total phenolics and total antioxidant capacity indicate the need for the use of wild species in the breeding programs of small fruits, especially strawberry and blackberry, in order to increase their nutritive value and the health benefits.     

The effect of addition of chokeberry, flowering quince fruits and rhubarb juice to strawberry jams on their polyphenol content, antioxidant activity and colour

The aim of the study was to establish whether the addition of berries (flowering quince, chokeberry) and rhubarb juice during jam processing improves its colour and enriches jams in polyphenol compounds other than those found in strawberries. The sum of phenolic compounds determined by HPLC was distributed in a wide concentration range depending on the cultivar. Jams prepared from Elkat cultivar had 27% more total phenolic compounds than jams prepared from Senga Sengana. The following compounds were identified in jams prepared from strawberries: p-coumaric, ferulic and ellagic acids, quercetin, kaempferol, anthocyanins, (+)-catechin, (−)-epicatechin and proanthocyanidins. Proanthocyanidins and ellagic acid are the major polyphenol compounds of all strawberries jams. The Elkat cultivar (47.34 mg/100 g) contained higher amounts of proanthocyanidins compared to Senga Sengana (29.95 mg/100 g). The addition of 10% of flowering quince and chokeberry to jams during their preparation resulted in the increase in the content of phenolic components in final products, especially for proanthocyanidins. The highest level of total polyphenols (P < 0.05) was found in strawberry mixed with chokeberry, 237.82 mg/100 g for Senga Sengana and 260.61 mg/100 g for Elkat. There has been a marked increase of proanthocyanidins content (5.4 and 4.0 times) in jams made from Senga Sengana and Elkat cultivars mixed with chokeberry. However, the addition of rhubarb juice did not increase the content of polyphenol in Senga Sengana jam (not statistically significant). Antioxidant activity of strawberry jam was determined by 2,2′azinobis-(3-ethylbenzthiazoline-6-sulphonic acid (ABTS), 1,1-Diphenyl-2-picrylhydrazyl radical (DPPH) and ferric reducing/antioxidant power methods (FRAP). The antioxidant activity of this mixed jam was more than two times higher (P < 0.05) than control sample of strawberry jam. Rhubarb juice had high effect on L* (lightness) value in case of all strawberry varieties. The redness (a*), and yellowness (b*) were significantly different in jams with supplement. Strawberry jam with chokeberries had smaller L* value than control and other samples, and the lowest a* and b* values. This variation could be due to the nature of the pigments in these fruit cultivars and the content of anthocyanins which resulted in more reddish colour.     

Effects of phenolic compounds in blueberries and muscadine grapes on HepG2 cell viability and apoptosis

Although blueberries and muscadine grapes have high contents of polyphenols, few studies have been conducted to assess their potential effects on cancer cells. The objective of this study was to systematically evaluate the effects of different fractions of phenolic compounds in blueberries and muscadine grapes on HepG2 liver cancer cell viability and apoptosis. Three cultivars of blueberries (‘Briteblue’, ‘Tifblue’ and ‘Powderblue’) and four cultivars of muscadine grapes (‘Carlos’, ‘Ison’, ‘Noble’, and ‘Supreme’) were assessed in this study. Polyphenols were extracted and further separated into phenolic acids, tannins, flavonols, and anthocyanins using a HLB cartridge and LH-20 column. The major compounds of different fractions were characterized. The phenolic acid fractions of muscadine grapes and blueberries showed a 50% inhibition of HepG2 cell population growth at the level of 1–2 mg/mL. The greatest inhibitory effects were observed from the anthocyanin fractions with 50% inhibitions of cancer cell population growth at concentrations of 70–150 and 100–300 μg/mL in blueberries and muscadine grapes, respectively. The flavonol and tannin fractions showed intermediate activities. In addition, DNA fragmentation was measured by using a Cell Death Detection ELISA kit to assess the induction of apoptosis. The anthocyanin fraction resulted in a two- to fourfold increase in DNA fragmentation compared to control in both muscadine grapes and blueberries. These findings of inhibition of cancer cell growth and induction of apoptosis suggest that blueberries and muscadine grapes may contribute to reduction in liver cancer risk.     

Identification and characterisation of low-molecular-weight phenolic compounds in bayberry (Myrica rubra Sieb. et Zucc.) leaves by HPLC-DAD and HPLC-UV-ESIMS

Leaves of each of two bayberry cultivars, Biqi and Dongkui, were divided into three categories by age, namely immature, intermediate, and mature. Phenolic compounds were analysed by the methods of HPLC-DAD and HPLC-UV-ESIMS. Gallic acid and EGCG were identified positively, and 13 other compounds (flavan-3-ol monomers, prodelphinidin oligomers, and flavonol glycosides) were partially identified. Gallic acid (7.5–87.8 mg/100 g) was the only phenolic acid detected and flavan-3-ols were abundant. Myricetin deoxyhexoside (535.4–853.0 mg/100 g) was the major flavonol glycoside. Among the three categories, immature leaves of both cultivars recorded the highest level of total phenolics, irrespective of whether they were measured by the Folin–Ciocalteu method (19404.0 mg/100 g in Biqi and 19626.0 mg/100 g in Dongkui) or as the sum of individual phenolic compounds (2255.9 mg/100 g in Biqi and 1797.1 mg/100 g in Dongkui). The results showed that bayberry leaves are a potentially rich source of beneficial phenolics.     

Fruit quality and bioactive compounds relevant to human health of sweet cherry (Prunus avium L.) cultivars grown in Italy

The fruit quality characteristics, phenolic compounds and antioxidant capacities of 24 sweet cherry (Prunus avium L.) cultivars grown on the mountainsides of the Etna volcano (Sicily, Italy) were evaluated. High-performance liquid chromatographic methods were used to identify and quantify sugars, organic acids and phenolics. A total of seven phenolic compounds were characterised as hydroxycinnamic acid derivatives (neochlorogenic acid, p-coumaroylquinic acid and chlorogenic acid) and anthocyanins (cyanidin 3-glucoside, cyanidin 3-rutinoside, pelargonidin 3-rutinoside and peonidin 3-rutinoside). The total anthocyanin content ranged from 6.21 to 94.20 mg cyanidin 3-glucoside equivalents/100 g fresh weight (FW), while the total phenol content ranged from 84.96 to 162.21 mg gallic acid equivalents/100 g FW. The oxygen radical absorbance capacity (ORAC) assay indicated that fruit of all genotypes possessed considerable antioxidant activity. The high level of phenolic compounds and antioxidant capacity of some sweet cherry fruits implied that they might be sources of bioactive compounds that are relevant to human health.     

Liaison of phenolic acids and biological activity of escalating cultivars of Daucus carota

The objective of the present study was to analyze and compare the phenolic compounds and their antioxidant capacities of new lines of Dacus carota. The selected cultivars showed high variation in the contents of total phenolics (30.26–65.39 mg/100 g FW) and total ascorbic acid (41.12–58.36 mg/100 g FW). Analysis on RP-HPLC revealed that hydroxycinnamic acids and its derivatives were major phenolic compounds present in D. carota extracts, whereas 5-caffeolquinic acid was a major hydroxycinnamic acid (ranged from 30.26 to 65.39 mg/100 g FW). DCP cultivar showed high total antioxidant capacity (77.69 mg/100 g), 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging capacity (52.36 mg/100 g), superoxide radical scavenging capacity (53.69 mg/100 g), and hydroxyl radical scavenging capacity (51.91 mg/100 g). A linear relationship was found between total phenolic acid contents and antioxidant capacity. Both phenolic compounds and antioxidant capacities varied significantly (ρ < 0.05) among cultivars. DCP cultivar was found to be a rich source of phenolics and ascorbic acid with high antioxidant activity.     

Strawberries from integrated pest management and organic farming: Phenolic composition and antioxidant properties

Consumer awareness, pesticide and fertilizer contaminations and environmental concerns have resulted in significant demand for organically grown farm produce. Consumption of berries has become popular among health-conscious consumers due to the high levels of valuable antioxidants, such as anthocyanins and other phenolic compounds. The present study evaluated the influence that organic farming (OF) and integrated pest management (IPM) practise exert on the total phenolic content in 22 strawberry samples from four varieties. Postharvest performance of OF and IPM strawberries grown in the same area in the centre of Portugal and harvested at the same maturity stage were compared. Chemical profiles (phenolic compounds) were determined with the aid of HPLC-DAD/MS. Total phenolic content was higher for OF strawberry extracts. This study showed that the main differences in bioactive phytochemicals between organically and IPM grown strawberries concerned their anthocyanin levels. Organically grown strawberries were significantly higher in antioxidant activity than were the IPM strawberries, as measured by DPPH and FRAP assays.     

Organic acids,antioxidant capacity,phenolic content and lipid characterisation of Georgia-grown underutilized fruit crops

Four underutilized Georgia-grown fruit crops, namely loquat (Eriobotrya japonica), mayhaw (Crataegus sp.), fig (Ficus carica), and pawpaw (Asimina triloba), and their leaves were analysed for total polyphenols by Folin–Ciocalteau method, and antioxidant capacity by ferric-reducing antioxidant power (FRAP) and Trolox-equivalent antioxidant capacity (TEAC) assays. Organic acids and phenolic compounds were identified by RP-HPLC. For lipid profile, fruits were separated into two fractions – seed and fruit (i.e., without seed); lipid was extracted using the Folch method and analysed for fatty acids, phytosterols, tocopherols, and phospholipids. The major organic acid identified in all samples was malic acid (177–1918 mg/100 g FW). The predominant phenolic acids in all the fruits were gallic (1.5–6.4 mg/100 g FW) and ellagic (0.2–33.8 mg/100 g FW), and the most abundant flavonoid was catechin (12.2–37.8 mg/100 g FW). Total lipid content varied from 0.1% in mayhaw fruit to 21.5% in pawpaw seed. Linoleic acid was the predominant fatty acid in all of the samples (28.2–55.7%).     

Vitamin C and carotenoids in organic and conventional fruits grown in Brazil

This study compared the concentration of vitamin C (ascorbic acid, AA, and dehydroascorbic acid, DHA) and carotenoids (lycopene and β-carotene) between three fruits produced by organic and conventional farming. Vitamin C and carotenoids were analysed by high-performance liquid chromatography. The Student t-test (α = 5%) was applied to determine differences between the organic and conventional production systems. AA content was significantly higher in organic acerola (4023.39 mg/100 g) compared to its conventional production (2294.53 mg/100 g). Conversely, AA content was significantly higher in conventional strawberries (42.45 mg/100 g) than the organic ones (30.74 mg/100 g). The conventional production also showed significantly higher contents of DHA (persimmon: 7.50 mg/100 g vs. 0.96 mg/100 g) and β-carotene (acerola: 6130.24 μg/100 g vs. 2486.38 μg/100 g) than the organic fruits. Lycopene was only detected in persimmons, but no significant difference was observed between farming systems. There was no evidence of the nutritional superiority of the organically grown fruits.     

Phenolic profile and antioxidant activity of highbush blueberry (Vaccinium corymbosum L.) during fruit maturation and ripening

The phenolic profile and quantitative composition of blueberries as well as the corresponding antioxidant activity of blueberries is well documented. Unfortunately, little is reported on the development of phenolic compounds and antioxidant activity during fruit maturation and ripening. In the present study, the total phenolic content and main phenolic compounds of four highbush blueberry cultivars (Vaccinium corymbosum L.) were analyzed at five stages of maturation and ripening. Antioxidant activity was screened with electron spin resonance spectrometry and trolox equivalent antioxidant capacity (TEAC) assay. An adequate picture of phenolic compounds developed during maturation and ripening was determined using HPLC-DAD. Anthocyanins of all varieties increased during successive harvest stages; meanwhile flavonols and hydroxycinnamic acids decreased from unripe green to ripe blue stage of berry ripening. Blueberry antioxidant activity, as well as total phenolic content tended to decrease during ripening.     

Evaluation of chemical constituents and antioxidant activity of sweet cherry (Prunus avium L.) cultivars

This research was undertaken to evaluate the sugars, organic acids, phenolic compositions and antioxidant capacities of sweet cherry cultivars (Van, Noir de Guben, Larian and 0‐900 Ziraat) grown in Turkey. High‐performance liquid chromatographic methods were used to identify and quantify four sugars (sucrose, glucose, fructose and sorbitol) and four organic acids (malic, citric, shikimic, and fumaric acid). The major organic acid was found as malic acid (8.54–10.02 g kg^?1 of FW). With regard to sugars, glucose was present in the largest amounts (44.71–48.31 g kg^?1 of FW) for sweet cherry cultivars. The sum of sugars ranged from 103.87 (Larian) to 113.13 g kg^?1 of FW (0‐900 Ziraat) and that of organic acids from 12.01 (0‐900 Ziraat) to 14.17 g kg^?1 of FW (Noir de Guben). A total of eleven phenolic compounds were identified and quantified in sweet cherry cultivars, including hydroxycinnamic acids (3), anthocyanins (5), flavan‐3‐ols (2) and flavonol (1) compounds. Total phenolic contents ranged from 88.72 (Van) to 239.54 (Noir de Guben) mg/100 g of FW, while antioxidant activities ranged from 2.02 to 7.75 μm Trolox equivalents g^?1 of FW.     

Fresh from the Ornamental Garden: Hips of Selected Rose Cultivars Rich in Phytonutrients

Morphological parameters (size, weight, color), the content of sugars, organic acids, lycopene, β‐carotene, and phenolics were determined in hips of Rosa canina (RCA), Rosa sweginzowii (RSW), Rosa rugosa (RUG), and selected ornamental Rosa cultivars Fru Dagmar Hastrup (FDH), Repandia (REP), Veilchenblau (RVB), Aloha (RAL), Bonica (BON), and Golden Gate (RGG). Although traditionally used RCA hips contained the highest amount of cyanidin‐3‐glucoside (83 μg/g DW) and were the reddest (h° = 17.5), they did not stand out in other analyzed parameters. RGG climber had the biggest hips (8.86 g), which also contained highest sugar levels (50.9 g/100 g DW). RAL stood out as the cultivar rich in organic acids (33.9 g/100 g DW), mainly because of high quinic acid content (17.6 g/100g DW). FDH and RSW hips were characterized by particularly high ascorbic acid levels (4325 mg/100 g DW and 4711 mg/100 g DW). Other ornamental cultivars contained low amounts of ascorbic acid compared to the analyzed species. The phenolic profile was species/cultivars‐specific. The greatest diversity of phenolic compounds was detected in RUG and FDH hips (55 and 54 different tentatively identified compounds with HPLC/MS). Flavanols represented the main phenolic class in most of the investigated species/cultivars and RGG hips contained the highest amount of catechin and proanthocyandin derivatives (15855 μg/g DW). Altogether RAL hips contained the highest quantity of phenolics (44746 μg/g DW) mainly due to high levels of hydrolysable tannins compared to other species/cultivars. Although small, hips of BON and REP were most abundant regarding β‐carotene and lycopene content, respectively.     

Determination of Phenolic Compounds in Strawberries (Fragaria ananassa Duch) by High Performance Liquid Chromatography with Diode Array Detection

This paper describes a method for simultaneous identification and quantification of phenolic compounds in strawberries followed by a reversed-phase high performance liquid chromatography (HPLC) with diode array detection. The studied phenolics were flavonoids (flavonols: quercentin, rutin, and kaempferol; flavanols: catechin and epicatechin; anthocyanidins: cyanidin and pelargonidin) and phenolic acids (hydroxybenzoic acid derivatives: gallic and ellagic acids; hydroxycinnamic acid derivatives: ferulic, coumaric, and cinnamic acids). The mobile phase consisted in a gradient prepared from formic acid in water (2 %, pH 3) and formic acid in methanol (2 %, pH 3), flow rate 0.7 mL min^?1 at 25 °C. Analyses were performed, using methanol as extractant, before and after acid hydrolysis with the aim of determining free and conjugated phenolic compounds in strawberries. The acid hydrolysis conditions (6 mol L^?1 HCl, 50 min at 90 °C) were shown to be suitable both for phenolic standards and strawberry extracts. Method validation, using phenolic standard solutions, included: linearity study, limits of detection and quantification, and calibration and analytical sensitivity quantifications. Precision and accuracy were studied in strawberry extracts. The results indicate that the developed method was linear, sensible, precise, and accurate, and the convenience of methanol can substitute acetonitrile as the most commonly used solvent in HPLC. The method was employed for knowing the phenolic profile in seven strawberry cultivars from Italy and Argentina, and besides, total phenolic content was analyzed by the Folin–Ciocalteu method; the total antioxidant activity was investigated using the ABTS method. Good correlations were observed among latter parameters, and total phenolics were obtained as the sum of each phenolic compound analyzed by photodiode array detection-HPLC.     

Physical attributes and chemical composition of organic strawberry fruit (Fragaria x ananassa Duch, Cv. Albion) at six stages of ripening

Organic strawberry fruits (Cv. ‘Albion’) were harvested at six different ripening stages and evaluated for physical and chemical parameters. Biometrical characteristics and moisture content did not change significantly during ripening. Total soluble solids, pH and colour development increased while titratable acidity and fruit firmness decreased 14.7% and 91%, respectively. Fructose, glucose, and sucrose followed similar tendencies. Final contents of these sugars were 2323.4, 1988.5, and 1578.4 mg/100 g. Citric, malic, and ascorbic acids followed a descending, irregular, and increasing tendency during ripening, respectively. Final contents of these acids were 822.8, 245.8, and 78.1 mg/100 g. Total anthocyanins content (TAC) increased during ripening, while the opposite was observed for total phenolic content (TPC). TAC and TPC in ripe fruit were 56.4 mg/100 g and 196 mg gallic acid equivalents (GAE)/100 g. Twenty eight phenolic compounds, mainly glycosides, were identified and quantified by HPLC-DAD–MS analysis. The concentration of these compounds was ripening dependent.     

A Comparative Study of Phenolic Antioxidant Activity and Flavonoid Biosynthesis‐Related Gene Expression Between Summer and Winter Strawberry Cultivars

Strawberry (Fragaria ananassa Duch.) possesses good antioxidant properties. Phenolic compounds in strawberries, such as anthocyanins and ellagic acid, mainly act as antioxidants. This study aimed to compare the phenolic content and expression patterns of genes involved in flavonoid biosynthesis between summer and winter strawberry cultivars affected by seasonal variation, degree of ripeness, and genotype. Antioxidant activity and the total content of phenols and flavonoids decreased with fruit ripening. Most notably, summer strawberry cultivars showed higher antioxidant activity than winter cultivars. The expression patterns of flavonoid biosynthetic genes tested were cultivar‐dependent and were also affected by ripening. These results help us understand the nutritional and physiological characteristics of selected cultivars and provide a range of information for strawberry consumption.     

高效液相色谱法对蓝莓果实中8 个有机酸含量的测定

建立同时测定蓝莓果实中8 个有机酸类成分含量的高效液相色谱法,并利用该方法测定26 个不同品种蓝莓果实中的有机酸含量。结果表明,所测品种中塞拉的有机酸含量最高,达25.135 26 mg/g鲜果,最低的为克瑞顿,仅含2.368 31 mg/g鲜果。该方法简便、快速、准确,具有良好的重复性和回收率,可作为蓝莓果实中有机酸含量的测定方法。     

Composition of Sugars,Organic Acids,and Total Phenolics in 25 Wild or Cultivated Berry Species

Abstract: Sugars, organic acids, and total phenolic content in fruit of 25 wild and cultivated berry species were identified and quantified with high‐performance liquid chromatograph. The composition of sugars, organic acids, and total phenolic compounds in various species of Vaccinium, Rubus, Ribes, and Fragaria genus was evaluated. Additonally, total phenolics of less known berry species of the Morus, Amelanchier, Sorbus, Sambucus, Rosa, Lycium, Actinidia, and Aronia genus were determined in wild growing as well as in cultivated fruits. Significant differences in the concentration of sugars and organic acids were detected among the berry species. Glucose and fructose were the most abundant sugars in berry fruits and the major organic acids were malic and citric acid. However, in kiwi fruit, sucrose represented as much as 71.9% of total sugars. Sorbitol has been detected and quantified in chokeberry, rowanberry, and eastern shadbush fruit. The highest content of total analyzed sugars was determined in rowanberry fruit, followed by dog rose, eastern shadbush, hardy kiwifruit, American cranberry, chokeberry, and jostaberry fruit. Rowanberry stands out as the fruit with the highest content of total analyzed organic acids, followed by jostaberry, lingonberry, red gooseberry, hardy kiwifruit, and black currant. The berries of white gooseberry, black currant, red currant, and white currant had the lowest sugar/organic acid ratio and were thus perceptively the sourest species analyzed. On the other hand, the species with highest sugar/organic acid ratio were goji berry, eastern shadbush, black mulberry, and wild grown blackberry. The highest amounts of total phenols were quantified in chokeberry fruit. Wild strawberry, raspberry, and blackberry had 2‐ to 5‐fold more total phenolics compared to cultivated plants. Practical Application: The fruit of analyzed berry species contained different levels of sugars, organic acids, and total phenolics. Moreover, it has been demonstrated that wild grown species generally contain more phenolics than cultivated ones. This information is interesting for nutritionists as well as berry growers and breeders who can promote the cultivation of species and new cultivars with higher phenolic content.     

Identification and quantification of phenolic compounds from sunflower (Helianthus annuus L.) kernels and shells by HPLC-DAD/ESI-MS

Phenolic compounds were extracted from defatted sunflower (Helianthus annuus L.) kernels and shells and characterised by HPLC with diode array and electrospray ionisation (ESI) mass spectrometric detection in the negative mode. Quantification of individual compounds was carried out by external calibration. Among the eleven compounds analysed 5-O-caffeoylquinic acid was predominant amounting up to 59.1 mg/100 g in the shells and 3050.5 mg/100 g in the kernels. The specific fragmentation patterns of mono- and dihydroxycinnamoylquinic acids allowed the unambiguous distinction of several stereoisomers which have not been described for sunflower seeds and seed shells so far. The total phenolic content of about 4200 mg/100 g on a dry matter basis revealed defatted sunflower meal to be a promising source of phenolic compounds that might be recovered and used as natural antioxidants. Furthermore, the press residues originating from sunflower oil extraction were shown to be still rich in phenolic antioxidants, thus, providing the opportunity to valorize these by-products in terms of sustainable agricultural production.     

Phenolic content,antioxidant and physico‐chemical properties of Sardinian monofloral honeys

In this study, fifty‐one monofloral Sardinian honeys from ten various floral origins were screened for their phenolic content, antioxidant activity, colour and electrical conductivity. The total phenolic amounts have been evaluated by Folin–Ciocalteu method, whereas quantification of several phenolic compounds (phenolic acids and flavonoids) has been carried out by HPLC‐DAD technique. The richest sample in phenolic compounds resulted strawberry tree honey with about 40 mg GAE/100 g, as well FRAP test and DPPH˙ test confirm that antioxidant activity of strawberry tree honey extract exceed both honey extracts and synthetic antioxidants like BHA and BHT. Among the studied phenolic compounds a total of five phenolic acids (ferulic, syringic, trans‐cinnamic, chlorogenic and p‐hydroxycinnamic) and nine flavonoids (catechin, kaempferol, rutin, quercetin, luteolin, apigenin, galangin, pinocembrin and pinobanksin) were identified. Our results show good correlations between total polyphenol amount and antioxidant activity and between colour and electrical conductivity.