Antioxidant power,bacteriostatic activity,and characterization of white grape pomace extracts by HPLC–ESI–MS

Polyphenolic fractions obtained from white grape pomace by aqueous extraction were analyzed to determine their antioxidant power (DPPH and TBARS methods), bacteriostatic activity, the effect of particle size on total extractable polyphenols (expressed as gallic acid equivalents (GAE)), and to characterize by HPLC–ESI–MS. The extraction of polyphenols from Albariño variety grape pomace was performed both on lab-scale and on pilot-plant scale using particles sizes of <1 mm, 3–5 mm and entire particle. Lab-scale assays showed that the lower the particle size the higher the raw extract (RE) percentage (%w/w), which values were 21.3 ± 0.37% (SD), 12.6 ± 0.38%, and 6.6 ± 0.44%, respectively. Several fractions were obtained from RE, either as result of applying liquid–liquid partition or gel permeation chromatography. The antiradical activities of the fractions were lower than that of gallic acid (17.8 ± 0.1 mg GAE/mol DPPH) but similar to that of catechin or procyanidin B₂ (46.0 ± 2.3 mg GAE/mol DPPH and 52.3 ± 6.3 mg GAE/mol DPPH). Several fractions showed bacteriostatic activity both at 50 and at 100 mg/L. Total aerobic bacterial enumeration (TABE, log UFC/cm²) of treated samples revealed a significant lower TABE than that for control. HPLC–ESI–MS studies demonstrated that fractions V and VI included monomers, dimers, and trimers of procyanidins, few of them galloylated. Fraction VII contained several oligomers and galloylated procyanidins.     

Selection of the Solvent and Extraction Conditions for Maximum Recovery of Antioxidant Phenolic Compounds from Coffee Silverskin

The extraction of antioxidant phenolic compounds from coffee silverskin (CS) was studied. Firstly, the effect of different solvents (methanol, ethanol, acetone, and distilled water) on the production of antioxidant extracts was evaluated. All the extracts showed antioxidant activity (FRAP and DPPH assays), but those obtained with methanol and ethanol had significantly higher (p?<?0.05) DPPH inhibition than the remaining ones. Due to the lower toxicity, ethanol was selected as extraction solvent, and further experiments were performed in order to define the solvent concentration, solvent/solid ratio, and time to maximize the extraction results. The best condition to produce an extract with high content of phenolic compounds (13 mg gallic acid equivalents/g CS) and antioxidant activity [DPPH?=?18.24 μmol Trolox equivalents/g CS and FRAP?=?0.83 mmol Fe(II)/g CS] was achieved when using 60 % ethanol in a ratio of 35 ml/g CS, during 30 min at 60–65 °C.     

Optimization of Antioxidant Compounds Extraction from Flesh of New Developed Apple Cultivar Using Response Surface Methodology

The response surface methodology (RSM) and the central composite rotatable design were used to optimize the antioxidant extraction from apple flesh of a new cultivar (Rural Issues and Agricultural Research Institute of Santa Catarina (EPAGRI) m-58/07). The extraction conditions were optimized by measured antioxidant capacities from the ferric-reducing power (FRAP) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) assays, and by the determination of total phenol content. The results showed that the most significant variable in the extraction procedure was solvent concentration. The optimal condition found was of 60 %, 5 mL/g, 30 °C, and 61 min for acetone aqueous solution, solvent to solid ratio, temperature, and time, respectively, resulting in optimal antioxidant capacities of 2,152.96 μmol TE/100 g DW by DPPH and 6,491.39 μmol Fe²⁺/100 g DW by FRAP essays, and total phenol amount of 485.62 mg GAE/100 g DW. The antioxidant capacity of EPAGRI m-58/07 was verified to be substantially higher than other cultivars commercially available.     

Optimization of microwave-assisted extraction of phenolics from potato and its downstream waste using orthogonal array design

While other extraction methods have been tempted, a microwave-assisted extraction (MAE) method coupled with the orthogonal array design was investigated for efficient extraction of the phenolic compounds in potato downstream wastes. Four parameters were examined for the MAE of the total phenolic content (TPC) and optimized at 60% ethanol, 80 °C, 2 min, solid-to-solvent ratio 1:40 (g/ml). The MAE was proven more efficient than the conventional solvent extraction by refluxing. The optimized model showed that the downstream wastes, both the supernatant and the residue contained high TPC, particularly the former (11.0 ± 0.26 mg GAE/g DW). The antioxidant activities (DPPH and FRAP) closely correlated with the TPC of the samples (r = 0.92–0.97). Chlorogenic acid and caffeic acid were found to be the predominant phenolic acids. The extracts of the downstream wastes from potato processing can be a promising candidate for functional foods and nutraceutical ingredients.     

Grape Marc Powder: Physicochemical and Microbiological Stability During Storage and Moisture Sorption Isotherm

In the present work, the stability of grape marc powder was evaluated during its storage at room conditions for 6 months. Grape juice marc from Vitis labrusca cv. “Isabel” was dried to 8.8?±?0.9 % moisture content (wet basis) in forced convection drying equipment at 70 °C, crushed and stored aseptically in dark polyethylene bags and kept at 25?±?2 °C for up to 6 months. Grape marc powder was microbiologically safe, free of Salmonella sp., Bacillus cereus, and fecal coliforms. Total phenolic compounds with 1,1-diphenyl-2-pic-ryl-hydrazyl (DPPH) scavenging capacity and ferric reducing antioxidant power (FRAP) were stable, although monomeric anthocyanins and compounds with the capability of scavenging 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radicals showed to be susceptible to degradation through the storage period. Moisture sorption isotherm at 25 °C for the powder material was determined by static gravimetric methodology. The sorption isotherm of the grape marc powder showed a sigmoidal shape (type II), typical of food materials. The experimental data was satisfactorily fitted by the GAB (Guggenheim–Anderson–de Boer) model, giving a monolayer moisture content (X _m) of 6.75 % (dry basis). Results indicate that grape marc powder can be considered as a potential functional ingredient with an acceptable stability.     

Optimisation of pressurised liquid extraction for antioxidative polyphenolic compound from Momordica charantia using response surface methodology

Pressurised liquid extraction (PLE) of antioxidant compounds from bitter gourd fruits (Momordica charantia) in aqueous ethanolic solvent was investigated using response surface methodology at laboratory scale to understand key impact of extraction variables. Extraction efficiency was optimised by measuring the yield of extraction, total phenolic content (TPC), total flavonoid content (TFC), ferric reducing/antioxidant power assay (FRAP) and radical scavenging activity (RSA). The optimal extraction conditions were reached at 80% ethanol concentration, 10‐min extraction time and at 160 °C. Under these extraction conditions, values of TPC (5.40 ± 0.30 g GAE per 100 g), TFC (1.50 ± 0.10 g QE per 100 g), FRAP (778.55 ± 10 μmol eq Fe (II) g^?1), yield (178.50 ± 5.50 mg g^?1 dc) and RSA (75.50 ± 4.50%) were achieved. Furthermore, statistical analysis revealed that antioxidative attributes of bitter gourd extract were strongly and positively correlated with extraction temperature and ethanol concentration rather than processing time. This study illustrated that PLE has the potential to extract antioxidant compounds from tropical fruit vegetables in an accelerated manner. Furthermore, influential parameters affecting the process could be optimised for further industrial intake.     

Antioxidant activity and phenolic content of pressurised liquid and solid–liquid extracts from four Irish origin macroalgae

The efficiency of solid–liquid extraction (SLE) and pressurised liquid extraction (PLE) for the recovery of antioxidant and polyphenols from the Irish macroalgae, Fucus serratus, Laminaria digitata, Gracilaria gracilis and Codium fragile, was assessed using the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays and the Folin–Ciocalteu total phenol content (TPC) assay. Fucus serratus had TPC and antioxidant activities thirty times higher than the other species. Solid–liquid extraction cold water (CW_SLE) had the highest TPC (81.17 μg GAE mg^?1 sample) derived from F. serratus, compared with the TPC of 61.12 μg GAE mg^?1 sample for the corresponding PLE extract. For both SLE and PLE extracts, low TPC levels were observed in L. digitata, G. gracilis and C. fragile. The majority of SLE extracts possessed higher FRAP and DPPH activities compared with their PLE counterparts. This study indicates that the high temperatures and pressures in PLE did not enhance the antioxidant activities relative to conventional SLE extraction.     

Antioxidant and Free Radical Scavenging Capacity of Extensively Used Medicinal Plants in Sri Lanka

The burden of chronic diseases is rapidly increasing worldwide. Diet and nutrition are important factors in the promotion and maintenance of good health throughout the entire life course. Physiological and biochemical alterations in the human body may result in overproduction of free radicals leading to oxidative damage to biomolecules (e.g. lipids, proteins, DNA). Use of medicinal plant based products has increased recently because of their exerted beneficial properties such as antioxidant, anticancer, hypoglycaemic and hypolipidaemic activities. The present study was designed to assess the in vitro antioxidant activity and free radical scavenging capacity of ten medicinal plants which are extensively used in the Ayurvedic treatment systems in Sri Lanka. Water extracts were prepared and evaluated for their free-radical scavenging capacity and antioxidant activity using a number of chemical assays; DPPH, ABTS and FRAP. The total Phenolic (TPC) and Total Flavonoid Content (TFC) were also assessed. The TPC and TFC values of the extracts varied from 295.94±3.65 – 5.22±0.08 (mg Gallic Acid Equivalent (GAE)/g dry weight) and 115.01±1.69 – 0.97±0.002 (mg Catechin Equivalent (CE)/g dry weight) respectively. The DPPH and ABTS radical scavenging activities were higher for the Nelli (Phyllanthus emblica) extract while the least activity was observed in Venivel (Cosciniumfenestratum) extract. The FRAP activity of the extracts was well proved with the DPPH and ABTS radical scavenging activities. A positive, significant linear relationship between antioxidant activity and TPC and TFC content showed that phenolic compounds and flavonoids were the dominant antioxidant components in the medicinal herbs studied.     

Influence of pressurised liquid extraction and solid–liquid extraction methods on the phenolic content and antioxidant activities of Irish macroalgae

The efficiencies of pressurised liquid extraction (PLE) and a traditional solid–liquid extraction (SLE) at extracting antioxidant polyphenols from Irish macroalgae Ascophyllum nodosum, Pelvetia canaliculata, Fucus spiralis and Ulva intestinalis were compared. PLE was more effective for extracting polyphenols with acetone/water (80:20); however, when food‐friendly solvents of ethanol/water (80:20) and water were employed, SLE resulted in higher phenolic content in brown macroalgal extracts. For example, the Fucus spiralis SLE water and ethanol/water extracts displayed total phenolic contents (TPCs) of 130.58 ± 2.78 and 142.81 ± 1.77 μg phloroglucinol equivalents (PGE) mg^?1 sample, respectively, compared with TPCs of 90.79 ± 1.16 and 124 ± 6.54 μg PGE mg^?1 sample for the corresponding PLE extracts. All SLE aqueous ethanolic macroalgal extracts possessed higher DPPH radical scavenging abilities (RSA) and ferric reducing antioxidant power (FRAP) than their PLE equivalents . This study indicates that the application of high extraction temperatures (50–200 °C) and pressures (500–3000 psi) used in PLE does not enhance the antioxidant activities of macroalgal extracts relative to SLE extraction. The ability to produce antioxidant food‐friendly macroalgal extracts using SLE could represent significant cost reductions on an industrial scale further enhancing the potential of macroalgal polyphenols to be used in functional food preparations.     

Optimization of Ultrahigh-Pressure Extraction of Polyphenolic Antioxidants from Green Tea by Response Surface Methodology

A new extraction technique, ultrahigh-pressure extraction, was used to obtain antioxidants from green tea. The response surface methodology was employed to optimize the extraction process. The effects of ethanol concentration (x ₁, 33.2–66.8 %), pressure (x ₂, 281.8–618.2 MPa), and liquid/solid ratio (x ₃, 11.6–28.4 ml/g) on the total phenolic content (y ₁) and α,α-diphenyl-β-picrylhydrazyl free radical scavenging activity (y ₂) were investigated. Analysis of variance showed that second-order polynomial models produced a satisfactory fitting of the experimental data with regard to total phenolic content (R ²?=?0.9996, P?<?0.0001) and antioxidant capacity (R ²?=?0.9986, P?<?0.0001). The optimal condition determined was as follows: ethanol concentration, 50 %; pressure, 490 MPa; and liquid/solid ratio, 20 ml/g. Under this condition, the maximum total phenolic content and antioxidant activity of 583.8?±?0.9 mg/g dry weight and 85.6?±?0.7 % could be achieved, respectively, which were well matched with the predicted value.     

Antioxidant capacities and total polyphenol content of nine commercially available tea juices measured by an in vitro digestion model

The total antioxidant capacity and total polyphenol content of 9 tea juices were examined following in vitro digestion model. Results show that there was a significant variation in total antioxidant capacity [16,392.30 ± 111.64–22,340.23 ± 46.73 μmol VC/L (DPPH), 3,194.24 ± 14.76–13,795.07 ± 37.46 μmol Trolox/L (ABTS), 2,540.61 ± 59.79–7,951.57 ± 31.91 μmol Trolox/L ferric reducing antioxidant power (FRAP)] and total polyphenol content (265.84 ± 9.52–876.62 ± 6.59 μg GAE/mL). Following the in vitro digestion, most of the juices of antioxidant capacities and 7 juices of the total polyphenol content were decreased. Before the in vitro digestion, a highly positive correlation was found between the total polyphenol content and FRAP value. After the gastric phase of digestion, there was a very strong positive linear correlation between the total polyphenol content and total antioxidant capacity. After the duodenal phase of digestion, the correlation between the total polyphenol content and total antioxidant capacity was very weak, and also, a very weak linear correlation was found between the antioxidant assays.     

Evaluation of antioxidant activities of Iranian sumac (R. coriaria L.) fruit and spice extracts with different solvents

The antioxidant capacity and phenolic content of three sumac (Rhus coriaria L.) samples, including brown sumac fruit, brown sumac powder and red sumac powder were investigated in the present study. Methanol, ethanol, distilled water, and a mixture of methanol and ethanol (1:1) were used as solvent systems. Antioxidant activities of extracts were screened using 1,1-diphenyl-2-picrylhydrazyl DPPH radical scavenging method. Phenolic content was determined through Folin–Ciocaltaeu procedure. The efficiency of the solvents used to extract phenols from the samples varied considerably. The phenolic content of brown sumac powder ranged from 2.906 to 2.997 gallic acid equivalents/100 g (GAE/100 g), while that of the brown sumac fruit was 2.438–2.529 GAE/100 g, and that of the red sumac powder was 2.172–2.263 GAE/100 g. Findings indicated that water extracts of sumac have effective antioxidant and radical scavenging activities as compared to other extracts.     

Polyphenolic profile,antioxidant properties and antimicrobial activity of grape skin extracts of 14 Vitis vinifera varieties grown in Dalmatia (Croatia)

The aim of the present study was to determine polyphenolic composition, related antioxidative and antimicrobial properties of grape skin extracts from 14 grape varieties (seven white and seven red grape) grown in Dalmatia (Croatia). The content of total phenols, flavonoids, catechins, flavanols and individual polyphenols ((+)-catechin, (−)-epicatechin, epicatechin gallate, procyanidin B1 and procyanidin B2, quercetin glucoside, resveratrol monomers, piceid and astringin) was variety dependent. Antioxidant properties were determined as DPPH radical-scavenging ability (IC₅₀), ferric reducing/antioxidant power (FRAP), Fe²⁺-chelating activity (IC₅₀), and using β-carotene bleaching assay. The high antioxidant capacity of all extracts, both red and white, has been observed and related to the relative amounts of polyphenolic compounds with good antioxidant properties. The antimicrobial activity was screened by broth microdilution test using Gram-positive (Staphylococcus aureus, Bacillus cereus) and Gram-negative bacteria (Escherichia coli O157:H7, Salmonella Infantis, Campylobacter coli). It was confirmed against all tested organisms. Minimum inhibitory concentrations (MICs), were found in the range 0.014–0.59 mg of gallic acid equivalents (GAE)/ml, with lower MICs of white cultivars, especially against Campylobacter and Salmonella.     

Extraction of antioxidants and flavonoids from yuzu (<Emphasis Type="Italic">Citrus junos</Emphasis> Sieb ex Tanaka) peels: a response surface methodology study

In the present investigation, extraction of antioxidants and flavonoids from the peels of yuzu fruit using a single factor experiment and a response surface methodology (RSM) based on central composite design was studied. Four independent variables were evaluated at five levels with total 29 experimental runs, including ethanol concentration (EtOH), ratio of liquid to material (L/S), extraction temperature (T), and extraction time (t). The total phenolic content (TPC), total flavonoids content (TFC), two indicators of antioxidant capacity (FRAP and DPPH), and three individual major flavonoids in yuzu (hesperidin, naringin, and phloretin) served as the response functions. Quadratic polynomial equations were obtained by multiple regression analysis to predict the optimal extraction conditions. The regression analysis showed that >95?% of variations were explained by the models of different responses considered. The responses were significantly influenced by all studied factors. The Multiresponse optimized conditions targeted at maximizing all the responses were found to be EtOH?=?65.550?%; T?=?43.864?°C; t?=?119.673 min; and L/S?=?37.168 ml/g, with a desirability of 0.950. At the optimized conditions, the experimental values of FRAP (964.9?±?23.1 mgTE/g DW), DPPH (453.0?±?5.2 mgTE/g DW), TPC (1161.2?±?25.2 mgGAE/g DW), (TFC393.4?±?mgQE/g DW), hesperidin (337.2?±?4.0 mg/g DW), naringin (244.9?±?1.1 mg/g DW), and phloretin (43.9 mg/g DW) were in a reasonable agreement with the predicted values. The extraction method was applied successfully to extract antioxidants and flavonoids from yuzu peels. It also allows a fast and cost-saving process for extraction of the studied phytochemicals, in addition to improvement of the quantity of the targeted extract.     

Development of a New Extraction Method for Heterocyclic Aromatic Amines Determination in Cooked Meatballs

Heterocyclic aromatic amines (HCAs) are mutagenic and carcinogenic compounds that are produced in meats cooked at high temperature. In this study, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 9H-pyrido[3,4-b]indole (norharman), and 1-methyl-9H-pyrido[3,4-b]indole (harman) were studied. A new extraction method was developed for the determination of heterocyclic amines with high-performance liquid chromatography (HPLC). Linearity for each HCA was observed with a high regression coefficient (r?=?0.9999, P?<?0.01 for IQ; r?=?0.9990, P?<?0.01 for MeIQx; r?=?0.9989, P?<?0.01 for 4,8-DiMeIQx; r?=?0.9934, P?<?0.05 for PhIP; r?=?1.000, P?<?0.01 for norharman; r?=?0.9991, P?<?0.01 for harman). Limits of detection for various HCAs were found between 0.04 and 1.40 ng/g. Limits of quantification were found in the range of 0.13–4.40 ng/g. Recovery rates varied from 68.9 % to 87.8 %. This method was compared with two different common HCA extraction methods in literature. The optimized new extraction method and the other two methods were used for the determination of HCAs in ten different cooked meatball samples. Sample extraction procedures of HCAs were investigated in more detail, and a rapid, accurate, precise, and reliable extraction method was developed.     

Antioxidant capacity and total phenolics of <Emphasis Type="Italic">Cyphostemma digitatum</Emphasis> before and after processing: use of different assays

In the framework of standardisation of new healthy food sources, this paper aimed to study the total phenolics and the antioxidant power of Cyphostemma digitatum (Vitaceae) in water and ethanol extracts, using 96-well micro plates with BMG FLUOstar Optima micro plate reader. Total phenolics by Folin–Ciocalteu method in the water extracts were significantly lower after processing, decreasing from 1.41 ± 0.06 g GAE/100 g in the raw leaves to 0.80 ± 0.08 g GAE/100 g in the processed sample; the ethanol extract revealed the same trend with higher values, decreasing from 1.95 ± 0.03 to 1.56 ± 0.12 g GAE/100 g. The antioxidant capacity was elucidated by four methods: TEAC, DPPH, FRAP and ORAC. No or very weak correlations were found between antioxidant assays and total phenolics; this confirms that the antioxidant capacity could be attributed to other molecules. The ORAC assay proved to be more powerful than the other assays; it showed 103.3 ± 2.5 mmol/100 g Trolox equivalents in the raw leaves ethanol extract and 91.9 ± 3.0 mmol/100 g in the processed sample. ORAC assay showed the opposite for the water extract where the antioxidant capacity increased from 16.7 ± 0.2 to 41.7 ± 2.7 mmol/100 g Trolox equivalents after processing, which could be attributed to new water-soluble compounds generated in the consumed form.     

Application of Analytical Methods for the Determination of Bioactive Compounds in Some Berries

Fluorometry, ESI-MS, FTIR, and radical scavenging assays were used for characterization of bioactive compounds and the levels of their antioxidant activities. Polyphenols, flavonoids, anthocyanins, and ascorbic acid and the level of antioxidant activity of water extracts of “Murtilla-like” [Myrteola nummularia (Poiret) Berg.], and other widely consumed berries were determined and compared. The contents of bioactive compounds and the levels of antioxidant activities in water extracts differed significantly in the investigated samples (P?<?0.05). “Murtilla-like” extracts contained polyphenols (mg GAE/g)—19.13?±?0.9, flavonoids, (mg CE/g)—3.12?±?0.1, anthocyanins (mg CGE/g)—120.23?±?5.4, and ascorbic acid (mg/g)—2.20?±?0.1; and antioxidant activities (μmolTE/g) by ABTS and CUPRAC assays were 200.55?±?8.7 and CUPRAC 116.76?±?5.7, respectively. Chemometrical processing was done on the basis of kinetic data of two variables (concentration and reaction time) by DPPH scavenging reaction. Polyphenol content highly correlated with antioxidant capacity (R² from 0.96 to 0.83). The quenching properties of berries were studied by the interaction of water polyphenol extracts with a small protein such as BSA by 3-D fluorescence and FTIR spectroscopy. These methods were used as additional tools for the characterization of polyphenols. Wild-grown non-investigated berries were compared with widely consumed ones, using their bioactive composition, antioxidant activities, and antiproliferative and fluorescence properties. In conclusion, the antioxidant properties of “Murtilla-like” can be used as a new source for consumption. The bioactivity of “Murtilla-like” is comparable with blueberries and raspberries. 3-D fluorescence and FTIR spectroscopy can be applied as additional analytical tools for rapid estimation of the quality of food products.

Polyphenols contents and antioxidant capacity of 68 Chinese herbals suitable for medical or food uses

The present study estimated in vitro antioxidant activities of 68 common Chinese herbals both for medical and food uses, using Folin–Ciocalteu, ferric-reducing/antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging assays. The results showed different extraction had various antioxidant properties. Six plant materials including Chinese White Olive, Clove, Pricklyash Peel, Villous Amomum Fruit, Chinese Star Anise and Pagodatree Flower appeared highest total phenolics (>45 mg gallic acid equivalents (GAE)/g) and flavonoids content (>45 mg rutin equivalents (RE)/g), which also showed highest antioxidant activity (FRAP value > 2.5 mmol/g, DPPH radical-scavenging capacity > 85%), indicating they have potentials for use as natural sources of antioxidant foods. The total phenolics content of these 68 plant extracts was significantly positively correlated (r² = 0.9467) with their antioxidant capacity. Therefore, the content of phenolic compounds could be used as an important indicator of its antioxidant capacity.     

A comprehensive study of polyphenols contents and antioxidant potential of 39 widely used spices and food condiments

Spices and condiments are rich sources of potent antioxidants. In the present investigation, total equivalent antioxidant capacities (TEAC) of 39 spices were studied using 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) scavenging, and cupric reducing antioxidant capacity (CUPRAC) assays. Their total phenolic contents (TPC) and total flavonoid contents (TFC) were also determined. TEAC, TPC, and TFC varied significantly (P?<?0.05) among these spices. ABTS, DPPH, and CUPRAC assay values of studied spices ranged from 1.42 to 112.94 mg ascorbic acid equivalents (AAE)/g, 1.14 to 91.09 mg Trolox equivalents (TE)/g, and 0.52 to 54.47 mg TE/g, respectively (dry weight basis; DW). Based on Folin–Ciocalteu assay, TPC ranged from 2.93 to 160.55 mg of gallic acid equivalents (GAE)/g DW. Strong correlations between TPC and TEAC values (R?=?0.966, 0.825, and 0.954 for ABTS, DPPH, and CUPRAC, respectively) were found. This indicates that phenolic compounds are potent antioxidants in these spices. Principal component analysis (PCA) indicated that cloves (flower buds of Syzygium aromaticum) had the most distinct and potent antioxidant capacity, followed by allspice (fruits of Pimenta dioica) and cinnamon (bark of Cinnamomum verum). Results of the present study provide adequate evidence that polyphenols are responsible for their compelling antioxidant capacities of studied spices. Thus, consumption of antioxidant-rich spices such as cloves, allspice, and cinnamon can significantly prevent oxidative stress in the human body.     

Total phenolic content and antioxidant capacity of extracts obtained from six important fruit residues

The extracts from kinnow peel, kinnow seeds, litchi pericarp, litchi seeds, grape seeds, and banana peel were screened for total phenolic content (TPC), trolox equivalent antioxidant capacity (TEAC), 1,1 diphenyl-2-picryl hydrazyl (DPPH) radical scavenging activity, as well as reducing power. Kinnow peel extract exhibited the highest reducing power, TEAC, and DPPH free radical scavenging activity, whereas, the phenolic content of 37.4 mg GAE/g-dw was highest for grape seed extract. Banana peel extract with a low TPC showed the lowest reducing power, TEAC as well as DPPH free radical scavenging activity among the fruit residue extracts examined in the present study. Correlation analysis between the reducing power and DPPH radical scavenging ability; reducing power and ABTS radical scavenging activity; and ABTS and DPPH radical scavenging abilities showed a high degree of correlation (r² = 0.85-0.91). However, r² of 0.36, 0.66, and 0.49 between TPC and DPPH radical scavenging activity; TPC and reducing power; and TPC and ABTS radical scavenging ability, respectively, indicated that some non-phenolic compounds also contributed to the total antioxidant activity in fruit residue extracts examined in this study. To the best of our knowledge, this is the first paper presenting comprehensive data on TPC, reducing power, and antioxidant activity for the six fruit residues. This study demonstrated that kinnow peel, litchi pericarp, litchi seeds, and grape seeds, can serve as potential sources of antioxidants for use in food and pharmaceutical industry.