Effect of air-drying temperature on physico-chemical properties,antioxidant capacity,colour and total phenolic content of red pepper (Capsicum annuum, L. var. Hungarian)

Red pepper has been recognised as an excellent source of antioxidants, being rich in ascorbic acid and other phytochemicals. Drying conditions, particularly temperature, leads to pepper modifications that can cause quality degradation. In this work, the effects of process temperatures between 50 and 90 °C on physico-chemical properties, rehydration, colour, texture, vitamin C, antioxidant capacity and total phenolics during the drying of red pepper were studied. The rehydration ratio decreased with temperature and the maximum water holding capacity was achieved at 50 °C. Both vitamin C content and the total phenolic content decreased as air-drying temperature decreased. The radical scavenging activity showed higher antioxidant activity at high temperatures (i.e. 80 and 90 °C) rather than at low temperatures (i.e. 50, 60 and 70 °C). Chromatic parameters (L*, a*, b*, C* and H°), non-enzymatic browning compounds and extractable colour were affected by drying temperature, which contributed to the discolouring of pepper during this process.     

Effect of high hydrostatic pressure pretreatment on drying kinetics, antioxidant activity, firmness and microstructure of Aloe vera (Aloe barbadensis Miller) gel

The effect of High Hydrostatic Pressure (HHP) and other pretreatments on the drying kinetics, antioxidant activity, firmness and microstructure of Aloe vera gel was investigated during convective drying at 70 °C. The pretreatments analyzed were high hydrostatic pressure, blanching, enzymatic and microwaves. Simulation of drying curves was studied through the application of several mathematical models such as Newton, Henderson and Pabis, Page, Modified Page, Wang and Singh, and Weibull. Among them, the Weibull model provided the best fit for the experimental data. All pretreatments increased the water diffusion coefficient compared to the control sample. Microwaves followed by HHP presented the fastest drying rates. All pretreatments modified the microstructure and hence the texture of the product. HHP and microwaves increased firmness while blanching and enzymatic treatments produced a softer final product. Blanching, microwaves and HHP enhanced A. vera antioxidant activity. However, the HHP pretreated samples showed the highest antioxidant activity compared to the rest. Based on these results, HHP together with convective drying offers the chance of producing dried aloe with high antioxidant attributes.     

Influence of air temperature on drying kinetics and antioxidant potential of olive pomace

This work aims to evaluate the influence of olive pomace drying (a solid by-product of the olive oil industry) on both antioxidant potential and drying kinetics. The two main fractions of olive pomace (pits, PI and pulps + peels, P + P) were characterized by image analysis and density measurement. The drying process was analyzed in experiments carried out at different temperatures (from 50 to 150 °C) and mathematically described from the diffusion and Weibull models. The antioxidant potential of the extracts (ethanol–water 80:20 v/v, 22 ± 1 °C, 170 rpm for 24 h) obtained from the dry product was analyzed by measuring the total phenolic content and antioxidant capacity and the main polyphenols were quantified by HPLC–DAD/MS–MS.     

Effect of different drying methods on drying characteristics,colour, total phenolic content and antioxidant capacity of Goldenberry (Physalis peruviana L.)

In this study, the effects of convective, microwave and microwave–convective drying methods on the drying characteristics, colour, total phenolic content and antioxidant capacity of goldenberry fruits were investigated. To select the most appropriate thin‐layer drying model for drying treatments, nine mathematical drying models were fitted to the experimental data. Based on the statistical tests used for evaluation, the Midilli et al. and Wang and Singh models were considered the best models to describe the drying behaviours of goldenberry fruits in all drying methods. The colour values (L*, a* and b*) of fresh fruit were decreased by drying. Compared with the fresh sample, the dried samples exhibited a 64–75% and 65–75% decrease in total phenolic content and antioxidant capacity, respectively. Among the different drying treatments, the values closest to those of fresh samples with respect to colour values, total phenolic content and antioxidant capacity were achieved with the 160 W microwave drying method.     

Enhancement of antioxidant activity,total phenolic and flavonoid content of black soybeans by solid state fermentation with Bacillus subtilis BCRC 14715

In the present study, a solid state fermentation of black soybeans with Bacillus subtilis BCRC 14715 was performed. The effect of fermentation on the changes of total phenolic and flavonoid content and antioxidant activities including 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging effect, and Fe²⁺-chelating ability exerted by various solvent (water, 80% methanol, 80% ethanol, 80% acetone) extracts of black soybeans was examined. It was found that fermentation enhanced the total phenolic and flavonoid content as well as antioxidant activity of the black soybean extract. Among the various extracts examined, the acetone extract of fermented black soybeans showed the highest total phenolic and flavonoid content. The acetone extract and the methanol extract of fermented black soybeans showed the highest DPPH free radical-scavenging effect and Fe²⁺-chelating ability, respectively. Analysis of extraction yields showed that the active principle associated with the DPPH radical-scavenging effect was most efficiently extracted from black soybeans using water, regardless of fermentation. Water and methanol effectively extract the Fe²⁺-chelating principles from non-fermented and fermented black soybeans, respectively.     

Effect of pulverization on the antioxidant activity of water caltrop (Trapa taiwanensis Nakai) pericarps

This study was to investigate the effect of pulverization treatment on the antioxidant properties of water caltrop pericarps. The results showed that crude fiber was the largest proportional constituent of water caltrop pericarps, comprising 72.3 g/100 g (dry basis). After 10 min milling, five fractions were obtained 1-5 different particle sizes (285, 211, 138, 62 and 41 μm, respectively). Comparing the effect of pulverization on the fiber component of each fraction, the fraction 1 exhibited higher hemi-cellulose but lower lignin than smaller particle size fraction except fraction 5. At a dosage of 250 μg/mL methanol extracts, the highest free radical-scavenging ability is obtained in the fraction 5, which is found to be 78.3 g/100 g, followed by the fractions 1-4. The same tendency was observed in the reducing power and cupric ions chelating ability. The fractions 1 and 5 contained significantly higher total phenolics and total flavonoids than fraction 2-4 (p < 0.05).     

Degradation kinetics of total phenolic compounds,capsaicinoids and antioxidant activity in red pepper during hot air and infrared drying process

Degradation kinetics of total phenolic compounds, capsaicinoids and antioxidant activity in red pepper during both hot air drying and infrared drying were investigated, as well as the correlation between antioxidant compounds and antioxidant capacity was discussed in current study. The fractional conversion kinetic and first order kinetic models were proved to describe the changes of total phenolic compounds vs. drying time and moisture content, respectively. Degradation of capsaicinoids and antioxidant capacity vs. drying time and moisture content both followed fractional conversion kinetic model. Infrared drying accelerated the degradation rate of total phenolic compounds and capsaicinoids vs. drying time as compared with hot air drying at the same temperature; however, a contrary result was found that infrared drying decreased the degradation rate of both total phenolic compounds and capsaicinoids vs. moisture content. Total phenolic compounds exhibited a stronger relationship with antioxidant capacity of red pepper analysed by multiple linear regression analysis.     

Effect of air temperature on drying kinetics and quality characteristics of osmo-treated jumbo squid (Dosidicus gigas)

The present study investigated the influence of air temperature on the drying kinetics, color, rehydration, total volatile basic nitrogen (TVBN), antioxidant capacity and texture of osmosed jumbo squid fillets during convective dehydration at 50, 60, 70, 80 and 90 °C. The Logarithmic and Two-term models could be used to describe the squid experimental drying curves. Discoloration of product was more noticeable at high drying temperatures where combined effects of non-enzymatic browning as well as protein denaturation modified the original color of the squid samples. Rehydration indexes showed a decrease while texture presented an increase with increasing air-drying temperature probably due to changes in food protein matrix. Total volatile basic nitrogen increased with process temperature. Antioxidant activity presented a decrease with temperature, especially at high drying temperatures. Results of this study demonstrated that the drying kinetics together with the reported quality attributes of the dried squid can be used to improve the final characteristics of the product.     

Antioxidant capacity,total phenolic and ascorbate content as a function of the genetic diversity of leek (Allium ampeloprasum var. porrum)

Extracts of the white shaft and green leaves of 30 leek cultivars were investigated for their antioxidant properties, total phenolic (TP) and l-ascorbic acid (AA) content. The measured antioxidant properties included free radical scavenging activities against peroxyl (ORAC) and 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH) and their Fe³⁺ reducing capacity (FRAP). The results from this study suggest that the green leek leaves generally have significantly stronger antioxidant properties than the white shaft. Correlation analysis between the TP and the AA content and the antioxidant activity showed that phenolics and ascorbic acid contribute significantly to the antioxidant activity of leek. The three antioxidant activity assays were all correlated for the extracts of the white shaft of the 30 leek cultivars. Principal component analysis (PCA) elucidated the influence of part and type of cultivar on the antioxidant capacity, TP, and l-ascorbic acid content, whilst the breeding strategy and seed company had no influence.     

Identification of phenolic compounds and appraisal of antioxidant and antityrosinase activities from litchi (Litchi sinensis Sonn.) seeds

Antioxidant and antitryrosinase compounds from Litchi sinensis Sonn. seeds were extracted with five different types of polar solvents. The five extracts, namely ethanol extract (EE), 50% ethanol extract (50% EE), methanol extract (ME), 50% methanol extract (50% ME), and water extract (WE), were used for the evaluations of total phenolic content, antioxidant capabilities and antityrosinase activity. The 50% EE showed the highest total antioxidant capacity, scavenging the 1,1-diphenyl-2-picryl hydrazyl (DPPH) radical and inhibitory activity against lipid peroxidation, and it was comparable to the activity of the synthetic antioxidant, butylated hydroxyl toluene. Fifty percent EE showed a better antityrosinase activity compared to the other extracts. After application of reverse phase high performance liquid chromatography, coupled to a diode array detector and electrospray ionisation mass spectra, five phenolic compounds, namely, gallic acid, procyanidin B2, (−)-gallocatechin, (−)-epicatechin and (−)-epicatechin-3-gallate were identified from 50% EE. This study suggests that litchi seed can potentially be used as a readily accessible source of natural antioxidants.     

Phenolic content and antioxidant activity of cantaloupe (cucumis melo) methanolic extracts

The objectives of this study were to determine phenolic content and antioxidant activity of methanolic extracts from different parts of cantaloupe (leaf, stem, skin, seed and flesh). The flesh extract afforded the highest yield (89.6 ± 0.3%) whilst the lowest yield was obtained from the seed (13.7 ± 0.5%) (p < 0.05). The leaf extract showed the highest total phenolic content (26.4 ± 0.3 mg GAE/g extract) and total flavonoid content (69.7 ± 3.37 μg RE/g extract) accompanied with best antioxidant activity through all antioxidant assays (p < 0.05). In addition, the stem extract also exhibited good antioxidant activity. Thus, these results suggest that methanolic extracts of cantaloupe leaf and stem may serve as a potential source of natural antioxidant for food and nutraceutical application.     

Quantification of phenolic contents and antioxidant capacity of Atlantic sea cucumber, Cucumaria frondosa

The antioxidant activity (oxygen radical absorbance capacity, ORAC) and total phenols and flavonoids were determined in extracts from digestive tract, gonads, muscles and respiratory apparatus of sea cucumber, Cucumaria frondosa. Total phenols content varied from 22.5 to 236.0 mg of gallic acid equivalents/100 g dw, and flavonoids from 2.9 to 59.8 mg of rutin equivalents/100 g. ORAC values ranged from 140 to 800 μmol of Trolox equivalents/g dw. Among all extracts, best antioxidant potencies were observed in ethyl acetate extracts from digestive tract, and in acetonitrile-rich fractions obtained from mixed extracts using acetonitrile/TFA (trifluoroacetic acid) acidified water on muscles, gonads and respiratory apparatus. The weakest potencies were observed with water extracts from digestive tract and respiratory apparatus, and with water-rich fractions obtained from mixed extraction of gonads and muscles. A significant correlation was observed between ORAC values and total phenol content in extracts and fractions of gonads and muscles, but ORAC and phenols were not correlated in digestive tract and respiratory apparatus extracts. ORAC values were significantly correlated (p < 0.05) with total flavonoids in all extracts. Successive eluates obtained from solid-phase extraction of water-rich fractions using C₁₈ cartridge showed ORAC values (105–500 μmol of TE/g) reaching up to 2.3 times the potency of their parent fractions. Flavonoids are suggested to be mainly responsible for observed activities. Our results provide a first quantitative evaluation of C. frondosa tissues as useful sources of antioxidants for human consumption.     

Determination of total phenolic content and antioxidant capacity of onion (Allium cepa) and shallot (Allium oschaninii) using infrared spectroscopy

Total phenolic content (TPC) and total antioxidant capacity (TAC) of four onion varieties (red, white, yellow and sweet) and shallot from selected locations (Washington, Idaho, Oregon, Texas and Georgia) were determined using Fourier transform infrared (FT-IR) spectroscopy (4000–400 cm⁻¹). The Folin–Ciocalteu (F–C) assay was used to quantify TPC and three assays were used to determine TAC, including 2,2-diphenyl-picrylhydrazyl (DPPH) assay, Trolox equivalent antioxidant capacity (TEAC) assay and ferric reducing antioxidant power (FRAP) assay. Partial least squares regression (PLSR) with cross-validation (leave-one-out) was conducted on onion and shallot extracts (n = 200) and their corresponding F–C, DPPH, TEAC and FRAP values were employed to obtain four independent calibration models for predicting TPC and TAC for the extracts. Spectra from an extra 19 independent extracts were used as an external validation set for prediction. A correlation of r > 0.95 was obtained between FT-IR predicted and reference values (by F–C, DPPH, TEAC and FRAP assay) with standard errors of calibration (SEC) and standard errors of cross-validation (SECV) less than 2.85, 0.35 and 0.45 μmol Trolox/g FW of extracts for TEAC, FRAP and DPPH assay, respectively; and 0.36 mg gallic acid/g FW of extracts for the F–C assay. In addition, cluster analysis (principal component analysis (PCA)) and discriminant function analysis (DFA) could differentiate varieties of onions and shallot based upon infrared spectral features. Loading plots for the various chemometrics models indicated that hydroxyl and phenolic functional groups were most closely correlated with antioxidant capacity. The use of mid-infrared spectroscopy to predict the total antioxidant capacity of vegetables provides a rapid and precise alternative to traditional wet chemistry analysis.     

Soluble phenols and antioxidant activity in mamey sapote (Pouteria sapota) fruits in postharvest

Mamey sapote (Pouteria sapota (Jacq.) H. E. Moore & Stearn) is a tropical species from the Sapotaceae family native to Mexico and Central America. Its tree produces an edible climacteric fruit, whose weight can range from 250 to 900 g. The flesh is soft, comprises about 78% of the fruit, and has high sugars to acidity ratio, which gives it a sweet taste when ripe. Because of current public interest to consume products that promote health, the aim of the work was to characterize soluble phenolic content and antioxidant activity in mamey sapote fruits from Chiapas, Mexico, at different maturity stages. Storage at 12 (± 1) °C was conducted for 18 d. When fruits ripened firmness flesh varied, in average, from 41.8 to 3.0 N, soluble solids content from 17.7 to 28.1 ºBrix, hue angle from 56.4 to 46.3º, and lightness from 67.3 to 42.0. Phenolic content was affected by ripening since average values of 2563 and 234 ??g/g were found in unripe and consumption maturities, respectively. In a soluble phenolics extract from flesh, gallic acid (GA), gallocatechin-3-gallate (G3G), epicatechin (ECT), and catechin (C) were found, being the latter the most abundant compound, which increased with ripening from 9.9 to 113.1 ??g/g, while GA, G3G, and ECT had average values of 4.7, 11.9, and 5.8 ??g/g, respectively, without significant variation. Antioxidant activity, expressed through the IC₅₀ parameter, remained practically unchanged and showed an average value of 12.9 ??g/mL. Based on phenolic composition the mamey sapote fruit may constitute a good source of antioxidant compounds.     

Total phenolic content,antiradical, antioxidant and antimicrobial activities of Rhododendron honeys

Fifty Rhododendron honey samples obtained from Black Sea Region of Turkey were screened for total phenolic content by the modified Folin–Ciocalteu method, for potential antioxidant activity using phosphomolybdenum assay and by the 1,1-diphenyl-2-picryl hydrazyl (DPPH) method for antiradical activity. The antimicrobial activity was studied by the agar diffusion method, using eleven bacteria and two yeasts.     

Chemical composition,anthocyanins, non-anthocyanin phenolics and antioxidant activity of wild bilberry (Vaccinium meridionale Swartz) from Colombia

Berries of Vaccinium meridionale Swartz native to Colombia were analysed for chemical composition, total phenolic content, anthocyanin content, and antioxidant activity. In addition, high-performance liquid chromatography with photodiode array detection (HPLC–DAD) and HPLC-electrospray ionisation tandem mass spectrometry (ESI–MS/MS) were used to determine anthocyanin and phenolic composition. Anthocyanin content was 329.0 ± 28.0 mg cyanidin 3-glucoside equivalents/100 g (fresh weight) FW and total phenolic content was 758.6 ± 62.3 mg gallic acid equivalent/100 g FW. Cyanidin 3-galactoside was the major anthocyanin while the most abundant non-anthocyanin phenolic was chlorogenic acid.     

Effect of nitrogen starvation on the phenolic metabolism and antioxidant properties of yarrow (Achillea collina Becker ex Rchb.)

In this study, the effects of long-term nitrogen deficiency (N 0.1 mM for 4 months) on growth, phenolic content and activity of phenylalanine ammonia lyase (PAL; EC 4.3.1.5) were investigated in the leaves, inflorescences and roots of yarrow (Achillea collina Becker ex Rchb.) grown in hydroponics. The antioxidant capacity of methanol extracts was also evaluated. Nitrogen starvation decreased plant growth and the leaves’ total nitrogen, amino acids, proteins, chlorophylls and carotenoids contents indicating that the primary metabolism was severely limited by low nitrogen availability. The amount of total phenolics and the antioxidant capacity were higher in leaves and roots of nitrogen-starved compared to control plants. The most abundant phenolic acids identified in yarrow were 5-O-caffeoylquinic acid (chlorogenic acid), and 3,5 and 4,5-di-O-caffeoylquinic acids. Nitrogen starvation significantly increased the contents of all these compounds and the PAL activity in leaf and root tissues. Results suggest that hydroponics, with proper manipulation of nutritional factors, might be a suitable system for the production of compounds with health benefits, such as caffeic acid derivatives, in yarrow.     

Effect of water content and temperature on glucosinolate degradation kinetics in broccoli (Brassica oleracea var. italica)

The effect of water content and temperature on glucosinolate thermal degradation in broccoli (Brassica oleracea var. italica) was investigated. Broccoli was freeze dried obtaining batches with water content between 13% and 82% (a_w from 0.32 to 0.99). These samples were heated at different temperatures (from 60 to 120 °C) and glucosinolate levels were monitored. To rule out enzymatic breakdown, myrosinase was inactivated prior to heating. Degradation could be described by first-order kinetics for all glucosinolates and all water contents. In the temperature range 60–100 °C the sample with 13% showed the lowest degradation rate, whereas at 120 °C the degradation rate increased with the water content. This particular behavior was reflected by the high activation energy value of the driest sample. Several hypotheses to explain the observed behavior are discussed.     

Stability of quercetin derivatives in vacuum impregnated apple slices after drying (microwave vacuum drying,air drying,freeze drying) and storage

Microwave vacuum drying (MVD) was investigated for apple slices enriched with quercetin derivatives by vacuum impregnation (VI). Additional freeze drying (FD) and air drying (AD) were conducted. Compared to native apples, the impregnated tissue resulted in higher moisture content, elevation of weight and significant browning, due to the incorporated VI solution. The total quercetin content and quercetin glycoside composition were not affected by MVD and FD. The vacuum conditions protect the polyphenols from oxygen dependent degradation and browning reactions. AD resulted in an average quercetin glycoside loss of 44% and undesirable changes, particularly discoloration. The degradation is caused by both non-enzymatic and enzymatic reactions. The pulsed microwave energy intake improved the drying result in structure and led to a faster drying process of 130 min. The bulk density of MVD apple chips (0.69 g/ml) ranged between 0.33 g/ml for FD and 0.75 g/ml for AD. The final moisture content was the lowest after FD (6.8 g/100 g), followed by 9.0 g/100 g after MVD and 12.7 g/100 g after AD. The shelf life was significantly influenced by storage temperature and time. After 12 month at 20 °C, the total quercetin content decreased by 21%.