Effects of Thermal Treatment on the Phenolic Content and Antioxidant Activity of Some Vegetables

Antioxidant Capacity of Polar and Non-Polar Extracts of Four African Green Leafy Vegetables and Correlation with Polyphenol and Carotenoid Contents

In sub-Saharan Africa, chronic malnutrition is often associated with intestinal inflammation and oxidative stress. African green leafy vegetables (GLVs), commonly consumed by these populations and rich in bioactive compounds, may improve the antioxidant status. The aim of this study was to measure the antioxidant capacity using complementary assays (DPPH, FRAP, ABTS, ORAC and NO scavenging) in polar and non-polar leaf extracts of four African GLVs, cassava (Manihot esculenta), roselle (Hibiscus sabdariffa), jute mallow (Corchorus olitorius), and amaranth (Amaranthus spp.), with spinach (Spinacia oleracea) chosen as a reference. Their antioxidant capacity was correlated with their total polyphenol (TPC), flavonoid (TFC), condensed tannin, lutein, and β-carotene contents. Identification of phenolic compounds by UHPLC-DAD-MS/MS revealed the presence of three main classes of compound: flavonols, flavones, and hydroxycinnamic acids. Cassava and roselle leaves presented significantly higher TPC and TFC than amaranth, jute mallow, and spinach. They also exhibited the highest antioxidant capacity, even higher than that of spinach, which is known for its important antioxidant effect. The antioxidant capacity was 2 to 18 times higher in polar than non-polar extracts, and was more strongly correlated with TPC and TFC (R > 0.8) than with β-carotene and lutein contents. These findings provide new data especially for cassava and roselle leaves, for which studies are scarce, suggesting an appreciable antioxidant capacity compared with other leafy vegetables.

The antioxidant and antiglycation activities of selected spices and other edible plant materials and their decay in sugar-protein systems under thermal stress

Antiglycation activities of herbs and spices, have been described in relation to their in vivo anti-diabetic or anti-aging activity at physiological temperature. Under the hypothesis that those natural antioxidants may inhibit the formation of Maillard intermediates, the behavior of several hydroalcoholic plant extracts was analyzed in sugar-protein systems. Allspice, thyme, green pepper and black pepper extracts were the most efficient inhibitors, decreasing furosine formation by 60, 45, 40 and 30%, respectively. 5-hydroxymethyl-2-furfural formation decreased in the presence of the extracts and protein glycation was inhibited by the thyme extract in advanced stages. Antiglycation activities were related to polyphenols content, to radical scavenging and to iron-reducing power. In the protein-sugar systems studied at the time in which 4000 ppm of furosine were formed, the antioxidant activity dropped between 30 and 40%. Polyphenols inhibit Maillard intermediates formation, revealing the incidence of oxidative pathways, but they are depleted as a function of time.

Anticancer and Immunomodulatory Benefits of Taro (Colocasia esculenta) Corms, an Underexploited Tuber Crop

Taro corms contain valuable bioactive molecules effective against cancer and cancer-related risk factors, such as carcinogens and biological agents, several pathophysiological conditions, including oxidative stress and inflammation, while controlling metabolic dysfunctions and boosting the immunological response. Such broad effects are achieved by the taro health-influencing compounds displaying antitumoral, antimutagenic, immunomodulatory, anti-inflammatory, antioxidant, anti-hyperglycemic, and anti-hyperlipidemic activities. Taro bioactivities are attributed to the combination of tarin, taro-4-I polysaccharide, taro polysaccharides 1 and 2 (TPS-1 and TPS-2), A-1/B-2 α-amylase inhibitors, monogalactosyldiacylglycerols (MGDGs), digalactosyldiacylglycerols (DGDGs), polyphenols, and nonphenolic antioxidants. Most of these compounds have been purified and successfully challenged in vitro and in vivo, proving their involvement in the aforementioned activities. Although these health-promoting effects have been recognized since ancient times, as well as other valuable features of taro for food profit, such as hypo-allergenicity, gluten-free, and carbohydrates with medium-glycemic index, taro crop remains underexploited. The popularization of taro intake should be considered a dietary intervention strategy to be applied to improve the overall health status of the organism and as supportive therapy to manage tumorigenesis.

Carica papaya seed enhances phytochemicals and functional properties in cornmeal porridges

Papaya seeds, a high source of dietary nutrients and phytochemicals are wasted when Carica papaya fruit is processed and consumed. This study investigates bioactivity of papaya seeds (PS) from 3 different locations in Kenya for potential valorization as porridge. PS was treated with acetic acid and sodium bicarbonate to improve pallatability. HPLC analysis revealed that PS flour added compounds which were absent from cornmeal (p-hydroxybenzoic, 2,4-dihydroxybenzoic and vanillic acids) and increased over 25% the pre-existing ones. Acid and alkali treatments increased the phenolic compounds content and antioxidant capacities of the seed 1 porridges in ≈19% average. The differential scanning calorimetry and the rapid visco analysis showed a significant decrease in the enthalpy required (≈44%) to gelatinize cornmeal-PS blend and the tendency for retrogradation (from 2188 to 700 cP average). Therefore, our findings indicate that PS can contribute to improved phytochemical and functional properties of cornmeal porridges.

Hydrothermal effects on physicochemical, sensory attributes, vitamin C, and antioxidant activity of frozen immature Dolichos lablab

Immature Dolichos bean is popular in the Asian region, which is a potent source of vitamin C, antioxidants as well as other macro and micronutrients. Extending shelf life with retaining maximum quality parameters through hydrothermal treatments (HTT) followed by freezing of immature Dolichos bean were carried out. In particular, samples were undergone HTT (n = 9), cooled at room temperature, packed in HDPE packs and stored in a freezer (-18 °C±2), whereas samples without HTT considered as control. The samples were analyzed for physicochemical, sensory attributes, vitamin C and antioxidant activity after three months of freeze storage. In the case of vitamin C, antioxidant activity and color retention, significant differences (p < 0.05) were observed among HTT samples. HTT resulted in improving the cooking quality, sensory characteristics and retaining fresh like traits especially antioxidant activity and vitamin C in Dolichos bean. The study revealed that higher temperature (85 °C-98 °C) HTT for a shorter period of time (3 min) could be suitable for immature Dolichos bean to retain quality parameters without great loss during storage.

Chemometric approach based characterization and selection of mid-early cauliflower for bioactive compounds and antioxidant activity

The present study was aimed to analyse bioactive compounds (total phenolics, ascorbic acid and sinigrin) and antioxidant activity in 14 mid-early cauliflower genotypes. Significant differences (pb 0.05) were observed among the genotypes for all bioactive compounds and antioxidant activity. Total phenolics content of curd were ranged from 20.36 to 48.93 mg gallic acid equivalent (GAE) 100 g-1 fresh weight (FW) which showed 2.5 times variation. The ascorbic acid content was maximum in DC522 (88.53 mg 100 g-1 FW) followed by Pusa Sharad (65.64 mg 100 g-1 FW) while minimum in DC310 (39.62 65.64 mg 100 g-1 FW). Wide variation was observed for cupric reducing antioxidant capacity and ferric reducing antioxidant power ranging from 9.04 to 20.83 mg GAE 100 g-1 FW and 13.11 to 26.31 mg GAE 100 g-1 FW, respectively. Sinigrin was found to be highest in DC306 (39.50 µmol 100 g-1 FW) for leaf and in DC326 (36.93 µmol 100 g-1 FW) for curd sample. The cauliflower genotypes were classified based on chemometric approaches namely principal component analysis (PCA) and agglomerative hierarchical clustering (AHC). The first two principal components (PC1 and PC2) explained 50.62% and 23.28% of total variance, respectively. The AHC as revealed by heat map classified cauliflower genotypes into four main groups based on measured traits. The information is useful for developing varieties and/or hybrids rich in bioactive compounds and antioxidant activity.

Optimization of Microwave-Assisted Extraction of Total Phenolic and Total Flavonoid Contents from Fruits of Docynia indica (Wall.) Decne. Using Response Surface Methodology

Docynia indica (D. indica) shows various useful biological activities, such as antioxidant, anti-inflammatory, antibacterial effects, and positive benefits for human health. Such biological activities relate to the main phytochemicals of D. indica including phenolic and flavonoid. However, isolation for phenolic and flavonoid by popular methods such as hot extraction, soxhlet extraction, and ultrasonic extraction have been relatively ineffective. Therefore, in this study, microwave-assisted extraction (MAE) was used for the extraction of total phenolic and total flavonoid from D. indica. The optimization experiments were conducted based on response surface methodology (RMS) according to a central composite design with four independent variables: extraction time (min), ethanol concentration (%, v/v), microwave power (W), and pH of the solvent. Three dependent variables were total phenolic content (TPC), total flavonoid content (TFC), and yield. The optimal conditions for the extraction of phenolic and flavonoid from D. indica were: extraction time of 50 min, ethanol concentration of 65%, microwave power of 440 W, and solvent pH of 5.4. These conditions corresponded to TPC, TFC, and yield values of 33.57 ± 0.12 (mg GAE/g), 25.01 ± 0.11 (mg QE/g) and 33.44 ± 0.14 (%), respectively.

Effects of heat treatment on the phenolic compounds and antioxidant capacity of quince fruit and its tisane's sensory properties

The quince fruit can be an alternative for producing healthy tea because it is a rich source of bioactive compounds. This study was conducted to evaluate the effects of heating (for 20, 40 and 60 min) on the bioactive compounds of quince and quality attributes its tisanes. To this aim, phenolic content of the treated sample (for 40 min according to sensory analysis) was evaluated by HPLC and antioxidant activity was measured using DPPH method. The analysis of sensory evaluation data demonstrated that the heating process significantly improved the color and taste of the quince tisanes. Thermal treatment (180 °C) for 40 min had maximum acceptability. Although, results confirmed negative effects of the heating process on phenolic content, it showed an increase in antioxidant activity. The HPLC data displayed significant reduction in total amount of five identified phenolic compounds from 460.51 to 25.49 mg/25 g extract by heat treatment. In contrast the roasted sample exhibited lower IC50 (663.88 µg/ml) than the unprocessed sample (1098.66 µg/ml). Considering the elevated antioxidant activity achieved through the heating process, the quince tisane can be considered as a healthy beverage.

Analysis of Antioxidant Activity and Texture Profile of Tender-Young and King Coconut (Cocos nucifera) Mesocarps under Different Treatments and the Possibility to Develop a Food Product

The present study is aimed at analyzing the antioxidant activity using the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) method and the texture using the Brookfield texture analyzer for blanched-solar dried, blanched-cooled with dehumidification, unblanched-solar dried, and unblanched-cooled with dehumidification mesocarps of two varieties of tender coconut, such as King coconut and Young coconut. Under the different treatments, there was a significant difference in the antioxidant activity and texture parameters such as “hardness” and “chewiness” at 5% level of significance. The highest (421.8 ± 12.33 mg/L) and the lowest (856.67±6.72 mg/L) antioxidant activities were recorded for blanched-solar dried mesocarp of King coconut and unblanched-cooled with dehumidification mesocarp of Young coconut, respectively. The texture analysis shows that there is a significant difference in the “hardness” and “chewiness” under different treatments at 5% level of significance. Among the treated mesocarps highest “hardness” value (6619.7±147.1) and “chewiness” value (1079.3±54.90) were recorded for King coconut blanched-solar dried mesocarp and lowest “hardness” value (595.67±36.88) and “chewiness” value (12.634±0.836) were recorded for Young coconut blanched-cooled with dehumidification mesocarp. Since the blanched-solar dried mesocarp of King Coconut has highest antioxidant activity and lowest “chewiness”, it is more suitable to develop a food product.

Volatile Compounds of Selected Raw and Cooked Brassica Vegetables

Brassica vegetables are a significant component of the human diet and their popularity is systematically increasing. The interest in plants from this group is growing because of numerous reports focused on their pro-health properties. However, some consumers are not enthusiastic about these vegetables because of their specific bitter taste and sharp, sulfurous aroma. In this study, the volatile composition of 15 Brassica cultivars (five Brussels sprouts, four kohlrabi, three cauliflower and three broccoli), both raw and cooked, was analyzed by solid phase microextraction and comprehensive two-dimensional gas chromatography with time of flight mass spectrometry (SPME-GC×GC-ToFMS). Differences were found between the analyzed vegetables, as well as different cultivars of the same vegetable. Moreover, the influence of cooking on the composition of volatile compounds was evaluated. All the vegetables were frozen before analyses, which is why the impact of this process on the volatile organic compounds (VOCs) was included. The most abundant groups of compounds were sulfur components (including bioactive isothiocyanates), nitriles, aldehydes and alcohols. Cooking in general caused a decrease in the abundance of main volatiles. However, the amount of bioactive isothiocyanates increased in most cultivars after cooking. The effect of freezing on the volatile fraction was presented based on the Brussels sprout cultivars. Most of the changes were closely related to the activity of the lipoxygenase (LOX) pathway enzymes. These are characterized by a marked reduction in alcohol contents and an increment in aldehyde contents. Moreover, important changes were noted in the concentrations of bioactive components, e.g., isothiocyanates. This research included a large set of samples consisting of many cultivars of each analyzed vegetable, which is why it provides a considerable body of general information concerning volatiles in Brassica vegetables.

Effect of various food processing and handling methods on preservation of natural antioxidants in fruits and vegetables

Bioactive compounds from plant sources are generally categorized as natural antioxidants with well-known health benefits. The health-promoting characteristics of natural antioxidants include anti-inflammatory, anti-diabetic, and hepatic effects as well as free radical scavenging. Herein, a comprehensive and comparative review are presented about the effects of conventional (thermal and mechanical) and relatively new (non-thermal) processing methods on phytochemicals and discussed the importance of implementing the use of those methods that could be of very helpful retaining the quality of the bioactive compounds in plant-based foods. Plant-based foods rich in phenolics, vitamin C, carotenoids, and other compounds undergo a range of processing operations before they are consumed. Most of these methods involve thermal treatments of fruits, stems, leaves, and roots. These techniques have varying effects on bioactive compounds and their activities, and the magnitude of these effects depends on process parameters such as temperature, time, and the food matrix. Thermal processing can be detrimental to bioactive compounds while nonthermal procedures may not cause significant deterioration of important health-promoting phytochemicals and in some cases can improve their bio-activity and bio-availability. The detrimental effects of conventional processing on the quality of natural antioxidants have been compared to the effects of innovative nonthermal food treatments such as gamma and ultraviolet irradiation, ultraviolet light, pulsed electric fields, and high hydrostatic pressure.

Natural Acidification with Low-pH Fruits and Incorporation of Essential Oil Constituents for Organic Preservation of Unpasteurized Juices

Essential oil constituents (EOCs) derived from antimicrobial plant extracts can be used for organic preservation of food products. However, the characteristic flavor resulting from EOCs limit the concentration that can be used in high-pH beverages. This work provides an innovative approach of organically preserving a high-pH beverage (watermelon juice) with a natural blend of low-pH fruits (apples and lemons) and EOCs simultaneously. This low-pH fruit blend not only lowers the pH of the food to below critical pH (4.6), but also reduces the potential off-flavors of EOCs, offering a good preservation approach. This was verified using a sensory trial (n = 50) coupled with storage studies and evaluation of various quality parameters using an extreme vertices mixture design with varying proportions of the fruit-base (watermelon juice), the acidulant (apple-lemon juice blend), and the antimicrobial agent (EOC blend). EOC and acidulant containing juices received better sensory scores than those without acidulant, but lower than when EOCs were absent. Microbial load of juices with EOCs after 14 days of storage did not deviate from day 0, while those without EOCs increased 3-fold on a logarithmic scale. Juices containing EOCs also had higher total phenolic content and antioxidant capacity. However, presence of EOCs did not impact pH, total soluble solids, titratable acidity or color, while acidification had significant effects on pH and titratable acidity. Optimum composition of juice formulations were prescribed according to a multi-parameter optimization algorithm. We concluded that the process of natural acidification (with apple-lemon juice blend) coupled with antimicrobial plant extracts is successful in extending the shelf-life of fruit juices with minimal effects on quality/sensory parameters.

PRACTICAL APPLICATION

This research proposes using a unique method for organic preservation of juices using very small amounts of essential oil constituents and acidification. Off-flavors that may arise can be mitigated without the use of chemical additives, but rather with a blend of tart fruit juices, such as apple and lemon juices. The EOCs and the acidulant act synergistically as a hurdle to inhibit microbial growth, so that thermal processing does not need to be employed.

Impact of drying and micronization on the physicochemical properties and antioxidant activities of celery stalk

BACKGROUND

The influence of convective drying and ball-mill treatment of celery stalk on particle size distribution, physicochemical properties, bioactive compounds and antioxidant activities were analyzed in this study.

RESULTS

Ball-milling of celery stalk dried at temperatures of 50, 75 and 100 °C resulted in decreased average particle sizes of 48.8, 10.5 and 7.2 µm, respectively. Bulk density was increased with reduced particle size. Darker (L*) and reddish (a*) powders were formed at higher temperatures, while ball-milling increased greenness (-a*) of powders dried at 50 and 75 °C. Total content of phenol compounds increased with increasing temperature. 2,2-Diphenyl-1-picrylhydrazyl radical scavenging activity and reducing power were affected by ball-milling for 24 h and drying at elevated temperatures. Iron chelating ability was unaffected by increasing temperature or reduced particle size.

CONCLUSION

Increasing drying temperatures not only decreased the average particle size of powders, but also increasingly reduced particle size after ball-milling. Micronization of celery stalk dried at the highest temperature had the best antioxidant activities. Drying and ball-milling were not highly deleterious to the major phenolic structures. © 2017 Society of Chemical Industry.

Polyphenol content and antioxidant capacity of fruit and vegetable beverages processed by different technology methods

The purpose of the natural drinks production is the preservation of biologically active compounds in maximal amount in prepared drinks. The issue is the loss of these substances due to conventional conservation methods, such as pasteurization. Pascalization, a conservation method using high pressure, performs a new trend in conservation. According to available research, it causes only a minimal loss of bioactive compounds. Influence of conservation technology of fruit and vegetable beverages on the content of bioactive substances - polyphenols, flavonoids and on their antioxidative activity has been investigated. Their content has been compared in fresh juice samples, in samples conserved by pasteurization and after the appliance of high pressure treatment - pascalization (HPP). HPP has a positive effect on total antioxidative capacity of juices - broccoli with apple (increase of the amount from 189.12 mg.100 mL-1 to 217.12 mg.100 mL-1) and beetroot and on total polyphenol content within all samples of beverages except from carrot juice. Decrease of the amounts of flavonoids has been observed within all beverages. For drinks after pasteurization treatment there is evident the decrease of total polyphenols content and total antioxidant activity, besides carrot juice, where the antioxidant capacity value had increased from 37.24 to 43.14 mg.100 mL-1. The flavonoid content of fruit and vegetable juices after heat treatment had increased only in the juice prepared from broccoli with apple (from 40.71 mg.100 mL-1 to 45.14 mg.100 mL-1), the content in other juices had decreased. However, the decrease of the flavonoid content is lower after heat treatment in comparison to HPP, except the samples of cabbage juice with apple. With the exception of flavonoids, HPP has been proved as a gentle conservation technology enabling preserving higher amounts of bioactive substances with antioxidative properties if compared with the heat treatment. For the samples treated by HPP there was observed statistically significant difference in comparison with fresh juice in all factors mentioned above (p <0.05).

By-product of Lavandula latifolia essential oil distillation as source of antioxidants

The objective of this work was to evaluate the antioxidant properties of Lavandula latifolia waste obtained after essential oil distillation. Samples of 12 wild populations of the Lavandula genus collected between 2009 and 2010 were hydrodistilled and their by-products were analyzed using the Folin–Ciocalteu, free radical scavenging activity (2,2-diphenyl-1-picrylhydrazyl), and the ferric reducing antioxidant power (FRAP) methods. Rosmarinic acid, apigenin, and luteolin contents were analyzed by high-performance liquid chromatography–diode array detection. The mean of total phenolic content ranged from 1.89 ± 0.09 mg gallic acid equivalents/g dry weight to 3.54 ± 0.22 mg gallic acid equivalents/g dry weight. The average value of the half maximal effective concentration (EC₅₀) for scavenging activity ranged from 5.09 ± 0.17 mg/mL to 14.30 ± 1.90 mg/mL and the variability of the EC₅₀ in FRAP ranged from 3.72 ± 0.12 mg/mL to 18.55 ± 0.77 mg/mL. Annual variation was found among this samples and the environmental conditions of 2009 were found to be more favorable. The plants collected from Sedano showed the highest antioxidant power. Our results show that rosmarinic acid and apigenin in L. latifolia contributed to the antioxidant properties of the waste. In conclusion, the by-product of the distillation industry could be valorizing as a source of natural antioxidants.

Phenolic content and antioxidant and antimutagenic activities in tomato peel, seeds, and byproducts

The phenolic content and antioxidant and antimutagenic activities from the peel and seeds of different tomato types (grape, cherry, bola and saladette type), and simulated tomato industrial byproducts, were studied. Methanolic extracts were used to quantify total phenolic content, groups of phenolic compounds, antioxidant activities, and the profile of phenolic compounds (by HPLC-DAD). Antimutagenic activity was determined by Salmonella typhimurium assay. The total phenolic content and antioxidant activity of tomato and tomato byproducts were comparable or superior to those previously reported for whole fruit and tomato pomace. Phenolic compounds with important biological activities, such as caffeic acid, ferulic acid, chlorogenic acids, quercetin-3-β-O-glycoside, and quercetin, were quantified. Differences in all phenolic determinations due to tomato type and part of the fruit analyzed were observed, peel from grape type showing the best results. Positive antimutagenic results were observed in all samples. All evaluated materials could be used as a source of potential nutraceutical compounds.

Natural antioxidant activity of commonly consumed plant foods in India: effect of domestic processing

Phytochemicals protect against oxidative stress which in turn helps in maintaining the balance between oxidants and antioxidants. In recent times natural antioxidants are gaining considerable interest among nutritionists, food manufacturers, and consumers because of their perceived safety, potential therapeutic value, and long shelf life. Plant foods are known to protect against degenerative diseases and ageing due to their antioxidant activity (AOA) attributed to their high polyphenolic content (PC). Data on AOA and PC of Indian plant foods is scanty. Therefore we have determined the antioxidant activity in 107 commonly consumed Indian plant foods and assessed their relation to their PC. Antioxidant activity is presented as the range of values for each of the food groups. The foods studied had good amounts of PC and AOA although they belonged to different food groups. Interestingly, significant correlation was observed between AOA (DPPH and FRAP) and PC in most of the foods, corroborating the literature that polyphenols are potent antioxidants and that they may be important contributors to the AOA of the plant foods. We have also observed that common domestic methods of processing may not affect the PC and AOA of the foods studied in general. To the best of our knowledge, these are the first results of the kind in commonly consumed Indian plant foods.