Antioxidant and micronutrient quality of fruit and root vegetables from the Indian subcontinent and their comparative performance with green leafy vegetables and fruits

Commonly consumed, fruit vegetables (12) and root vegetables (15) in the Indian subcontinent in cooked and uncooked states assessed for inhibition of thiobarbituric acid reactive substances (TBARS), superoxide radical scavenging activity (SOSA), ferrous iron chelating ability (FICA) and nine micronutrients, exhibited large variability in these parameters. SOSA and FICA were significantly associated (r = 0.803, p < 0.001) with each other. Inhibition of TBARS showed marginal correlation with both FICA (0.38, p < 0.05) and SOSA (0.29, p > 0.05). There were significant cooking losses for each of the assessed antioxidant capacity parameters (p < 0.05). Contents of ascorbic acid, per 100 g of cooked fruit and root vegetables were high (61.9 and 31.3% of recommended daily allowance (RDA)). However, both the food classes were not good sources of beta‐carotene, riboflavin and thiamine (1.66–5.26% RDA). When compared with our data on 30 cooked green leafy vegetables (GLV) and 30 fresh fruits, root vegetables showed significantly (p < 0.05) higher levels of zinc and selenium. Cooked root vegetables were comparable with cooked GLVs but uncooked GLVs gave the highest values for inhibition of TBARS (0.73 ± 0.21 mM vitamin E/100g). SOSA (40.7 ± 15.6 mM tannic acid/100g) and FICA (41.6 ± 14.9 mM EDTA/100g) were highest for uncooked fruit vegetables. Root vegetables had the highest levels of polyphenols (251.4 ± 107.3 mg/100g). For the present study, popular fruits and vegetables such as guava, spinach, bitter gourd (Momordica charantia), yam, ginger and beetroot, and also less common ones like bael (Aegle marmelos), kokum (Garcinia indica) and mango‐ginger (Curcuma ameda), showed potential in vitro to combat oxidative stress. Copyright © 2005 Society of Chemical Industry     

Effect of blanching on the antioxidant properties of some tropical green leafy vegetables

Eight popularly consumed green leafy vegetables in Nigeria namely: Structium sparejanophora, Amarantus cruentus, Telfairia occidentalis, Baselia alba, Solanum macrocarpon, Corchorus olitorus, Vernonia amygdalina, and Ocimum gratissimum were blanched in hot water for 5 mins. The antioxidant properties of the fresh and blanched green leafy vegetables were subsequently determined. The total phenol, ascorbic acid and the antioxidant potentials as typified by reducing property and free radical scavenging activity was also determined. The results of the study revealed that blanching cause a significant (P<0.05) increase in the total phenol [fresh (0.1–0.3 g/100 g), blanched (0.2–0.6 g/100 g)] content of the green leafy vegetables except in Amarantus cruentus and Vernonia amygdalina where there was no change. Conversely, there was a significant (P<0.05) decrease in the vitamin C [fresh (43.5–148.0 mg/100 g), blanched (15.8–27.3 mg/100 g)], reducing property [fresh (0.5–1.5 absorbance), blanched (0.1–0.6 absorbance)] and free radical scavenging ability [fresh (20.0–51.4%), blanched (16.4–47.1%)] of the blanched green leafy vegetables except in Structium sparejanophora, where there was no change in the reducing property (0.6 absorbance) and free radical scavenging ability (59.8%) of the blanched vegetable. In view of this it could be concluded that blanching of vegetables though makes green leafy vegetables more palatable and less toxic, however it reduces their antioxidant properties drastically.     

Enhanced bioaccessibility of β‐carotene from yellow‐orange vegetables and green leafy vegetables by domestic heat processing

Effect of heat treatment involved in domestic cooking on the bioaccessibility of β‐carotene from yellow‐orange as well as green leafy vegetables was evaluated. Heat treatment of these vegetables by pressure‐cooking, stir‐frying and open‐pan boiling had a beneficial influence on the bioaccessibility of β‐carotene. The extent of increase in the per cent bioaccessibility of β‐carotene as a result of pressure‐cooking was 21–84%. Stir‐frying in presence of a small quantity of oil brought about an enormous increase in the bioaccessibility of β‐carotene from these vegetables, the extent of increase being 67–191%. Open‐pan boiling of vegetables increased the bioaccessibility of β‐carotene in the range 23–36%. Thus, among the three domestic heat processing methods, stir‐frying results in maximum bioaccessibility of this provitamin. The use of suitably heat‐processed vegetable sources of β‐carotene could form a dietary strategy to derive this micronutrient maximally by the population dependent on plant foods.     

Antioxidant activity of some leafy vegetables of India: A comparative study

Eleven edible leafy vegetables of India have been analysed for their free radical-scavenging activity in different systems of assay, e.g. DPPH radical-scavenging activity, superoxide radical-scavenging activity in riboflavin/light/NBT system, hydroxyl radical-scavenging activity, and inhibition of lipid peroxidation induced by FeSO₄ in egg yolk. Total antioxidant activity was measured, based on the reduction of Mo(VI) to Mo(V) by the extract and subsequent formation of green phosphate/Mo(V) complex at acid pH. The extracts were found to have different levels of antioxidant properties in the systems tested. Considering all the activities, it can be said that Ipomoea reptans has good activity amongst the eleven plant materials screened for their antioxidant properties. Lowest activity was found in Nyctanthes arbortristis. Many flavonoids and related polyphenols contribute significantly to the total antioxidant activity of many fruits and vegetables. However, there was no correlation between antioxidant activity and total phenol/flavonoid content.     

The production of provitamin A‐rich vegetables in home‐gardens as a means of addressing vitamin A deficiency in rural African communities

Vitamin A deficiency remains a public health problem in the developing world. The highest prevalence of vitamin A deficiency is in Africa and Asia (>30%). Dietary modification, a long‐term strategy to address vitamin A deficiency, complements food fortification and vitamin A supplementation programmes. Provitamin A carotenoids from foods of plant origin are more affordable than preformed vitamin A from animal foods, and many resource‐poor households rely on yellow/orange‐fleshed vegetables and fruits and dark‐green leafy vegetables as their main source of vitamin A. The provitamin A carotenoid content in plant foods varies widely and differences among cultivars of the same food exist. Several factors influence the bioavailability of provitamin A carotenoids. The potential contribution of plant foods to vitamin A status depends on the retention of provitamin A carotenoids after storage, preparation and processing. Home‐gardens can provide households with direct access to provitamin A‐rich vegetables that are not readily available or within their financial reach. The components and critical issues of home‐garden projects are described. Copyright © 2006 Society of Chemical Industry     

Chemical characterization and functional properties of selected leafy vegetables for innovative mixed salads

The content of bioactive compounds and antioxidant capacity of nine vegetables of conventional and unconventional utilization in salad mixtures were studied. The total phenolic and flavonoid contents ranged between 39.6–148.5 mg GAE/100g FW and 76.3–217.4 mg QE/100g FW, respectively. Ascorbic acid content ranged between 16.4 and 198.8 mg AAE/100g FW. Antioxidant capacity was assessed using DPPH, FRAP, and ORAC methods; values were in the range of 48.9–245.8 mg TE/100g FW, 67.7–335.8 mg TE/100g FW, and 104.86–833.9 mg TE/100g FW, respectively. Red cabbage, beet greens, parsley, and rocket exhibited the highest antioxidant capacities. Catechin was the most abundant phenolic compound identified in the free fraction, and p‐coumaric acid, quercetin, and caffeic acid in the hydrolyzed fraction. Results suggested that the presence of these phenolics could be of great importance in preventing some chronic and degenerative diseases when regularly consumed. Nonconventional vegetables showed high antioxidant properties, therefore, it is important to promote their consumption.

Practical applications

Not all vegetables have the same phenolic composition, and not all phenolics have the same antioxidant capacity. Knowledge of the bioactive content and antioxidant capacity profile in each vegetable could be of interest to consumers and the food industry for selecting the more suitable leaves to make salad mixtures with high nutritional and functional values. These compounds can prevent some chronic‐degenerative diseases related to oxidative stress, so it is important introduce them regularly into the diet. Moreover, the evaluation of nontraditional vegetables is intended to bring consumers toward a new source of bioactive compounds, prompting their consumption, and providing added value to certain plant parts that are sometimes considered as waste products.     

In vitro accessibility of β‐carotene from cooked Sri Lankan green leafy vegetables and their estimated contribution to vitamin A requirement

Vitamin A deficiency is an important issue for public health in Sri Lanka, where pro‐vitamin A carotenoids from green leafy vegetables provide most of the dietary vitamin A. The objective of this study was to analyse the β‐carotene content of seven types of green leafy vegetables and calculate the contribution of one traditionally cooked portion to the recommended daily allowance (RDA) of retinol. The total amount and in vitro accessibility of β‐carotene were determined using HPLC. The in vitro method simulates the conditions in the human intestinal tract. The all‐trans‐β‐carotene content in the fresh blanched vegetables ranged from 149 µg g^?1 dry weight (DW) in leaves of Alternanthera sessilis (mukunuwanna) to 565 µg g^?1 DW in Amaranthus caudatus (thampala). One portion (100 g) of green leaves cooked without fat (coconut) only contributed from 140 to 180 µg mg^?1 of the recommended daily allowance. A. sessilis, Centella asiatica (gotukola), Spinacea oleracea (nivithi) and A. caudatus, cooked with coconut fat contributed 140–680 µg mg^?1. However, stir‐fried or ‘malluma’ preparations (with coconut products) of Sesbania grandiflora (kathurumurunga) and Manihot esculenta (manioc) may provide more than 1.59–4.37 times the RDA of retinol. These results show that not only the choice of green leaves used but also the addition of fat while cooking is of great importance. Copyright © 2005 Society of Chemical Industry     

Influence of commercial freezing and storage on vitamin C content of some vegetables

Vitamin C levels of commercially frozen okra, potatoes, green beans, broccoli, spinach and peas, including the impact of processing and storage, were studied. Depending on the vegetable type, prefreezing operations caused a 19.1–51.5% decrease in the initial vitamin C levels. The freezing process alone did not influence the vitamin levels except in the cases of green beans and spinach. Total losses (%) were between 27.6 and 57.9 for the vegetables at the end of commercial frozen storage (6 months). All the data obtained from this study confirmed that, depending on the vegetable type, prefreezing operations have a major impact on the vitamin C contents and this influence persists in the frozen storage.     

Protein and mineral contents of green leafy vegetables consumed by sokoto population

Six green leafy vegetables used extensively in food preparations in northern Nigeria were analysed. Crude protein and ash contents varied from 13.1 to 29.2% and 7.0 to 18.6% respectively. ‘Lalo’ (Corchorus Sp.) had the highest content of sodium (0.31%), iron (0.31%) phosphorus (0.48%) and magnesium (0.47%). There was a significant positive correlation between phosphorus and sodium (r=0.97**), phosphorus and iron (0.81*) and calcium (0.81*) contents.     

Carotenoid composition and vitamin A activity of medicinally important green leafy vegetables

Carotenoid composition of green leafy vegetables (GLVs, n = 30) with medicinal value was analyzed by HPLC; vitamin A activity (as retinol equivalent, RE) of provitamin A carotenoids was calculated. Results show that among GLVs studied, the level of β-carotene (50–130 mg/100 g dry wt) was higher in nine GLVs than other carotenoids while lutein (50–187 mg/100 g dry wt) and zeaxanthin (1–5 mg/100 g dry wt) were higher in 12 GLVs than other xanthophylls. α-Carotene was detected only in nine GLVs, ranging from 1 to 37 mg/100 g dry wt. Interestingly, Chenopodium album, Commelina benghalensis and Solanum nigrum were found to contain higher levels of both lutein and β-carotene in the range of 84–187 and 50–115 mg/100 g dry wt, respectively. The values of retinol equivalents (RE) ranged from 641 to 19101 and were higher (>10,000) in six GLVs of the 30. The results demonstrate that GLVs studied contained higher levels of RE and lutein.     

10种生、熟蔬菜中Vc含量及抗氧化性对比研究

通过用钼酸铵分光光度法测定生、熟青椒、尖椒、洋葱、胡萝卜、豆角、西红柿、茄子、苦瓜、芹菜、卷心菜10种蔬菜中Vc的含量。其反应原理是在SO42-离子存在的条件下,选用钼酸铵作为显色剂,利用反应生成的钼蓝,Vc在波长730nm处有强吸收,其浓度在2～22μg/mL范围内与吸收值呈良好的线性关系,该法简单、快速、准确测定Vc含量。结果表明,10种蔬菜在生熟两种情况时Vc含量有明显的变化,生蔬菜中Vc含量普遍高于相应熟蔬菜。最后,用DPPH法对比研究生熟蔬菜的抗氧化性,实验进一步证实Vc含量与其抗氧化性二者呈现一定的量效关系。     

Antioxidant activities of volatile and non‐volatile fractions of selected traditionally brewed Korean rice wines

Antioxidant activities of traditionally brewed Korean rice wines have recently been reported. The objective of this study was to identify the antioxidant activities of the volatile and non‐volatile fractions of three Korean rice wines, and further to identify the active ingredients responsible for the antioxidant properties. Volatile and non‐volatile components of three rice wines, Measilju, Kukwhaju and Gugijaju, were separated into seven fractions according to their polarities. Antioxidant activities were determined by an aldehyde–carboxylic acid assay for the volatile fractions and a lipid–malondialdehyde assay for the non‐volatile fractions. Volatile constituents of each fraction were identified and quantified using gas chromatography–mass spectrometry. In addition, antioxidant activities of specific authentic chemicals from the volatile fractions of the wines were measured, and the antioxidant properties of the volatile fractions were determined. Identification of volatile compounds potentially showing high antioxidant activities were conducted in each fraction of the three wines. Among the volatile compounds identified from volatile fractions of the wines, benzeneethanol, 2‐furanmethanol and 4‐ethyl‐2methoxyphenol showed the highest antioxidant activities, when added at higher concentrations (~100 µg/g). Identification of antioxidant properties, as well as the specific compounds responsible for these antioxidant properties, could aid Korean rice wine product developers, in terms of strategic planning for sales in the Korean market. Copyright © 2014 The Institute of Brewing & Distilling     

Antioxidant compounds in green and red peppers as affected by irrigation frequency,salinity and nutrient solution composition

BACKGROUND: There is a need to encourage more sustainable agricultural practices, reducing inputs of water and fertilisers while minimising any negative impact on fruit quality. The effect of irrigation frequency, salinity and potassium and calcium fertilisation on the content of bioactive compounds and quality attributes of green and red peppers grown with and without substrate was evaluated. RESULTS: Low irrigation frequency and salinity improved the quality attributes (dry matter, soluble solids content and titratable acidity) of pepper. Low irrigation frequency increased vitamin C content by 23% in green peppers, while in red fruits it was not affected. In contrast, total carotenoids and provitamin A only increased in red fruits by 30% and 15%, respectively, as a consequence of low irrigation frequency. When the effect of potassium and calcium doses was investigated, it was shown that a high proportion of potassium increased the vitamin C, provitamin A and total phenolic content of red and green peppers, whereas pepper grown at low calcium doses, presented the highest content in carotenoids and provitamin A. CONCLUSION: Low irrigation frequency and fertilisation with high potassium and low calcium doses improved pepper quality increasing the content of bioactive compounds. Copyright © 2009 Society of Chemical Industry     

Development and validation of an HPLC method for the determination of thiamine and riboflavin in green leafy vegetables using clara-diastase

There is no literature on the use of the currently available form of clara-diastase (≥ 35 U/mg; Fluka Product No. 86959) in the analysis of vitamins B(1) and B(2) . Consequently, a method for the determination of total riboflavin and total thiamine in green leafy vegetables by high-pressure liquid chromatography (HPLC) following sample preparation by sequential acid hydrolysis, enzymatic hydrolysis with clara-diastase ≥ 35 U/mg, and for B1, derivatization to thiochrome, was developed and validated. Prepared samples are run at 35 °C on a 250 × 4.6 mm column of 5 μm Kromasil 100 C(18) , using a 0.8 mL/min flow of a 72:28 mixture of 5 mmol/L ammonium acetate and methanol as mobile phase and fluorescence detection. The linear response ranges and limits of detection are, respectively, 3.0 to 60.0 and 0.15 ng/mL for B(1) , and 3.1 to 155.0 and 0.103 ng/mL for B(2) . Of the 4 green leafy vegetables examined, young turnip tops had the highest B(1) and B(2) levels (0.19 and 0.20 mg/100 g fresh weight), followed by spinach (0.12 and 0.09 mg/100 g), lettuce (0.11 and 0.05 mg/100 g), and chard (0.04 mg/100 g).     

Thermophysical properties and thermal behavior of leafy vegetables packaged in clamshells

Little is known about the thermophysical properties of fresh-cut lettuce other than heat of respiration. Empirical correlations based on food composition remain the only way to estimate the thermophysical properties of fresh-cut lettuce. The objectives of this study were (i) to determine the thermophysical properties of several baby-leaf lettuce and brassica greens and (ii) to verify the measured thermophysical properties by using them in a heat transfer model and comparing the predicted product temperatures with measured product temperatures in a simulated interruption of a cold chain. Density, leaf thickness, thermal conductivity, specific heat and water activity from nine varieties of baby-leaf lettuce and brassica greens were measured. A broken cold chain was simulated in a low temperature incubator set at 10 °C for a length of time before readjustment at 2 °C. Results showed that density (1078–1112 kg m⁻³), leaf thickness (0.18–0.54 mm), thermal conductivity (0.55–0.70 W (m °C)⁻¹) and specific heat (3.1–4.3 kJ (kg °C)⁻¹) varied significantly (P < 0.05) between varieties. However, no significant differences were observed for water activity (0.959 ± 0.006). Using thermophysical properties as input in the heat transfer model, experimental and calculated temperatures were well correlated (R² = 0.98) with a root mean square error of 0.57 °C over the 10–40 mg CO₂ (kg h)⁻¹ range of respiration rate. The measured thermophysical properties adequately predicted the temperature of the baby-leaf greens during simulated broken cold chains. A sensitivity analysis performed with the heat transfer model showed that the thermal conductivity, the specific heat and the density were relatively more important on the thermal behaviour of the baby-leaf greens than the heat of respiration.     

Antioxidant capacity of methanolic and water extracts prepared from food‐processing by‐products

This study aims to evaluate the antioxidant capacity of mango peel, roselle seed, okara (by‐product of soya milk industry), cocoa shell and pink guava (by‐product of pink guava industry) in comparison to 6‐hydroxy‐2,5,7,8‐tetramethylchroman‐2‐carboxylic acid (Trolox). The β‐carotene bleaching, 1,1‐diphenyl‐2‐picrylhydrazyl and reducing power assays were used to determine the antioxidant capacity of selected by‐products by measuring the absorbance at 470, 520 and 700 nm, respectively. The results showed that methanolic extracts of pink guava and cocoa shell exhibited the highest antioxidant activity and free radical scavenging activity compared to other studied samples. Roselle seed water extract exhibited the highest antioxidant activity and free radical scavenging when extracted with water. Pink guava possessed the highest reducing power in methanolic extract at a concentration of 0.16 mg mL^?1. At the same concentration, mango peel exhibited the highest reducing power when extracted with water. The present study shows that pink guava, roselle seed and cocoa shell are potential sources of antioxidant components that can be exploited as food preservative agents or nutraceuticals. Copyright © 2006 Society of Chemical Industry