Osmotic potential and soluble solids concentration in onion (Allium cepa) bulbs

Non-structural carbohydrate composition of onion (Allium cepa L) bulbs is known to vary between varieties according to soluble solids concentration (SS), which may reduce the effect of SS on osmotic potential. This was confirmed in an experiment where osmotic potential (Ψ_π) was determined psychometrically, and SS concentration refractometrically, in juice from entire, mature bulbs of 35 varieties of onion. ‘Fresh market’ varieties ranged in mean SS from 63 to 125 g kg- and in mean Ψ_π from ?0.97 MPa to ?1.17MPa, whereas ‘dehydrating’ varieties ranged in mean SS from 167 to 227 g kg-¹ and in mean Ψ_π from ?1.23 MPa to ?1.41 MPa. Compared to sugar solutions of constant composition, with increasing SS, there was a relatively slow decline in Ψ_π toward a lower limit at the SS levels of dehydrating varieties. The relationship between Ψ_π and SS was explained equally well (r² = 0.83; DF = 172) by non-linear and bent-stick regression models, the latter indicating breakpoints close to the SS level separating fresh market variety samples from those of dehydrating varieties. Variety differences in the relationship between Ψ_π and SS indicated among dehydrating varieties in particular are worthy of further investigation because of their possible physiological and quality implications.     

Flavonoids in Onion Cultivars (Allium cepa L.)

ABSTRACT: Total phenol and flavonoid contents were analyzed by HPLC coupled with a diode array detector in 5 traditional onion cultivars from Tenerife (Guayonje, San Juan de la Rambla, Carrizal Alto, Carrizal Bajo, and Masca) and a commercial cultivar (Texas Early Grano 502). Five quercetin chemical species (isoquercetin, quercetin diglucoside, quercetin monoglucoside 1, quercetin monoglucoside 2, and free quercetin) and kaempferol were identified and quantified in the onion samples. Quercetin monoglucoside 1 and quercetin diglucoside were the major flavonoids accounting for 80% of the total quercetin content. The mean quercetin monoglucoside 1: quercetin diglucoside ratio (QMG/QDG) was 1: 2.2. There were differences between the onion cultivars in the cases of total phenol, quercetin diglucoside, isoquercetin, QMG/QDG ratio, and kaempferol. The Texas cultivar had a higher QMG/QDG ratio and a higher kaempferol content than the traditional cultivars. The correlation study showed significant correlations between the analyzed phenolic components.     

Comparison of mineral and trace element contents in onion cultivars (Allium cepa L.)

BACKGROUND: P, Na, K, Ca, Mg, Fe, Cu, Zn, Mn and Se were determined in five traditional onion cultivars (Allium cepa L.) from Tenerife (Guayonje, San Juan de la Rambla, Carrizal Alto, Carrizal Bajo and Masca) and a commercial cultivar (Texas Early Grano 502) grown under the same agronomic, soil and climatic conditions in order to find out differences between these cultivars. RESULTS: Carrizal Alto presented the highest K content and lowest P, Na, Fe, Zn, Mn and Se. Texas cultivar had the highest P, Mg and Se contents, and the lowest contents of Ca, Cu and Mn. There were clear differences in the mineral and trace elements contents between the two seed origins of San Juan de la Rambla cultivar. Many correlations were found between the parameters analyzed, emphasizing the Fe? Zn and Ca? Mn correlations. CONCLUSION: There were differences in the mineral and trace element composition between the onion cultivars. The environment and agronomic practices could affect the genetic information of the seeds, determining changes in the mineral and trace element composition. Linear discriminant analysis is a useful tool for differentiating onion samples according to cultivar and seed origin. Copyright © 2008 Society of Chemical Industry     

Traditional and modern uses of onion bulb (Allium cepa L.): a systematic review

Abstract

Onion, (Allium cepa L.), is one of the most consumed and grown vegetable crops in the world. Onion bulb, with its characteristic flavor, is the third most essential horticultural spice with a substantial commercial value. Apart from its culinary virtues, A. cepa is also used traditionally for its medicinal virtues in a plethora of indigenous cultures. Several publications have been produced in an endeavor to validate such traditional claims. Nonetheless, there is still a dearth of up-to-date, detailed compilation, and critical analysis of the traditional and ethnopharmacological propensities of A. cepa. The present review, therefore, aims to systematically review published literature on the traditional uses, pharmacological properties, and phytochemical composition of A. cepa. A. cepa was found to possess a panoply of bioactive compounds and numerous pharmacological properties, including antimicrobial, antioxidant, analgesic, anti-inflammatory, anti-diabetic, hypolipidemic, anti-hypertensive, and immunoprotective effects. Although a large number of in vitro and in vivo studies have been conducted, several limitations and research gaps have been identified which need to be addressed in future studies.     

Amount of characteristic compounds in 15 cultivars of onion (Allium cepa L.) in controlled field trials

BACKGROUND: In order to develop the production of sweet onions (Allium cepa L.) and onions with a high content of flavonols and fibre in Norway, it was necessary to evaluate available cultivars with respect to their content of selected chemical compounds. A field trial with 15 different cultivars was conducted at Landvik in southern Norway. Compounds that reflect onion pungency and sweetness (pyruvate, sugars) and parameters known to have a beneficial impact on health (fructo‐oligosaccharides (FOS), flavonols, antioxidant capacity) were analysed. RESULTS: The sweetest onions with respect to low content of pyruvate and high amount of fructose and glucose ranged in pyruvate content from 2.7 to 3.6 µmol mL^?1. These cultivars were juicy and contained low amounts of FOS and total flavonols. The most pungent onions contained the highest amounts of FOS among the cultivars: 4.53, 3.80 and 5.81 g per 100 g fresh weight (FW) respectively. They also had a high content of flavonols (86.6, 159.2 and 97.6 mg per 100 g FW) and high dry weight content (14.6, 13.5 and 15.6 g per 100 g). CONCLUSION: The sweetest onion cultivars were found to be ‘NUN 9746’, ‘Musica’, ‘Domenica Supersweet’, ‘Colossus’ and ‘Cronus’. The most pungent cultivars were ‘Powell Brown’ and ‘Tilbury’, which also contained the highest amounts of flavonols and gave the highest Trolox equivalent antioxidant capacity (TEAC) values among the 15 cultivars. Copyright © 2007 Society of Chemical Industry     

Effects of cultivar,lifting time and nitrogen fertiliser level on quercetin content in onion (Allium cepa L.) at lifting

Commercial cultivars of onion (Allium cepa L.) were grown at Torslunda research station, Sweden with different levels of nitrogen fertiliser and lifted at different growth stages. Soon after lifting, before any drying or curing, tissue from the fleshy edible part of onions was extracted in ethanol and the raw extracts were analysed by high‐performance liquid chromatography without any previous hydrolysis. It was confirmed that the main flavonoid compounds were quercetin monoglucoside and quercetin diglucoside, whereas only trace amounts of quercetin aglycone and other flavonoids were found. The greatest variation in quercetin content, in the range 100–500 mg kg^?1 fresh weight, occurred between years. The concentration of quercetin glucosides in the onions was strongly correlated (R² = 0.98) with the total amount of global radiation in August. Individual onions with fallen leaves had significantly higher concentrations of quercetin glucosides than individuals in the same row with erect leaves. Only minor differences were found between the three cultivars analysed. Higher levels of nitrogen fertiliser had only minor effects on onion yield and size and resulted in lower or equal amounts of quercetin glucosides. Nitrogen leakage from the soil, a potential source of environmental problems, could therefore be minimised by avoiding high nitrogen fertiliser levels with almost no effect on onion flavonol content. Late lifting of onions (80% fallen leaves) resulted in up to 45% higher concentrations of quercetin glucosides compared with early lifting (50% fallen leaves). Copyright © 2006 Society of Chemical Industry     

Effects of Onion (Allium cepa L.) and Garlic (Allium sativum L.) Essential Oils on the Aspergillus versicolor Growth and Sterigmatocystin Production

Abstract: In the present study the effects of individual and combined essential oils (EOs) extracted from onion (Allium
cepa L.) bulb and garlic (Allium sativum L.) clove on the growth of Aspergillus versicolor and sterigmatocystin (STC) production were investigated. The EOs obtained by hydrodistillation were analyzed by GC/MS. Twenty one compounds were identified in onion EO. The major components were: dimethyl‐trisulfide (16.64%), methyl‐propyl‐trisulfide (14.21%), dietil‐1,2,4‐tritiolan (3R,5S‐, 3S,5S‐ and 3R,5R‐ isomers) (13.71%), methyl‐(1‐propenyl)‐disulfide (13.14%), and methyl‐(1‐propenyl)‐trisulfide (13.02%). The major components of garlic EO were diallyl‐trisulfide (33.55%), and diallyl‐disulfide (28.05%). The mycelial growth and the STC production were recorded after 7, 14, and 21 d of the A. versicolor growth in Yeast extract sucrose (YES) broth containing different EOs concentrations. Compared to the garlic EO, the onion EO showed a stronger inhibitory effect on the A. versicolor mycelial growth and STC production. After a 21‐d incubation of fungi 0.05 and 0.11 μg/mL of onion EO and 0.11 μg/mL of garlic EO completely inhibited the A. versicolor mycelial growth and mycotoxins biosynthesis. The combination of EOs of onion (75%) and garlic (25%) had a synergistic effect on growth inhibition of A. versicolor and STC production. Practical Application: A substitution of synthetic preservatives with natural antimicrobial compounds in food safety to control fungal contamination and mycotoxin production.     

Quercetin content in stored onions (Allium cepa L.): effects of storage conditions,cultivar, lifting time and nitrogen fertiliser level

Storage experiments with commercial cultivars of onion (Allium cepa L.) were performed at low constant temperature (1°C) and at higher variable temperature (～8°C). Cultivar differences in quercetin glucoside content were significant, but neither nitrogen fertiliser level nor lifting time had more than minor effects at start of storage or after 3 or 5 months of storage. The role of onion size for quercetin glucoside content and composition was inconsistent but seemed to be of minor importance. Irrespective of storage conditions, the content of quercetin glucosides only showed minor reduction and the composition was unchanged. After 5 months of storage, onion sprouting was recorded during a shelf‐life period of 9 weeks at room temperature. Early lifting resulted in onions with low sprouting and good storage abilities without negative effects on quercetin glucoside content. The results suggest that it may be possible to minimise nitrogen fertiliser levels without negative effects on onion yield, quercetin glucoside content or storage capacity. Copyright © 2007 Society of Chemical Industry     

Changes in flavor precursors, pungency, and sugar content in short-day onion bulbs during 5-month storage at various temperatures or in controlled atmosphere

Short-day onion bulbs (cv. TG 1015Y) were stored in 1% O(2,) 99% N(2) air at 5 °C (controlled atmosphere [CA]), or in ambient air at 5, 24, or 30 °C, for 5 mo. Changes in flavor precursors, pungency, and sugar content were investigated. After 5 mo of storage, 1-propenyl-L-cysteine sulfoxide concentrations increased continuously at 5 °C, gradually decreased in CA, slightly increased for 3 mo, and returned to initial levels at 24 °C and decreased below initial levels at 34 °C. Methyl-L-cysteine sulfoxide concentrations remained unchanged in all storage conditions. Onion pungency levels significantly increased at 5 °C, and decreased at 30 °C. Storage in CA and at 24 °C resulted in some fluctuations in pungency but the levels remained similar to initial levels. The calculated pyruvic acid concentrations were approximately 1.0 μmole/mL higher than the measured concentrations, and showed an increase at 5 °C and a slight reduction at 30 °C, consistent with the pungency results. Storage at 5 °C and in CA resulted in slight increases in fructose and glucose concentrations for 3 to 4 mo with subsequent rapid decreases, while sucrose concentrations remained unchanged. However, at 24 and 30 °C, fructose and glucose concentrations continuously decreased, accompanied by a continuous increase in sucrose concentrations. Storage in CA maintained the quality of onions best, as evidenced by the smallest changes in flavor precursors, pungency, and sugar concentrations, while storage at 5 °C resulted in increased pungency. Storage at 24 and 30 °C was tested for the purpose of comparison only; these temperatures are not recommended for commercial storage.     

Antimicrobial and antioxidant activity of crude onion (Allium cepa,L.) extracts

Antioxidant and antimicrobial activity of the ethyl acetate and water subfractions of methanolic extracts of three Spanish onion varieties were assayed. Flavonoids were mainly present in ethyl acetate subfraction being 34.92 ± 0.75, 7.95 ± 0.16, 0.38 ± 0.01 μmol of rutin eq. g^?1 D.W. and its antioxidant capacity was 74.86 ± 1.77, 24.59 ± 0.67, 4.55 ± 0.44 μmol Trolox g^?1 D.W. of Grano de Oro, Fuentes de Ebro and Calçot de Valls varieties, respectively. The antimicrobial activity of flavonol standards and onion extracts was evaluated against some food spoiler microorganisms. Quercetin and kaempferol were inhibitory against gram positive bacteria such as Bacillus cereus, Staphylococcus aureus, Microcroccus luteus and Listeria monocytogenes. Gram negative bacteria Escherichia coli and Pseudomonas aeruginosa were less sensible to the antimicrobial effect of both flavonol standards and Candida albicans was totally resistant. Among the onion extracts tested only ethyl acetate subfraction showed antimicrobial inhibition.     

Identification of Thiols in Yellow Onion (Allium cepa L.) Using Solvent Vented Large Volume Injection GC‐MS

Thiols are often highly odor active molecules and as such can significantly contribute to aroma while being present at extremely low concentrations. This paper details the identification of thiols in yellow onion juice by solvent extraction followed by thiol enrichment using a mercuric agarose gel column. Due to the inherent thermal instability and low concentrations of thiols in onion, chromatographic analysis utilized larger volume solvent elimination injections. New sulfur compounds in onion included 1,1‐propanedithiol, bis‐(1‐sulfanylpropyl)‐sulfide, 1‐methylsulfanyl‐1‐propanethiol, 1‐propylsulfanyl‐1‐propanethiol, and 1‐allylsulfanyl‐1‐propanethiol. A discussion on the potential route of formation for each compound is included along with the orthonasal and retronasal evaluations of the synthesized molecules. This work investigated and identified 5 newly identified compounds present in onions that can impart onion character at low concentrations levels.     

Analysis of the Major Flavonol Glycosides Present in Four Varieties of Onion (Allium cepa) and Changes in Composition Resulting from Autolysis

The major flavonoids of mature onion bulb were confirmed as the 3,4′-O-diglucoside (Qdg) and 4′-O-monoglucoside (Qmg) of quercetin using a combination of chromatographic comparisons, mass spectrometry and nuclear magnetic resonance spectroscopy. These two components account for over 85% of the total flavonoids in three varieties of onion with Qdg as the main component. Quercetin is detected in these long stored onions but only at low levels of less than 2% of the total. The remaining flavonoid fraction (approx 15%) comprises upto 17 different components of which quercetin-3-O-glucoside and isorhamnetin glucoside are prominent members although each contribute less than 1% of the total flavonoid fraction. There are significant differences in the levels of Qdg and Qmg between the four different onion varieties analysed; Qdg varying from 50–1300 mg kg^-1 fresh onion tissue and Qmg from 36–394 mg kg^-1. Maceration of the tissue for the three varieties tested led to a loss of Qdg and the appearance of Qmg and free quercetin. In the variety Rijnsburger 50% of the Qdg was degraded in 5 h and had completely disappeared after 24 h. These changes in Qdg can be quantitatively explained by increases in Qmg and free quercetin. The possible significance of quercetin glycosides in the diet is discussed. © 1997 SCI     

Long-term storage of onion and the factors that affect its quality: A critical review

Storage of onions is a multifaceted issue, which involves many preharvest and postharvest factors. One of the major factors that affect onion storage is the selection of the proper cultivar, since there are significant differences in storability between the cultivars and not all of them are suitable for storage. Proper preharvest and postharvest conditions are essential for storability of onion bulbs, whereas they also affect marketability (weight losses, texture and color depth of bulbs) and quality (chemical composition, nutritional value, antioxidant activity). Irrigation and fertilization are essential preharvest factors that substantially affect storability, whereas curing methods and storage conditions (temperature, relative humidity, controlled atmospheres) and processing treatments are postharvest factors. This review article examines the effect of long-term storage on the main quality features of onions, such as the incidence of sprouting and root growth, water losses, and changes in chemical composition (mineral composition, sugar content, nutritional value) and antioxidant activity (phenolic and flavonoid contents, DPPH [2,2-diphenyl-1-picrylhydrazyl] scavenging activity).     

鲜洋葱和干洋葱挥发性化学成分比较

采用固相微萃取方法,用气相色谱-质谱联用结合计算机谱图检索,对两个不同品种的鲜洋葱和干洋葱挥发性化学成分进行分析鉴定。结果表明:鲜洋葱和干洋葱样品共鉴定出挥发性成分49种,各样品挥发性成分种类分别为30、28、28种和25种,分别占其色谱流出组分总量的94.25%、96.01%、83.40%和86.11%它们主要是含硫化合物、醇类、醛类和酯类等;干洋葱挥发性成分与新鲜洋葱相比在组成和相对含量都存在着较大差异。     

Desorption isotherms,net isosteric heat and the effect of temperature and water activity on the antioxidant activity of two varieties of onion (Allium cepa L)

The standard static gravimetric method was used to determine moisture desorption isotherms (MDIs) of two onion varieties (Goudami and Galmi Violet) at 30 °C, 45 °C and 60 °C in the water activity ranging from 0.055 to 0.83. The combined effects of temperature and water activity on the antioxidant activities of the onion varieties were also studied. GAB, Oswin, Smith and BET equations were tested to fit the experimental data. The net isosteric heat of sorption was calculated. Equilibrium moisture content (EMC), total phenolic content (TPC) and antiradical activity were also measured. The isotherm and the EMC vary significantly with the onion variety and drying temperature, irrespective of water activity (a_w). Desorption isotherms were best described by the GAB model. The maximum net isosteric heats for Galmi Violet (32.58 kJ mol^?1) were greater than those of Goudami (23.50 kJ mol^?1) at each EMC. The TPC and antiradical activity of the Galmi Violet were significantly (P ≤ 0.05) higher than that of the Goudami at all investigated temperatures and water activities.     

Quantitative analysis of the major γ glutamyl peptides in onion bulbs (Allium cepa)

Quantitative analysis of the major γ glutamyl peptides present in cultivars of onion (Allium cepa L) bulbs representing brown, white and red varieties was achieved by ion exchange and electrophoretic separations and by quantitation involving integration of ninhydrin-developed spots on thin layer chromatography. γ Glutamyl trans-prop(I)enyl cysteine sulphoxide was found to be the major γ glutamyl peptide in each of the three cultivars at levels between 1.24 and 2.18 mg g^?1 fresh weight, followed by S-2-carboxypropyl glutathione (0.45-0.60 mg g^?1 fresh weight) and γ glutamyl phenylalanine (0.09-0.16 mg g^?1 fresh weight). Conclusive identification of each of the compounds was achieved by NMR spectroscopy and by GC-MS of the n-butyl, trifluoroacetyl derivatives of the hydrolysis products.