Storage technology of onion bulbs c.v. Rouge Amposta: effects of irradiation, maleic hydrazide and carbamate isopropyl, N-phenyl (CIP) on respiration rate and carbohydrates

The effects of γ-irradiation, maleic hydrazide (MH) and carbamate isopropyl, N-phenyl (CIP) on the carbohydrate content, respiration rate (RR) sprouting and rotting of red onion bulbs ( Allium cepa L.) c.v. Rouge Amposta stored at 4, 10 and 20 °C were investigated. Between 6 and 8 weeks soluble sugars increased in concentration and varied between 6.0 and 6.5% fresh weight both at 10 and 20 °C. However, this peak did not exceed 6.0% fresh weight at 4 °C. The basal amount of soluble sugars was about 3% fresh weight. The content appeared to be influenced by temperature, with greater accumulation at 10 and 20 °C than at 4 °C. The RR increased when the bulbs sprouted, whereas it was reduced by the following treatments: irradiation, MH and CIP, the respiration of irradiated bulbs decreased during the final stage of storage because of the death of the sprouts. The chemical treatment used were effective in controlling sprouting of the bulbs during storage, although not as effective as irradiation and chilling.     

GAMMA IRRADIATION IMPROVED THE QUALITY OF ONION FLAKES USED BY ARGENTINE CONSUMERS

A study was carried out on the microbiological status of local and imported packed onion flakes available at retail markets in Argentina. The effectiveness of selected doses of gamma irradiation to decontaminate imported onion flakes and the effects of irradiation on some technological properties were also investigated. Imported onion flakes were contaminated with a high percentage of spore‐forming microorganisms. Imported onion flakes were irradiated at doses of 7, 9, 11, 15, 18 and 23 kGy, and stored at temperatures between 20 and 25C, and relative humidities ranging from 50 to 80%. Irradiation doses between 7 and 11 kGy reduced the aerobic plate count by three log cycles. Doses between 7 and 15 kGy reduced yeast and mold counts by two log cycles. A dose of 7 kGy was sufficient to reduce the sulfite‐reducing Clostridia count to less than detectable levels. We concluded that a dose of at least 7 kGy was necessary to decontaminate imported dry onion marketed in Argentina. No variation in water content or water activity was attributed to selected irradiation doses. Irradiation in the 7–11 kGy range markedly increased the saline extract optical index of imported onion flakes. Gamma irradiation did not significantly affect the flavor intensity as determined by enzymatic production of pyruvic acid.     

RESIDUAL PECTINESTERASE ACTIVITY IN DEHYDRATED ONION AND GARLIC PRODUCTS

During the dehydration of onion and garlic products, use of high temperatures is undesirable due to the potential loss of aroma and flavor characteristics. As a consequence, residual pectinesterase (PE) activity may be found in these dehydrated spices. This study reports the presence of PE activity in raw onions and in dehydrated onion and garlic products. Pectinesterase activity is higher in the raw onion stem disks, and dehydrated products made from this tissue, than in the bulbs. Dehydrated onion products induced gelation of citrus pectin solutions and tomato purees. Although some inactivation of PE in dehydrated onion water suspensions and extracts was observed after 10 min at 50C, complete inactivation required 2 min at 82C. Commercial dehydration operations may require reevaluation to eliminate residual PE activity in dehydrated onion and garlic products.     

Characterization of Shortday Onion Cultivars of 3 Pungency Levels with Flavor Precursor, Free Amino Acid, Sulfur, and Sugar Contents

ABSTRACT:  This study was conducted to characterize shortday onions of 3 pungency levels with regard to the composition of flavor related compounds. A total of 9 onion breeding lines/cultivars were selected, per each of low, medium, and high pungency level, with pyruvic acid contents of 1.9 to 2.8, 4.8 to 5.4, and 7.2 to 8.3 μmoles/mL, respectively. The contents of flavor precursors (S-1-propenyl-L-cysteine sulfoxide [1-PeCSO] and S-methyl-L-cysteine-sulfoxide [MCSO]), free amino acids, free sugars, soluble solids (SSC), and total sulfur (S) in onion bulbs were measured. The flavor precursor contents ranged from 0.03 to 0.16 mg/g fresh weight (FW) for MCSO, 0.07 to 0.65 mg for 1-PeCSO, and 0.12 to 0.77 mg in total, and precursor contents increased with the pungency levels. Onions of different pungency levels did not differ in the contents of individual or total free amino acids, and the most abundant amino acids were glutamine and arginine. The total sugar contents ranged from 50 to 75 mg/g FW, and total S contents (3.5 to 5.1 mg/g dry weight) were not correlated with the pungency levels. However, pungency levels were correlated inversely with bulb weight and positively with SSC, presumably by the effect of dilution. This study indicates that onion pungency is primarily determined by the content of flavor precursor compounds and not by total S, total sugars, or individual/total free amino acids in shortday bulbs.     

Role of precursors on greening in crushed garlic (Allium sativum) bulbs, and its control with freeze-dried onion powder

BACKGROUND: Lachrymatory factor (LF) synthase in onion bulbs reacts with S‐1‐propenyl‐L ‐cysteine sulfoxide (1‐PeCSO), a key compound in garlic greening. In this study, freeze‐dried onion powder containing LF synthase was used in treatments to control garlic greening. Prior to the use of freeze‐dried onion powder to treat greening garlic bulbs, model reactions were conducted to confirm the reactivity of 1‐PeCSO in onion bulbs to garlic greening. RESULTS: While pink pigments were generated from 1‐PeCSO, green pigments were produced from the combination of 1‐PeCSO and S‐2‐propenyl‐L ‐cysteine sulfoxide (2‐PeCSO). However, pigments were formed in the systems containing 1‐PeCSO, amino acid and alliinase. Even non‐greening garlic bulbs stored at 20 °C turned green with the reaction of 200 g L^?1 1‐PeCSO; therefore 1‐PeCSO isolated from onion bulbs had the same role as 1‐PeCSO in garlic bulbs in terms of greening. Onion bulbs turned green after the addition of 600 g L^?1 2‐PeCSO. The addition of freeze‐dried onion powder inhibited garlic greening, and treatment with 15 g kg^?1 onion powder gave the best storage stability of crushed garlic bulbs. CONCLUSION: The addition of freeze‐dried onion powder inhibited the greening in crushed garlic bulbs, and treatment with 15 g kg^?1 onion powder gave the best storage stability of crushed garlic bulbs. Copyright © 2011 Society of Chemical Industry     

Use of canonical variate analysis to differentiate onion cultivars by mineral content as measured by ICP-AES

Three onion cultivars viz. Renate, Ailsa Craig and SS1 were characterised according to their mineral content. The concentrations of the macronutrients phosphorus, potassium, calcium, manganese and sulphur and the micronutrients iron, boron, manganese, copper and zinc were analysed in freshly harvested and stored onion bulbs using ICP-AES (Inductively coupled plasma-atomic emission spectroscopy). Onions were treated pre-harvest with additional sulphur (100 kg ha⁻¹) and/or calcium (300 kg ha⁻¹) applied in four combinations at the time of seed drilling, however these treatments did not affect the total concentrations of sulphur or calcium in the harvested bulbs. The data were subjected to canonical variate analysis in order to determine the most appropriate variate to discriminate between cultivars. Two canonical variates were sufficient to differentiate between the three cultivars, with the first canonical variate describing differences in micronutrients between the genotypes and the second separating the cultivars by differences in sulphur concentration.     

Structural and chemical differences in the cell wall regions in relation to scale firmness of three onion (Allium cepa L.) selections at harvest and during storage

BACKGROUND: Firmness in vegetables is an important textural attribute affecting consumer attitudes toward freshness and quality. Firmness, structural carbohydrates, polygalacturonase (PG), and pectin methylesterase (PME) activity were measured in three onion (Allium cepa L.) lines at harvest and after 4, 8, and 12 weeks of storage. RESULTS: The high‐dry‐matter onion, MBL87‐WOPL, had the firmest bulbs at harvest and delayed softening during storage. MBL87‐WOPL had the thickest cell wall/middle lamella region, and highest levels of dry matter and total uronic acid. Furthermore, MBL87‐WOPL had the lowest levels of PG and PME activity during storage. Pegasus, a poor‐storing cultivar, had the softest bulbs at harvest, lowest levels of uronic acid, and thinnest cell wall/middle lamella. A good storing, moderately firm onion cultivar (MSU4535B) presented intermediate levels of firmness and total uronic acid content. Differences in uronic acid in water‐soluble pectin accounted for much of the difference in total uronic acid among lines. Cellulose concentrations were similar among all lines at harvest. In addition, cellulose concentrations decreased in all lines during storage. Transmission electron microscopy performed on bulbs at harvest and after 12 weeks of storage indicated that degradation of the middle lamella had occurred during storage, leading to cell separation. CONCLUSION: Our results suggest that differences in onion scale firmness at harvest may be due to differences in water‐soluble pectin uronic acid concentrations. Furthermore, the rate of bulb softening during storage at 6.6 °C was greater in onion lines with higher levels of PME and PG activity in storage. Copyright © 2008 Society of Chemical Industry     

原料的不同预处理方式对洋葱油得率的影响

就洋葱粉的干燥方式、含水率和破碎粒度3个因素对超临界流体萃取洋葱油的得率予以探讨。研究表明,以含水率为6%,粒径在0.45~0.90 mm冻干洋葱粉为原料,可获得较高的提取得率。     

Influence of elicitors on alk(en)yl‐L‐cysteine sulfoxides and related amino acids in onion (Allium cepa) tissue cultures

Conditions were developed whereby onion tissue cultures could produce alk(en)yl‐L‐cysteine sulfoxides (ACSOs) at levels exceeding those in mature onion bulbs. Callus cultures grown in Gamborg's B5 basal medium with minimal organics supplemented with 2,4‐dichlorophenoxyacetic acid (at 2.5 μM) and 6‐benzyl‐aminopurine (at 1 μM) exhibited greening and partially differentiated roots within 6 months culture, and could be maintained for over 1 year. Within 10–12 months, callus cultures produced up to twice as much 1‐propenyl‐L‐cysteine sulfoxide (1‐PeCSO) and up to 6 times as much methyl‐L‐cysteine sulfoxide (MCSO) as found in mature onion bulbs. These callus cultures also had greater levels of glutamic acid, glycine and valine than mature onion bulbs. The supplementation of growth media with the elicitors, salicylic acid (SA), onion cell wall fragments (CWF) and acid‐cleaved chitosans (ACC) had differential effects of ACSO yields in 10–12 month old callus cultures. CWF suppressed tissue levels of both 1‐PeCSO and MCSO, SA suppressed tissue levels of MCSO more so than 1‐PeCSO, and ACC suppressed tissue levels of 1‐PeCSO with little effect on MCSO levels.     

Pectic substances in onion and garlic skins

Pectic substances from onion (white and red varieties) and garlic skins were isolated by extraction with ammonium oxalate. White onion and garlic skins were found to contain 11 to 12% pectin which can be recovered as a by-product in the dehydration industries. Characterisation of these pectic substances in terms of jelly grade, molecular weight, degree of esterification, methoxyl and uronide content was attempted. Pectins from white onions were superior to red onions in terms of jelly grade. Both types of onion pectins appeared to be of the rapid set type while the garlic skin pectin was of the medium set variety. Equivalent weight, methoxyl content and degree of esterification by themselves did not give any clear indication of pectin grade. Intrinsic viscosity values gave good correlation between jelly grade and molecular weight. The pectic substances from garlic skin differed from onion skin in certain respects and most remarkably in its viscosity behaviour.     

Biochemical Studies on Some Chemical Characteristics of Sliced Egyptian Onions

Biochemical studies were carried out on two widely distributed Egyptian onion varieties (Behairy and Selected Giza 6). Several treatments (soaking in tap water, boiling water, cold water, warm ethanol, or sodium chloride solution) were proposed to overcome onion reddening during industrial processing. Some chemical characteristics (L-ascorbic acid, free amino acids, volatile sulfur compounds, carbonyl compounds, pungency and color) were determined in fresh, treated and stored sliced onions. Unsaturated fatty acids can be considered as a secondary source for carbonyl compounds and are involved in the formation of red pigments. Pronounced changes among hydrocarbons and little changes in sterols were due to application of various treatments and storage. In general, the most efficient treatments towards keeping onion quality were soaking the sliced onions in cold water or 5% (w/v) sodium chloride for 24 hr before onion dehydration.     

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).     

FLAVOR AND QUALITY CHANGES IN SWEET ONIONS DURING STORAGE AT ROOM TEMPERATURE

Flavor and quality parameters of onions (Allium cepa ‘Walla Walla Sweet’) were monitored for up to 7 weeks following harvest. Shelf-life of bulbs harvested earlier in the season was shorter than that of onions harvested 3 weeks later. Soluble solids of inner scales and average pyruvate, 3,4-dimethyl thiophene and disulfides content increased during the 4 week shelf-life at 22C of the onions harvested in June. These increases resulted in the final contents to be comparable to those of onions harvested on July 2, 1992, which were relatively stable. The pyruvate concentration was comparable to that of a mild, nonpungent onion. Correlations between pyruvate, thiophene and soluble solids were not significant. The relationship between 3,4-dimethyl thiophene, disulfides and onion flavor is discussed.     

Application of flow cytometric DNA measurements in the detection of irradiated onions

Nuclei from meristem tissue cells of onion bulbs γ-irradiated (60–90 Gy) for sprout inhibition and non-irrádiated control bulbs were isolated periodically during ambient (27–32°C) storage, stained with the fluorochrome 4′,6-diamidino-2-phenylindole and their DNA distribution histograms measured by flow cytometry (FCM). Nuclei from irradiated onions showed a broader DNA distribution profile appearing as a wide (high) coefficient of variation (CV, 4–78%) of the G₀/G₁ peak as compared with non-irradiated samples (CV, 2.39%). The DNA index (DI) of the diploid cells in control onions was 1 as against 0.74 in irradiated samples which indicated the presence of G₀/G₁ cells with abnormal DNA content in the meristem tissue cells of irradiated onions. The results indicate the potential application of quantitating changes in DNA content using FCM by determining CV of the G₀/G₁ peak as well as DI for differentiating irradiated from non-irradiated onion bulbs.     

Freeze-dried fresh onion powder prevents green discolouration (greening) in macerated garlic

Green discolouration (greening) of macerated garlic products is a major concern in the garlic-processing industry, and is caused by reactions between free amino acids and 2-propenyl 1-propenyl (2-Pe/1-Pe) thiosulphinates in the garlic. Efficacy of freeze-dried fresh onion powder that contains the active onion enzyme lachrymatory factor synthase (LFS) to prevent greening in processed garlic was evaluated. LFS converts 1-propenesulphenic acid to the volatile lachrymatory factor (LF). We hypothesised that this conversion would decrease the production of 2-Pe/1-Pe thiosulphinates, and thus, would reduce the subsequent discolouration of the garlic. Cooked onion powder added to fresh garlic, which was equivalent to adding crude 1-PeCSO, resulted in intensified green discolouration and increased 2-Pe/1-Pe thiosulphinate levels. On the other hand, fresh onion powder added to fresh garlic (0.5 g powder to 100 g fresh garlic) prevented greening and decreased the 2-Pe/1-Pe thiosulphinate levels. Similarly, a crude onion enzyme solution prevented greening in a garlic homogenate. The 2-propenyl 2-propenyl thiosulphinate (allicin) content was inconsistently altered by the addition of onion powder. However, the expected production of LF by the fresh onion powder or enzyme solution was not detected by gas chromatography, possibly due to changes in the sample matrix. This method using fresh onion powder is an effective technique for preventing greening of fresh garlic that does not use artificial food additives or cause safety concerns.     

Assessment of the flavour of fresh uncooked onions by taste‐panels and analysis of flavour precursors,pyruvate and sugars

Flavour in fresh onions is dominated by volatile sulphenic and thiosulphenic acids that are liberated once alk(en)yl cysteine sulphoxide (ACSO) flavour precursors are cleaved by the enzyme alliinase after tissue disruption. The levels of pyruvate and ACSOs in over 100 samples of onions marketed in the UK were measured, and compared with assessment by taste‐panels. There was a linear relationship between the content of ACSOs and pyruvate. Measurements of pyruvate indicated that the marketing classification of some types of onion did not correspond to their pyruvate levels. A significant linear relationship was found between a sensory measure of strength and pyruvate over the range 1.2–9.3 µmol pyruvate g^?1 fresh weight. In most cases, when a flavour classification of sweet, mild or strong was applied to a sample of onions based on pyruvate content, the taste‐panels agreed with the categorization. The taste‐panels were unable to identify a sweet flavour in onions, except at low levels of pyruvate. Taste‐panels were able to define a likeability character (attractiveness of flavour) for onions, which correlated with the level of pyruvate. However, for some varieties, the flavour classification or likeability did not correspond to predictions based on pyruvate levels alone. Pyruvate measurements were seen as a suitable method for routine quality control once the characteristics of a variety of onion had been established, but initial evaluations should include well‐designed taste‐panel assessments. Copyright © 2004 Society of Chemical Industry     

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.     

Assessment of bulb pungency level in different Indian cultivars of onion (Allium cepa L.)

Onion (Allium cepa L.) is an important vegetable crop consumed primarily for its ability to enhance the flavor of other foods. The quality of onion depends on its pungency. While highly pungent onions are popular in India, less pungent ones are preferred in other countries. However, the variability in pungency in bulbs of different cultivars however has not been investigated. The present investigation was therefore undertaken to determine the pungency in three popular Indian onion cultivars viz. N-2-4-1, B-780 and Phule Safed. Randomly selected bulb samples of the cultivars were analyzed for the content of pyruvic acid, total soluble solids (TSS) and reducing, non-reducing and total sugars. The red variety N-2-4-1 showed higher level of pungency, while other two varieties were comparatively less pungent.     

Underestimation of pyruvic acid concentrations by fructose and cysteine in 2,4-dinitrophenylhydrazine-mediated onion pungency test

Onion pungency has been routinely measured by determining pyruvic acid concentration in onion juice by reacting with 2,4-dinitrophenylhydrazine (DNPH) since 1961. However, the absorbency of the color adduct of the reaction rapidly decreased in onion samples as compared to that of the pyruvic acid standards, resulting in underestimations of the pyruvic acid concentrations. By measuring the absorbency at 1 min, we have demonstrated that accuracy could be substantially improved. As a continuation, the causes of degradation of the color adduct after the reaction and pyruvic acid itself before the reaction were examined in this study. Alliinase action in juice (fresh or cooked) and bulb colors did not influence the degradation. Some organic acids indigenously found in onion, such as ascorbic acid, proline, and glutamic acid, did not reduce the absorbency. However, fructose within the onion juice or supplemented caused the degradation of the color adduct, whereas sucrose and glucose had a lesser effect. Degradation rates increased proportionally as fructose concentrations increased up to 70 mg/mL. Cysteine was found to degrade the pyruvic acid itself before the pyruvic acid could react with DNPH. Approximately 90% of the pyruvic acid was degraded after 60 min in samples of 7 mM pyruvic acid supplemented with 10 mg/mL cysteine. Spectral comparisons of onion juice containing fructose naturally and pyruvic acid solution with supplemented fructose indicated identical patterns and confirmed that the color-adduct degradation was caused by fructose. Our study elucidated that fructose, a major sugar in onion juice, caused the degradation of color adduct in the onion pungency test and resulted in underestimation of the pyruvic acid concentration.