Implications of spatial and temporal changes in concentration of pyruvate and glucose in onion (Allium cepa L.) bulbs during controlled atmosphere storage

BACKGROUND: Pungency and perceived sweetness are important quality assurance parameters for onion producers; however, there is still a paucity of information describing the spatial changes within the bulb of some taste‐related compounds during storage. Accordingly, onion bulbs of cultivars (cvs.), SS1 (low pungency, low dry matter) and Renate (pungent, high dry matter) bulbs, were divided into 12 sections and both spatial and temporal variations of pyruvate and glucose were recorded during standard controlled atmosphere storage. RESULTS: Pyruvate within cv. SS1 bulbs reached 8.3 µmol g^?1 fresh weight (FW) from pre‐storage levels of less than 3.4 µmol g^?1 FW, whilst pyruvate changes in cv. Renate remained in the ‘pungent’ category, between 12 µmol g^?1 FW and 15 µmol g^?1 FW; thus having fewer implications for marketing and quality assurance. Glucose concentrations were significantly higher for both cvs. in the neck region as compared to basal tissue. Higher glucose levels were recorded in the core of the bulb than in outer scales of cv. Renate. The opposite was found for cv. SS1. There was an inverse correlation of ? 0.69 and ? 0.87 between glucose and pyruvate for cvs. SS1 and Renate, respectively. CONCLUSION: In order to measure overall bulb flavour, it is recommended that sampling procedures, particularly for routine pungency determination, be carried out on bulb quarters or wedges rather than equatorial sections. Copyright © 2009 Society of Chemical Industry     

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.     

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     

Characterisation of cultivars of Jamaican ginger (Zingiber officinale Roscoe) by HPTLC and HPLC

In this study, a novel high performance thin layer chromatography (HPTLC) technique for fingerprinting of Jamaican ginger was developed and its application to the chemo-profiling of four cultivars of Jamaican ginger illustrated. Applications of the method to maturation and storage studies involving ginger oleoresins are also presented. The method showed good resolution of the pungent compounds characteristic of ginger: 6-gingerol, 8-gingerol, 10-gingerol and 6-shogaol, with five other discrete zones being described as additional references. HPTLC fingerprints of the ginger cultivars showed chemical homogeneity with small qualitatively observed differences in the intensities of the gingerol and shogaol zones. Quantification of these compounds by high-performance liquid chromatography (HPLC) revealed significant differences in total pungency among the cultivars. Essential oil yields from the cultivars also varied significantly. The described characterisations will prove useful in the authentication of Jamaican ginger.     

A pyruvate dehydrogenase-based amperometric biosensor for assessing pungency in onions (Allium cepa L.)

A disposable prototype electrochemical biosensor was constructed using pyruvate dehydrogenase immobilised on mediated Meldolas Blue electrodes to determine pungency in onions (Allium cepa L.). The optimum operating potential was +50 mV vs. Ag/AgCl reference/counter electrode. The biosensor was able to differentiate between mild and pungent bulbs with pyruvate concentrations ranging between ≈4 and 8 mM in freshly extracted juices. Resolution was 0.5 mM and thus was comparable to the standard Schwimmer and Weston-based colorimetric assay currently employed by industry for determining pungency in macerated onion tissue.     

Quality characteristics of different red pepper cultivars (<Emphasis Type="Italic">Capsicum annuum</Emphasis> L.) for hot paprika production

Twelve hybrids obtained by crossing of different Hungarian cultivars and the Spanish ‘Jaranda’, ‘Jariza’ and ‘Jeromín’ have been studied. The aim of this work was to select those peppers with high capsaicinoids content, and good agronomic and industrial characteristics, as ‘Jeromín’, the only local cultivar used for pungent (hot) paprika, has a low and irregular pungency depending on the year. The crop productive characteristics, ASTA colour, carotenoid pigment content and pungency of the paprika has been studied and elaborated following the traditional procedure of La Vera (Extremadura, Spain). The productive characteristics and pigment concentration of the crossings were, in general, similar to that of local cultivars, and all of them could be suitable for hot paprika production, because their capsaicinoid content was higher than that of ‘Jeromín’ (78 mg kg⁻¹ dwt of total capsaicinoids). The most pungent hybrids were Kibedicsipos × Jariza, Jeromín × Szegedi178 and Jaranda × Szegedi179, with a total capsaicinoid content of 1,240, 1,107, and 997 mg kg⁻¹ dwt, respectively. Their paprikas showed a carotenoid pigment content higher than that of ‘Jaranda’, which is considered as a high quality paprika.     

Studies on the chemical and flavor qualities of white pepper (Piper nigrum L.) derived from five new genotypes

Here, we examine the chemical quality (total protein, total lipid, starch, piperine, and essential oil) and flavor quality of white pepper (Piper nigrum L.) derived from five new genotypes (Jianyin-1, Banyin-1, Banyin-2, Banyin-3, and Banyin-4). We employed headspace solid-phase micro-extraction gas chromatography mass spectrometry (HS-SPME-GC-MS) to analyze major volatiles, electronic nose (E-nose) to analyze volatiles of unknown nature, and sensory testing to assess flavor quality of white pepper derived from these five genotypes. The piperine and essential oil values were significantly higher in Jianyin-1 than in any of the other samples, and this was in accordance with the sensory evaluation results, which indicated that this sample also possesses the most intense pungency notes of all of the samples. The characterization of the chemical quality, volatile compounds, and volatile profiles of all five pepper cultivars showed a clear difference between Jianyin-1 and all of the other samples, perhaps indicative of its unique hybrid origin for the four latter genotypes. The E-nose pattern matching used to examine the volatiles of unknown nature of white pepper derived from all five genotypes further supported our sensory and instrumental data and suggested that Jianyin-1 is a promising and pungent pepper cultivar useful for cultivation for human consumption.     

Quantitative Evaluation of the Pyruvic Acid Content in Onion Samples with a Fully Validated High-Performance Liquid Chromatography Method

Onion cultivars with low pungency have been increasing in popularity because they are more attractive for fresh, uncooked use. The pyruvic acid amount is commonly used as a measure of onion pungency. For the first time the validation of a reversed-phase high-performance liquid chromatography method for the quantitative analysis of pyruvic acid in onion extracts was carried out. The established chromatography method based on the use of a 50 mM phosphate buffer (pH 2.5) eluent system provided good precision (RSD% in the range of 1.25–1.29, in the long-period) and accuracy (recovery% in the range of 97.70–111.62, in the long-period) as well as appreciably low limit of detection and limit of quantitation values (11.03 and 33.41 ng/mL, respectively). The validated method proved successful in the analysis of the onion extract from Dorata di Parma cultivar after a preliminary solid-phase extraction step. A significant adherence with results from previous spectrophotometric determinations turned out.     

Characterization of total capsaicinoids,colour and volatile compounds of Habanero chilli pepper (Capsicum chinense Jack.) cultivars grown in Yucatan

Total capsaicinoids, colour and volatile compounds of 10 Habanero chilli pepper (Capsicum chinense Jack.) cultivars grown in Yucatan, grouped by their colours: four red, five orange and one brown, were determined. The content of capsaicinoids, responsible for the pungency of chilli peppers, varied between 41.8 and 65.9 mg g⁻¹ dry fruit. Mean concentration of orange cultivars was 55.0 mg g⁻¹, while red cultivars had 45.0 mg g⁻¹ dry fruit, indicating that the first ones are more pungent. The composition of volatile compounds of the Habanero chilli peppers differs clearly for the different cultivars. Orange and brown cultivars have in general higher amounts of esters, with their fruity odour notes, than red cultivars. These differences are reflected in the amount of total volatiles, which is higher in orange and brown cultivars in comparison with red cultivars. From these results it can be concluded that orange and brown cultivars are better in terms of their flavour-relevant chemical composition than red cultivars.     

Lipase-catalyzed synthesis of pungent capsaicin analogues

Pungency in peppers (Capsicum spp.) is a sensation produced by a group of molecules known as capsaicinoids. Capsaicin has been reported as the capsaicinoid with the strongest pungency. Based on the molecular structure of capsaicin the enzymatic synthesis and pungent properties of structural analogues was investigated. These analogues were based on modification of the length of the acyl chain (from C4 to C16) and the chemical substituents of the aromatic ring (–OH and –OCH₃). The syntheses were carried out in 2-methyl-2-butanol with lipase B of Candida antarctica, with conversions ranging from 83% to 97.5%. The initial reaction rates were not significantly influenced by the nature of acyl-donor but rather by the substituents in the aromatic ring of the evaluated amines. The relative pungency of 10 capsaicin analogues was sensorially evaluated, using a sensory method for relative pungency. All the compounds were tested at a dose equivalent to 20 times the threshold capsaicin concentration. Two analogues were found pungent; the vanillylamides of caprylic (C-8) and capric (C-10) acids, showing a relative pungency of 66% and 36%, respectively, while the vanillylamides of caproic (C-6) and lauric (C-12) acids had a very low relative pungency (2.1% and 1.2%, respectively). From these results structural features related to pungency are discussed.     

Capsaicin accumulation is related to nitrate content in placentas of habanero peppers (Capsicum chinense Jacq.)

BACKGROUND: The presence of capsaicin, the pungent principle of peppers, is restricted to the fruits of hot cultivars. This compound, which is produced in the fruits' placenta, requires 3 mol of nitrogen to be formed. Hence nitrogen availability may affect pepper pungency through its content in the fruit tissues. On the other hand, potassium may also affect pepper pungency given its positive effect on fruit development. In order to address this issue, plants of habanero pepper (Capsicum chinense Jacq.) were hydroponically cultured with various doses of nitrate and potassium and the contents of these ions and capsaicin were analyzed in the different fruit tissues. RESULTS: Treatments did not produce major effects on pod yield or size during the experimental period, and pepper pods from plants growing under low nitrate concentrations presented no significant differences in total nitrate content. However, lower nitrate, as well as low capsaicin contents, were found in the isolated placentas from peppers grown on the lowest nitrate doses. Variations in potassium availability resulted in differences in pod production per plant, but not in capsaicinoid accumulation. CONCLUSION: Under the assayed conditions, nitrate content in the placenta affects capsaicin synthesis. Copyright © 2010 Society of Chemical Industry     

ANTIOXIDANTS IN ONION (ALLIUM CEPA L) CULTIVARS GROWN IN INDIA

Health benefits of phenolics are prompting vegetable breeders to identify cultivars with enhanced functional properties. Ten onion cultivars grown under North Indian conditions were evaluated for their total phenolics, flavonoids, quercetin and total antioxidant activity for two consecutive years. Total phenolics, flavonoids and antioxidant activity exhibited significant variation ( P <  0.05) among cultivars. Red cultivars, namely Sel-383, N-53, Pusa red and Sel-402, constituted a high phenolic group, with a mean content higher than 100 mg/100 g gallic acid equivalents. Mean flavonoid content was highest in cultivars, Pusa red, Sel-402, H-44 and N-53 ( > 40 mg/100 g). White cultivars namely, Pusa white flat, Pusa white round and Early grano, consistently showed low phenolics, flavonoids and total antioxidant activity. Total antioxidant activity as determined by ferric reducing antioxidant power (FRAP), cupric reducing antioxidant capacity (CUPRAC) was highest in cultivars Sel-383, N-53, Pusa red and Sel-126. Over both consecutive years, phenolics correlated positively with total antioxidant activity ( R ²  =  0.95 FRAP and R ²  =  0.87 CUPRAC). Over all red cultivars, Sel-383 and Pusa red are promising cultivars for incorporation in existing breeding programs for the production of onions with high antioxidant content.

PRACTICAL APPLICATIONS

Onion, being a major constituent of Indian diet, is a potential source of phenolics and flavonoids. Selection of the phenolic-rich cultivars, preferably the red ones with high antioxidant activity, can deliver a variety of health benefits. The breeders can use total phenolics and flavonoids as parameters to develop varieties with increased levels of target antioxidants.     

Current studies on onion and its pungency Part 2. Interactive effects of sulfur fertilization and drying under the aspect of solar energy utilization

It is known that the consumer acceptance of fresh and dried onions is influenced mainyl by its flavour strength. Consequently, the interactive effects of eight treatments, which were combinations of four levels of elemental sulfur fertilizer (0, 357, 714 and 1071 kg/ha) and two drying methods i. e. solar energy and electrical vacuum drying on several characteristics associated with the nutritional potential, pungency, drying and rehydration efficiency of onion, were evaluated. Results revealed that sulfur fertilization, especially at 714 kg/ha, increased significantly (p ≤ 0.05) total solids, fructan, water soluble carbohydrates (WSC) and vitamin C; however slight decreases in individual sugars were recorded. Total-, background- and enzymatically formed pyruvic acid as pungency precursors, volatile sulfur content and sulfur containing amino acids (methionine, cystine and cysteine) increased significantly by sulfur application particularly at a rate of 714 kg/ha. The drying process induced significant losses in all nutritional and pungency indices, where the electrical vacuum drying was more deteriorative. Gas chromatograms of onion volatile oil indicated that sulfur fertilization resulted in a considerable increase in all volatile components particularly the major ones i. e. propanethiol (n-propyl mercaptan), propionaldehyde, di-1-propyl disulfide and methyl propenyl disulfide, which have the purest and strongest onion odour. The horizontal solar tunnel drier with a maximum temperature of 60°C proved to be favourable for drying of onion slices, as it not only led to maintenance of the volatile odour components and a good colour, but also to reduction of drying time (6 hrs) and promotion of the rehydration ratio of the dried onion slices.     

酸处理对干燥香菇甲醛、镉及挥发性风味物质的影响

为降低香菇中甲醛和重金属镉的含量,本试验研究不同酸前处理对去除香菇甲醛和镉含量的影响,并对去除方法进行正交试验优化。结果表明,乳酸作为脱除剂,在pH4.5、料液比1:4 g/mL、振荡温度35 ℃条件下,香菇的甲醛和镉脱除率最大,分别是88.06%和79.57%。最后利用气相色谱-离子迁移质谱（gas chromatography-ion mobility spectroscopy,GC-IMS）测定乳酸前处理对香菇挥发性风味物质的影响,结果表明,香菇样品中共有28种挥发性物质,包括9种醛类、8种酮类、6种醇类、4种酯类以及1种酸类化合物。经过乳酸预处理干燥后的香菇,2-戊酮、环己酮、γ-丁内酯等含量增加,3-辛酮、丁醛等含量大幅降低。干燥香菇中洋葱味、辛辣味等刺激性味道减少,奶油香、果香增加,气味浓郁,层次丰富。     

Capsicum production, technology, chemistry, and quality. Part 1: History, botany, cultivation, and primary processing

The genus Capsicum (Fam. Solanaceae) was known to ancient cultures and was more recently historically associated with the discovery of the New World. This genus provides many species and varieties used in flavoring foods popular in the cuisines of many parts of the world. From the pungent chilli to the colorful paprika and the bell pepper, with its remarkable aroma, the genus is of great interest for its chemistry, sensory attributes, and physiological action. The Capsicums, among the spices, are second only to black pepper in trade both in volume and value. The production of the different pungency forms, the processed seasonings, and the concentrated oleoresins, through technologically advanced processes and in specified standard grades, are critically reviewed. The pungency of Capsicum fruits, its evaluation, chemical structure relationship, its increasing acceptance and preference by a variety of populations are of great research interest. The wide traditional use in the growing regions and its intense physiological effects have attracted the attention of researchers of many different disciplines. These aspects are reviewed in four sequential parts. Part I deals with history, botany, cultivation, and primary processing.     

Improved consistency in DNPH-mediated pyruvic acid analysis of onion juice by modifying the sample processing order

Onion pungency is commonly measured on absorbency of the wine pink color that results from adding NaOH to the heated mixture of dinitrophenylhydrazine (DNPH) and onion juice. However, significant variation exists among several modifications of the original Schwimmer and Weston (SW) method. We observed differences in pyruvic acid concentrations of 20%-30% between our automated method and a batch method with manual absorbency readings. To determine the source of the differences, we examined the heating time and waiting time of the sample-DNPH mixtures and found no differences. The differences were caused by differential color degradation between the pyruvic acid standards and onion juice samples. These differences could be minimized by reading the absorbency within 1 min of NaOH addition. Using this information, we devised the one-by-one method to control the reading time at 30 s. We compared 5 different analysis methods of 40 onion samples representing 4 onion colors. The automated, high-performance liquid chromatography, and SW methods had similar results, with only about a 5% difference. However, the batch method resulted in differences of approximately 24% as compared to the automated method. The one-by-one method produced very comparable results, within 5%, to the automated method. By modifying the procedure to ensure a uniform and fast reading time, we increased the consistency between the pungency analysis methods. Therefore, fast and uniform absorbency reading time is essential for an accurate measurement of pungency in undiluted onion juice.     

The effect of potassium sulphite on the recovery of micro-organisms from dehydrated onion

The addition of potassium sulphite to onion powder and onion flake homogenates improved the recovery of several microbial groups constituting the aerobic flora of many onion samples. The counts of sulphite-reducing anaerobic spores were not affected. A correlation is found between each sample's content of the pungent principle and the degree to which the addition of sulphite recovers its aerobic microbial flora. Aerobic spore-forming bacilli, Gram positive and catalase negative streptococci, Gram and oxidase negative and occasionally pigmented bacilli and yeasts and moulds formed the greater part of the dehydrated onion flora. Escherichia coli was isolated in relatively low numbers from only 4 of the samples. All 243 samples showed a Staphylococcus aureus count of less than 10/g.     

Determination of Recognition Threshold and Just Noticeable Difference in the Sensory Perception of Pungency of Zanthoxylum bangeanum

Zanthoxylum bungeanum, also called the Szechuan pepper, is a pungent-flavored spice. Together with the chili pepper, it constitutes the typical flavor of famous Chinese Szechuan cuisine. With the worldwide popularity of Sichuan cuisine and pungent food, the research on sensory perception of pungency of Z. bungeanum becomes more important and necessary. This article first determined the sensory recognition threshold and just noticeable difference of pungency of Z. bungeanum. The pungent extract, containing hydroxyl α-sanshool (63.6%), hydroxyl β-sanshool (22.8%), and hydroxyl γ-sanshool (7.4%) from Z. bungeanum was used as the tested sample prepared in ethanol–water solution. Ten selected assessors participated in three sessions of sensory tests in standard sensory evaluation booths established according to ISO 8589 by following two-alternative forced choice procedure. The data showed that the recognition threshold was 0.036 mg pungent extract per 1 mL ethanol–water solution and just noticeable difference exponentially increased with the increase of the concentration of pungent extract solution. The response of pungency among assessors followed Weber’s Law with a stable Weber fraction (0.118) from 0.0360 to 0.500 mg pungent extract per 1 mL. Nevertheless, the fraction changed when the concentration of pungent extract solution was above 0.500 mg per 1 mL.     

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.