Effect of curing at different temperatures on biochemical composition of onion (Allium cepa L.) skin from three freshly cured and cold stored UK-grown onion cultivars

Onions are cured in order to form a complete, dry, outer skin which reduces water loss and suppresses incidence of disease, and can promote a darker skin finish. Currently in the UK, standard curing practises for onions involves heating at 28 °C for six weeks (65–75% RH), however, reducing curing temperatures may help to reduce energy usage. There is little empirical data on the effects of curing temperature on flavonol concentration in the skin of brown onions and on flavonol and anthocyanin concentration in the skin of red onions. Therefore, the aim of this study was to elucidate the compounds responsible for the change in onion skin colour when cured at different temperatures.Brown cvs. Sherpa and Wellington, and red onions cv. Red Baron, were cured at 20, 24 or 28 °C for six weeks. Replicated skin samples were analysed immediately after curing and after seven months cold storage at 1 ± 0.5 °C. Measurement of objective colour showed that skin of cvs. Sherpa and Wellington was darker and had a lower hue angle (H°) immediately after being cured at 28 °C compared to 20 °C. In contrast, skin of cv. Red Baron had a higher H° but no change in lightness (L*) when cured at 28 °C compared to 20 °C. Fructose, sucrose and glucose concentrations were analysed as they are thought to play a role in regulating the synthesis of flavonols and anthocyanins, both coloured compounds found in onion skin; however no significant correlations were found between colour data and sugar concentrations. Flavonols were measured in the skin of all cvs. and anthocyanins in the skin of cv. Red Baron. Quercetin glucoside and anthocyanin concentrations in the skin of onions cv. Red Baron immediately after curing were higher in those cured at 20 °C. Total flavonols and total anthocyanins were negatively correlated with H° in the skin of onions cv. Red Baron, but there was no similar correlation between total flavonols and H° for onion cvs. Sherpa and Wellington. This suggests that anthocyanins and flavonols may play a major role in varying skin colour of red onions cv. Red Baron cured at different temperatures; however, the difference between curing temperatures may not have been sufficient to represent a correlation between darkening of cvs. Sherpa and Wellington and flavonol concentration. Further investigation is therefore required to fully elucidate the compounds responsible for colour changes observed in brown onions.     

Postharvest application of ethylene and 1-methylcyclopropene either before or after curing affects onion (Allium cepa L.) bulb quality during long term cold storage

The storability of onion bulbs is dependent on the incidence and rate of sprout growth. Exogenous ethylene applied continuously has been demonstrated to act as a sprout suppressant in onion. However, the ethylene binding inhibitor, 1-methylcyclopropene (1-MCP), can also suppress sprouting in onion. Given this seemingly contradictory result, the precise role that ethylene plays during onion storage and the effect of curing on its efficacy is not understood.‘Sherpa’ and ‘Wellington’ onion bulbs were treated before or after curing (28 °C for 6 weeks) with a single dose of 10 μL L⁻¹ ethylene or 1 μL L⁻¹ 1-MCP for 24 h at 20 °C, or no treatment (control). Replicated out-turns were sampled during 38 weeks storage at 0–1 °C. Sprout growth (31 weeks after harvest) was reduced in ‘Sherpa’ treated before curing with ethylene or before or after curing with 1-MCP. However, sprout growth of ‘Wellington’ was not affected by any treatment. Following treatment, the cured, thick-skinned ‘Wellington’ released a lower concentration of treatment gas compared with the newly harvested, thin-skinned ‘Sherpa’. Onion bulb respiration rate increased immediately after being treated with ethylene but to a lesser extent or not at all when treated with 1-MCP. Fructose concentrations of onions treated with ethylene or 1-MCP before curing were not significantly different, however, after curing concentrations were about 2-fold higher compared with the control. Mean glucose and sucrose concentrations for both cultivars were higher immediately after being treated before curing with ethylene or 1-MCP than control bulbs. It appears that inhibition of sprout growth can be achieved using just a short 24 h treatment with ethylene or 1-MCP. However, skin thickness or permeability, which is dependent on cultivar and curing, may affect ethylene or 1-MCP influx and therefore efficacy of sprout suppressant action.     

Fate of flavonoids in the outer skins of onion (Allium cepa L.) throughout curing

Reducing the current U.K. curing temperature from 28 to 20 °C would help to reduce energy costs; however, onion skin appearance and consumer acceptability may be detrimentally affected. The aim of this study was to elucidate the compounds responsible for the difference in color between brown and red onions cured at 20 and 28 °C by monitoring dynamic biochemical changes in the skin at set intervals during curing and after storage from two years' data. Sugar concentrations appeared to play no role in the difference in onion skin appearance when cured at different temperatures. Using regression, principal component, and partial least-squares discriminant analyses, the decrease in skin H° after the curing of brown onion cultivars at 28 °C was linked to a decrease in individual flavonol concentrations, possibly due to their oxidation at higher temperatures into brown pigmented compounds. Red onion cultivars cured at lower temperatures and for a shorter curing period had higher concentrations of individual anthocyanins as well as a darker skin color. Skin water content was reduced significantly in only the first 6 days of curing. Taken together, this suggests that current U.K. curing practice could be carried out at a lower temperature (20 °C) and/or for a shorter duration, resulting in reduced curing costs and possibly improved skin appearance.     

ALIPOMA OF THE EXTENSOR TENDON SHEATHS IN A HORSE

This report describes the identification and surgical removal of a lipoma from the extensor tendon sheaths of a horse. To the authors' knowledge, this is the first report of a lipoma of the extensor tendon sheaths of a horse. Ultrasonographic evaluation was crucial to patient management, providing information regarding the soft tissue mass characteristics, tumor margins and synovial involvement prior to surgical exploration. Surgical removal was performed and was curative.     

Effect of extraction procedure on measured sugar concentrations in onion (Allium cepa L.) bulbs

Bulb samples from a range of onion cultivars grown over three consecutive years were freeze-dried and the resulting powders extracted using three previously reported methods. The extracts were analyzed for fructose, glucose, and sucrose content using HPLC coupled with ELSD, and for fructans using MALDI-MS. The three methods gave differing results, indicating that the extraction procedure is crucial in the determination of the concentration and ratios of nonstructural carbohydrates in onion bulbs. O'Donoghue et al.'s method (O'Donoghue, E. M.; Somerfield, S. D.; Shaw, M.; Bendall, M.; Hedderly, D.; Eason, J.; Sims, I. J. Agric. Food Chem. 2004, 52, 5383-5390), which utilized a more polar solvent (62.5% (v/v) aqueous methanol) and also had the benefit of shorter extraction times and lower temperatures, was far superior to 80% (v/v) ethanol-based methods in extracting significantly greater amounts of fructose, glucose, and sucrose from all onion bulbs tested. Discrepancies between and within cultivars tested also demonstrated that the ratio of monosaccharides to sucrose was affected by extraction method, such that some caution should be given to interpreting some previous work on elucidating the nonstructural carbohydrate composition in onion.     

Effect of water deficit irrigation and inoculation with Botrytis cinerea on strawberry (Fragaria x ananassa) fruit quality

Deficit irrigation (DI) detrimentally affected berry size but had a profound effect on fruit physiology and biochemistry. Strawberry cv. Elsanta fruit from DI-treated plants had higher levels of abscisic acid (ABA). Dry matter content as a proportion of fresh weight was increased by a quarter in fruit from water-stressed plants as compared to fruit harvested from plants held at or near field capacity. Concomitant to this, the concentration of some taste-related (viz. monosaccharides and sugar/acid ratios) and health-related compounds/parameters (viz. antioxidant capacity and total phenolics) were generally much greater in DI-treated fruit. The effect of inoculation with Botrytis cinerea on fruit quality was also tested. Fruit derived from inoculated plants displayed symptoms of gray mold postharvest disease earlier than noninoculated fruit and had double the concentration of ABA. Inoculation had no significant effects on all other target analytes measured. There was no interaction between water treatment and inoculation. The possible mechanisms for increased synthesis of ABA and the different effects of pathogen-induced stress versus drought stress on fruit quality are discussed.