Plant Science Laboratory, Cranfield University, Bedfordshire MK43 0AL, United Kingdom.
J Agric Food Chem. 2010 Nov 24;58(22):11709-15. doi: 10.1021/jf1028015. Epub 2010 Nov 1.
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.
将英国目前的 curing 温度从 28°C 降低到 20°C 将有助于降低能源成本；然而，洋葱外皮的外观和消费者的可接受性可能会受到不利影响。本研究的目的是通过监测在 curing 和储存期间每隔一段时间洋葱皮的动态生化变化，从两年的数据中阐明导致在 20°C 和 28°C 下 curing 的洋葱呈现棕色和红色之间差异的化合物。在不同温度下 curing 时，糖浓度似乎对洋葱皮外观的差异没有影响。使用回归、主成分和偏最小二乘判别分析，在 28°C 下 curing 棕色洋葱品种后皮肤 H°的降低与个别类黄酮浓度的降低有关，这可能是由于它们在较高温度下氧化成棕色色素化合物。在较低温度和较短 curing 时间下 curing 的红洋葱品种具有较高浓度的个别花青素以及较深的皮肤颜色。只有在 curing 的前 6 天，皮肤水分含量才会显著降低。总的来说，这表明英国目前的 curing 实践可以在较低的温度（20°C）和/或较短的时间内进行，从而降低 curing 成本，并可能改善皮肤外观。
