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.     

枣果皮色素物质的初步研究（摘要）

[目的]鉴定枣果皮色素物质的成分。分别提取‘鲁北冬枣’、‘辣椒枣’、‘成武冬枣’和‘大白铃’果皮中的色素物质,并利用HPLC-MS技术进行色素物质的成分鉴定。[方法]在4个枣品种中均可检测到8种黄烷醇类物质,4～5种黄酮醇类物质,未检测到花色苷类物质。各类物质在不同品种中含量有所不同,其中‘大白铃’中含量最多,黄烷醇类物质和黄酮醇类物质含量分别为11和1.78mg/g,约为其他品种含量的1倍。槲皮素3-芸香苷是枣果皮中主要的黄酮醇类物质。[结论]为进一步研究枣果皮转红机制提供理论基础。     

枣果皮色素物质的初步研究

[目的]鉴定枣果皮色素物质的成分。分别提取‘鲁北冬枣’、‘辣椒枣’、‘成武冬枣’和‘大白铃’果皮中的色素物质,并利用HPLC-MS技术进行色素物质的成分鉴定。[方法]在4个枣品种中均可检测到8种黄烷醇类物质,4～5种黄酮醇类物质,未检测到花色苷类物质。各类物质在不同品种中含量有所不同,其中‘大白铃’中含量最多,黄烷醇类物质和黄酮醇类物质含量分别为11和1.78mg/g,约为其他品种含量的1倍。槲皮素3-芸香苷是枣果皮中主要的黄酮醇类物质。[结论]为进一步研究枣果皮转红机制提供理论基础。     

Incidence of P,Mn and B deficiencies on the levels of the whole and individual flavonoid groups in tomato leaves

Alterations occur in the normal content of total and individual flavonoids with P, Mn and B deficiencies, in tomato leaves.

P and Mn deficiencies do not alter the total flavonoid level. Nevertheless, these deficiencies lead to different contributions of each flavonoid group (flavonols, flavones and flavanones) to the whole content.

B deficiency produces a very significant increase in total flavonoid content. Compounds that contribute the most to this accumulation are flavones.     

Phenolic acid and flavonol water extracts of Delonix regia red flowers

Traditional healthy beverages in several African counties were home-made by water extraction of flowers of Delonix regia (Boj.) Raf. This tree belongs to the local biodiversity of plants used in the local medicine. It is also part of the traditional bioproducts marketed within African village communities. Scaling-up at pilot plant level, by mimicking this local recipe, lead to concentrated bioproducts containing various natural phenolic compounds, most of them have never been yet published. A three-steps process was used to prepare concentrated of water-extracted soluble phenolics. This process included: phenol extraction of dried plant by overnight diffusion in acidified water, clarification then concentration of the macerate, using membrane technology. Total phenol contents were determined as gallic acid equivalents using the Folin-Ciocalteu method. Total flavonoid contents, as delphinidin equivalents, were determined using the UV-vis colorimetric method. Comparison of concentration factors of both phenol families (phenolic acids and flavonols) contained in the 3 co-products obtained during the process were made between crude extracts, cross-flow microfiltration extracts and reverse osmosis concentrated extracts. Individual phenol compounds found in the products obtained were characterized and quantified by HPLC-DAD and by HPLC-MS². Among the 11 phenol compounds identified in the water-extracts, 3 have been already identified in the literature (2 phenolic acids and 1 flavonol), and 8 new compounds, in noticeable amounts, have never been cited. We have confirmed the presence of phenolic acids such as 3,4,5-trihydroxybenzoic (gallic acid), 3,4-dihydroxybenzoic (protocatechuic acid) and of quercetin. We have characterized for the first time the presence of 2-hydroxy 5-[(3,4,5 trihydroxyphenyl) carbonyl oxy] benzoic acid and of 7 other flavonols belonging to the quercetin, kaempferol and isorhamnetol compound families. Using both LCMS and NMR analyses, they have been identified and quantified as: rutin, quercetin 3-O-glucoside, quercetin 3-O-galactoside, quercetin trihexoside, quercetin 3-O-robinobioside, kaempferol rhamnosylhexoside and isorhamnetol rhamnosyl-hexoside.     

Flavonol and phenolic acid composition of sweet cherries (cv. Lapins) produced on six different vegetative rootstocks

The effect of rootstock (‘MaxMa 14’, ‘Weiroot 13’, ‘PiKu 1’, ‘Weiroot 158’, ‘Gisela 5’ and ‘F12/1’) on phenolic acid and flavonol content of “Lapins” sweet cherry was investigated. Phenolic acids and flavonols were isolated from sweet cherries and analyzed by using reversed phase high-performance liquid chromatography (RP-HPLC). The major phenolic acids in sweet cherries were neochlorogenic acid (18–50 mg kg⁻¹), chlorogenic acid (19–62 mg kg⁻¹) and p-coumaric acid derivatives (15–125 mg kg⁻¹). The amount of flavonol quercetin-3-rutinoside (8–37 mg kg⁻¹) was significant as well. There are significant variations in the phenolic compound content among sweet cherry fruits grown on trees grafted on different vegetative rootstocks. The significantly higher chlorogenic acid, neochlorogenic acid, p-coumaric derivative and quercetin-3-rutinoside contents were found in sweet cherry fruits grown on trees grafted on ‘Weiroot 13’ and ‘PiKu 1’ rootstocks. Sweet cherries produced on trees grafted on other rootstocks had significantly lower phenolic compound content.     

Cultivar variation in apple peel and whole fruit phenolic composition

The quali-quantitative distribution of phenolic compounds varies considerably between apple flesh and peel, but the concentration of phenolics is substantially higher in the peel than flesh. Because the peel comprises only a small percentage of the entire fruit weight, its significance as a donor of phenolics is disputable. We assessed the contribution of the peel to the total phenolic yield of 19 apple cultivars. Calculations were based on the weight of the whole fruit and the peel (which is frequently discarded) and the concentration of individual phenolic compounds. On average, 8, 24, 32, 50 and 66% of chlorogenic acid, (+)-catechin, (−)-epicatechin, phloridzin, and rutin, respectively, were present in the peel, which constitutes about 6–8% of the whole apple weight. With the exception of chlorogenic acid, 50% or more, on average, of the above phenolics were present in the peel of ‘Granny Smith’, ‘Idared’, ‘Red Rome’, ‘Jonamac’ and ‘Gloster’ apples; the highest percentage was found in ‘Starking Delicious’ apple peel (82%). The lowest peel contribution to total phenolic content per whole apple ranged between 26 and 29% and was observed in ‘Pilot’, ‘McIntosh’ and ‘Prima’ apples. Presented results may be useful for further investigations of the relationship between phenolics and agronomical parameters or future selection of apple genotypes having improved nutritional quality when consumed as fresh or as processed apple products.     

Proximal optical sensing of cucumber crop N status using chlorophyll fluorescence indices

Sustainable N management of intensive vegetable crops requires accurate and timely on-farm assessment of crop N status. Proximal fluorescence-based sensors are promising tools for monitoring crop N status, by providing non-destructive optical measurements of N-sensitive indicator compounds such as chlorophyll and flavonols. The ability of the Multiplex^® fluorescence sensor to determine crop N status was evaluated in two indeterminate cucumber crops grown in contrasting seasons (autumn and spring). Three fluorescence indices, leaf chlorophyll (SFR) and flavonols (FLAV) contents, and their ratio (Nitrogen Balance Index, NBI) were evaluated, and their consistency between the two crops compared. Actual crop N status was assessed by the Nitrogen Nutrition Index (NNI), calculated as the ratio between the actual and the critical crop N contents (i.e., the minimum N content for maximum growth). There were strong relationships between each of SFR, FLAV and NBI with crop NNI, for most weekly measurements made throughout the two crops. For the three indices, coefficients of determination (R²) were mostly 0.65–0.91 in the autumn crop, and 0.71–0.99 in the spring crop. SFR values were generally comparable between the two crops, which enabled the derivation of common relationships with NNI for individual phenological phases that applied to both cropping seasons. FLAV and NBI values were not comparable between the two crops; FLAV values were appreciably higher throughout the spring crop, which was attributed to the higher solar radiation. Consequently, phenological relationships of FLAV and NBI with NNI were established for each individual cropping season. Our findings suggested that SFR was the most consistent index between cropping seasons, and that NBI was the most sensitive index within each season. Regardless of the index and crops, all fluorescence indices were weakly related to crop NNI during the short vegetative phase while stronger relationships were found in the reproductive and harvest phases. This study also showed that the three fluorescence indices were sensitive to and able to distinguish deficient from optimal crop N status, but that they were insensitive to discriminate optimal from slightly excessive N status. Overall, this study demonstrated that fluorescence indices of chlorophyll content (SFR), flavonols content (FLAV) and nitrogen sufficiency (NBI) can be used as reliable indicators of crop N status in cucumber crops; however, there was variability in FLAV and NBI values between cropping seasons and a lack of sensitivity in the range of optimal to slightly excessive crop N status.