Flavonoid and Carbohydrate Contents in Tropea Red Onions:  Effects of Homelike Peeling and Storage

Abstract

The content of anthocyanins, flavonols, and carbohydrates of Tropea red onions (Allium cepa L.) was determined by HPLC and HPLC-MS. Cyanidin derivatives constitute >50% of total anthocyanins, but delphinidin and petunidin derivatives, which have not been reported in red onions thus far, were also detected. The flavonoid distribution in the different layers of the bulbs indicates that, after homelike peeling, the edible portion contains 79% of the total content of quercetin 4'-glucoside but only 27% of the anthocyanins. Storage of onions for 6 weeks in different conditions, all of them mimicking home storage habits, resulted in a decrease to 64-73% of total anthocyanins. The same trend was verified for the total antioxidant activity, which was reduced to 29-36%. A decrease in glucose and fructose content correlated with anthocyanin degradation was also observed. Storage at low temperature seems to better preserve the onion anthocyanins.

Industrial Processing of Pickled and Pasteurized Onion (Allium Cepa L.)

“…Odour and taste of onion foods are released by the enzyme alliin lyase (EC 4.4.1.4). The flavonoid distribution in the different layers of the bulbs indicates that the edible part of the onion contains 79 % of the total content of quercetin 4"-glucoside but only 27 % of the anthocyanins [12]. Storage of onions for 6 weeks in different conditions, all of them mimicking home storage habits, resulted in a decrease to 64 -73 % of total anthocyanins, which may be taken into consideration by processing the onions as well as possible [8].…”

“…Assuming use of fresh onion as 100 decreased was freeze dried 45, laboratory frozen 18, hot air dried 9-10, commercially frozen 6-6, boiled 5-2 and pickled 0.01 [8]. Home like peeling and storage have resulted in significantly losses in pyruvate, flavour, flavonoids, anthocyanins and antioxidant activity, whereas freeze-drying resulted in products that retained the characteristic flavour of fresh onion more efficiently [11,12]. Onions (Allium cepa L.) are consumed worldwide and make an important contribution of sensory properties with antioxidants such as phenolic acids, flavonoids, aroma compounds and anthocyanins [7].…”

Influence of postharvest processing and storage on the content of phenolic acids and flavonoids in foods

“…The following list gives an enumeration of all the measures or procedures investigated: Maturity, ripening and time of harvest [63,74,82,99,115,116,176,178,179,188,189,194] 58,112,142,162,181,191,196], differentiation in fractions [114,167,174], peeling [109,142,153,180], special pressing or extraction [2, 64,72,165], enzymatic treatment and maceration [51], irradiation [53,158,175,183], drying [8,102,132,152,159], sensory effects [51], germination [88], browning-blanching and polyphenoloxidase (PPO) activity [124], proveniences [8,12,63,107,110,112,…”

“…Some are related to the existence of synthesis and regulation pathways controlled by enzymes, others are connected to habitat (such as season and climate conditions) and degradation caused by human activities (such as degree of ripeness, cultural practices, food preparation and processing). Peeling, skinning, trimming, depitting and/or leaf selection may cause a partial or total decrease in flavonol levels: data obtained, analysing the flavonol content in the different layers of onion bulbs (skins, outer fleshy layer, edible portion), show that, after normal household peeling, 79% of the total content of quercetin 49-glucoside is still present in the edible portion [153].…”

Efecto De Las Altas Presiones Hidrostáticas Sobre La Estructura Y Estabilidad De Tejidos Vegetales. Relación Con La Extractabilidad De Compuestos Bioactivos

“…En la cebolla, la quercetina se encuentra mayoritariamente unida a azúcares formando glicósidos (Gennaro et al, 2002). De acuerdo a Hollman y Arts (2000), la concentración de quercetina en cebolla es de 300 mg/kg, superior al contenido de este compuesto en otros vegetales como el brócoli (100 mg/kg), la manzana (50 mg/kg) o el té (30 mg/kg).…”