Characterization of Industrial Onion Wastes (Allium cepa L.): Dietary Fibre and Bioactive Compounds

Abstract

The food industry produces a large amount of onion wastes, making it necessary to search for possible ways for their utilization. One way could be to use these onion wastes as a natural source of high-value functional ingredients, since onion are rich in several groups of compounds, which have perceived benefits to human health. The objective of this work is to gain knowledge of any differences between the different onion wastes obtained from industry and non-commercial bulbs to use them as food ingredients rich in specific compounds. The results showed that brown skin and top-bottom could be potentially used as functional ingredient rich in dietary fibre, mainly in insoluble fraction, and in total phenolics and flavonoids, with high antioxidant activity. Moreover, brown skin showed a high concentration of quercetin aglycone and calcium, and top-bottom showed high concentration of minerals. Outer scales could be used as source of flavonols, with good antioxidant activity and content of dietary fibre. However, inner scales could be an interesting source of fructans and alk(en)yl cystein sulphoxides. In addition, discarded onions (cvs Recas and Figueres) could be used as a good source of dietary fibre, and cv Recas also as a source of phenolics compounds.

Total phenolics, antioxidant and xanthine oxidase inhibitory activity of three colored onions (Allium cepaL.)

“…The absorbance of the mixture was measured at 760 nm after incubation for 2 h at room temperature. Gallic acid was used as a reference standard, and the results were expressed as milligram gallic acid equivalents (mg GAE)/100 g wet weight of onion sample (Benítez et al 2011;Nile & Khobragade 2011b TAS TPC TAS TPC TAS TPC TAS TPC TAS TPC Red Bulbs 50.18 ± 1.1 132 ± 1.2 12.1 ± 0.02 92 ± 1.2 25.16 ± 1.1 186 ± 2.2 22.3 ± 1.7 152 ± 5.2 5.2 ± 0.8 62 ± 1.3 White Bulbs 35.6 ± 1.7 112 ± 1.9 8.2 ± 0.4 78 ± 2.1 18.5 ± 1.8 156 ± 1.5 20.1 ± 2.5 140 ± 7.8 2.2 ± 0.6 56 ± 1.1 Yellow Bulbs 42.2 ± 1.2 120 ± 1.8 10.5 ± 0.8 81 ± 1.8 22.1 ± 1.0 165 ± 2.9 24.1 ± 1.9 144 ± 1.9 3.5 ± 0.2 68 ± 1.5…”

“…Previous studies reported that onion contains various phenolics, fiber and flavonoids in skin and external layers of onions are relatively high. In addition onion bulbs also contain sulfurous compounds and fructans (a type of oligosacchride) that could be beneficial for human health (Benítez et al 2011;Jang et al 2013). Regarding the onion sections, a decrease in phenolic content was observed from outer to inner sections.…”

Onions: A Source of Flavonoids

“…This high level of production gives as a result more than 500,000 tons of onion skin waste (OSW) which are discarded within the European Union every year [117]. Therefore, the resulting wastes and by-products have become a major problem [118].…”

“…The onion waste has been identiied as a potential source of lavor compounds, dietary iber components, nonstructural carbohydrates like fructans and fructooligosaccharides, and lavonoids particularly quercetin glycosides [117,122]. Most of the studies have been performed at a laboratory scale, so further research is necessary in order to scale up these processes to the industry requirements, assessing their economical viability.…”

Effect of Potato Ethanol Residue on Rat Plasma Cholesterol Levels

“…Byproducts derived from crops often contain dietary fiber (DF), which has been reported to have physiological functions. [2][3][4] Blood cholesterol is known to be a risk factor for atherosclerosis and cardiovascular disease, 5) and lowering its level is desirable. In Japan, potatoes are sometimes used in producing alcoholic beverages such as shochu.…”