Physicochemical characteristics of rapidly dried onion powder and its anti-atherogenic effect on rats fed high-fat diet Yasunori Hamauzu a,⇑ , Toshiya Nosaka b , Fuyu Ito c , Takanori Suzuki a , Shuichi Torisu c , Miyoko Hashida d , Akira Fukuzawa e , Masakatsu Ohguchi c , Shigeru Yamanaka c a Graduate School of Agriculture, Shinshu University, 8304 Minamiminowa, Kamiina-Gun, Nagano 399-4598, Japan b Nagano College of Nursing, 1694, Akaho, Komagane City, Nagano 399-4117, Japan c Faculty of Textile Science and Technology, Shinshu University, 3-15-1, Tokida, Ueda City, Nagano 386-8567, Japan d Novozymes Japan Ltd., Chiba 261-8501, Japan e New Ton Club, Nagano 386-0012, Japan article info Article history: Received 21 October 2010 Received in revised form 25 March 2011 Accepted 5 May 2011 Available online 11 May 2011 Keywords: Rapidly dried powder Onion skin Quercetin derivatives Polysaccharides Enzyme treatment Arteriosclerosis Rats abstract Rapidly dried onion (Allium cepa L. cv. Momiji No. 3) powder (OP) prepared from the outer layers (from second to fourth scale leaves from the surface) of onion bulbs was analysed for its quercetin and polyuro- nide contents, the effects of enzymatic treatment and the anti-atherogenic effect on rats fed a high-fat diet. Quercetin 4 0 -glucoside (50%), free quercetin (30%) and quercetin 3,4 0 -diglucoside (20%) were identi- fied as quercetin derivatives, and boiling-water extraction was effective in extracting these compounds. OP contained 12.9% of polyuronides, the basic skeleton of pectin. Enzymatic degradation (cellulase and pectinase, 50 °C for 12 h, pH 6.0) of OP was effective in obtaining a slurry of smaller particle sizes. The free quercetin increased and the glucosides decreased with enzyme treatment. In Wistar rats fed an OP-added high-fat diet, the total cholesterol, HDL-cholesterol and triglyceride concentrations were not significantly different from the rats fed a high-fat diet without OP. However, the atherogenic index (AI) of Wistar rats fed an OP-added high-fat diet was lower (AI = 3.3) than rats fed the diet without OP (AI = 4.1). The incremental elastic modulus (IEM) of the aorta from rats fed the OP-added diet was also significantly lower than that of the rats fed the diet without OP. The AI and IEM values of the rats fed the OP-added diet were quite similar to the values of rats fed the diet without OP but were allowed spon- taneous exercise. These results suggest that OP intake is effective for decreasing the risk of arteriosclerosis. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The outer scales of onion (Allium cepa L. cv. Momiji No. 3), including the brown skin and the outer fleshy scales, are significant by-products of the industrial preparation of onions. These outer scales are mostly discarded. However, effective utilisation of these is desirable because of the high cost of disposing them. Recently, these scales have been processed into a powdered form produced by high-speed drying apparatus that can pulverise them at a high temperature over a short period. This product has been success- fully commercialised in Nagano in Japan. The ‘rapidly dried onion powder’ (OP) seems to be superior to the intact leaves because it is easier to handle, store and so forth. OP also seems to have a high nutritional value (e.g. protein 6.6%, fat 1.8%, carbohydrates 23.5%, calcium 1.2%, w/w, determined by the Japan Food Research Labora- tories, Tokyo, Japan) because it contains a large proportion of the edible parts of onion scales and brown skin that have various effec- tive antioxidants (Ly et al., 2005). Therefore, OP is expected to have significant health benefits equalling or surpassing those of onions. Onion intake has been associated with a reduced risk of coro- nary heart disease in epidemiological studies, and flavonoids, such as quercetin, are believed to be an important factor affecting this (Knekt, Jarvinen, Reunanen, & Maatela, 1996; Knekt et al., 2002). The outer scales of onion contain higher quercetin derivatives (quercetin 4 0 -glucoside, free quercetin and quercetin 3,4 0 -digluco- side) than the middle or inner scales, and the total quercetin con- tent has been reported to be 10 times higher than that of the inner scales (Mogren, Olesson, & Gertsson, 2006). Therefore, if OP con- tains a high amount of quercetin, it may potentially have a high anti-atherogenic function. In addition to flavonoids, dietary fibre is another important food component that has been associated with reduced risk of heart dis- ease. Pereira et al. (2004) reported that the consumption of dietary fibre from cereals and fruits is inversely associated with the risk of coronary heart disease. Pectin, a type of dietary fibre derived from 0308-8146/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2011.05.027 ⇑ Corresponding author. Tel./fax: +81 265 77 1413. E-mail address: hamauzu@shinshu-u.ac.jp (Y. Hamauzu). Food Chemistry 129 (2011) 810–815 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem