Characterisation of Chilean hazelnut (Gevuina avellana) tissues: light microscopy and cell wall polysaccharides Fernando Dourado, 1 Pedro Vasco, 2 Anto ´nio Barros, 2 Manuel Mota, 1 Manuel A Coimbra 2 and Francisco M Gama 1 * 1 Centro de Engenharia Biolo ´gica, IBQF, Largo do Pac ¸o, Universidade do Minho, P-4710-057 Braga, Portugal 2 Departamento de Quı´mica, Universidade de Aveiro, P-3810-193Aveiro, Portugal Abstract: By applying several differential staining techniques and light microscopy, the structure and composition of Chilean hazelnut (Gevuina avellana) seeds were analysed. The structure of the G avellana seed is very simple, with a thin, heavily lignified seed coat and two voluminous cotyledons. The embryo food reserves are uniformly distributed over the cotyledon cells. The cell wall polysaccharides were recovered from the alcohol-insoluble residue by mild treatment with warm chlorite solution and sequential extraction with alkali solutions of increasing concentration. FT-IR spectra in the 1200–850 cm 1 region were used together with chemometric techniques to distinguish the hemicellulosic and pectic polysaccharides in the extracts. The most abundant extracts were fractionated by graded precipitation in ethanol. A xyloglucan was identified by 1 H and 13 C NMR as the major hemicellulosic polysaccharide, with a sugar composition of 4Glc:3.5Xyl:1Gal:0.5Fuc. The hazelnut cell walls are composed of equivalent amounts of pectic polysaccharides, xyloglucans and cellulose. # 2003 Society of Chemical Industry Keywords: hazelnut; Gevuina avellana; seed structure; cell walls; light microscopy; FT-IR; xyloglucan INTRODUCTION The plant cell wall is primarily composed of polysac- charides, which can be classified as cellulose, and cell wall matrix components, namely pectins and hemi- celluloses. 1 Xyloglucans make up about 20% of the primary cell walls of dicotyledonous plants. 2 Xyloglu- cans are neutral polysaccharides composed of a linear backbone of b-D-(1→4)-Glcp branched at C-6 with a- D-Xylp. The Xyl may also be substituted at C-2 by b- Galp, and this residue may be substituted at C-2 by a-L-Fucp, giving highly branched structures. Cell wall polysaccharides are used in foods as thickeners, stabilisers, gelling agents and, in some cases, emulsifiers. 3 Their inclusion in foods permits the manufacture of a vast array of products which are not only stable to a wide range of transport and storage conditions but also have the properties desired by the consumer. 4 Growing knowledge of the cell wall composition and structure has led to a better understanding of (1) the physiological role of polysaccharides in dietary fibre, 5–7 (2) agro-industrial applications of seed or fruit meals, 8,9 (3) the enzymatic degradation of poly- saccharides 8,10–15 and (4) the chemistry of texture changes of foods. 16–19 Also, in recent years, polysac- charides of plant origin have emerged as an important class of bioactive natural products. 20–22 FT-IR spectroscopy in association with chemo- metric techniques, when applied in the wavenumber region between 1200 and 850 cm 1 , has been used as a reliable and fast method for evaluation of the polysac- charide composition of pectic and hemicellulosic samples derived from orange and olive tissues 23,24 and to follow the effects of processing on cell wall polysaccharide extracts of fresh and dried pears. 25 This methodology was used here to characterise the cell wall polysaccharides extracted from the Chilean hazelnut (Gevuina avellana Mol, fam Proteaceae). Also, a histological study on elucidation of the seed structure and location of the embryo food reserves was carried out. Information regarding this fruit is rather scarce. Currently under-exploited, it can be a valuable alternative when considering food sources with high protein and oil content (rich in unsaturated fatty acids). 26 The high content of palmitoleic acid (37%) 26 increases the importance of the hazelnut oil for (Received 4 April 2002; accepted 16 May 2002) * Correspondence to: Francisco M Gama, Centro de Engenharia Biolo ´gica, IBQF, Largo do Pac ¸o, Universidade do Minho, P-4710-057 Braga, Portugal E-mail: fmgama@deb.uminho.pt Contract/grant sponsor: INCO-DC; contract/grant number: 96-2205 Contract/grant sponsor: Research Unit 62/94, QOPNA (Aveiro, Portugal) Contract/grant sponsor: FCT (Portugal); contract/grant number: PRAXIS XXI/BPD/18824/99 # 2003 Society of Chemical Industry. J Sci Food Agric 0022–5142/2003/$30.00 158 Journal of the Science of Food and Agriculture J Sci Food Agric 83:158–165 (online: 2003) DOI: 10.1002/jsfa.1287