HEMICAL COMPONENTS to be low molecular weight(and therefore more soluble) precursors of cellulose Coultate(1989) writes that the name as applied now covers the xylans, the mannans and the glucomannans, and he galactans and the arabinoxylans, however others use the name to include B-glucans also (Hoseney, 1986) Cell walls are important in several contexts 1. As a structural framework with which the grain is organized 2. As a physical boundary to access by enzymes produced outside the cell 3. As as source of energy in ruminants and of dietary fibre in single stomached animals ncluding man 4. They or their derivatives affect processing of raw or cooked cereal products Cell walls of different cereals have some com- mon components but composition is not con- sistent among species. Cellulose is one component present in all cell walls, it is the material of the simplest and the youngest structures. In most cases additional carbohydrates of varying com plexity are deposited as a matrix, and some protein also becomes included Lignin is a com- nt of secondary thicke pericarp of all cereal grains. It is found in the FiG 3 10 Cell walls of barley endosperm fluorescing as a ales but this is relevant to processing only in result of staining with calcofluor White MR. The bright those grains of which they remain a part after Fuorescence of the starchy endosperm cell walls contrasts threshing(i.e. oats, barley and rice). The walls previously unpublished photograph kindly supplied of nucellus and seedcoat(see Ch 2)are generally Dr S. Shea Miller, Centre for Food and Animal Reseat g1 unlignified; they may contain some corky material. Agriculture Canada, Ottawa.) The pigment strand, which is continuous with the seedcoat in grains where a crease is present, are common components of other primary cell is lignified and later becomes encrusted with walls a material of unknown composition. Similar Walls with high B-D-glucan content, such as unidentified material encrusts testa cell walls on endosperm cell walls in oats and barley, can be their inner surfaces (Zee and O'Brien, 1970). identified under the fluorescence microscope wed by Fincher and sto9长mmm Walls of cereal endosperm(aleurone and starchy- fluorescence is intense and excitation by a wide endosperm) consist predominantly of arabino- range of wavelengths is possible(Fulcher and xylans and(1-3, 1-4)-p-glucans, with smaller Wong, 1980) mounts of cellulose, heteromannans, protein Rice is exceptional in containing significant and esterified phenolic acids. They are unlignified proportions of pectin and xyloglucan, together and contain little, if any, pectin and xyloglucan, with small amounts of hydoxyproline-rich protein or hydroxyproline-rich glycoprotein, all of which The cellulose content of rice cell wall63 ccJ CHEMICAL C to be low molecular weight (and therefore more soluble) precursors of cellulose. Coultate (1989) writes that the name as applied now covers the xylans, the mannans and the glucomannans, and the galactans and the arabinoxylans, however others use the name to include B-glucans also (Hoseney, 1986). Cell walls are important in several contexts. 1. As a structural framework with which the grain is organized. 2. As a physical boundary to access by enzymes produced outside the cell. 3. As as source of energy in ruminants and of dietary fibre in single stomached animals, including man. 4. They or their derivatives affect processing of raw or cooked cereal products. Cell walls of different cereals have some com￾mon components but composition is not con￾sistent among species. Cellulose is one component present in all cell walls, it is the material of the simplest and the youngest structures. In most cases additional carbohydrates of varying com￾plexity are deposited as a matrix, and some protein also becomes included. Lignin is a com￾mon component of secondary thickening in the pericarp of all cereal grains. It is found in the pales but this is relevant to processing only in those grains of which they remain a part after threshing (i.e. oats, barley and rice). The walls of nucellus and seedcoat (see Ch. 2) are generally unlignified; they may contain some corky material. The pigment strand, which is continuous with the seedcoat in grains where a crease is present, is lignified and later becomes encrusted with a material of unknown composition. Similar unidentified material encrusts testa cell walls on their inner surfaces (Zee and O'Brien, 1970). The more precise composition of cell walls has been reviewed by Fincher and Stone (1986). Walls of cereal endosperm (aleurone and starchy￾endosperm) consist predominantly of arabino￾xylans and (1~3,1~4)-B-glucans, with smaller amounts of cellulose, heteromannans, protein and esterified phenolic acids. They are unlignified and contain little, if any, pectin and xyloglucan, or hydroxyproline-rich glycoprotein, all of which FiG 3.10 Cell walls of barley endosperm fluorescing as a result of staining with calcofluor White MR. The bright fluorescence of the starchy endosperm cell walls contrasts with that of the walls in the triple aleurone layer (cf. Ch 2) (Previously unpublished photograph kindly supplied by Dr S. Shea Miller, Centre for Food and Animal Research, Agriculture Canada, Ottawa.) )MPONENTS are common components of other primary cell walls. Walls with high 13-D-glucan content, such as endosperm cell walls in oats and barley, can be identified under the fluorescence microscope, because of a specific precipitation reaction with Calcofluor White MR (new) (Fig. 3.10). The blue fluorescence is intense and excitation by a wide range of wavelengths is possible (Fulcher and Wong, 1980). Rice is exceptional in containing significant proportions of pectin and xyloglucan, together with small amounts of hydoxyproline-rich protein. The cellulose content of rice cell walls is also CHEMICAL COMPONENTS CHEMICAL COMPONENTS CHEMICAL COMPONENTS