TECHNOLOGY OF CEREALS unusually high(25-30%), and mannose-contain- The term is frequently qualified to reflect the 15%Bars in some may contribute as much method of analysis employed because different methods produce different values(it should also A significant non-carbohydrate molecule inti- be noted that some methods are themselve mately associated with arabinoxylans in wheat inconsistent). The following types of fibre may and other cereal cell walls is ferulic acid a phenol be encountered the definitions are based on a carbonic acid very abundant in plant products, glossary by Southgate et al. (1986) It is esterified to the primary alcoholic group of he residue left after boiling the the arabinose side chain(Amado and Neukom, defatted food in dilute alkali and then in dilute 1985). The formation of diferulic acid cross-links acid The method recovers 50-80% of cellulose, is at least partly responsible for the gelation of 50% of lignin and 20% of hemicellulose ueous four extracts or solutions of cereal Results are inconsistent. the presence of oxidizing agents Acid detergent fibre (ADF)- The cellulose Ferulic acid exhibits intensive blue fluorescence plus lignin in a sample; it is measured as the when irradiated with light of 365 nm. The residue after extracting the food with a hot reaction is particularly marked in aleurone cell dilute H2SO4 solution of the detergent cety walls and thus can be used for identifying these trimethylammonium bromide(CTAB) in ground cereal products under the fluorescence Neutral detergent fibre (ndf)- The residue microscope left after extraction with a hot neutral solution of fractionation into water soluble and insoluble sodium dodecyl sulphate (sds) also known as pentosans by various protocols is common analy- sodium lauryl sulphate. It is designed to divide tical practice as it has been found to distinguish the dry matter of feeds very nearly into those different functional properties. Thus it is the which are nutritionally available by the normal water-soluble pentosans(mainly arabinoxylans) digestive process and those which depend of wheat that have a very high water absorbing microbial fermentation for their availability apacity. They are linear molecules while those Dietary fibre- All the polymers of plants that of the insoluble fraction are highly branched. The cannot be digested by the endogenous secretions backbone of arabinoxylans consists of D-glucan of the human digestive tract units linked by p-(1-4)glycosidic bonds. Single The last definition differs from those that a-L-arabinofuranose residues are attached ran- precede it in that it is not based on the method domly to the xylan and cause the water solubility by which it is determined It represents the value of the arabinoxylans. As much as 23% of water that the analytical methods seek to achi in a bread dough may be associated with pento Other terms are also in use, such as 'unavailable sans(Bushuk, 1966). It has been suggested carbohydrate'and 'plantin, which depart from (Hoseney, 1984)that pentosans reduce the rate the indication that only fibrous material (i.e. of CO2 diffusion through the dough, behaving in occurring as fibres) is included. Instead it this way similarly to gluten suggests a matrix of plant materials. It will probably be some time before a consensus is Fibre achieved because of lack of agreement on whether a functional or compositional definition is more Extraction of individual cell wall components appropriate. In the meantime methods that is complex and unsuitable for routine analysis. distinguish several classes of indigestible material Nevertheless an estimate of cell wall content will be the most useful. That of Southgate et al is often required, particularly in relation to nutri-( 1986) distinguishes among cellulose, non-cell tional attributes of a product. analytical procedures losic polysaccharides and lignin. That of Asp have been devized to determine undigestible et al.(1983)distinguishes soluble and insoluble laterial as fibre,, but not all experts are agreed bre Insoluble components include galacto-and as to which chemical entities should be included gluco-mannans, cellulose and lignin, and the64 TECHNOLOGY OF CEREALS unusually high (25-30%), and mannose-contain- The term is frequently qualified to reflect the ing sugars in some may contribute as much as method of analysis employed because different 15%. methods produce different values (it should also A significant non-carbohydrate molecule inti- be noted that some methods are themselves mately associated with arabinoxylans in wheat inconsistent). The following types of fibre may and other cereal cell walls is ferulic acid, a phenol be encountered, the definitions are based on a carbonic acid very abundant in plant products. glossary by Southgate et al. (1986). It is esterified to the primary alcoholic group of Crude fibre - The residue left after boiling the the arabinose side chain (Amado and Neukom, defatted food in dilute alkali and then in dilute 1985). The formation of diferulic acid cross-links acid. The method recovers 50-80% of cellulose, is at least partly responsible for the gelation of 10-50% of lignin and 20% of hemicellulose. aqueous flour extracts or solutions of cereal Results are inconsistent. pentosans in the presence of oxidizing agents. Acid detergent fibre (ADF) - The cellulose Ferulic acid exhibits intensive blue fluorescence plus lignin in a sample; it is measured as the when irradiated with light of 365 nm. The residue after extracting the food with a hot reaction is particularly marked in aleurone cell dilute H2S04 solution of the detergent cetyl walls and thus can be used for identifying these trimethylammonium bromide (CTAB). in ground cereal products under the fluorescence Neutral detergent fibre (NDF) - The residue microscope. left after extraction with a hot neutral solution of Fractionation into water soluble and insoluble sodium dodecyl sulphate (SDS) also known as pentosans by various protocols is common analy- sodium lauryl sulphate. It is designed to divide tical practice as it has been found to distinguish the dry matter of feeds very nearly into those different functional properties. Thus it is the which are nutritionally available by the normal water-soluble pentosans (mainly arabinoxylans) digestive process and those which depend on of wheat that have a very high water absorbing microbial fermentation for their availability. capacity. They are linear molecules while those Dietary fibre - All the polymers of plants that of the insoluble fraction are highly branched. The cannot be digested by the endogenous secretions backbone of arabinoxylans consists of D-glucan of the human digestive tract. units linked by 0-( 1-4) glycosidic bonds. Single The last definition differs from those that a-L-arabinofuranose residues are attached ran- precede it in that it is not based on the method domly to the xylan and cause the water solubility by which it is determined. It represents the value of the arabinoxylans. As much as 23% of water that the analytical methods seek to achieve. in a bread dough may be associated with pento- Other terms are also in use, such as ‘unavailable sans (Bushuk, 1966). It has been suggested carbohydrate’ and ‘plantzx’, which depart from (Hoseney, 1984) that pentosans reduce the rate the indication that only fibrous material (i.e. of COz diffusion through the dough, behaving in occurring as fibres) is included. Instead it this way similarly to gluten. suggests a matrix of plant materials. It will probably be some time before a consensus is achieved because of lack of agreement on whether a functional or compositional definition is more Fibre Extraction of individual cell wall components appropriate. In the meantime methods that is complex and unsuitable for routine analysis. distinguish several classes of indigestible material Nevertheless an estimate of cell wall content will be the most useful. That of Southgate et al. is often required, particularly in relation to nutri- (1986) distinguishes among cellulose, non-cellu￾tional attributes of a product. Analytical procedures losic polysaccharides and lignin. That of Asp have been devized to determine undigestible et al. (1983) distinguishes soluble and insoluble material as ‘fibre’, but not all experts are agreed fibre. Insoluble components include galacto- and as to which chemical entities should be included. gluco-mannans, cellulose and lignin, and the