CHEMICAL COMPONENTS and monoglycerides to give glycerol and free fatty physiological function is not understood but it acids. The unsaturated fatty acids can be con- increases during germination( Kruger and reed verted to hydroperoxides which, in turn, are 1988) changed to hydroxy acids by lipoxygenase, lipo- peroxidase and other enzymes, as well as by non- Insoluble proteins enzymic processes(Youngs, 1986) Lipoxygenase is an effective bleaching agent; The state of knowledge of many insoluble a coupled oxidation destroys the yellow pigments cereal proteins has now advanced even to com- in wheat endosperm. Cosmetically, this is bene- plete sequencing of th acids. This is true ficial in bread doughs but undesirable in pasta of prolamins of maize which are known as zeins products in which the yellow colour is valued since they come from Zea. Barley prolamins are Hoseney, 1986). hordeins, rye prolamins are secalins and oat prolamins are avelins. a different basis for Phytase nomenclature is applied to the naming of wheat prolamins which are called gliadi Phytase catalyzes hydrolysis of phytic acid The cereal prolamins have been reviewed by (inositol hexaphosphoric acid )to inositol and free Shewry and Tatham(1990). On the basis of orthophosphate. In wheat its activity increased sequencing, four major groups of zeins have been six-fold on germination and more activity was defined The groups differ in their amino acid found in hard wheats than in soft(Kruger and content as well as the sequence in which they Reed, 1988). In oats the activity is much lower occur. As prolamins they are by definition rich than in wheat, rye and triticale(Lockhart and in proline and glutamine, and low in lysine and Hurt, 1986) tryptophan. The groups are designated a, B,y In rice the phytin level dropped from 2.67 to and 8. The B-and 8-groups are relatively rich in 1.48 mg/g of dry mass after one day of germina- methionine and the d-group is also rich in cysteine tion, then to 0.44 mg/g after five days. Phytase and histidine ctivity levelled off after seven days juliano 198 Zeil Pheno/ oxidases The predominant group is the a-group, contri buting 75-80% of the total insoluble fraction of In the mature wheat grain several polyphenol zein. By electrophoresis the apparent molecular oxidases are present in the starchy endosperm, weights of the two major a-zeins are 19, 800 and they are more concentrated in the bran. On 22,000. They can be separated by isoelectric germination an increase, including new iso- focussing into a series of monomers and oligomers enzyme synthesis, occurs, mainly in the coleoptile though some of the latter can be extracted only and roots. Monophenolase also increases. Durum after reduction of the s-s bonds by which the wheat has less activity than other wheat types monomers are held together. It is frequently Kruger and Reed, 1988) found in peptide sequences that the domain in the centre is quite different from those at the c- Catalase and peroxidase and N-terminal parts. In a-zeins the C-terminal domain consists of 10 amino acids in a unique atalase and peroxidase are haemoproteins. sequence, similarly the N-terminus has a unique Peroxidase is involved in the degradation of sequence of 36-37 residues in which one or aromatic amines and phenols by hydrogen per- two cysteine residues are present The central oxidase. Its activity is greater in wheat than in domain comprises repetitive blocks of 20 resi- other cereals Catalase catalyzes degradation of dues that are rich in leucine and alanine. the hydrogen peroxide to water and oxygen. Its tertiary structure of a-zeins, divined from circularCHEMICAL COMPONENTS 69 and monoglycerides to give glycerol and free fatty physiological function is not understood but it acids. The unsaturated fatty acids can be con- increases during germination (Kruger and Reed, verted to hydroperoxides which, in turn, are 1988). changed to hydroxy acids by lipoxygenase, lipo￾Insoluble proteins peroxidase and other enzymes, as well as by non￾enzymic processes (Youngs, 1986). Lipoxygenase is an effective bleaching agent; The state of knowledge of many insoluble a coupled oxidation destroys the yellow pigments cereal proteins has now advanced even to com￾in wheat endosperm. Cosmetically, this is bene- plete sequencing of their amino acids. This is true ficial in bread doughs but undesirable in pasta of prolamins of maize which are known as zeins, products in which the yellow colour is valued since they come from Zea. Barley prolamins are (Hoseney , 1986). hordeins, rye prolamins are secalins and oat prolamins are avelins. A different basis for nomenclature is applied to the naming of wheat prolamins which are called gliadins. Phytase Phytase catalyzes hydrolysis of phytic acid The cereal prolamins have been reviewed by (inositol hexaphosphoric acid) to inositol and free Shewry and Tatham (1990). On the basis of orthophosphate. In wheat its activity increased sequencing, four major groups of zeins have been six-fold on germination and more activity was defined. The groups differ in their amino acid found in hard wheats than in soft (Kruger and content as well as the sequence in which they Reed, 1988). In oats the activity is much lower occur. As prolamins they are by definition rich than in wheat, rye and triticale (Lockhart and in proline and glutamine, and low in lysine and Hurt, 1986). tryptophan. The groups are designated a, p, y In rice the phytin level dropped from 2.67 to and 6. The p- and 6-groups are relatively rich in 1.48 mg/g of dry mass after one day of germina- methionine and the &-group is also rich in cysteine tion, then to 0.44 mg/g after five days. Phytase and histidine. activity levelled off after seven days (Juliano, a-Ze in s 1985). The predominant group is the a-group, contri￾buting 75-80% of the total insoluble fraction of Phenol oxidases In the mature wheat grain several polyphenol zein. By electrophoresis the apparent molecular oxidases are present in the starchy endosperm, weights of the two major a-zeins are 19,800 and they are more concentrated in the bran. On 22,000. They can be separated by isoelectric germination an increase, including new iso- focussing into a series of monomers and oligomers, enzyme synthesis, occurs, mainly in the coleoptile though some of the latter can be extracted only and roots. Monophenolase also increases. Durum after reduction of the S-S bonds by which the wheat has less activity than other wheat types monomers are held together. It is frequently (Kruger and Reed, 1988). found in peptide sequences that the domain in the centre is quite different from those at the C￾and N-terminal parts. In a-zeins the C-terminal domain consists of 10 amino acids in a unique Catalase and peroxidase Catalase and peroxidase are haemoproteins. sequence, similarly the N-terminus has a unique Peroxidase is involved in the degradation of sequence of 36-37 residues in which one or aromatic amines and phenols by hydrogen per- two cysteine residues are present. The central oxidase. Its activity is greater in wheat than in domain comprises repetitive blocks of 20 resi￾other cereals. Catalase catalyzes degradation of dues that are rich in leucine and alanine. The hydrogen peroxide to water and oxygen. Its tertiary structure of a-zeins, divined from circular