Composition and biological value of protein from four varieties of maize (Zea mays L.) in two stages of maturation / Composição e valor biologico das proteinas de quatro variedades de milho (Zea mays L.) em dois estagios de maturação

AUTOR(ES)
DATA DE PUBLICAÇÃO

1980

RESUMO

The principal aim of the present work was a comparative chemical and nutritional study of four varieties of corn in two stages of maturation: green (20 days after polli nation) and dry. The four varieties studied are characterized by the following endosperm genotypes with respect to carbohydrates and protein: Normal Maya (Su02); Sweet Piramex (suo2); Opaque Maya (Su02) and Nutrimaiz or Sweet-Opaque (su02). The chemical investigat~on involved determinations of percentual composition, variation in the content of the main structural components, amino acid composition of the protein fractions and of .the whole flour. The results indicated that there are a marked modification of the grain composition during maturation and that the differences between the varieties are conditioned by the respective genotypes. Considerable variations were observed in the percentual compositions of the four varieties. Non protein nitrogen, ash, and fiber decreased with maturation whereas the lipid content increased. The Sweet Piramex and Nutrimaiz showed 8.0 and 9.3% of lipid, respectively, in the dry stage of maturation, against 5.0 and 6.4 for the Normal Maya and Opaque Maya. Fractional extraction of proteins disclosed a similar behaviour of varieties with respect to endosperm genotypes,that is, a similarity exists between Normal Mãya and Sweet Piramex (02) and between Opaque Maya and Nutrimaiz (02) regarding variation of the contents of different protein fractions, during the maturation processo All varieties showed a greater content of saline-soluble proteins (albumins and globulins) in the green stage their concentration being greate in Nutrimaiz and Opaque Maya, but diminishipg with maturation. The variations observed were: 58.2 to 16.0; 56.1 to 21.0; 60.7 to 40.land 69.8 to 49.6% in the varieties Normal Maya, Sweet Piramex, Opaque Maya and Nutrimaiz, respectively. O the other hand, the zein fraction varied from 16.4 to 40.0% and from 14.9 to 37.2% in Normal Maya and Sweet Piramex for green and dry stages of maturation, compared with 8.0 to 10.8% for Opaque Maya and 5.1 to 6.0% for Nutrimaiz Opaque Maya and Nutrimaiz contained in the dry stage 25.8 and 29.8% of glutelin 3, where as Normal Maya and Sweet Piramex contained 14.0 and 18.0%, respectively. Each protein fraction had a characteristic composition; the albumin, globulin and glutelin 3 presenting a better amino acid pattern. Thus Nutrimaiã and Opaque Maya floursshowed a more favourable composition in any maturing stage than the remaining varieties. The main deficiencies found in the composition of Normal Maya and Sweet Piramex are related to the essencial amino acids lysine (2.4 and 2.7%) and triptophan (0.4 and 0.4%, respectively) whereas in both Opaque Maya and Nutri maiz lysine accounted for 4.6% and triptophan for 1.2 and 0.9%. The leucine/isoleucine ratio is much higher in the Maya Normal 5.3) and Sweet Piramex (4.7) as compared with that of Opaque Maya (3.3) and Nutrimaiz (3.2) which results in lower nutritional quality for the first two varieties. Nutritional evaluation was done by PER and nitrogen balance determinations. The PER dropped on maturation frem 1.9 to 1.2 for the Maya Normal and 2.0 to 1.4 for the Sweet Piramex whereas it remained practically constant, around 2.6, for the Maya Opaque and Nutrimaiz. These values shall be compared with 2.9 for the casein diet. The biological value drepped frem 70%, in the green stage, to 50.8 and 55% in the mature (dry) stage for the Maya Normal and Sweet Piramex, respectively. For Nutrimaiz and Maya Opaque the biological value remained essentially constant areund 74%. Regarding the growth promoting capacity in rats, statistic studies showed that there was no signigicant difference between the varieties Opaque Maya and Nutrimaiz compared with casein, whereas Sweet Piramex and Normal Maya showed, in relation to casein, significant differenceat 5% leveI in the green stage and at 1% leveI in the dry stage. This leads to the conclusion that the Nutrimaiz and Maya Opaque were superior to the Normal Maya and Sweet Piramex in both stage of maturation. Thl ! rk.l1 1)l p m..+;""+ Mtiizirited the favourable characteristics of the paternal genes, which confers on it a better chemical composition than that of the ancestral varieties, thus, originating a variety of more favourable protein composition. It contains, in addition, sugars of better quality and a higher percentage of oil. These characteristics ensure to Nutrimaiz nutritional properties equalor superior to those of Maya Opaque, offering prospects of a greater consumption of com in its natural or processed formo

ASSUNTO(S)

maize proteinas food milho - variedades alimentos - conteudo de proteina protein

ACESSO AO ARTIGO

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