Starch Hydrolysis by the Ruminal Microflora ,

Abstract

The effects of grain type and processing on ruminal starch digestion are well documented but poorly understood at the biochemical and molecular levels. Waxy grains have starches high in amylopectin and are more readily digested than nonwaxy grains. However, the composition of the endosperm cell matrix and the extent to which the starch granules are embedded within it also affect starch digestion rates. Continued work is needed to determine the influence of specific cell matrix proteins, protein-starch interactions and cell wall carbohydrates on starch availability. The microbial populations that metabolize starch are diverse, differing in their capacities to hydrolyze starch granules and soluble forms of starch. Surveys show that the amylases are under regulatory control in most of these organisms, but few studies have addressed the types of amylolytic enzymes produced, their regulation and the impact of other plant polymers on their synthesis. Research in these areas, coupled with the development and use of isogeneic or near-isogeneic grain cultivars with biochemically defined endosperm characteristics, will enhance our ability to identify mechanisms to manipulate ruminal starch digestion.

In situ and in vitro ruminal starch degradation of untreated and formaldehyde-treated wheat and maize

“…However, the wheat starch degradability may be overestimated because the proportion of undegraded DM which is lost through bag pores is much higher for wheat than for maize, and is mainly made up of starch (Michalet-Doreau, 1990). In cereals, the extent of starch digestion in the rumen is dictated by the nature of surrounding materials, protein matrix and endosperm cell walls (Kotarski et al, 1992). Differences in starch degradation rate between cereals might be partly explained by differences in the degradation rate of the protein matrix which surrounds the starch granules (McAllister et al, 1993 (1990a) and in numerous in situ studies (Kassem et al, 1987;Morgan et al, 1989;McAllister et at, 1990b;Finlayson, 1991, 1994 (Kassem et al, 1987;Ravelo et al, 1988;Morgan et al, 1989;McAllister et at, 1990b); or when the amount of formaldehyde added to the cereal was multiplied by 3 (Morgan et at, 1989) or by 5 as in our study, starch degradability decreased with increasing level of formaldehyde.…”

Desempenho produtivo de novilhos Nelore confinados alimentados com silagem de milho processada

“…O processamento do milho serve para expor os grânulos de amido à digestão (BeaucheMin et al, 1994), formando fissuras, quebrando ou expandindo o amido, por meio da eliminação da película externa do grão, o pericarpo, que constitui barreira física que dificulta o ataque microbiano e a ação das enzimas digestivas (koTarSki et al, 1992).…”

Produção, composição, consumo e digestibilidade em vacas recebendo milho reidratado e ensilado com silagem de cana de açúcar como volumoso

“…O pericarpo do grão de milho e a matriz protéica em torno do grânulo de amido são as principais barreiras ao acesso dos microrganismos ruminais aos grânulos de amido (KOTARSKI et al, 1992). A barreira imposta pelo pericarpo ao grão do milho pode ser reduzida pela moagem dos grãos, processo pelo qual esta película é rompida e a área de contato dos microrganismos e enzimas com os grânulos de amido é aumentada exponencialmente.…”

“…O processamento do milho aumenta a exposição dos grânulos de amido e facilitar os processos enzimáticos de degradação e digestão do amido pela microbiota ruminal para (BEAUCHEMIN et al, 1994). A formação de fissuras, quebra em variados tamanhos de partícula ou expanção do grânulo de amido, tornam mais fácil o acesso e ação das enzimas bacterianas e digestivas do animal (KOTARSKI et al, 1992). Entretanto, a maior parte dos tipos de processamentos do milho atuam em nível da barreira externa do grão (pericarpo), agindo com menor intensidade sobre a matriz proteica, que recobre os grânulos de amido.…”