The effect of endosperm vitreousness on fermentation characteristics and in vitro digestibility of maize

[摘要] ENGLISH ABSTRACT: The purpose of this study was to investigate the variation that exists between maize samples regardingparticle size separation, in vitro fermentation kinetics and in vitro dry matter (DM) disappearance. A secondobjective was to quantify possible relationships between the Roff Milling Index (RMI) of maize and any of themeasured in vitro parameters. Three trials were conducted: a particle size distribution trial, a gas productiontrial and an in vitro DM degradability and starch disappearance trial.Overall, nine maize samples, which differed in terms of cultivar and endosperm type, were collected fromdifferent origins for the study. The samples were selected in terms of their Milling Index (MI). Three of thenine samples had a high MI that ranged between 109 and 118, three had a low MI that ranged between 67and 71 and the other three samples had a medium MI that ranged between 85 and 92. Although the MI is nota direct indication of the hardness or softness of the endosperm, it was believed to be indirectly associatedwith vitreousness.In the first trial, the different maize samples were milled through a 1 mm screen and sieved through a seriesof three sieves 150, 125 and 106 μm, respectively. It was found that RMI was not a reliable indicator topredict particle size distribution, especially in terms of the coarse (>150 μm) and very fine (<106 μm)particles.In the gas production trial, the nine different maize samples were subjected to a gas production system for aduration of 48 hours. Here gas production and rate of gas production of the different maize types in bufferedrumen liquor were measured during incubation. After fitting the gas volume data to the respective models,the non-linear parameters b, c and L were subjected to a main effects ANOVA with the aid of Statistica,version 9 (2009). Main effects were treatment and repetition. Means were separated by means of a Scheffétest and significance was declared at P < 0.05. The results were compared to the RMI of the different maizetypes and it was concluded that RMI was not a reliable predictor of gas production or rate of gas productionof different maize types.In the third trial, in vitro DM degradability and starch disappearance of the different maize types weremeasured. In vitro DM degradability was conducted in the Ankom DAISYII incubator apparatus and the incubation times were 0, 2, 4, 8, 12 and 24 hours. Starch disappearance was measured on residues of thesamples incubated for 0, 2 and 4 hours. After fitting the DM disappearance data to the respective models,the non-linear parameters a, b, c and L were subjected to a main effects ANOVA with the aid of Statistica,version 9 (2009). Main effects were treatment and repetition. Means were separated by means of a Scheffétest and significance was declared at P<0.05. The results indicated variation between maize samples,especially in terms of the a-, b- and L-values. The RMI did not appear to be a reliable predictor of digestibilityparameters.

[发布机构] Stellenbosch University