Determination of optimal duration and number of sampling for in vitro incubation studies

Abstract

This study was conducted to investigate the optimal duration of incubation and number of sampling for in vitro studies. In experiment 1, three dietary protein sources, such as soybean meal (SBM), soybean hull (SBH) and corn gluten meal (CGM) were used to estimate in vitro their N digestibility with protease extracted from Streptomyces griceus. The incubation times were 0, 0.5, 1, 2, 3, 4, 6, 8, 10, 12, 14, 16, 20, 24, 30, 36, 48, 60 and 72 h and optimal duration of incubation and number of sampling were determined by assessing regression equations. It seems that crude protein (CP) degradation of SBM and SBH were more accurately fitted into the simple exponential model in comparison to that of CGM. However, negative values were observed at 12, 14 and 60 h. According to the linear regression, the estimated values could be compared among themselves by incubation time and interval. The parameter values such as fraction-b and rate constant of degradation was compared with data from initial 19 incubation time point. Estimated fraction-b and rate of constant value were similar each other during whole incubation time and interval. While the estimated values were almost similar during the incubation, and the values of approximate 95% confidence limit were increased as number of incubation time point was decreased. Therefore, fraction-b and rate of constant value are not acceptable when the number of time point is below 6. Fraction-b values were decreased for 48 h incubation compared with that of 72 h incubation. Fraction-c value was calculated with residues of CP after 48 or 72 h incubation, and the different of fraction-c values resulted lead to different regression result.