ISEP conference in Brazil

Published 9. September 2019

September, 9-12th of 2019.

Ouro Minas Palace Hotel - Belo Horizonte, MG - Brazil

Processing of soybean meal influences in vitro kinetics of protein digestion in the small intestine

M. A. Ton Nu1,2*, J. S. Zannatta2, H. Schulze1 and R. T. Zijlstra2
1 Agilia a/s, Skjernvej 42, Videbaek, 6920, Denmark ; 2University of Alberta, Edmonton, Alberta, AB T6G 2P5, Canada;

The study investigated the processing effect on in vitro kinetics of protein digestion of soybean meal – non-processed (SBM) and after thermo-mechanical, enzyme-facilitated processing (TEP); and of TEP vs. fermented soy protein (FSP) vs. soy protein concentrate (SPC). Samples (n=72) were incubated in triplicate sequentially with pepsin at pH 3.5 for 1.5 h (stomach phase) and with pancreatin and bile extract at pH 6.8 for 0 to 6 h (small intestine phase).
Protein was classified into CPfast, CPslow and CPresistant corresponding to digested CP within the first 0.5 h, from 0.5 to 4 h and after 4 h, respectively. The TEP increased digested CP by 13% (P<0.001) and CPfast by 24% (P=0.039), reduced CPresistant by 11% (P=0.002) and tended to decrease CPslow by 49% (P=0.060) compared with non-processed SBM. In vitro digestibility of CP was greater (P<0.001) in TEP than in FSP and SPC at each time point.

The kinetic equation showed that TEP tended to have greater maximum protein digestion rate than FSP (0.70 vs. 0.24%/h; P=0.058). The CPresistant content was lower in TEP than in SPC (141 vs. 280 g/kg DM; P=0.022). Therefore, protein would be digested faster with less chance to reach the large intestine in TEP than SPC and FSP. In conclusion, processing of SBM enhanced the in vitro kinetics of protein digestion in small intestine. Thermo-mechanical, enzyme-facilitated processing of SBM enhanced in vitro protein digestion kinetics to a greater extent than fermentation and extensive extraction.

Keywords: digestibility, fermented soy, pig, resistant protein, soy protein concentrate

The protein digestion kinetic profile of feed ingredients influences the absorption rate of amino acids (AA) and peptides and their postprandial appearance in blood, and is consequently related to whole body utilization of protein, whether as energy source or for muscle protein synthesis (Chen, 2017; Ten Have et al., 2007). Understanding effects of processing on protein characteristics and kinetics provides knowledge for optimal processing of feed ingredients to maximize protein utilization in animals.

The objectives of the study were: (1) to evaluate the effect of thermo-mechanical and enzyme-facilitated processing of soybean meal (non-processed (SBM) vs. after processing (TEP)) and (2) to compare the effect of various processes (TEP vs. fermentation to produce fermented soy protein (FSP) vs. extensive extraction to produce soy protein concentrate (SPC)) on in vitro kinetics of protein digestion in small intestine.

Materials and methods
We evaluated 3 batches of SBM, before and after TEP (AlphaSoy, Agilia a/s, Videbaek, Denmark), 3 sources of FSP and 3 sources of SPC. We used a modified two-step in vitro model (Boisen and Fernández, 1995; Chen, 2017) to simulate gastric and small intestine digestion. Briefly, samples were incubated in triplicate sequentially at 39°C with pepsin at pH 3.5 for 1.5 hour and then with pancreatin and bile extract at pH 6.8 for 0, 0.5, 1, 2, 4 and 6 hours. The in vitro kinetics of protein digestion in the small intestine were described by fitting a Gompertz equation: % digested CP = A x (A/W0)exp(-e*Ku*Time), where A is the maximum % digested CP at the asymptote point; W0 is the initial % digested CP at 0 h; Ku is the maximum relative digestion rate (%/h) at inflection and Ti is inflection time (h). Protein fractions were classified into CPfast, CPmedium and CPresistant corresponding to the amount of digested CP within the first 0.5 h, from 0.5 to 4 h and after more than 4 h, respectively. 

Results and discussion
Processing of SBM by TEP increased (P<0.001) digested CP in the small intestine by 13% on average and increased (P=0.018) the maximum digested CP by 6% (Figure 1A). Processing made protein more accessible to digestive enzymes; therefore, TEP contained less CPresistant (26.4 vs. 29.6%) and more CPfast (64.1 vs. 51.8%) than SBM (P<0.05). These in vitro results corresponded with the higher protein and AA digestibility in TEP than SBM in weaned piglets observed previously (Ton Nu et al., 2018) using the same ingredients. Among processing techniques, TEP had the greatest ileal digested protein (P<0.05) resulting in the greatest (P=0.016) maximum digested CP compared with FSP and SPC (Figure 1B). Extensive extraction to produce SPC increased (P=0.022) the amount of CPresistant by 50% compared with TEP. In 14-35 day old piglets fed milk or soy protein diets, the average digestion time in the small intestine is 3.6 hours  (Wilson and Leibholz, 1981). Therefore, protein digestion within 4 h is crucial so that less protein reaches the lower gut. Consequently, protein fermentation and diarrhea incidence will be reduced in weaned piglets. The enhanced in vitro digestion kinetics of protein and the lower resistant CP in TEP indicated that protein would be digested more rapidly with increased chance of AA absorption in the small intestine compared with non-processed SBM, SPC and FSP.


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