PSXIV-23 - In vitro evaluation of protein kinetics of soy-based ingredients

Abstract: Protein kinetics is the evaluation of how quickly a protein can be digested, absorbed, and entered into the portal system. It is more indicative of growth, feed efficiency, and protein deposition than the extent of digestibility per se. Feed ingredients may have the same digestibility (SID), but will differ in the speed of protein digestion. It was therefore decided to evaluate differences in speed of in vitro protein hydrolysis between 9 different soy-based protein ingredients: soybean meal (SBM), enzyme-treated soy protein (ESP), 3 types of soy protein concentrate (SPC), 2 types of extruded soy (ExS), and 2 types of fermented soybean meal (FSBM). Protein hydrolyzation rate was determined in vitro for the soy-based samples (SBM, ESP, SPC1, SPC2, SPC3, ExS1, ExS2, FSBM1, and FSBM2) using a pH-stat method that quantifies progress of protein hydrolysis by indirect measurement of released acid during hydrolysis. For each sample a 10 mL aqueous suspension containing 1 mg N/mL was prepared and adjusted to pH 8.0 at 39^oC using 0.1 M NaOH. 1 mL of a proteolytic enzyme-solution (trypsin, chymotrypsin and intestinal peptidase) was added to each sample to start protein hydrolysis followed by auto-titration (Mettler Toledo Titrator T9) with 0.1 M NaOH for 120 minutes. The volume of 0.1 M NaOH added to maintain pH at 8 throughout the incubation was recorded and used to calculate degree of hydrolysis (DH). The curve representing DH followed a second-order reaction kinetics and regression was used to estimate the rate constant (k) for each sample. The control sample (SBM) and ESP were analyzed in quadruplicates, the rest of the samples were in duplicates. A pairwise t-test was conducted in the statistical software R (version 4.0.0) to separate means. Significant difference was declared at P < 0.05. Degree of protein hydrolysis increased exponentially for all tested protein ingredients. The speed of protein hydrolysis (k-value) varied with soy-based protein ingredient (Table 1). The higher the k-value is representative of faster protein hydrolysis. There was a numerical 40% increase (P > 0.05) of ESP k-value when compared to the control, which was SBM. The SPC and FSBM samples were significantly lower (P < 0.05) when compared to ESP, SBM and ExS2, with ExS1 sample being intermediate. In conclusion, soy processing technique (enzymatic, fermented, extrusion, or alcohol extraction) affects speed of in vitro protein hydrolysis. Therefore, more research is needed to see if these results coincide with protein utilization in vivo.