Enhancing Bioaccessibility of Plant Protein Using Probiotics: An In Vitro Study

Abstract

As plant-based diets become more popular, there is an interest in developing innovations to improve the bioaccessibility of plant protein. In this study, seven probiotic strains (Bifidobacterium animalis subsp. lactis B420, B. lactis Bl-04, Lactobacillus acidophilus NCFM, Lacticaseibacillus rhamnosus HN001, Lacticaseibacillus paracasei subsp. paracasei Lpc-37, Lactiplantibacillus plantarum Lp-115, and Lactococcus lactis subsp. lactis Ll-23) were evaluated for their capacity to hydrolyze soy and pea protein ingredients in an in vitro digestion model of the upper gastrointestinal tract (UGIT). Compared to the control digestion of protein without a probiotic, all the studied strains were able to increase the digestion of soy or pea protein, as evidenced by an increase in free α-amino nitrogen (FAN) and/or free amino acid concentration. The increase in FAN varied between 13 and 33% depending on the protein substrate and probiotic strain. The survival of probiotic bacteria after exposure to digestive fluids was strain-dependent and may have affected the strain's capacity to function and aid in protein digestion in the gastrointestinal environment. Overall, our results from the standardized in vitro digestion model provide an approach to explore probiotics for improved plant protein digestion and bioaccessibility of amino acids; however, human clinical research is needed to evaluate the efficacy of probiotics on amino acid absorption and bioavailability in vivo.

Keywords: amino acids; bioaccessibility; plant protein; probiotics; protein digestion.

Figure 1

Content of soluble protein relative to control digestion (without a probiotic) measured after in vitro digestion of soy (A), pea (B), and whey (C) protein. B420 = Bifidobacterium animalis subsp. lactis B420; Bl-04 = B. lactis Bl-04; NCFM = Lactobacillus acidophilus NCFM; HN001 = Lacticaseibacillus rhamnosus HN001; Lpc-37 = Lacticaseibacillus paracasei subsp. paracasei Lpc-37; Lp-115 = Lactiplantibacillus plantarum Lp-115; and Ll-23 = Lactococcus lactis subsp. lactis Ll-23. Statistical difference between probiotic treatment and digestion without added probiotic (control), * p < 0.05, ** p < 0.01, *** p < 0.001. In the figure, results without an asterisk are non-significant (p ≥ 0.05).

Figure 2

Free amino acids in the soluble phase after in vitro digestion of soy and pea protein. (A) Concentration of free amino acids (mean values, mg/g protein in a simulation) in soy protein digests in the absence (control treatment) or presence of the tested probiotic strains. (B) Concentration of free amino acids (mean values, mg/g protein in a simulation) in pea protein digests in the absence (control treatment) or presence of the tested probiotic strains. In (A,B), essential amino acids (His-Val) are listed first from left to right in the bar graphs, and then non-essential amino acids (Ala-Tyr). (C) Comparison of probiotic digests to control digests in terms of absolute change in free amino acid content from baseline to the levels measured after digestion. The comparisons are reported as ratios against the control treatment where a ratio of 1.0 denotes no difference; ratio < 1, lesser change than in control; and ratio > 1, greater change than in control. B420 = Bifidobacterium animalis subsp. lactis B420; Bl-04 = B. lactis Bl-04; NCFM = Lactobacillus acidophilus NCFM; HN001 = Lacticaseibacillus rhamnosus HN001; Lpc-37 = Lacticaseibacillus paracasei subsp. paracasei Lpc-37; Lp-115 = Lactiplantibacillus plantarum Lp-115; and Ll-23 = Lactococcus lactis subsp. lactis Ll-23; total EAA = total essential amino acids (His, histidine; Ile, isoleucine; Leu, leucine; Lys, lysine; Met, methionine; Phe, phenylalanine; Thr, threonine; Trp, tryptophan; Val, valine); total BCAA = total branched chain amino acids (isoleucine, leucine, valine); total AA = total amino acids.

Figure 3

Concentration of cadaverine, histamine, putrescine, and spermidine before and after in vitro digestion of soy and pea protein. Other analyzed biogenic amines (tyramine, 2-methylbutylamine, 2-phenylethylamine, ethylamine, methylamine, spermine, tryptamine) were not detected in samples collected at baseline or after digestion. Results are expressed as log10 CFU (colony-forming units) presented as the mean with standard deviation. B420 = Bifidobacterium animalis subsp. lactis B420; Bl-04 = B. lactis Bl-04; NCFM = Lactobacillus acidophilus NCFM; HN001 = Lacticaseibacillus rhamnosus HN001; Lpc-37 = Lacticaseibacillus paracasei subsp. paracasei Lpc-37; Lp-115 = Lactiplantibacillus plantarum Lp-115; and Ll-23 = Lactococcus lactis subsp. lactis Ll-23. * Statistical difference between control and probiotic after digestion, p < 0.05.

Figure 4

Total counts of probiotics at baseline and after in vitro digestion of soy (A), pea (B), and whey (C) protein. Results are expressed as log10 CFU (colony-forming units) presented as the mean with standard deviation. B420 = Bifidobacterium animalis subsp. lactis B420; Bl-04 = B. lactis Bl-04; NCFM = Lactobacillus acidophilus NCFM; HN001 = Lacticaseibacillus rhamnosus HN001; Lpc-37 = Lacticaseibacillus paracasei subsp. paracasei Lpc-37; Lp-115 = Lactiplantibacillus plantarum Lp-115; and Ll-23 = Lactococcus lactis subsp. lactis Ll-23.