Abstract
Nine Lactobacillus strains known for surface proteinase activity were chosen from our collection and tested for their ability to grow in pea seed protein-based medium, and to hydrolyze purified pea proteins in order to produce peptides with antioxidant (AO) activity. Two strains, Lactobacillus rhamnosus BGT10 and Lactobacillus zeae LMG17315, exhibited strong proteolytic activity against pea proteins. The AO activity of the pea hydrolysate fraction, MW <10 kDa, obtained by the fermentation of purified pea proteins with Lactobacillus rhamnosus BGT10, was tested by standard spectrophotometric assays (DPPH, ABTS, Fe3+-reducing capacity) and the recently developed direct current (DC) polarographic assay. The low molecular weight fraction of the obtained hydrolysate was separated using ion exchange chromatography, while the AO activity of eluted fractions was determined by means of a sensitive DC polarographic assay without previous concentration of samples. Results revealed that the fraction present in low abundance that contained basic peptides possessed the highest antioxidant activity. Based on the obtained results, it can be concluded that Lactobacillus rhamnosus BGT10 should be further investigated as a candidate strain for large-scale production of bioactive peptides from legume proteins.
Highlights
Pea seeds are a rich source of highly digestible proteins comparable to other commonly used legumes (Gausseres et al, 1997; Barac et al, 2010; Kotlartz et al, 2011)
Changes in AO activity showed a positive correlation with the increase in bacterial cell number (r=0.98), confirming the ability of the Lb. rhamnosus BGT10 strain to significantly increase the antioxidant activity of pea seed-based medium during fermentation
To evaluate the antioxidant potential of pea proteinderived peptides produced by Lb. rhamnosus BGT10, Fig. 4. (A) Fractionation of protein hydrolysate (PH)
Summary
Pea seeds are a rich source of highly digestible proteins comparable to other commonly used legumes (Gausseres et al, 1997; Barac et al, 2010; Kotlartz et al, 2011). Common techniques for AO activity analysis of small peptide fractions produced by protein hydrolysis usually include gel filtration, solid phase extraction, ion exchange chromatography, chromatography of hydrophobic interactions (HIC) or a reverse-phase high-performance liquid chromatography (RP-HPLC) for resolving peptide fractions. These separation techniques are usually followed by lyophilization of the obtained fractions prior to classic AO assays, which are both material and time consuming (Pownall et al, 2010; Tang et al, 2010). The recently developed highly sensitive direct current (DC) polarographic assay (Sužnjević et al, 2011), which has been validated using complex mixtures containing peptides such as beer, honey and herbal infusions, can be effectively applied for direct estimation of AO activity measurement in highly diluted peptide samples without previous concentration
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