Protein composition and nutritional aspects of pea protein fractions obtained by a modified isoelectric precipitation method using fermentation

Abstract

Pea albumins are promising for their nutritional, biological, and techno-functional properties. However, this fraction is usually discarded in the industry due to its low protein content compared to globulin fraction and the presence of some anti-nutritional compounds. In the present study, we used an alternative method of pea protein extraction based on alkaline solubilization/isoelectric precipitation in which the reduction of pH was achieved by lactic acid fermentation using specific starters instead of mineral acids. Hence, the main objective of this study was to examine the protein profile and the content of anti-nutritional and nutritional active compounds in pea albumin-rich fractions obtained by the isoelectric extraction method without (control) or with fermentation with different lactic acid bacteria (Streptococcus thermophilus, Lactiplantibacillus plantarum, and their co-culture). Different pea cultivars (Cartouche, Ascension, and Assas) were used here for their differences in protein profile. The results revealed a higher total nitrogen content in albumin-rich fraction for fermented samples and, in particular, for co-culture. The majority of total nitrogen was determined as non-protein (~50%), suggesting the degradation of proteins by LAB to small peptides and amino acids, which were solubilized in the soluble fraction (albumin) as confirmed by size exclusion chromatography (SEC-HPLC) analysis. Moreover, the higher antioxidant activity of fermented albumin samples was attributed to the production of small peptides during extraction. Lactic acid fermentation also resulted in a significant reduction of trypsin inhibitor activity, α-galactoside, and phytic acid content of this fraction compared to control.

Identification of volatile and odor‐active compounds in pea protein fractions obtained by a modified extraction method using fermentation

“…The acidification process was concluded once the pH reached 4.8, aligning with the globulins' isoelectric point. The pH reduction occurred more rapidly in the coculture, taking approximately 4-5 hours, compared with the monoculture, which took approximately 9-10 hours (Emkani et al, 2023). The final concentration of the bacteria at the end of the fermentation was around 10 9 CFU/mL.…”

“…The selection of the bacteria was done according to a study performed by our group (Emkani et al 2023).…”

“…The bacterial culture was performed according to Emkani et al (2023). Briefly, freeze-dried bacteria were rehydrated in MRS medium for LP and M17 medium for ST and then incubated at their optimal temperature (37 • C for LP, 43 • C for ST) for 24 h. The cells were isolated on agar medium, and a single colony was incubated in 10 mL of liquid medium for 24 h. A culture was created by inoculating 10 mL of broth with 1 mL of preculture, stopped at stationary phase (around 12 h for LP, 7 h for ST).…”

“…The extraction method was according to the protocol proposed by Emkani et al (2021) and Emkani et al (2023). In summary, seeds from the Assas cultivar were initially cracked using a Rotor Beater Mill SK300 (RETSCH GmbH, Haan, Germany) to break the grains and separate the hull.…”

“…They have also shown the albumin fraction obtained by this method had a higher content of total nitrogen compared with conventional acidification without damaging the structure of globulin fraction, which is used as pea protein isolate in industry. This was explained by the proteolytic activity of the lactic acid bacteria (LAB) leading to the production of small peptides and amino acids that were solubilized and recovered in the soluble albumin-rich fraction (Emkani et al, 2023). Considering the enzymatic activity of LAB during the metabolism of different nutrients and production of precursors of volatile compounds (such as different amino acids), which can positively improve the aromatic profile of legume proteins, the purpose of this study was to identify the volatile compounds of albumin and globulin fractions obtained without (control) or with fermentation by S. thermophilus (ST) and L. plantarum (LP) or their coculture (STLP).…”