Background: Yellow field peas (Pisum sativum L.) are a highly promising source of plant-based proteins due to their affordability, high nutritional profile, low-fat content, lack of major allergens and environmental sustainability among pulses. However, their utilization in food products is constrained by anti-nutritional factors (ANFs), which, while beneficial for plant defense, impair the nutritional value, protein digestibility, and overall protein quality of plant-based food products. Processing methods may provide a means to reduce ANFs and improve protein quality, but lysine, an indispensable amino acid (IAA), remains highly susceptible to chemical modifications during processing, further diminishing the nutritional value of the processed products.

Methods: This study examined the effects of thermal (boiling, autoclaving, micronization, and baking) and non-thermal (high-hydrostatic pressure (HHP)) treatments on yellow field pea flour, as well as the impact of baking and HHP on pea protein derivatives (protein concentrate, 80% protein isolate, and 90% protein isolate). A starch-rich byproduct (coarse fraction) separated through air classification along with the protein-enriched fine fraction (protein concentrate) was also included in this study for evaluation. The focus was on assessing ANF contents including trypsin inhibitor activity (TIA), lectins, phytic acid (PA), polyphenols, and condensed tannins (CT), as well as amino acid profiles, in vitro protein digestibility, in vitro protein quality (via in vitro Protein Digestibility Corrected Amino Acid Score, in vitro PDCAAS), and reactive lysine content (using an ortho-phthaldialdehyde (OPA) fluorometric assay).

Results: In terms of ANFs, thermal treatments (particularly boiling and baking) significantly reduced TIA, lectin, PA, and polyphenols, with boiling proving the most effective, decreasing lectin content by 99.88% and TIA by over 88.60% in the flour. HHP demonstrated moderate ANF reductions but led to substantial increases in lectin and CT contents, with the flour showing a substantial increase in CT of up to 521.57%. With respect to protein quality, tryptophan with amino acid scores (AAS) of 0.91 – 0.97, was the first limiting amino acid in untreated and treated flours and protein concentrates, as well as the coarse fraction, whereas sulfur-containing amino acids (AAS of 0.84 – 0.91) were most limiting in untreated and treated protein isolates and baked protein concentrate. The in vitro protein digestibility (determined by the true fecal protein digestibility, TPD1) of both protein isolate samples (95.77% – 97.33%) was higher than that of coarse fraction, flour, and protein concentrate samples (88.90% – 94.60%). Only boiled flour (91.57%) showed a significant increase in in vitro PDCAAS, while other processing methods gave no improvement or a decrease for yellow field pea samples. Furthermore, reactive lysine content was comparable to total lysine in untreated flour and protein concentrate, but decreased significantly following boiling and baking, with boiling causing a decrease of over 70% in the reactive lysine content of the flour. In contrast, HHP treatment preserved reactive lysine better than other treatments, with reductions of only up to 4.73% in both flour and 90% pea protein isolate.

Conclusion: In conclusion, boiling was the most effective method for reducing ANFs and improving the in vitro PDCAAS in yellow field pea flour. HHP-treated samples retained reactive lysine but unexpectedly increased the concentrations of lectins and condensed tannins in most pea samples.

Significance and Novelty: This study highlights the differential effects of thermal and non-thermal processing on yellow field pea samples, emphasizing the need for tailored processing strategies to minimize ANFs while maximizing nutritional quality. It also demonstrates the importance of using specialized assays for accurately assessing reactive lysine to fully capture the true nutritional value and quality of processed products. The outcomes provide insights for researchers and food processors in optimizing processing methods to enhance the utilization of yellow field pea proteins and develop more nutritious, and sustainable plant-based products.