Quantitative paper-based SERS method for the rapid determination of sulfur amino acid residues in Pisum sativum

Abstract

It is known that peas, a sustainable ingredient in plant-based meat analogs and other proteinaceous food products, contain low levels of sulfur amino acid (SAA) residues. Developing additional inexpensive and rapid methods for determining SAA residues in protein is key to alleviating or resolving any concerns of possible micronutrient deficiencies associated with pea protein. This study evaluated surface-enhanced Raman spectroscopy (SERS) and the quantification of nascent signals stemming from cysteine residues in complex sample matrix solutions with low concentrations of analytes chemisorbed to silver using timed exposures. Silver nanoparticle printed SERS (Ag P-SERS) substrates showed a dynamic range of 1–9 ppm for cysteine and 0–42,000 ppm for bovine serum albumin (BSA). A distinct peak at 667 cm^-1 in the SERS spectra of pea extracts corresponded to the ν(C-S) stretching mode of cysteine residues. The results demonstrate that low levels of Cys could be rapidly quantified with SERS and used to differentiate pea flour from 10 cultivars. This scientific development could have a far-reaching impact on the development of plant-based protein sources with nutritional profiles that rival those of animal proteins.