Amino Acid Quantification in Bulk Soybeans by Transmission Raman Spectroscopy

Abstract

Soybeans are a commodity crop of significant economic and nutritional interest. As an important source of protein, buyers of soybeans are interested in not only the total protein content but also in the specific amino acids that comprise the total protein content. Raman spectroscopy has the chemical specificity to measure the twenty common amino acids as pure substances. An unsolved challenge, however, is to quantify varying levels of amino acids mixed together and bound in soybeans at relatively low concentrations. Here we report the use of transmission Raman spectroscopy as a secondary analytical approach to nondestructively measure specific amino acids in intact soybeans. With the employment of a transmission-based Raman instrument, built specifically for nondestructive measurements from bulk soybeans, spectra were collected from twenty-four samples to develop a calibration model using a partial least-squares approach with a random-subset cross validation. The calibration model was validated on an independent set of twenty-five samples for oil, protein, and amino acid predictions. After Raman measurements, the samples were reduced to a fine powder and conventional wet chemistry methods were used for quantifying reference values of protein, oil, and 18 amino acids. We found that the greater the concentrations (% by weight component of interest), the better the calibration model and prediction capabilities. Of the 18 amino acids analyzed, 13 had R(2) values greater than 0.75 with a standard error of prediction c.a. 3-4% by weight. Serine, histidine, cystine, tryptophan, and methionine showed poor predictions (R(2) < 0.75), which were likely a result of the small sampling range and the low concentration of these components. It is clear from the correlation plots and root-mean-square error of prediction that Raman spectroscopy has sufficient chemical contrast to nondestructively quantify protein, oil, and specific amino acids in intact soybeans.

Impact of Radio Frequency, Microwaving, and High Hydrostatic Pressure at Elevated Temperature on the Nutritional and Antinutritional Components in Black Soybeans

“…In this study, the content of essential amino acids in raw seeds was 154 g/kg DM, occupying 35.5% of the total amount. Schumerich and others () reported the essential acids in bulk soybeans accounted for 37.5% of the total protein, comparable with our samples. Considering the specific essential amino acids, lysine, phenylalanine and valine were the major components with the relative content >5% of the total amino acids, while the sulfur amino acids methionine was the most limiting amino acids (0.88%).…”

Raman and Fourier transform infrared spectroscopy application to the Puno and Titicaca cvs. of quinoa seed microstructure and perisperm characterization

“…3B), and they are due to NeH bend and CeN stretching vibration, respectively. The line at 924 cm −1 can be assigned to amino acid proline as well as low intensity bands at 633 cm −1 , with doublets at 824 and 843 cm −1 (Schulmerich et al, 2013). According to Stikic et al (2012), the seed of the Puno cultivar has higher contents of proline and alanine.…”

Single amino acid utilization for bacterial categorization

“…Compared with tag-based methods 18 , this electrochemical detection method can directly detect AAs without any chromophore or fluorophore groups. Moreover, this method is more economical and easier than spectroscopic methods such as nuclear magnetic resonance (NMR) and Raman spectroscopy 19,20 . Thus, this Cu n SPE detection method can be a practical tool in the measurement of AA utilization for bacterial differentiation.…”