Improved accuracy of geographical origin identification of shiitake grown in sawdust medium: A compound-specific isotope model-based pilot study.

In countries like South Korea and the USA, origin labeling of shiitake grown using imported Chinese-inoculated medium is an issue. Therefore, we evaluated the use of compound-specific isotope analysis (CSIA) for the accurate identification of the geographical origin of shiitake (Korean, Chinese-inoculated medium, and Chinese); Chinese-inoculated medium shiitake were cultivated in Korea using inoculated sawdust medium from China. The CSIA-discriminant model showed an overall accuracy of 100% in the geographical classification of the original set and 96.4% for the cross-validated set. Glutamate and aspartate δ15N values were the most important variables for differentiating shiitake based on their origins. Compared to that observed upon using the bulk stable isotope analysis, the CSIA model was associated with significantly improved predictability of origin identification. Our findings elucidate the importance of isotope signatures in developing a reliable origin labeling method for shiitake cultured on the sawdust medium for the global market.

Compound-specific δ13C and δ15N analyses of fatty acids and amino acids for discrimination of organic, pesticide-free, and conventional rice (Oryza sativa L.).

Herein, we improve the procedure for organic rice authentication using compound-specific δ13C and δ15N analyses of fatty acids and amino acids, addressing the increasing demand for accurate methods to confirm organic authenticity. Organic rice (OR) and pesticide-free rice (PFR) featured higher values of δ15Nbulk than conventional rice (CR), whereas the corresponding differences between OR and PFR were insignificant. Additionally, OR, PFR, and CR could be discriminated based on some δ13Camino-acid and δ15Namino-acid values. δ13Cbulk was correlated with most δ13Cfatty-acid (r ≥ 0.596) values, and δ15Nbulk was strongly correlated with most δ15Namino-acid (r ≥ 0.834) values. The first component in the orthogonal projection to latent structure-discriminant analysis model allowed for a clear separation between OR and PFR, and good predictability (Q2Y = 0.506). Thus, the present study improves the reliability of organic authentication when bulk stable isotope ratio analysis alone is insufficient for the accurate discrimination of OR, PFR, and CR.

Fatty Acid- and Amino Acid-Specific Isotope Analysis for Accurate Authentication and Traceability in Organic Milk.

The present study describes compound-specific δ13C and δ15N analyses of fatty acids and amino acids for improving the accurate authentication of organic milk (OM) against conventional milk (CM) collected in Korea. Most δ13Cfatty-acid and δ13Camino-acid values were lower in OM than in CM ( P < 0.05); however, most δ15Namino-acid values displayed weak discriminative power for OM authentication. Higher isotopic fractionation was observed in δ13Cfatty-acid than in δ13Camino-acid and δ15Namino-acid, with fractionation trends differing with individual amino acids. In particular, δ13Clinoleic-acid of -33.5‰ and δ13Cmyristic-acid of -28‰ were determined to be promising year-round threshold values for Korean OM authentication. The δ13Cbulk was highly correlated with δ13CAla ( r = 0.92) and δ13Coleic-acid, trans ( r = 0.77), and strong positive correlations were observed between δ13CVal and δ13CIle ( r = 0.98) and between δ15NThr and δ15NSer ( r = 0.90). Chemometric modeling for OM authentication produced a high quality model ( R2 X = 0.547, R2 Y = 0.865, and Q2 = 0.689) with reliable chemical markers, notably δ13Cmyristic-acid, δ13Clinoleic-acid, and δ13Cstearic-acid. Furthermore, the models developed for seasonal separation in OM ( Q2 = 0.954) and CM ( Q2 = 0.791) were of good quality. Our findings, based on compound-specific isotope data, improve the reliability of OM authentication in cases where bulk stable isotope ratio analysis alone is insufficient. They also provide valuable insight into the control of fraudulent OM labeling in Korea, with potential application in other countries.

The relative influence of derivatization and normalization procedures on the compound-specific stable isotope analysis of nitrogen in amino acids.

RATIONALE: Within the last decade, applications of compound-specific stable isotope analysis of nitrogen (δ15 N values) in amino acids (CSIA-AA) have developed rapidly, particularly within organismal ecology. Unlike with bulk stable isotope analysis (BSIA), the reproducibility of δ15 N-AA measurements has not been critically assessed. Two primary concerns include the diversity of techniques available for the derivatization of amino acids prior to analysis by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) and the myriad of standardization practices and quality assurance procedures used across studies. METHODS: We examined the relative effect of three normalization procedures, (1) internal reference calibration, (2) compound-specific calibration, and (3) scale-normalization, on the accuracy and precision of δ15 N-AA measurements by GC/C/IRMS and the comparability of δ15 N-AA measurements by two derivatization techniques, methoxycarbonylation-esterification and acetylation-esterification, across a range of organisms. RESULTS: The overall accuracy and precision of δ15 N-AA measurements were improved following both compound-specific calibration and scale-normalization, as was the comparability of δ15 N-AA measurements of individual amino acids between derivatization techniques across organisms. The mean difference of scale-normalized δ15 N-AA values across all organisms between the two derivatization techniques was 0.19‰, much less than the typical analytical error associated with δ15 N-AA measurements (±1‰). CONCLUSIONS: Adoption of standardized calibration procedures will be important to establishing reproducibility in δ15 N-AA measurements, particularly across derivatization techniques. It is both technically practical and desirable for users of CSIA-AA to adopt practices in quality control and assessment similar to those outlined for BSIA, including the compound-specific calibration of δ15 N-AA values, followed by scale-normalization. Copyright © 2017 John Wiley & Sons, Ltd.

Compound-specific δ13C and δ15N analysis of amino acids: a rapid, chloroformate-based method for ecological studies.

RATIONALE: Compound-specific stable isotope analysis of amino acids has proven informative to many ecological systems, but only a handful of analytical methods are routinely employed. We evaluated a simple, rapid procedure in which biological samples undergo short-duration acid hydrolysis and the resulting amino acids are derivatized with methyl chloroformate for gas chromatography/combustion/isotope-ratio mass spectrometry (GC/C/IRMS). METHODS: Amino acid derivatives were separated on a polar gas chromatography column, combusted, and δ(13)C and δ(15)N values were measured. Tests of reproducibility and accuracy were conducted for amino acid reference mixtures and biological samples. A brief case study of turtles was used to assess whether isotopic data were consistent with a priori ecological expectations. RESULTS: The methyl chloroformate based reaction successfully converted 15 amino acids from acid hydrolysates of biological materials into separable derivatives. The δ(13)C and δ(15)N values had high average measurement precision (σ <1‰). Reference materials were measured accurately, with good agreement between EA/IRMS and GC/C/IRMS determinations. Analysis of turtle blood samples yielded data consistent with their trophic ecology. CONCLUSIONS: This derivatization method is a rapid means of determining carbon and nitrogen isotopic ratios of amino acids present in the biological materials often sampled for ecological studies. While amino acids with charged or polar side chains do not have uniformly high recoveries, the average precision of measurements is comparable with that of other, more established methods. Batches of samples may be prepared from many raw materials in less than a day, representing a significant reduction in preparation time over prevailing methods.