Development and application of an enzyme-linked immunosorbent assay (ELISA) for the quantification of amygdalin, a cyanogenic glycoside, in food

Determination of Amygdalin in Apricot Kernels and Almonds Using LC-MS/MS

BACKGROUND

Cyanogenic glycosides are secondary metabolites in plants. In almonds and apricot kernels, amygdalin is an abundant cyanogenic glycoside. Upon consumption, amygdalin is enzymatically metabolized into hydrogen cyanide. Depending on the number of kernels consumed and the amygdalin concentration, ingestion of amygdalin-containing kernels may result in adverse effects. To better understand the US marketplace, the development and validation of analytical methods to reliably measure amygdalin in apricot kernels and almonds is needed to support the collection of occurrence and consumption data in retail products.

OBJECTIVE

The aim of this study was to develop and validate a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantitation of amygdalin in apricot kernels and almonds following the U.S. Food and Drug Administration (FDA). Foods Program Guidelines for the Validation of Chemical Methods, 3rd Edition.

METHODS

Apricot kernels and almonds were cryogenically homogenized and extracted using methanol containing an internal standard (IS), geniposide, followed by filtration, dilution, and LC-MS/MS analysis. Matrix effects were minimized using dilution. Quantitation was achieved using an external, solvent-based calibration.

RESULTS

The amygdalin response was linear (r2 > 0.99) over a range of 0.05-50 µg/mL. The recovery of amygdalin spiked at 10-10 000 µg/g in sweet apricot kernels, raw almond, and dry-roasted almond ranged from 90 to 107% with RSDs ≤6%. The method limit of detection and limit of quantitation was 0.8 and 2.5 ng/g, respectively. Amygdalin concentrations in 18 market samples ranged from 2 to 24 000 µg/g. Corresponding estimates of cyanide concentration ranged from 0.2 to 1420 µg/g.

CONCLUSIONS

Method performance meets the acceptance criteria defined by FDA guidelines and is fit for purpose for the analysis of amygdalin in apricot kernels and almonds.

HIGHLIGHTS

An LC-MS/MS method is developed for the quantification of amygdalin in apricot kernels and almonds.

Recent progress of personal glucose meters integrated methods in food safety hazards detection

Development of personal glucose meters (PGMs) for blood glucose monitoring and management by the diabetic patients has been a long history since its first invention in 1968 and commercial application in 1975. The main reasons for its wide acceptance and popularity can be attributed mainly to the easy operation, test-to-result model, low cost, and small volume of sample required for blood glucose concentration test. During past decades, advances in analytical techniques have repurposed the use of PGMs into a general point-of-care testing platform for a variety of non-glucose targets, especially the food hazards. In this review, we summarized the recent published research using PGMs to detect the food safety hazards of mycotoxins, illegal additives, pathogen bacteria, and pesticide and veterinary drug residues detection with PGMs. The progress on PGM-based detection achieved in food safety have been carefully compared and analyzed. Furthermore, the current bottlenecks and challenges for practical applications of PGM for hazards detection in food safety have also been proposed.

Ultrasensitive and simultaneous detection of 6 nonsteroidal anti-inflammatory drugs by colloidal gold strip sensor

In this work, an oxicam group-selective monoclonal antibody against 6 nonsteroidal anti-inflammatory drugs (NSAID; meloxicam, lornoxicam, piroxicam, sudoxicam, droxicam, and tenoxicam) was prepared. Also, a spacer arm with carboxyl group was derived at the hydroxyl of meloxicam to generate the meloxicam hapten. The half-maximal inhibitory concentrations (IC₅₀) were, respectively, 0.31 ng/mL for meloxicam, 0.49 ng/mL for lornoxicam, 2.90 ng/mL for piroxicam, 1.95 ng/mL for sudoxicam, 3.08 ng/mL for droxicam, and 5.36 ng/mL for tenoxicam. A colloidal gold immunochromatographic strip based on the monoclonal antibody was developed for the detection of these 6 NSAID in milk. The results could be obtained by the naked eye in 10 min, and the cut-off values and the visual limits of detection in real samples were 5, 5, 10, 10, 25, and 25 ng/mL, and 0.25, 1, 0.5, 0.5, 1, and 1 ng/mL, respectively. This immunochromatopgraphic strip is a suitable tool for on-site detection and screening of oxicam NSAID in milk samples.

Problems and Pitfalls in the Analysis of Amygdalin and Its Epimer

α-[(6-O-β-d-Glucopyranosyl-β-d-glucopyranosyl)oxy]-(αR)-benzeneacetonitrile, or R-amygdalin, is the most common cyanogenic glycoside found in seeds and kernels of the Rosaceae family and other plant genera such as Passiflora. Many commercially important seeds are analyzed for amygdalin content. In "alternative medicine", amygdalin has been sold as a treatment for cancer for several decades without any rigorous scientific support for its efficacy. We have found that there are some inconsistencies and possible problems in the published analytical chemistry of amygdalin. It is shown that some analytical approaches do not account for the presence of the S-isomer; therefore, a fast reliable method was developed using a chiral stationary phase and HPLC. This approach allows "real-time" monitoring and complete and highly efficient separations. It is found that the S-amygdalin continuously forms in aqueous solutions. A striking result is that the conversion of amygdalin is glassware dependent. "Clean" vials from various vendors can show drastically different reaction rates of the conversion to the isomer (S-amygdalin, also called neo-amygdalin). The epimerization kinetics are dependent on the solvent, temperature, pH, and the nature of the container. For example, epimerization in water was complete in <15 min in a new glass vial taken from the box, whereas it can take >1 h in specially cleaned glassware. Conversely, epimerization can be significantly delayed at high temperature if high-density polyethylene is used as the container. Hence, inert plastic containers are recommended for storage of aqueous amygdalin solutions. Commercial preparations of R-amygdalin actually contain greater quantities of S-amygdalin and ∼ 5% of other degradation products.

Synthesis and Characterization of Hapten-Protein Conjugates for Antibody Production against Cyanogenic Glycosides

Consumption of cyanogenic plants can cause serious health problems for humans. The ability to detect and quantify cyanogenic glycosides, capable of generating cyanide, could contribute to prevention of cyanide poisoning from the consumption of improperly processed cyanogenic plants. Hapten-protein conjugates were synthesized with amygdalin and linamarin by using a novel approach. Polyclonal antibodies were generated by immunizing four New Zealand White rabbits with synthesized amygdalin-bovine serum albumin and linamarin-bovine serum albumin immunogen. This is the first time an antibody was produced against linamarin. Antibody titer curves were obtained from all the four rabbits by using a noncompetitive enzyme-linked immunosorbent assay. High antibody titer was obtained at dilutions greater than 1:50,000 from both immunogens. This new method is an important step forward in preventing ingestion of toxic cyanogenic glycosides.