Validation and Determination of Quinolizidine Alkaloids (QAs) in Lupin Products by Gas Chromatography with Flame Ionization Detection (GC-FID)

An insight into recent updates on analytical techniques for bioactive alkaloids

INTRODUCTION

Alkaloids represent a wide class of naturally existing nitrogen-containing organic compounds having diverse biological activities. They are primary bioactive substances extracted from diverse plant parts. Due to their diverse biological activities, they are frequently used as medicines. The alkaloids have diverse pharmacological impacts on the human body; alkaloids are used for prevention, treatment, and reduction of discomfort associated with chronic illnesses. As most alkaloids exist in plants in complex form, combined with numerous other natural plant components, it is essential to recognize and characterize these molecules using different analytical techniques.

OBJECTIVES

We aimed to review the literature on the methods and protocols for the analysis of naturally occurring alkaloids.

METHODS

We carried out a literature survey using the PubMed, Scopus, and Google Scholar databases and other relevant published materials. The keywords used in the searches were "alkaloids," "analytical methods," "HPLC method," "GC method," "electrochemical methods," and "bioanalytical methods," in various combinations.

RESULTS

In this article, several classes of alkaloids are presented, along with their biological activities. Moreover, it includes a thorough explanation of chromatographic techniques, hyphenated techniques, electrochemical techniques, and current trending analytical methods utilized for the isolation, identification, and comprehensive characterization of alkaloids.

CONCLUSIONS

The various analytical techniques play an important role in the identification as well as the characterization of various alkaloids from plants, plasma samples, and urine samples. The hyphenation of various chromatographic techniques with mass spectrometry and NMR spectroscopy plays a crucial role in the characterization of unknown compounds.

Quantitation of Lupinus spp. Quinolizidine Alkaloids by qNMR and Accelerated Debittering with a Resin-Based Protocol

Quinolizidine alkaloids (QAs) are toxic secondary metabolites of the Lupinus species, the presence of which limits the expansion of lupin beans consumption, despite their high protein content. Evaluation of the level of alkaloids in edible Lupinus species is crucial from a food safety point of view. However, quantitation of QAs is complicated by the fact that not all important alkaloids used for quantitation are commercially available. In this context, we developed a method for the simultaneous quantitation of eight major lupin alkaloids using quantitative NMR spectroscopy (qNMR). Quantitation and analysis were performed in 15 different seed extracts of 11 Lupinus spp. some of which belonged to the same species, with different geographical origins and time of harvest, as well as in all aerial parts of L. pilosus. The mature seeds of L. pilosus were found to be a uniquely rich source of multiflorine. Additionally, we developed a protocol using adsorption or ionic resins for easy, fast, and efficient debittering of the lupine seeds. The protocol was applied to L. albus, leading to a decrease of the time required for alkaloids removal as well as water consumption and to a method for QA isolation from the debittering wastewater.

A New Fluorescence Detection Method for Tryptophan- and Tyrosine-Derived Allelopathic Compounds in Barley and Lupin

Barley (Hordeum vulgare) is one of the most widely cultivated crops for feedstock and beer production, whereas lupins (Lupinus spp.) are grown as fodder and their seeds are a source of protein. Both species produce the allelopathic alkaloids gramine and hordenine. These plant-specialized metabolites may be of economic interest for crop protection, depending on their tissue distribution. However, in high concentrations they pose a health risk to humans and animals that feed on them. This study was carried out to develop and validate a new method for monitoring these alkaloids and their related metabolites using fluorescence detection. Separation was performed on an HSS T3 column using slightly acidified water-acetonitrile eluents. Calibration plots expressed linearity over the range 0.09-100 pmol/µL for gramine. The accuracy and precision ranged from 97.8 to 123.4%, <7% RSD. The method was successfully applied in a study of the natural range of abundance of gramine, hordenine and their related metabolites, AMI, tryptophan and tyramine, in 22 barley accessions and 10 lupin species. This method provides accurate and highly sensitive chromatographic separation and detection of tryptophan- and tyrosine-derived allelochemicals and is an accessible alternative to LC-MS techniques for routine screening.

Development of an HPLC-MS/MS Method for the Determination of Alkaloids in Lupins

Lupin alkaloids (LAs) represent a class of toxic secondary metabolites in plants, in particular in Lupinus spp.; they are produced as a defense mechanism due to their strong bitter taste and are very dangerous for human and animals. In this work, a sensitive and reliable high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) analytical method for the identification and quantification of thirteen lupin alkaloids was developed and validated according to FDA guidelines. Efficient extraction and clean-up steps, carried out by solid-phase extraction, were finely tuned on the basis of the characteristics of the analytes and lupin samples, providing good selectivity with minimized matrix interference. The effectiveness of the method was proven by the satisfactory recovery values obtained for most of the analytes and a matrix effect ≤23% for all tested levels. In addition, a sensitive and reliable determination of the target compounds was obtained; LOQs were between 1 and 25 µg Kg^-1, i.e., below the requested maximum levels (<200 mg Kg^-1). The method was applied to evaluate the LAs profile in different batches of raw L. albus L. samples, varying in size and across farming treatments.

Rapid and Simultaneous Quantification of Five Quinolizidine Alkaloids in Lupinus angustifolius L. and Its Processed Foods by UPLC-MS/MS

Quinolizidine alkaloids (QAs) are toxic secondary metabolites of Lupinus plants. This study reports the simultaneous quantification of five alkaloids from Lupinus angustifolius L. and its processed foods by ultraperformance liquid chromatography with electrospray ionization mass spectrometric detection. After optimizing the extraction conditions, the analytical method was validated for the QAs in lupin beans and in three major processed foods through detection and quantification limits, linearity, precision, and accuracy. The detection and quantification limits of the QAs were 0.5-1.7 and 1.5-5.7 mg kg^-1, respectively. The linearity was greater than 0.9992 and the precision was less than 3.1%. The recoveries of three different concentrations of each QA were 89.5-106.2%. For both raw lupin beans and processed foods, lupanine was the major QA, and 13-hydroxylupanine and angustifoline were detected in lower amounts. This method could be widely used for accurate risk assessment of QAs.