Chip-based nanoflow high performance liquid chromatography coupled to mass spectrometry for profiling of soybean flavonoids

Microfluidics potential for developing food-grade microstructures through emulsification processes and their application

The food sector continues to face challenges in developing techniques to increase the bioavailability of bioactive chemicals. Utilising microstructures capable of encapsulating diverse compounds has been proposed as a technological solution for their transport both in food and into the gastrointestinal tract. The present review discusses the primary elements that influence the emulsification process in microfluidic systems to form different microstructures for food applications. In microfluidic systems, reactions occur within small reaction channels (1-1000 μm), using small amounts of samples and reactants, ca. 102-103 times less than conventional assays. This geometry provides several advantages for emulsion and encapsulating structure production, like less waste generation, lower cost and gentle assays. Also, from a food application perspective, it allows the decrease in particle dispersion, resulting in a highly repeatable and efficient synthesis method that also improves the palatability of the food products into which the encapsulates are incorporated. However, it also entails some particular requirements. It is important to obtain a low Reynolds number (Re < approx. 250) for greater precision in droplet formation. Also, microfluidics requires fluid viscosity typically between 0.3 and 1400 mPa s at 20 °C. So, it is a challenge to find food-grade fluids that can operate at the micro-scale of these systems. Microfluidic systems can be used to synthesise different food-grade microstructures: microemulsions, solid lipid microparticles, microgels, or self-assembled structures like liposomes, niosomes, or polymersomes. Besides, microfluidics is particularly useful for accurately encapsulating bacterial cells to control their delivery and release on the action site. However, despite the significant advancement in these systems' development over the past several years, developing and implementing these systems on an industrial scale remains challenging for the food industry.

Late Elongated Hypocotyl Positively Regulates Salt Stress Tolerance in Medicago truncatula

Abiotic stress, such as drought, osmotic, and salinity stresses, seriously affects plant growth and crop production. Studying stress-resistant genes that enhance plant stress tolerance is an efficient way to facilitate the breeding of crop species with high stress tolerance. In this study, we reported that the core circadian clock component, the LATE ELONGATED HYPOCOTYL (LHY) orthologue MtLHY, plays a positive role in salt stress response in Medicago truncatula. The expression of MtLHY was induced by salt stress, and loss-of-function mutants of MtLHY were shown to be hypersensitive to salt treatment. However, overexpression of MtLHY improved salt stress tolerance through a higher accumulation of flavonoids. Consistently, exogenous flavonol application improved the salt stress tolerance in M. truncatula. Additionally, MtLHY was identified as a transcriptional activator of the flavonol synthase gene, MtFLS. Our findings revealed that MtLHY confers plant salt stress tolerance, at least by modulating the flavonoid biosynthesis pathway, which provides insight into salt stress tolerance that links the circadian clock with flavonoid biosynthesis.

Liquid chromatography-high resolution mass spectrometry for the analysis of phytochemicals in vegetal-derived food and beverages

The recent years witnessed a change in the perception of nutrition. Diet does not only provide nutrients to meet the metabolic requirements of the body, but it also constitutes an active way for the consumption of compounds beneficial for human health. Fruit and vegetables are an excellent source of such compounds, thus the growing interest in characterizing phytochemical sources, structures and activities. Given the interest for phytochemicals in food, the development of advanced and suitable analytical techniques for their identification is fundamental for the advancement of food research. In this review, the state of the art of phytochemical research in food plants is described, starting from sample preparation, throughout extract clean-up and compound separation techniques, to the final analysis, considering both qualitative and quantitative investigations. In this regard, from an analytical point of view, fruit and vegetable extracts are complex matrices, which greatly benefit from the use of modern hyphenated techniques, in particular from the combination of high performance liquid chromatography separation and high resolution mass spectrometry, powerful tools which are being increasingly used in the recent years. Therefore, selected applications to real samples are presented and discussed, in particular for the analysis of phenols, polyphenols and phenolic acids. Finally, some hot points are discussed, such as waste characterization for high value-compounds recovery and the untargeted metabolomics approach.

Functional conservation and divergence of GmCHLI genes in polyploid soybean

Polyploidy is prevalent in nature. As the fate of duplicated genes becomes more complicated when the encoded proteins function as oligomers, functional investigations into duplicated oligomer-encoding genes in polyploid genomes will facilitate our understanding of how traits are expressed. In this study, we identified GmCHLI1, a gene encoding the I subunit of magnesium (Mg)-chelatase, which functions in hexamers as responsible for the semi-dominant etiolation phenotype in soybean. Four GmCHLI copies derived from two polyploidy events were identified in the soybean genome. Further investigation with regard to expression patterns indicated that these four copies have diverged into two pairs; mutation in the other copy of the pair that includes GmCHLI1 also resulted in a chlorophyll-deficient phenotype. Protein interaction assays showed that these four GmCHLIs can interact with each other, but stronger interactions were found with mutated subunits. The results indicate that, in polyploidy, deficiency in each copy of duplicated oligomer-encoding genes could result in a mutant phenotype due to hetero-oligomer formation, which is different from the model of allelic dosage or functional redundancy. In addition, we interestingly found an increase in isoflavonoids in the heterozygous etiolated plants, which might be useful for improving soybean seed quality.

Picoelectrospray ionization mass spectrometry using narrow-bore chemically etched emitters

Electrospray ionization mass spectrometry (ESI-MS) at flow rates below ~10 nL/min has been only sporadically explored because of difficulty in reproducibly fabricating emitters that can operate at lower flow rates. Here we demonstrate narrow orifice chemically etched emitters for stable electrospray at flow rates as low as 400 pL/min. Depending on the analyte concentration, we observe two types of MS signal response as a function of flow rate. At low concentrations, an optimum flow rate is observed slightly above 1 nL/min, whereas the signal decreases monotonically with decreasing flow rates at higher concentrations. For example, consumption of 500 zmol of sample yielded signal-to-noise ratios ~10 for some peptides. In spite of lower MS signal, the ion utilization efficiency increases exponentially with decreasing flow rate in all cases. Significant variations in ionization efficiency were observed within this flow rate range for an equimolar mixture of peptide, indicating that ionization efficiency is an analyte-dependent characteristic for the present experimental conditions. Mass-limited samples benefit strongly from the use of low flow rates and avoiding unnecessary sample dilution. These findings have important implications for the analysis of trace biological samples.

Recent developments in microfluidic chip-based separation devices coupled to MS for bioanalysis

In recent years, the development of microfluidic chip separation devices coupled to MS has dramatically increased for high-throughput bioanalysis. In this review, advances in different types of microfluidic chip separation devices, such as electrophoresis- and LC-based microchips, as well as 2D design of microfluidic chip-based separation devices will be discussed. In addition, the utilization of chip-based separation devices coupled to MS for analyzing peptides/proteins, glycans, drug metabolites and biomarkers for various bioanalytical applications will be evaluated.