Direct Analysis of Underivatized Amino Acids in Plant Extracts by LC-MS/MS (Improved Method)

Targeted and untargeted metabolomics reveals deep analysis of drought stress responses in needles and roots of Pinus taeda seedlings

Drought stress is one of major environmental stresses affecting plant growth and yield. Although Pinus taeda trees are planted in rainy southern China, local drought sometime occurs and can last several months, further affecting their growth and resin production. In this study, P. taeda seedlings were treated with long-term drought (42 d), and then targeted and untargeted metabolomics analysis were carried out to evaluate drought tolerance of P. taeda. Targeted metabolomics analysis showed that levels of some sugars, phytohormones, and amino acids significantly increased in the roots and needles of water-stressed (WS) P. taeda seedlings, compared with well-watered (WW) pine seedlings. These metabolites included sucrose in pine roots, the phytohormones abscisic acid and sacylic acid in pine needles, the phytohormone gibberellin (GA4) and the two amino acids, glycine and asparagine, in WS pine roots. Compared with WW pine seedlings, the neurotransmitter acetylcholine significantly increased in needles of WS pine seedlings, but significantly reduced in their roots. The neurotransmitters L-glutamine and hydroxytyramine significantly increased in roots and needles of WS pine seedlings, respectively, compared with WW pine seedlings, but the neurotransmitter noradrenaline significantly reduced in needles of WS pine seedlings. Levels of some unsaturated fatty acids significantly reduced in roots or needles of WS pine seedlings, compared with WW pine seedlings, such as linoleic acid, oleic acid, myristelaidic acid, myristoleic acid in WS pine roots, and palmitelaidic acid, erucic acid, and alpha-linolenic acid in WS pine needles. However, three saturated fatty acids significantly increased in WS pine seedlings, i.e., dodecanoic acid in WS pine needles, tricosanoic acid and heptadecanoic acid in WS pine roots. Untargeted metabolomics analysis showed that levels of some metabolites increased in WS pine seedlings, especially sugars, long-chain lipids, flavonoids, and terpenoids. A few of specific metabolites increased greatly, such as androsin, piceatanol, and panaxatriol in roots and needles of WS pine seedlings. Comparing with WW pine seedlings, it was found that the most enriched pathways in WS pine needles included flavone and flavonol biosynthesis, ABC transporters, diterpenoid biosynthesis, plant hormone signal transduction, and flavonoid biosynthesis; in WS pine roots, the most enriched pathways included tryptophan metabolism, caffeine metabolism, sesquiterpenoid and triterpenoid biosynthesis, plant hormone signal transduction, biosynthesis of phenylalanine, tyrosine, and tryptophan. Under long-term drought stress, P. taeda seedlings showed their own metabolomics characteristics, and some new metabolites and biosynthesis pathways were found, providing a guideline for breeding drought-tolerant cultivars of P. taeda.

Nutrient transfer and antioxidant effect of adzuki bean before and after GABA enrichment

In order to study the nutritional changes of γ-aminobutyric acid (GABA) enrichment in adzuki bean germination, vacuum combined with monosodium glutamate (MSG) was used as the germination stress of adzuki bean. The nutrient transfer before and after GABA enrichment in adzuki bean germination under vacuum combined with MSG stress were studied by means of chromatography and scanning electron microscope (SEM). The antioxidant activity and hypoglycemic effect of different solvent extracts before and after germination of adzuki bean were evaluated by experiments in vitro. The results showed that the nutritional characteristics of adzuki bean rich in GABA changed significantly (P < 0.05), the total fatty acids decreased significantly (P < 0.05), and the 21 amino acids detected increased significantly. After germination, the starch granules of adzuki bean became smaller and the surface was rough Germination stress significantly increased the antioxidant and hypoglycemic activities of the extracts from different solvents (P < 0.05), and the water extracts had the best effect on DPPH and ⋅OH radical scavenging rates of 88.52 and 83.56%, respectively. The results indicated that the germinated adzuki bean rich in GABA was more nutritious than the raw adzuki bean and had good antioxidant activity. It hoped to provide technical reference for rich food containing GABA.

Underivatized Amino Acid Chromatographic Separation: Optimized Conditions for HPLC-UV Simultaneous Quantification of Isoleucine, Leucine, Lysine, Threonine, Histidine, Valine, Methionine, Phenylalanine, Tryptophan, and Tyrosine in Dietary Supplements

Amino acids (AAs) are considered as the building blocks of life. Unlike nonessential AAs, the human body cannot synthesize essential AAs and should be supplied in food or dietary supplements. The aim of the work is simultaneous HPLC-UV determination of 10 structurally related AAs without pre- or postderivatization in powdered dietary supplements (PDSs). This was challenging, especially because PDS has no standardized procedures for its quality control. HPLC-UV chromatograms of the 10 AAs were recorded using a gradient elution of the mobile phase on a CLC-C18 column at 225 nm. The elution started with 100% of phosphate buffer (pH 7.4, 10 mM) for 10 min; then, the concentration of acetonitrile increased linearly to reach 50% for another 15 min at room temperature. Good separation was achieved within a 25 min run time without pre- or postderivatization. The method was carefully validated according to the ICH guidelines over the linearity range of 100-200, 50-200, 20-150, 50-400, 20-250, 75-175, 50-250, 50-250, 50-300, and 5-100 μg/mL for l-lysine, l-threonine, l-histidine, l-valine, l-methionine, l-isoleucine, l-leucine, l-tyrosine, l-phenylalanine, and l-tryptophan, respectively, with mean recoveries ranges between 98.91 and 100.77. The method was found to be precise, and the relative standard deviation (RSD) was found to be between 0.28 and 1.92 with recoveries between 97.91 and 101.11. The method was found to be robust that resists deliberate changes in pH, flow rate, and mobile-phase percentages. It was successfully applied for the analysis of PDSs. The proposed method could be very useful for the quality control of the 10 structurally related AAs during their synthesis and for testing raw materials and pharmaceutical preparations.

Physico-Chemical Characteristics and Amino Acid Content Evaluation of Citric Acid by-Product Produced by Microbial Fermentation as a Potential Use in Animal Feed

The production of citric acid produces 70% waste product or by-product. This by-product is produced by microbial fermentation which could be used as an alternative raw material for animal feed because it still contains citric acid, which could help to reduce pathogenic bacteria. The objective of this study is to evaluate the physical and chemical value of citric acid by-product from rice (CABR) to compare the properties with those of rice bran and broken rice and to determine its potential as an alternative energy source in animal feed. The chemical composition of CABR was calculated using proximate analysis. The color of CABR was darker, and the bulk density value was 549.65 (g/L) (p < 0.05). With free flow, the angle of repose was 40°, and the particle size had less polygonal starch granules. CABR had a low pH of 4.77 and contained 19.80% crude protein, 11.97% crude fiber, and 4005.72 kcal/kg of energy. CABR had a higher crude protein value than broken rice and rice bran and a higher gross energy value than broken rice but less than rice bran. It also had a higher crude fiber value (p > 0.05). The results suggest that CABR could be utilized as an energy and protein source for animal feed formulations.

Need for speed: evaluation of dilute and shoot-mass spectrometry for accelerated metabolic phenotyping in bioprocess development

With the utilization of small-scale and highly parallelized cultivation platforms embedded in laboratory robotics, microbial phenotyping and bioprocess development have been substantially accelerated, thus generating a bottleneck in bioanalytical bioprocess sample analytics. While microscale cultivation platforms allow the monitoring of typical process parameters, only limited information about product and by-product formation is provided without comprehensive analytics. The use of liquid chromatography mass spectrometry can provide such a comprehensive and quantitative insight, but is often limited by analysis runtime and throughput. In this study, we developed and evaluated six methods for amino acid quantification based on two strong cation exchanger columns and a dilute and shoot approach in hyphenation with either a triple-quadrupole or a quadrupole time-of-flight mass spectrometer. Isotope dilution mass spectrometry with 13C15N labeled amino acids was used to correct for matrix effects. The versatility of the methods for metabolite profiling studies of microbial cultivation supernatants is confirmed by a detailed method validation study. The methods using chromatography columns showed a linear range of approx. 4 orders of magnitude, sufficient response factors, and low quantification limits (7-443 nM) for single analytes. Overall, relative standard deviation was comparable for all analytes, with < 8% and < 11% for unbuffered and buffered media, respectively. The dilute and shoot methods with an analysis time of 1 min provided similar performance but showed a factor of up to 35 times higher throughput. The performance and applicability of the dilute and shoot method are demonstrated using a library of Corynebacterium glutamicum strains producing L-histidine, obtained from random mutagenesis, which were cultivated in a microscale cultivation platform.

Broad targeted analysis of neurochemicals in rat serum using liquid chromatography tandem mass spectrometry with chemical derivatization

In this study, an efficient and sensitive assay for the detection of 42 polar neurochemicals, including neurotransmitters, amino acids, and biogenic amines, was established by combining reversed-phase liquid chromatography tandem mass spectrometry with chemical derivatization. An optimally designed benzoyl chloride derivatization was easily conducted in a one-pot reaction and stable neurochemical derivatives were obtained under mild conditions within 5 min (except for acetylcholine and melatonin). Derivatization also enabled the introduction of heavy labeling of the analytes through the use of labeled derivatization agents. Chromatography separation was performed on an HSS T3 column within 15 min by gradient elution. Multiple reaction monitoring acquisition mode enabled quantitation of neurochemicals with limits of detection of 0.05 to 11.63 nM and lower limits of quantitation of 0.09 to 46.50 nM in rat serum. The assay was well validated in terms of linearity and extraction recovery. Furthermore, the instrumental precision, specificity, matrix effect, accuracy, precision, stability, dilution effect, and carry-over effect were also validated. Finally, the overall efficacy of the assay was experimentally tested using serum from six Sprague-Dawley rats. The results demonstrated that the developed method is effective for broad targeted analysis of 42 neurochemicals in serum.