Tree bark is a highly specialized array of tissues that plays important roles in plant protection and development. Bark tissues develop from two lateral meristems; the phellogen (cork cambium) ...produces the outermost stem–environment barrier called the periderm, while the vascular cambium contributes with phloem tissues. Although bark is diverse in terms of tissues, functions and species, it remains understudied at higher resolution.
We dissected the stem of silver birch (Betula pendula) into eight major tissue types, and characterized these by a combined transcriptomics and metabolomics approach. We further analyzed the varying bark types within the Betulaceae family.
The two meristems had a distinct contribution to the stem transcriptomic landscape. Furthermore, inter- and intraspecies analyses illustrated the unique molecular profile of the phellem. We identified multiple tissue-specific metabolic pathways, such as the mevalonate/betulin biosynthesis pathway, that displayed differential evolution within the Betulaceae. A detailed analysis of suberin and betulin biosynthesis pathways identified a set of underlying regulators and highlighted the important role of local, small-scale gene duplication events in the evolution of metabolic pathways.
This work reveals the transcriptome and metabolic diversity among bark tissues and provides insights to its development and evolution, as well as its biotechnological applications.
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Low-frequency Raman (LFR) spectroscopy probes vibrational modes related to long-range order (i.e., crystallinity) that can provide unique information on the solid-state/structural ...characteristics among other properties. Furthermore, the recent advancements in instrumentation (most notably, narrow wavelength band filters) and data analysis has allowed to overcome some of the previous limitations of this technique. In fact, LFR spectroscopy has now enjoyed a surge in popularity with applications found in many research areas. This mini-review article provides a comprehensive summary of established and exciting new LFR applications for pharmaceutical analysis. Aspects of the underlying theory, instrumentation and data analysis (including application of chemometric and computational techniques) are also discussed in detail.
Low‐wavenumber Raman spectroscopy is demonstrated for its potential to analyse mineralization abnormalities in human teeth. Four different dental samples were analysed in this study, denoted as ...healthy control, mild hypomineralization, enamel caries, and AI (severely degraded due to Amelogenesis imperfecta). All specimens were imaged using principal component analysis. The spectra from low‐ wavenumber and midwavenumber regions were simultaneously collected allowing for direct comparison between the two regions. This approach provided a method to characterize structural and chemical variation within samples. Structurally different hydroxyapatite was found to be present in the surface and bulk of the enamel. The thin outer layer of the enamel contained the most structurally ordered mineral. The obtained Raman images enabled characterization and comparison of lesion domains as well as relative hydroxyapatite abundances across all dental samples.
A variety of human tooth samples were mapped using Raman spectroscopy. Data analysis was carried out using principal component analysis. This was complimented by characterization of the main hydroxyapatite Raman band ‐
ν1PO43−. The obtained structural information from the low‐frequency range was directly compared and correlated to spectral features in the more commonly used midfrequency region.
Raman, near‐infrared, and mid‐infrared (MIR) spectroscopic techniques were evaluated for the potential to non‐destructively quantify bioactive compounds in commercially grown New Zealand plums. These ...spectroscopic data sets were qualitatively assessed using principal component analysis where groupings based on the cultivar and growing location were observed. The different techniques separated based on different compositional differences. Four cultivars grown in two different growing locations were assessed for total anthocyanin content, vitamin C content, phenolic content, and total antioxidant capacity. These parameters (measured using traditional methods) were correlated to the spectroscopic data using partial least squares regression and support vector machine (SVM) classification where appropriate. Raman and MIR showed the most promise for quantifying vitamin C content, and Raman showed the most promise for quantifying anthocyanin content. Some parameters were better suited to classification, and in this regard, Raman spectroscopy provided a robust method for classifying growing location and MIR for cultivar classification.
Raman, near‐infrared, and mid‐infrared spectroscopic techniques were evaluated for the potential to non‐destructively quantify bioactive compounds such as vitamin C and anthocyanin in commercially grown New Zealand plums. In addition, these spectroscopic methods were shown to classify the samples spectra based on cultivar, growing location, and high/low anthocyanin content.
This study uses Raman and IR spectroscopic methods for the detection of adulterants in marine oils. These techniques are used individually and as low-level fused spectroscopic data sets. We used cod ...liver oil (CLO) and salmon oil (SO) as the valuable marine oils mixed with common adulterants, such as palm oil (PO), omega-3 concentrates in ethyl ester form (O3C), and generic fish oil (FO). We showed that support vector machines (SVM) can classify the adulterant present in both CLO and SO samples. Furthermore, partial least squares regression (PLSR) may be used to quantify the adulterants present. For example, PO and O3C adulterated samples could be detected with a RMSEP value less than 4%. However, the FO adulterant was more difficult to quantify because of its compositional similarity to CLO and SO. In general, data fusion improved the RMSEP for PO and O3C detection. This shows that Raman and IR spectroscopy can be used in concert to provide a useful analytical test for common adulterants in CLO and SO.
The early detection of fruit disorders is crucial to maintaining a consistent, high‐quality kiwifruit product. Chilling injury is a physiological disorder found in kiwifruit that can be challenging ...to identify until it reaches a severe stage or the fruit is cut and opened. Considering this, Raman spectroscopy combined with chemometrics was investigated for sound and chill‐damaged ‘Zesy002’ kiwifruit. We carried out spectral analysis on fruit harvested in 2018 and 2019. Damaged and sound fruit samples were separated based on spectral signatures from phenyl propanoids and sugars. Furthermore, the 2018 fruit sample set was used to construct, validate, and test models using support vector machine, principal component analysis–linear discriminant analysis, and partial least squares–discriminant analysis. Additionally, the robustness of the model was assessed using the 2019 fruit sample set considering test set accuracy, sensitivity, and specificity. Support vector machine models were developed and resulted in a 93% accuracy, 85% sensitivity, and 100% specificity to differentiate the test set fruit (2018 season). Principal component analysis–linear discriminant analysis models and partial least squares–discriminant analysis model built with the same data set gave >83% and 93% test accuracy, respectively. Models showed robustness with samples from the 2019 season. This study provides insights into the potential of using Raman spectroscopy for identifying chilling injury in kiwifruit.
We applied Raman spectroscopy to distinguish chill‐damaged kiwifruit from normal fruit combined with principal component analysis and classification techniques such as support vector machines, principal component analysis–discriminant analysis, and partial least squares–discriminant analysis. Models showed robustness with consecutive seasonal data and SVM classification (>90%) demonstrated a high potential of using it as a tool for discriminating among fruit for quality.
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•Low- and mid-frequency Raman spectra were compared for quantitative analysis.•Ternary mixtures of piroxicam solid-state forms β, α2 and monohydrate were used.•The crystal forms could ...easily be distinguished based on low-frequency spectra.•The low-frequency spectral region was better for quantitative analysis.
This study considers the potential of low-frequency (terahertz) Raman spectroscopy in the quantitative analysis of ternary mixtures of solid-state forms. Direct comparison between low-frequency and mid-frequency spectral regions for quantitative analysis of crystal form mixtures, without confounding sampling and instrumental variations, is reported for the first time. Piroxicam was used as a model drug, and the low-frequency spectra of piroxicam forms β, α2 and monohydrate are presented for the first time. These forms show clear spectral differences in both the low- and mid-frequency regions. Both spectral regions provided quantitative models suitable for predicting the mixture compositions using partial least squares regression (PLSR), but the low-frequency data gave better models, based on lower errors of prediction (2.7, 3.1 and 3.2% root-mean-square errors of prediction RMSEP values for the β, α2 and monohydrate forms, respectively) than the mid-frequency data (6.3, 5.4 and 4.8%, for the β, α2 and monohydrate forms, respectively). The better performance of low-frequency Raman analysis was attributed to larger spectral differences between the solid-state forms, combined with a higher signal-to-noise ratio.
Raman and infrared spectroscopy, used as individual and low-level fused datasets, were evaluated to identify and quantify the presence of adulterants (palm oil, PO; ω-3 concentrates in ethyl ester, ...O3C and fish oil, FO) in krill oil. These datasets were qualitatively analysed with principal component analysis (PCA) and classified as adulterated or unadulterated using support vector machines (SVM). Using partial least squares regression (PLSR), it was possible to identify and quantify the adulterant present in the KO mixture. Raman spectroscopy performed better (r
= 0.98; RMSEP = 2.3%) than IR spectroscopy (r
= 0.91; RMSEP = 4.2%) for quantification of O3C in KO. A data fusion approach further improved the analysis with model performance for quantification of PO (r
= 0.98; RMSEP = 2.7%) and FO (r
= 0.76; RMSEP = 9.1%). This study demonstrates the potential use of Raman and IR spectroscopy to quantify adulterants present in KO.
A series of melt-quenched disks of amorphous celecoxib were obtained using two different cooling rates (>100 °C/min and ∼25–30 °C/min) and subjected to different compression pressures (125, 250, and ...500 MPa) and dwell times (0, 30, and 60 s). The kinetics of crystallization for these differently prepared melt-quenched disks were probed using a number of methods. Low-frequency Raman spectroscopy was used to monitor isothermal crystallization kinetics, whereas dynamic differential scanning calorimetry served as a complimentary technique to identify changes in form. Although both compression parameters destabilized the amorphous celecoxib, the dwell time was found to have a more critical overall effect. Additionally, the sample history was affirmed to be a factor for limiting the magnitude of compression-induced destabilization.
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