The application of compound-specific isotope analysis of fatty acids for traceability of sea cucumber (Apostichopus japonicus) in the coastal areas of China

Effects of HCO3- and CO2 conversion rates on carbon assimilation strategies in marine microalgae: Implication by stable carbon isotope analysis of fatty acids

Marine microalgae are an essential component of marine plankton and critical primary producers, playing a vital role in marine ecosystems. The seawater carbonate system is a dynamic equilibrium system, and changes in any component can alter the carbonate balance. In CO2-concentrating mechanisms (CCMs), carbonic anhydrase (CA) regulates CO2 concentration by catalyzing the interconversion between CO2 and HCO3-. Therefore, limiting the activity of extracellular carbonic anhydrase (exCA) alters the rate at which carbonate equilibrium is reached and further affects the carbon assimilation process in microalgae. In this study, two different microalgae, Phaeodactylum tricornutum and Nannochloropsis oceanica, were selected to investigate the effects of changes in the carbonate system on photosynthetic carbon assimilation in microalgae by inhibiting exCA activity with acetazolamide (AZ). Inhibition of exCA activity reduces specific growth rates and photosynthetic efficiency of microalgae. The total alkalinity, HCO3- concentration, and CO2 concentration of the cultures increased with the decrease of pH, but the changes of the ribulose 1,5- bisphosphate carboxylase/oxygenase (Rubisco) activities of the two microalgae were different. In addition, the two microalgae possessed different lipid and carbohydrate synthesis strategies, but both restricted triacylglycerol (TAG) synthesis. Meanwhile, the microalgal cells had to utilize more 13CO2 when HCO3- and CO2 conversion rates were limited and restricted. This led to the continuous accumulation of 13C in fatty acids and the elevation of δ13CFAs. In conclusion, our study provides a new perspective on the role of microalgae in correlating carbonate changes with photosynthetic carbon assimilation strategies under mechanistic constraints on inorganic carbon utilization.

A review of recent compound-specific isotope analysis studies applied to food authentication

Compound-specific stable isotope analysis (CSIA) of food products is a relatively new and novel technique used to authenticate food and detect adulteration. This paper provides a review of recent on-line and off-line CSIA applications of plant and animal origin foods, essential oils and plant extracts. Different food discrimination techniques, applications, scope, and recent studies are discussed. CSIA δ13C values are widely used to verify geographical origin, organic production, and adulteration. The δ15N values of individual amino acids and nitrate fertilizers have proven effective to authenticate organic foods, while δ2H and δ18O values are useful to link food products with local precipitation for geographical origin verification. Most CSIA techniques focus on fatty acids, amino acids, monosaccharides, disaccharides, organic acids, and volatile compounds enabling more selective and detailed origin and authentication information than bulk isotope analyses.. In conclusion, CSIA has a stronger analytical advantage for the authentication of food compared to bulk stable isotope analysis, especially for honey, beverages, essential oils, and processed foods.

The exogenous autophagy inducement alleviated the sea cucumber (Stichopus japonicus) autolysis with exposure to stress stimuli of ultraviolet light

BACKGROUND

Autolysis is the most important restrictive factor for the live sea cucumber trade and commercial transportation. Thus, it is essential to investigate the mechanism of autolysis activation or deactivation in the sea cucumber. In this study, monodansylcadaverine staining and Western blotting experiment methods indicated the implication of autophagy in the ultraviolet (UV) exposed sea cucumbers. The health condition was observed after the sea cucumbers (Stichopus japonicus) were gastric perfusion with autophagic inhibitor (3-methyladenine) or inducer (rapamycin) and exposure to UV light for half an hour.

RESULTS

The protein expressions of LC3-II and Atg5 appeared immediately after UV exposure and then vanished 1 h later. The autophagosome formation in coelomic fluid cells confirmed the autophagy appearance pattern of LC3-II and Atg5. The sea cucumber individuals maintained the health condition during the entire event of autophagy. The autophagic inhibitor along with UV exposure contributed to sea cucumber's swollen intestinal tissues, but the autophagic inducer functioned to alleviate and neutralize the UV effect.

CONCLUSIONS

The autophagy procedure analysis demonstrated that autophagy plays a role to maintain the health condition of sea cucumber during autolysis inducement. The autolysis of sea cucumber can be alleviated or postponed by the exogenous autophagy inducer and this finding would benefit the live sea cucumber transportation. © 2021 Society of Chemical Industry.

Improved accuracy of geographical origin identification of shiitake grown in sawdust medium: A compound-specific isotope model-based pilot study

In countries like South Korea and the USA, origin labeling of shiitake grown using imported Chinese-inoculated medium is an issue. Therefore, we evaluated the use of compound-specific isotope analysis (CSIA) for the accurate identification of the geographical origin of shiitake (Korean, Chinese-inoculated medium, and Chinese); Chinese-inoculated medium shiitake were cultivated in Korea using inoculated sawdust medium from China. The CSIA-discriminant model showed an overall accuracy of 100% in the geographical classification of the original set and 96.4% for the cross-validated set. Glutamate and aspartate δ¹⁵N values were the most important variables for differentiating shiitake based on their origins. Compared to that observed upon using the bulk stable isotope analysis, the CSIA model was associated with significantly improved predictability of origin identification. Our findings elucidate the importance of isotope signatures in developing a reliable origin labeling method for shiitake cultured on the sawdust medium for the global market.

Validation and analysis of the geographical origin of Angelica sinensis (Oliv.) Diels using multi-element and stable isotopes

Background

Place of origin is an important factor when determining the quality and authenticity of Angelica sinensis for medicinal use. It is important to trace the origin and confirm the regional characteristics of medicinal products for sustainable industrial development. Effectively tracing and confirming the material’s origin may be accomplished by detecting stable isotopes and mineral elements.

Methods

We studied 25 A. sinensis samples collected from three main producing areas (Linxia, Gannan, and Dingxi) in southeastern Gansu Province, China, to better identify its origin. We used inductively coupled plasma mass spectrometry (ICP-MS) and stable isotope ratio mass spectrometry (IRMS) to determine eight mineral elements (K, Mg, Ca, Zn, Cu, Mn, Cr, Al) and three stable isotopes (δ¹³C, δ¹⁵N, δ¹⁸O). Principal component analysis (PCA), partial least square discriminant analysis (PLS-DA) and linear discriminant analysis (LDA) were used to verify the validity of its geographical origin.

Results

K, Ca/Al, δ¹³C, δ¹⁵N and δ¹⁸O are important elements to distinguish A. sinensis sampled from Linxia, Gannan and Dingxi. We used an unsupervised PCA model to determine the dimensionality reduction of mineral elements and stable isotopes, which could distinguish the A. sinensis from Linxia. However, it could not easily distinguish A. sinensis sampled from Gannan and Dingxi. The supervised PLS-DA and LDA models could effectively distinguish samples taken from all three regions and perform cross-validation. The cross-validation accuracy of PLS-DA using mineral elements and stable isotopes was 84%, which was higher than LDA using mineral elements and stable isotopes.

Conclusions

The PLS-DA and LDA models provide a theoretical basis for tracing the origin of A. sinensis in three regions (Linxia, Gannan and Dingxi). This is significant for protecting consumers’ health, rights and interests.

The influence of carbon limitation on growth of Heterosigma akashiwo: A case study in fatty acids composition

Heterosigma akashiwo is an algal blooms species, and thus selected as the target microalgae in this work. This study attempted to investigate the influence of carbon limitation on the growth of H. akashiwo. Experiments were carried out in CO₂-unlimited and CO₂-limited systems (both include three nutritional groups). The stable isotope signatures and compound-specific stable three nutritional groups carbon isotopic composition of fatty acids were measured. Here we hypothesized that the carbon limitation could lead to the enriched of stable isotope ratios in the H. akashiwo. The results showed that carbon limitation made δ¹³C and δ¹³C_FAs values more and more enriched in H. akashiwo. δ¹³C values were enriched in normal group of H. akashiwo within CO₂-limited. δ¹⁵N values were enriched in nitrogen deficiency of H. akashiwo within both CO₂-unlimited and CO₂-limited. Furthermore, compared with the exponential phase, the enriched in δ¹³C was detected during the stationary phase in H. akashiwo within CO₂-limited. A total of 8 major FAs were detected in H. akashiwo. Within CO₂-unlimited, nitrogen deficiency promoted the synthesis of 4 FAs (14:1n-5c, 16:0, 18:0 and 18:3n-6c) in exponential phase. Within CO₂-limited, nitrogen deficiency promoted the synthesis of FAs 14:0, 16:0 and 18:3n-3c, while phosphorus deficiency promoted the synthesis of all 6 FAs in exponential phase. δ¹³C_FAs of H. akashiwo within CO₂-limited showed the valley values and were significantly greater than those within CO₂-unlimited. Furthermore, δ¹³C_FAs of stationary phase were greater than those of exponential phase. δ¹³C_14:1n-5c in nitrogen deficiency were the highest of the three nutrient groups within CO₂-unlimited. This may point out that δ¹³C_FAs could become an indicator of marine phytoplankton blooms. Overall, the present study may provide a novel approach to investigate the physiology and lipid metabolism of H. akashiwo blooms by using stable isotope ratios coupled with FAs profiles.

Using stable isotope signatures to delineate the geographic point-of-origin of Keemun black tea

BACKGROUND

Confirmation of food labeling that claims production in a small geographic region is critical to traceability, quality control and brand protection. In the current study, isotope ratio mass spectrometry (IRMS) was used to generate profiles of δ¹³ C and δ¹⁵ N to determine if the stable isotope signatures of Keemun black tea differ within the three counties that claim production. Other factors (cultivar type, leaf maturity and manufacturing process) were considered for their potential effects.

RESULTS

Both cultivar type and leaf maturity have remarkable impact on the δ¹⁵ N values of tea leaves, and that the cultivar influenced the δ¹³ C values. Keemun black tea from Qimen county could be easily discriminated from samples from Dongzhi and Guichi counties based on δ¹⁵ N signatures. The k-NN model was cross-validated with an accuracy of 91.6%. Environmental factors and/or genotype seem to be the major reasons for δ¹⁵ N differences in Keemun black tea from the selected regions.

CONCLUSION

This article provides a potential effective method to delineate the geographic point-of-origin of Keemun black tea based on δ¹⁵ N signatures. © 2018 Society of Chemical Industry.