Conjugated Linolenic Acid (CLnA) vs Conjugated Linoleic Acid (CLA): A Comprehensive Review of Potential Advantages in Molecular Characteristics, Health Benefits, and Production Techniques.

Conjugated linoleic acid (CLA) has been extensively characterized due to its many biological activities and health benefits, but conjugated linolenic acid (CLnA) is still not well understood. However, CLnA has shown to be more effective than CLA as a potential functional food ingredient. Current research has not thoroughly investigated the differences and advantages between CLnA and CLA. This article compares CLnA and CLA based on molecular characteristics, including structural, chemical, and metabolic characteristics. Then, the in vivo research evidence of CLnA on various health benefits is comprehensively reviewed and compared with CLA in terms of effectiveness and mechanism. Furthermore, the potential of CLnA in production technology and product protection is analyzed. In general, CLnA and CLA have similar physicochemical properties of conjugated molecules and share many similarities in regulation effects and pathways of various health benefits as well as in the production methods. However, their specific properties, regulatory capabilities, and unique mechanisms are different. The superior potential of CLnA must be specified according to the practical application patterns of isomers. Future research should focus more on the advantageous characteristics of different isomers, especially the effectiveness and safety in clinical applications in order to truly exert the potential value of CLnA.

Interactions between liposoluble antioxidants: A critical review.

Liposoluble antioxidants, including natural and synthetic antioxidants, are substances to prevent lipid oxidation. From previous studies, the interaction of antioxidants may be the main reason for the poor correlation between liposoluble phytochemicals and antioxidant activity in oils. This review brings together information concerning the types and mechanisms of antioxidant interactions in terms of structure and active groups. A critical summary of the interactions between liposoluble antioxidants (synergistic effects, antagonistic effects and additive effects) is given. Factors including the diverse structure, combinations with different concentrations or proportions, and the reaction system which affect the interactions between liposoluble antioxidants, along with the opportunities and challenges in future study are also discussed. However, the influencing factors and mechanism still require further investigation. It is proposed that the studies in whole foods system and in vivo along with the related interaction mechanism should be considered in future.

Combinatorial metabolic engineering of Escherichia coli for de novo production of 2'-fucosyllactose.

2'-Fucosyllactose (2'-FL) is a kind of fucosylated lactose of human milk oligosaccharides (HMOs). In this work, Escherichia coli MG1655 was metabolically engineered to increase 2'-FL production. The 2'-FL titer was raised from 0.0118 to 0.8062 g/L by increasing three gene copies of α1,2-fucosyltransferase (FutC) and by deleting the lon, wcaJ, lacZ, and lacI genes in the competitive pathways. Additionally, the 2'-FL titer was raised to 2.9 g/L by fusing a TrxA tag at the N-terminus of FutC, and then to 3.4 g/L by deleting glutathione reductase (Gor). Finally, the 2'-FL reached 3.3 g/L in the final strain E. coli MG27 through the de novo pathway in shake flask, and reached 10.3 g/L in a 3-L fermentor.

Metabolic engineering for the synthesis of steviol glycosides: current status and future prospects.

With the pursuit of natural non-calorie sweeteners, steviol glycosides (SGs) have become one of the most popular natural sweeteners in the market. The SGs in Stevia are a mixture of SGs synthesized from steviol (a terpenoid). SGs are diterpenoids. Different SGs depend on the number and position of sugar groups on the core steviol backbone. This diversity comes from the processing of glycoside steviol by various glycosyltransferases. Due to the differences in glycosylation, each SG has unique sensory properties. At present, it is more complicated to extract high-quality SGs from plants, so the excavation of the metabolic pathways of engineered microorganisms to synthesize SGs has been extensively studied. Specifically, the expression of different glycosyltransferases in microbes is key to the synthesis of various SGs by engineered microorganisms. To trigger more researches on the functional characterization of the enzymes encoded by these genes, this review describes the latest research progresses of the related enzymes involved in SG biosynthesis and metabolic engineering.Key points• Outlines the research progress of key enzymes in the biosynthetic pathway of SGs• Factors affecting the catalytic capacity of stevia glucosyltransferase• Provide guidance for the efficient synthesis of SGs in microbial cell factories.

The relationship between flavor formation, lipid metabolism, and microorganisms in fermented fish products.

Traditional fermented fish products are favored due to their unique flavors. The fermentation process of fish is accompanied by the formation of flavor substances through a complex metabolic reaction of microorganisms, especially lipolysis and lipid oxidation. However, it is difficult to precisely control the reaction of microorganisms during the fermentation process in modern industrial production, and fermented fish products have lost their traditional characteristic flavors. The purpose of this review is to summarize the different kinds of fermented fish, core microorganisms in it, and flavor formation mechanisms, providing guidance for industrial cultural starters. Future research on the flavor formation mechanism is necessary to confirm the relationship between flavor formation, lipid metabolism, and microorganisms to ensure stable flavor and safety, and to elucidate the mechanism directly toward industrial application.

Production of proteins and commodity chemicals using engineered Bacillus subtilis platform strain.

Currently, increasing demand of biochemicals produced from renewable resources has motivated researchers to seek microbial production strategies instead of traditional chemical methods. As a microbial platform, Bacillus subtilis possesses many advantages including the generally recognized safe status, clear metabolic networks, short growth cycle, mature genetic editing methods and efficient protein secretion systems. Engineered B. subtilis strains are being increasingly used in laboratory research and in industry for the production of valuable proteins and other chemicals. In this review, we first describe the recent advances of bioinformatics strategies during the research and applications of B. subtilis. Secondly, the applications of B. subtilis in enzymes and recombinant proteins production are summarized. Further, the recent progress in employing metabolic engineering and synthetic biology strategies in B. subtilis platform strain to produce commodity chemicals is systematically introduced and compared. Finally, the major limitations for the further development of B. subtilis platform strain and possible future directions for its research are also discussed.

Current advance in biological production of short-chain organic acid.

As natural metabolites, organic acids have been widely applied in food, pharmaceutical, and bio-based materials industries. Particularly, the short-chain organic acids, including C2, C3, C4, C5, and C6 organic acids, are necessary intermediate metabolites in cells and are also alternatives to some commercial chemical products. As the necessary metabolites in cells, most major short-chain organic acids can be produced through microbial fermentation. Specifically, with the development of synthetic biology, metabolic engineering could endow cells with the ability to produce more short-chain organic acid products including propionic acid, pyruvate, lactic acid, 3-hydroxypropionic acid, malic acid, succinic acid, fumaric acid, butyric acid, itaconic acid, α-ketoglutaric acid, glutaric acid, citric acid, gluconic acid, muconic acid, adipic acid, xylonic acid, and so on. The recent advances in the biological production of short-chain organic acids, as well as the challenges and perspectives, are summarized in this review to promote the generation of microbial cell factories for the production of short-chain organic acids.Key points• Outlines the production strategy of short-chain organic acids• Provide guidance for efficient synthesis of short-chain organic acids• Impacts the necessary factor of acid resistance on the successful production of host cells.

Structure determination of conjugated linoleic and linolenic acids.

Conjugated linoleic and linolenic acids (CLA and CLnA) can be found in dairy, ruminant meat and oilseeds, these types of unsaturated fatty acids consist of various positional and geometrical isomers, and have demonstrated health-promoting potential for human beings. Extensive reviews have reported the physiological effects of CLA, CLnA, while little is known regarding their isomer-specific effects. However, the isomers are difficult to identify, owing to (i) the similar retention time in common chromatographic methods; and (ii) the isomers are highly sensitive to high temperature, pH changes, and oxidation. The uncertainties in molecular structure have hindered investigations on the physiological effects of CLA and CLnA. Therefore, this review presents a summary of the currently available technologies for the structural determination of CLA and CLnA, including the presence confirmation, double bond position determination, and the potential stereo-isomer determination. Special focus has been projected to the novel techniques for structure determination of CLA and CLnA. Some possible future directions are also proposed.

Biotransformation and chiral resolution of d,l-alanine into pyruvate and d-alanine with a whole-cell biocatalyst expressing l-amino acid deaminase.

Pyruvate is an important pharmaceutical intermediate and is widely used in food, nutraceuticals, and pharmaceuticals. However, high environmental pollution caused by chemical synthesis or complex separation process of microbial fermentation methods constrain the supply of pyruvate. Here, one-step pyruvate and d-alanine production from d,l-alanine by whole-cell biocatalysis was investigated. First, l-amino acid deaminase (Pm1) from Proteus mirabilis was expressed in Escherichia coli, resulting in pyruvate titer of 12.01 g/L. Then, N-terminal coding sequences were introduced to the 5'-end of the pm1 gene to enhance the expression of Pm1 and the pyruvate titer increased to 15.13 g/L. Next, product utilization by the biocatalyst was prevented by knocking out the pyruvate uptake transporters (cstA, btsT) and the pyruvate metabolic pathway genes pps, poxB, pflB, ldhA, and aceEF using CRISPR/Cas9, yielding 30.88 g/L pyruvate titer. Finally, by optimizing the reaction conditions, the pyruvate titer was further enhanced to 43.50 g/L in 8 H with a 79.99% l-alanine conversion rate; meanwhile, the resolution of d-alanine reached 84.0%. This work developed a whole-cell biocatalyst E. coli strain for high-yield, high-efficiency, and low-pollution pyruvate and d-alanine production, which has great potential for the commercial application in the future.

Production of conjugated fatty acids: A review of recent advances.

Conjugated fatty acids (CFAs) have received a deal of attention due to the increasing understanding of their beneficial physiological effects, especially the anti-cancer effects and metabolism-regulation activities. However, the production of CFAs is generally difficult. Several challenges are the low CFAs content in natural sources, the difficulty to chemically synthesize target CFA isomers in high purity, and the sensitive characteristics of CFAs. In this article, the current technologies to produce CFAs, including physical, chemical, and biotechnical approaches were summarized, with a focus on the conjugated linoleic acids (CLAs) and conjugated linolenic acids (CLNAs) which are the most common investigated CFAs. CFAs usually demonstrate stronger physiological effects than other non-conjugated fatty acids; however, they are more sensitive to heat and oxidation. Consequently, the quality control throughout the entire production process of CFAs is significant. Special attention was given to the micro- or nano-encapsulation which presented as an emerging technique to improve the bioavailability and storage stability of CFAs. The current applications of CFAs and the potential research directions were also discussed.

Effects of chemical refinement on the quality of coconut oil.

Refinement is usually used to remove undesired components to improve coconut oil quality. In the present study, crude coconut oil (CCO) was refined in four stages: conventional degumming, neutralization, bleaching, and deodorization. Physiochemical indices during the refinement were evaluated: peroxide value (PV), free fatty acid (FFA), fatty acid composition; fat composition; triacylglycerol profile, micronutrient (e.g., tocopherols and sterols) and contaminant (e.g., 3-monochloropropane-1,2-diol esters (3-MCPD esters), and glycidyl esters (GEs) levels. Compared to CCO, the quality of refined oil was improved by reducing PV and FFA levels. No significant changes in triacylglycerol compositions were found during refinement. However, unsaturated fatty acids like oleic and linoleic acids were decreased after refinement. Also, some micronutrients like tocopherol and sterol were decreased from 12.39 to 0.10 mg/kg and from 679.69 to 426.50 mg/kg, respectively. The undesired contaminants, i.e., 3-MCPD esters and GEs, increased markedly during refinement.

Antarctic Krill (Euphausia superba) Oil: A Comprehensive Review of Chemical Composition, Extraction Technologies, Health Benefits, and Current Applications.

Antarctic krill (Euphausia superba) oil has been receiving increasing attention due to its nutritional and functional potentials. However, its application as a novel food ingredient has not yet been fully explored. This review summarizes the chemical composition, extraction technologies, potential health benefits, and current applications of krill oil, with the aim of providing suggestions for its exploitation. Krill oil is a unique lipid consisting of diverse lipid classes and is characterized by a high concentration (39.29% to 80.69%) of phospholipids (PLs) associated with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). It also contains considerable amounts of bioactive minor components such as astaxanthin, sterols, tocopherols, vitamin A, flavonoids, and minerals. The current technologies used in krill oil production are solvent extraction, nonsolvent extraction, super/subcritical fluid extraction, and enzyme-assisted pretreatment extraction, which all greatly influence the yield and quality of the end-product. In addition, krill oil has been documented to have various health benefits, including anti-inflammatory effects, cardiovascular disease (CVD) prevention, women's health, neuroprotection, and anticancer activities. Although krill oil products used for dietary supplements have been commercially available, few studies have attempted to explore the underlying molecular mechanisms to elucidate how exactly the krill oil exerts different biological activities. Further studies should focus on this to improve the development of krill oil products for human consumption.

The relationship between lipid phytochemicals, obesity and its related chronic diseases.

The prevalence of obesity has received global attention in recent years, and lipid consumption has been considered as one of the direct reasons for obesity and related diseases. However, increasing evidence has indicated that edible vegetable oils could exert non-negligible physiological benefits in the daily diet, including suppression of appetite, lowering of blood lipids, prevention of adipocyte synthesis, and reduction of inflammatory response. Bioactive phytochemicals in lipids and oils, such as tocopherol, phenolic compounds, and phytosterol, play an important role in these effects according to in vitro and in vivo studies. For these reasons, the present review focusses on minor bioactive components in oil and their anti-obesity effects, aiming to provide a systematic overview of the relationships between these minor components and obesity and related diseases.

Process analysis and modeling of a single-step lutein extraction method for wet microalgae.

Lutein is a commercial carotenoid with potential health benefits. Microalgae are alternative sources for the lutein production in comparison to conventional approaches using marigold flowers. In this study, a process analysis of a single-step simultaneous extraction, saponification, and primary purification process for free lutein production from wet microalgae biomass was carried out. The feasibility of binary solvent mixtures for wet biomass extraction was successfully demonstrated, and the extraction kinetics of lutein from chloroplast in microalgae were first evaluated. The effects of types of organic solvent, solvent polarity, cell disruption method, and alkali and solvent usage on lutein yields were examined. A mathematical model based on Fick's second law of diffusion was applied to model the experimental data. The mass transfer coefficients were used to estimate the extraction rates. The extraction rate was found more significantly related with alkali ratio to solvent than to biomass. The best conditions for extraction efficiency were found to be pre-treatment with ultrasonication at 0.5 s working cycle per second, react 0.5 h in 0.27 L/g solvent to biomass ratio, and 1:3 ether/ethanol (v/v) with 1.25 g KOH/L. The entire process can be controlled within 1 h and yield over 8 mg/g lutein, which is more economical for scale-up.

Investigation of Chlorella vulgaris UTEX 265 Cultivation under Light and Low Temperature Stressed Conditions for Lutein Production in Flasks and the Coiled Tree Photo-Bioreactor (CTPBR).

Lutein has an increasing share in the pharmaceutical and nutraceutical market due to its benefits to eye health. Microalgae may be a potential source for lutein production while the expense limits the commercialization. In this study, a coiled tubular tree photobioreactor (CTPBR) design was investigated for cultivating the cold tolerant microalgae Chlorella vulgaris UTEX 265 under various conditions for lutein production. The influence and interaction of light irradiance strength, lighting cycle, and temperature on microalgae and lutein production efficiency at low temperature range were also studied in flasks via response surface method (RSM). The results demonstrated that 14 h day-light, 120 µmol photons m-2 s-1, and 10 °C was the optimal condition for algae growth and lutein production at low temperature experimental ranges. C. vulgaris UTEX 265 showed good potential to produce lutein in cold weather, and the optimum lutein production was contrary to the specific lutein content but corresponds to the trend of optimum growth. Additionally, fast growth (µ = 1.50 day-1) and good lutein recovery (11.98 mg g-1 day-1) in CTPBR were also achieved at the low irradiance stress condition and the low temperature photo-inhibition conditions.

Carotenoids from microalgae: A review of recent developments.

Carotenoids have been receiving increasing attention due to their potential health benefits. Microalgae are recognized as a natural source of carotenoids and other beneficial byproducts. However, the production of micro-algal carotenoids is not yet sufficiently cost-effective to compete with traditional chemical synthetic methods and other technologies such as extraction from plant based sources. This review presents the recent biotechnological developments in microalgal carotenoid production. The current technologies involved in their bioprocessing including cultivation, harvesting, extraction, and purification are discussed with a specific focus on downstream processing. The recent advances in chemical and biochemical synthesis of carotenoids are also reviewed for a better understanding of suitable and economically feasible biotechnological strategies. Some possible future directions are also proposed.