Enzymatic hydrolysis of steryl ferulates and steryl glycosides

Expression of a Recombinant Cholesterol Esterase from Mustela putorius furo in Pichia pastoris and Its Applicability for γ-Oryzanol Hydrolysis

Ferulic acid (FA) exhibits antioxidant and anti-inflammatory properties, making it valuable for numerous industrial applications. Traditionally, FA is produced by the alkaline hydrolysis of γ-oryzanol, which is typically associated with wastewater generation. Recently, an increasing demand of natural FA necessitates its green production via enzymatic hydrolysis of γ-oryzanol, a mixture comprising triterpene alcohol ferulates and phytosteryl ferulates. Thus far, γ-oryzanol can be hydrolyzed by only four commercial cholesterol esterases with low yields. Herein, we report a recombinant cholesterol esterase from Mustela putorius furo (MPFCE) for the enzymatic hydrolysis of γ-oryzanol. The enzyme yielded 25.5% FA, which is the highest reported through enzymatic means thus far. The hydrolysis profile revealed that the enhanced yield primarily resulted from the near-complete hydrolysis of phytosteryl ferulates, together with slight hydrolysis of triterpene alcohol ferulates. MPFCE serves as a potential candidate for the enzymatic production of FA through targeted hydrolysis of γ-oryzanol.

Characterization and determination of free phytosterols and phytosterol conjugates: The potential phytochemicals to classify different rice bran oil and rice bran

Phytosterols are important beneficial compounds found in rice bran (RB) and rice bran oil (RBO). Although relationships have been confirmed between the forms of phytosterols and their bioactivities, the analysis of different forms of phytosterols in RB and RBO has been lacking. In this study, high temperature gas chromatography-mass spectrometry (HTGC-MS) was combined with the single standard to determine multi-components (SSDMC) method to determine free sterols (FSs) and steryl glycosides (SGs) in RB and RBO. High-performance liquid chromatography (HPLC) was used to determine steryl ferulates (SFs). There was clear variation in the composition of FS, SF and SG, indicating that different forms of phytosterols can discriminate between different RB and RBO. The developed method may be also useful for the detection of other compounds of interest in oils, oil seeds or cereals.

Synthesis of Steryl Hydroxycinnamates to Enhance Antioxidant Activity of Rapeseed Oil and Emulsions

In recent years, steryl esters have found potential applications in food, pharmaceutical and cosmetic industries. Therefore, three hydroxycinnamate steryl esters (HSEs): β-sitosteryl sinapate (β-SSA), β-sitosteryl caffeate (β-SCA), and β-sitosteryl ferulate (β-SFA) were synthesized by chemical approach and their antioxidant activity (AA) were analyzed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) assays. The values of inhibitory concentration (IC₅₀) of each ester needed to inhibit 50% of the DPPH radical (IC_50(DPPH) = 238.9, 78.3, 290.0 µmol/L for β-SSA, β-SCA, and β-SFA, respectively) and ABTS radical cation (IC_50(ABTS) = 174.6, 106.7, 206.0 µmol/L for β-SSA, β-SCA, and β-SFA, respectively) were estimated and compared with antioxidant potential of phenolic acids. Moreover, the effect of HSEs addition in the concentrations range between 0.01% and 0.5% on the AA of refined rapeseed oil, mayonnaise and margarine was evaluated. Chemical structures of the synthesized HSEs and their concentrations strongly affect the AA of fat products. Oil and emulsions supplemented with higher concentrations of HSEs had significantly higher AA than control samples. Unfortunately, lower concentrations of HSEs (0.01% and 0.02%) did not increase the AA of fat products. However, steryl phenolates added in higher amounts can be considered as potential antioxidants delaying the oxidation processes of studied fats.

The production, properties, and applications of thermostable steryl glucosidases

Extremophilic microorganisms are a rich source of enzymes, the enzymes which can serve as industrial catalysts that can withstand harsh processing conditions. An example is thermostable β-glucosidases that are addressing a challenging problem in the biodiesel industry: removing steryl glucosides (SGs) from biodiesel. Steryl glucosidases (SGases) must be tolerant to heat and solvents in order to function efficiently in biodiesel. The amphipathic nature of SGs also requires enzymes with an affinity for water/solvent interfaces in order to achieve efficient hydrolysis. Additionally, the development of an enzymatic process involving a commodity such as soybean biodiesel must be cost-effective, necessitating an efficient manufacturing process for SGases. This review summarizes the identification of microbial SGases and their applications, discusses biodiesel refining processes and the development of analytical methods for identifying and quantifying SGs in foods and biodiesel, and considers technologies for strain engineering and process optimization for the heterologous production of a SGase from Thermococcus litoralis. All of these technologies might be used for the production of other thermostable enzymes. Structural features of SGases and the feasibility of protein engineering for novel applications are explored.

Enzymatic hydrolysis of steryl glucosides, major contaminants of vegetable oil-derived biodiesel

Biodiesels are mostly produced from lipid transesterification of vegetable oils, including those from soybean, jatropha, palm, rapeseed, sunflower, and others. Unfortunately, transesterification of oil produces various unwanted side products, including steryl glucosides (SG), which precipitate and need to be removed to avoid clogging of filters and engine failures. So far, efficient and cost-effective methods to remove SGs from biodiesel are not available. Here we describe for the first time the identification, characterization and heterologous production of an enzyme capable of hydrolyzing SGs. A synthetic codon-optimized version of the lacS gene from Sulfolobus solfataricus was efficiently expressed and purified from Escherichia coli, and used to treat soybean derived biodiesel containing 100 ppm of SGs. After optimizing different variables, we found that at pH 5.5 and 87 °C, and in the presence of 0.9 % of the emulsifier polyglycerol polyricinoleate, 81 % of the total amount of SGs present in biodiesel were hydrolyzed by the enzyme. This remarkable reduction in SGs suggests a path for the removal of these contaminants from biodiesel on industrial scale using an environmentally friendly enzymatic process.

Quantification of vitamin D3 and its hydroxylated metabolites in waxy leaf nightshade (Solanum glaucophyllum Desf.), tomato (Solanum lycopersicum L.) and bell pepper (Capsicum annuum L.)

Changes in vitamin D(3) and its metabolites were investigated following UVB- and heat-treatment in the leaves of Solanum glaucophyllum Desf., Solanum lycopersicum L. and Capsicum annuum L. The analytical method used was a sensitive and selective liquid chromatography electrospray ionisation tandem mass spectrometry (LC-ESI-MS/MS) method including Diels-Alder derivatisation. Vitamin D(3) and 25-hydroxy vitamin D(3) were found in the leaves of all plants after UVB-treatment. S. glaucophyllum had the highest content, 200 ng vitamin D(3)/g dry weight and 31 ng 25-hydroxy vitamin D(3)/g dry weight, and was the only plant that also contained 1,25 dihydroxy vitamin D(3) in both free (32 ng/g dry weight) and glycosylated form (17 ng/g dry weight).

Improved bioavailability of dietary phenolic acids in whole grain barley and oat groat following fermentation with probiotic Lactobacillus acidophilus , Lactobacillus johnsonii , and Lactobacillus reuteri

The aim of this study was to improve the bioavailability of the dietary phenolic acids in flours from whole grain barley and oat groat following fermentation with lactic acid bacteria (LAB) exhibiting high feruloyl esterase activity (FAE). The highest increase of free phenolic acids was observed after fermentation with three probiotic strains, Lactobacillus johnsonii LA1, Lactobacillus reuteri SD2112, and Lactobacillus acidophilus LA-5, with maximum increases from 2.55 to 69.91 μg g(-1) DM and from 4.13 to 109.42 μg g(-1) DM in whole grain barley and oat groat, respectively. Interestingly, higher amounts of bound phenolic acids were detected after both water treatment and LAB fermentation in whole grain barley, indicating higher bioaccessibility, whereas some decrease was detected in oat groat. To conclude, cereal fermentation with specific probiotic strains can lead to significant increase of free phenolic acids, thereby improving their bioavailability.

The effect of in vitro digestion on steryl ferulates from rice (Oryza sativa L.) and other grains

Polished and cargo rice, wild rice, rice bran, corn bran, and wheat bran were subjected to a static in vitro digestion model, to monitor changes in their steryl ferulate content and composition. Free sterols, possible hydrolysis products of steryl ferulates, were also measured. Additionally, steryl ferulate bioaccessibility was calculated as the percentage of steryl ferulates liberated from the grain matrix into the digestive juice. Steryl ferulate content ranged between 6.1 and 3900 μg/g and decreased by 1-63% due to digestion. A parallel increase in free sterols of more than 70% was observed in all samples. Additionally, bioaccessibility of steryl ferulates was found to be almost negligible. These findings suggest that intestinal enzymes immediately hydrolyze steryl ferulates, which are liberated from the grain matrix, and thus they are practically unavailable for absorption in the small intestine. This further indicates that the hydrolysis products of steryl ferulates could be bioactive in the gut.

Simultaneous analysis of free phytosterols/phytostanols and intact phytosteryl/phytostanyl fatty acid and phenolic acid esters in cereals

An approach based on solid-phase extraction for the effective separation of free phytosterols/phytostanols and phytosteryl/phytostanyl fatty acid and phenolic acid esters from cereal lipids was developed. The ester conjugates were analyzed in their intact form by means of capillary gas chromatography. Besides free sterols and stanols, up to 33 different fatty acid and phenolic acid esters were identified in four different cereal grains via gas chromatography-mass spectrometry. The majority (52-57%) of the sterols and stanols were present as fatty acid esters. The highest levels of all three sterol and stanol classes based on dry matter of ground kernels were determined in corn, whereas the oil extract of rye was 1.7 and 1.6 times richer in fatty acid esters and free sterols/stanols than the corn oil. The results showed that there are considerable differences in the sterols/stanols and their ester profiles and contents obtained from corn compared to rye, wheat, and spelt. The proposed method is useful for the quantification of a wide range of free phytosterols/phytostanols and intact phytosteryl/phytostanyl esters to characterize different types of grain.