Aspergillus oryzae β-D-galactosidase immobilization on glutaraldehyde pre-activated amino-functionalized magnetic mesoporous silica: Performance, characteristics, and application in the preparation of sesaminol

Aspergillus oryzae β-D-galactosidase (β-Gal) efficiently hydrolyzes sesaminol triglucoside into sesaminol, which has higher biological activity. However, β-Gal is difficult to be separate from the reaction mixture and limited by stability. To resolve these problems, β-Gal was immobilized on amino-functionalized magnetic nanoparticles mesoporous silica pre-activated with glutaraldehyde (Fe3O4@mSiO2-β-Gal), which was used for the first time to prepare sesaminol. Under the optimal conditions, the immobilization yield and recovered activity of β-Gal were 57.9 ± 0.3 % and 46.5 ± 0.9 %, and the enzymatic loading was 843 ± 21 Uenzyme/gsupport. The construction of Fe3O4@mSiO2-β-Gal was confirmed by various characterization methods, and the results indicated it was suitable for heterogeneous enzyme-catalyzed reactions. Fe3O4@mSiO2-β-Gal was readily separable under magnetic action and displayed improved activity in extreme pH and temperature conditions. After 45 days of storage at 4 °C, the activity of Fe3O4@mSiO2-β-Gal remained at 92.3 ± 2.8 %, which was 1.29 times than that of free enzyme, and its activity remained above 85 % after 10 cycles. Fe3O4@mSiO2-β-Gal displayed higher affinity and catalytic efficiency. The half-life was 1.41 longer than free enzymes at 55.0 °C. Fe3O4@mSiO2-β-Gal was employed as a catalyst to prepare sesaminol, achieving a 96.7 % conversion yield of sesaminol. The excellent stability and catalytic efficiency provide broad benefits and potential for biocatalytic industry applications.

Specialized metabolites degradation by microorganisms

Secondary metabolites are specialized metabolic products synthesized by plants, insects, and bacteria, some of which exhibit significant physiological activities against other organisms. Plants containing bioactive secondary metabolites have been used in traditional medicine for centuries. In developed countries, one-fourth of medicines directly contain plant-derived compounds or indirectly contain them via semi-synthesis. These compounds have contributed considerably to the development of not only medicine but also molecular biology. Moreover, the biosynthesis of these physiologically active secondary metabolites has attracted substantial interest and has been extensively studied. However, in many cases, the degradation mechanisms of these secondary metabolites remain unclear. In this review, some unique microbial degradation pathways for lignans and C-glycosides are explored.

Recent status of sesaminol and its glucosides: Synthesis, metabolism, and biological activities

Sesamum indicum is a major and important oilseed crop that is believed to promote human health in many countries, especially in China. Sesame seeds contain two types of lignans: lipid-soluble lignans and water-soluble glucosylated lignans. The major glucosylated lignans are sesaminol glucosides (SGs). So far, four sesaminol isomers and four SGs are identified. During the naturally occurring process of SGs production, sesaminol is generated first from two molecules of E-coniferyl alcohol, and then the sugar is added to the sesaminol one by one, leading to production of SGs. Sesaminol can be prepared from SGs, from sesamolin, and through artificial synthesis. SGs are metabolized in the liver and intestine and are then transported to other tissues. They exhibit several biological activities, most of which are based on their antioxidant and anti-inflammatory activities. In this paper, we present an overview of the current status of research on sesaminol and SGs. We have also discussed their synthesis, preparation, metabolism, and biological activities. It has been suggested that sesaminol and SGs are important biological substances with strong antioxidant properties in vitro and in vivo and are widely used in the food industry, medicine, and cosmetic products. The recovery and utilization of SGs from sesame seed cake after oil processing will generate massive economic benefits.

Structural insights into a bacterial β-glucosidase capable of degrading sesaminol triglucoside to produce sesaminol: toward the understanding of the aglycone recognition mechanism by the C-terminal lid domain

The sesaminol triglucoside (STG)-hydrolyzing β-glucosidase from Paenibacillus sp. (PSTG1), which belongs to glycoside hydrolase family 3 (GH3), is a promising catalyst for the industrial production of sesaminol. We determined the X-ray crystal structure of PSTG1 with bound glycerol molecule in the putative active site. PSTG1 monomer contained typical three domains of GH3 with the active site in domain 1 (TIM barrel). In addition, PSTG1 contained an additional domain (domain 4) at the C-terminus that interacts with the active site of the other protomer as a lid in the dimer unit. Interestingly, the interface of domain 4 and the active site forms a hydrophobic cavity probably for recognizing the hydrophobic aglycone moiety of substrate. The short flexible loop region of TIM barrel was found to be approaching the interface of domain 4 and the active site. We found that n-heptyl-β-D-thioglucopyranoside detergent acts as an inhibitor for PSTG1. Thus, we propose that the recognition of hydrophobic aglycone moiety is important for PSTG1-catalyzed reactions. Domain 4 might be a potential target for elucidating the aglycone recognition mechanism of PSTG1 as well as for engineering PSTG1 to create a further excellent enzyme to degrade STG more efficiently to produce sesaminol.

Lignans of Sesame (Sesamum indicum L.): A Comprehensive Review

Major lignans of sesame sesamin and sesamolin are benzodioxol--substituted furofurans. Sesamol, sesaminol, its epimers, and episesamin are transformation products found in processed products. Synthetic routes to all lignans are known but only sesamol is synthesized industrially. Biosynthesis of furofuran lignans begins with the dimerization of coniferyl alcohol, followed by the formation of dioxoles, oxidation, and glycosylation. Most genes of the lignan pathway in sesame have been identified but the inheritance of lignan content is poorly understood. Health-promoting properties make lignans attractive components of functional food. Lignans enhance the efficiency of insecticides and possess antifeedant activity, but their biological function in plants remains hypothetical. In this work, extensive literature including historical texts is reviewed, controversial issues are critically examined, and errors perpetuated in literature are corrected. The following aspects are covered: chemical properties and transformations of lignans; analysis, purification, and total synthesis; occurrence in Seseamum indicum and related plants; biosynthesis and genetics; biological activities; health-promoting properties; and biological functions. Finally, the improvement of lignan content in sesame seeds by breeding and biotechnology and the potential of hairy roots for manufacturing lignans in vitro are outlined.

Identification and characterization of a novel bacterial β-glucosidase that is highly specific for the β-1,2-glucosidic linkage of sesaminol triglucoside

A gene (PSTG2) coding for a novel β-glucosidase belonging to glycoside hydrolase family 3 was identified in the vicinity of the previously identified β-glucosidase gene [sesaminol triglucoside (STG)-hydrolyzing β-glucosidase, PSTG1] in the genome of Paenibacillus sp. strain KB0549. Compared with PSTG1, recombinant PSTG2 more specifically acted on the β-1,2-glucosidic linkage of the STG molecule to transiently accumulate a larger amount of 6-O-(β-D-glucopyranosyl)-β-D-glucopyranosylsesaminol.

Quality Characterization and Oxidative Stability of Camellia Seed Oils Produced with Different Roasting Temperatures

In this study, the effects of roasting camellia (Camellia oleifera Abel.) seed oils at different temperatures (65°C, 100°C, 120°C, and 140°C) on the oxidative stability and composition of the oils were investigated. The results showed that, in terms of the quality of the oils, the roasting temperature influenced the total phenolic content (which ranged from 1.64～2.45 GAE mg/g for the different oils) and total flavonoid content (which ranged from 0.36～0.45 QE mg/g for the different oils), while the fatty acid profile and tocopherol content were not influenced by the roasting temperature. We also investigated the kinetic parameters of camellia seed oil during oxidation via Rancimat (at temperatures ranging from 110~140°C). It turned out that the natural logarithms of the oxidative stability index (OSI) varied linearly with respect to temperature (R²: 0.958～0.997). This was done on the basis of the Arrhenius equation that indicates that the activation energies (Ea) for oxidative stability are 65.7～78.4 KJ/mol. Simultaneously, we found that increasing the roasting temperature could increase the antioxidant stability of Maillard reaction products in camellia seed oil. The effects of roasting include the assurance that the camellia seed oil so produced will comply with the relevant governmental health codes and standards and have a longer shelf life.

Paenibacillus relictisesami sp. nov., isolated from sesame oil cake

A facultatively anaerobic, Gram-stain-positive, rod-shaped bacterium, designated strain KB0549T, was isolated from sesame oil cake. Cells were motile, round-ended rods, and produced central or terminal spores. The cell wall peptidoglycan contained meso-diaminopimelic acid as the diamino acid. The major fatty acids were anteiso-C15:0 and anteiso-C17:0. The DNA G+C content of strain KB0549T was 51.9 mol%. On the basis of 16S rRNA gene sequence phylogeny, strain KB0549T was affiliated with the genus Paenibacillus in the phylum Firmicutes and was most closely related to Paenibacillus cookii with 97.4% sequence similarity. Strain KB0549T was physiologically differentiated from P. cookii by the high content of anteiso-C17:0, inability to grow at 50 °C, spore position, and negative Voges-Proskauer reaction. Based on these unique physiological and phylogenetic characteristics, it is proposed that the isolate represents a novel species, Paenibacillus relictisesami sp. nov.; the type strain is KB0549T (=JCM 18068T=DSM 25385T).

Purification, gene cloning, and biochemical characterization of a β-glucosidase capable of hydrolyzing sesaminol triglucoside from Paenibacillus sp. KB0549

The triglucoside of sesaminol, i.e., 2,6-O-di(β-D-glucopyranosyl)-β-D- glucopyranosylsesaminol (STG), occurs abundantly in sesame seeds and sesame oil cake and serves as an inexpensive source for the industrial production of sesaminol, an anti-oxidant that displays a number of bioactivities beneficial to human health. However, STG has been shown to be highly resistant to the action of β-glucosidases, in part due to its branched-chain glycon structure, and these circumstances hampered the efficient utilization of STG. We found that a strain (KB0549) of the genus Paenibacillus produced a novel enzyme capable of efficiently hydrolyzing STG. This enzyme, termed PSTG, was a tetrameric protein consisting of identical subunits with an approximate molecular mass of 80 kDa. The PSTG gene was cloned on the basis of the partial amino acid sequences of the purified enzyme. Sequence comparison showed that the enzyme belonged to the glycoside hydrolase family 3, with significant similarities to the Paenibacillus glucocerebrosidase (63% identity) and to Bgl3B of Thermotoga neapolitana (37% identity). The recombinant enzyme (rPSTG) was highly specific for β-glucosidic linkage, and k_cat and k_cat/K_m values for the rPSTG-catalyzed hydrolysis of p-nitrophenyl-β-glucopyraniside at 37°C and pH 6.5 were 44 s⁻¹ and 426 s⁻¹ mM⁻¹, respectively. The specificity analyses also revealed that the enzyme acted more efficiently on sophorose than on cellobiose and gentiobiose. Thus, rPSTG is the first example of a β-glucosidase with higher reactivity for β-1,2-glucosidic linkage than for β-1,4- and β-1,6-glucosidic linkages, as far as could be ascertained. This unique specificity is, at least in part, responsible for the enzyme’s ability to efficiently decompose STG.

Isolation and identification of a potent radical scavenger (canolol) from roasted high erucic mustard seed oil from Nepal and its formation during roasting

Roasting of high erucic mustard (HEM) seed has been reported to give a typical flavor and increase the oxidative stability of the extracted oil. A potent radical scavenging compound was successfully isolated from roasted HEM seed oil in a single-step chromatographic separation using an amino solid-phase extraction column. Nuclear magnetic resonance and mass spectrometry spectra revealed the compound as 2,6-dimethoxy-4-vinylphenol (generally known as canolol), and its identity was fully confirmed by chemical synthesis. The formation of canolol during roasting was compared among HEM varieties (Brassica juncea, B. juncea var. oriental, Brassica nigra, and Sinapis alba) together with a low erucic rapeseed variety. HEM varieties were shown to produce less than one-third of canolol compared to rapeseed at similar roasting conditions. This observation was linked to a lower free sinapic acid content together with a lower loss of sinapic acid derivatives in the HEM varieties compared to rapeseed. Around 50% of the canolol formed in the roasted seed was shown to be extracted in the oil. Roasting of HEM seed before oil extraction was found to be a beneficial step to obtain canolol-enriched oil, which could improve the oxidative stability.

Intestinal distribution and excretion of sesaminol and its tetrahydrofuranoid metabolites in rats

Sesame seeds (Sesamum indicum L.) are unique because of potent and various physiological activities imparted by their bioactive lignans. This investigation studied the intestinal distribution and excretion of sesaminol in Sprague-Dawley (SD) rats. To investigate the distribution of sesaminol (per oral 220 mg/kg), the changes in concentration of sesaminol and its metabolites were determined in the intestines and plasma within the 24 h period after tube feeding of sesaminol to SD rats. Results show that the epimerization of sesaminol appeared to be catalyzed by acid in the simulated gastric fluids. The major sesaminol epimer was characterized as 2-episesaminol using 2D-NMR. These findings indicate that sesame sesaminol and its epimer are poorly absorbed prior to reaching the rectum and that substantial amounts pass from the small to the large intestine, where they are metabolized by the colonic microflora to tetrahydrofuranoid metabolites. Sesaminol in plasma was largely present as phase II conjugates, and the seven metabolites were detected as the 2-episesaminol, sesaminol-6-catechol, methylated sesaminol-catechol, R,R-hydroxymethylsesaminol-tetrahydrofuran, S,R-hydroxymethylsesaminol-tetrahydrofuran, enterolactone, and enterodiol. Excretions of sesaminol in urine and feces within the 24 h period were equivalent to 0.02 and 9.33% of the amount ingested, respectively.

Biotransformation of sesaminol triglucoside to mammalian lignans by intestinal microbiota

Plant lignans occur widely in foods, with flaxseed recognized as their richest source. Some plant lignans can be converted by intestinal microbiota to the mammalian lignans, enterodiol and enterolactone, which may have protective effects against hormone-related diseases such as breast cancer. This study determined whether plant lignans in sesame seed, particularly sesaminol triglucoside (STG), could be metabolized to mammalian lignans. STG is a furofuran lignan with methylenedioxyphenyls. The transformation of furofuran lignans to mammalian lignans by intestinal microbiota involves the hydrolysis of glucoside, demethylenation of a methylene group, oxidation of dibenzylbutanediol to dibenzylbutyrolactone, and reductive cleavage of furofuran rings. STG has methylenedioxyphenyl moieties in their structures that may require additional oxidative demethylenation of the methylenedioxyphenyl ring for conversion to mammalian lignans. However, STG is metabolized, via intestinal microbiota, to a catechol moiety. The major STG metabolite was characterized as 4-[((3R,4R)-5-(6-hydroxybenzo[d][1,3]dioxol-5-yl)-4-(hydroxymethyl)tetrahydrofuran-3-yl)methyl]benzene-1,2-diol using NMR and mass spectrometry, and STG could be converted to enterolactone and enterodiol by rat intestinal microflora.