Inactivation of Bacillus amyloliquefaciens spores by a combination of sucrose laurate and pressure-assisted thermal processing

Enzymatic Synthesis of Glucose Fatty Acid Esters Using SCOs as Acyl Group-Donors and Their Biological Activities

Sugar fatty acid esters, especially glucose fatty acid esters (GEs), have broad applications in food, cosmetic and pharmaceutical industries. In this research, the fatty acid moieties derived from polyunsaturated fatty acids containing single-cell oils (SCOs) (i.e., those produced from Cunninghamella echinulata, Umbelopsis isabellina and Nannochloropsis gaditana, as well as from olive oil and an eicosapentaenoic acid (EPA) concentrate) were converted into GEs by enzymatic synthesis, using lipases as biocatalysts. The GE synthesis was monitored using thin-layer chromatography, FTIR and in situ NMR. It was found that GE synthesis carried out using immobilized Candida antarctica B lipase was very effective, reaching total conversion of reactants. It was shown that EPA-GEs were very effective against several pathogenic bacteria and their activity can be attributed to their high EPA content. Furthermore, C. echinulata-GEs were more effective against pathogens compared with U. isabellina-GEs, probably due to the presence of gamma linolenic acid (GLA) in the lipids of C. echinulata, which is known for its antimicrobial activity, in higher concentrations. C. echinulata-GEs also showed strong insecticidal activity against Aedes aegypti larvae, followed by EPA-GEs, olive oil-GEs and N. gaditana-GEs. All synthesized GEs induced apoptosis of the SKOV-3 ovarian cancer cell line, with the apoptotic rate increasing significantly after 48 h. A higher percentage of apoptosis was observed in the cells treated with EPA-GEs, followed by C. echinulata-GEs, U. isabellina-GEs and olive oil-GEs. We conclude that SCOs can be used in the synthesis of GEs with interesting biological properties.

Synthesis, PASS predication, in vitro antimicrobial evaluation and pharmacokinetic study of novel n-octyl glucopyranoside esters

Octyl β-d-glucopyranoside (OBG), prepared from d-glucose and octan-1-ol employing MW method, was subjected to direct dimolar valeroylation in pyridine at room temperature (25 °C) with valeroyl chloride. This mainly furnished the corresponding 3,6-di-O-valeroate in 57% yield indicating the regioselectivity at C-6 and C-3 positions. For structural elucidation and to get newer glucopyranosides of potential antimicrobial 3,6-di-O-valeroate was further converted into four novel 2,4-di-O-acyl esters reasonably in good yields. Per-O-acetate and per-O-benzoate of OBG were also prepared for SAR study. PASS predication and in vitro antimicrobial studies established them as better antifungal agent than that of antibacterial. SAR study along with AdmetSAR and SwissADME suggested that incorporation of alkanoyl and aromatic ester groups on octyl glucopyranoside core increase antimicrobial potentiality in very low concentration (10 μgmL^-1). Molecular docking revealed that novel 2,4-di-O-tosyl ester and 2,3,4,6-tetra-O-benzoyl ester may act as competitive inhibitors of lanosterol 14-alpha demethylase.

In vitro antibacterial activities and mechanism of sugar fatty acid esters against five food-related bacteria

The objective of this study was to evaluate the antibacterial activities of sugar fatty acid esters, with different fatty acid and saccharide moieties, against five food-related bacteria including Bacillus cereus, Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Salmonella typhimurium. Sucrose monocaprate showed the strongest antibacterial activity against all tested bacteria, especially Gram-positive bacteria. The minimum inhibitory concentrations (MICs) for Gram-positive bacteria and Gram-negative bacteria were 2.5 and 10 mM, respectively. The minimum bactericidal concentrations (MBCs) for Gram-positive bacteria were 10 mM. Time-kill assay also showed that sucrose monocaprate significantly inhibit the growth of tested bacteria. The permeability of the cell membrane and intracellular proteins were both changed by sucrose monocaprate according to cell constituents' leakage, SDS-PAGE and scanning electron microscope assays. It is suggested that sucrose monocaprate, with both emulsifying and antibacterial activities, have a potential to serve as a safe multifunctional food additive in food industries.

Kinetics of Bacillus cereus spore inactivation in cooked rice by combined pressure-heat treatment

The efficacy of pressure-heat treatment was evaluated for the inactivation of Bacillus cereus spores in cooked rice. The spores of B. cereus ATCC 9818 were inoculated (1.1 × 10(8) CFU/g) in a parboiled rice product (pH 6.0, water activity of 0.95) and inactivated to an undetectable level (<10 CFU/g) by treatment of 600 MPa and process temperatures of 60 to 85 °C or 0.1 MPa and 85 °C. Kinetic inactivation parameters were estimated with linear and nonlinear models. The potential recovery of injured bacteria was also evaluated during storage of the treated product for 4 weeks at 4 and 25 °C. Depending on the process temperature, a 600-MPa treatment inactivated spores by 2.2 to 3.4 log during the 30-s pressure come-up time, and to below the detection limit after 4- to 8-min pressure-holding times. In contrast, a 180-min treatment time was required to inactivate the spores to an undetectable level at 0.1 MPa and 85 °C. The decimal reduction time of spores inactivated by combined pressure-heat treatment ranged from 1.08 to 2.36 min, while it was 34.6 min at 85 °C under atmospheric conditions. The nonlinear Weibull model scale factor increased, and was inversely related to the decimal reduction time, and the shape factor decreased with increasing pressure or temperature. The recovery of injured spores was influenced by the extent of pressure-holding time and process temperature. This study suggests that combined pressure-heat treatment could be used as a viable alternative to inactivate B. cereus spores in cooked rice and extend the shelf life of the product.

Effect of lactose monolaurate on pathogenic and nonpathogenic bacteria

The antimicrobial activities of sucrose monolaurate and a novel ester, lactose monolaurate (LML), were tested. Gram-positive bacteria were more susceptible than Gram-negative bacteria to both esters. The minimal bactericidal concentrations of LML were 5 to 9.5 mM for Listeria monocytogenes isolates and 0.2 to 2 mM for Mycobacterium isolates.