Lactobacillus casei expressing methylglyoxal synthase causes browning and heterocyclic amine formation in Parmesan cheese extract.

Undesired browning of Parmesan cheese can occur during the latter period of ripening and cold storage despite the relative absence of reducing sugars and high temperatures typically associated with Maillard browning. Highly reactive α-dicarbonyls such as methylglyoxal (MG) are products and accelerants of Maillard browning chemistry and can result from the microbial metabolism of sugars and AA by lactic acid bacteria. We demonstrate the effects of microbially produced MG in a model Parmesan cheese extract using a strain of Lactobacillus casei 12A engineered for inducible overexpression of MG synthase (mgsA) from Thermoanaerobacterium thermosaccharolyticum HG-8. Maximum induction of plasmid-born mgsA led to 1.6 mM MG formation in Parmesan cheese extract and its distinct discoloration. The accumulation of heterocyclic amines including ß-carboline derivatives arising from mgsA expression were determined by mass spectrometry. Potential MG-contributing reaction mechanisms for the formation of heterocyclic amines are proposed. These findings implicate nonstarter lactic acid bacteria may cause browning and influence nutritional aspects of Parmesan by enzymatic conversion of triosephosphates to MG. Moreover, these findings indicate that the microbial production of MG can lead to the formation of late-stage Maillard reaction products such as melanoidin and ß-carbolines, effectively circumventing the thermal requirement of the early- and intermediate- stage Maillard reaction. Therefore, the identification and control of offending microbiota may prevent late-stage browning of Parmesan. The gene mgsA may serve as a genetic biomarker for cheeses with a propensity to undergo MG-mediated browning.

Biogenic synthesis, characterization of gold and silver nanoparticles from Coleus forskohlii and their clinical importance.

In modern era, the great interest and demand among chemists and researchers for metal nanoparticles is increasing in the application of biomedical fields, textiles, cosmetics and various sectors. Consequently, the present study reports an eco-friendly, cost-effective, rapid and easy method to produce environment-friendly metal nanoparticles to prevent exhaustion of metal resources. In this context, gold and silver metal nanoparticles were green synthesized using the Root Extract of Coleous forskohlii (RECo) as capping and reducing agent. The synthesized gold (GNPs) and silver nanoparticles (SNPs) were characterized using UV-Visible spectrophotometer, High-resolution transmission electron microscopy (HR-TEM), Particle size analysis (PSA), Fourier-transform infrared spectroscopy (FT-IR) and X-Ray Diffractometer (XRD). Their clinical importance was analysed using anti-oxidant assay (DPPH - 2,2-diphenyl-1-picrylhydrazyl and Phosphomolybdenum PMA) and cytotoxicity (MTT assay) against HEPG2 (liver cancer cell lines). Further, the antimicrobial activity against two microorganisms were tested using disc diffusion method against Proteus vulgaris pathogen and Micrococcus luteus pathogen. RECo-GNPs and SNPs were found to be stable in aqueous medium for a longer time and exhibited favorable anti-oxidant, anti-bacterial and anti-cancer activity. The phytoconstituents present in the root extract of Coleous forskohlii was elucidated using GC-MS analysis.

Lactobacillus demonstrate thiol-independent metabolism of methylglyoxal: Implications toward browning prevention in Parmesan cheese.

Endogenous production of α-dicarbonyls by lactic acid bacteria can influence the quality and consistency of fermented foods and beverages. Methylglyoxal (MG) in Parmesan cheese can contribute toward undesired browning during low temperature ripening and storage conditions, leading to the economic depreciation of affected cheeses. We demonstrate the effects of exogenously added MG on browning and volatile formation using a Parmesan cheese extract (PCE). To determine the influence of Lactobacillus on α-dicarbonyls, strains were screened for their ability to modulate concentrations of MG, glyoxal, and diacetyl in PCE. It was found that a major metabolic pathway of MG in Lactobacillus is a thiol-independent reduction, whereby MG is partially or fully reduced to acetol and 1,2-propanediol, respectively. The majority of lactobacilli grown in PCE accumulated the intermediate acetol, whereas Lactobacillus brevis 367 formed exclusively 1,2-propanediol and Lactobacillus fermentum 14931 formed both metabolites. In addition, we determined the inherent tolerance to bacteriostatic concentrations of MG among lactobacilli grown in rich media. It was found that L. brevis 367 reduces MG exclusively to 1,2-propanediol, which correlates to both its ability to significantly decrease MG concentrations in PCE, as well as its significantly higher tolerance to MG, in comparison to other lactobacilli screened. These findings have broader implications toward lactobacilli as a viable solution for reducing MG-mediated browning of Parmesan cheese.

Specificity of papaya lipase in esterification with respect to the chemical structure of substrates.

Esterification, catalyzed by papaya (Carica papaya) lipase (CPL), was studied with various alcohols and carboxylic acids under competitive conditions. Acids studied were straight-chain saturates of different chain lengths, with octanoic acid as the reference. Alcohols chosen were aliphatic straight-chain, branched, secondary, tertiary, terpene, and aromatic alcohols of different chain lengths, using 1-hexanol as the reference. The initial reaction rate increased with increasing chain length of the acid from C4:0 to C18:0, followed by a slight decrease with C20:0. In the case of alcohols, an optimum chain length of 8 carbon atoms was obtained for the straight-chain aliphatic group (C2 to C16). Ethanol, 1-propanol, and secondary and tertiary alcohols showed rather low reactivity. Branching of the alcohols was found not to affect the reactivity in esterification; among the terpenes, beta-citronellol [(2E)-3, 7-dimethyl-6-octenol] and geraniol [(2E)-3,7-dimethylocta-2, 6-dien-1-ol] were found to be more reactive than nerol [(2Z)-3, 7-dimethylocta-2,6-dien-1-ol]. The highest reaction rate was found for the aromatic benzyl alcohol (phenylmethanol).

Papaya (Carica papaya) lipase with some distinct acyl and alkyl specificities as compared with microbial lipases.

Lipase from papaya (Carica papaya) latex (CPL), Candida antarctica lipase B (Novozym 435, NOV) and Rhizomucor miehei lipase (Lipozyme IM 20, LIP) were used as biocatalysts for the esterification of caprylic acid with straight-chain saturated C(4)-C(18) alcohols and unsaturated C(18) alcohols, such as cis-9-octadecenyl (oleyl, C(18:1), n-9), cis-6-octadecenyl (petroselinyl, C(18:1), n-12), cis-9,cis-12-octadecadienyl (linoleyl, C(18:2), n-6), all-cis-9,12,15-octadecatrienyl (alpha-linolenyl, C(18:3), n-3) and all-cis-6,9,12-octadecatrienyl (gamma-linolenyl, C(18:3), n-6) alcohols. With CPL, highest activity was found in the esterification of octanol and decanol, whereas both NOV and LIP showed a broad chain-length-specificity for the alcohols. CPL, as opposed to the microbial lipases, strongly discriminated against all the saturated long-chain ( > C(12)) and unsaturated C(18) alcohols.

Studies on the lipozyme-catalyzed synthesis of butyl laurate.

The effects of temperature, speed of agitation, enzyme concentration, etc., on butyl laurate synthessis using Mucor miehei lipase (Lipozymetrade mark) have been studied. Although the soluble enzyme was quite thermcstable in aqeous solution, it deactivated rapidly at and above 40 degrees C in the presence of butanol. This enzyme immobilized on an anion-exchange resin (Lipozymetrade mark) showed enhanced stability (as compared to the soluble form) to denaturation by butanol under the same conditions. The denaturation of M. miehei lipase was found to be a function of the butanol concentration in the aqueous phase, and rapid denaturation takes place at the concentration corresponding to its saturation at that temperature. (c) 1995 John Wiley & Sons, Inc.