RESUMEN
Cashew nut samples were irradiated at gamma-radiation doses of 0.25, 0.5, 0.75, and 1 kGy, the permissible dose range for insect disinfestation of food commodities. A weak and short-lived triplet (g = 2.004 and hfcc = 30 G) along with an anisotropic signal (g perpendicular = 2.0069 and g parallel = 2.000) were produced immediately after irradiation. These signals were assigned to that of cellulose and CO 2 (-) radicals. However, the irradiated samples showed a dose-dependent increase of the central line (g = 2.0045 +/- 0.0002). The nature of the free radicals formed during conventional processing such as thermal treatment was investigated and showed an increase in intensity of the central line (g = 2.0045) similar to that of irradiation. Characteristics of the free radicals were studied by their relaxation and thermal behaviors. The present work explores the possibility to identify irradiated cashew nuts from nonirradiated ones by the thermal behaviors of the radicals beyond the period, when the characteristic electron paramagnetic resonance spectral lines of the cellulose free radicals have essentially disappeared. In addition, this study for the first time reports that relaxation behavior of the radicals could be a useful tool to distinguish between roasted and irradiated cashew nuts.
Asunto(s)
Anacardium/química , Espectroscopía de Resonancia por Spin del Electrón , Irradiación de Alimentos , Nueces/química , Anacardium/efectos de la radiación , Radicales Libres/análisis , Rayos gamma , Calor , Cinética , Nueces/efectos de la radiaciónRESUMEN
Studies were carried out on the production of pullulanase by a newly isolated strain Bacillus cereus FDTA-13. High titres of the enzyme were obtained in a medium containing branched polysaccharides. To further enhance the yield, induction of pullulanase using conventional inducers were studied. Maltooligosaccharides (maltose to maltotetraose) when added in the medium individually, or in a 1:1 combination of maltotriose and maltotetraose resulted different levels of pullulanase compared to control. Growth under carbon limited conditions (5 g l(-1)) with inducers resulted remarkably enhanced pullulanase activity. Pullulanase activity was severely repressed in presence of glucose. Low levels of pullulanase was observed in nitrogen limited medium, even with combinations of several maltosaccharides.
Asunto(s)
Bacillus cereus/enzimología , Glicósido Hidrolasas/biosíntesis , Estabilidad de Enzimas , Glicósido Hidrolasas/metabolismoRESUMEN
The phyto-constituents of Gymnema sylvestre are used in the treatment of diabetes and obesity. The present work reports on the extraction of gymnemic acid through gymnemagenin from callus cultures of G. sylvestre. Components were separated on pre-coated silica gel 60 GF254 plates with chloroform:methanol (8:2) and scanned using a densitometric scanner at 205 nm in the near-UV region. Linearity of determination of gymnemagenin was observed in the range 2-10 microg. The average percentage recovery of gymnemagenin from leaf callus extracts was 98.9+/-0.3.
Asunto(s)
Alcaloides/química , Gymnema sylvestre/química , Saponinas/análisis , Triterpenos/análisis , Cromatografía en Capa Delgada , Hojas de la Planta/química , Tallos de la Planta/química , Semillas/química , Técnicas de Cultivo de TejidosRESUMEN
Strains of Aspergillus terreus and A. niger, known to produce xylanase with undetectable amounts of cellulase, were studied for xylanase (EC 3.2.1.8) production on various lignocellulosic substrates using solid state fermentation. Of the lignocellulosic substrates used, wheat bran was the best for xylanase production. The effects of various parameters, such as moistening agent, level of initial moisture content, temperature of incubation, inoculum size and incubation time, on xylanase production were studied. The best medium for A. terreus was wheat bran moistened with 1:5 Mandels and Strenberg mineral solution containing 0.1% tryptone, at 35 degrees C, and at inoculum concentration 2x107-2x108 spores 5 g-1 substrate; for A. niger, the best medium was wheat bran moistened with 1:5 Mandels and Strenberg mineral solution containing 0.1% yeast extract, at 35 degrees C, and at an inoculum concentration of 2x107-2x108 spores 5 g-1 substrate. Under these conditions, A. terreus produced 68.9 IU ml-1 of xylanase, and A. niger, 74.5 IU ml-1, after 4 d of incubation. A crude culture filtrate of the two Aspergillus strains was used for the hydrolysis of various lignocellulosic materials. Xylanase preparations from the two strains selectively removed the hemicellulose fraction from all lignocellulosic materials tested.
Asunto(s)
Aspergillus/enzimología , Celulosa/metabolismo , Lignina/metabolismo , Xilosidasas/biosíntesis , Reactores Biológicos , Fibras de la Dieta/metabolismo , Fermentación , Agua , Xilano Endo-1,3-beta-Xilosidasa , Xilosidasas/aislamiento & purificaciónRESUMEN
Microbiological quality of chewable tobacco mixes traditionally known as "Gutkha" was studied. The microbiological analysis of 15 samples analyzed revealed high bacterial and fungal counts. The total viable counts were in the range of 1.8 x 10(4) to 7.2 x 10(4) CFU g(-1) and the yeast and mold count from 3.6 x 10(3) to 7.1 x 10(4) CFU g(-1). The proteolytic and lipolytic counts were 9 x 10(2) to 2.6 x 10(3) CFU g(-1) and 2.6 x 10(3) CFU g(-1), on an average, respectively. Lecithinase-positive Staphylococcus aureus was found in 2 of the 15 samples analyzed; the counts were up to 3.4 x 10(3) CFU g(-1). Coliform and Salmonella spp. were found to be absent. Aflatoxins B , B2, and G2 were found to be present in all the samples. These samples were exposed to gamma radiation (60Co) at 1-, 2-, 3-, 5-, 10-, and 25-kGy doses. The decrease in total viable count and fungal count was noticed with increase of radiation dose. The 3-kGy dose was observed to be the sterilization dose for Gutkha. At this dose no survival of organisms was noticed and no revival was observed during postirradiation storage at room temperature for 6 months.
Asunto(s)
Bacterias/aislamiento & purificación , Irradiación de Alimentos , Hongos/aislamiento & purificación , Plantas Tóxicas , Tabaco sin Humo , Aflatoxinas/análisis , Recuento de Colonia Microbiana , Plantas Comestibles/microbiología , Dosis de RadiaciónRESUMEN
Aspergillus sp. 5 (strain 5) and Aspergillus sp. 44 (strain 44) produced xylanase (34.3 and 32.7 IU ml-1, respectively) with very low levels of cellulases when grown on 1% wheat bran medium. Xylanase was non-covalently immobilized on Eudragit S-100 for saccharification. The system retained 70 and 80% of strain 5 and strain 44 xylanase activity, respectively. On immobilization, optimum temperature of activity broadened between 50 and 60 degrees C as compared to 50 degrees C in the case of the free enzymes. No significant shift in the pH optima was observed on immobilization. However, immobilization increased enzyme stability mainly by decreasing the temperature sensitivity to the inactivation reaction. The K(m) values increased from 5.6 to 8.3 mg ml-1 for strain 5 xylanase and 7.0 to 9.0 mg ml-1 for strain 44 xylanase. Enzymatic saccharification of xylan and wheat bran was improved on xylanase immobilization. Immobilized xylanase from both the strains produced three times more sugar as compared to free xylanase. In repeated batch saccharification studies immobilized xylanase was recycled three times without loss of enzyme activity.
Asunto(s)
Resinas Acrílicas/química , Aspergillus/genética , Proteínas Recombinantes/metabolismo , Xilosidasas/genética , Xilosidasas/metabolismo , Aspergillus/fisiología , Estabilidad de Enzimas , Enzimas Inmovilizadas , Concentración de Iones de Hidrógeno , Cinética , Ácidos Polimetacrílicos , Proteínas Recombinantes/genética , Temperatura , Triticum/química , Triticum/metabolismo , Xilano Endo-1,3-beta-Xilosidasa , Xilanos/química , Xilanos/metabolismoRESUMEN
One hundred fifty wild strains of Xanthomonas were isolated on five selective and nonselective media. The comparative effectivity of the five media has been discussed. Fifteen polysaccharide-producing strains shortlisted were identified up to species level. These were studied for polysaccharide production in shake flasks using YM media. The highest final yield of 21.3 g/L of the amount of carbon source supplied has been obtained in the optimum medium in shake-flask experiments from Xanthomonas campestris (ICa-125 strain isolated from cabbage. Rheological properties of the exocellular polysaccharide (EPS) have been compared with standard xanthan. EPS from X. campestris ICa-125 was found to be superior with respect to heat stability and effect of electrolytes as compared to standard xanthan.