摘要:

A specific PCR‐ELISA detection system was established for the testing of food products forSalmonellacontamination. Initially a shortened microbial enrichment comprising two steps, a non‐selective and selective incubation each of 8 hours at 37°C, is carried out. DNA is then isolated from 1 ml of the final selective enrichment culture and purified.In vitroamplification of the recovered DNA is performed in a competitive PCR in the presence of internal standard DNA to exclude the possibility of false negative results arising from food‐borne inhibitory factors.Salmonellaspecific amplicons were identified through specific probe hybridization and colorimetric endpoint detection in a microtiter plate, a format which allows a high throughput due to its high potential for automation.

ISSN:0890-5436    

DOI:10.1080/08905439809549939

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Flavour development during storage of fermented alcoholic cider relies primarily on the activity of an indigenous mixed microflora of yeasts and bacteria. Physical factors such as storage temperature and initial dissolved oxygen level are also shown to significantly influence the organoleptic quality. Over the range of 5 to 25°C, 15°C was found to provide the best temperature for storage, with 25°C resulting in an unacceptable, oxidized and sulphury tasting product. Similar undesirable characteristics occurred due to a rise in initial dissolved oxygen (DO) to 5% saturation prior to storage at 15°C, a DO level that can result from fermenter to storage vat pumping. The juice source, fresh or re‐constituted concentrate was also shown to influence flavour development. The latter does not contain the mixed microflora necessary to promote desirable organoleptic changes, including malolactic fermentation.

ISSN:0890-5436    

DOI:10.1080/08905439809549940

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Rosmarinic acid is a natural antioxidant and is found as a secondary metabolite in rosemary(Rosmarinus officinalis). It is of interest in food preservation due to its antioxidant and antimicrobial activities. Previously maintained shoot‐based clonal line of rosemary designated as R‐l (based on RA content, total phenolics content, tolerance toPseudomonas spand RA stimulation) was used in this study to compare RA biosynthesis in shoot vs callus cultures. Callus cultures were generated from shoot cultures of R‐l line following transformation withAgrobacterium rhizogenes‐containing a natural plasmid that alters plant development. The shoot and transformed callus cultures of R‐l were isolated and maintained separately on hormone free Murashige and Skoog medium (MS/HF). The effect of light and dark conditions on callus growth and RA production was investigated. RA biosynthesis in shoot cultures was also compared due to its relevance to greenhouse production and organ culture. We found that callus maintained in light grows more rapidly when compared to shoot grown in light and callus grown in dark. The ratio of biomass accumulated by callus (Light): callus (Dark): Shoot was 4:1:1 based on fresh weight and 4:1:2 based on dry weight. The ratio of peak RA levels (expressed mg/g DW) was 1:1:10. RA production in callus was small compared to shoot and light had no effect on peak RA level in the callus system, but it effected the growth rate significantly.

ISSN:0890-5436    

DOI:10.1080/08905439809549941

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Eucalyptuswood samples were treated with 3% aqueous sulphuric acid to obtain xylose‐containing solutions. The liquors from treatments were neutralized, contacted with charcoal and supplemented with nutrients to obtain culture media suitable for proliferating the carotenoid‐producing yeast,Phaffia rhodozymaNRRL Y‐17268. Two fed‐batch strategies (with continuous or intermittent feeding) were assayed as operational procedures for improving the carotenoid production. Biomass concentration of 10.3 g cells/L and volumetric pigment concentration of 8.15 mg total carotenoids/L (with 7.19 mg astaxanthin/L) were reached with continuous feeding, whereas improved results (30.6 g cells/L and 33.5 mg total carotenoids/L with 30.5 mg astaxanthin/L) were obtained with intermittent feeding.

ISSN:0890-5436    

DOI:10.1080/08905439809549942

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Two microbial lipases fromGeotrichum sppandRhizopus sppisolated previously in this laboratory and a commercial lipase fromCandida cylindraceawere evaluated as biocatalysts for the enrichment of gamma‐linolenic acid (GLA, 18:3 n‐6) from a fungal oil derived fromMucor spp. Lipase fromGeotrichum spp, as compared to lipases fromCandida cylindraceaandRhizopus sppwas found to be most effective in the enrichment of GLA in unesterified fatty acids upon esterification of the fungal oil fatty acids with n‐butanol. The level of GLA in the unesterified fatty acid could be raised from 10.9 % in the starting material to about 30 % in the unesterified fatty acids after a reaction period of 4 h. Selective hydrolysis of the fungal oil using lipase fromRhizopus sppresulted in about 1.5‐fold enrichment of gamma‐linolenic acid in the unhydrolysed acylglycerols. The other Upases tested were ineffective in the enrichment of GLA by selective hydrolysis of the fungal oil triacylglycerols.

ISSN:0890-5436    

DOI:10.1080/08905439809549943

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This work evaluated the ability of strains representing six species ofBifidobacteriumwith probiotic potential to survive and maintainβ‐galactosidase activity through a two‐step, low‐temperature storage period. Cultures were also evaluated for their ability to ferment skim milk and retain viability during storage at 4°C.Bifidobacterium longumATCC 15707,B. breve15700, andB. bifidum29521 maintained the greatest viabilities at > 1 x 107CFU/mL, andB. infantis15702 maintained the highestβ‐galactosidase activity at > 1 U/ml (with < 1 × 105CFU/mL) after ‐60 to 4°C storage. In fermented skim milk,B. breve15700,B. bifidum29521, andB. animalis25527 tolerated a final product pH of 4.75 with > 1 × 108CFU/mL remaining after 14 days of storage at 4°C. Overall, it was found that highest levels of β‐galactosidase activities did not necessarily correlate to the highest plate‐count populations.

ISSN:0890-5436    

DOI:10.1080/08905439809549944

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The production of citric acid from carob pod extract by cell recycle ofAspergillus nigerat different pHs was investigated. Best results in terms of citric acid concentration, productivity, yield and sugar utilization were obtained with a substrate pH of 5.0. The citric acid concentration (85.5 g/l) and the productivity (4 g/ld) remained constant up to the second and third cycles, respectively.

ISSN:0890-5436    

DOI:10.1080/08905439809549945

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

For the production of lactic acid byLactobacillus plantarumNCIM 2084, response surface methodology (RSM) using central composite rotatable design (CCRD) was adopted for optimising the media composition with respect to liquefied starch, wheat bran extract, ammonium nitrate and sodium acetate. A set of 28 experiments were carried out and cannonical analysis was employed. Significant (p ≤ 0.25) effects were observed for the first three variables. Quadratic and interaction effects of the variables were more prominent than the linear effects. The respective optimum concentrations obtained were 9.99, 0.05, 2.48 and 0.08% giving a substrate conversion of 92% and a lactic acid concentration of 72.9 g/L in 24 h. It has been possible to replace the expensive yeast extract by. a combination of wheat bran extract and ammonium nitrate.

ISSN:0890-5436    

DOI:10.1080/08905439809549946

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We studied the influence of immobilised yeasts on fermentation parameters and beer quality using a continuous gas‐lift bioreactor system withSaccharomyces warumentrapped in calcium pectate beads. The higher the amount of biomass, the shorter the fermentation time. At an immobilised biomass volume to wort ratio of 0.35:1 (v/v), productivity began to fall and the specific rate of saccharide utilisation decreased. The optimum level for productivity and beer quality was obtained at the ratio of 0.27:1 (v/v) biocatalyst volume to the wort volume. Beer with suitable flavour, low level of diacetyl (less than 0.1 mg/1) and an optimum ratio of the higher alcohols to esters content (4.53:1) has been produced with a residence time of 13.16 h and maximum specific rate of saccharide utilisation of I.106 g/g.h. Except for higher nitrogen and lower amyl alcohols contents, the parameters characterising the beer quality produced in this bioreactor were close to the parameter values of classically produced beer.

ISSN:0890-5436    

DOI:10.1080/08905439809549947

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Time Temperature Integrators (TTI) are simple devices to monitor temperature exposure history and relate it to food shelf life behaviour. Four colorimetric enzyme reaction systems are proposed as the basis for TTI use and results for their kinetic characterisation under isothermal conditions are presented. Nonisothermal experiments have shown that the proposed system response reflected accurately the dynamic nature of the environment temperature. The reliability of the proposed TTI systems was demonstrated by a case study on chilled fish shelf life prediction after storage temperature abuse.

ISSN:0890-5436    

DOI:10.1080/08905439809549948

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor