Modificación del método de Pack para la microdeterminación de diacetilo en cultivos mixtos / [Modification of the Pack method for the microdetermination of diacetyl in mixed cultures]

Prill and Hammer’s method (4) for microdetermination of diacetyl was modified by several authors (1-3, 7), but retaining the same principle: diacetyl is converted into dimethylglyoxime by reaction with hydroxylamine; the oxime is subsequently converted into a pink ammonoferrous glyoximate and its colour is measured by absorbance at 530 nm. In the present communication a procedure based on the method of Pack et al. (3) is proposed with the following modifications: 1. Omission of carboy and suction flask; 2. Elongation of the connecting tubing between sample and trap tubes and relocation of the trap tubes to a higher level. 3. Replacement of rubber tubing by pvc connection and of rubber stoppers by neoprene ones. 4. A more accurate regulation of the nitrogen flow. 5. Protection of the Fe SO4 against oxidation. 6. Omission of the rinse of the trap tips with K2 HPO4 solution. 7. Use of diacetyl as a standard instead of dimethylglyoxime.

Modificación del método de Pack para la microdeterminación de diacetilo en cultivos mixtos. / [Modification of the Pack method for the microdetermination of diacetyl in mixed cultures]

Prill and Hammers method (4) for microdetermination of diacetyl was modified by several authors (1-3, 7), but retaining the same principle: diacetyl is converted into dimethylglyoxime by reaction with hydroxylamine; the oxime is subsequently converted into a pink ammonoferrous glyoximate and its colour is measured by absorbance at 530 nm. In the present communication a procedure based on the method of Pack et al. (3) is proposed with the following modifications: 1. Omission of carboy and suction flask; 2. Elongation of the connecting tubing between sample and trap tubes and relocation of the trap tubes to a higher level. 3. Replacement of rubber tubing by pvc connection and of rubber stoppers by neoprene ones. 4. A more accurate regulation of the nitrogen flow. 5. Protection of the Fe SO4 against oxidation. 6. Omission of the rinse of the trap tips with K2 HPO4 solution. 7. Use of diacetyl as a standard instead of dimethylglyoxime.

Leuconostocs en leche cruda: aislamiento e identificación de especies de utilización rápida de lactosa. / [Leuconostocs in raw milk: isolation and identification of species rapidly utilizing lactose]

Fast lactose fermenting Leuconostoc species and subspecies were isolated from raw milk. Samples were obtained from dairy farms of the surroundings of Buenos Aires city. A lactose, non selective, isolation medium was employed (YCL). Differentiation of leuconostocs from Lactobacillus viridescens and L. confusus was avoided on account of the use of this medium. 801 typical colonies of lactic acid bacteria were selected from YCL agar; 710 of them were identified as lactic acid bacteria from which 114 strains belonged to the genus Leuconostoc. These last strains were then tested for species and subspecies differentiation by dextran production and sugar fermentation. Leuconostoc mesenteroides subsp. dextranicum and L. lactis were identified. Four strains identified as Leuconostoc spp do not belong to any known species.