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M L SPECK

Publications and source records attributed to M L SPECK.

13 recordsLinked to original sources
PubMed1965

BITTER PEPTIDE ISOLATED FROM MILK CULTURES OF STREPTOCOCCUS CREMORIS.

Certain cultures of Streptococcus cremoris produced a bitter taste that occurred in the whey portion of milk cultures. Whey from a culture which produced bitterness was fractionated on Sephadex. The fraction in which the bitter taste was concentrated was chromatographed successively on paper with butanol-acetic acid-water (5:1:4), and then butanol-2-butanone-water (2:2:1). In each instance, the bitter component was in the most rapidly moving band that gave a positive ninhydrin test. The bitterness was observed to be caused by a peptide containing the following numbers of each amino acid: arginine, 1; glutamic acid, 2; glycine, 2; isoleucine, 2; leucine, 2; phenylalanine, 1; proline, 5; and valine, 4. N-terminal amino acids could be detected by coupling with 2,4-dinitrofluorobenzene or phenylisothiocyanate, or by hydrolysis with leucine aminopeptidase. When treated with carboxypeptidase, only leucine and valine appeared at the C-terminal end, and these were detected simultaneously.

Alanine↗
PubMed1964

EXTRACELLULAR PROTEINASE OF STREPTOCOCCUS LACTIS.

Williamson, W. T. (North Carolina State of the University of North Carolina, Raleigh), S. B. Tove, and M. L. Speck. Extracellular proteinase of Streptococcus lactis. J. Bacteriol. 87:49-53. 1964.-Streptococcus lactis was shown to produce an extracellular proteolytic enzyme(s). A 120-fold purification of the proteinase was obtained from the cell-free culture medium by ammonium sulfate fractionation, calcium phosphate gel treatment, and chromatography on diethylaminoethyl cellulose. Only 32% of the activity was destroyed by heating at 98 C for 1 hr. The requirement of free sulfhydryl groups for enzyme activity was indicated by inhibition with p-chloromercuric benzoate. Diisopropyl fluorophosphate did not inhibit the proteinase.

Benzoates↗
PubMed1963

Injury and death of Streptococcus lactis due to freezing and frozen storage.

Cells of Streptococcus lactis were harvested in the early stationary phase, washed, and resuspended in either skim milk (10% nonfat milk) or buffered distilled water (0.0003 m dipotassium phosphate, pH 7.2). Samples of each suspension were frozen and stored at -20 C for intervals up to 28 days. Colony counts of the frozen culture were made using lactic agar and a "restricted" lactic agar medium (Tryptone reduced to 0.5%) to determine injury and death. Death was determined by the difference in plate counts on lactic agar before and after freezing. Injured cells were determined by the difference in plate counts on the two plating media. Greatest injury of the cells occurred during early stages of frozen storage and decreased with time, and death continuously increased. Injury and death were more pronounced when cells were frozen in water than when frozen in 10% nonfat milk solids. Certain cultures survived better when frozen rapidly, whereas with others survival was greater when freezing was slow. Successive freezing, thawing, and propagation of the culture gradually eliminated cells which showed injury by freezing.

Agar↗
PubMed1963

IDENTIFICATION OF STIMULATORY FACTOR INVOLVED IN SYMBIOTIC GROWTH OF STREPTOCOCCUS LACTIS AND STREPTOCOCCUS CREMORIS.

Dahiya, R. S. (North Carolina State College, Raleigh) and M. L. Speck. Identification of stimulatory factor involved in symbiotic growth of Streptococcus lactis and Streptococcus cremoris. J. Bacteriol. 85:585-589. 1963.-Single-strain cultures of Streptococcus lactis and S. cremoris isolated from a commercial starter culture showed symbiotic growth in milk. This study dealt with identification of the main component responsible for high acid production resulting from the combined growth of these cultures. Paper chromatography and bioautography were adapted to isolate the main stimulatory factor excreted by the slower-growing culture (S. lactis) in the culture media. It was identified as adenine on the basis of ultraviolet absorption spectra and paper chromatographic R(F) value. Pure adenine possessed the same properties and was also stimulatory to the faster-growing culture (S. cremoris) when added to milk.

Adenine↗
PubMed1963

IDENTIFICATION OF GROWTH STIMULANTS FOR STREPTOCOCCUS LACTIS.

Koburger, J. A. (North Carolina State College, Raleigh), M. L. Speck, and L. W. Aurand. Identification of growth stimulants for Streptococcus lactis. J. Bacteriol. 85:1051-1055. 1963-The growth of Streptococcus lactis in milk was accelerated by pancreas extract, and three distinct components that were detected by bioautography were isolated and identified. These were purified by precipitation with silver ions, and their silver salts were regenerated in acidic solution. After adsorption and elution from characoal, contaminating alpha-amino compounds were destroyed by treatment with ninhydrin. Final purification was by chromatography. Identification of the purified fractions was by paper chromatography, and by ultraviolet and infrared spectra. The active compounds were found to be inosine, hypoxanthine, and adenine.

Acids↗
PubMed1962

Activation of dry starter cultures in milk.

The revitalization of mixed strain dried starter cultures at 22 and 32 C in sterile skim milk was materially accelerated when the substrate was fortified with 0.2% pancreas-extract solids. At 22 C, all cultures grew up satisfactorily in 18 hr, and in unfortified milk none of the cultures reached comparable growth in this period. When the cultures were grown at 32 C, the dried cultures developed adequately in 7.5 hr, but required 9 to 10 hr in plain milk. Culture growth was enhanced in milk containing pancreas extract to the extent that the amount of dried culture required to produce adequate acidity in normal incubation times could be markedly reduced. At 32 C, certain cultures could be reduced to 12.5% of recommended amounts, and at 22 C certain ones could be reduced by 50%. Revitalization of the dried cultures in milk containing pancreas extract did not affect the growth of subcultures in plain milk. Also, when dried cultures initiated growth in fortified milk at 32 C their subsequent growth at 22 C in milk alone was not affected. The faster rate of culture growth in milk containing pancreas extract should permit, with more certainty, the establishment of active mother and bulk starters. Furthermore, economy of dried cultures, as well as of time, could be realized by the use of fortified milk.

Animals↗