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Biomedical subjects

P F Fox

Publications and source records attributed to P F Fox.

At least 37 records · Page 2Linked to original sources
PubMed2001

A survey of lipolytic and glycolytic end-products in commercial Cheddar enzyme-modified cheese.

The concentrations of L- and D-lactic acid and free fatty acids, C4:0 to C18:3, were quantified in a range of commercial enzyme-modified Cheddar cheeses. Lactic acid in Cheddar enzyme-modified cheeses varied markedly depending on the manufacturer. Differences in the ratio of L- to D-lactic acid indicate that cheeses of different age were used in their manufacture or contained varying levels of nonstarter lactic acid bacteria. The level of lipolysis in enzyme-modified cheese was higher than in natural Cheddar cheese; butyrate was the predominant free fatty acid. The addition of exogenous acetate, lactate, and butyrate was also indicated in some enzyme-modified cheeses and may be used to confer a specific flavor characteristic or reduce the pH of the product. Propionate was also found in some enzyme-modified cheese products and most likely originated from Swiss-type cheese used in their manufacture. Propionate is not normally associated with natural Cheddar cheese flavor; however, it may be important in the flavor and aroma of Cheddar enzyme-modified cheese. Levels of lipolysis and glycolysis appear to highly controlled as interbatch variability was generally low. Overall, the production of enzyme-modified Cheddar cheese involves manipulation of the end-products of glycolysis (lactate, propionate, and acetate) and lipolysis to generate products for specific applications.

Acetates↗
PubMed2000

The two-stage coagulation of milk proteins in the minimum of the heat coagulation time-pH profile of milk: effect of casein micelle size.

Milks with casein micelles larger or smaller than control milk were prepared by differential centrifugation. The heat stability of these modified milks increased markedly throughout the pH range 6.4 to 7.1 with decreasing casein micelle size. Within the region of the minimum in the heat coagulation time-pH profile, the control milk coagulated by a two-stage process, but the modified milks, because of their narrower casein micelle size distribution, coagulated by a single-stage process at the pH of minimum stability. The content of kappa-CN and protein hydration increased as the size of the casein micelles decreased, and the level of glycosylation of kappa-CN and protein surface hydrophobicity increased as a function of micelle size. The effect of casein micelle size on the heat stability of milk is likely to be related to changes in the above physico-chemical properties.

Animals↗
PubMed2000

Heat stability of buttermilk.

Buttermilk prepared on a laboratory scale from raw cream, or on a commercial scale from flash-pasteurized cream (90 degrees C for 1 to 2 s), exhibited a type B heat coagulation time-pH profile (i.e., stability increased as a function of pH). The high heat stability of buttermilk in the pH range of the minimum of a type A milk (pH approximately 6.8 to 7.0) appears to be related to differences in the serum phase constituents (i.e., a low calcium and beta-Lg concentration and a high nonmicellar kappa-CN content).

Animals↗
PubMed1999

Purification and characterization of an extracellular proline iminopeptidase from Arthrobacter nicotianae 9458.

An extracellular proline iminopeptidase, with a molecular mass of about 53 kDa, was purified from Arthrobacter nicotianae 9458 and characterized. The enzyme had temperature and pH optima of 37 degrees C and 8.0, respectively, was completely inactivated by heating for 1 min at 80 degrees C and showed highest activity on Pro-pNA. The proline iminopeptidase was characterized by activity at low temperature, NaCl concentrations up to 7.5% and by high sensitivity to pH values 6.0, serine enzyme inhibitor PMSF and divalent cations, Fe2+, Sn2+, Cu2+, Zn2+, Hg2+, Co2+ and Ni2+. The extracellular proline iminopeptidase from A. nicotianae 9458 was able to hydrolyze proline-containing peptides at the pH, temperature and NaCl concentration typical of the surface of smear-ripened cheese and may contribute to proteolysis of these cheeses during ripening.

Aminopeptidases↗
PubMed1999

Purification and characterization of two extracellular proteinases from Arthrobacter nicotianae 9458.

Two extracellular serine proteinases with molecular masses of about 53-55 and 70-72 kDa, were purified from Arthrobacter nicotianae 9458 and characterized. The enzymes differed with respect to temperature optimum, 55-60 and 37 degrees C, respectively, tolerance to low values of pH and temperature, heat stability, sensitivity to EDTA and sulfhydryl blocking agents, and hydrophobicity. Both proteinases were optimally active in the pH range of 9.0 and 9.5, had considerable activity at pH 6.0 on alpha s1- and beta-caseins, and tolerated NaCl over 5%. Specificity on casein fractions was generally similar and beta-casein was more susceptible to hydrolysis than alpha s1-casein. The proteinases of Arthrobacter spp. may play a significant role in ripening of the smear surface-ripened cheeses.

Arthrobacter↗
PubMed1999

Aspects of enzymology and biochemical properties of Brevibacterium linens relevant to cheese ripening: a review.

Brevibacterium linens is a major surface microorganism that is present in the smear of surface-ripened cheeses. The enzymology and biochemical characteristics of B. linens influence the ripening and final characteristics of smear surface-ripened cheeses. Proteolytic, peptidolytic, esterolytic, and lipolytic activities, which are of particular importance in the ripening process, are discussed in detail. This review also describes the production of volatile compounds, especially sulfur-containing ones, by B. linens, which are thought to be important in respect to the flavor of smear surface-ripened cheeses. The unique orange-colored carotenoids and the factors effecting their production by B. linens are also presented. The catabolism of aromatic amino acids, bacteriocin production, plasmids, and miscellaneous biochemical and physiological properties (peptidoglycan type, antibiotic resistance, insecticide degradation, and biotechnological applications) of B. linens are discussed. The problem associated with the current taxonomical classification of B. linens strains caused by strain variation is evaluated. Finally, the application of B. linens cell extracts or its proteolytic enzymes as cheese ripening accelerants for semi-hard or hard cheese varieties is considered.

Amino Acids↗
PubMed1997

Isolation and identification of further peptides in the diafiltration retentate of the water-soluble fraction of Cheddar cheese.

Several peptides were isolated from the diafiltration retentate, prepared using 10 kDa membranes, of the water-soluble extract from a commercial mature Cheddar cheese and identified by amino acid sequencing and mass spectrometry. Most of the peptides were from the N-terminal half of the beta-casein, but peptides from alpha s1- and alpha s2-caseins were also identified; the extract also contained alpha-lactalbumin. Identified peptides showed the important role played by lactococcal cell envelope proteinases in the degradation of primary proteolytic products from alpha s1- and beta-caseins, produced by chymosin and plasmin respectively. Plasmin seemed to be involved in the hydrolysation of alpha s2-casein. Several phosphopeptides were identified and the action of phosphatase on these peptides was evident.

Amino Acid Sequence↗
PubMed1997

Purification and characterization of a prolidase from Lactobacillus casei subsp. casei IFPL 731.

A peptidase showing a high level of specificity towards dipeptides of the X-Pro type was purified to homogeneity from the cell extract of Lactobacillus casei subsp. casei IFPL 731. The enzyme was a monomer having a molecular mass of 41 kDa. The pH and temperature optima were 6.5 to 7.5 and 55 degrees C, respectively. Metal chelating agents completely inhibited enzyme activity, indicating that the prolidase was a metalloenzyme. The Michaelis constant (K(m)) and Vmax for several proline-containing dipeptides were determined.

Amino Acid Sequence↗
PubMed1997

Specificity of an extracellular proteinase from Brevibacterium linens ATCC 9174 on bovine beta-casein.

The specificity of the extracellular proteinase from Brevibacterium linens ATCC 9174 on bovine beta-casein was studied. Hydrolysis was monitored over time by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (PAGE) and urea-PAGE. The major pH 4.6-soluble peptides were isolated by high-performance liquid chromatography and identified by N-terminal amino acid sequencing and mass spectrometry. The major sites of hydrolysis were Ser-18-Ser-19, Glu-20-Glu-21, Gln-56-Ser-57, Gln-72-Asn-73, Leu-77-Thr-78, Ala-101-Met-102, Phe-119-Thr-120, Leu-139-Leu-140, Ser-142-Trp-143, His-145-Gln-146, Gln-167-Ser-168, Gln-175-Lys-176, Tyr-180-Pro-181, and Phe-190-Leu-191. The proteinase had a broad specificity for the amino acid residues present at the P1 and P'1 positions but showed a preference for hydrophobic residues at the P2, P3, P4, P'2, P'3, and P'4 positions.

Amino Acid Sequence↗
PubMed1997

Isolation and characterization of a tributyrin esterase from Lactobacillus plantarum 2739.

An intracellular tributyrin esterase from Lactobacillus plantarum 2739 was purified to homogeneity by chromatography on DEAE cellulose, Sephacryl 200, carboxymethylcellulose, and Mono Q. The enzyme E2 was separated on DEAE cellulose from a second esterase, E1, and a minor esterase. Additional minor esterases were separated from E2 during chromatography on Sephacryl. E2 was a monomer with a relative molecular mass of approximately 85 kDa. The enzyme was most active at pH 7 and 35 degrees C and retained about 30% of maximal activity at pH 5 and about 18% at 12 degrees C. E2 was strongly inhibited by 1 mM phenylmethylsulfonyl fluoride, Hg2+, or Ag+ and was moderately stimulated by Ca2+ and Mg2+. E2 was active on beta-naphthyl esters of fatty acids from C2 to C10 with a preference for beta-naphthyl butyrate. Tributyrin and, to a lesser extent, tricaprylin and milk fat were also hydrolyzed. Partially purified E1 was more active on tributyrin than was E2. The sequence of the first 15 N-terminal amino acids of purified E2 was Ser-Asn-Glu-His-Thr-Gln-Glu-Val-Leu-Asn-Gln-Thr-Val-Ala-Asp. The enzyme showed a decimal reduction value at 70 degrees C of 2.5 min. The Michaelis constant of E2 on beta-naphthyl butyrate was 0.36 mM.

Amino Acid Sequence↗
PubMed1996

Acceleration of cheese ripening.

The characteristic aroma, flavour and texture of cheese develop during ripening of the cheese curd through the action of numerous enzymes derived from the cheese milk, the coagulant, starter and non-starter bacteria. Ripening is a slow and consequently an expensive process that is not fully predictable or controllable. Consequently, there are economic and possibly technological incentives to accelerate ripening. The principal methods by which this may be achieved are: an elevated ripening temperature, modified starters, exogenous enzymes and cheese slurries. The advantages, limitations, technical feasibility and commercial potential of these methods are discussed and compared.

Cheese↗
PubMed1996

Peptides inhibitory to endopeptidase and aminopeptidase from Lactococcus lactis ssp. lactis MG1363, released from bovine beta-casein by chymosin, trypsin or chymotrypsin.

Peptides inhibitory to the 70-kDa endopeptidase (PepO) from the cytoplasm of Lactococcus lactis ssp. lactis MG1363 were isolated from the supernatant (pH 4.6) of chymosin, tryptic and alpha-chymotryptic hydrolysates of beta-casein (beta-CN) by reversed-phase HPLC and identified by sequencing and mass spectrometry. Chymosin released beta-CN f193-209, kinetic constant (Ki) of which for inhibition of PepO was 60 microM. This peptide also inhibited (Ki = 1700 microM) the 95-kDa aminopeptidase (PepN) from L. lactis ssp. lactis MG 1363. Trypsin released two PepO-inhibitory peptides: one, beta-CN f69-97, was not degradable by PepO (Ki = 4.7 microM), while the other, beta-CN f141-163, was degradable by PepO but competitively inhibited hydrolysis of methionine enkephalin by PepO. A peptide, beta-CN f69-84, which inhibited PepO with a Ki of 8.1 microM, was isolated from the alpha-chymotryptic hydrolysate. Peptides released from beta-CN by trypsin or chymotrypsin had very little inhibitory activity against PepN. PepO degraded beta-CN f193-209 very slowly compared with the hydrolysis of methionine enkephalin. All four inhibitory peptides (beta-CN f193-209, f69-97, f69-84, f141-163) were readily degraded by thermolysin.

Amino Acid Sequence↗
PubMed1996

Specificity of an extracellular proteinase from Brevibacterium linens ATCC 9174 on bovine alpha s1-casein.

The specificity of the extracellular proteinase from Brevibacterium linens ATCC 9174 on bovine alpha s1-casein was studied. Hydrolysis was monitored over time by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (PAGE) and urea-PAGE. The major pH 4.6-soluble peptides were isolated by high-performance liquid chromatography and identified by N-terminal amino acid sequencing and mass spectrometry. The time course of peptide formation indicated that His-8-Gln-9, Ser-161-Gly-162, and either Gln-172-Tyr-173 or Phe-23-Phe-24 were the first, second, and third bonds cleaved, respectively. Other cleavage sites included Asn-19-Leu-20, Phe-32-Gly-33, Tyr-104-Lys-105, Leu-142-Ala-143, Phe-150-Arg-151, Gln-152-Phe-153, Leu-169-Gly-170, and Thr-171-Gln-172. The proteinase had a broad specificity for the amino acid residues at the P1 and P'1 positions but showed a preference for hydrophobic residues at the P2, P3, P4, P'2, P'3, and P'4 positions.

Amino Acid Sequence↗
PubMed1996

Purification and characterization of a dipeptidase from Pseudomonas fluorescens ATCC 948.

A dipeptidase from a cell extract of Pseudomonas fluorescens ATCC 948 was purified to homogeneity by ion-exchange chromatography, hydroxyapatite chromatography, gel filtration, and FPLC Phenyl Superose chromatography. The enzyme was located in the cytoplasmic fraction. The dipeptidase appeared to be a monomer with a molecular mass of about 46 kDa, and activity was optimal at pH 8.0 and 50 degrees C. Although activity decreased markedly at temperatures > 50 degrees C, about 50% of maximal activity was retained at 10 degrees C. The activity was inhibited by EDTA, but could be reactivated with Co2+ and partially reactivated with Ca2+. Reducing agents, such as dithiothreitol and 8-hydroxyquinoline, also strongly inhibited the enzyme. The dipeptidase hydrolyzed only dipeptides and showed a particular aptitude for substrates containing a hydrophobic AA at the N-terminus. Dipeptides containing a proline residue were not cleaved. Kinetic studies indicated that the dipeptidase hydrolyzed Leu-Leu with a Michaelis-Menten constant of 0.43 mM and a turnover number of 1812/s.

Calcium↗