Components Contributing to the Improvement of Meat Taste during Storage

The changes in both taste and taste components of beef, pork, and chicken during storage were examined.

The brothy taste intensity of pork and chicken was significantly stronger after conditioning than before. On the other hand, for beef, there was no significant difference in the brothy taste intensity before or after conditioning. The analysis of major taste components showed that the levels of free amino acids in all meats were higher after conditioning than before. The differences in the levels of free amino acids before versus after conditioning were large in pork and chicken and very small in beef. Oligopeptide levels were lower in beef after conditioning than before, but they were higher in pork and chicken after conditioning than before. These results corresponded to results of the sensory evaluation studies described above, indicating that free amino acids and oligopeptides contributed to the improvement of meat taste during storage.     

Biosynthetic Threonine Deaminase from Proteus morganii

Biosynthetic threonine deaminase was purified to an apparent homogeneous state from the cell extract of Proteus morganii, with an overall yield of 7.5%. The enzyme had a s⁰_20,w of 10.0 S, and the molecular weight was calculated to be approximately, 228,000. The molecular weight of a subunit of the enzyme was estimated to be 58,000 by sodium dodecyl sulfate gel electrophoresis. The enzyme seemed to have a tetrameric structure consisting of identical subunits. The enzyme had a marked yellow color with an absorption maximum at 415 nm and contained 2 mol of pyridoxal 5′-phosphate per mol. The threonine deaminase catalyzed the deamination of l-threonine, l-serine, l-cysteine and β-chloro-l-alanine. Km values for l-threonine and l-serine were 3.2 and 7.1 mm, respectively. The enzyme was not activated by AMP, ADP and ATP, but was inhibited by l-isoleucine. The Ki for l-isoleucine was 1.17 mm, and the inhibition was not recovered by l-valine. Treatment with mercuric chloride effectively protected the enzyme from inhibition by l-isoleucine.     

Antimicrobial Activity of Kumazasa (Sasa albo-marginata)

The organic solvent extract of Kumazasa leaves (Sasa albo-marginata) showed antimicrobial activity against bacteria, fungi and yeast. Kumazasa at a concentration of 0.2-1.0% showed stronger antimicrobial activity than potassium sorbate or sodium benzoate at the same concentration. Both acidic and phenolic fractions of the extract showed strong antimicrobial activity. Thirty acidic and phenolic compounds were identified by GC and GC-MS analysis. Acetic, propionic, benzoic, phenylacetic, salicylic, 3-hydroxybenzoic and o-anisic acids, and guaiacol, phenol, 4-ethylphenol, xylenol and 4-vinylphenol were the main components. It was estimated that these components play an important role in the formation of the antimicrobial activity of Kumazasa extract.     

13C-NMR Spectra and Streochemistry of Isoechinulins A,B and C

¹³C-NMR spectra of isoechinulins A, B and C, metabolites from Aspergillus ruber, were fully assigned on the basis of chemical shifts and multiplicities and comparison with their analogues. Taking advantage of the symmetrical structure of the diketopiperazine ring, the stereochemistry of the trisubstituted carbon-carbon double bond in a dehydrotryptophyl moiety was determined as Z (cis) by measuring the coupling constants, , in the proton nondecoupled spectrum of isoechinulin B.     

Carboxyl Proteinase from the Wood Deteriorating Basidiomycete Pycnoporus coccineus :Substrate Specificity with Oxidized Insulin Peptide B1 ~ B16 and B15 ~ B24, Angiotensin and Proangiotensin

The specificity of highly purified carboxyl proteinase from Pycnoporus coccineus (formerly designated Trametes sanguined) was investigated with oligopeptides at pH 2.7. Hydrolysis of oxidized insulin peptide Bl ~ B16 was observed at two peptide bonds (His¹⁰-Leu¹¹ and Ala¹⁴-Leu¹⁵) during 3-hr incubation. The enzyme did not hydrolyze oxidized insulin peptide B15 ~ B24. Hydrolysis of angiotensin (formerly designated angiotensin II) was observed at the Tyr⁴-Ile⁵ bond. Hydrolysis of proangiotensin (formerly designated angiotensin I) was also at the Tyr⁴-Ile⁵ bond. In conclusion, peptide bonds which have a hydrophobic amino acid in the P′₁ position (as defined by Schechter and Berger, Biochem. Biophys. Res. Commun., 27, 157 (1967)) are preferentially cleaved by the trypsinogen activating carboxyl proteinase of Pycnoporus coccineus.     

Simple Synthesis of (R)-5-Hexadecanolide

Chemical modification of tryptophan residues in abrin-a with N-bromosuccinimide (NBS) was studied with regard to saccharide-binding. The number of tryptophan residues available for NBS oxidation increased with lowering pH, and 11 out of the 13 tryptophan residues in abrin-a were eventually modified with NBS at pH 4.0, while 6 tryptophan residues were modified at pH 6.0 in the absence of specific saccharides. Modification of tryptophan residues at pH 6.0 greatly decreased the saccharide-binding ability of abrin-a, and only 2% of the hemagglutinating activity was retained after modification of 3 residues/mol. When the modification was done in the presence of lactose or galactose, 1 out of 3 residues/mol remained unmodified with a retention of a fairly high hemagglutinating activity. However, GalNAc did not show such a protective effect. NBS-oxidation led to a great loss of the fluorescence of abrin-a, and after modification of 3 tryptophan residues/mol, the fluorescence intensity at 345 nm was only 38% of that of the unmodified abrin-a. The binding of lactose to abrin-a altered the environment of the tryptophan residue at the saccharide-binding site of abrin-a, leading to a blue shift of the fluorescence spectrum. The ability to generate such fluorescence spectroscopic changes induced by lactose-binding was retained in the derivative in which 2 tryptophan residues/mol were oxidized in the presence of lactose, but not in the derivative in which 3 tryptophan residues/mol were oxidized in the absence of lactose. Importance of the tryptophan residue(s) in the saccharide-binding of abrin-a is suggested.     

Studies on Browning Reactions between Sugars and Amino Compounds

N-d-Glucosyl-p-aminobenzoic acid has been found to form melanoidins in methanol solution acidified with hydrogen chloride at 25°. From the reaction mixture 5-hydroxymethyl-furfural (HMF) has been isolated and identified as its 2,4-dinitrophenylhydrazone. So, comparisons between the browning reaction of HMF or furfural with aromatic amine and that of the corresponding n-glycosides have been made under the same condition. From the results obtained, it has been shown that, under the described condition, furfural is almost inactive for browning, while on the contrary, HMF is active and plays an important role in the browning reaction.     

S-Carboxymethylcysteine Synthase from Escherichia coli

An enzyme that catalyzes the synthesis of S-carboxymethyl- l-cysteine from 3-chloro- l-alanine (3-Cl-Ala) and thioglycolic acid was found in Escherichia coli W3110 and was designated as S- carboxymethyl-l-cysteine synthase. It was purified from the cell-free extract to electrophoretic homogeneity and was crystallized. The enzyme has a molecular weight of 84,000 and gave one band corresponding to a molecular weight of 37,000 on SDS-polyacrylamide gel electrophoresis. The purified enzyme catalyzed the β-replacement reactions between 3-CI-AIa and various thiol compounds. The apparent Km values for 3-Cl-Ala and thioglycolic acid were 40 mM and 15.4 mM. The enzyme showed very low activity as to the α,β-elimination reaction with 3-Cl-Ala and l-serine. It was not inactivated on the incubation with 3-Cl-Ala. The absorption spectrum of the enzyme shows a maximum at 412 nm, indicating that it contains pyridoxal phosphate as a cofactor. The N-terminal amino acid sequence was determined and the corresponding sequence was detected in the protein sequence data bank, but no homogeneous sequence was found.     

Applying Proteolytic Enzymes on Soybean

An indole derivative having blue fluorescence was produced in cooked soybean digested at 37°C for 24 hr with an acid proteinase Molsin (optimum pH: 2.8) from Aspergillus saitoi or a usual acid proteinase pepsin (optimum pH: 1.6) from beef stomach. This indole derivative was identical with a condensation product from l-tryptophan and n-hexanal. Based on MS, NMR, IR and UV spectrometry, the condensation product was identified as l-pentyl-2, 3, 4, 9-tetrahydro-lH-pyrido [3, 4-b]-indole-3-carboxylic acid [trivial name: 1-pentyl-l, 2, 3, 4-tetrahydro-2-carboline carboxylic acid-(3)].

Data were presented of the formation of the above indole derivative and of the resulting consumption of l-tryptophan and n-hexanal.

The possible ocurrence of the formation of Harmala alkaloids, i.e. 2-carboline derivatives, through in vitro digestion of soybean with acid proteinases was discussed.

A carbonyl-trapping ability of l-tryptophan was suggested.