Showing papers in "Journal of Food Biochemistry in 1992"
TL;DR: In this article, myosin heavy chain (MHC) content of cooked gels of pollock and croaker surimi decreased during preincubation (setting) at temperatures ranging from 4-50C.
Abstract: Myosin heavy chain (MHC) content of cooked gels of pollock and croaker surimi decreased during preincubation (“setting”) at temperatures ranging from 4–50C. Decreases in MHC content were attributed to either nondisulfide covalent cross-linking or proteolysis. Depending upon which process dominated at a given temperature, formation of stronger or weaker gels occurred, respectively. Maximum production of cross-linked polymers occurred at the optimum setting temperatures, i.e., at 25C for pollock surimi and 40C for croaker surimi. Subsequent cooking of these set gels at 90C decreased the amount of cross-linked polymers formed at the optimum setting temperature. Addition of free lysine-HCl inhibited formation of cross-linked polymers of MHC during setting and the increase in cooked gel strength for both species. This supports published evidence that cross-linking of MHC during setting may be of the e-amino-(γ-glutamyl) lysine I type, mediated by a transglutaminase enzyme.
141 citations
TL;DR: Electrophoretic analyses indicated that one water soluble protein dominates the almond protein composition, and pepsin was the most efficient in hydrolyzing the almond proteins.
Abstract: The major U.S. marketing varieties of almonds contained moisture, protein, fat, and ash in the range 4.35–5.86%, 16.42–22.17%, 53.59–56.05%, and 2.69–2.93%, respectively. Two fatty acids, oleic (range 52.44–67.07%) and linoleic (range 22.05–38.67%) accounted for up to 90% of the total fat. The majority of almond proteins (≥ 95%) are water soluble with a minimum solubility at pH ≤ 4.0. Sodium chloride (1.0 M) decreased the almond protein solubility in aqueous medium. Electrophoretic analyses indicated that one water soluble protein dominates the almond protein composition. This oligomeric major protein is made up of two kinds of polypeptides (molecular weight range 20,000–22,000 and 38,000–41,000) linked via disulfide bonds. Among the proteases tested, pepsin was the most efficient in hydrolyzing the almond proteins.
90 citations
TL;DR: In this paper, myofibrils and salt-soluble (SSP) proteins of chicken breast muscle were heated to induce gels and dynamic oscillating measurements showed multiple transitions in the shear storage modulus and loss modulus for all three protein fractions in the temperature range of 40-65C.
Abstract: Suspensions of myofibrils and salt-soluble (SSP) or insoluble (SIP) proteins of chicken breast muscle in 0.6 M NaCl at pH 6.0 were heated to induce gels. Dynamic oscillating measurements showed multiple transitions in the shear storage modulus and loss modulus for all three protein fractions in the temperature range of 40–65C. However, changes in these viscoelasticities were most pronounced for SSP and least appreciable for SIP. Gel penetration test also revealed a descending order of SSP < myofibrils < SIP in gel strength. The three fractions of myofibrillar proteins appeared to follow a similar gelation mechanism but vary in the density of the gel networks.
90 citations
TL;DR: In this article, the authors present a discussion of thermodynamic and enzymatic conversations of precursors to flavor compounds, including the cyclization of Geranyl Pyrophosphate to (+)-Sabinene Lipases and Carboxylester-Lipase Mediated Reactions.
Abstract: Thermal and Enzymatic Conversions of Precursors to Flavor Compounds: An Overview Monoterpene Biosynthesis: The Cyclization of Geranyl Pyrophosphate to (+)-Sabinene Lipases: Useful Biocatalysts for Enantioselective Reactions of Chiral Flavor Compounds Carboxylester-Lipase Mediated Reactions: A Versatile Route to Target the Chiral Molecules Biosynthesis and Studies on the Biotechnological Production of Aliphatic *g- and *d-Lactones Precursor Atmospheric Technology: Efficient Aroma Enrichment in Fruit Cells Glycosidic Precursors of Varietal Grape and Wine Flavor Glucosides of Limonoids Oxytenated C[1[3-Norisoprenoids: Important Flavor Precursors Free and Bound Flavor Constituents of White-Fleshed Nectarine Thermally Degraded Thiamin: A Potent Source of Interesting Flavor Compounds Studies on the Formation of Furaneol in Heat-Processed Foods Flavor Compounds Formed from Lipids by Heat Treatment Formation of Meat-like Flavor Compounds Peptides as Flavor Precursors in Model Maillard Reactions Meat Flavor Generation from Cysteine and Sugars Analysis and Reactivity of Glucosones Formation of Smoke Flavor Compounds by Thermal Lignin Degradation Reaction Kinetics for the Formation of Heterocyclic Compounds in a Temperature and Pressure Controlled Experiment
68 citations
TL;DR: Findings suggested that the tough texture problem, sometimes observed in farmed sturgeons, may be minimized by allowing the sturgeon meat to go through rigor prior to cooking.
Abstract: ATP depletion and other biochemical changes were related to texture indices of cooked sturgeon meat from struggled and anesthetized fish. The rates of ATP depletion, pH decline and time of rigor onset were slow in both sturgeon groups compared to other finfish. ATP depletion and accumulation of inosine and hypoxanthine were significantly faster in sturgeon allowed to struggle before death than in anesthetized fish. Penetrometer tests revealed that cooked sturgeon meat was firmer prior to ATP depletion and the onset of rigor than in the postrigor state. Fish allowed to struggle prior to death had a softer cooked meat than anesthetized fish during the first few days of iced storage. Compression tests showed that texture of cooked meat was firmest when the muscle was in rigor and also showed that meat from struggled fish was softer than that from anesthetized fish. These findings suggested that the tough texture problem, sometimes observed in farmed sturgeon, may be minimized by allowing the sturgeon meat to go through rigor prior to cooking.
49 citations
TL;DR: In this paper, the activities of subcutaneous adipose tissue lipases and esterases were assayed at different stages (0 to 15 months) in the processing of dry-cured ham.
Abstract: The activities of subcutaneous adipose tissue lipases and esterases were assayed at different stages (0 to 15 months) in the processing of dry-cured ham. The formation of free fatty acids during the process was also determined. Maximal generation of free fatty acids occurred during the first 10 months. Simultaneously, the triglyceride content decreased while the diglycerides increased during the aging period. Neutral and basic lipases showed maximal activity at the beginning of the process but only neutral lipase remained as the main enzyme responsible for the reported lipolysis during the drying ripening stages. Adipose tissue esterases showed excellent stability but the generation of volatile free fatty acids was negligible, suggesting a minor role of these enzymes.
38 citations
TL;DR: The liver extract of squid Illex argentinus has a proteolytic activity at pH 2.6-3.1, with optimum at pH 6.1 as mentioned in this paper, where the sarcoplasmic and myofibrillar proteins were hydrolyzed to low molecular fractions.
Abstract: The liver extract of squid Illex argentinus has a proteolytic activity at pH 2–8, with optimum at pH 2.6–3.1. At pH 6 the enzymes retain about 30 and 55% of the maximum proteolytic activity towards hemoglobin and casein, respectively. In squid mantle meat treated with the extract 24 h at 4C and 20C, the sarcoplasmic and myofibrillar proteins were hydrolyzed to low molecular fractions, as was shown by SDS-PAGE. Soaking isolated collagen fibers in the liver extract resulted after 24 h in almost complete solubilization of the fibers in buffered SDS/urea solutions. The solubilized product contained only low molecular weight components. A significant hydrolysis of the proteins in the squid mantle, treated with the liver extract at 20 or 4C, was accompanied by a decrease in toughness of the cooked product by about 65 and 40%, respectively, as compared to the toughness of untreated cooked samples. Cooking of the mantle directly in the liver extract had practically no tenderizing effect.
21 citations
TL;DR: In this paper, a modified diffusion plate was evaluated for its efficacy in measuring polygalacturonase (PG) activities in simulated and commercial cucumber pickle brines, and it was shown that clear zone diameters formed in the diffusion plate assay were highly correlated to changes in specific viscosity obtained by the conventional viscometry assay procedure.
Abstract: A modified diffusion plate assay was evaluated for its efficacy in measuring polygalacturonase (PG) activities in simulated and commercial cucumber pickle brines. The diffusion plate assay was capable of detecting low PG activities (7 × 10-5 PG units/mL). Clear zone diameters formed in the diffusion plate assay were highly correlated to changes in specific viscosity obtained by the conventional viscometry assay procedure. Slight, dark-stained zones appeared with an ionic strength of 1.6 (NaCl) and increased in diameter with increasing ionic strength. Ionic strengths of commercial pickle brines (0.9–1.8) did not interfere with the diffusion plate assay for detecting PG activity. The diffusion plate assay was observed to be a suitable and convenient alternative to the viscometry procedure for monitoring PG activities in brines used for the bulk storage of pickles.
17 citations
TL;DR: The black velvet tamarind is potentially a good source of nutrients for human food and animal feed and has potential for use as a food ingredient for humans and animals.
Abstract: Fruits of Black (African) velvet tamarind (Dialium guineense Wild), separated into pulp and seed, were analyzed for proximate composition, selected inorganic ions and vitamin C. Significant differences (P > 0.001) were observed in the values of moisture (5.9 and 4.9), organic matter (97.5 and 98.2), dry matter (94.1 and 95.1), crude protein (15.7 and 4.2), crude fat (5.4 and 2.6), ash (2.5 and 1.8), crude fiber (6.6 and 2.2) and total carbohydrate (70.6 and 86.6) for seed and pulp, respectively. Expectedly, the level of ascorbic acid was significantly (P > 0.001) higher in the pulp (35.7 mg/100g) than in the seed (6.4 mg/100g). Varying levels of selected inorganic ions were also detected. The black velvet tamarind is potentially a good source of nutrients for human food and animal feed.
17 citations
TL;DR: In this paper, a Preparative Isoelectric Focusing (IEF) method was applied to separate skim milk proteins using the Rotofor device in a pH 3-10 gradient containing 4 M urea/1% triton X-100.
Abstract: A preparative isoelectric focusing (IEF) method was applied to separate skim milk proteins using the Rotofor device in a pH 3–10 gradient containing 4 M urea/1% triton X-100. Each of the 20 fractions obtained from the Rotofor device was then analyzed by polyacrylamide gel electrophoresis (PAGE). Both urea-PAGE and SDS-PAGE were used to separate purified caseins and skim milk resulting in comparable two-dimensional patterns. The major bovine caseins (αs1, αs2, β, K-casein) were resolved better on urea-PAGE. The αs1-and β-casein were focused at pH ∼ 4.5 and 4.8, respectively, whereas αs2-caseins focused as several bands at pH 6.2–6.8. The A variant of K-casein focuses at Fractions 6–9 which is slightly more acidic than the B variant that focuses at Fractions 7–13. No sample pretreatment was necessary to analyze skim milk proteins and urea-PAGE clearly resolved bands of all major caseins and whey proteins. Preparative isoelectric focusing followed by PAGE was found to be a useful and powerful method to analyze milk proteins in two-dimensions. This technique facilitates the analysis of the relative amounts of proteins in milk, as well as simplifies the detection of changes and foreign proteins in milk.
15 citations
TL;DR: The oligopeptide fraction, when compared to a simulated free amino acid mixture, was significantly more effective in enhancing the mucosal protein content in fasted rats and methotrexate-administrated rats fed the oligopePTide fraction were more resistant to methotRexate-induced enterocolitis.
Abstract: In order to utilize peptide-bound rather than free glutamine for enteral nutrition, a method was developed for producing a high-glutamine oligopeptide mixture from gluten by treatment with protease. Commercially available gluten was hydrolyzed first with molsin and then with actinase to produce a hydrolysate. Sephadex G-15 adsorption chromatography applied to the hydrolysate afforded a nearly 50% glutamine containing oligopeptide fraction with a yield of 33% on a nitrogen basis. We evaluated this oligopeptide fraction by feeding trials with fasted and methotrexate-administrated rats. The oligopeptide fraction, when compared to a simulated free amino acid mixture, was significantly more effective in enhancing the mucosal protein content in fasted rats. Also, methotrexate-administrated rats fed the oligopeptide fraction were more resistant to methotrexate-induced enterocolitis than those fed a simulated free amino acid mixture.
TL;DR: Exposure to pH 12 or 5 M urea were the most effective chemical treatments for reducing hemagglutinating activity and Terminal sialic acid residues may not be an important determinant of PHA-P activity.
Abstract: Lectins are toxic heat-stable glycoproteins, termed phytohemagglutinins, that depress the nutritional quality of Phaseolus vulgaris. Purified phytohemagglutinin (PHA-P) was separated from dark red kidney beans (Montcalm cultivar) by affinity chromatography and subjected to various treatments including: thermal (70–100C; chemical (2 M NaCl, 5 M urea, 5% mercaptoethanol, pH 12 and pH 3) and enzymatic (peptidases, proteases and carbohydrases). At 70C, the PHA-P activity decreased with a linear response. Exposure to pH 12 or 5 M urea were the most effective chemical treatments for reducing hemagglutinating activity. Treatment with proteases resulted in 88–98 % reductions in PHA-P activity. Man-nosidase treatment resulted in a slight but significant (P < 0.01) reduction in activity; however, amylases and neuraminidase had no effect on activity. Terminal sialic acid residues may not be an important determinant of PHA-P activity.
TL;DR: Results suggest that glucose in molasses functions as a repressor of invertase formation in L. plantarum and S. faecium, and that the use of derepressed mutants should allow a significant decrease in the amount of molasses required for a satisfactory fermentation.
Abstract: The purpose of this study was to determine the optimum concentration of blackstrap molasses required in conjunction with the use of several species of homofermentative lactic acid bacteria in the fermentation of hydrolyzed cod gurry. Blackstrap molasses at a concentration of 7.5% was found to be optimum for achieving a successful lactic acid fermentation of hydrolyzed cod gurry. Among the three homofermentative lactic acid bacteria studied (Lactobacillus plantarum, Pediococcus acidilactici and Streptococcus faecium) L. plantarum resulted in the most rapid fementation. S. faecium was the least desirable bacterium on the basis of fermentation rates and extent of pH decrease after 72 h of incubation. All three organisms failed to utilize significantly the sucrose derived from molasses, even though sucrose was the most abundant carbohydrate in the molasses. P. acidilactici was unable to utilize sucrose when present as a sole carbohydrate, while L. plantarum and S. faecium decreased the pH in broth cultures with sucrose as a sole carbohydrate. These results suggest that glucose in molasses functions as a repressor of invertase formation in L. plantarum and S. faecium, and that the use of derepressed mutants should allow a significant decrease in the amount of molasses required for a satisfactory fermentation.
TL;DR: In this article, β-Galactosidases from E. coli and Aspergillus flavus were encapsulated in liposomes using the reverse phase evaporation method.
Abstract: β-Galactosidases from E. coli and Aspergillus flavus were encapsulated in liposomes using the reverse-phase evaporation method. There was an inverse relationship between buffer molarity and encapsulation efficiency. The presence of cholesterol and stearylamine or dicetylphosphate along with phosphatidyl choline increased encapsulation efficiency significantly. Liposomes containing either bacterial or fungal β-galactosidase were stable in buffer as well as freshly pasteurized milk for up to 20 days at 4C. Lactose hydrolysis was negligible in milk containing liposomes with bacterial β-galactosidase, while there was significant (25%) hydrolysis of lactose in milk containing liposomes with fungal β-galactosidase during 20 days of storage at 4C. Results of this study suggest that liposomes containing β-galactosidase can be prepared and added to milk without affecting the lactose content for up to 20 days of refrigeration (4C).
TL;DR: In this article, Red Globe peaches were harvested at the threshold-mature stage and either stored at OC after preripening at 20C for 48 h or stored directly at 2C.
Abstract: Red Globe peaches were harvested at the threshold-mature stage and either stored at OC after preripening at 20C for 48 h or stored directly at 2C. Total pectin increased from 7.49 mg/g fresh weight in the threshold-mature sample to 10.21 mg/g in pre-ripened fruit stored at OC and 12.83 mg/g in fruits stored directly at 2C. Depending on extraction and storage protocol, between 26% and 73% of total pectin was solubilized. Chelator-soluble fractions had a low degree of esterification (DE ca. 20%), whereas other fractions were highly methylated (DE ca. 56% to 74%). Average DE did not vary between samples. DEAE-cellulose chromatography revealed an uneven distribution of methoxyl groups. Two prominent peaks were observed in chromatograms of chelator-soluble extracts from threshold-mature fruit and fruit stored directly at 2C. One peak was observed in chelator-soluble pectin from preripened fruit stored at OC.
TL;DR: The effect of redox potential in the range +100 to −250 mV on the muscle cathepsins B, H and L, lysosomal acid lipase and acid esterase and on neutral and basic lipases and neutral esterases from adipose tissue is presented.
Abstract: This work presents the effect of redox potential in the range +100 to −250 mV on the muscle cathepsins B, H and L, lysosomal acid lipase and acid esterase and on neutral and basic lipases and neutral esterase from adipose tissue. Cathepsins B, H and L need reducing conditions (below −50 mV) for maximal activity. Lysosomal acid lipase remains unaffected while activity of muscle acid esterase decreases sharply below −175 mV. The activity of basic lipase from adipose tissue is also reduced below −80 mV while neutral lipase remains unaffected. The activity of neutral esterase is drastically reduced to negligible values below −100 mV. Copyright © 1992, Wiley Blackwell. All rights reserved
TL;DR: Among the three homofermentative bacteria studied, Lactobacillus plantarum, Streptococcus faecium, and Pediococcus acidilactici, consistent results regarding the most rapid rate of pH reduction and the lowest final pH were obtained with L. Plantarum.
Abstract: The purpose of this study was to determine the optimum concentrations of corn syrup required with the use of several species of homofermentative lactic acid bacteria and a commercial mixed culture inoculum in the fermentation of hydrolyzed cod gurry. Among the three homofermentative bacteria studied, Lactobacillus plantarum, Streptococcus faecium, and Pediococcus acidilactici, consistent results regarding the most rapid rate of pH reduction and the lowest final pH were obtained with L. plantarum. S. faecium was the least desirable organism on the basis of fermentation rates and the extent of pH reduction after 72 h of incubation. Corn syrup at a concentration of 4.0% (w/w) was found to be optimum for achieving a rapid and successful lactic acid fermentation of hydrolyzed cod gurry with Lactobacillus plantarum. Corn syrup at a concentration of 4.5% was found to be optimum for rapidly achieving a final pH of 4.0 with the commercial mixed inoculum Stabisil. The maltose content of corn syrup was utilized at a notably slower rate than glucose by all three microorganisms during the first 18 h of incubation. Throughout the fermentations, maltotriose was utilized significantly by only L. plantarum.
TL;DR: In this paper, three different methodologies were used to assess the glucosinolate content in four broccoli cultivars: thymol, enzyme immobilization and gas liquid chromatography (GLC) techniques.
Abstract: Three different methodologies were used to assess the glucosinolate content in four broccoli cultivars. The assessment was performed by the thymol, enzyme immobilization and gas liquid chromatography (GLC) techniques. The cultivars used were Green Valiant, Green Duke, Marathon and Samurai. The three techniques demonstrated that Samurai and Green Valiant were the cultivars with the highest content of glucosinolates. It was also evident that, compared to stem and leaves, the floret of the four cultivars exhibited in general the highest amount of this component. Of the tested methodologies, the GLC technique showed the lowest data variability, although this technique was unable to estimate all the glucosinolates present in the broccoli samples because of its poor performance for the quantitation of indole and sulfinyl glucosinolates. In conclusion, the thymol technique appeared the most adequate procedure for the assessment of glucosinolates in broccoli samples.
TL;DR: In this article, it was shown that for either bound or soluble iron, there is a common rate-determining step for both bound and non-bound iron, and that both of them are similar with respect to their ability to catalyze lipid oxidation and their generation of hydroxyl free radicals.
Abstract: Iron over the range of 25–250 μM FeCl3 in the presence of ADP and histidine bound in increasing amounts to fish sarcoplasmic reticulum. Binding of iron was not reversed either by washing in water or after oxidation of the membrane lipid. There was no difference in the rate of lipid oxidation measured as TBA-reactive substances catalyzed by iron bound to the sarcoplasmic reticulum or by iron in the soluble phase of the assay medium when expressed on an iron basis. These results imply that for either bound or soluble iron there is a common rate-determining step. In addition, soluble and bound iron were similar with respect to both inhibition by thiourea of their ability to catalyze lipid oxidation and their generation of hydroxyl free radicals measured by production of methane sulfinic acid from dimethyl sulfoxide in the presence of hypoxanthine and xanthine oxidase.
TL;DR: In this article, the authors determined the ATP degradation products in Chilipepper rockfish by HPLC and found that AMP and hypoxanthine levels were low and did not change much during storage.
Abstract: Trimethylamine (TMA) and ammonia contents in Chilipepper rockfishes were determined by ion specific electrodes, as a late indicator of fish freshness. After 9 days of storage in ice, TMA contents significantly increased, indicating that bacterial spoilage was in progress. The pattern of changes in ammonia contents was similar to that of TMA.
Determination of ATP degradation products in Chilipepper rockfish by HPLC showed that AMP and hypoxanthine levels were low and did not change much during storage. The concentration of IMP initially increased and then continuously decreased as inosine accumulated. Only trace amounts of hypoxanthine were detected in rockfish tissues. Chilipepper rockfish appears to differ from other Sebastes species in that ATP degradation results in inosine accumulation rather than hypoxanthine.
TL;DR: In this paper, a procedure was developed to isolate 10-oxo-trans-8-decenoic acid (ODA) from mushrooms using column and thin-layer chromatography.
Abstract: A procedure was developed to isolate 10-oxo-trans-8-decenoic acid (ODA) from mushrooms. ODA was produced by homogenizing mushrooms in phosphate buffer with added linoleic acid, extracted from the supernatant after centrifugation, and purified using column and thin-layer chromatography. The purified compound was then characterized using ultraviolet, infrared and mass spectrometry, and nuclear magnetic resonance spectroscopy.
The purified compound, containing 97.5% ODA, was a white, waxy solid with a pKa of 4.68. ODA was soluble in acetone, chloroform, ethanol, ethyl ether, methanol, methylene chloride and water, and slightly soluble in pentane, hexane, heptane and benzene. The TBA test was found to be a viable method for the quantification of ODA.
TL;DR: Three isozymes of polyphenol oxidase (PPO I, PPO II and PPO III) were purified from lobster by ion-exchange chromatography and preparative isoelectric focusing using a Rotofor cell, and the catalytic specificities of the PPO isoz enzymes were relatively higher with dihydroxyphenylalanine as substrate than with chlorogenic acid.
Abstract: Three isozymes of polyphenol oxidase (PPO I, PPO II and PPO III) were purified from lobster (Homarus americanus) by ion-exchange chromatography and preparative isoelectric focusing using a Rotofor cell. The purified isozymes migrated as single protein bands in polyacrylamide gels with Rf values corresponding to molecular weights of 32,180, 35,480 and 39,300, respectively. The pI values of the PPO isozymes were 3.89, 4.26 and 4.54, respectively. PPO I was most active at pH 6.5 and most stable from pH 6.0 to 7.0; PPO II was most active within the pH range 6.0 to 7.0, and most stable within the pH range 4.0 to 9.0; while PPO III was most active at pH 7.0 and most stable in the pH range 6.0 to 8.0. The temperature optimum for the PPO-dihydroxyphenylalanine oxidation reaction was 35C with PPO I and 45C with PPO II or III. Lobster PPO I lost about 30% of its initial activity after 30 min incubation at 45C, while PPO II and II retained virtually all their activity after the same heat treatment. The catalytic specificities of the PPO isozymes were relatively higher with dihydroxyphenylalanine as substrate than with chlorogenic acid.
TL;DR: Using optical microscopy and scanning electron microscopy, the reddish-purple color produced by staining with toluisine-blue turned lighter during curing, suggesting that the collagen in salmon-nose cartilage changes qualitatively during curing.
Abstract: liced salmon-nose cartilage was cured in 4% acetic acid up to 168h. Using optical microscopy, we observed the reddish-purple color produced by staining with toluisine-blue turned lighter during curing. This meant that the mucopoly-saccharide level of cartilage matrix decreased, causing the structure of the cartilage to become porous. In addition, using scanning electron microscopy, loosenings of collagen fibers was observed after 72 h of curing, thus making the structure of the cartilage fragile. DSC thermograms showed that the denaturation temperature of the native collagen fibers was lowered and an additional peak appeared during curing. These findings lead us to suggest that the collagen in salmon-nose cartilage changes qualitatively during curing.
TL;DR: The effects of various food components on the in vitro digestibility of proteins, measured by the immobilized digestive enzyme assay (IDEA) system, were investigated in this paper, showing that the presence of emulsified (1% lecithin) vegetable oil (0, 0.5, 1 and 2%) did not affect digestibility.
Abstract: The effects of various food components on the in vitro digestibility of proteins, measured by the immobilized digestive enzyme assay (IDEA) system, were investigated. The digestibility of unprocessed and processed sodium caseinate and soybean protein was examined. Varying concentrations of sucrose (0, 5, 10 and 20%) or starch (0, 0.5, 1 and 2%) had no significant effects on digestibility of protein. Similarly, the presence of emulsified (1% lecithin) vegetable oil (0, 0.5, 1 and 2%) did not affect digestibility. Therefore, these common ingredients of foods did not affect the extent of hydrolysis of the protein samples under the conditions of the IDEA method, suggesting that this assay is suitable for use with complex foods.
TL;DR: In this article, the effects of ozone (O 3 ) introduced into recycled cucumber pickle brines on cellulase (Cx) and polygalacturonase (PG) activities, potassium sorbate, color and bacteria content were examined.
Abstract: The effects of ozone (O 3 ) introduced into recycled cucumber pickle brines on cellulase (Cx) and polygalacturonase (PG) activities, potassium sorbate, color and bacteria content were examined. Cx and PG were effectively inactivated by O 3 . The amount of O 3 required to inactivate a large range of Cx and PG activities was about 176 to 246 μg/ml of recycled brine that was added in 10-14 min. The O 3 treatments also destroyed potassium sorbate and bacteria in the recycled brines. While being treated with O 3 , brine color faded as measured at 400 nm, and after exposure to O 3 , the color gradually returned to its original absorbance. Utilization of O 3 provides an alternative method of inactivating Cx and PG in recycled pickle brines; however, the effects of O 3 treated brines on cucumber fermentation and subsequent pickle quality must also be evaluated prior to implementing commercial treatments
TL;DR: The immobilized linamarase was more stable than the free enzyme at room temperature (25C) and 41C and gave a bell-shaped curve with maximal activity at pH 6.0; these data indicated two catalytic ionizable residues with pKa 5.7 and pKa 6.5.
Abstract: Linamarase from cassava cortex was immobilized on polyacrylamide gel. A crude extract of the enzyme containing most of the intracellular proteins was used for the technique to simulate the enzyme in cassava. Immobilization of the enzyme increased the Michaelis constants for all substrates when compared with the native enzyme. Both free and immobilized linamarase hydrolyzed p-nitrophenylβ D-glucoside, linamarin and p-nitrophenylβ-D-galactoside.
The immobilized enzyme was more stable than the free enzyme at room temperature (25C) and 41C. Both forms gave a bell-shaped curve with maximal activity at pH 6.0; these data indicated two catalytic ionizable residues with pKa 5.7 and pKa 6.5.
TL;DR: A biotinylation-bioselective adsorption procedure was developed for single-step purification of bovine sulfhydryl oxidase from solubilized skim milk membrane vesicles and the resulting enzyme preparation appeared to be homogeneous by gel electrophoresis and the specific activity increased over 3000 fold in comparison to whey.
Abstract: A biotinylation-bioselective adsorption procedure was developed for single-step purification of bovine sulfhydryl oxidase from solubilized skim milk membrane vesicles. Sulfhydryl oxidase was specifically biotinylated by reaction of its chemically reactive sulfhydryl group with a disulfide-containing biotinylation reagent giving a mixed disulfide between the enzyme and the biotinyl moiety. The biotinylated enzyme was then selectively adsorbed on a monomeric avidin matrix. After washing all nonspecifically bound proteins from the matrix, the enzyme was released by reduction of the disulfide with dithiothreitol. Both the biotinylation and the isolation are performed at pH 7.0 under extremely mild conditions. The resulting enzyme preparation appeared to be homogeneous by gel electrophoresis and the specific activity increased over 3000 fold in comparison to whey. The monomeric avidin matrix can be regenerated and used indefinitely. This purification procedure should be generally applicable to proteins with a chemically reactive sulfhydryl group.
TL;DR: The present research showed that histidine residues of rat plasma albumin were less susceptible to destruction than those of bovine serum albumin and that ascorbate and copper ions decrease the histidine content of rat serumalbumin under in vitro and in vivo conditions.
Abstract: It was recently reported by us that the histidine content of pure bovine serum albumin decreased from 15.6 to 2.2 residues per mol when incubated aerobically with 5 mM ascorbate and 0.8 mM copper sulfate at pH 6.5, 25C and 22 h in a model experiment. The purpose of the present research was to determine if ascorbate and copper ions decrease the histidine content of rat serum albumin under in vitro and in vivo conditions. The present research showed that histidine residues of rat plasma albumin were less susceptible to destruction than those of bovine serum albumin. Previously isolated rat serum albumin lost 12.2 of 16.6 histidine residues per mol after 24 h incubation with 50 mM ascorbate-8 mM copper sulfate at pH 7.0 and 37C. When fresh rat plasma was incubated under identical conditions with 50 mM ascorbate-8 mM copper sulfate and the albumin subsequently isolated the histidine lost was 6.4 of the 16.6 residues. No loss of histidine occurred in either experiment under anaerobic conditions (N2). When incubated for 5 h at 37C and pH 7 with 0.5, 1.0 and 3.0 mM ascorbate-8 mM copper sulfate, fresh rat plasma albumin lost 2.6, 2.9 and 2.8 histidine residues, respectively. When rats were intubated with ascorbate-copper sulfate (50 and 8 mM final concentrations, respectively), 1.2 histidine residues were lost after 2 h.
TL;DR: The kinetic mechanism of catalysis by malic dehydrogenase isolated from yam (Dioscorea rotundata) tuber has been delineated and initial velocity studies revealed an ordered sequential mechanism.
Abstract: The kinetic mechanism of catalysis by malic dehydrogenase (EC 1.1.1.37) isolated from yam (Dioscorea rotundata) tuber has been delineated. Initial velocity studies with the enzyme in the presence and absence of products of the reaction revealed an ordered sequential mechanism. The K m values obtained from secondary plots were 0.05, 0.08, 0.48 and 2.56 mM for NADH, OAA, and NAD + and L-malic acid, respectively. Product inhibition studies in both the forward and backward reactions support an ordered Bi-Bi sequential mechanism. This begins with an obligatory binding of NAD + to form the first binary complex and a final release of NADH
TL;DR: White yam invertase (E.C. 3.26) was extracted from Dioscorea rotundate tuber and purified 30 fold and was less specific for maltose, lactose, raffinose, melezitose, planteose, and lychnose than for sucrose.
Abstract: White yam invertase (E.C. 3.2.1.26) was extracted from Dioscorea rotundate tuber and purified 30 fold. The enzyme consists of two molecular forms, termed invertases I and II, with average molecular weights of 263,000 ± 1000 and 230,000 ± 2000, respectively. Both enzymes had a temperature optima of 40C, and pH optima of 4.7 and 6.0 for invertases I and II, respectively. The Km values for invertases I and II were 4.65 mM and 9.25 mM, respectively, with sucrose as substrate. The enzymes were less specific for maltose, lactose, raffinose, melezitose, planteose, and lychnose than for sucrose.