Stability of Metabolically Conjugated Precursors of Meat and Milk Flavor Compounds in Various Solvents

The stability of selected metabolic conjugates (phenylglucuronide, phenylphosphate, and naphthylsulfate) was determined in model systems composed of water and various ratios (3:1, 1:1, 1:3) of selected solvents (hexane, chloroform, ethyl acetate, diethyl ether, or methanol) held at either 22°C or 40°C for 30 min under various pH conditions (pH 1.5, 3.2, or 6.5). Notable hydrolysis occurred only for the more polar solvents held in contact with acidic aqueous phases. Conditions were identified for minimizing hydrolysis of conjugates during extraction of fat and free alkylphenols from milk and meat products with diethyl ether. They were pH near neutral, short exposure time, near ambient temperature, presence of excess water, and saturation of aqueous phase with sodium chloride.     

Gene cloning and characterization of a trehalose synthase from Corynebacterium glutamicum ATCC13032

Trehalose synthase (TreS) is an enzyme which produces trehalose from maltose through intramolecular transglycosylation. In this study, a gene (cg2529) encoding for TreS from Corynebacterium glutamicum (CgTS) was cloned and expressed in Escherichia coli. The hexahistidinetagged CgTS showed an optimum temperature and pH of 35°C and pH 7.0, respectively. This enzyme was not thermostable, but stable in a broad pH range from pH 5.0 to 8.5. Its activity slightly increased by 5 mM Mg²⁺ and Fe²⁺, while it was strongly inhibited by 5 mM sodium dodecyl sulfate (SDS). CgTS catalyzed the conversion from maltose into trehalose, and vice versa. Lowering reaction temperature by 5°C from the optimum temperature significantly reduced hydrolysis activity to produce glucose as a by-product compared to transglycosylation activity to produce trehalose, leading to increase in the conversion yields from maltose into trehalose. Consequently, the maximum conversion yield by CgTS reached 69% at 25°C after 9 hr of reaction.     

Production of Fungal α-Galactosidase and Its Application to the Hydrolysis of Galactooligosaccharides in Soybean Milk

Production of extracellular α-galactosidase of Aspergillus oryzae was induced remarkably well by the addition of soybean carbohydrate to culture medium. Addition of stachyose or raffinose induced slight production. Soybean carbohydrate, stachyose, and raffinose also served well for the synthesis of invertase. Maximum hydrolysis of p-nitrophenyl-α-D-galactopyranoside (PNPG) by the enzyme occurred at pH 4.0, and optimum temperature for hydrolysis of PNPG was 50° C. The enzyme seemed to be stable from 30-50° C. The mixture of α-galactosidase and invertase totally hydrolyzed raffinose and stachyose at 50° C, pH 4.0 in 2 hr. The mixed preparation of the enzyme substantially hydrolyzed galactooligosaccharides in soybean milk at 50° C, pH 6.3 in 2 hr.     

Thermal Degradation of Flavor Enhancers, Inosine 5'-monophosphate, and Guanosine 5'-monophosphate in Aqueous Solution

The mechanism of thermal degradation of inosine 5′-monophosphate (IMP) and guanosine (GMP) was investigated kinetically in aqueous solution as a function of pH and temperature. The degradation of IMP and GMP followed first order kinetics. The rate constants were considerably affected by pH and temperature. The half-life times at 100°C were: IMP, 8.7 hr (pH 4.0), 13.1 hr (pH 7.0), 46.2 hr (pH 9.0); GMP, 6.4 hr (pH 4.0), 8.2 hr (pH 7.0), 38.5 hr (pH 9.0). These times were shortened to about one-third by raising the temperature 10°C. The predominant degradation products were nucleosides and phosphoric acid, indicating that the main reaction of the thermal degradation was the hydrolysis of the phosphoric ester bond in the nucleotides.     

Enzymatic Hydrolysis of Crayfish Processing By-products

Ten commercial proteases (neutral and alkaline) were evaluated for hydrolysis of crayfish processing by-products (CPBs). Hydrolysis conditions were optimized for the alkaline protease Optimase^TM APL-440 by response surface methodology (RSM). Two model equations were proposed with regard to effects of pH, temperature (T), time (t), enzyme/ substrate (E/S) ratio, and substrate concentration (S) on the amount of 0.3M TCA soluble peptides (TSP) and degree of hydrolysis (DH). Interaction effects between pH and T were observed (P<0.001). Based on TSP, optimum hydrolysis conditions were determined to be pH 8–9, 65°C, 2.5 hr reaction time, 75%(w/v) substrate concentration, and 0.3% (v/w) enzyme.     

Enzymatic Lactose Hydrolysis for Prevention of Lactose Crystallization in a Whey Spread

The enzymatic lactose hydrolysis for elimination of sandiness was studied in a whey-buttermilk spread of previously optimized composition (18% fat, 12% protein, 17% lactose). Soluble enzyme preparations of either the acid (Aspergillus) or the neutral (Kluyveromyces) type were suitable for the minimum 30% hydrolysis required to prevent the lactose crystallization. Two types of acid enzymes used at either 1 mg or 2 mg per g hydrolyzed mixture produced the desired effect after 2 hr of hydrolysis at 30°C. Similar results were obtained with two types of neutral enzymes at 2 mg per g hydrolyzed mixture after either 2 or 4hr of hydrolysis at 30°C.     

Improvement of the functional properties of sorghum protein by protein-polysaccharide and protein-protein complexes

Sorghum protein was conjugated with dextran or galactomannan under controlled conditions (60 °C, 79% relative humidity), or cross-linked with transglutaminase (TGase) to improve the functional prop-erties. SDS-PAGE patterns showed that the conjugated and cross-linked proteins had higher molecular mass bands above the stacking gel. Although sorghum protein and its polysaccharide mixture were insoluble at pH 4 — 6, the polysaccharide conjugates were soluble at all level of pHs, despite being composed of higher molecular sizes. Heat stability of the polysaccharide conjugates was greatly improved in that there were no turbidity at 100 °C, while TGase-treated samples sup-pressed heat-induced aggregation up to 60 °C. The emulsifying proper-ties of the polysaccharide conjugates and TGase treated sample were also greatly improved.     

Dephosphorylation of Phytic Acid in Rice Bran

Incubation time and temperature, moisture content, and pH were examined to determine the conditions necessary for the hydrolysis of phytic acid in rice bran. The extent of hydrolysis increased with increase in moisture content, and autoclaving for 1 hr at 121°C destroyed a significant proportion of the phytic acid at high moisture contents. Maximum hydrolysis of phytic acid occurred by heating at pH 4.5. Incubation of rice bran slurry for 24 hr at 55°C, pH 5.1 reduced the phytic acid level by approximately 80%.     

Measurement of Glycosylated Vitamin B6 in Foods

To examine the levels of glycosylated vitamin B6 in 22 foods, each food was stirred for 2 hr at pH 6.8 and then incubated for 2 hr at pH 5.0 and 37°C with β-glucosidase (60 units per g food). Vitamin B6 content of foods was measured microbiologically before and after enzyme treatment as well as with acid hydrolysis. Animal products contained no measurable amount of glycosylated B6. Grains and legumes generally had a high level of this bound form (6–57% of the total vitamin B6). Of the fruits analyzed, orange juice had the highest level of glycosylated vitamin B6 (47%). Among fresh vegetables studied, raw carrots had the highest level (51%). For broccoli and cauliflower, the glycosylated value was higher for the processed food as compared to the raw food.     

Analysis of Dietary Fiber in Feces of Rats Fed with Fiber Supplemented Diets

A procedure based on Southgate's fractionation scheme with subsequent colorimetric determination of monomeric constituents in the individual fractions was used for the analysis of feces of rats fed with diets supplemented with cereal bran or its fiber components. Prior to fractionation, dehydrated feces were extracted with chloro-form:methanol (2:1) mixture and hot 80% methanol and then subjected to treatment with both amylolytic (MERCK glucoamylase, 60°C, 2 hr) and proteolytic (CALBIOCHEM pepsin, 40°C, 48 hr) enzymes. Colorimetrically determined values of noncellulosic polysaccharides and cellulose (calculated as sums of hexoses, pentoses, and uronic acids) agreed satisfactorily with those determined by detergent fiber analysis. The sums of neutral sugars determined colorimetrically correlated closely with the values obtained by GLC analysis after Saeman's hydrolysis (2 hr with 72% (w/w) H₂SO₄ at 20°C and 2 hr with 2N H₂SO₄ at 100°C) of defatted samples. The GLC data were, however, consistently higher, especially those for hexoses; the difference was more pronounced with feces than with tested bran material. Confidence in the analysis was strengthened by the observation that the results of proximate and fiber analyses closely approached 100%.     

Effect of Soybean Cooking Temperature on the Texture and Protein Digestibility of Miso

Miso samples were prepared with soybeans cooked for 10 min at different temperatures (up to 100°C). Appreciable changes in the amount of 0.2 M trichloroacetic acid-soluble nitrogen (TCA-soluble N) and the pattern of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of fermented miso samples were observed in the temperature range between 90°C and 100°C. No further changes in the TCA-soluble N and SDS-PAGE pattern of miso were observed when the cooking time was prolonged up to 3 hr at 100°C. On the other hand, a 2 hr cooking period at 100°C was required to achieve a level of softness for cooked soybeans to give an acceptable texture of miso.     

Processing to Improve Quality of Dehydrated Precooked Pinto Beans

The firmness of precooked and rehydrated beans after soaking in water at 30°C/2 hr and 82°C/1 hr was lower than that after soaking at 82°C/1 hr or 22°C/12 hr. The 22°C/12 hr soaking yielded the lowest butterflying (8.0%). Steam precooking at 100°C/1 hr produced less splitting, lighter color, and firmer texture than pressure precooking. High initial humidity dehydration reduced splitting. Beans after soaking at 30°C/2 hr and 82°C/1 hr, precooking at 100°C/1 hr, and dehydrating at 65°C/6 hr with initial 95% relative humidity were better regarding firmness, butterflying (11.6%), and moisture content (10.4%).     

Viability of Lactobacillus plantarum in Orange Juice under Low pH and Temperature Conditions

A strain of Lactobacillus plantarum, isolated from fermenting orange juice (OJ), was inoculated into unpasteurized or reconstituted OJ and held under low pH/low temperature conditions. Viability decreased more rapidly at subfreezing temperatures near – 5°C than at lower or higher temperatures. Viability decreased 0.37 log CFU/mL/hr at - 6.6°C and 0.05 log CFU/mL/hr at - 18°C. Rates of population decrease in frozen samples at - 5°C were about three times greater than in unfrozen samples at the same temperature. An inverse linear relationship existed between rate of population decrease (log CFU/mL/day) at - 7°C and OJ pH, with the rate of decrease at pH 4.1, about 1 log cycle lower than at pH 3.5 (0.024 and 0.60, respectively).     

Effects of fermentation conditions and soybean peptide supplementation on hyaluronic acid production by Streptococcus thermophilus strain YIT 2084 in milk

To increase the hyaluronic acid (HA) yield from Streptococcus thermophilus YIT 2084, fermentation conditions (pH, temperature, agitation, aeration) were optimized in milk-based medium, and the effects of supplemental soybean peptides, which have different molecular weight distributions, were determined. HA production was enhanced to approximately 100 mg/l at pH 6.8 and 33–40 °C. Agitation speed and aeration rate slightly affected HA production. Soybean peptides including those of high molecular weight (approximately 27 to 130 kDa) further increased HA production to 208 mg/l under the optimal condition (pH 6.8, 35 °C, 100 rpm), which was 20-fold greater than non-optimal condition. HA production was no longer related to the specific growth rate. The HA produced under the optimal condition included a large amount of high-molecular-weight fraction of 100 to 2000 kDa, compared with under the basal condition without optimization.     

INACTIVATION OF MALT PEPTIDASES DURING MASHING*

Malt contains at least eight different peptidases: three carboxypeptidases (pH optima 4·8, 5·2, 5·7), three aminopeptidases active on aminoacyl-β-naphthylamides (pH optima in hydrolysis of peptides at pH 5·8-6 5), and two (amino)peptidases acting on Leu-Tyr and Ala-Gly at higher pH (pH optima 8·6, 7·8). We have studied the progressive inactivation of these peptidases during mashing with a temperature programme from 45° to 70° C (pH 5·8 → 5·7). All peptidases were stable at 45° C. The five aminopeptidases were inactivated at different rates during a 30-min incubation at 55° C. The carboxypeptidases retained 70–100% of their activities at this temperature, and one of them had 40% residual activity after 60 min at 70° C. Liberation of amino acids continued at a considerable rate during the incubation at 70° C, probably catalysed by the heat-stable carboxypeptidase. Malt carboxypeptidases are therefore more heat-stable in mashing conditions than the aminopeptidases. This property, in combination with their high activities and suitable pH optima, makes them the most important enzymes in the production of free amino acids in mashing.     

Effect of Low-Calcium-Requiring Calcium Activated Factor on Myofibrils under Varying pH and Temperature Conditions

The effect of low-calcium-requiring calcium-activated factor (μM CAF) on the myofibrils under varying pH at 5°C and 25°C was examined spectrophotometrically (absorbance at 278 nm), electrophoretically (sodium dodecyl sulfate polyacrylamide gel electrophoresis), and microscopically (phase microscopy and transmission electron microscopy). Results indicated that at conditions similar to those of postmortem storage (i.e., pH 5.5–5.8 and 5°C), μM CAF retained 24–28% of its maximum activity (pH 7.5 at 25°C). This 24–28% of maximum activity was sufficient to reproduce most of the known changes associated with the tenderization process during postmortem aging. It was concluded that because of the activity of μM CAF under postmortem conditions, it seems reasonable to suggest that μM CAF may be responsible, in part, for some of the postmortem changes observed.     

Purification and Characterization of a Novel Protopectin-Solubilizing Enzyme from Aspergillus niger Z-25

A mutant, Aspergillus niger Z-25 derived from A. niger XZ-131 with N⁺ supplementation, produced a protopectin-solubilizing enzyme (protopectinase). The enzyme was purified to homogeneity by a procedure involving ammonium sulfate fractionation and gel chromatographies on DEAE-Sephadex A-50 and Sephadex G-100 columns. The molecular weight of the protopectinase was estimated at 68.4 KD by SDS-polyacrylamide gel electrophoresis. The enzyme was stable from pH 3.0 to 7.0 and up to 60°C. The optimum pH and temperature for enzyme activity was 4.0 and 50°C, respectively. The purified enzyme had 268-U/mL PPase (protopectinase) activity on citrus protopectin, and also showed 100-U/mL PGase (polygalacturonase) activity, which catalyzed the hydrolysis of polygalacturonic acid. The Km value for protopectin was 0.215 mg/mL, while the Km value for polygalacturonic acid was 39.09 mg/ml. The PPase/PGase q-value was 2.68, more than 0.5. Therefore the enzyme was considered a novel pectinase and classified as protopectinase.     

Influence of enzymatic hydrolysis,pH and storage temperature on the emulsifying properties of canola protein isolate and hydrolysates

The aim of this work was to enhance emulsification properties of canola proteins through enzymatic proteolysis and pH variaton. Canola protein isolate (CPI) and hydrolysates (CPHs) were used to form emulsions at pH 4.0, 7.0 and 9.0 followed by storage at 4 or 25 °C for 7 days. Controlled enzymatic hydrolysis led to increased peptide bond cleavage with time (0.23 g/100 g in CPI to 7.18 g/100 g after 24‐h Alcalase hydrolysis). Generally, oil droplet sizes were smaller for emulsions made at pH 9.0, which suggest better quality than those made at pH 4.0 and 7.0. Trypsin hydrolysate emulsions were the most physically stable at pH 7.0 and 9.0; in contrast, the pepsin hydrolysate emulsions were unstable at all conditions. The results suggest that selective enzymatic hydrolysis could play an important role in enhancing successful incorporation of canola proteins and peptides into food systems as protein emulsifiers.     

Chemical and Biochemical Hydrolysis of Persian Sturgeon (Acipenser persicus) Visceral Protein

Chemical (pH 3.3, 70 °C, 85 °C; pH 12, 70 °C, 85 °C) and biochemical (Alcalase, Protamex, Neutrase, Flavourzyme, and Trypsin) hydrolysis of Persian sturgeon (Acipenser persicus) visceral protein was investigated. The results of this study revealed that there are significant differences between enzymes in terms of degree of hydrolysis (DH%; P < 0.05). Alcalase-hydrolyzed fish protein had the highest DH% (50.13%), and Trypsin-hydrolyzed fish protein had the minimum DH% (14.21%). The highest DH% in chemical hydrolysis was related to pH 3.3 at 85 °C (68.87%). The highest protein recovery (83.64%) and protein content (73.34) were related to enzymatic hydrolysis by Alcalase. The results of current study showed the significant effect of hydrolysis conditions on fish protein hydrolysate properties. Microbial enzymes could produce fish hydrolysates with higher degree of hydrolysis when compared to animal enzyme. Also, in chemical hydrolysis it is clear that hydrolysis at the lower pH and at higher temperature causes to more protein recovery and degree of hydrolysis.     

Functional properties of plant proteins Part IV. Foaming properties of modified proteins from faba beans

The foaming ability (foam capacity and stability) of protein isolates from faba beans (Vicia faba L.) depends closely on the manner of isolation and treatment of the isolates. Unmodified isolates possess a moderate foaming ability with a maximum foam capacity of 210 % in alkaline solution (pH 10.0) at concentrations of about 3 %. The foam capacity and stability can be improved by treatment with isopropanol or moderate temperature, as well as by denaturing by alkali or by specially heating at 80 °C. Thereby modified preparations are formed possessing a foam capacity of more than 400 % and a foam stability of 80-100%. High concentrations of protein favour the formation of stable foams. Succinylation improves the foam formation properties of proteins. Maximum values of foam capacity (≈ 400%) are produced at a high degree of succinylation, that is after blocking more than 80% of protein amino groups, in neutral solution, while the foam stability under these conditions decreases. Heating at 80 °C, high'protein concentrations (10 %) and a weak acidic milieu (pH 5.5) favour the formation of stable foams from succinylated proteins.