Water Retention and Solubility of Soy Proteins and Corn Germ Proteins in a Model System

Response surface methodology was used to study water retention and protein solubility of soy flour (SF), concentrate (SC), and isolate (SI), and corn germ protein flour (CGPF). Water retention increased with pH (6 to 8) and incubation temperature (10–70°C), but not with increasing incubation time (10–30 min). SC had highest water retention per gTam, followed by CGPF, SF, and SI. Water retention in relation to protein content was higher in CGPF than in the three soy products. Protein solubility was significantly affected by pH and temperature of incubation. Protein solubility increased when pH (6 to 8) and incubation temperature increased (30–70°C) in all samples. SI had highest protein solubility, and CGPF had the lowest.     

Physical and Molecular Properties of Wheat Gluten Films Cast from Heated Film-Forming Solutions

The effect of heating film-forming solutions on physical and molecular properties of cast wheat gluten (WG) films was determined. Glycerol-plasticized films were cast from alkaline (pH 10), heat-treated (55,75, or 95°C for 10 min) solutions of WG in aqueous ethanol. Protein solubility (PS) of films in water decreased (P<0.05) with increasing temperature. Gel permeation chromatograms showed reduced extractability of protein fractions other than ω-gliadins in WG films. This reduced extractability was due to disulfide (S-S) bond formation. SDS-PAGE patterns of native WG and WG film samples suggested increased cross-linking through covalent S-S bonds in films from solutions heated at 75 or 95°C. Water resistance in potential packaging applications of WG edible films could be modified by adjusting heat-treating temperature.     

Trypsin Treatment to Improve Freeze Texturization of Minced Bream

Mild trypsin proteolysis (enzyme concentration 0.05% at 15°C, pH 7.4; mixing 30 min at 20 rpm) of bream mince improved mince susceptibility to freeze texturization. Formation of porous-fibrous texture of heat-set, freeze-texturized minces was associated with strong fragmentation of myosin heavy chain (MHC), decrease in extractability of myofibrillar protein and increased insoluble protein and thermal drip. Some deamidation of protein was also observed. We concluded that limited trypsin proteolysis accelerated transglutaminase mediated cross-linking of protein by acyl transfer reactions. Protein polymerization through plastein reactions and intermolecular hydrophobic interaction probably also occurred.     

Protein Denaturation of Frozen Pacific Whiting (Merluccius productus) Fillets

Protein denaturation in Pacific whiting fillets stored at ?8, ?20, ?34, and ?50°C was investigated over a 10-mo period by several methods, including salt-soluble protein extractability, Ca⁺⁺-ATPase activity, and the torsion test. Changes in quality of fillets stored at ?8°C were significantly greater than those stored at lower temperatures. Fillets stored at ?34 and ?50°C showed no significant advantage over those stored at ?20°C as measured by salt-soluble protein extractability and Ca⁺⁺-ATPase activity. However, fillets stored at the lower temperatures had slightly higher torsion shear strain.     

Protein Extractability and Thermally Induced Gelation Properties of Myofibrils Isolated from Pre- and Postrigor Chicken Muscles

Purified chicken myofibrils were suspended in 0.6M NaCl at various pH values to study gelation properties of the myofibrils. Postrigor breast myofibrils showed a greater protein extractability and gel strength than prerigor breast myofibrils, but the reverse was found for leg myofibrils. Salt-soluble protein was least extractable at pH 5.50 for both breast and leg myofibrils. The pH for optimum gelation, indicated by increased penetration force, was 6.00 for breast and 5.50 for leg myofibrils. Heating at 1°C/min from 20 to 70°C produced stronger breast but weaker leg myofibril gels than isothermal heating at 70°C for 20 min. Muscle rigor state showed a greater effect on protein extractability and gel strength for breast myofibrils than for leg myofibrils.     

The effect of cooking on proteins from acha (Digitaria exilis) and durum wheat

The effect of cooking on proteins from acha and durum wheat was assessed from an analysis of protein extractability, gel electrophoretic profiles, in-vitro protein digestibility (IVPD) and the amino acid compositions of wholemeal flour and residue proteins. Heating wholemeal flour samples at 100–140°C (t = 10–40 min) resulted in 0–30% and 45–55% decreases in acha and durum protein solubility, respectively. In general, high molecular weight (30–70 k Da) protein subunits were more susceptible to heat damage. For both cereals, sodium dodecyl sulphate (SDS; 10 g litre^?1) and/or dithiothrcitol (DTT; 10 mM ) increased protein solubility in unheated and heated samples. The IVPD index was 90–91% and was not significantly altered by cooking (100–120°C, t = 40 min). Cooking at extreme temperatures (140°C, t = 40 min) reduced the IVPD by 8% (P = 0.05). Osborne fractionation resulted in a durum or acha residue level of 7.8% or 55.2%. Treatment with solvent containing propanol, SDS and/or DTT at room temperature followed by SDS-polyacrylamide gel electrophoresis of non-solubilised proteins showed that the glutelin fraction of acha, with the exception of a 65 kDa subunit, was insoluble owing to strong inter-subunit hydrophobic and disulphide interactions. Wholemeal acha flour and residue protein showed a significantly greater level of hydrophobic and sulphur amino acids as well as glutamine which is associated with H-bonding. The possibility that cereal protein solubility is also dependent on protein-carbohydrate links is discussed.     

Functional Properties of Heat-Treated Egg Yolk Low Density Lipoprotein

Egg yolk low density lipoprotein (LDL) was heated at various temperatures from 55°C to 100°C for 5 min and transmission, extractability of lipid, emulsifying property and foaming property of each solution were examined. Transmission of LDL solution decreased for treatments above 60°C and was almost 0 at 75°C. Above 70°C, lipid extractability gradually decreased with increase of treatment temperature. Emulsifying property and apparent viscosity were significantly correlated with the extractability of lipid.     

Thermal inactivation of hepatitis A virus in suspension and in dried mussels (Mytilus edulis)

We examined the effects of three different temperatures (60, 85 and 100 °C) and durations of time (1 min at 100  ° C to 30 min at 60  ° C) on hepatitis A virus (HAV) in suspension and dried mussels (Mytilus edulis). In suspension, 3.61, 4.48, 5.06 and 5.66 log₁₀ tissue culture infectious dose (TCID)₅₀/mL were reduced by 60  ° C for 5 min, 60  ° C for 15 min, 60  ° C for 30 min and 85  ° C for 3 min, respectively. In dried mussels, 1.34, 1.94, 3.16, 2.36, 3.53 and 4.38 log₁₀TCID₅₀/mL were reduced by 60  ° C for 5 min, 60  ° C for 15 min, 60  ° C for 30 min, 85  ° C for 3 min, 85  ° C for 6 min and 85  ° C for 10 min, respectively. HAV inactivation from suspension and dried mussels was achieved by 85  ° C for 6 min and 15 min, respectively, and also by a 1 min at 100  ° C. At 60, 85 and 100  ° C, the 1‐log (D‐values) inactivation from both suspension and dried mussels was 6.33 and 7.93, 0.98 and 3.05, and 0.28 and 0.38 min, respectively. A higher temperature and/or a thermal treatment time shorter than 85  ° C for 6 min (100  ° C for 1 min) could be used for commercial target foods for complete HAV inactivation.     

Optimization of Processing Parameters for the Preparation of Flounder Frame Protein Product

Flounder frame was used as a raw material for the preparation of protein product. Processing parameters were evaluated using both fresh and frozen ground frames. The results indicate the following optima: (1) pH of extraction medium, ii; (2) extraction time, 60 min; (3) volume to weight ratio, 10: 1; (4) extraction temperature, 23°C. Isoelectric precipitation was conducted at pH 5 using KCI or H₃PO₄. Results indicate that NaOH was more effective than Ca(OH)₂ in solubilizing frame protein at pH 11. Ground frozen flounder frames gave a 10% decrease in protein extractability when compared to fresh frames using NaOH as the extractant and a 22% decrease when Ca(OH)₂ was employed as the extractant. Approximately 70% of the protein is recovered using the NaOH-HCI system.     

Effect of Chemical Additives on Toughening of Fillets of Frozen Alaska Pollack (Theragra chalcogramma)

Fillets of Alaska pollack (Theraga chalcogramma), a gadoid, were treated with solutions of citrate, sodium pyruvate, or H₂O₂, frozen and stored for 9 wk at -10°C. Protein extractability, texture, cooked moisture content, and activity of trimethylamine oxide demethylase were monitored during storage. None of the treatments slowed normal decline in protein extractability during frozen storage, however, sodium citrate and H₂O₂ significantly (P < 0.1) inhibited development of dimethylamine (DMA). This inhibition of DMA development did not, however appear to be associated with a decrease in the rate of toughening evidenced in H₂O₂-treated fillets. Sodium citrate and sodium pyruvate significantly slowed rate of toughening during storage, and this effect may be related to their positive effect on water-holding capacity.     

Increased Aflatoxin Production by Aspergillus parasiticus Under Conditions of Cycling Temperatures

The effects of cycling temperatures (5°C for 12 hr and 25°C for 12 hr) on aflatoxin production by Aspergillus parasiticus NRRL 2999 in yeast extract sucrose (YES) medium were studied. Cycling temperatures, after preincubation at 25°C for various times, resulted in more aflatoxin B₁, G₁, and total aflatoxin production than did constant incubation at either 25°C, which is generally considered to be the optimum for aflatoxin production, or 15°C, which is the same total thermal input as the 5-25°C temperature cycling. With increased preincubation time at 25°C, toxin production increased and the lag phase of growth was shortened or not evident. Cultures that were preincubated at 25°C for 1, 2, and 3 days prior to onset of temperature cycling showed the greatest increase in maximum aflatoxin production over the 25°C and 15°C constant temperatures. Cultures that were not preincubated at 25°C but subjected to constantly fluctuating temperatures produced maximum amounts of aflatoxin equivalent to cultures incubated at a constant 25°C. The maximum aflatoxin production at all temperatures studied occurred during the late log phase of growth and at pH minimums. Aflatoxins were found in higher concentrations in the broth than the mycelia under temperature cycling conditions, at 15°C, and at 25°C during the first 21 days of incubation, whereas greater amounts of toxin were retained in mycelium at 25°C in the later incubation period (28-42 days).     

Gel‐forming ability of surimi from grass carp (Ctenopharyngodon idellus): influence of heat treatment and soy protein isolate

The effects of setting conditions and soy protein isolate (SPI) on textural properties of surimi produced from grass carp were investigated. Effects of setting temperature, setting time and protein concentration on the breaking force and distance were evaluated and compared utilizing response surface methodology. Models for breaking force and breaking distance of grass carp surimi were established. Protein concentration was the major factor affecting the gel strength of grass carp surimi. Breaking force and distance of grass carp surimi gels decreased with increase of protein ratio from SPI at 30 °C and 40 °C for 60 min setting and heating at 85 °C for 30 min, but the breaking force obtained for addition of 100 g kg^?1 SPI protein to grass carp surimi was higher than that for surimi alone at 60 °C for 60 min incubation and heating at 85 °C for 30 min. Copyright © 2005 Society of Chemical Industry     

Physical Characteristics of Surimi Seafood as Affected By Thermal Processing Conditions

Texture, color and microbiological characteristics of surimi seafood were measured at three processing temperatures (93°, 85°, and 75°C) and various times (0–120 min). The time required to provide a zero aerobic plate count at 93°, 85°, and 75°C was 5,15, and 15 min, respectively. Both thermal processing temperature and time affected whiteness and shear strain of surimi seafood. As the thermal processing temperature and time increased, the shear strain and whiteness decreased. The higher the thermal processing temperature and longer time, the lower were the shear strain and whiteness. Results indicated 15 min at 75° or 85°C were the optimum thermal processing conditions.     

A comparison of biochemical changes in cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) fillets during frozen storage

Changes in the muscle proteins of frozen cod fillets, which produce significant amounts of formaldehyde, and frozen haddock fillets, which produce negligible formaldehyde, were compared. Protein extractability and hydrophobicity and the amino acid contents of soluble and insoluble proteins, as well as formaldehyde formation, were investigated in matching pairs of cod and haddock fillets stored at ?10 and ?30 °C (control). Formaldehyde production in cod was much higher (845 and 1065 nmol g^?1 at 20 and 30 weeks respectively) than in haddock (93 and 101 nmol g^?1 after 20 and 30 weeks respectively) at ?10 °C. However, a rapid decrease in solubility of proteins, increase in hydrophobicity and decrease in the amino acid content of salt‐soluble proteins at ?10 compared with ?30 °C were observed in both species. The results showed that there were no significant differences in the nature of the protein changes between these two species, thus indicating that factors other than formaldehyde were involved in the denaturation of proteins and the formation of aggregates during frozen storage of cod and haddock fillets, especially at ?10 °C. © 2001 Society of Chemical Industry     

Effect of pH and Ionic Strength on the Heat Stability of Rapeseed 12S Globulin (Cruciferin) by the ANS Fluorescence Method

The heat stability of rapeseed 12S globulin (cruciferin) was examined using 8-anilinonaphthalene-1-sulphonic acid (ANS) as a fluorescence probe. Heating cruciferin (0·06–0·3 mg ml⁻¹ in 10 mM glycyl–glycyl piperizine buffer, pH 7·0, with 0·1–1·0 M NaCl) for 20 min increased its hydrophobicity as monitored by ANS fluorescence measurements. The mid-point temperature for the heat effect (T_m) increased linearly with increasing solvent pH (T_m (°C)=4·16 pH+41 (μ=0.1)) or sodium chloride concentration (T_m (°C)=14·7 [NaCl]+71 (pH=7·0)). The range of T_m values for cruciferin was 45–96°C. At 20°C cruciferin was unstable at pH<3·0 but relatively stable under alkaline conditions (pH 8–10). Though possessing an oligomeric structure, cruciferin appears to heat denature in accordance with the two-stage deactivation model for simple globular proteins.     

Properties of polyphenol oxidase in mango (Mangifera indica) kernel

Polyphenol oxidase (PPO) activity of filtered extract of ground mango kernel suspension (400 g litre⁻¹) was studied spectrophotometrically at 420 nm using catechol as substrate. The enzyme was most active at pH 6·0 and 25°C. Activity was reduced by 50% at pH values of 5·0 and 7·1, and also at temperatures of 14°C and 30°C. The calculated activation energy and the Michaelis constant (K_m) were 21·4 kcal mol⁻¹ °C⁻¹ and 24·6 mM , respectively. The V_max value was 2·14 units g⁻¹ mango kernel. The time to heat inactivate PPO decreased rapidly to < 10 min with increasing temperature of ⩾ 70°C at 50% activity. © 1998 SCI.     

PROCESSING AND QUALITY EVALUATION OF SOURSOP (ANNONA MURICATA L) NECTAR

Soursop (Annona muricata L) nectar was processed from pasteurized unstored or pasteurized frozen pulp. Nectars of pH 3.6–3.7 with 0.1% xanthan gum were produced from either 6° or 8° Brix pulp and increased to 13° or 15° Brix by addition of sucrose. The effect of storage (4C or 30C for 12 weeks) was investigated on nectar pH, titratable acidity (TA), browning, consistency, microbes and sensory attribute. At 8 weeks of storage, consistency was similar in all nectars, except for thinning of nectar from pasteurized, unstored pulp (8°–15° Brix) stored at 4C for 12 weeks. Nectars produced from frozen pulp had significantly (p < 0.01) lower pH and higher TA than nectars from unstored pulp. Browning increased in all products except nectar produced from unstored 8° Brix pulp adjusted to 15° Brix and then stored at 4C. This nectar was most highly ranked and had an overall rating of being liked moderately to liked very much after 12 weeks of storage. Microbial growth occurred in all nectars between 8–12 weeks of storage.     

Optimization of the Process Parameters to Establish the Quality Attributes of DPPH Radical Scavenging Activity,Total Phenolic Content,and Total Flavonoid Content of Apple (Malus domestica) Honey Using Response Surface Methodology

The response surface methodology was used to study the combined effect of temperature (60 to 80°C), time (10 to 15 min), and pH (3 to 6) on the antioxidant activity (1,1-diphenyl-2-picrylhydrazyl-radical scavenging activity, total phenolic content, and total flavonoid content) of apple honey. Statistical analysis revealed that all the responses were significantly (p < 0.05) affected by independent process variables. 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity, total phenolic content, and total flavonoid content increased with the increase in time and temperature due to the formation of browning pigments. The antioxidant properties of apple honey significantly (p < 0.05) decreased with increase in pH from 3 to 6. The thermal treatment of apple honey at 80°C was found to be more effective than at 70 and 60°C. The average increase in 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity, total phenolic content, and total flavonoid content of raw apple honey due to combined effect of three process variables was 9.6% ± 1.9, 13.7 ± 2.5 mg gallic acid equivalent/100 g and 49.3 ± 3.3 mg quercetin/100 g, respectively. The results showed that the most desirable optimum conditions for temperature, time and pH for 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity (92.39%), total phenolic content (133.55 mg gallic acid equivalent/100 g of honey), and total flavonoid content (25.82 mg quercetin/100 g of honey) were 80°C, 15 min and 3.01, respectively. The results demonstrated that thermal treatment significantly increased the antioxidant activity of apple honey.     

5-Hydroxymethylfurfural (HMF) formation during subcritical water extraction

The aim of this study was to investigate the effect of material type (artichoke leave, lemon peel, flaxseed meal), extraction temperature (50, 100, 120, 140, 160, 180, 200 °C) and static extraction time (5, 15, 30, 45 min) on 5-hydroxymethylfurfural (5-HMF) formation during subcritical water extraction. 5-HMF content of artichoke leave and lemon peel extracts increased 7.2 and 26.1 times with the rise of extraction temperature from 160 to 180 °C for 5 min during subcritical water extraction, respectively. Besides, 5-HMF content of artichoke leave, lemon peel and flaxseed meal extracts increased 1.4, 2.0 and 4.5 times as static extraction time increased from 15 to 45 min at 180 °C during subcritical water extraction, respectively. The highest 5-HMF content of artichoke leave and lemon peel extracts were obtained as 58.83 and 231.21 mg/L at 180 °C and 45 min, respectively. However, for flaxseed meal, the highest 5-HMF content (222.94 mg/L) was obtained at 200 °C and 15 min during subcritical water extraction.     

Investigating rennet coagulation properties of recombined highly concentrated micellar casein concentrate and cream for use in cheese making

Highly concentrated micellar casein concentrate (HC-MCC) contains ～18% casein with ～70% of whey proteins removed by microfiltration and diafiltration of skim milk, followed by vacuum evaporation for further concentration. When blended with cream, HC-MCC forms recombined concentrated milk (RCM), which could be used as a starting material in cheese making. Our objective was to investigate the rennet coagulation properties of RCM while varying parameters such as casein level, pH, rennet level, and coagulation temperature. The HC-MCC was mixed with cream using low shear at 50°C for 10 min, followed by cooling to 31, 28, or 25°C and adding rennet, and rheological properties were determined. Rennet coagulation time [RCT, the time at which storage modulus (G′) = loss modulus (G″)] decreased from 8.7 to 7.4 min as casein level increased from 3.2 to 5.7%, without a significant additional difference in RCT at casein levels >5.7%. The initial G″ (G″₀) increased about 10-fold when casein levels were increased from 3.2 to 10.9%, whereas no change in initial G′ (G′₀) was observed. When G′ was measured relative to RCT (i.e., 1, 1.5, or 2 times RCT after RCT was reached, and expressed as G′₁, G′_1.5, and G′₂), log relationship was found between relative G′ and casein level (R² > 0.94). Lowering coagulation temperature from 31 to 25°C increased G″₀ by 6 fold and extended RCT from 7.4 to 9.5 min. After coagulation, relative G′ was initially higher at the lower temperature with G′₁ of 3.6 Pa at 25°C and 2.0 Pa at 31°C, but delayed in further development with G′₂ of 0.8 kPa at 25°C and 1.1 kPa at 31°C. Lowering pH of RCM from 6.6 to 6.2 resulted in reduced RCT from 11.9 to 6.5 min with increased relative G′ after coagulation. When less rennet was used, RCT increased in a linear inverse relationship without changes in relative G′ or G″. The microstructure of RCM coagulum (～11% casein), observed using transmission electron microscopy, confirmed that RCM curd had a rigid protein matrix containing extensively cross-linked protein strands.