Supercritical CO2 Extraction of β-Carotene from Sweet Potatoes

Using supercritical CO₂ to extract β-carotene there was approximately a five-fold or a three-fold increase in amount of carotenoids extracted from freeze-dried tissue relative to the amount extracted from oven-dried or fresh tissue, respectively. The most efficient conditions were at 48°C and 41.4 MPa. Of the total carotenoid content ～20% was inaccessible to supercritical CO₂. The HPLC carotenoid profile of sweet potatoes showed that the unextracted tissue contained 90%β-carotene, primarily as all-trans (ca. 99%). Supercritical CO₂ extracts contained up to 94%β-carotene. The isomer composition of β-carotene of supercritical extracts showed ～ 14% 13-cis and 11% 9-cis.     

Characterisation of soybean glycinin and β-conglycinin fractionated by using MgCl2 instead of CaCl2

A simple two step precipitation method was used to investigate the effect of MgCl₂ instead of CaCl₂ on fractionation of soybean glycinin and β-conglycinin. Compositional and physicochemical properties of the resulting protein fractions were characterised. The optimised procedure, in terms of protein yield, purity, phytate content and physicochemical properties, was obtained when the addition of 5 m m MgCl₂ was used. After application of 5 m m MgCl₂, the phytate content of the glycinin-rich and β-conglycinin-rich fractions was about 0.4% and 1.3%, respectively, but the addition of 5 m m CaCl₂ increased the phytate content of the glycinin-rich fraction to 1.25% and decreased that of β-conglycinin-rich fraction to 0.67%. Low phytate protein product was suitable for use in infant formula and acidic food. The solubility of the glycinin-rich fractions with MgCl₂ was significantly higher than that with CaCl₂ at pH < 4.5. Application of MgCl₂ improved thermal stability of the β-conglycinin-rich fraction.     

α;2-Macroglobulin Inhibition of Endogenous Proteases in Fish Muscle

Kinetic parameters for α;₂-macroglobulin inhibition of selected proteases (collagenase, cathepsin D, trypsin and chymotrypsin) were determined along with the extent of inhibition of the corresponding fish muscle proteases. Protease inhibition by α;₂-macroglobulin occurred in the presence of large macromolecular substrates but not in the presence of synthetic substrates. The inhibitor remained active at refrigerated temperatures (4–7°C). The α;₂-macroglobulin did not have any inhibitory effects on proteases in intact fish muscle tissue possibly due to lack of penetration of the tissues, but showed various levels of inhibition of proteases in tissue homogenates. Inhibitor concentration of 0.1% per weight of tissue homogenate resulted in about 17% loss of proteolytic activity while 0.4% inhibitor concentration caused complete loss of protease activity.     

EFFECTS OF CRUDE α2-MACROGLOBULIN ON PROPERTIES OF BLUEFISH (Pomatomus saltatrix) GELS PREPARED BY HIGH HYDROSTATIC PRESSURE AND HEAT TREATMENT

Bovine serum extract containing α₂-macroglobulin was added to bluefish meat pastes to various final concentrations of 0% (control), 0.05%, 0.10%, or 0.20%, and gels were prepared from the treated fish pastes by heat at 60C for 60 min, or by hydrostatic pressure at 3,742 atm for 30 min. α₂-Macroglobulin caused significant color changes in the gels even though increasing inhibitor concentration showed no further changes. L* values were increased by inhibitor addition while a* and b* values were decreased. Storage studies at 0C indicated that hardness and elasticity of the heat-induced gels were higher for the α₂-macroglobulin containing samples than the control samples within 7 days of storage, whereas a similar effect was not observed with pressure-induced gels. SDS-PAGE studies indicated that pressure treatment retained more myosin in the fish gels than the heat treatment. The heat-induced gels with α₂-macroglobulin also retained more myosin than those without the protease inhibitor.     

ISOLATION AND IDENTIFICATION OF A NOVEL ASPERGILLUS JAPONICUS JN19 PRODUCING β-FRUCTOFURANOSIDASE AND CHARACTERIZATION OF THE ENZYME

A novel strain, Aspergillus sp. JN19, producingβ‐fructofuranosidase (FFase), was isolated from soil. According to the physiological and biochemical characteristics and its 18S rDNA gene sequence analysis, it was identified as Aspergillus japonicus. The optimal conditions for production of fructofuranosidase by A. japonicus JN‐19 were investigated. The initial concentration of sucrose was 15 to 18%. Yeast extract was the best nitrogen source. K₂HPO₄ was effective in increasing enzyme production. The enzyme activity was increased to about 1.3 times by addition of 0.2% carboxymethylcellulose in the medium. The highest FFase activity was 55.42 U/mL at pH 5.5 and 30C, and production yield of fructooligosaccharides was 55.8%. Some characteristics of purified FFase were also studied.     

1H and 23Na NMR Relaxation Studies of the NaCl/β-Lactoglobulin System Equilibrated at Various Water Activities

NMR relaxation times (T₁) of ¹H and ²³Na were determined at 8, 14, 60, MHz and at 14, 52 MHz, respectively, in the NaCl/β-lactoglobulin system equilibrated at water activities ranging from 0.11 to 0.97. A two-state model was used for both nuclei which allowed the calculation of proportions of bound and free species. It was shown that bound water and Na⁺ increased at medium water activities in the presence of increasing NaCl. The discrepancy with adsorption isotherms data was explained by (1) limitations of the mass balance equation used to calculate interacting salt by gravimetry and (2) the fact that NMR probed the totality of ions in the vicinity of the protein, whereas adsorption isotherms were indicative of sodium choride tightly bound to the protein. It was also shown that the protein and Na⁺ shared available water molecules at medium and low water activity.     

ISOLATION AND SOME PROPERTIES OF THE THERMOSTABLE β-GALACTOSIDASE OF PYROCOCCUS WOESEI EXPRESSED IN ESCHERICHIA COLI

The enzyme with β-galactosidase activity from E. coli BL21(DE3) transformant containing the gene encoding enzyme from Pyrococcus woesei (DSM 3773) was isolated using cell extraction in 0.01 M phosphate buffer (pH 7.2), protein thermopredpitation at 85C, precipitation at acetone/extract ratio of 1:1 (v/v) and gel filtration on Sephadex G-200. The increase in the enzyme specific activity was determined using ONPG as substrate. The activity increased from 2.9 × 10³ U/mg protein to 37 × 10³ U/mg. Thermoprecipitation removed 78% of E. coli protein and retained 92% of the cell extract activity. The acetone precipitation and gel filtration applied in the next purification steps led to homogeneous enzyme with specific activity of 37,700 U/mg protein. The isolated enzyme had a half-life of 23 h and 9 h during incubation at 85C and 100C, respectively, in 0.1 M citrate-phosphate buffer (pH 5.4).     

PACKAGING PRESERVATION OF β-CAROTENE IN SWEET POTATO FLAKES USING FLEXIBLE FILM AND AN OXYGEN ABSORBER

Sweet potato flakes are potentially an affordable, shelf-stable source of provitamin A β-carotene. Because β-carotene is susceptible to oxidative degradation, particularly in dehydrated food materials exposed to atmospheric oxygen, several packaging conditions were evaluated for enhancement of β-carotene retention in sweet potato flakes during storage. The flakes were packaged in either a polypropylene film (high oxygen permeability) with air headspace or a nylon laminate film (low oxygen permeability) with air headspace, under vacuum, or with an Ageless oxygen absorber sachet enclosed. Packaged flakes were stored in the dark at ambient laboratory temperature (～23C), and β-carotene content was determined at intervals from 0 to 210 day storage using reversed-phase liquid chromatography. Among the packaging conditions tested, β-carotene retention was enhanced incrementally as the apparent availability of oxygen was reduced (nylon > polypropylene; oxygen absorber > vacuum > air headspace). The combined use of oxygen absorbers and flexible oxygen barrier film gave excellent retention of β-carotene during the 210 day trial.     

PRODUCTION OF CO2 AND C2H4 AFTER GAMMA IRRADIATION OF STRAWBERRY FRUIT

Strawberry fruit (Fragaria ananassa, Duch. cv ‘Kent’) were irradiated at doses from 0 to 4 kGy and stored at 10°C to verify whether irradiation at very low doses could delay postharvest ripening while causing minimal damage to the tissues. CO₂ and C₂H₄ production were used as stress indicator. Anthocyanins and titratable acidity were measured as maturity parameters. CO₂ and C₂H₄ production increased six hours after irradiation. The increase in CO₂ production was proportional to the dose of irradiation and was highest at 4 kGy. Maximum C₂H₄ production was reached at 1 kGy. The different response of CO₂ and C₂H₄ production to irradiation suggests that the membrane system supporting C₂H₄ production was more sensitive to gamma rays than mitochondrial CO₂ production. Irradiation at 0.3 kGy slightly delayed color development in the fruit. Overall, the results indicated that it may be possible to use irradiation at a low dose to delay ripening while causing only minimal tissue damage.     

EFFECT OF ADDITION OF α-, β-, AND κ-CASEIN, AND Na-CASEINATE ON VISCOELASTIC PROPERTIES OF SKIM MILK CURD

Creep compliance was used to determine the effects of the addition of α-, β-, and κ-casein, and Na-caseinate on the viscoelastic properties of skim milk curd. The results of all measurements can be represented by a six-element mechanical model. Addition of α- and β-casein, and Na-caseinate (1.80g/L) to raw skim milk reduced the instantaneous modulus of rigidity and final viscosity of the curd, while κ-casein addition at the same level increased both viscoelastic parameters. Shielding of κ-casein and depletion of serum Ca⁺⁺ ions by α- and β-casein is thought to have caused the reduction of curd rigidity and viscosity. Subsequent experiments indicated that the addition of β-casein before and after rennet hydrolysis produced different curd strength with the latter producing a stronger curd.     

SPECIFICITY OF THE FERRIC-H2SO4 REAGENT FOR ALGINATES

SUMMARY— Alginate in foods was isolated from papain digests of the samples as the insoluble calcium salt. dispersed by sodium hexametaphosphate and a 1- to 5-ml aliquot of the dispersion 50–250 μg of sodium alginate) dried at 100°C. Heating of the anhydrous sample in the presence of the ferric-H₂SO₄ reagent for 12 min at 60°C produced a pink color with maximum absorption at 490–515 mμ and maximum density after aging for 90 min at 29±1°C. Under these conditions, proteins, amino acids (except tryptophane), other carbohydrates, vitamins. food additives and incipients did not interfere. The presence of water in the medium rendered the reaction nonspecific and increasing the temperature above 60°C or heating for longer periods at lower temperatures resulted in color formation by other polyuronides, especially pectin and pectic acid. Recoveries of alginate from several products were good: Milk, 94–98%; ice cream, 93.5–98%; pasteurized process cheese spread. 92.6-95%; chocolate milk, 92.4-95%; dietetic foods, 90-97.2%.     

Relative Proteolytic Action of Milk-Clotting Enzyme Preparations on Bovine α-, β- and β-casein

Concentrations of seven milk-clotting enzyme preparations were standardized to equal clot times. Portions of bovine α_s-, β- and κ-casein were treated with enzymes. Proteolytic activity of the coagulants on each casein fraction was determined using the TNBS (2,4,6-trinitrobenzene-sulfonic acid) procedure. Recombinant chymosin showed the lowest degree of proteolysis on α_s- and β-caseins. Excessive proteolysis of calf rennet appeared to be due to the pepsin fraction. M. miehei and M. pusillus var Lindt proteases showed similar degradation of caseins, but M. pusillus var Lindt was more proteolytic when β-casein was the substrate. C. parasitica protease showed the highest degree of proteolysis on α_s- and β-caseins but was the least proteolytic on κ-casein.     

MOLECULAR CHARACTERIZATION OF THE β-CONGLUTIN OF LUPIN SEEDS

β‐conglutin from Lupinus campestris was extracted and purified by gel filtration chromatography. The protein with molecular mass around 190 kDa showed by SDS‐PAGE three major polypeptides of 53, 60 and 63 kDa and a minor polypeptide of 30 kDa. Isoelectric focusing of the native protein gave three isoforms with isoelectric points of 6.2, 6.3 and 6.4. Its sedimentation coefficient was 8.0S, with a hydrodynamic diameter of 110 Å and possessed antigenic determinants in common with 7S proteins from common bean and soybean.