THE INFLUENCE of pH ON the KINETICS of ACID HYDROLYSIS of SUCROSE

Sucrose acid hydrolysis was studied as a potential chemical time-temperature integrator to use under pasteurization conditions. A nonisothermal method was used to determine the kinetic parameters of this reaction at different pH values in the range of 0.8 to 2.5 and covering the range of temperatures from 50 to 90G. the nonisothermal method was first validated with the classical two-step isothermal method at pH 2.5. Kinetic parameters showed to be highly collinear (correlation of 0.99), but it was concluded that the activation energy can be assumed independent of pH and equal to 99 kJ/mole with the preexponential factor being proportional to the H⁺ concentration. Results are favorable for the future application of this system in the evaluation of pasteurization processes. Since the activation energy was found to be independent of the pH, this system is useful as a TTI for validation of mathematical models, but not so much for monitoring quality factors, except those with an equal activation energy.     

GRANULE SIZE DISTRIBUTION AND RHEOLOGICAL BEHAVIOR OF HEATED MODIFIED WAXY AND UNMODIFIED MAIZE STARCH DISPERSIONS

The effect of granule size distribution, supported by microscopic analysis, on the steady shear and dynamic shear rheological behavior of 5% gelatinized modified waxy maize starch (MWMS) dispersions heated at 80C for time periods from 0.5 to 30 min was examined and data obtained with 5% unmodified maize starch (UMS) dispersions was used to provide additional insight. The MWMS dispersions showed a faster and more extensive swelling than the UMS dispersions at 80C. They also exhibited rheopectic (anti-thixotropic) time-dependent and shear thinning with yield stress behavior. UMS dispersions showed shear thickening characteristics after short heating times that gradually turned to shear thinning as the heating time was increased. Dynamic tests on MWMS dispersions showed G' was about ten times higher than G". G' showed a small dependence on frequency over 0.6–63 rad/s while G", after an increase at low frequencies, became less sensitive. The gelatinized MWMS dispersions can therefore be classified as 'weak gels.' The flow behavior index of UMS dispersions was strongly     

EFFECTIVE PURIFICATION PROCEDURE OF ASPERGILLUS ORYZAEα-AMYLASE FROM SOLID STATE FERMENTATION CULTURES INCLUDING CONCANAVALIN A-SEPHAROSE

Solid state fermentation cultures of Aspergillus oryzae NRRL 3485 on moistened wheat bran produced high levels of α-amylase as judged by the specific activity of water extracts (500–700 units/mg protein) and by the enzyme concentration (around 0.15 g/L) in those extracts. The purification of α-amylase by affinity chromatography on Concanavalin A-Sepharose is described. A first DEAE-Sepharose chromatography step (binding of the enzyme contained in the water extract and further elution with 0.2 M NaCl, pH 5) was necessary in order to remove contaminants that hinder the binding of the glycoprotein α-amylase to the lectin. Elution was performed with 7.5 mM α-D-methylmannoside. The enzyme was obtained highly concentrated and purified with a specific activity of 2000 units/mg protein and a recovery of around 60%, free of α-glucosidase, amyloglucosidase and color contaminants. The purity of the enzyme preparation was assessed through nondenaturing gel electrophoresis and sucrose gradient centrifugation. An improvement of the performance of the purification procedure is presented in which the maximum capacities of both the anion exchanger and the lectin matrices were exploited.     

OPTIMUM STERILIZATION: A COMPARATIVE STUDY BETWEEN AVERAGE and SURFACE QUALITY

Sterilization temperatures to maximize volume average or surface quality retention were calculated for one-dimensional conduction heating foods as a function of (1) Food Properties, (2) Processing Conditions and (3) Processing Criteria. A target lethality at the least-lethality point was used as a constraint, and optimal temperatures were qualitatively and quantitatively compared for equal design variables.
Average quality optimum conditions depend linearly on the inverse square of the D_refq-value for the quality factor. These conditions do not vary linearly with all the other influential variables, opposite to what had been observed for surface quality. Optimum temperature for maximum average quality is always higher than the corresponding one for surface quality, but the difference is not constant. A systematic approach to the dependence of average quality optimal conditions on all the relevant parameters was carried out and quantitative relations were obtained. Optimum average quality retention is independent of surface heat transfer resistance.     

COLOR, POLYPHENOLOXIDASE, AND SENSORY CHANGES IN BANANA JUICE AS AFFECTED BY HEAT AND ULTRAFILTRATION

A study was conducted to determine the effects of banana maturity (less mature; maturity stage 3, more mature; maturity stage 7), heat treatment of banana puree, heat pasteurization of juice, and ultrafiltration (UF) of juice on color, polyphenoloxidase (PPO) activity, and flavor of puree and juice. Heating puree to 90C inactivated PPO and reduced browning in puree and juice, especially in puree from more mature bananas which had greater PPO activity. PPO activity decreased considerably during cold-setting and filtration of juice, and was not detectable in unheated, pad-filtered juice from less mature bananas. UF of juice through a 10,000 mwco membrance, but not a 30,000, removed all PPO activity and reduced juice browning. Pasteurization of juice (hot fill at 90C) increased browning, but not as much as PPO activity in the puree. Pasteurization had no effect on juice flavor if the puree had been heated to 90C previously as puree, but altered the flavor (i. e., more cooked banana flavor) of juice that had not been previously heated to 90C. Pasteurized juice that had not been heated to 90C as puree had similar flavor (no significant difference) as pasteurized juice that had been heated to 90C as puree.     

STABILITY OF ASCORBIC ACID IN ORANGE JUICES AFTER INITIAL USE AT HOME BEGINS

Ascorbic acid (AA) stability in orange juices, both fresh and commercially packaged in different types of containers (Tetrabrik, glass and tin), was studied. The purpose was to ascertain how well AA is retained once use at home has commenced. The AA levels of the orange juices were measured at 0, 1, 3, 5, 67, 24, 48, 72 and 168h following squeezing in the case of fresh oranges and for commercially packaged juices following opening of the container. Storage was at 4 or 25C. Fresh juice was stored in an open jar; packaged juice in the container in which it came. When stored 7 days at 4C, retention ranged from 93.8 to 95%.     

Effect of Egg Yolk and Egg Yolk + Salt on Rheological Properties and Particle Size Distribution of Model Oil-in- Water Salad Dressing Emulsions

The role of egg yolk and egg yolk + salt in stabilizing oil-in-water (o/w) salad dressing emulsions pre-stabilized with xanthan and propylene glycol alginate was studied using creep tests, steady shear, and particle size analysis. Results show that each combination significantly affects rheological stability of model o/w salad dressing emulsions. All emulsions exhibited viscoelasticity and wcrc characterized by three parameters: η₁, E₁ and η_N. Steady shear measurements showed that both egg yolk and salt increased viscosity radically. Particle size data showed significant changes with both addition of egg yolk and salt to the model system.     

The effect of different sweeteners in low-calorie yogurts — a review

Recently, increased demand for low-calorie products and foods with alternative sweeteners has gained special attention. Intense sweeteners avoid the problems of health risks associated with caloric sweeteners. This paper presents information about the technical characteristics of the more widely used artificial sweeteners and the possibility of their application in low-calorie yogurts.     

LIQUID-LIQUID EQUILIBRIUM OF THE THREE LIQUID PHASES AT EQUILIBRIUM SYSTEM WATER-PHOSFHORIC ACID-DI-ISOPROPYL ETHER AT 25 AND 40°C.

Solubility and liquid-liquid equilibrium data have been obtained for the ternary system Water-Phosproric Acid-Di-isopropyl Ether at 25 and 40^°C. This system presents a three-phase1 region at bcth temperatures. Data for the tie lines end the solubility curve in the zone above the three-phase region at 25^°C have been obtained by analyzing the phcsphcric acid and the di-isopropyl ether composition in the conjugated phases. Di-isoprcpyl ether i"as analyzed by NMR, using acetic acid as internal standard. It was impossible to apply conventional cloud point method to this zone due to the presence of an isooptic region.     

Factors Affecting the Gelation Properties of Hydrolyzed Sunflower Proteins

The effects of temperature and several chemicals on gelation time and strength of gels formed by heating (pH 8) 5% solutions of trypsin hydrolyzed sunflower proteins were studied by dynamic rheological methods. The storage modulus reached a maximum at 80°C. Ca₂Cl (and NaCl at > 0.2M) accelerated gelation and weakened the gel. NaCOCH₃Na₂SO₄ and NaSCN decreased the storage modulus. Urea decreased gelstrength and at high concentrations slowed gelation. Time for gelation diminished and gel strength increased with increasing mercaptoethanol concentration up to 0.1M. Propylene glycol at 5–20% concentrations accelerated gelation and at 5% also increased gel strength. Trypsin hydrolyzed sunflower proteins could be useful in products requiring strong gels at high temperatures.