THERMAL AND HIGH PRESSURE INACTIVATION KINETICS OF VICTORIA GRAPE POLYPHENOL OXIDASE: FROM MODEL SYSTEMS TO GRAPE MUST

Polyphenol oxidase (PPO) was extracted from white grapes (var. Victoria, South Africa) and partially purified by ammonium sulfate precipitation. Detailed kinetic studies on thermal and high‐pressure inactivation of grape PPO were preformed in McIlvaine buffer (pH = 4.0), in reconstituted grape must and in grape must. Thermal inactivation of PPO in McIlvaine buffer followed a first‐order model while in reconstituted grape must and grape must a biphasic inactivation behavior has been observed. Under all conditions investigated, a first‐order kinetic model could describe the pressure inactivation data. It was found that PPO is more thermostable and pressure‐stable in must than in reconstituted grape must and McIlvaine buffer at the same pH = 4.0.     

Finding an optimal dynamic advertising policy

In this paper a solution is presented to an important marketing problem : the timing of advertising expenditure. Using a differential equation to model the relationship between the sales and advertising rates and using profit as a criterion, a synthesis of the optimal dynamic advertising policy as a function of the current sales level and length of the campaign is derived. In addition, using profit as a criterion, the profitability under an optimal dynamic advertising policy is compared with the profits obtained using an optimal static policy. It is shown that a significant increase in profits can result from employing the optimal dynamic policy.     

Influence of Fruit Composition, Maturity and Mold Contamination on the Color and Appearance of Strawberry Wine

Color composition of strawberry wines made from ripe, overripe, and mold-contaminated fruit (Benton and Totem varieties) was monitored over 6 wk storage. Overripe fruit with its higher anthocyanin and total phenolics gave wines with better color than fully ripe fruit. Totem fruit had higher anthocyanin, lower polyphenol oxidase activity and lower total phenolics than the Benton variety and produced wines with better color. Mold contamination increased juice viscosity, reduced fermentation rate, and accelerated color degradation. Anthocyanin content and Hunter L values of wines were highly correlated with panel color evaluations.     

Modeling the Contribution of Sugars, Ascorbic Acid, Chlorogenic Acid and Amino Acids to Non-enzymatic Browning of Potato Chips

The contribution of potato constituents to color development in fried chips was evaluated using model systems. Soluble constituents of potato slices were removed using water and ethanol. Leached slices were infiltrated with pH 6.2 solutions containing sucrose, reducing sugars (glucose and fructose), ascorbic, chlorogenic and amino acids (asparagine and glutamine) in quantities typical for potatoes. Infiltrated slice composition was evaluated by HPLC. Slices were fried and the color measured. Reducing sugars showed linear association with L* and hue angle and quadratic relationship with chroma of chips. Ascorbic acid affected chip color at low reducing sugar levels (40 mg/100g tuber); sucrose also contributed to chip color development.     

BUOYANCY INDUCED FLOWS DUE TO ENERGY SOURCES IN COLD QUIESCENT PURE AND SALINE WATER

From the simple density state equation of Gebhart and Mollendorf (1977), a relatively compact similarity formulation has resulted for vertical boundary layer flows, as developed by Gebhart and Mollendorf (1978). This treatment accommodates the occurrence of density extrema in the flow field. Calculations have been given there, and elsewhere, for many different vertical flow conditions, as well as for some horizontal ones. However, similarity does not in general result for non-isothermal assigned or resulting midplane conditions, when an unstratified ambient medium is not at the temperature at which the density extremum occurs. However, this is a common circumstance in applications. Here this limitation is removed in a perturbation analysis of three vertical flows: that arising from a vertical surface with uniform heat flux, a plane plume and the flow arising from a concentrated horizontal line source imbedded in a vertical adiabatic surface, i.e., a wall plume. Comparison of perturbation and similarity solutions is also made for the isothermal condition, to corroborate the perturbation formulation. The new formulation also avoids some calculation difficulties which attend buoyancy force reversal across the boundary region. Additional similarity solutions are also given in this range for the isothermal surface condition.     

MODELING FINES ELUTRIATION FROM A SPOUTED BED OF PULP FIBERS

A model was developed to describe the elutriation of fines from a spouted bed of pulp fibers, which is a new method to separate fines from fibers. During spouting the pulp fibers are aggregated in fiber floes, which we model as coarse porous spheres. In general, we can distinguish three liquid regions inside and around a coarse particle in a shear flow: bulk liquid, liquid passing through the sphere, and liquid circulating inside it. A system of three ordinary differential equations describing the balance of fines in these regions was solved numerically. A source term was included to account for the release of fines during the dynamic equilibrium between formation and break-up of fiber floes. Comparison between theory and experiment showed that a simplified two-region model, which contains two adjustable parameters, is adequate to describe the elutriation data.     

Radish Anthocyanin Extract as a Natural Red Colorant for Maraschino Cherries

Red radish anthocyanin extract (RAE) was investigated to color brined cherries as an alternative to FD&C Red No. 40. Primary and secondary bleached cherries were colored using two concentrations of RAE (600 and 1200 mg/L syrup, C1 and C2) and FD&C Red No. 40 (200 ppm). Color and pigment stability of secondary bleached cherries and syrup colored with RAE were evaluated during storage (25°C). CIELAB, chroma and hue angle, showed that RAE imparted color extremely close to that of FD&C Red No. 40, for > 6 mo storage. Monomeric anthocyanin degradation followed first-order kinetics, with half-lives of 29 and 33 wk for syrups colored with RAE C1 and RAE C2, respectively. Higher anthocyanin concentration exerted a protective effect on color stability. Exposure to light slightly accelerated L*, a*, and monomeric anthocyanin degradation.     

Methanol from Wood II. Current Research and Development Programs

The current research projects on gasification of biomass for synthesis gas production are reviewed. Particularly the various pilot plants presently under construction or already in operation at the demonstration scale of 10–50 tons wood/day are discussed in some detail, with emphasis on the demonstration programme of the European Community

Special features, possible disadvantages and areas still requiring additional R & D efforts are indicated for each project. The paper concludes with an outlook on the possible role of catalysis in both primary and secondary gasification and with a discussion on economic feasibility, economics of scale and the need for creative ideas on successfully downscaling of the process.