THE KINETIC PROPERTIES OF LACTASE,PAPAIN AND LIPASE IMMOBILIZED ON A SINGLE SUPPORT1

Lactase, papain and lipase enzymes were immobilized concomitantly on derivatized Sepharose 4-B. Equal molar concentrations of each enzyme were allowed to react with activated Sepharose and a preferential binding of lipase and papain over lactase was observed. This preferential binding was explained by differences in diffusion rates of enzymes resulting in greater availability of binding sites within the beads to certain enzyme species. The effects of pH of assay, temperature of assay and substrate concentrations on each individual enzyme were determined. Soluble forms of each enzyme were used for comparison. There were some differences in pH and temperature optima for the immobilized enzymes. However, the affinity of the enzymes for their substrates was substantially the same.     

Effect of Silicone Quenching and Acid Polishing on the Strength of Glass

Soda-lime glass rods 5 mm in diameter were quenched in silicone oil and also in a saturated hydrocarbon oil of similar viscosity. The effect of etching, etching and quenching, and etching, quenching, and re-etching was examined in relation to the strength of the rods. Rods quenched in the silicone oil were no stronger than those quenched in the hydrocarbon oil. Etched rods had a strength of 300,000 psi. Quenching these high-strength rods reduced their strength to 110,000 psi. This decrease in strength may be explained in terms of the formation of crystalline and noncrystalline microflaws during the heating and cooling cycle. Re-etching, after quenching, resulted in rods with a maximum strength of 384,000 psi.     

Grain Growth in Two-Phase Ceramics: Al2O3 Inclusions in ZrO

The effect of Al₂O₃ inclusions with a greater average size (0.6 μm) than the average particle size of the major phase powder (<0.1 μm) on grain gowth was examined by sintering ZrO₂/Al₂O₃ composites (0,3,5,10, and 20 vol%) at 1400°C and then heat-treating at temperatures up to 1700°C. Normal grain growth was observed for all conditions. The inclusions appeared to have no effect on grain growth until the ZrO₂ grain size was ∼1.5 times the average inclusion size. Grain growth inhibition increased with volume fraction of the Al₂O₃ inclusion phase. At temperatures 1600°C, the inclusions were relatively immobile and most were located within the ZrO₂ grains for volume fractions <0.20; at higher temperatures, the inclusions could move with the grain boundary to coalesce. Grain growth was less inhilited when the inclusions could move with the boundaries, resulting in a larger increase in grain size than observed at lower temperatures. Analogies between mobile voids, entrapped within grain at lower temperature due to abnormal grain growth during the last state of sintering, and the observations concerning the mobile inclusions are made suggesting that grain-boundary movement can "sweep" voids to grain boundaries and eventually of four-grain junctions, where they are more likely to disappear by mass transport.     

OPTIMAL PRODUCTION PLANNING AND INVENTORY CONTROL*

This paper is concerned with the optimal production planning and inventory control. The first problem is a multiperiod production scheduling problem in which the objective is to minimize the operating cost for a planning period. This cost is composed principally of the sum of the production cost and inventory carrying cost. The second problem considers an inventory system with two decision variables in each planning period. These are the production schedule and work force which are to be determined so as to minimize the operating cost which includes the costs of changing the production rate, of changing the work force and of carrying the inventory. The maximum principle in the discrete form is used to reduce both the first problem which has N decision variables and the second problem which has 2N decision variables respectively to a series of two decision variables problems. The so-called sequential simplex pattern search technique is used to determine the optimal values of these two decision variables. Numerical examples are given to demonstrate the method.     

DYNAMIC PROGRAMMING FOR PROCESS OPTIMIZATION 1. AN ALGORITHM FOR DESIGN OF MULTI-STAGE GRAIN DRYERS

A dynamic programming algorithm for determining the optimum operational parameters and size of a multi-stage concurrent flow dryer with intermediate tempering stages was developed. The objective function was based on energy and capital costs. The operational parameters were constrained by the desired final moisture content and the maximum allowable value of important grain quality factors. The two- and three-stage concurrent flow dryers have a higher investment cost than the single stage unit, but were less expensive to operate due to the decreased grainflow rate in the single-stage unit. On the basis of operating cost, the multi-stage concurrent flow dryer was preferable to a comparable crossflow dryer for drying corn.     

Retention of Micronutrients by Polymer Coatings Used to Fortify Rice

Nutrient deficiency diseases are public health problems in developing nations. Our objective was to design a rice-fortification method using materials approved for use in foods to retain significant quantities of added nutrients during the common practice of boiling rice in excess water and draining it. We accomplished this by applying nutrients to rice in edible polymer coatings. Various starches and cellulosic polymers were evaluated with respect to flexibility, strength, stickiness and nutrient retention. Combining hydroxypropyl methylcellulose and methylcellulose (3:1) gave the best results. Nutrient retentions for 1g of coated rice cooked in 100 ml water and drained were: Vitamin A, 70%; iron, 100%; niacin, 18%; thiamin, 18%, riboflavin, 21%.