No abstract

No abstract

Sucrose solubility means the concentration of sucrose in a saturated solution which is in equilibrium with sucrose in the solid state. Solubility of sucrose in water is of fundamental importance in defining the supersaturation, or driving force of sucrose crystal growth. Solubility of sucrose in mixtures of water with different organic solvents has important uses in some branches of the chemical and pharmaceutical industries, in analytics, etc. It is especially the case for ethanol, methanol, propyleneglycol, glycerol, acetone and pyridine.A molecule of sucrose has eight hydroxyl groups, three hydrophilic oxygen atoms (bound in a circle) and 14 hydrogen atoms. This enables the formation of hydrogen bonds with water molecules, hydration of sucrose molecules and therefore easy dissolution of sucrose in water. In nonaqueous solvents, sucrose solubility is significantly lower than in water and sucrose does not dissolve in non-polar solvents. Sucrose shows much higher values of solubility in ammonia, dimethylsulphoxide, aminoethanol and methylamine. Lower values exist for sulphur dioxide, formic and acetic acid, dimethylformamide, pyridine, glycol, methanol, ethanol and dioxan.Solubility of sucrose is influenced by temperature and by the amount and type of other dissolved molecules (impurities, non-sugars). Only a few of the impurities do not affect sucrose solubility or decrease it. Most impurities increase solubility. This is especially true of non-sugars which remain in sugar juices after their purification by standard procedures of sugar technology. Expression of concentration and composition of sucrose solutionsConcentration of sugar solutions is expressed in different ways depending on current application. Among the usual ways we can count weight percent (formerly Brix), mass and mole fraction, weight, sucrose to water ratio, molality, molar concentration and partial density. The cited quantities are defined for pure and impure solutions in the following text. A molecule of sucrose has eight hydroxyl groups, three hydrophilic oxygen atoms (bound in a circle) and 14 hydrogen atoms. This enables the formation of hydrogen bonds with water molecules, hydration of sucrose molecules and therefore easy dissolution of sucrose in water. In nonaqueous solvents, sucrose solubility is significantly lower than in water and sucrose does not dissolve in non-polar solvents. Sucrose shows much higher values of solubility in ammonia, dimethylsulphoxide, aminoethanol and methylamine. Lower values exist for sulphur dioxide, formic and acetic acid, dimethylformamide, pyridine, glycol, methanol, ethanol and dioxan.Solubility of sucrose is influenced by temperature and by the amount and type of other dissolved molecules (impurities, non-sugars). Only a few of the impurities do not affect sucrose solubility or decrease it. Most impurities increase solubility. This is especially true of non-sugars which remain in sugar juices after their purification by standard procedures of sugar technology. Expression of concentration and composition...

Rice (Oryza sativa L.), a major cereal crop, is the staple food source for half of the world population. Rice is an excellent source of energy, in the form of starch, and it gives the benefit of providing proteins with a higher nutritional quality than those of other cereal grains (M���������� et al. 1998). At present, many possible applications of microwave (MW) energy in the food industry are known. MW drying was demonstrated to be an alternative means for the rice drying (W�������� & K����� 1986). Major components and the enzymic system of rice can be influenced during MW treatment. Since starch comprises approximately 90% of the dry matter of the rice endosperm, the research on rice cooking behaviour has focused on this fraction. W�������� and K����� (1986) used two long-grain cultivars and one medium-grain cultivar of rice for drying under vacuum by means of MW energy to determine the effects on the physicochemical properties and eating characteristics. Amylographic characteristics were used to obtain more information on the influence of the starch fraction of rice on its cooking behaviour. No significant differences were found in both maximum viscosity and setback viscosity between the air-dried controls and MW dried rice. M������ and T������ (1993) reported the effect of MW treatment on the contents of total and enzyme resistant starch in white and brown rice (three Australian cultivars -Calrose, Doongara and Waxy). The starch content was maintained or increased by cooking in a MW oven except with cv. Waxy. The increase was consistent with starch gelatinisation and therefore, with greater susceptibility to enzymic attack. Cooked rice had a higher content of resistant starch than the corresponding raw product, possibly because of the production of retrograded starch. It can be concluded that although the content of the resistant starch in rice increased by the techniques known to increase the resistant starch in other foods (heating, cooking, cooling and freezing), the impact was not as great. Z���� et al. (1996) treated two japanase cultivars of rice (700 W, 3 min, 500 g batches) with MW and determined physicochemical properties, cooking quality and enzyme activities. It was found that both cultivars of rice had debranching enzymes, and that α-amylase activities were significantly lower than those of the untreated controls. Cooking qualities, such as water absorption capacity, pH, and iodine blue value of cooking water, β-amy- The properties of rice after microwave irradiation were evaluated by means of amylograph and enzymic determination of the total and the damaged starch. The content of the total starch was not affected by the immediate energy output used for irradiation but that of the damaged starch increased with microwave energy absorbed and the temperature of treatment, mainly at the moisture of 30% and the temperature of 100°C. The results of damaged starch determination are in accordance with the amylographic readings of changes at maximum viscosity. Amylographic characteristics suggest mini...

No abstract