Production of high fructose syrup from cassava and sweet potato flours and their blends with cereal flours.

Despite being a rich source of starch, root crops such as cassava and sweet potato have not been widely exploited for the production of high fructose syrup (HFS), which is a highly valued sweetener for the food and beverage industries. The major factors contributing to the cost of production of HFS are the cost and labor-intensive steps in the production of starch, different processing temperatures and pH for the enzyme reactions, poor extractability of starch, etc. With the objective of overcoming the cost associated with the preparation of starch, the feasibility of using native cassava/sweet potato flours and their blends with rice flour and wheat flour, as the raw material for HFS production was investigated. The saccharified slurry from cassava--rice flour blends contained 70-72 g reducing sugars/100 g, which was higher than that released from native cassava flour (~69%). Blends of sweet potato with rice or wheat yielded saccharified mash with lower content of reducing sugars (60-66%). Although the percentage conversion to fructose after isomerization was similar for cassava/sweet potato or their blends with cereal flours (42-43%), fructose yield was higher in native cassava flour and cassava-rice blends (28-29 g/100 g) than the other flour blends.

Kinetics of thermal softening of cassava tubers and rheological modeling of the starch.

Cassava or tapioca (Manihot esculenta Crantz) tubers having high amount of carbohydrate are utilized after boiling or processing into starch and flour. Textural properties of raw and cooked tubers depend on variety, maturity, growing environment, physico-chemical and starch properties. Starch is used in food preparations as gelling and thickening agent, stabilizer and texture modifier. This study aims at analyzing and modeling the textural, dynamic rheological and gelatinization properties of selected cassava varieties. The thermal softening behavior was analyzed by linear regression and fractional conversion techniques, rheological properties of the gelated starch by Maxwell and power law models. The varieties were classified based on their physico-chemical, texture profile, rheological and gelatinization properties by multivariate analysis. The textural, rheological and gelatinization properties were significantly affected by the varieties (p < 0.05). Thermal softening of tubers was modeled by dual mechanism first order kinetic model with rate constant values ranging from 0.081 to 0.105 min(-1). Linear regression models with extremely good fit were obtained to explain the relationship between the degree of cooking and relative firmness. The dynamic spectra of the gelated starch showed the characteristics of concentrated biopolymer dispersion and described using Maxwell and power law model. The results showed that textural, rheological and gelatinization properties varied considerably among the varieties and besides the physico-chemical properties, interaction between them and structural make up of the tuber parenchyma had a great influence on cooking quality and rheological properties.

Effect of steam pressure treatment on the physicochemical properties of Dioscorea starches.

Dioscorea alata and Dioscorea rotundata starches were subjected to steam pressure treatments (0.35, 0.7, and 1.05 kg cm(-)(2)) for different periods. The total amylose content in the treated starches was not significantly affected, but the soluble amylose content decreased 3-5-fold. Reducing values and lambda(max) of the iodine complexes were unaffected. Viscosity of the starch paste was reduced by the treatments, and at higher pressures and longer time of treatments, the peak viscosity values were reduced to very low values. Pasting temperatures were enhanced considerably. Swelling volumes underwent reduction, but no change in solubility occurred. Clarity and paste stability were markedly lowered. The results suggest that starch granules are compressed by the steam pressure treatment, leading to vast changes in physicochemical properties.

Cassava fermentation and associated changes in physicochemical and functional properties.

Fermentation of cassava is an important processing technique followed in different parts of the world. Although fermentation is known to bring about vast changes in the physicochemical and functional properties of the tubers, attempts have seldom been made to consolidate and critically analyze the available information. Glaring inconsistencies and contradictions noticeable in some of the results reflect the differences and variations in the artisanal processes followed in the preparation of these products. It also stresses the need for a systematic study of not only the quoted products, but also a number of other fermented cassava products that have not been well documented.