A Study of the Internal Structure in Cassava and Rice Amylopectin

Cassava and rice amylopectins and their ϕ,β‐limit dextrins were debranched and the unit chain compositions were analyzed by gel permeation chromatography and high performance anion‐exchange chromatography. The content of amylose and super‐long amylopectin chains was 15.5‐15.6% and 0.8‐1.2% in cassava and 15.1‐18.7% and 3.4‐8.6% in rice starches, respectively. The internal unit chain profiles of the amylopectin samples were obtained from the ϕ,β‐limit dextrins. Short B‐chains were subdivided into a major group (BS_major) with a degree of polymerization (DP) of 8‐25 and a minor group of “fingerprint” B‐chains (B_fp) with DP 3‐7. Cassava and rice amylopectins possessed different amounts and patterns of B_fp‐chains. The rice samples contained higher amounts of B_fp‐chains, which suggested larger size of its clusters when compared with cassava. The content of the shortest “fingerprint” A‐chains (A_fp) was also variable, especially between the rice cultivars. The position of the internal chains in the original amylopectin chain profile was traced. The reconstructed B‐chain profiles fitted well with the original profiles. This implied that most of the B‐chains carried external chain segments of similar lengths, which corresponded to the experimentally measured average length.     

Gelatinization and Thermal Properties of Modified Cassava Starches

The thermal properties of seven commercial modified cassava starches, including oxidized, acetylated, cross‐linked, and combined acetylated and cross‐linked starches were studied by differential scanning calorimetry (DSC) in the glassy and rubbery states. Increase in gel hardness in the rubbery state during storage was also monitored, as well as gelatinization behavior. The modified starches were prepared from granular starch and had a degree of substitution in the range 0–0.053. The glass transition temperatures (T_g) of the modified starches were 3–6°C significantly lower than that of the non‐modified starch. The physical aging peak temperatures were also significantly reduced by 2–3°C, compared to the non‐modified starch, while aging enthalpies increased. Starch modifications did not decrease amylopectin retrogradation significantly. During storage, the oxidized starch gel became significantly harder than the non‐modified starch gel, while the hardness of the acetylated and/or cross‐linked starch gels was significantly reduced, which confirmed that acetylation or cross‐linking can decrease hardness, even when the extent of modification is limited. Different modifications controlled different properties of the starch system, with cross‐linking and acetylation influencing the gelatinization behavior and the changes in starch gel texture during storage, respectively.     

Transformation and Balance of Cyanogenic Compounds in the Cassava Starch Manufacturing Process

The balance of total cyanogenic compounds and distribution of each compound including bound cyanide, cyanohydrin and free cyanide were evaluated in a cassava starch factory, having a production capacity around 100 t starch per day. The production of starch began with transferring washed roots to the rasper, followed by a series of extractors, separators, dewatering centrifuge and flash dryer, with an average water consumption of 11.4 t per ton dry starch. The total amount of cyanogenic compounds entering the process varied from 28 to 43 kg HCN equivalent per day, depending on the root quality. In roots, 64% of bound cyanide was primarily found and it significantly decreased to 22% after rasping whereas the cyanohydrin content increased from 34% to 62%. Most of cyanogenic compounds, predominantly present as cyanohydrin (55 to 70%), was discharged in liquid and solid wastes, accounting for 92% and 5% of total cyanide in roots, respectively. Only a negligible amount of cyanogenic compounds remained in the starch products, having less than 2 mg HCN equivalent per kilogram dry starch. Typically, water from the separators with 91% total cyanide content was recycled to the root washer before being discharged as wastewater, whereas the liquid from the coarse extractor (43% of total cyanide) was recycled to the rasper. This could cause the accumulation of cyanogen in the process and, therefore, in the finished products. With knowledge of the balance and transformation of cyanogens in starch processing, it is possible to assure the quality of low‐cyanide starch by modifying starch process features such as water circulation and pH adjustment.     

Physical structure behavior to wettability of electrospun poly(lactic acid)/polysaccharide composite nanofibers

Poly(lactic acid) has been electrospun into submicron fibers with embedded cassava starch matrix. The fibers had average fiber diameters between 140 and 680?nm. The starch content varied from 10 to 20% in total solids. Water contact angles were measured on sheets of these fiber materials and correlated with the fiber size and starch content. Water contact angles varied from 80 to 120° which shows that the fiber composition can control the mat properties from hydrophilic to hydrophobic. The results also showed variation in the average fiber diameters alone did not always affect sheet wettability. These results show the importance of the relationship between the electrospun fiber sheet topography and material composition to the wettability of polysaccharide electrospun nanofibers.     

Hydration and physicochemical properties of small‐particle cassava starch

Acid hydrolysis followed by ball milling was applied to cassava starch in order to fracture the granules. Lintnerisation led to degradation first in the amorphous domains and increased the crystallinity. The resulting increase in internal defects and brittleness made the granules more susceptible to breakage upon milling. Ball milling, although leading to some degree of crystallinity loss, could effectively reduce the size of acid‐hydrolysed starch while the total double helix remained relatively unchanged. The resulting small‐particle starch was structurally more heterogeneous (wider T_m range). Swelling of small‐particle starch was accompanied by solubilisation of water‐soluble fragments at a temperature greater than 60 °C. The properties of individual granules are strongly influenced by the hydration and physicochemical properties of their amorphous and crystalline domains. © 2002 Society of Chemical Industry     

Granule Sizes of Canna (Canna edulis) Starches and their Reactivity Toward Hydration,Enzyme Hydrolysis and Chemical Substitution

Small and large granule fractions were isolated from canna starch (Canna edulis, green leaf cultivar), and their morphology, physicochemical properties, susceptibility towards granular starch hydrolyzing enzymes and chemical reaction with propylene oxide were investigated. Canna starch consisted of a mixed population of large, medium and small granules; the mean of granule diameter was 47.4 μm. The small granules presented round and polygonal shapes, whereas the large granules had oval and elliptical shapes. Significant variations in digestibility of the various granules size by granular starch hydrolyzing enzymes were observed. During the first 24 h, the hydrolysis rate of small granules was higher than that of native and large granule starches. After 72 h, however, the degree of hydrolysis of small granule, large granule and native starches had reached the extent of 19.6%, 32.0% and 27.2%, respectively. The larger the granule size, the higher the MS obtained when modified with propylene oxide, which was due to the higher swelling power of the large granules. The results obtained from this study suggest that small granules had lower water and chemical affinity when compared with the bigger ones. The difference in the reactivity of small and large granules could be presumably attributed to the starch components (amylose and amylopectin) and their organization of glucan chains in ordered and/or less ordered structure of these two fractions.     

Cassava Starch Technology: The Thai Experience

Cassava starch is an important export commodity of Thailand, about 2 × 10⁶ t are expected annually. Initially, cassava was mainly processed to meal and flour. Due to the high market demand for cassava products, the Thai cassava starch industry was established and has developed from small to large‐scale with improved processing technology. At present, a production capacity of one factory is, on average, 200 t starch per day. Transition from small to large‐scale production was accompanied by varietal development of root having high starch yield and technological improvement of starch production with shorter processing time and better starch quality. Most process technologies are still imported and adopted from those of other starches. The Thai cassava starch industry still encounters impediments, including high production cost, high resource consumption, starch loss, and adverse environmental impact especially sulfur, cyanide, solid and liquid waste. This industry continues to develop, in order to remain internationally competitive.