Weakening the integrity of waxy starch granules by selective degradation of amorphous matrices using gaseous hydrogen chloride.

Waxy corn starch with 6-12 % moisture was degraded by gaseous hydrogen chloride (HCl(g)) then characterized chromatographically and microscopically to investigate the relationship between moisture-resulting changes in unit chain properties of starch and its susceptibility to swelling. Starches with the highest degradation extents at different moisture content had recoveries of 76-83 % (w/w) and the weight-average degrees of polymerization of 66-93 anhydroglucose unit. Additionally, the HCl(g)-degraded starches were still of birefringent granules but with internal cavity. When increasing the swelling temperature from 25 to 40 °C, some granules showed enlarged internal cavity, and some were fragmented. Change in granule morphology, accompanied by leaching of constituting polymers, was particularly evident for starch with preferential degradation of B1 chains over B2+ chains as the moisture content decreased from 9 % to 6 %. These findings not only manifest the impact of changes in B2+ and B1 chains on the swelling characteristic of HCl(g)-degraded granules, but also demonstrate an approach for weakening the integrity of granules by selective degradation of amorphous matrices using HCl(g).

Degradation of corn starch with different moisture content by gaseous hydrogen chloride.

Corn starch, subjected to solid-state degradation using gaseous hydrogen chloride, was characterized to investigate the parameter effects on starch properties and further explore the thermal behavior of inter-crystalline amorphous lamellae of starch. The obtained starch granules exhibited A-type polymorph with 75-98 % recovery (w/w). Degreasing moisture content (6-12 %) with increasing duration (1-8 h) and temperature (25-45 °C) progressively decreased the weight-average degree of polymerization to 55-75 anhydroglucose unit and increased the gelatinization temperature range. However, starch degraded at 6 % moisture and 25 °C exhibited much higher polydispersity index than those degraded at 9-12 % moisture, accompanied by the decreased start but comparable onset gelatinization temperatures. This thermodynamic difference was inherent but diminished gradually with increasing degradation temperature. These findings suggest that the degradation at 9-12 % moisture starts from the bulk amorphous region of starch then sequentially reaches its inter-crystalline amorphous lamellae, while the simultaneous degradation of both regions is for starch with 6 % moisture.

Properties of High-Swelling Native Starch Treated by Heat-Moisture Treatment with Different Holding Times and Iterations.

Tapioca and potato starches were used to investigate the effect of heat-moisture treatment (HMT; 95-96 °C, 0-60 min, 1-6 iterations) on gelatinization properties, swelling power (SP), solubility and pasting properties. Tapioca starch had similar content and degree of polymerization of amylose, but a higher amylopectin short/long chain ratio, to potato starch. After HMT, the gelatinization temperature range was narrowed for tapioca starch, but was widened for potato starch. Decreases in SP and solubility were less for tapioca than potato starches, coinciding with a progressive shift to the moderate-swelling pasting profile for tapioca but a drastic change to the restricted-swelling profile for potato. Moreover, decreasing extents of SP and maximum viscosity for HMT tapioca starch were, respectively, in the range of 47-63% and 0-36%, and those of HMT potato starch were 89-92% and 63-94%. These findings indicate that the granule expansion and viscosity change of starch during gelatinization can be tailored stepwise by altering the HMT holding time and iteration.

Progressive alterations in crystalline structure of starches during heat-moisture treatment with varying iterations and holding times.

Corn, tapioca and potato starches after heat-moisture treatment (HMT) at 95-96 °C for 0-60 min with 1-6 iterations were characterized for their gelatinization properties to elucidate the HMT-generated differences in crystalline structure of the starches. The enthalpy changes (ΔH) of all HMT starches were decreased, and the decreases in ΔH of the whole and of the fraction corresponding to well-ordered region of crystalline structure were both in the order of corn < tapioca < potato. With increasing HMT iteration and holding time, the same order was also observed for the shifting extent of pasting properties of HMT starches to that of restricted-swelling granules. The findings demonstrate the crystalline structure of starch consists of less- and well-ordered regions, and suggest that the extent of intermingling of these regions might be in the order of corn < tapioca < potato starches.

Indigestible pyrodextrins prepared from corn starch in the presence of glacial acetic acid.

This study was conducted to evaluate the feasibility of using acetic acid (0-2.5%) as the catalyst in the production of pyrodextrins from corn starch at 140-180 °C, and to elucidate the effects of catalyst concentration and pyrolytic temperature on the characteristics of indigestible pyrodextrins. In the absence of acetic acid, noticeable changes to the loss of birefringence, increased solubility, plateau of molecular weight reduction, decreased reducing sugar content and digestibility were observed at 180 °C. By using catalyst, the alterations in the aforementioned characteristics of pyrodextrins were intensified. Moreover, by using 0.5-1.0% catalyst, the substantial alterations in birefringence, solubility and molecular weight were observed concurrently for pyrodextrins formed at 170 °C. Further increasing the concentration of acetic acid to 1.0-2.5% decreased the intervening temperature to 160 °C. The findings suggest that indigestible pyrodextrins with desired characteristics could be tailored via using various combinations of catalyst concentration and pyrolytic temperature.

Effect of granular characteristics on pasting properties of starch blends.

Pasting and morphology properties of starch blends composed of waxy (waxy rice and waxy corn) and non-waxy (normal corn, tapioca and potato) starches at various ratios were investigated for elucidating effect of granular characteristics on pasting of blends. Pasting profiles of blends were between those of the component starches alone, while the changes varied with starch source. Results reveal obvious water competition during pasting for blends composed of waxy starch and highly swelling non-waxy (tapioca or potato) starch. On the contrary, starch blends composed of waxy starch and non-waxy (normal corn) starch with restricted swelling showed less water competition during pasting, and the pasting attributes could be estimated from those of the component starches following the mixing ratio. Results indicate that the pasting properties of starch blends composed of waxy and non-waxy starches depend on not only the mixing ratio, but also the granular characteristics of component starch.

Genotype diversity in structure of amylopectin of waxy rice and its influence on gelatinization properties.

A set of 13 waxy rice genotypes prepared by chemically-induced mutation of non-waxy rice variety TNG67 and 7 waxy rice varieties widely planted in Taiwan were screened for various structural and gelatinization properties of starches. Wide variation on physicochemical properties and molecular structure of amylopectin for the 20 waxy rice starches were obtained and relationship between gelatinization properties and molecular structure of starch were discussed. More attributes on swelling and gelatinization thermal properties, comparing to pasting attributes, showed significant correlation with molecular structure parameters. The swelling and gelatinization thermal properties of waxy rice starch did not show significant correlation with molecular size of amylopectin, while significant correlations were found between the swelling or gelatinization thermal properties and chain length of amylopectin. Results suggest that the swelling and pasting of waxy starch is essentially dominated by granule architecture and is dependent on the interactions among amylopectin chains.

Characteristics of taro (Colocasia esculenta) starches planted in different seasons and their relations to the molecular structure of starch.

Physico-chemical properties and molecular structure of starches from three cultivars (Dog hoof, Mein, and KS01) of taro tubers planted in summer, winter, and spring were investigated. The effects of the planting season on the physico-chemical properties and the molecular structure of starch were determined, and the relations between the physico-chemical properties and the molecular structure of starch are discussed. Results indicate that taro starches from tubers planted in summer had the largest granule size, a low uniformity of gelatinization, and a high tendency to swell and collapse when heated in water. Taro starch planted in summer also showed an elasticity during gelatinization that was higher than that of starches planted in the other seasons. In addition to the planting season and the variety, rheological and pasting properties of taro starches studied are influenced not only by the amylose content but also by the chain-length distribution of amylopectin, whereas swelling power and solubility only depend on the amylose content of starch. Taro starch with relatively high amylose content, high short-to-long-chain ratio, and long average chain length of long-chain fraction of amylopectin displayed high elasticity and strong gel during heating.

Molecular degradation rate of rice and corn starches during acid-methanol treatment and its relation to the molecular structure of starch.

The degradation rates of rice and corn starches with different contents of amylose treated in methanol containing 0.36% HCl at 25 degrees C for 1-15 days were evaluated by monitoring the weight average degree of polymerization of starch. A two-stage degradation pattern during acid-methanol treatment was found for the starches studied, which were the slow (first) and the rapid (second) degradation stages. Waxy starches showed a shorter time period of the first stage than that of nonwaxy starch. Rice starch showed a shorter time period of the first stage and a higher degradation rate of the second stage than the counterpart corn starch with similar amylose content. Despite the botanic source and amylose content of starch, the degradation rate of starch in the second stage significantly (p < 0.05) correlated to the S/L ratio (r = -0.886) and polydispersity (r = 0.859) of amylopectin branch chains of native starch.