Acid modification of starch granules in alcohols: effects of temperature, acid concentration, and starch concentration

Modification methods toward the production of porous starch: a review

Starch is a complex carbohydrate formed by the repeating units of glucose structure connected by the alpha-glycosidic linkages. Starch is classified according to their derivatives such as cereals, legumes, tubers, palms, fruits, and stems. For decades, native starch has been widely utilized in various applications such as a thickener, stabilizer, binder, and coating agent. However, starches need to be modified to enhance their properties and to make them more functional in a wide range of applications. Porous starch is a modified starch product which has attracted interest of late. It consists of abundant pores that are distributed on the granule surface without compromising the integrity of its granular structure. Porous starch can be produced either by enzymatic, chemical, and physical methods or a combination thereof. The type of starch and selection of the modification method highly influence the formation of pore structure. By carefully choosing a suitable starch and modification method, the desired morphology of porous starch can be produced and applied accordingly for its intended application. Innovations and technologies related to starch modification methods have evolved over the years in terms of the structure, properties and modification effects of different starch varieties. Therefore, this article reviews recent modification methods in developing porous starch from various origins.

Fourier transform infrared and Raman spectroscopic study of the effect of the thermal treatment and extraction methods on the characteristics of ayocote bean starches

Starches isolated from four ayocote bean varieties were modified by thermal treatment to determinate the effect of the treatment on the structural changes of ayocote bean starch. Scanning electron microscopy indicates that the starch granules have oval and round shapes, with heterogeneous sizes and fractures when the extraction method is used. The presence of new bands at 2850 and 1560 cm-1 in the FT-IR spectra showed that the thermal treatment of ayocote beans induced an interaction between the protein or lipid and the amylose or amylopectin, while the sharpest band at 3400 cm-1 indicated a dehydration process in the starch granule in addition to the presence of the band at 1260 cm-1, indicating the product of the retrogradation process. The thermal treatment reduced the crystallinity as well as short-range order. Raman spectroscopy revealed that acute changes occurred in the polysaccharide bonds after thermal treatment. This study showed that the thermal treatment affected the structural properties of ayocote bean starches, the interactions of the lipids and proteins with starch molecules and the retrogradation process of starch.

Biodegradation of starch films: the roles of molecular and crystalline structure

The influences of molecular, crystalline and granular structures on the biodegradability of compression-molded starch films were investigated. Fungal α-amylase was used as model degradation agent. The substrates comprised varied starch structures obtained by different degrees of acid hydrolysis, different granular sizes using size fractionation, and different degrees of crystallinity by aging for different times (up to 14 days). Two stages are identified for unretrograded films by fitting degradation data using first-order kinetics. Starch films containing larger molecules were degraded faster, but the rate coefficient was independent of the granule size. Retrograded films were degraded much slower than unretrograded ones, with a similar rate coefficient to that in the second stage of unretrograded films. Although initially the smaller molecules or the easily accessible starch chains on the amorphous film surface were degraded faster, the more ordered structure (resistant starch) formed from retrogradation, either before or during enzymatic degradation, strongly inhibits film biodegradation.

Determination of the maximum water solubility of eight native starches and the solubility of their acidic-methanol and -ethanol modified analogues

The maximum water solubilities of eight native starches from potato, shoti, tapioca, maize, waxy maize, amylomaize-7, wheat, and rice and their acid-methanol and acid-ethanol modified analogues have been determined. Maximum solubilities of 18.7 and 17.4 mg/mL were obtained for waxy maize and tapioca and 12.4 mg/mL for potato and maize starches by autoclaving 220 mg/10 mL at 121 degrees C; 8.7 mg/mL was obtained for shoti starch by stirring in 85:15 (v/v) Me(2)SO-H(2)O at 20 degrees C; and 7.0 and 5.2mg/mL for rice and amylomaize-7 starches by stirring in 1M NaOH at 20 degrees C. The acid-alcohol treated starches were 4-9 times more soluble than their native starches. The compositions of the solubilized starches had, in general, much higher ratios of amylose to amylopectin than the ratios in their native granules. A major exception to this was the acid-methanol treated potato, shoti, and rice starches that had much lower ratios of amylose to amylopectin than the ratios in their granules.

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.