Hydrothermal treatment and iodine binding provide insights into the organization of glucan chains within the semi-crystalline lamellae of corn starch granules.

The importance of glucan chains that pass through both the amorphous and crystalline lamellae (tie chains) in the organization of corn starch granules was studied using heat-moisture treatment (HMT), annealing (ANN), and iodine binding. Molecular structural analysis showed that hylon starches (HV, HVII, and HVIII) contained higher proportion of intermediate glucan chains (HVIII > HVII > HV) than normal corn (CN) starch. Wide angle X-ray scattering revealed that on HMT, the extent of polymorphic transition in hylon starches decreased with increasing proportion of intermediate and long chains. Iodine treated hylon starches exhibited increased order in the V-type polymorphism as evidenced by the intense peak at 20° 2θ and the strong reflection intensity at 7.5° 2θ and the extent of the change depended on the type of hylon starch. DSC results showed that the gelatinization enthalpy of CN and waxy corn starch (CW) remained unchanged after ANN. However, hylon starches showed a significant increase in enthalpy with more distinct endotherms after ANN. It can be concluded that tie chains influence the organization of crystalline lamellae in amylose extender mutant starches.

The impact of milling and thermal processing on phenolic compounds in cereal grains.

Consumption of wholegrain foods has been recommended for healthy diets. The beneficial health properties of wholegrain products have been associated with the presence of higher amounts of dietary fiber and antioxidants and lower calories as compared to their respective refined ones. Phenolic compounds are mainly attributed to antioxidant properties of wholegrain foods. This review article provides a single comprehensive source that describes effects of milling and thermal processing on phenolic compounds and antioxidant properties in cereals. In general, milling and pearling processes affect the distribution of phenolic, compounds and thus antioxidant properties vary among the milling fractions. Thermal processes such as baking and extrusion could cause negative or positive effects on phenolic compounds and antioxidant properties of the end product subject to grain type and processing conditions. Thus factors that enhance health benefits of wholegrain cereal products have been discussed.

Influence of amylopectin structure and degree of phosphorylation on the molecular composition of potato starch lintners.

Morphology, molecular structure, and thermal properties of potato starch granules with low to high phosphate content were studied as an effect of mild acid hydrolysis (lintnerization) to 80% solubilization at two temperatures (25 and 45°C). Light microscopy showed that the lintners contained apparently intact granules, which disintegrated into fragments upon dehydration. Transmission electron microscopy of rehydrated lintners revealed lacy networks of smaller subunits. The molecular composition of the lintners suggested that they largely consisted of remnants of crystalline lamellae. When lintnerization was performed at 45°C, the lintners contained more of branched dextrins compared to 25°C in both low and intermediate phosphate-containing samples. High-phosphate-containing starch was, however, unaffected by temperature and this was probably due to an altered amylopectin structure rather than the phosphate content. After lintnerization, the melting endotherms were broad with decreased onset and increased peak melting temperatures. The relative crystallinity was lower in lintners prepared at 45°C. A hypothesis that combines the kinetics of lintnerization with the molecular and thermal characteristics of the lintners is presented.

Structural and physical properties of granule stabilized starch obtained by branching enzyme treatment.

Chemical cross-linking of starch is an important modification used in the industry for granule stabilization. It has been demonstrated that treatment with branching enzyme (BE) can stabilize the granular structure of starch and such treatment thereby provides a potential clean alternative for chemical modification. This study demonstrates that such BE-assisted stabilization of starch granules led to partial protection from BE catalysis of both amylose (AM) and amylopectin (AP) in their native state as assessed by triiodide complexation, X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). The granule stabilizing effects were inversely linked to hydration of the starch granules, which was increased by the presence of starch-phosphate esters and suppressed by extreme substrate concentration. The data support that the granule stabilization is due to the intermolecular transglycosylation occurring in the initial stages of the reaction prior to AM-AP phase separation. The enzyme activity needed to obtain granule stabilization was therefore dependent on the hydration capability of the starch used.

Mechanism of hydrolysis of native and cooked starches from different botanical sources in the presence of tea extracts.

A series of experiments were conducted to highlight the mechanism of inhibition of hydrolysis and differences in hydrolysis among starches from different sources in the presence of green or black tea extract. The first experiment showed that black tea extract was more effective at reducing final viscosity for all starches. The second experiment showed that black tea was more effective at inhibiting starch hydrolysis compared to green tea when starch, tea extract, and pancreatin were added at the beginning of pasting. The third experiment, when starches were pretreated with tea extracts, showed that both treatments reduced starch hydrolysis. Analysis of supernatant free phenolic content and of soluble dextrins showed that amyloglucosidase activity was affected, with exceptions for potato starch. These observations suggest that starch hydrolysis is affected by interactions and also by the impact on specific enzymes based on starch structure.

Quantification of total iodine in intact granular starches of different botanical origin exposed to iodine vapor at various water activities.

Iodine has been used as an effective tool for studying both the structure and composition of dispersed starch and starch granules. In addition to being employed to assess relative amylose contents for starch samples, it has been used to look at the molecular mobility of the glucose polymers within intact starch granules based on exposure to iodine vapor equilibrated at different water activities. Starches of different botanical origin including corn, high amylose corn, waxy corn, potato, waxy potato, tapioca, wheat, rice, waxy rice, chick pea and mung bean were equilibrated to 0.33, 0.75, 0.97 water activities, exposed to iodine vapor and then absorbance spectra and LAB color were determined. In addition, a new iodine quantification method sensitive to <0.1% iodine (w/w) was employed to measure bound iodine within intact granular starch. Amylose content, particle size distribution of granules, and the density of the starch were also determined to explore whether high levels of long linear glucose chains and the surface area-to-volume ratio were important factors relating to the granular iodine binding. Results showed, in all cases, starches complexed more iodine as water content increased and waxy starches bound less iodine than their normal starch counterparts. However, much more bound iodine could be measured chemically with waxy starches than was expected based on colorimetric determination. Surface area appeared to be a factor as smaller rice and waxy rice starch granules complexed more iodine, while the larger potato and waxy potato granules complexed less than would be expected based on measured amylose contents. Corn, high amylose corn, and wheat, known to have starch granules with extensive surface pores, bound higher levels of iodine suggesting pores and channels may be an important factor giving iodine vapor greater access to bind within the granules. Exposing iodine vapor to moisture-equilibrated native starches is an effective tool to explore starch granule architecture.

Characterization of irradiated starches by using FT-Raman and FTIR spectroscopy.

Fourier transform infrared (FTIR) and Fourier transform Raman (FT-Raman) methods were used for rapid characterization and classification of selected irradiated starch samples. Biochemical changes due to irradiation were detected using the two vibrational spectroscopic techniques, and canonical variate analysis (CVA) was applied to the spectral data for discriminating starch samples based on the extent of irradiation. The O-H (3000-3600 cm(-1)) stretch, C-H (2800-3000 cm(-1)) stretch, the skeletal mode vibration of the glycosidic linkage (900-950 cm(-1)) in both Raman and infrared spectra, and the infrared band of water adsorbed in the amorphous parts of starches (1550-1750 cm(-1)) were employed in classification analysis of irradiated starches. Spectral data related to water adsorbed in the noncrystalline regions of starches provided a better classification of irradiated starches with 5 partial least-squares (PLS) factors in the multivariate model.