Artificial saliva-induced structural breakdown of rice flour gels under simulated chewing conditions.

Rice flour gels with different amylose contents were subjected to instrumental compression cycles under artificial saliva-spraying conditions to simulate oral mastication and their structural breakdowns were evaluated in terms of rheological and tomographic characteristics. Both mechanical disruption of the gel structure by successive compressions and enzymatic degradation by artificial saliva featured in the simulated chewing process. Highly linear correlations (R2 > 0.95) were observed in the log plots of peak chewing force and time. The rice flour gels containing higher levels of amylose required high forces to be deformed by compression. Micro-CT analysis demonstrated that the rice flour gels with a weak cohesive texture were fragmented into smaller pieces by chewing, consequently providing channels for artificial saliva to penetrate inside the gel samples. The cohesive nature of foods appeared thus to play an important role in their disruption rate during chewing, probably influencing the masticatory performance with salvia and subsequent swallowing.

Influence of arabic gum on in vitro starch digestibility and noodle-making quality of Segoami.

The effects of arabic gum on the quality attributes of rice noodles were characterized in terms of physical properties as well as in vitro starch digestibility. Segoami (high amylose rice) was used to develop rice noodle with low predicted glycemic index (pGI). First, the processing condition for Segoami noodle was investigated at different levels of water content (100%-175%) and steaming time (1-5 min). The impact of various levels of arabic gum (0.5%-2%) of Segoami noodles was also evaluated. In the results, the optimal processing condition was determined at the condition of 150% water content and 1 min of steaming time, when the lowest cooking loss and highest cohesiveness were observed. The addition of arabic gum (0.5-1.5%) lifted down glucose release curve and significantly reduced pGI of Segoami noodles. The higher level of arabic gum showed the higher cooking loss, but lower hardness and cohesiveness. Consequently, the 1.5% level of arabic gum was most effective in reducing in vitro starch digestibility and improving cooking properties of Segoami noodles.

Elucidation of rheological, microstructural, water mobility, and noodle-making properties of rice flour affected by turanose.

The effects of turanose on the physicochemical properties of rice flour systems (aqueous suspension, dough, and noodles) were investigated in terms of rheology, microstructure, and water mobility. Inclusion of turanose increased the pasting viscosities of rice flour by maintaining a closely-packed structure at high temperatures that was confirmed by the real-time microscopic measurements during heating. The elevated probability of intergranular interactions by turanose apparently raised both storage (G') and loss (G″) moduli of the rice flour pastes as well as their respective viscosities. NMR spin-spin relaxation times showed two distinct water populations in the turanose-rice flour samples. The Mixolab experiments demonstrated that the rice doughs with higher levels of turanose exhibited greater dough stability as well as higher degrees of starch gelatinization and retrogradation. Furthermore, the extruded rice noodles containing turanose exhibited a higher expansion ratio and a firmer texture that contributed to lowering the cooking loss by 24.5%.

Effect of dry heat treatment on physical property and in vitro starch digestibility of high amylose rice starch.

The influence of dry heat treatment (DHT) of high amylose rice starch was investigated on starch digestibility and physical properties and their characteristics were compared through the PCA analysis. High amylose rice starch was prepared by DHT under different temperatures (110, 130, and 150°C) and times (0, 1, 2, and 4h). The gelatinization temperature and enthalpy decreased as temperature and time increased, revealing the change of semi-crystalline region. There were significant increases in gel strength and pasting viscosity above 130°C, whereas gel strength and pasting viscosity were reduced with increasing heating time. On in vitro starch digestibility of DHT starch gel, the rapidly digestible starch and predicted glycemic index of DHT starches were lower than those of native starch. Both the lowest predicted glycemic index and the highest gel strength was observed at 130°C for 1h. In the results of PCA analysis, the heating temperature was negatively correlated with in vitro starch digestibility as well as pasting viscosity and gel strength. These results demonstrated that DHT could be useful of enhancing the physical and nutritional properties of high amylose rice starch.

Classification of hydrocolloids based on in vitro starch digestibility and rheological properties of Segoami gel.

The influence of hydrocolloids on in vitro starch digestibility and rheological properties of Segoami (a new rice variety fortified with amylose and dietary fiber) gel was investigated in terms of type (sodium alginate, arabic gum, guar gum, locust bean gum, and xanthan gum) and addition levels (0.3-0.7% for rice flour weight) of hydrocolloids. In addition, the behavior of hydrocolloids was analyzed by principal component analysis (PCA) based on both properties of various Segoami-hydrocolloids gels. The first and second principle components (PC) explained 80.93% of the total variation; PC1 and PC2 explained 50.40% and 30.53% of the total variance, respectively, implying that the two components provided a strong summary of the data. PC1, represented in vitro starch digestibility and was affected by the addition level of hydrocolloids: PC2, represented rheological parameters and was highly affected by the type of hydrocolloids. Moreover, there was a non-linear relationship between in vitro starch digestibility and rheological properties of Segoami-hydrocolloids gels. The hydrocolloids used in this study showed similar features according to the addition levels of hydrocolloids regardless of type. Segoami-0.5% arabic gum gel was the optimum preparation for retarding in vitro starch digestibility and maintaining rheological properties.

Optimized preparation of anthocyanin-rich extract from black rice and its effects on in vitro digestibility.

The procedure for obtaining anthocyanin-enriched extracts from black rice was optimized by response surface methodology, and the effects of the optimized extract on in vitro starch digestibility were investigated in a wheat flour gel model. The experimental results were well-described by a polynomial multiple regression model (R2 = 0.8812, p = 0.0546) with regard to anthocyanin content in anthocyanin-enriched extracts from black rice. The optimal conditions for obtaining anthocyanin-enriched extracts from black rice were 50.78% ethanol and 1 N HCl (0.60 mL), yielding a predicted anthocyanin content of 624.27 mg cyanidin 3 glucoside extract. The optimized anthocyanin-enriched extract was a stronger inhibitor of α-glucosidase than acarbose. Furthermore, the predicted glycemic index values of gels prepared with the optimized extract were significantly lower than that of wheat flour gel. These results indicate that the optimized extract suppressed starch hydrolysis by inhibiting digestive enzymes.

In vitro starch digestion and cake quality: impact of the ratio of soluble and insoluble dietary fiber.

The influence of the ratio of soluble dietary fiber (SDF) and insoluble dietary fiber (IDF) on the in vitro starch digestion, predicted glycemic index (pGI), and the physicochemical properties of fiber-enriched cakes were evaluated. The hydration and pasting properties were affected by the ratio of SDF and IDF. According to the increase of IDF ratio (SDF ratio reduction) in 3 g fiber-enriched cakes, slowly digestible starch (SDS) contents increased, while the rapidly digestible starch (RDS) contents decreased. The pGI values were significantly different with control in 3 g fiber-enriched cake containing more than 50% IDF contents (p<0.05). But the pGI values of 6g fiber-enriched cake samples were not significantly different by SDF and IDF ratio. With the exception of the SDF 100% cake, volume index, hardness, and color values of the fiber-enriched cakes increased according to reductions in the SDF ratio. The cakes containing 3 g of total dietary fiber (the same ratio of SDF and IDF) per serving were shown to have low pGI and acceptable quality attributes. Specially, total dietary fiber amount and IDF ratio are more effective than SDF ratio to lower the pGI value.

Rheological characterization of levan polysaccharides from Microbacterium laevaniformans.

Levan polysaccharides were produced from Microbacterium laevaniformans and its rheological behaviors were characterized as a function of concentration and temperature. The intrinsic viscosity of the purified levan was determined to be 0.38dL/g at 25 degrees C which was relatively higher than that of levans from other microbial sources. The flow behaviors of the levan solutions were characterized by the increase in the shear stress, giving more increments in the shear rate. Thus, the levan solutions exhibited the pseudoplastic behavior, which was characterized by the power law model. In addition, the flow behaviors of the levans were satisfactorily fitted to the Arrhenius equation where the activation energy of flow (Ea) decreased from 24.07 to 13.53kJ/mol (R2=0.98-0.99) with increasing concentrations. Moreover, the exponential equation was favorably applied to describe the effect of concentration on the apparent viscosity of the levan polysaccharides.