Physicochemical properties and microstructure of Chinese yam (Dioscorea opposita Thunb.) flour

Effect of extrusion using plasma-activated water on the structural, physicochemical, antioxidant and in vitro digestive properties of yam flour

The synergistic effects of plasma-activated water (PAW) and twin-screw extrusion (TSE) on the structural, physicochemical, antioxidant, and digestive properties of yam flour (YF) were studied. Compared to common TSE, PAW-TSE reduced the protein, starch, and polyphenol contents, swelling power, and gel property of YF, while PAW-TSE enhanced the flavonoid content, whiteness index, solubility, and antioxidant property of YF. Moreover, the results of structural characterization and differential scanning calorimetry indicated that the long-range or short-range ordering, and gelatinization enthalpy of starch in YF were reduced after PAW-TSE, while the structure ordering of proteins in YF increased. Furthermore, the in vitro digestibility results demonstrated a reduction in the rate of enzymatic hydrolysis, coupled with an increase in total contents of slowly digestible and resistant starch after PAW-TSE. It should be noted that TSE using PAW prepared by a longer plasma treatment resulted in a more significant improvement effect on YF.

Correlation Study between Multi-Scale Structure and In Vitro Digestibility of Starch Modified by Temperature Difference

Physical techniques are widely applied in the food industry due to their positive impact on food quality and the environment. Temperature differences can effectively modify starch, but the resulting changes in starch structure and quality remain unclear. In this study, the corn starch was processed with high temperature, low temperature, and temperature difference (TD), including high temperature before low temperature (H-L) and low temperature before high temperature (L-H). The results showed that high temperature induced the umbilicus to concave inward shape and sharply decreased the amylose content, while low temperature increased the surface micropores and reduced the A-chain. TD reduced the fluorescence intensity and increased the clearness of the growth ring. TD elevated the relative crystallinity (RC), short-range order, A/B1 chains, hydrolysis parameters, and resistant starch (RS), and reduced amylose content, B2/B3 chains, and viscosity. Moreover, the corn starches treated by H-L had lower amylose content and higher RC, 1047/1022, A-chain, and RS than those treated by L-H. Overall, high temperature degraded the amylose and low temperature destroyed the amylopectin. During the TD, H-L can accelerate the starch molecular rearrangement more than the opposite temperature treatment order. These results will help produce novel starches for better food applications.

Molecular mechanism for the influence of yam starch multiscale structure on the sensory texture of cooked yam

Yam is a dual-purpose crop as both medicine and food. However, the mechanism controlling the eating quality of yam remains to be elucidated. This study explored the influence of starch multiscale structure on the texture of yam. The results indicated that FS and RC yam have higher hardness and chewiness, while BZ, XM, and PL yam possess waxiness, Fineness, and Stickiness. Statistically, high amylose (AM) can increase hardness, chewiness, and compactness; and average molecular size (Rh) is positively correlated with stickiness, fineness, and waxiness. Specifically, medium- and long-chain amylose (1000 < X ≤ 10,000) and amylopectin (24 < X ≤ 100), particularly medium-chain amylose (1000 < X ≤ 5000) and long-chain amylopectin (24 < X ≤ 36), primarily affect sensory and rheological stickiness. The long chains of amylose form a straight chain interspersed in the crystalline and amorphous regions to support the entire lamellar structure. Higher proportion of amylose long chains, promoting the starch's structural rigidity, which in turn enhanced its hardness-related attributes. Moreover, a higher ratio of long chains within amylopectin results in tightly intertwined adjacent outer chains, forming double helix crystalline zones. This consequently augmenting the texture quality linked to stickiness-related attributes.

Chemical, structural, and techno-functional characterization of yam (Dioscorea) flour from South West Ethiopia

Yam (Dioscorea spp.) is a versatile tuber crop that holds nutritional, cultural, and economic values. Yam is a major source of carbohydrates for tropical Countries and provides various nutrients and health benefits. This study aims to characterize the chemical, structural, and thermal properties of yam flour using various analytical techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermal analysis. Additionally, the pasting and rheological properties of yam flour were evaluated, as they are crucial for product development and enhancing the value of this unconventional vegetable. D. cayenensis complex had the highest total starch (64.63 ± 1.61 %) and soluble sugar (4.95 ± 0.46 %) content, which was significantly higher than other yam species. The amylose content of yam flours showed significant (p < 0.05) differences among the yam species. D. cayenensis flour exhibited significantly the highest peak (2923.66 cP) and steak back viscosity (2097.66 cP) among the yam species associated with their greater amylose content. There were notable variations in pasting and gelatinization parameters among the species. The peak temperatures of D. bulbifera and D. cayenensis complex were significantly (p < 0.05) higher than D. cayenensis and D. rotundata flours. The rheological measurements of yam flours demonstrated solid-like behavior with varying intensities. Furthermore, the morphology of tuber yam flour particles was oval to ellipsoidal shaped, with some appearing ovoid, and the smaller granules appearing spherical. The X-ray diffraction showed that all yam flours exhibit a B-type pattern. This study provide a better understanding of this unconventional vegetable's potential applications in the food industry and contribute to its value addition.

Understanding the multi-scale structure, physicochemical and digestive properties of extruded yam starch with plasma-activated water

In this study, the synergistic effect of plasma-activated water (PAW) combined with twin-screw extrusion (TSE) on multi-scale structure, physicochemical and digestive properties of yam starch (YS) was studied. PAW-TSE resulted in higher amylose content in YS than TSE alone. Compared with single TSE, the relative crystallinity, short-range ordered degree, and gelatinization enthalpy of YS were increased by PAW-TSE according to the results of X-ray diffraction, Fourier transform infrared, Raman spectroscopy, and differential scanning calorimetry. Furthermore, rapid viscosity and dynamic rheological analysis showed that the peak and breakdown viscosity of PAW-TSE treated YS paste were considerably reduced, and the storage modulus and loss modulus were significantly increased, indicating that the gel strength and thermal stability were improved. In addition, the resistant starch (RS) content of YS treated by PAW-TSE increased from 6.04 % to 21.21 %. Notably, the effect of PAW-TSE on YS enhanced with the preparation time of PAW increased. Finally, correlation analysis indicated that the characteristic indexes of PAW had a significant impact on the long or short-range ordered structure, thermal properties, and in vitro digestibility of YS during extrusion. Therefore, PAW-TSE, as an emerging dual modification technology, will greatly expand the application of extrusion technology.

Physicochemical characterizations of five Dioscorea alata L. starches from China

D. alata is an important edible and medicinal plant in China. Its tuber is rich in starch but the understanding of the physiochemical properties of D. alata starch is limited. In order to explore the processing and application potential of different D. alata accessions in China, five kinds of D. alata starch (LY, WC, XT, GZ, SM) were isolated and characterized. The study showed that D. alata tubers contained abundant starch, enriched in amylose and resistant starch (RS). D. alata starches showed B-type or C-type diffraction pattern, had higher RS content and gelatinization temperature (GT), lower fa and viscosity when compared to D. opposita, D. esculenta, and D. nipponica. Among D. alata starches, D. alata (SM) showing the C-type diffraction pattern, had the lowest proportion of fa with 10.48 %, the highest amylose, RS2 and RS3 content of 40.24 %, 84.17 % and 10.48 % respectively, and the highest GT and viscosity. The results indicated that D. alata tubers are potential sources for novel starch with high amylose and RS content, and provided a theoretical basis for further utilizations of D. alata starch in food processing and industry application.

Simulated In Vitro Digestive Characteristics of Raw Yam Tubers in Japanese Diet: Changes in Protein Profile, Starch Digestibility, Antioxidant Capacity and Microstructure

The consumption of raw yam tuber through grated yam "tororo" is a major and popular diet in Japan. However, few studies have been undertaken to evaluate the digestive characteristics of raw yam tubers. This study aimed to fill this gap by investigating the changes in the protein profile, protein and starch digestibility, antioxidant capacity and microstructure of two typical yam tubers (Nagaimo N-10 and Nebaristar) in the Japanese diet, applying a simulated in vitro digestion method. Results showed that both samples contained a considerable protein content of about 11% (dry basis) and a protein digestibility of 43-49%. The electrophoretic patterns confirmed that dioscorin was the main protein of the yam tuber, and it could be digested into peptides and free amino acids with low molecular weight during in vitro digestion. The starch hydrolysis results suggested that eating raw yam tuber cannot induce a fast glycemic increase for consumers due to a low starch digestibility of 4.4-6.1%. In addition, Nebaristar showed a higher bioaccessibility in some key amino acids and total phenolic content than the Nagaimo N-10. This study provides some essential nutritional information and simulated digestion behaviours of the raw yam tubers, which could be useful for consumers and industries when buying and processing yam tubers from the perspective of changes in the nutritional profile during digestion.