Effect of adding wheat (Triticum aestivum L.) farina with varied integrity of endosperm cell wall on dough characteristics, dried noodles quality and starch digestibility

Impact of rehydration on multi-scale structural transformations and starch digestibility of dried noodles

To understand the relationship between the structure and starch digestibility of dried noodles, the changes in multi-scale structure and in vitro starch digestibility of dried noodles with different protein contents (ranging from 10 % to 15 %) during rehydration were tracked. The results indicated that the hardness of dried noodles decayed according to the first-order exponential decay function, with rapid and slow stages. This depended on near-linear protein aggregation and near-logarithmic starch gelatinization. The gelatinization degree reached 70.9 to 79.4 % in the early stage of rehydration. Water absorption kinetics and distribution analysis revealed that the moisture migrating into the noodles was initially utilized for starch gelatinization. This led to the formation of a honeycomb gel structure at the edge of the noodles, which gradually spread from the edge to the center, as observed by SEM and CLSM. As rehydration progressed, the starch digestion degree increased. The digestion rate (k1) decreased with the formation of the composite gel structure, while k2 showed an increased trend. Additionally, with the increase in the protein content of noodles, the aggregation degree and increment were enhanced. This resulted in the formation of a more compact composite gel structure, which reduced the rate and extent of starch digestion within the noodles. When the noodles were overcooked, the C∞ of the high-protein samples was reduced by approximately 10 % compared to that of the low-protein samples. Overall, the formation of the composite gel structure reduces the heterogeneity of the noodles from the edge to the center, resulting in a closer starch digestion rate in fast and slow steps. Besides, the rapid and massive aggregation of proteins at high protein content contributed to the formation of a compact gel structure, which in turn interfered with the rate and extent of starch digestion.

Changes in overall digital structure, starch properties and moisture distribution reveal how the hardness of wheat noodles evolves under different cooking status

To elucidate the relationship between the structural evolution of starch within noodles during cooking and the hardness, the panoramic and local microstructure of cooked noodles were quantitatively analyzed, and the structure of starch in noodles were measured. We found that in the case of starch within cooked noodles with a high degree of swelling, the quantitative analysis of each ring was sufficient to represent the structural differences. Changes occurring in starch inside noodles during cooking were not homogeneous. The structural modifications of starch in the outer ring were greater than in the inner ring along with the extension of cooking time. The main reason responsible for the high hardness was attributed to low swelling degree and high short-range order of starch in the center. Water migration from the periphery to the center of the noodles, which was closely related to the fine structure of amylopectin, determined the state of central starch. Wheat starch with more large amylopectin molecules and more long amylopectin chains could enhance the inhibition of water migration and decrease the swelling degree of starch in the center, in order to endow a high hardness to noodles. These results will be useful for the ingredients selection for the production of noodles with desirable quality. In addition, the analysis method established in this work promoted the realization of quantitative comparison of the cooked noodles microstructure, that is an effective tool to clarify the structural basis of macroscopic quality of noodles.

Impact of pre-meal immersion on multi-scale structural changes and starch digestibility of cooked dried noodles

Pre-meal immersion is a common process for both the consumption of dried noodles and development of takeaway noodles, but its impact on the structure and digestibility of dried noodles is still unclear. In this study, dried noodles cooked for the optimal time were immersed at 80 °C for different time durations. Multi-scale structural changes, including texture, molecular structure, microstructure, and in vitro starch digestibility were studied using a combination of kinetic (first-order exponential decay function, the Peleg model, and LOS plots), physicochemical, and microscopic analysis. The relationship between multi-scale structural changes and starch digestibility was derived. As the immersion progressed, the hardness first rapidly decayed and then reached equilibrium. The decay rate in the initial stage depended on the gluten content. In most cases, the immersion process caused depolymerization of gluten proteins and further gelatinization of starch granules, which was observed from an increase in the free -SH content and decrease in the short-range ordered structure, although there were fluctuations over immersion time. Structural changes resulted in the corresponding changes in substance migration. However, a high gluten content (∼15% w/w) imparted a denser microstructure to the noodles, weakening the deterioration effects compared with a low gluten content (∼10% w/w). In vitro digestion experiments proved that samples with higher gluten content had higher starch digestion rates and lower starch digestion extent during immersion. Correlation analysis revealed that there was a negative correlation between k1 and the tightness of the gel. This study helps to reveal the structural mechanisms of starch digestibility in cooked noodles during immersion.

Comparative study on nutritional and technological properties of two varieties of black wheat flour and their noodle-making potential

Comparative studies were conducted on physicochemical and technological properties of two black wheat (BW) varieties (cultivated in Shanxi Agricultural University) and their noodle-making potential. Whole-grain BW noodles showed acceptable cooking loss (≤10%) and strong antioxidant capacity. However, their textural quality remains to be enhanced. Regarding refined flour (RF) of the two BW varieties, Yunhei 14207 showed more anthocyanins, brighter color, and greater thermal stability (as reflected by the higher pasting temperature). 16W16 resulted in greater gluten content and better gluten quality of flour and higher dough stability, which contributed to the lower cooking loss and stronger tensile property of noodles. RF noodles of Yunhei 14207 displayed brighter appearance, although they had weaker tensile property. The stronger gluten network in noodles of 16W16 protected phenolics from release and degradation during drying, cooking, and steaming. Despite phenolics loss, RF noodles of Yunhei 14207 showed antioxidant capacity up to 14.97 mg TE/100 g. This research would promote understanding of characteristics of BW varieties. Considering the stronger gluten network of 16W16, its fortification in common wheat noodles at high proportion (>50%) may be promising to develop antioxidant noodles with further improved sensory quality.