Research on migration path and structuring role of water in rice grain during soaking

Effects of boiling time on physicochemical properties of refrigerated rice: Analysis of rice structure and broth gel composition in a boiled-then-steamed process

Refrigerated rice holds great potential in the cold-chain prepared food industry. However, refrigeration often deteriorates the quality of rice, and cooking methods influence the quality of rice. The boiled-then-steamed process, which involves draining the rice broth, significantly affects the storage properties of rice. Thus, in this study, the impact of boiling time on the quality and structural changes of rice during refrigeration was investigated. In addition, the impact of rice broth gel components on the storage quality and colloidal stability of rice were examined. The results showed that extending the boiling time significantly improved rice moisture retention and reduced hardness and crystallinity. After 7 d of storage, the hardness of rice boiled for 8 min and 16 min decreased by 53.61 % and 81.13 %, respectively. The crystallinity of rice boiled for 2 min and 16 min was 17.89 % and 8.04 %, respectively. The 8-min-boiled rice exhibited the best texture and microstructural stability during refrigeration. The reduction in molecular short-range order and retrogradation enthalpy further confirmed that this method effectively slowed the retrogradation process of rice. Additionally, the composition characteristics of rice broth gel significantly influenced the refrigerated quality, affecting the distribution of moisture and starch structure within the rice. Amylose leaching reached its threshold after 8 min of boiling. The cooking method proposed in this study provides an effective and natural solution for enhancing the quality stability of refrigerated rice, offering potential benefits for the cold-chain food industry.

Development of in vitro oral processing model for different rice: Effects of saliva volume and chewing time on physicochemical properties of rice boluses

The in vitro model is widely preferred for digestion research due to its simplicity, reproducibility, and ethical advantages. However, the differences between in vivo and in vitro digestion present challenges. This study first developed an in vitro oral processing system to explore the influence of saliva volume and chewing time on the physicochemical properties of japonica rice (JR), indica rice (IR), and waxy rice (WR). The results revealed that both saliva volume and chewing time significantly influenced properties like texture, particle size, starch hydrolysis, protein distribution, and microstructure, with chewing time exerting a greater impact. Starch hydrolysis was closely linked to particle size, with fragmentation being the primary factor. An artificial neural network (ANN) model was used to effectively correlate the in vitro simulation conditions with physiological characteristics. By integrating in vivo data, optimized simulation conditions were determined for each rice type: JR-saliva 197.85 ± 21.42 mg/g, chewing 21.02 ± 1.51 s; IR-saliva 198.64 ± 22.41 mg/g, chewing 22.36 ± 0.45 s; WR-saliva 127.11 ± 21.63 mg/g, chewing 14.74 ± 0.90 s.

Study on taste release and perception mechanism of japonica rice during oral processing

The sensorial experience of japonica rice is a critical factor that profoundly influences consumer choice. Despite this, the mechanisms underlying the release and perception of flavors during the oral processing of japonica rice are still not clearly understood. To address this gap, we conducted an in-depth investigation into the flavor release and gustatory perception dynamics of japonica rice during mastication using high-performance liquid chromatography (HPLC) and molecular docking simulations. Our findings revealed that umami taste was predominant during the initial stages of oral processing, whereas sweetness emerged as the dominant flavor in the subsequent phases. Moreover, we identified 16 key taste-active compounds that are released during the oral processing of japonica rice. Utilizing partial least squares regression (PLSR) analysis, we observed that glucose, sucrose, proline, maltose, and fructose were positively and significantly associated with the perception of sweetness in japonica rice. Concurrently, aspartic acid and glutamic acid contributed to the enhancement of umami perception, while concurrently diminishing the perception of sweetness and sourness. Further molecular docking studies demonstrated that glucose and sucrose interact with the amino acid residues of the sweet taste receptors T1R2/T1R3, engaging in hydrogen bonding and hydrophobic interactions. These interactions potentiate the activity of T1R2/T1R3, thereby facilitating the detection of sweetness. Similarly, aspartic acid and glutamic acid bind to the amino acid residues of the umami receptors T1R1/T1R3, establishing hydrogen bonds and hydrophobic interactions. This binding enhances the activity of T1R1/T1R3, leading to an augmented perception of umami.

Cooked germ-remained milled rice presents high stability in water-holding capacity and textural properties during frozen storage-The protection effect of oil-phase reabsorption

To enhance the stability in textural attributes of frozen cooked rice, this study has found and proposed a new strategy: retaining the rice germ in milling process. Each rice germ is comparable to a native lipid-rich microcapsule attached to the endosperm part. In the gelatinization process, leached germ oil was reabsorbed in the outer layer of rice granule. Small lipidic molecules complexed with amylose and formed type I complex, while big lipidic molecules formed separate oil phase in the matrix. This mixed construction endowed cooked germ-remained milled rice with smaller magnitude of change in the water holding capacity and the ratio of stickiness/hardness, and fewer freezable water content than white rice. This work opens an attractive field to reinforce the structural stability of cooked rice against freezing stress without exogenous additives, and benefits to screen suitable raw materials for the development of frozen rice products.

Quality control of cooked rice: Exploring physicochemical changes of the intrinsic component in production

Sensory deterioration exists in marketed cooked rice. The migration and interaction of intrinsic components occur under multiple conditions in each industrial production process and cause relevant physicochemical changes in cooked rice. This review aims to establish a scientific knowledge system of intrinsic component transition and migration in cooked rice kernel during processing to solve qualitative deficiencies in cooked rice products. The main influencing factors of intrinsic component structural change in cooked rice and the quality control points that should be considered are summarized. Further studies are needed to establish proper evaluation standards for cooked rice products to meet the growing consumer demands.

Effects of immersion with electro-activated alkaline water on gel properties, biochemicals and odor characteristics of myofibrillar proteins

This study aimed to investigate the effects of alkaline water electrolysis (AWE) - assisted washing on gelling properties, microstructure, protein conformation, and flavor composition of golden pompano surimi. The experimental results showed that rinsing yield, water holding capacity (WHC), gel strength, and textural properties were effectively improved with AWE for 1 and 3 min. The rheological properties indicated a highly elastic gel with a dense and compact microstructure after soaking in AWE for 1 and 3 min, indicating that short-term alkaline immersion enhances cross-linking between myofibrillar proteins. Additionally, increasing the electrolysis time from 0 to 3 min effectively retained immobilized water due to increased aggregation of neighboring proteins, leading to a higher proportion of α-helix structures. Furthermore, AWE treatment for 3 min markedly reduced undesirable volatile compounds, including 1-butanol, hexanal, and 1-octen-3-ol, enhancing the hardness, chewiness, gumminess, and WHC of surimi. In conclusion, AWE-assisted washing emerges as an effective and reliable approach for upgrading the quality of surimi gel.

Effect of salt and alkali on the viscoelastic behavior of noodle dough sheet with different wheat starch granule sizes

The underlying mechanisms of salt and alkali on the viscoelastic behaviors of noodle dough sheets with varied B/A-type starch ratios were investigated from water state, protein polymerization and conformation, and microstructure. The viscoelastic behaviors of dough sheets increased with increasing B/A-type starch ratio, regardless of the presence of salt and alkali, indicating the addition of salt and alkali did not change the effect law of starch granule size on dough viscoelasticity. The viscoelastic moduli of dough decreased in the presence of salt and alkali, and the effect was more obvious as the ratio of B/A-type starch decreased, which was mainly determined by the interactions of protein-protein, protein-starch, and starch-starch in dough systems. In the low ratio of B/A-type starch dough sheets, NaCl enhanced the non-covalent interactions and β-sheet structure, while alkali promoted the covalent cross-linking of protein. In the high ratio B/A-type starch dough samples, the big starch surface area provided by a high phase volume of starch granules led to the domination of starch-starch interactions over the protein phase, thus determining the viscoelastic behavior of dough. SEM images showed that NaCl caused the gluten to form a fibrous structure, while alkali induced a membrane-like and more closed structure. NaCl and alkali showed different influences on water distribution, molecular conformation, and network structure of dough sheets with varied B/A-type starch ratios and thus contributed to the different viscoelastic behaviors.

A comparative study of different soybean oil forms on the physicochemical properties of surimi myofibrillar protein gel: The role of soybean protein isolate and κ-carrageenan

Natural soybean oil, Pickering emulsion, high-internal-phase emulsion (HIPE), and emulsion gel were prepared to investigate their effects on the physicochemical properties of surimi myofibrillar protein gels. Their effects on gel strength ranked as: emulsion gel > Pickering emulsion > HIPE > soybean oil. At the same oil content, the emulsion gel exhibited higher G' than the other forms whereas natural oil exhibited the lowest G', and T22 was smaller in the emulsion gel group, indicating that the emulsion gel enhanced the interaction between water molecules and protein macromolecules. FT-IR testified that 9 % natural oil reduced the β-sheet content to 26.34 %, whereas Pickering emulsion, HIPE, and emulsion gel recovered the β-sheet content to 31.30 %, 36.17 %, and 32.69 %, respectively. Emulsion gel led to fewer voids, and the oil droplets in emulsion gel were more regularly spherical and homogeneously dispersed in the gel matrix, which might be attributed to the filling effects as well as "bridging action" of soybean protein isolate and κ-carrageenan within surimi proteins. In conclusion, we demonstrated emulsion gel as a good replacer to mitigate the negative effect of oil on the texture and structure of surimi gels, which would be a promising approach for oil supplementation in surimi production.

Prolonging heat-moisture treatment time at medium moisture content optimizes the quality attributes of cooked brown rice through starch structural alteration

Brown rice (BR), one of the popular whole grains worldwide, is still limited to consumption due to its rough texture after cooking. Through inspecting structural alteration, this work discloses how heat-moisture treatment (HMT) moisture content (15 %-25 %) and time (1.0 h-3.0 h) modify the starch digestibility and cooked BR texture. The medium moisture content (20 %) allowed the highest pasting viscosity and a uniform network structure of cooked BR. Prolonging the HMT time from 1.0 h to 2.0 h at medium moisture content hindered starch swelling and improved stability. Meanwhile, the relative crystallinity, the surface compactness in nanoscale and R995/1022 decreased, while the gel network structure was improved, contributing to the softened cooked BR texture and the enhanced starch digestibility. Although the resistant starch content raised to 13.55 % after 3.0 h of HMT, the springiness, gumminess and chewiness of cooked BR degraded, and this should be considered in certain conditions.

Effect of Water Content in Semidry Grinding on the Quality of Glutinous Rice Flour

The grinding process is one of the key factors affecting the quality of glutinous rice flour (GRF). As an emerging grinding method, semidry grinding aims to solve the problems of the high yield of wastewater in traditional wet grinding and the high content of damaged starch in dry grinding, in which the water content has a great influence on the quality of GRF. However, semidry grinding has not yet been formally put into production due to limitations such as the long time required to adjust the water content of rice grains. Therefore, this work was carried out to shorten the soaking time of glutinous rice (GR) by hot air pretreatment, and to conduct a systematic and in-depth study of the effect of water content on the quality of GRF, including water distribution, water hydration properties, thermal properties, rheological properties, and microstructure. The results showed that the GRF with higher water content had lower water solubility and higher enthalpy of pasting, which were due to the low content of damaged starch and the high degree of crystallization. The particle size of the GRF became smaller as the interaction between water and starch was enhanced and the GR was softened. In addition, the viscosity and elasticity of the GRF were also improved with an increase in water content. This work provides theoretical guidance for the improvement of semidry grinding to a certain extent.

Chewing characteristics of rice and reasons for differences between three rice types with different amylose contents

This study investigated the physicochemical structural changes in different types of rice (japonica rice [JR], indica rice [IR], and waxy rice [WR]) during oral digestion and explored the reasons for differences in oral digestion between the three different types. The results showed that, compared with JR (42.41 ± 3.06 mg/g) and WR (26.82 ± 0.67 mg/g), IR had the highest amylose content (49.95 ± 3.33 mg/g) and, related to this, hydrolysis rate. A correlation analysis showed that, the higher the amylose content, the harder the texture of rice, leading to longer chewing times and, as a result, a greater degree of hydrolysis. In addition, the higher the amylose content, the lower the exudate content and viscosity of rice, which affects chewing time and frequency, thereby affecting the degree of hydrolysis. Both X-ray computed tomography and scanning electron microscopy indicated that cooked IR had the loosest structure and the most pores, that were conducive to chewing and crushing and therefore contributed to the high hydrolysis rate. Analysis of the exudate structure showed that the amount of exudate affected rice pores. More exudates lead to pore coverage and a tight structure.

Effects of soaking treatment on water distribution of rice grains, starch characteristics and eating quality of wet rice noodles

Herein, rice was subjected to different soaking processes on water distribution of rice grains, starch characteristics, and eating quality of fresh wet rice noodles. Results demonstrated that, when soaked at temperatures between 10 °C and 40 °C for 120 min, rice grains reached saturation in water absorption, and the hardness gradually stabilized. However, the moisture continued to penetrate the interior of rice grains after 120 min, leading to an increase in moisture content, higher water permeability, and enlarged water migration channels. With extended soaking time periods, the content of damaged starch in rice flour considerably decreased. Although the gelatinization temperature of rice starch decreased after soaking, the enthalpy required for gelatinization increased. The relative crystallinity of rice starch demonstrated an increasing trend, followed by a decreasing trend, and reached its highest value of 18.18 % after 60 min of soaking. To summarize, the texture indices of fresh rice noodles demonstrated an increasing trend, although stretching and cooking quality demonstrated a trend of initially increasing and then decreasing with no considerable changes observed between 120 and 240 min of soaking. In summary, moderate soaking treatment can enhance the edible quality of fresh wet rice noodles.

Research on corn starch and black bean protein isolate interactions during gelatinization and their effects on physicochemical properties of the blends

The interaction between starch and protein during food processing is crucial for controlling food quality. This study aims to understand the interactions between corn starch and black bean protein isolate (BBPI) at various gelatinization phases and their effects on the physicochemical properties of the blends. BBPI reduced the rheological properties of the corn starch/BBPI mixed system during gelatinization, increasing light transmittance and gelatinization temperature, while decreasing total viscosity and enthalpy change. The changes in starch and protein microstructure during gelatinization indicated that BBPI adhered to the starch particle surface or partially penetrated the swollen starch particles. Fourier transform infrared spectroscopy (FT-IR) revealed that BBPI decreased the number of hydrogen bonds within starch, with no newly formed functional groups in the mixed system. Furthermore, BBPI reduced the composite relative crystallinity (RC). The effect of protein addition on water migration in the mixed system demonstrates that protein and starch compete for water during gelatinization, preventing water molecules from diffusing into starch particles.

Effects of distribution, structure and interactions of starch, protein and cell walls on textural formation of cooked rice: A review

The constitution and forms of rice determine its processing and cooking properties and further control the cooked rice quality. As the two main components, starch and protein content correlations and their characteristics have been extensively explored. However, rice is mainly consumed as polished kernels, components distribution, cytoplasmic matrix, and cell walls work together, and the properties of extracted components or flour are difficult to reflect the quality of cooked rice accurately. Thus, this review summarizes the multi-scale structure changes of main components during real rice cooking conditions. The dynamic thermal changes and leaching behaviors in rice kernels are compared with pure starch or rice flour. The in situ changes and interactions of starch granules, protein bodies, and cell walls during cooking are reviewed. Based on this, different textural evaluation methods are compared, and the advantages and disadvantages are pointed out. The oral chewing perception and bionic chewing simulation for textual evaluation have gradually become hot. Both rice quality controllers and eating quality evaluators attempt to establish an accurate quality evaluation system with the increased demand for high-quality rice.

Different nitrogen fertilizer application in the field affects the morphology and structure of protein and starch in rice during cooking

Nitrogen fertilization is one of the most important cultivation practices that affects the eating quality of rice. During the cooking process, nitrogen fertilizer application in the field changed the structure of protein and starch during cooking, which eventually reduced the rice eating quality. However, the morphology and structure of rice during cooking under high nitrogen fertilizer application in the field have not been explored. The relationship between the morphological and structural changes of rice protein and starch during cooking and the rice eating quality has not been studied. In this study, we conducted field trials at two nitrogen fertilizer levels (0 N and 350 N), and the rice was cooked after harvest. Our results showed that the peak viscosity of rice flour was 3326 cp and 2453 cp at 0 N and 350 N, respectively, and the peak viscosity of rice starch was 3424 cp and 3378 cp, respectively. Rice proteins played an important role in the starch gelatinization properties and thermodynamic properties. High nitrogen fertilizer application increased the protein content of rice from 5.97 % to 11.32 %, and more protein bodies adhered to the surface of amyloplasts eventually inhibiting starch gelatinization. The rice proteins could bind to amylose-lipid complexes during cooking, promoting the formation of V-type diffraction peaks. What is more, under high nitrogen fertilizer, rice protein had more β-sheets, which slowed the entry of water into the interior of starch molecules and prevented the destruction of the short-range ordered structure of starch. Our study provides the possibility to further improve the eating quality of rice under nitrogen fertilizer treatment.

The textural properties of cooked convenience rice upon repeated freeze-thaw treatments are largely affected by water mobility at grain level

Brown rice (BR) is a promising source for convenience rice that are mostly stored frozen. However, freezing and thawing may cause deterioration in rice texture quality. To investigate how rice texture is influenced by freeze-thaw cycles, BR, the pretreated BR with partially ruptured bran layer (UER) and white rice (WR) were cooked and treated with repeated freeze-thaw cycles, with their textural properties, variations in moisture distribution and starch structure being measured. Results showed that the repeated freeze-thaw treatment induced a progressive reduction in hardness and stickiness of all cooked rice. The reduced hardness of rice could be explained by the enlarged pore size of starch inside rice under scanning electron microscopy. Moisture migration in WR was the fastest responding to multiply freeze-thaw cycles, followed by UER, while water mobility in BR was slowest. Moreover, WR, BR and UER resulted in a similar extent of amylopectin retrogradation and chains length distribution after repeated freeze-thaw cycles. It indicated similar and minor effect of starch variations on determining the texture of different rice samples against freeze-thawing. Water mobility tended to be a main factor leading to the textural difference of fully gelatinized rice samples. This study focused on the relationship between water distribution and starch retrogradation, providing a better understanding on influences of multiple freeze-thawing on textural quality of cooked rice maintaining different extents of surface layer.

Walnut peptide loaded proliposomes with hydroxyapatite as a carrier: Fabrication, environmental stability, and in vitro digestion attribute

To explore the feasibility of hydroxyapatite (HAP) as the carrier for proliposomes and improve the stability of walnut peptides (WPs), WPs-loaded proliposomes (WPs-PROLIPs) with hydroxyapatite (HAP) as the carrier were fabricated, and the physicochemical properties, environmental stability as well as in vitro simulated digestion release performance of the proliposomes were investigated. The proliposomes with HAP possessed smaller particle sizes and higher encapsulation efficiencies than those without HAP. FTIR analysis revealed that hydrogen bonds formed between HAP and phospholipids in the proliposomes. The inclusion of HAP in WPs-PROLIPs led to the improvement of the thermal degradation stability and environmental stabilities of the system. HAP also induced the conversion of free water into bound water in the proliposomes, as evaluated by LF NMR. In addition, proliposomal encapsulation did not affect the antioxidant activity of WPs-PROLIPs and the lateral order of the liposome membrane. Finally, in vitro digestion showed that the addition of HAP endowed the proliposomes with a retarded free fatty acid release effect, which was dependent on the weight ratio of phospholipids to HAP. These results offer opportunities for the use of HAP as a feasible carrier and lyoprotectant for proliposomes encapsulating biopeptides.

Effects of Soaking on the Volatile Compounds, Textural Property, Phytochemical Contents, and Antioxidant Capacity of Brown Rice

Brown rice is a staple whole grain worldwide. Hence, the effects of cooking on the nutritional properties of brown rice are important considerations in the field of public health. Soaking is a key stage during rice cooking; however, different rice cookers use different soaking conditions and the effects of this on the physiochemical properties and nutritional composition of cooked brown rice remain unknown. In this study, the setting of varied soaking conditions was realized by a power-adjustable rice cooker, and the effects of soaking temperature (40, 50, 60 and 70 °C) and time (30 and 60 min) on cooked brown rice were thoroughly analyzed. Textural results revealed that cooked brown rice was softer and stickier after soaking. Grain hardness decreased by increasing the soaking temperature and time. Furthermore, stickiness after soaking for 60 min was higher than that after 30 min, and this decreased with the soaking temperature. There was no significant unpleasant flavor after soaking, and the volatile compound profile between soaked and unsoaked brown rice was similar. Neither soaking temperature nor time had any significant effect on the phytochemical contents (phenolic compounds, α-tocopherol and γ-oryzanol) or antioxidant capacity of cooked brown rice, whereas γ-aminobutyric acid content was effectively preserved within a certain soaking temperature range. Textural properties can be effectively controlled by soaking temperature and time, and nutritional properties remain stable when soaking at 40-70 °C for 30-60 min.

Corner coil heating mode improves the matrix uniformity of cooked rice in an induction heating cooker

Nowadays, an increasing number of people worldwide use induction heating cookers to cook rice for consumption. This work reveals the influence of induction heating cooker heating modes on the quality attributes of cooked rice. Three heating modes, including bottom coil heating mode (mode 1), corner coil heating mode (mode 2), and side coil heating (mode 3), were used. Among the three modes, mode 2 allowed for an intermediate heating rate during rice cooking. For mode 2, the minimized temperature difference between the upper layer (including the central upper layer and peripheral upper layer) and the lower layer (including the central lower layer and peripheral lower layer) can reduce the effect of water absorption time difference on rice quality. Consequently, the rice cooked using mode 2 exhibited improved matrix uniformity, as indicated by the similar moisture content (59.92–61.89%), hardness (15.87–18.24 N), and water mobility (the relaxation time and peak area of the third relaxation peak) of rice samples at four different positions in the pot. The rice cooked by mode 2 showed better texture appearance and a more uniform porous microstructure. Consistently, the cooked rice samples by mode 2 at different positions did not show substantial differences in their starch digestion features.

Influence of the Addition of Extruded Endogenous Tartary Buckwheat Starch on Processing and Quality of Gluten-Free Noodles

Extruded starch could be used as a thickener for food processing due to its pre-gel properties. This study aimed to explore the influence of the addition of extruded endogenous Tartary buckwheat starch (ES) on the process and quality of gluten-free noodles. ES was mixed with Tartary buckwheat flour in different proportions (10–40%) to prepare the blended flour and noodles. When the content of ES was increased, the swelling power of blended flour at 90 °C had no significant changes, and the decrease in peak viscosity of blended flour was reduced. This indicated that the high-content ES could afford better thermal stability for blended flour and inhibit the swelling ability. The higher level of ES was beneficial to the formation and stabilization of dough, and the improvement of noodle tensile strength. Furthermore, there was no difference in cooking loss between noodles with 30% and 40% ES addition. The microstructure and water distribution of the noodles prepared by blended flour indicated that the gel-entrapped structure organized by the higher content ES could be closely related to the above results. In conclusion, higher ES could contribute to improving the processing properties and quality of noodles.

Effects of vacuum soaking on the hydration, steaming, and physiochemical properties of japonica rice

Soaking is an essential step in the processing of various rice products. In this study, the influences of vacuum soaking on hydration, steaming, and physiochemical properties of rice were investigated. Results showed that vacuum soaking accelerated water absorption as well as affected the mobility and density of water protons inside rice during soaking. Vacuum soaking could considerably shorten the optimal steaming time from 58 to 32 min and reduce the adhesiveness of steamed rice. Microstructure analysis of rice revealed that porous structure was formed on rice surface and the arrangement of starch granules became loosened after vacuum soaking. Moreover, vacuum soaking slightly reduced the relative crystallinity of rice starches without altering the crystalline type. The gelatinization temperature as well as the peak and trough viscosity was also decreased after vacuum soaking. Our study suggested that vacuum soaking was conducive to improve the soaking and steaming properties of rice.

Kinetics of water absorption expansion of rice during soaking at different temperatures and correlation analysis upon the influential factors

Five model equations were used to study the water absorbing expansion kinetics of rice during soaking. The results indicated that the changes of water absorbing expansion in Japonica and Indica rice during soaking at 25, 40, 50, 60 and 70 ℃ can be well simulated (R² > 0.97) by the five model equations. The linear and polynomial equation could fit the changes of model coefficients and all obtained coefficient parameters could be combined in only one equation to predict the water absorbing characteristics of Japonica and Indica rice. The correlation between the basic nutritional components and model coefficients was further analyzed. The results indicated that the water absorbing rate had significant (P < 0.05) negative correlation with protein content, the apparent amylose content had significant (P < 0.05) negative correlation with the maximum expansion ratio, the length and width of rice affect its water absorbing characteristics.

A visualization and quantification method to evaluate the water-absorbing characteristics of rice

A visualization and quantification image analysis method is developed to evaluate the water-absorbing characteristics of rice. A projected image of soaked rice was obtained by a scanner in real time, the expansion ratio of the soaked rice in the projected image was calculated with computer software, and the change in the internal structure was analyzed. The results showed that water absorption had a positive correlation with expansion and the cracks occurred in the internal structure of rice could accelerate the water absorption. The maximum expansion ratio of Japonica rice gradually increased with increased milling time, but that of Japonica glutinous rice was not significantly different (P > 0.05). A high soaking temperature shortened the time to reach the maximum expansion ratio and resulted in a lower expansion ratio in the Indica and Indica glutinous rice but had no significant effect (P > 0.05) in the Japonica and Japonica glutinous rice.

Effect of structure evolution of starch in rice on the textural formation of cooked rice

The content and composition of rice kernels are closely related to the textural properties of cooked rice. In this study, the mechanistic explanations of textural changes were linked to proton mobility, leaching behavior, and the molecular features of rice components during cooking. The decreasing trend of hardness and the formation of stickiness was mainly determined by the molecular mobility of components. The molecular weight (Mw) of starch and protein in leached solids increased with the leaching at 70-100 °C. The Mw of rice kernels at different cooking temperatures and times was similar, but the molecular size and volume varied at different stages of cooking. The dismission of the crystalline structure, C1 resonance, and lamellar structures after cooking at 100 °C for 10 min indicated that the structural evolution of starch in rice kernels was time- and temperature-dependent. These results provide a promising foundation for developing strategies to control rice cooking.