Wheat Starch Effects on the Textural Characteristics of Puffed Brown Rice Cakes

A process was described for creating puffed wheat starch based or hybrid starch and rice snack foods processed in a rice cake puffing machine. Puffed cakes consisting of wheat starch and whole grain brown rice, created by mixing wheat starch beads with brown rice before processing and puffing for 10 sec (cooking time) at 210°C, exhibited greater flexibility and fracture strength than traditional rice cakes. The density of puffed wheat starch cakes decreased with increasing moisture content independent of particle size for particles 0.8–5 mm in diameter. The addition of sucrose and shortening promoted the formation of lower density puffed cakes at lower moistures, while salt had little effect.     

Characterization of Waxy Rice Cakes (Mochi) with Rapid Hardening Quality by Instrumental and Sensory Methods

The textural properties of cooked waxy rice cakes made from four waxy rice varieties including the unique varieties Kantomochi 172 (K172) and BC3 with the property of rapid hardening were analyzed by instrumental and sensory methods. For the instrumental analysis, a compression test, adhesiveness test, and tensile test were conducted. The waxy rice cakes made from K172 and BC3 showed significantly higher compressive force and resistance to break under tensile load. Significant difference in amylopectin chain‐length distribution was observed between each variety, and this difference strongly reflected the hardness of waxy rice cakes. The peak area ratio of amylopectin branch chains with 6–12 degrees of polymerization negatively correlated with the compressive force required for 50 and 80% strain. Sensory evaluation showed that the waxy rice cakes made from these varieties had a significantly harder, less stretchable, less smooth surface, whereas the scores for adhesiveness and ease to cut off (hagire) were preferable to those for other rice varieties.     

Flavor Volatiles of Rice During Cooking Analyzed by Modified Headspace SPME/GC‐MS

The flavor volatiles in three Japanese rice cultivars, Nihonbare, Koshihikari, and Akitakomachi, during cooking were directly extracted by using a modified headspace solid‐phase microextraction (SPME) method and analyzed by gas chromatography‐mass spectrometry (GC‐MS). A total of 46 components were identified, including aldehydes, ketones, alcohols, and heterocyclic compounds, as well as fatty acids and esters, phenolic compounds, hydrocarbons, etc. The amount of key odorant compounds increased with cooking, while the amount of low‐boiling volatiles decreased. The similarities and differences of the three rice cultivars were determined through a comparison of their volatile components. Nihonbare was characterized by a higher amount of indole but an absence of the chemical class of fatty acid esters. In contrast, both Koshihikari and Akitakomachi had a higher amount of 4‐vinylphenol and an abundance of those esters. Koshihikari and Akitakomachi were quite similar in regard to those flavor volatiles. Furthermore, the observations in the research may suggest that the volatile components at cooking stage (I) were the representatives of the flavor volatiles of uncooked rice, while the volatile constituents at cooking stage (IV) were the representatives of the flavor volatiles of cooked rice.     

Effect of Aqueous Impregnation of Rice Kernels with Gum Arabic and Xanthan on Storage Stability of Frozen Rice Cakes

Rice kernels were steeped (10°C, 5 h) in an aqueous solution containing gum arabic (0.36%) and xanthan (0.24%) and then drained, wet‐milled, and steamed to prepare rice cakes. The cakes were then frozen (–40°C for 50 min). The effect of the gum addition on the textural properties of the cakes during storage for 46 h at 25°C after being thawed was examined. Using the combination of gum arabic and xanthan mitigated the quality deterioration of rice cakes such as aggregation of rice flour, which had been induced by xanthan alone. Also, the increase in hardness during storage was substantially reduced by soaking rice kernels in the gum arabic/xanthan solution. Overall results revealed that the steeping in the gum solution improved the storage stability of rice cakes.     

Effect of Germination on Flavor Volatiles of Cooked Brown Rice

The effect of germination on flavor volatiles of cooked brown rice among three different rice cultivars was investigated using the headspace solid‐phase microextraction method combined with gas chromatography‐mass spectrometry. The results showed that some flavor compounds varied significantly throughout the germination process and others did not show distinct changes. The amount of total volatiles, most lipid‐oxidation products, and phenolic compounds decreased in the initial stage of germination but increased significantly at a later stage. The amounts of ethanol and ethyl acetate increased significantly in the initial stage of germination and maintained almost the same levels during further germination. The amount of dimethyl sulfide increased significantly during germination; it showed the most significant change among all volatile compounds.     

Use of Mixolab in Predicting Rice Quality

Mixolab is a new instrument with capability to measure starch pasting properties on actual dough. It characterizes dough rheological behavior using a dual constraints of mixing and temperature. Rice samples (183) collected from 15 provinces across China were tested to determine the possibility of using Mixolab in predicting rice quality. Mixolab measurements, torque (Nm) at different mixing and heating stages (C1 to C5) were compared with rice quality characteristics (gelatinization temperature and consistency, amylose and protein contents), Rapid Visco‐Analyser (RVA) parameters and sensory assessments scores of cooked rice. Our results showed that Mixolab parameters were good indicators of amylose and protein content and quality suggested by significant correlations among Mixolab parameters, and between Mixolab and RVA measurements. Based on a subsample of 30 rice cultivars, correlation coefficients between the Mixolab parameter C4 and sensory assessment characteristics of palatability and total sensory score was negatively significant (P < 0.05). C_b (C3 – C4) was also significantly correlated with flavor (P < 0.05). The rice samples that gave high palatability and total sensory scores had low C4 values and low amylose contents. The cooked rice with high flavor had high values of C_b and GT but low protein content. It is possible to determine physicochemical properties of rice flour and sensory characteristics of cooked rice using Mixolab parameters.     

Effect of Presoaking on Textural,Thermal, and Digestive Properties of Cooked Brown Rice

Brown rice kernels (japonica type) were soaked in water at different temperatures (25 or 50°C) before cooking to a moisture content of 20 or 30%. Soaked brown rice was cooked in either the soaking water (SW) or in distilled water (DW) (rice solids to water ratio 1:1.4). Color, texture, and in vitro digestive properties of the cooked rice were examined. When the soaking temperature was higher (50°C vs. 25°C), water absorption and starch leaching were greater. To reach 20% moisture, the rice required 1 hr of soaking at 50°C but 2 hr of soaking at 25°C. Both the moisture content of the soaked rice and the soaking temperature affected the texture of the cooked brown rice. Rice that attained 20% moisture content during soaking was harder and less adhesive when cooked compared with rice that attained 30% moisture content. The rice soaked at 50°C was slightly softer but more adhesive when cooked than rice soaked at 25°C. The soaking temperature and moisture content of the rice kernels also affected the digestive properties of the cooked rice. The cooked brown rice that had attained 30% moisture before cooking was digested to a greater extent than rice that had attained 20% moisture. Even at equal moisture content, the rice soaked at the higher temperature (50°C) was digested more readily. It was assumed that the amount of soluble material leached during soaking differed according to the soaking temperature and moisture content, which subsequently affected the texture and digestive properties of the cooked brown rice. The rice cooked in its own soaking water was harder and more adhesive, had higher levels of resistant starch (RS), and exhibited smaller glycemic index (GI) values than its counterpart cooked with distilled water. This result indicated that the soluble material leached during soaking made the cooked rice harder and less digestible, perhaps due to interactions between these molecules and the gelatinized rice during cooking.     

Influence of Rice Proteins on Eating Quality of Cooked Rice and on Aroma and Flavor of Sake

An improved method for the extraction of storage proteins from rice endosperm under conditions safe for producing food was developed. The contribution of the protein extracts to the eating quality of cooked rice and to the aroma and flavor of sake was examined. Sensory analysis was performed to evaluate the eating quality of cooked rice enriched with the protein extracts. Prolamin‐enrichment increased the hardness of cooked rice, and glutelin‐enrichment degraded the appearance of cooked rice. Physical analyses confirmed that prolamin‐enrichment changed, whereas the glutelin‐enrichment did not change the physical properties of cooked rice. Light and scanning electron microscopy of rice protein extracts revealed small particles of the prolamin extract and larger aggregated particles of the glutelin extract; these features remained after heating. The aroma and flavor of sake were negatively affected by the addition of the protein extracts. Especially, addition of prolamin significantly lowered the evaluation score of the aroma obtained by sensory analysis.     

A Better Understanding of Factors That Affect the Hardness and Stickiness of Long‐Grain Rice

Eight U.S. long‐grain rice cultivars were studied for chemical compositions, physicochemical properties, and leaching characteristics in relation to hardness and stickiness of rice flour paste and cooked rice. There were differences in the chemical composition of rice kernels among the eight rice cultivars, including crude protein (6.6–9.3%), crude fat (0.18–0.51%), and apparent amylose content by iodine colorimetry (19.6–27.0%). Differences were also observed in gelatinization temperatures and enthalpies, pasting temperatures and viscosities, leached/insoluble amylose, soluble solids, and hardness and stickiness of rice flour pastes and cooked rice kernels. The quantity and molecular size distribution of the leached starch molecules varied greatly among the samples. Protein and crude lipid contents negatively correlated with hardness of rice flour paste and cooked rice, but positively correlated with stickiness. Apparent amylose content correlated with gel properties but not cooked rice texture, whereas the ratio of A and short B chains to long B chains of amylopectin correlated significantly with cooked rice texture.     

Quality and Fortificant Retention of Rice Noodles as Affected by Flour Particle Size

Rice noodles, which are widely consumed noodles in Southeast Asia, were evaluated as a potential carrier for fortificants such as vitamin A, folic acid, and iron. Because flour particle size was found to affect the noodle properties, this study was conducted to investigate the effect of five different particle sizes (≤63, 80, 100, 125, and 140 µm) of dry‐milled rice flour on the cooking quality, microstructure, texture, and sensory characteristics of the rice noodles. The retention of fortificant in the noodles at every stage of processing as affected by the flour particle size was also determined. It was found that the rice noodles produced from flour with the smallest particle size studied (≤63 µm) had the best quality and were the most liked by the consumers. In addition, the noodles had the most compact and regular structure, which could be attributed to having the most severely gelatinized starch. This starch would have caused the least leaching of the fortificant into the surrounding water during the boiling stage of the rice noodle processing. Retention of iron in the cooked fortified rice noodles prepared from flour with the smallest particle size was high at around 87%, whereas that of vitamin A and folic acid were below 15%. Because the losses of the fortificant from the rice noodles were mostly owing to the boiling process, further improvements of the rice noodle processing conditions are required for reduction of the vitamin losses.     

Two‐Dimensional Vibration Spectroscopy of Rice Quality and Cooking

Rice samples were taken from a study of rice milling properties that affect quality. The spectra of milled and cooked samples were taken in the near‐infrared, mid‐infrared, and Raman region. These spectra, two regions at a time, were regressed by a two‐dimensional technique to develop contour maps that indicated the correlation of two spectral regions. These relationships demonstrate that it is possible to recognize the hydration effects caused by gelatinization (cooked samples vs. milled rice). Three water (O‐H stretch) spectral bands (960, 1445, 1,930 nm) in the near‐infrared (NIR) show marked differences between milled and cooked rice. The difference spectra indicated that there were additional phenomena occurring besides the addition of water. These differences are apparent in both C‐O‐H and N‐H bands, which indicate that water is interacting with both starch and protein. The two‐dimensional technique developed in this laboratory was used to get a better interpretation of what occurs during cooking. The Raman spectrum, which is relatively insensitive to water (O‐H stretch), revealed only changes in protein that could be associated with denaturization.     

Physicochemical Properties and In Vitro Starch Digestibility of Cooked Rice from Commercially Available Cultivars in Canada

The influence of amylose content, cooking, and storage on starch structure, thermal behaviors, pasting properties, and rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) in different commercial rice cultivars was investigated. Long grain rice with high‐amylose content had a higher gelatinization temperature and a lower gelatinization enthalpy than the other rice cultivars with intermediate amylose content (Arborio and Calrose) and waxy type (glutinous). The intensity ratio of 1047/1022 cm^–1 determined by Fourier Transform Infrared (FT‐IR), which indicated the ordered structure in starch granules, was the highest in glutinous and the lowest in long grain. Results from Rapid ViscoAnalyser (RVA) showed that the rice cultivar with higher amylose content had lower peak viscosity and breakdown, but higher pasting temperature, setback, and final viscosity. The RDS content was 28.1, 38.6, 41.5, and 57.5% in long grain, Arborio, Calrose, and glutinous rice, respectively, which was inversely related to amylose content. However, the SDS and RS contents were positively correlated with amylose content. During storage of cooked rice, long grain showed a continuous increase in pasting viscosity, while glutinous exhibited the sharp cold‐water swelling peak. The retrogradation rate was greater in rice cultivars with high amylose content. The ratio of 1047/1022 cm^–1 was substantially decreased by cooking and then increased during storage of cooked rice due to the crystalline structure, newly formed by retrogradation. Storage of cooked rice decreased RDS content and increased SDS content in all rice cultivars. However, no increase in RS content during storage was observed. The enthalpy for retrogradation and the intensity ratio 1047/1022 cm^–1 during storage were correlated negatively with RDS and positively with SDS (P ≤ 0.01).     

Effects of Milling and Cooking Conditions of Rice on In Vitro Starch Digestibility and Blood Glucose Response

The objective of this study was to investigate the effects of milling and cooking conditions of cooked rice prepared from cultivar Koshihikari on in vitro starch digestibility and in vivo glucose response in humans. In addition, compression and adhesiveness tests were conducted for texture analysis of the cooked rice. Brown rice (BR) and surface‐abraded BR (SABR, ≥99.5% of the original weight) were digested more slowly than white rice (91% of the original weight) when cooked rice grain was used for the in vitro test, but they were digested more rapidly in the initial stage of the reaction when cooked rice ground by a meat grinder was used. The increase in water added for cooking significantly increased the extent of starch digestion with BR and SABR. The changes in blood glucose levels after the ingestion of cooked rice were dependent on the sample type. The cooking conditions dramatically influenced the glucose response after the ingestion of BR. A significant correlation was found between blood glucose levels at 45 min and the extent of starch digestion with ground samples, whereas no relationship was found with cooked rice grain samples for in vitro digestibility.     

Retrogradation of Rice Flour Gel and Dough: Plasticization Effects of Some Food Additives

Certain food additives commonly used in flour products also have a plasticization effect on product shelf life regarding retrogradation. Sucrose, sorbitol, glycerol, citric acid, and acetic acid at 25, 25, 25, 0.5, and 0.5%, respectively, were added to two different starch gel systems: slurry (high‐amylose rice flour gel) and dough (waxy rice flour dough). All plasticizers increased gelatinization temperature, decreased enthalpy (ΔH), and promoted a more homogeneous system. Sucrose had the greatest effect on gelatinization increase. Rice dough was more susceptible to plasticizers, resulting in higher moisture content and a more amorphous structure. Retrogradation was highly positively correlated with amylose content, moisture retention, ratio of protons of water/starch, and previous occurrence of retrogradation. Moisture retention was increased in plasticizer‐added samples, especially waxy rice dough. Over a longer storage period, sucrose and sorbitol showed an antiplasticization effect in waxy rice flour dough, but glycerol and acid caused higher retrogradation in high‐amylose rice flour gel.     

Utilization of Hydroxypropylated Waxy Rice and Corn Starches in Korean Waxy Rice Cake to Retard Retrogradation

A traditional waxy rice gel cake in Korea, Injulmi, was prepared with hydroxypropylated waxy rice and corn starches (molar substitutions 0.13 and 0.11, respectively), and the textural and retrogradation characteristics of the cake were compared with a conventional cake made of waxy rice flour. In the pasting viscogram, hydroxypropylated starches exhibited reduced pasting temperatures, but increased peak viscosities compared with the unmodified starches. Under differential scanning calorimetry, the T_g′ and ice melting enthalpy of the starch gel cakes were reduced by hydroxypropylation, which indicated that the modified starches had higher water‐holding capacity than the unmodified starches. The degree of retrogradation, as measured by the hardness of the gel cake and the melting enthalpy, was significantly reduced by hydroxypropylation and hydroxypropylated waxy rice starch was more effective in retarding the retrogradation than hydroxypropylated waxy corn starch