Yukiharu Ogawa

Impact of structural characteristics on starch digestibility of cooked rice.

To examine the impact of structural characteristics of cooked rice grains on their starch digestibility, a simulated in vitro gastro-small intestinal digestion technique was applied to intact and homogenised cooked rice samples. The starch hydrolysis percentage increased during simulated small intestinal digestion, in which approximately 65% and 24% of the starch was hydrolysed within the first 5min, for homogenised and intact cooked rice, respectively. The kinetic constant of homogenised cooked rice, which was regarded as an estimated digestion rate, was ∼8 times higher than the intact cooked rice. The homogenised and intact samples were also examined for any microstructural changes occurring during the in vitro digestion process using fluorescent and scanning electron microscopy. In the intact samples, the aleurone layers of the endosperm remained as thin-film like layers during in vitro digestion and thus may be regarded as less digestible materials that influence cooked rice digestibility.

APPLICATION OF X-RAY CT FOR DETECTION OF PHYSICAL FOREIGN MATERIALS IN FOODS

A medical X-ray CT scanner was used as a non-destructive inspection method for the detection of selected non-metallic materials embedded in various fluids and food materials. The X-ray absorption characteristics of tested materials were expressed as X-ray CT numbers. It was found that the CT number of a foreign object was affected by a systemic error (a point spread function), even if its size was greater than 1 pixel in the video image provided by the scanner. Within the interface region between the foreign object and its surrounding matrix, CT numbers were found to vary smoothly between characteristic values for the object and the matrix thus pointing to important effects to consider when developing X-ray CT techniques for the detection and identification of foreign materials in foods. Specific threshold values for CT numbers of selected foodstuffs were defined for successful detection of foreign materials. This study also pointed out the limitation of using X-ray linear absorption coefficients from typical CT systems to detect certain combination of foreign materials and foodstuffs.

Impact of the degree of cooking on starch digestibility of rice - An in vitro study.

The impact of cooking degree on the starch digestibility of a non-waxy, cooked rice was examined through a simulated gastro-small intestinal in vitro digestion model. The starch hydrolysis of both non-homogenised and homogenised cooked rice samples during simulated digestion was also compared in order to examine the impact of grain structure on starch digestibility. Polished rice grains were cooked in boiling water for 10min (partially cooked) and 20min (fully cooked) to obtain samples of different cooking degree. No significant differences in the equilibrium starch hydrolysis (%) were observed among the partially and fully cooked grains, although significant differences were observed among the uncooked and cooked samples. The equilibrium starch hydrolysis (%) of homogenised rice was higher than its non-homogenised counterpart. These results showed that rice starch digestibility should not be affected by the cooking degrees related to starch gelatinisation, but was influenced by the modification/destruction of the grain structure during mechanical processing.

A simple method for studying whole sections of rice grain.

We developed a new and simple method to collect sections of a whole brown rice kernel for investigation of histological properties. A single kernel of rice was dehydrated through a graded ethanol series, transferred to xylene, and embedded in paraffin. During sectioning of the blocks using a rotary microtome, we used a special adhesive tape to collect and place the sections on slides so they remained flat. The use of the adhesive tape technique combined with autofluorescence characteristics allowed us to visualize cell walls throughout an entire longitudinal or transverse section of a whole rice kernel. We obtained scanning electron microscopy images of the sections to determine section quality.

Compression Deformation and Structural Relationships of Medium Grain Cooked Rice

ABSTRACT Cooked rice quality is based on a number of factors including texture. Texture and structure of foods are closely related and aspects of the relationship can be explored by correlating compression measurements to structural observations of the compressed material. To obtain compression measurements, single cooked, milled rice grains were compressed in a texture analyzer to a specific percentage (% compression) of the original grain; the uncompressed grain is 0%. The experiment, using single grains in each case, was repeated multiple times. Compression percentages of 20, 30, 40, 50, 60, and 70% were measured against a constant resistance force in the texture analyzer. Structures of cooked rice grains at the various compression levels were compared by brightfield and fluorescence microscopy. The outside of an uncompressed, intact, cooked rice grain is swollen and distorted while the interior has three or more odd-shaped holes (voids). Each void is largest in the center of the grain and decreases in...

The importance of an oral digestion step in evaluating simulated in vitro digestibility of starch from cooked rice grain

To examine the effect of oral digestion step in a simulated in vitro starch digestion model, the digestibility of intact, homogenized and actual chewed cooked rice grains was investigated and analyzed. The kinetics of starch digestibility were calculated from changes in the hydrolysis percent of starch that were achieved during simulated small intestinal digestion stage. Morphological and histological microscopic tissue structures were also examined. Compared with the trend of starch hydrolysis changes of the actual chewed grain, 1.3U/ml of salivary α-amylase concentration treated for 60min was regarded as a mimicked condition to the simulate in vitro oral digestion step in this study. The results showed that the equilibrium percent of starch hydrolysis for all of the samples ranged from 84.2% to 95.9% with no significant differences observed regardless of whether the oral digestion step was included (p>0.05). In contrast, the kinetic constant, which is one of the measure of starch digestion rate during small intestinal stage, significantly increased with the degree of grain homogenization increased: 120s>actual chewed ≥1s>intact, for both the gastrointestinal and oral plus gastrointestinal processes. These results indicated that the kinetic constant was influenced by the change of cooked rice grain structure in oral digestion step that would be related to increase in enzyme accessibility to rice starch. Thus, rice grain digestibility was affected by grain-scale structural changes, including grain tissue damages which were normally observed during the oral digestion step.

Parboiling reduced the crystallinity and in vitro digestibility of non-waxy short grain rice

The impact of parboiling on starch digestibility of cooked rice was examined through an in vitro digestion model. Results indicated that the equilibrium starch hydrolysis of polished rice was the highest (86.55%), followed by that of parboiled-polished (83.94%), brown (80.59%) and parboiled rice (76.95%). X-ray diffraction analysis indicated that A-type crystals were predominant in brown rice and polished rice, while A-, B- and V-type crystalline structures coexisted in parboiled rice and parboiled-polished rice. Thin and compact layers were observed on the surfaces of parboiled rice and were considered to be physical barriers that reduce the starch digestibility. The study demonstrates that parboiling could change the crystallinity and reduce the starch digestion of rice significantly.

The microstructure of starchy food modulates its digestibility

ABSTRACT Starch is the main carbohydrate in human nutrition and shows a range of desired food properties. It has been demonstrated that fast digestion of starchy food can induce many health issues (e.g., hyperglycaemia, diabetes, etc.); therefore, how to modulate its digestion is an interesting topic. Previous studies have revealed that the microstructure and digestibility of starchy food of different botanical origin or from multiple processes are quite different; modulating starch digestion by retaining or altering its microstructure may be effective. In the present review, the current knowledge of the relationship between microstructural changes to starchy food and its digestibility at molecular, cell and tissue, and food processing levels is summarized. New technologies focused on microstructure studies and ways to manipulate food microstructure to modulate starch digestibility are also reviewed. In particular, some insights focusing on the future study of microstructure and the digestibility of starchy food are also suggested.

3D image of protein visualization in a whole rice grain using an automatic precision microtome system

The 3D image formation technique using confocal microscopy has allows visualization of the 3D chemical structure in small parts of the bio-body. However, the large-scale 3D structure such as the distribution of chemical components throughout the whole body has not been shown. To allow such large scale visualization of the 3D internal analysis technique for bio-body has been developed.

Influence of postharvest drying conditions on resistant starch content and quality of non-waxy long-grain rice (Oryza sativa L.)

ABSTRACT This study investigated the effect of postharvest drying conditions on resistant starch (RS) content and quality of rice. Paddy was subjected to hot-air drying at 40, 65, 90, and 115°C, and sun drying. Drying conditions altered head rice yield, RS and overall firmness of cooked rice, and some pasting properties of rice flour. No significant variation in RS of uncooked rice and surface firmness of cooked rice was observed among the samples. However, RS of cooked rice from sun drying was lower than the others. Higher temperature in hot-air drying resulted in a slightly increase in RS of cooked rice.