The distribution of chemical constituents is known not to be even within a rice kernel. To improve the eating quality of rice or to give it some special traits by adjusting the milling intensity, we investigated the distribution of amylose, nitrogen (N), and specific minerals (P, K, Mg, Ca, and Mn) in rice kernels of 11 cultivars with various characteristics cultivated under similar conditions. The distributions of these constituents were determined using flour samples prepared consecutively by abrasive milling from the outer to the inner portions of hulled rice. In all the cultivars tested, N and the minerals were found to be more abundant in the outer than in the inner portion, but amylose was rich in the inner portion. P, Mg, K, and Mn were extremely rich in the outer portion, while N and Ca were only relatively rich there. Koshihikari, which is the most popular cultivar in Japan because of its excellent eating quality, showed the highest Mg/K ratio in the outermost portion of polished rice. The color of flour samples became pure white going from outside portions toward the center of the kernel, even if the sample was from red rice or purple-black rice because only the surface of hulled rice contains pigments. These findings suggest that the outer portion contains various compounds other than starch and the inner portion contains relatively pure starch. Rice palatability and other characteristics can be improved through controlling the degree of milling using the biased distribution of chemical constituents within a rice kernel.
The mode of mastication of soft foods was examined through visual analysis with cineradiography and self description by experimental subjects, using agar and gelatin gels as test foods. The mode altered from compression with the tongue and hard palate to shearing with the dentition as the hardness of model samples was increased. The thresholds of hardness requiring a shift of mastication mode from compression to shearing were 0 .08 kg for the agar gel and 0.03 kg for the gelatin gel, although the gelatin gel shear strain was larger. Rupture stress was also found to be an important factor in changing the mode . A value from 150-250 g/cm2 was observed to be the threshold. Visual analysis of cineradiography revealed that the food texture may be recognized by initial compression (deformation rate, about 12%) between the tongue and hard palate , around thei ncisive papilla. Very soft food was treated in the same way as liquid food , although it has nofl uidity. The mastication mode of a food may be determined according to the texture . The food was masticated either by compression with the tongue and hard palate or by shearing with the teeth . It was suspected that the process of initial compression of food with the tongue and the incisive papilla region is the first step of texture recognition.
We examined the role of soluble fiber viscosity in small intestinal mucin secretion. Viscosities were defined as the area under the viscosity curve (VAUC). Rats were fed a control diet or diets containing konjac mannan (KM) [low, medium, or high molecular weight (LKM, MKM, HKM), respectively] at 50 g/kg diet for 10 d. Luminal mucin content and goblet cell number increased in proportion to the molecular weight of KM. Such effects with the HKM diet were nullified by the concurrent ingestion of 2 g cellulase/kg diet. Diet containing LKM, MKM, HKM, guar gums (high or low molecular weight; HGG, LGG), psyllium (PS), or pectin (PC) at 50 g/kg was fed to rats. Fibers with higher VAUC (MKM, HKM, HGG, and PS) increased goblet cell numbers, but not those with lower VAUC (LKM, LGG, and PC). Luminal mucins were greater in rats fed HKM, PC, and PS diets. Goblet cell numbers and VAUC were correlated (r = 0.98; P < 0.01). In rats fed the HKM diet, ileal Muc2 gene expression was not affected, but that of Muc3 was lower than in those fed the control diet, indicating that the increase in luminal mucins after ingestion of HKM diet occurred independently of enhanced Muc gene expression. An incorporation study of 5'-bromo-deoxyuridine (BrdU) showed the position of the uppermost-BrdU labeled cell along the villi was higher in rats fed the HKM diet than in those fed the control diet. The results suggest that soluble fibers, except PC, upregulate baseline secretion of luminal mucins by increasing goblet cell numbers in proportion to fiber VAUC.
The concentrations of sugars and organic acids as well as the total soluble solid (TSS) in different parts of the strawberry fruit were characterized. The data were used to create simulated fruit juice jellies, in order to clarify how the sugar and organic acid levels affect the taste. Such an approach eliminates the influence of external factors such as size, color, and texture when using real fruits in sensory evaluations. Further, the use of a jelly allowed us to simulate the concentration differences between various parts of the fruit. In the strawberry fruit, the sugar content is higher in the apex than in the peduncle; however, the level of organic acids is the same throughout. It was revealed that the sweetness and sourness in the apex and peduncle could be sufficiently recognized by humans as tastes. Also, a layered jelly sample replicating the sugar and acid distribution in real strawberry was perceived as less sweet and more sour, compared to a homogeneous one with the same overall composition. The likely reason is that the sourness in the peduncle is accentuated by the low TSS level, which decreases the TSS/total organic acid ratio that affects the sweetness/sour perceptions. Based on these results, factors for the appropriate sensory evaluation of fresh fruits in general were considered. Specifically, the distribution of sugars and organic acids in the fruit should be analyzed first, and bite‐sized parts with concentrations close to the average provide the most accurate evaluation results.
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