Changes in color and texture of wheat noodles during chilled storage

Wheat noodles cooked for different periods of time were stored at 5 °C, and color changes in their cross sections were quantitatively assessed by digital image analysis. The color of noodles with flattened moisture distributions whitened greatly during the early stages of chilled storage due to the retrogradation of starch, with the color change showing a significant correlation with the changes in noodle fragility. Color changes were also measured for wheat noodles and noodles containing modified starch with internal moisture distributions, and local changes within the noodles were kinetically analyzed. The addition of modified starch significantly reduced the color change in the noodle interior, where the moisture content was relatively low. Scanning calorimetric measurements indicated differences in the gelatinized state of modified starch and original wheat starch at low moisture contents, which affected the rate of color change in the interior of noodles containing modified starch.     

Vicia villosa B4 lectin inhibits nucleotide pyrophosphatase activity toward UDP-GalNAc specifically

Plant seed lectins play a defense role against plant-eating animals. Here, GalNAc-specific Vicia villosa B₄ lectin was found to inhibit hydrolysis of UDP-GalNAc by animal nucleotide pyrophosphatases, which are suggested to regulate local levels of nucleotide sugars in cells. Inhibition was marked at low concentrations of UDP-GalNAc, and was reversed largely by the addition of GalNAc to the reaction mixture. In contrast, lectin inhibited enzymatic hydrolysis of other nucleotide sugars, such as UDP-Gal and UDP-GlcNAc, only to a small extent, and GalNAc did not affect such an inhibition. The binding constant of the lectin for UDP-GalNAc was as high as 2.8×10⁵ M^?1 at 4°C, whereas that for GalNAcα-1-phosphate was 1.3×10⁵ M^?1. These findings indicate that lectin inhibition of pyrophosphatase activity toward low concentrations of UDP-GalNAc arises mainly from competition between lectin and enzyme molecules for UDP-GalNAc. This type of inhibition was also observed to a lesser extent with GalNAc-specific Wistaria floribunda lectin, but not apparently with GalNAc-specific soybean or Dolichos biflorus lectin. Thus, V. villosa B₄ lectin shows unique binding specificity for UDP-GalNAc and has the capacity to modulate UDP-GalNAc metabolism in animal cells.