In recent years, interest in rare sugars has been increasing. The conversion of common sugars into rare ones can be broadly classified into two approaches: biochemical methods which utilize biocatalysts such as enzymes and microorganisms, and chemical methods which rely on the Lobry de Bruyn-Alberda van Ekenstein (LBAE) transformation under alkaline conditions. Although the biochemical approach offers high selectivity, it is labor-intensive requiring extensive effort to identify suitable catalysts. This paper focuses on the chemical approach, which, while less selective, offers greater versatility. Specifically, this paper provides an overview of several methods for producing rare sugars from common reducing sugars under subcritical water conditions. These methods include homogeneous reactions in subcritical water, aqueous organic solvents, buffer solutions, and basic amino acid solutions, as well as heterogeneous reactions using eggshells or seashells which are primarily composed of calcium carbonate.

We compared the textural and sensory properties of rice materials prepared by cooking rice paste obtained by grinding rice in water or a slurry obtained by mixing dry- or wet-milled rice flour with water. Rice paste showed less starch damage and had a smaller average particle size than rice flour. When cooked, the rice paste and rice flour slurry formed a gel-like material. The rice paste material was significantly softer and less adherent than the rice flour material. Dynamic viscoelasticity measurements showed that the rice paste material tended to be less viscous than the rice flour material. Sensory evaluation revealed that the rice paste and wet-milled rice flour materials had a good appearance and were evaluated as smooth, whereas the dry-milled rice flour material was perceived as less sticky, but with a rougher texture. Owing to their characteristics, these novel materials have application potential in nursing foods and gluten-free foods.