Final answer:
Alginates stored in air or water form a polysaccharide gel due to their hygroscopic properties which allow them to absorb moisture and create a colloidal gel network.
Step-by-step explanation:
Alginate storage in either air or water typically results in the substance forming into a polysaccharide gel. Alginates such as sodium alginate, potassium alginate, ammonium alginate, calcium alginate, and propylene glycol alginate (PGA) absorb moisture due to their hygroscopic properties. This absorption capacity contributes to the formation of a colloidal system when they come into contact with water. Colloidal particles, such as those found in alginates, form gels by trapping water molecules within a network of polysaccharide branches. This action is similar to other colloidal systems like gelatin or starch, which also disperse in water to form gels.
Furthermore, these properties make alginates useful in different applications, including as a thickening agent in foods, in wound dressings due to their absorbency and gentle texture, and in dental impressions for their ability to accurately capture detail.