Important role of starch in the freeze-thaw damage of Nama-An particles prepared from adzuki beans (Vigna angularis)

In order to elucidate the mechanism of freezing damage of adzuki Nama-An (non-sugar bean jam), changes in the tissue structure of Nama-An and degree of damage according to different freeze-speeds and thawing conditions were investigated in this study. After Nama-An was frozen at −20 °C for 3 months, the An particle size shrank from 67.6 to 51.6 μm. Although the particle size was restored to 60.4 μm after being thawed at 20 °C, the An particles were not completely recovered, and many hollows were formed on the surface of the particles. Also, when An was stored at −20 °C, some spaces and voids were formed inside the particles and starch granules because starch granules might retrogradate and be dehydrated. The soluble carbohydrate extracted from the particles was in low level both in thawing and non-thawing conditions, although it tended to increase with freezing storage periods. The starch of raw beans had a lower swelling power and retrogradated easily, depending upon its structures and the ratio of amylose to amylopectin. The findings suggest that freezing damage of adzuki Nama-An may be mainly due to the major constituent, starch.