Atomic force microscopy of the water-soluble pectin of peaches during storage

Yellow peaches (Prunus persicu L. Batsch.) were stored under a controlled atmosphere of 2% O2 + 10% CO2, or a normal atmosphere at 2 C, in order to investigate the effects of storage conditions, atmosphere and time on the structure of a single water-soluble pectin (WSP) molecule. The microstructural changes of the branches and widths of WSP were studied by atomic force microscopy (AFM) on the 1st, 15th and 45th days under the assigned atmosphere. The probability of small-width WSP increased with time in both groups, but the probability was larger in the normal-atmosphere group. The microstructure of WSP molecules and polymers showed that the aggregate separation increased with storage time. The degradation of WSP molecules was inhibited by controlled-atmosphere storage. The majority of the chains were composed of four basic units with widths of 11.719, 15.625, 19.531 and 35.156 nm, which could be visualized and calculated exactly by AFM. These results indicate that parallel linkages or intertwists between the basic units are fundamental conformations for WSP molecules.