1981 Volume 50 Issue 3 Pages 363-371
The degree of peeling easiness, i.e. easiness to remove the pellicle from the kernel in roasted nuts, was numerized using"peeling score". Peeling score was obtained by grading the peeling easiness of roasted nuts into four grades, based on the peeling time, the time required to peel off the pellicle from kernel with a knife without damaging embryo. The peeling score correlated to the peeling time of raw nuts (r=0.78**), and also to the strength of adhesive force between the pellicle and embryo of raw nuts evaluated by a rheometer (r=0.81**). The peeling score seemed to be useful to evaluate briefly the easiness of peeling off the pellicle in chestnuts, and to improve the efficiency of selection in chestnut breeding.
The pellicle of Japanese chestnut was completely stripped by incubating the nut in sodium chlorite solution, which was known to solubilize phenolic compounds, without visibe damage to the surface tissues and pleats of the embryo. This fact suggested that the phenolic compounds of the pellicle played an important role in the adhesion between the pellicle and embryo.
Free and polymerized phenolic compounds in the pellicle were determined separately by precipitaing the latter with gelatin. In Japanese chestnuts, which are difficult to peel off their pellicles, the amount of total phenolic compounds in pellicles increased rapidly with their maturation, and the increments were mainly composed of polymerized ones. The change in the amount of phenolic compounds with developmental stages of nuts corresponded to that of the peeling time of the pellicle from kernels, and the positive correlation of 0.89** was obtained between the amount of phenolic compounds and the peeling time in raw nuts. In Chinese chestnuts, whose pellicles are easily removed from kernels, the amount of total phenolic compounds contained in the pellicles of matured nuts was less than 50% of that of matured Japanese chestnuts. The increase of polymerized phenolic compounds with nut maturation was also less than that of Japanese chestnuts.
These results suggested that the rapid increase of phenolic compounds, especially polymerized ones, with nut maturation might be involved in the relative easiness of peeling off the pellicles of chestnuts.