PRELIMINARY ELEMENTS OF REFLECTION ON THE POSSIBLE PRESENCE OF VITREOUS OR TRANSLUCENT WALNUT KERNELS

In France, walnut distributors are often disturbed by the presence of a proportion of « vitreous » walnut kernels which appear vitreous after drying and at the beginning of the breaking operation. The Creysse Experimental Station has undertaken a study in 1995 to try to understand this phenomena. Observations were targeted at the formation of the nut (type of soil / fertiliser / irrigation), before- and after-harvest parameters (date of harvest / maturity / period spent on ground / time before drying / drying conditions). The analyses, which were carried out on dry nuts (november) and after six months of conservation, were based on the general aspect of the kernels (calibre, colour, etc.), as well as biochemical analyses on the walnut kernels. The early results show a relation to :
– Irrigation : a significant difference between shortened or prolonged irrigation on the percentage of glassy walnut kernels following harvest and conservation,
– Harvest date : the walnuts harvested by vibration are more vitreous than those which fell naturally; there is a higher percentage of vitreous walnut kernels in those harvested in the husk,
– Period spent on the ground : unlike other parameters (particularly colour), the percentage of vitreous walnut kernels tends to decrease with the increase of time spent on the ground. Hypothetically, it can be suggested that this phenomena is either connected to a change in the water content of nuts, with this content decreasing over time as the nut dries, or that the percentage of vitreous kernels is lower when the walnut kernels are coloured, or that these two parameters coincide.
– Drying conditions: Walnuts dried at a lower temperature and at for a longer time have a higher « vitreous rate ».
« Vitreous walnuts » do not seem to present any anomalies at the level of general biochemical parameters. This puts aside the notion of a lipid metabolism perturbation which would explain the « vitreous » appearance of the analysed nuts. Perhaps it is necessary to look for the origin of this vitreous aspect at the level of a histological anomaly in walnuts. When considering the relations which we have brought to evidence, it is still too early to formulate any conclusions, because the year factor certainly has a considerable influence on each mode. These observations must be pursued and validated over time.

IV International Walnut Symposium

J.P. Prunet, T. Ginibre

kernel, glassyness, walnut

https://doi.org/10.17660/ActaHortic.2001.544.77