<i>Juglans nigra</i>, the black walnut tree, produces nuts with yellow-green hulls beginning in spring and continuing through fall. These immature hulls are a convenient, abundant source of juglone, 5-hydroxy-1,4-naphthoquinone, established as a medicinal compound and component in dye formulas. These properties are useful in the educational setting as well. Inhibition of microbial growth reduces risk to students, and the potential for dramatic color change allows younger, less skilled students to identify when a process has occurred. This also increases the usefulness and relevance of new research findings as modified class activities or experiments for these students.<br/><br/>The use of fresh plant material in K–16 activities proves to be a limitation, as there is only a short window of time for gathering and utilizing samples during the school year. An experimental design in which instructors could successfully refrigerate this plant matter would better accommodate when scheduling the procedure for students to perform. In addition to seasonal availability, juglone is also highly photosensitive. This is a significant barrier to integration of this work to other settings, as a future goal of this study is to increase student access to activities that use materials in their own yards or at a nearby store. The same extraction and characterization scheme was used to compare the concentration of juglone extracted from walnuts refrigerated for up to eight weeks versus fresh plant material. Immature black walnuts were collected from tree canopies in Warren County, Tennessee, with half being processed for extraction and half being placed in a refrigerator. Walnut hulls were grated to pulp, combined with one of four solvents, stirred overnight, and filtered. The extract was characterized using UV-VIS, and the juglone concentration was compared to that of walnuts that were processed as fresh plant material.

To chill or not to chill: The effect of long term refrigeration of black walnuts on juglone extraction in comparison to fresh hulls

2019 Spring National Meeting

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