Headspace analysis of laboratory samples of potato tubers treated with 1,4‐dimethylnaphthalene, carvone, pulegone and citral

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Abstract
1,4‐Dimethylnaphthalene, carvone [2‐methyl‐5‐(1‐methylethenyl)‐2‐cyclohexene‐1‐one], pulegone [5‐methyl‐2‐(1‐methylethylidene) cyclohexanone] and citral (3,7‐dimethyl‐2,6‐octadienal) were applied as liquids on an alumina solid carrier to samples of potato tubers stored in boxes. The headspace concentrations of the chemicals were related to the degree of growth regulation found in this and earlier solid carrier application experiments and were compared to studies using constant vapour concentration applications which had been conducted previously by other workers. Headspace concentrations of all four chemicals increased with increasing application rates indicating non‐ideal behaviour. Pulegone (100 mg kg−1), carvone (100 mg kg−1) and citral (100 and 500 mg kg−1) did not prevent sprouting. Headspace concentrations of these treatments were less than the constant vapour concentrations previously shown to inhibit sprouting. Pulegone (500 mg kg−1) and carvone (500 mg kg−1) successfully inhibited sprouting. Initial headspace concentrations of these treatments were within the constant vapour concentration range previously shown to prevent sprouting. Headspace concentrations of all four chemicals decreased during the 14‐week treatment period. Headspace concentrations of 1,4‐dimethylnaphthalene, when applied at the recommended solid carrier application rate of 100 mg kg−1 were within the constant vapour concentration range previously shown to prevent sprouting. Headspace concentrations of 1,4‐dimethylnaphthalene between 3 and 6 mg m3 would be necessary if the chemical were to be successfully applied as a vapour. For these experiments a gas chromatographic (g.c.) analytical method using porous polymer adsorbents was developed. The method was rapid, with a coefficient of variation of 5%.