The evaporation of water through a plastic membrane coated with plant was (30-70 μg cm(2)) from grape berries or fractions thereof was determined. The hydrocarbon, alcohol and aldehyde fractions caused the highest reduction of evaporation. Their effect was identical to the complete wax or to mineral paraffin wax. The main constituent of the grape cuticle wax, the triterpene oleanolic acid, had no effect on evaporation in the artificial system. Free docosanoic acid did not suppress evaporation whereas the mixture of free fatty acids (the main constituents are the C24 and C26 acids) from grape wax reduced evaporation slightly. The results from this artificial system suggest that the alcohol, hydrocarbon and aldehyde fractions are the active components of the grape cuticle which prevent water loss.

SummaryThe fine structure of the surface wax of leaves of sultana vines (Vitia viiUJera var. sultana) has been examined using the carbon replica technique. Leaf wax was found to be morphologically similar to the wax on the surface of grapes and to consist of a series of overlapping platelets. A brief period (30 sec) of exposure to light petroleum vapour disorganized the platelet structure of both leaf and fruit wax. This treatment markedly increased the cuticular transpiration of both fruits and leaves. The results are discussed in relation to the known chemical composition of these waxes. It is suggested that the surface wax, which consists of overlapping platelets that are hydrophobic in nature, may be important in controlling cuticular transpiration in both the fruit and leaves of grape.vines.

Berries of Vitis vinifera L . cv. Sultanina (Sultana, Thonpson Seedless) were partly immersed in commercial oil emulsion before drying in an oven at 40"c. The treatedpart dried to a yellow colour without visible surface bloom, which is characteristic of firlly treared berries, while the untreatedpart dried to a bluish-violet cotour with surface bloom characteristic of untreated berries. Colour development was prevented in partly treated berries if they were fully immersed in oil emulsion before they had lost about 50% of their fresh weight. The browning reaction was inhibited in isolated grape skins by sodium diethyldithiocarbamate. The results support the hypothesis that browning of sultanas during drying under mild conditions is caused by o-diphenol oxidase (E.C.1.10.3.1) acting on substrates released from cell compartments when cell integrity is lost. Uneven colour development in commercially produced, dried sultanas can be prevented by a second spraying with oil emulsion within 7 days of the first.

19 2 0 2 1 2 2 23 2 4 19%-34, 229 ex$. Two quantitative methods for the determination of waxy substances on the surfaces of grapes are compared. These methods applied t o the varieties of grapes used for drying in Australia gave the following results for total extractable waxy substances (pg./sq. cm.) : sultanas 125-140, currants 111, gordos 178, Waltham Cross 107.

No abstract

A relatively simple and inexpensive apparatus has been developed for the rapid determination of the surface contamination of dried vine fruits by grit. Up to 80 measurements can be made in an 8‐hour day by a semi‐skilled operator. Grit is separated from samples (200 g) of dried fruit by sieving, and grit particles greater than 50 μm diameter are collected on a small sieve. After separation of organic matter and grit in a saturated solution of potassium carbonate the height of grit in a tube of diameter 2 mm gives an index of the grit content of the fruit. Values obtained with the gritometer show significant correlation with values obtained using a previously accepted slower method.

No abstract

No abstract