SummaryWax on the surface of prune plums, sampled from 2 weeks before fruit was mature until 2 weeks after, was shown by electron microscopy, using the carbon· replica technique, to occur in a two-layer structure. The iruier layer consisted of a matrix of thin platelets, while the outer layer was composed of fragile projections, many of which appeared tubular. The incidence and complexity of the projections in the outer layer increased as the fruit matured.Deposits of wax remained uniform at about 300l-'g/cm2 during the time that samples were taken and the thickness was estimated to be 3-5 1-'. The influence of this waxy layer in retarding the water loss from prunes during drying by counterflow and parallel-flow procedures is discussed.

Storage experiments were done at 25"C, 75% r.h. to assess the relative importance of the mechanisms by which SO, is lost from dried apricots having a moisture content of 25% and packaged in pouches that were (a) highly permeable and (b) impermeable to SO, and oxygen. Test packs: were sealed and stored in two atmospheres, air and nitrogen. The storage life of dried apricots under the above conditions was also determined.The loss of SO, due to oxidation by oxygen which entered th.e permeable packages was about twice that caused by oxygen which was entrapped in the headspace. The latter was about the same as the loss o f S 0 , by permeation.A further appreciable loss occurred by irreversible combination of SO, with constituents of the dried fruit.

SUMMARY The influence of many individual factors on the uptake of sulfur dioxide by apricot, peach, and pear tissue before drying was tested in equipment designed to permit accurate control over sulfuring conditions. Exploratory trials showed that estimates of sulfur dioxide uptake were unreliable unless standardized sampling methods were used. Absorption rate was affected appreciably by type of fruit, surface area as influenced by size, and the use of irrigation, and less so by variety and maturity. Sulfur dioxide uptake through the skin was slow. Combinations of gas concentration and exposure time were the most important processing variables affecting absorption. Variation in air speed and temperature had little influence upon absorption. Holding cut fruits for up to 10 hr before sulfuring did not cause a decrease in gas uptake. Excess water on the fruit surface from spraying tended to decrease absorption, while steam‐blanching retarded it appreciably. Any disorganization of tissue, whether from increasing maturation, storage, or processing, retarded sulfur dioxide uptake, probably through sealing, of penetration pathways. The ready desorption of sulfur dioxide from tissue removed from the sulfuring environment indicated low chemical fixation at that stage.

No abstract

The development of the wax layer or bloom has been observed on prune plums throughout the growing season (177 days), using the carbon replica and thin�sectioning techniques of electron microscopy. Changes in their average fresh weight, surface area, percentage of total and soluble solids, and the amount of wax per fruit and per square centimetre were determined also at 12 intervals during their growth.