During storage of apples at 1° the concentration of a‐farnesene in the ‘coating’ (mainly cuticle) and adjacent cells increased to a maximum and then declined. At the highest maximum farnesene was 15% of the total lipid of the coating. Evidence is presented for a role of a‐farnesene in superficial scald. More a‐farnesene was found in earlier picked apples and more in the scald‐liable Granny Smith than in the scald‐resistant Crofton variety. During storage a‐farnesene moved from the fruit to the oiled wraps until wraps contained more than twice as much as the fruit. Diphenylamine reduced the production of a‐farnesene in later picked apples.

a-Farnesene was oxidised to conjugated trienes with an absorbance maximum at 269 nm and the oxidation was inhibited by diphenylamine both in hexane solution and in the natural coating of stored apples. The results suggest that superficial scald is caused by the oxidation of a-famesene and that the control of scald by diphenylamine is due to its antioxidant action. The mechanism of scald induction is discussed.

No abstract

The a-farnesene content of apples usually passed through a maximum during storage. Studies in the range 0 to 15"c indicated that the highest maximum was reached at approximately 5"c. The concentration of total lipid and fatty acids in the coating increased with temperature. Application of a-famesene to the surface before storage inhibited further production of a-farnesene and reduced the production of total lipid and fatty acids.Application of a-farnesene by dipping in ethanolic solution caused injury to the outer cortex which differed from typical scald. Application within marked circles induced typical scald only with previously oxidised famesene. In comparing experiments over five years, conjugated trienes gave a higher correlation with scald than a-famesene or the peroxide value.Superficial scald is discussed in relation to the concentration of a-famesene and its oxidation products and the concentration of natural antioxidants. Tests for artificial antioxidants are discussed. IntroductionMuch evidence for a r61e of a-farnesene in superficial scald was given in previous p a p e r~. l -~ This evidence includes the transfer of a-farnesene to the oiled wrap, the relation of scald to the oxidation of a-farnesene, and the effect of air movement on its evaporation. The oxidation of a-farnesene was studied by Anet,4 who identified two conjugated triene hydroperoxides with U.V. absorbance peaks similar t o those reported for extracts of the natural coating of long-stored apples2Measurements of changes in the concentration of afarnesene during storage of apples at 5 and 15"c in 1967 were included in the experiments on evaporation already reported.3 Comparable samples from the same source in 1967 were stored at 0"c in cartons and analysed at intervals. Comparison of results obtained at the 3 temperatures indicated that the highest concentration of a-farnesene was reached at 5"c, and this result was of sufficient interest to suggest repetition of the effect of temperature in 1968. Attempts to induce superficial scald by applying a-farnesene to the surface of the fruit were initiated in 1968, and peroxide values as a measure

Oxidation of ascorbic acid by atmospheric oxygen has been studied by many workers, as it is the reaction mainly concerned in the loss of this vitamin during the preparation of processed foods. I n canned foods, however, free oxygen is present in restricted amounts at the time of sealing and disappears entirely within one month of canning (Homer,7 ; Feaster, Tompkins, and Pearce,4 ) . Nevertheless, ascorbic acid loss in canned foods continues at a steady rate throughout the storage life. This continued loss must be due to an anaerobic destruction of ascorbic acid.In strongly acid solution ascorbic acid decomposes to furfural and carbon dioxide (Herbert et al., 6 ; Lamden and Harris, ll), and the same reaction may occur more slowly in less acid or neutral products. I n the author's investigations, the decomposition was studied in buffer solutions of p H 2.2-6.0. The effect of other substances, known to be present in foods, was also investigated. The preliminary measurements were made at 100°C. to obtain results more rapidly, and subsequently a further series of studies was made at 3OOC. METHODSOne-ml. aliquots of citrate-phosphate" buffer with an ascorbic acid concentration of 0.01M (176 mg./100 ml.) were sealed in small glass tubes in the presence of nitrogen or carbon dioxide. The latter was used only for studies at 100°C. where the carbon dioxide, being insoluble, did not affect the pE. Aliquots were analyzed immediately and also after varying periods a t 30" and 100°C. Before storage at 30°C. all tubes were pasteurized at 100°C. for 10 minutes.Each tube was cracked open and the contents washed into a 25-1111. volumetric flask and made to volume with 2% oxalic or 3% metaphosphoric acid. Oxalic acid was used when furfural was determined. Ascorbic acid (uncorrected) was determined by titrating a 5-ml. aliquot with 2.6 dichlorophenol-indophenol. 'Apparent ascorbic acid" was determined by titrating another aliquot after condensing the ascorbic acid with formaldehyde (Wokes, Organ, and Jacoby, 12) and subtracted from the total titre to give true ascorbic acid. All results refer to true ascorbic acid. Determination of furfural was hased on the method of Duncan (3). Another 5-ml.aliquot was diluted t o 50 ml. after adding 5 ml. of 2% oxalic acid and 10 ml. of 0.2M Na2HPOI. I n an Evelyn colorimeter tube were mixed 5 ml. of the diluted solution and . 5 ml. of a mixture of one volume of freshly distilled aniline and nine volumes of glacial acetic acid. After standing for an hour in the dark at 20°C. the absorption was measured in the colorimeter, using a 520-filter. The concentration of furfural was obtained from a standard curve. Determinations were also made of carbon dioxide produced from ascorbic acid after 104 weeks a t 30°C. After introducing 25 ml. of buffer containing 0.01M ascorbic acid into a 50-ml. Florence flask, the neck was drawn out and sealed in. vacuo. After incubation a file mark was made near the tip and the flask placed in a water bath. A 'Preliminary experiments gave similar results in phosphate, ac...

The rates of anaerobic decomposition of ascorbic acid and the yields of furfural were measured from p H < 0 to p H 6. Other products of decomposition were an unidentifiedreducing substance and 2,j-dihydro-2-furoic acid. Three reactions were distinguished: a reaction involving irnionised ascorbic acid and catalysed by hydrogen ions, with furfural as the major product; a reaction involving both rhe unionised form and rhe monovalent ascorbate ion with an optimumpH near pKr (4.2): and a reaction promoted by fructose, particularly at higher pH. The possible products of the last two reactions are discussed.

SummaryThe volatile aldehydes and ketones produced by whole Granny Smith apples at 30°C. were identified by paper chromatography and spectral absorption of the dinitrophenylhydrazones, and by conversion of the aldehydes to hydroxamic acids. Acetaldehyde was found to be the major constituent, with smaller amounts of propionaldehyde and acetone.

During storage Granny Smith apples were ventilated with air at two flow rates differing by a factor of 10. The a-farnesene evaporated, a-farnesene retained by the fruit, and the severity of scald were determined. Increasing the ventilation increased the evaporation of a-farnesene. In two cases the amount evaporated was approximately equal to that retained. In some cases increased ventilation gave less retention of a-farnesene by the fruit and less scald, but in others the difference was negligible because increased evaporation stimulated production. The factors controlling evaporation and the concentration of a-farnesene remaining in the fruit during storage are discussed. IntroductionThe evidence already presented1v2 for a r61e of a-famesene in superficial scald includes the effects of variety and maturity, the transfer of a-farnesene to the oiled wrap, and the inhibition of its oxidation by diphenylamine. It remains to be considered whether the r81e of a-farnesene is the same as that of the volatile or gaseous substances postulated by Brooks et a1.3 as the cause of scald. Their theory was based primarily on observations that increased air movement over the fruit reduced scald. If a-farnesene is involved, air movement should increase its loss by evaporation and reduce its concentration in the fruit.In experiments over three seasons samples of 20-25 apples were stored in drums ventilated with air at 2 or 20 l/h. The a-famesene evaporated, a-farnesene remaining in the fruit, and the severity of scald were determined. Comparisons were made in 1965 between untreated and diphenylamine-treated apples, in 1966 between apples from two districts, and in 1967 between two storage temperatures.