EFFECT OF DOUBLE PAPER BAGGING ON INCIDENCE OF STAIN AND VOLATILES ONHOKUTO APPLES DURING COLD-STORAGE

The apple cv. Hokuto is very susceptible to a new skin-browning disord er called stain during storage. To study the cause of 'Hokuto' stain, young fruits were individually covered with commercial double paper ba gs from early June to late September. These shaded fruits were harvest ed in late October and stored at 0 degrees C for up to six months. Inc idence of stain between bagged and unbagged (control) fruits during st orage at 0 degrees C was recorded and volatiles in their skins were de termined by gas chromatography-mass spectrometry and gas chromatograph y. There was less stain in bagged fruit than in unbagged ones. The sam e 50 volatiles were identified in the skin of bagged and unbagged frui ts during storage. Differences in content of volatile compounds in the skin of bagged fruit were compared to those in unbagged fruit, noting the compositions whose contents were smaller in the skin of bagged fr uit than those in unbagged ones. The difference in content of trans-2- hexenal was the greatest among the volatiles, followed by 2-methyl-but an-1-ol, n-hexanal, n-propanol, trans-3-hexenol, n-hexyl propionate an d n-amyl acetate, in that order. No difference was found in (E, E)-alp ha-farnesene whose oxidation products are believed to cause superficia l scald. Exposure of healthy 'Hokuto' apples to seven volatiles and fa rnesene (mixed isomers) at 20 degrees C for 20 hours showed that both trans-2-hexenal and n-hexanal induced stain-like injury at the lowest concentration, followed by n-amyl acetate, n-hexyl propionate and 2-me thyl-butan-1-ol, in that order. No symptoms of stain appeared on fruit s exposed to n-propanol, trans-3-hexenol and farnesene. Comparison in stain-like injury between C-6-aldehydes and its C-6-alcohols i.e, tran s-2-hexenal and trans-2-hexenol, n-hexanal and n-hexanol, revealed tha t the injury was greater in C-6-aldehyde than in its respective C-6-al cohol. Application of linolenic and linoleic acids, respective precurs ors of trans-2-hexenal and n-hexanal, on 'Hokuto' apple skin at 0 degr ees C for four days induced stain-like injury in both unsaturated acid s. The injury was greater in linolenic acid than in linoleic acid. How ever, the degree of the injury decreased remarkably in nitrogen gas. R esults suggest that shading of the apples by double paper bags reduces concentration of trans-2-hexenal characteristically and that the shad ing is related to metabolism of linolenic acid to trans-2-hexenal, whi ch were used in these experiments to induce stain-like injury to 'Hoku to' apples.