|關鍵字： 番木瓜；污斑；果房包覆；乳汁；泰維克；不織布；papaya；skin freckle；cluster wrapping；latex；Tyvek；non woven material
|摘要： 春、冬季的番木瓜果實表皮會出現生理性污斑(skin freckle)，嚴重影響果實的外觀，本試驗主要探討污斑的成因與減少污斑的方法。首先探討氮肥的影響，‘NTU 10號’與‘台農二號’植株於始花期後，每2週施用四種不同氮肥量作為處理，分別為每株11.9、25.0、38.2、51.2g硫酸銨。於施肥7個月後以及停止施肥後1個月採樣分析果實及葉片成分。試驗結果，以每株施用38.2g硫酸銨效果較佳，而施用高氮肥處理(51.2g/株)，果實於後熟後腐爛率明顯提高，而且‘台農二號’的果皮轉色較差，糖度也略低於其他處理。在礦物元素分析，隨著氮肥施用，葉片與果實N/Ca值增加，亦會間接影響鉀元素的吸收。每株施用11.9g硫酸銨處理，明顯有缺氮的情形，尤其是葉片較果實敏感，會誘導葉片總酚類化合物增加。另外，‘NTU 10號’與‘台農二號’番木瓜在催熟前污斑發生面積相似，但催熟後‘台農二號’會急劇上升，相對來說‘NTU 10號’在催熟後污斑的變化不大，顯示‘台農二號’為污斑較敏感的品種，而不同氮肥處理對污斑發生面積較無直接關聯。 其次在污斑指數高及低的季節，採集不同生長階段的果實，作相關的生理及生化成分分析，隨著果實生長發育，果皮中磷、鉀、鎂濃度會逐漸遞增，其中在11月份鈣、鋅濃度，至污斑出現時並無隨果實生育而遞減，反而維持平穩，顯示污斑發生並非元素缺乏所引起，推測因營養較多導致細胞壁較為堅硬，導致果實成熟時，膨壓增加，進而使細胞結構發生分裂而形成污斑。而果肉中氮、磷、鈣、鎂、鐵、錳、鋅、銅濃度皆會隨果實生長發育逐漸下降，至果肉完全轉色時維持平穩，而鉀濃度在生長期間僅少量變化，總酚類化合物與苯丙胺酸脫氨裂解酶活性亦隨著果實轉色而逐漸遞增。 污斑發生的原因可能與低溫有關，果實在套袋後因袋內溫度較為穩定而減少污斑產生。南投地區可能因為溫差較大而使污斑發生面積高於高雄地區。果實生長至一定大小，於污斑未出現前進行果房包覆96天可明顯降低污斑的發生，套袋材質以泰維克布的減少污斑效果較不織布佳。套袋後果皮較明亮且有光彩，但會降低果重，而水分含量、乾重、乳汁量、糖度則無明顯差異。果實在套袋48天後，果肉中鉀、鈣、鎂濃度皆較對照組低。套袋時間增加至96天後影響反而較小，僅鉀、錳濃度較對照組低。另外，套泰維克布處理的果皮其總酚類化合物與苯丙胺酸脫氨裂解酶活性較低。果皮污斑的發生可能與果實在逆境下所引發的褐化反應有關。Skin freckles on papaya fruits, as a rule, appear in spring and winter and thus affect fruit appearance seriously. The objectives of this study were to investigate the cause of this disorder and to reduce the occurrence of freckles. In the experiment of nitrogen treatments, four concentrations of ammonium sulphate (NH4)2SO4 were applied to ‘NTU 10’ and ‘Tainung No.2’ papaya trees (11.9、25.0、38.2、51.2 g/tree) at intervals of every two weeks. Compositions of leaves and fruits were measured seven months after fertilization and again one month after stop applying fertilizer. The result of the experiment showed that 38.2 g/tree was the best concentration used among treatments. The rate of fruit decay was a serious problem from high nitrogen fertilization. Peel color change of ‘Tainung No.2’ papaya was somewhat delayed, and the total soluble solids were also lower than other treatments. Increasing N/Ca ratio of leaves and fruits was found with increased nitrogen fertilizer, and thus indirectly affected potassium accumulation. Treatment with 11.9g ammonium sulphate per tree resulted in fruits and leaves nitrogen deficiency, especially in leaves. However, accumulation of total phenolic compound was found. Before ripening the freckle incidence area of ‘NTU 10’ and ‘Tainung No.2’ papaya fruits were similar, but ‘Tainung No.2’ was more serious after ripening. There was no significant correlation between N fertilization and the appearance of freckles. ‘Tainung No.2’ was consistently more susceptible than ‘NTU 10’ papaya fruits. In season of high and low skin freckles occurrence during fruit growth and development, chemical analysis of phosphorus, potassium, magnesium concentrations in the peel showed the tendency of gradual increase. Concentration of calcium and zinc in peel leveled off in November while freckle appeared. This seemed to indicate that freckles were not related to the mineral deficiency. It is assumed that the hardening of the cell wall and increasing in turgor pressure during the ripening of fruits could lead to the degeneration of wall structure and the occurrence of freckles. At the later stage of fruits development, the phosphorus, calcium, magnesium, iron, manganese, zinc, copper in pulp decreased progressively and stabilized until complete turning of pulp color. Potassium content change very little during entire period of fruit growth. Total phenolic compound and phenylalanine ammonia-lyase activity of fruit increased during the period of peel and pulp color change. The main cause of the skin freckle was related to the low-temperature. Wrapping fruits in bags to reduce the temperature fluctuation improved the situation. In Nantou County more skin freckles occurred than in Kaohsiung due to the differences in temperature in the two areas. Cluster wrapping of fruits with Tyvek material before the appearance of freckles, while still attached to the tree, could reduce the physiological disorder after bagging for 96 days. Tyvek material was better than Non-woven material for the purpose. Moreover, wrapping increased brightness and chroma of the peel, but reduced fruit weight at harvest. No significant differences in water content, dry matter, total soluble solids, and latex volume of fruits were found between Tyvek and non-wrapping treatments. The potassium, calcium and magnesium of pulp were less after 48 days wrapping with cluster Tyvek than non-wrapping treatment. With increasing in time of bagging, only potassium, manganese concentrations were decreased. Total phenolic compound and phenylalanine ammonia-lyase activity were less after cluster wrapping with Tyvek. In conclusion, skin freckles occurrence seems to be associated with browning of fruits and environmental stress.