高溫對番木瓜(Carica papaya L.)果實後熟軟化之影響

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作者: 趙筱倩;林慧玲
刊名: 臺灣園藝
期刊所屬國別:
出版年: 2009
關鍵字: high temperature;番木瓜;papaya;softening;ethylene;β-galactosidase;軟化;乙烯;β-半乳糖苷酶
摘要: 番木瓜採收成熟度會影響果實採後品質與貯藏能力,尤其番木瓜果實後熟軟化快速,有嚴重的運輸損耗,另一方面‘台農二號’番木瓜果實又會發生果肉不軟化現象,稱為‘橡皮木瓜’。本試驗探討番木瓜果實後熟變化及影響軟化之因子,及高溫對番木瓜果實後熟之影響與橡皮木瓜發生原因。 ‘台農二號’番木瓜果實呼吸率與乙烯釋放率變化與腔內二氧化碳與乙烯氣體濃度變化相似。因此可藉由測定腔內氣體濃度得知果實之生理狀態。一般而言,外銷最佳成熟度(果皮25%轉色)果實呼吸率為20.69 ml CO2 kg-1 hr-1,乙烯釋放率為0.036 μl C2H4 kg-1 hr-1,腔內二氧化碳濃度為2.17 %,乙烯濃度為0.032 ppm;當果實後熟達可食用階段呼吸率為47.6-50.7 ml CO2 kg-1 hr-1,乙烯釋放率為5.18 μl C2H4 kg-1 hr-1,腔內二氧化碳濃度4.6-5.7 %,乙烯濃度為6.2- 9.9 ppm。果實後熟期間,果皮由綠轉黃,色相角自120.6°下降至65.9°。而葉綠素螢光也可用以輔助果實後熟狀態之測定。當‘台農二號’番木瓜果實後熟軟化時,除了呼吸率與乙烯釋放率上升外,失重率、澱粉、不可溶果膠含量與總鈣含量會下降,可溶性糖與可溶性果膠含量會增加。在番木瓜果實軟化原因中,失水可能造成細胞膨壓的下降,進而影響果實硬度;當後熟第2天硬度明顯下降之後無明顯變化,但失重率依然持續下降,因此膨壓的下降與軟化前期較為有關。澱粉含量的下降也可能造成硬度下降,但番木瓜果實內澱粉含量相當低,因此影響成分可能較小。果膠溶解程度變化與硬度快速變化相符,水溶性鈣比例的增加也顯示果膠結構逐漸鬆散;β-葡萄糖苷酶活性上升,可能輔助降解細胞壁多醣體結構。因此番木瓜果實後熟軟化可能受乙烯反應與組織內細胞壁物質的降解所相輔造成。 高溫造成‘台農二號’番木瓜果實乙烯釋放量下降,主要原因是ACC氧化酶對於高溫敏感,導致活性下降。高溫處理會造成轉色不良及抑制軟化之現象。當熱傷害累積到一定程度,果肉會出現硬塊。40℃高溫處理6天,果實即使經由催熟處理,部分果肉依然無法完全軟化。由於高溫抑制果肉的呼吸作用及乙烯生合成,造成果實後熟作用受阻,導致果皮與果肉之轉色不良,並抑制β-半乳糖苷酶活性與β-葡萄糖苷酶活性,及減緩果膠溶解速度。以上結果顯示高溫可能誘導番木瓜橡皮肉之發生,並且與乙烯釋放率下降及果膠溶解速度緩慢有關。The maturity of papaya fruit when harvested affects postharvest quality and storage capacity. For example, if the papaya fruit softens quickly, there is serious loss of product during transportation. On the other hand, when ‘Tainung No.2' papaya fruit pulp does not soften, it known as ‘rubber papaya'. This research will discuss the changes in papaya fruit as it ripens; suggest an index of ripening stage and what factors affect softening; examine the effect of temperature on papaya fruit ripening and if high temperature causes rubber papaya. ‘Tainung No.2' papaya fruit respiration rate is similar to its internal carbon dioxide concentration, while ethylene production rate is similar to its internal ethylene concentrations. Therefore, by measuring the atmospHeric composition of fruit cavity, the pHysiological state of fruit can be known. In general, the best export maturity (25% of skin turning color) had a respiration rate of 20.69 ml CO2 kg-1 hr-1; ethylene produce rate of 0.036μl C2H4 kg-1 hr-1; internal carbon dioxide concentration of 2.17 %; and an internal ethylene concentration of 0.032ppm. When fruit ripened to the stage of edibility, it had a internal respiration rate of up to 47.6-50.7 ml CO2 kg-1 hr-1; internal ethylene concentration of 5.18μl C2H4 kg-1 hr-1; internal carbon dioxide concentration of 4.6-5.7%; and an internal ethylene concentration of 6.2-9.9ppm. During fruit ripening, fruit skin changed from green to yellow in a hue angle expressed as 120.6° to 65.9°. ChloropHyll fluorescence can also be used to support the determination of the ripening state of fruit. When the ‘Tainung No.2' papaya fruit ripened and softened, respiration rate and ethylene production rate increased, an indication of the ripening process. Weight, starch, insoluble pectin content, and total calcium content were significantly decreased, while soluble sugar and soluble pectin content increased, all of which are chemical reactions carried out in fruits ripening. Water loss may be the reason for the papaya softening, because the decline in cellular turgor, affects fruit firmness. Two days after ripening, the firmness decreased but then there was no other significant changes. However, the weight loss rate continued to decrease, so turgor was more related to early stage softening. The decrease in starch content also caused firmness to decrease, but the starch content of papaya fruit is very low, thus the effect of starch may be relatively small. Firmness changed at the same rate at which pectin dissolved. Additionally, an increase in the ratio of water-soluble calcium resulted in a loosening in the pectin structure. Increased β-glucosidase activity caused the degradation of cell wall polysaccharides. The ripening and softening of papaya fruit may be affected by the complementary reaction of ethylene response and degradation of cell wall material. High temperature treatment caused ‘Tainung No.2' papaya fruit ethylene production rate to decrease, mainly because of ACC oxidase's sensitivity to high temperatures, which resulted in decrease in ACC oxidase activity. Heat treatment also caused poor color change and inhibited the softening process, and accumulated thermal damage resulted in hard lumps. For example, even after 6 days at 40℃ and 3 days ripening with calcium carbide at 30℃, some pulp still had not softened. High temperatures caused inhibition of respiration and ethylene biosynthesis which blocked fruit ripening. This further resulted in peel and pulp color changing poorly; the inhibition of β-galactosidase and β-glucosidase activity; and the slowdown of the pectin dissolution rate. In conclusion, 40℃ temperature may induce the occurrence of papaya rubber pulp because of the decrease in the ethylene rate and the slow dissolution of pectin.
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