熱處理對軟熟愛文芒果寒害之影響及其可能機制

Abstract

‘愛文’芒果(Mangifera indica L. cv. Irwin)為台灣重要的外銷鮮果之一，現行之蒸熱檢疫處理有成本偏高、設備不足無法大量處理及可能造成熱傷害等缺點。由於軟熟’愛文’芒果較耐低溫，使得低溫檢疫處理可能性增加；但1℃以下之檢疫溫度仍有造成寒害影響果實品質的疑慮。為了延長低溫貯藏壽命或進行低溫檢疫滅蟲處理，本試驗首先觀察低溫對軟熟’愛文’芒果之影響。接著嘗試利用貯藏前熱處理來減輕寒害發生，找出最佳條件並探討其中可能的機制。 軟熟’愛文’芒果於5℃貯藏其病害及寒害症狀發展皆緩於其他貯藏溫度，最適合用於軟熟’愛文’芒果之貯藏。0℃貯藏2週出現寒害，並隨著貯藏時間增加而加重；經0℃貯藏2週及回溫3天後，會出現果皮褐化的寒害症狀，且離子滲漏百分率從貯藏前26.85％增加至60.23％，果皮顏色L*值從46.69降至40.56，a*值從23.26降至15.18，硬度和可滴定酸含量分別從0.37 kg cm-2和0.25％降至0.25 kg cm-2和0.18％，其中離子滲漏百分率和a*值與寒害嚴重程度相關性較高。以52℃溫湯處理15分鐘、46℃熱風處理6或9小時及42℃熱風處理9或12小時減輕寒害徵狀效果最佳，能維持較低的離子滲漏百分率，且對果實硬度、可溶性固性物及可滴定酸含量無明顯影響；但溫湯處理能有效減少低溫貯藏之後病害的發生，熱風處理則不具此效果。於0℃貯藏2週後再加5℃模擬貯運1週，對果實寒害與品質無明顯影響。 貯藏前經過熱處理的果實其果皮丙二醛含量偏高，低溫貯藏間有稍微增加，但各組間無明顯差異；還原態抗壞血酸含量在貯藏期間各組皆無明顯變化出現，表示這兩種物質與軟熟’愛文’芒果寒害發生無明顯相關性。分析抗氧化酵素的活性顯示，貯藏前熱理果實之SOD、CAT和GR活性較對照組高；經0℃貯藏2週及20℃回溫3天後，熱處理果實的SOD、APX和GR活性皆較對照組高。推測溫湯處理減輕軟熟’愛文’芒果寒害發生，可能和藉由提高抗氧化酵素活性有關，因而降低低溫逆境形成之活性氧族對生物膜系的攻擊，減少寒害症狀出現。

‘Irwin’ mango (Mangifera indica L.) is one of the major export fruit products in Taiwan. Since Taiwan is an epidemic area of oriental fruit fly, quarantine treatment is required for exporting mango fruit to markets absent from this insect. However, there are some drawbacks of vapor heat treatment, the current quarantine treatment for mango in Taiwan, such as high treatment fee, facility availability limitation, and heat damage risk. The fact that the chilling tolerance of ripe ‘Irwin’ mango fruit is better than mature-green counterpart has made cold quarantine treatment possible in this commodity. Unfortunately, ripe ‘Irwin’ mango suffered chilling injury and quality deterioration under 1℃ for 2 weeks, the condition for disinfestation of oriental fruit fly. In order to extend the shelf life of mango fruits under cold storage and to establish optimum condition for cold quarantine treatment, this research first to observe the influence of different storage temperatures on ripe ‘Irwin’ mango, and then to investigate the effects of various prestorage heat treatments on chilling injury alleviation on mango after 0℃ storage for 2 weeks as well as its possible mechanism. The optimum storage temperature for ripe ‘Irwin’ mango was 5℃, because of slow rates of chilling injury and disease appearance when compared with other trials. Chilling injury symptom of ripe ‘Irwin’ mango was observable by eyes after storage at 0℃ for two weeks, and the symptom became more severe with storage time. After the cold storage and 3 additional day at 20℃, the browning of fruit peel was more obvious, and the electrolyte leakage percentage increased from 26.85% to 60.23%; the L* value of skin color decreased from 46.69 to 40.56; the a* value dropped to 15.18 from 23.26; the firmness and titratable acidity declined from 0.37 kg cm-2 and 0.25% to 0.25 kg cm-2 and 0.18%, respectively. The percentage of electrolyte leakage and a* values showed a good correlation (R2