Ripening Development and Quality of Melting and Non-melting Flesh Peach C*rs

融化與非融化果肉桃子成熟期生理變化和品質評價
Ming-Wei S. Kao1, Jeffrey K. Brecht, Jeffrey G. Williamson, Donald J. Huber
Horticultural Sciences Department, Institute of Food and Agricultural
Sciences, University of Florida, 1117 Fifield Hall, P.O. Box 110690, Gainesville, FL 32611-0370
Additional index words. Prunus persica, respiration, ethylene, polygalacturonase, pectin methylesterase, freestone, clingstone

Abstract

Some physiological and biochemical properties of melting flesh (MF) and nonmelting flesh (NMF) peaches [Prunus persica (L.) Batsch]were determined during ripening for 5 days at 20 ^oC. Respiration rates and ethylene production of MF ‘Flordaprince’, MF ‘TropicBeauty’, NMF ‘UFSun’, and NMF ‘Gulfking’ were measured at different harvest skin ground color-based maturity stages. The MF c*rs at harvest were mostly preclimacteric or at the onset of ripening. The NMF c*rs generally had higher ethylene production at harvest and throughout ripening than the MF c*rs; thus, the NMF fruit had started ripening on the tree before harvest. Some of the NMF fruit harvested at more advanced stages quickly became postclimacteric during the storage period. Quality determination after fruit ripening showed that MF ‘TropicBeauty’ had the highest soluble solids content (SSC), but also the highest titratable acidity (TA). The NMF c*rs had lower TA than the MF c*rs. NMF ‘Gulfking’ consistently had high SSC/TA, which was the result of it having the lowest TA. The NMF c*rs retained firmer texture than the MF c*rs during ripening. The flesh firmness of the NMF c*rs was four to five times greater than that of the MF c*rs. To investigate the reason for this significant textural difference, the activities of the cell wall modification enzymes pectin methylesterase (PME) and polygalacturonase (PG) were quantified in all four c*rs at advanced ripeness stages. PME activity appeared to be more directly related with peach fruit softening than PG activity.

在20^oC條件下，測定了桃子(Prunus persica(L.)batsch)在5天熟化過程中的部分生理生化特性，測定了不同采收期的呼吸速率和乙烯生成量。基于皮層顏色的成熟階段。收獲期的中頻品種多為氣候前期品種或成熟初期品種。在收獲期和整個成熟期，NMF品種的乙烯產量通常高于MF品種；因此，在收獲前，NMF水果已經開始在樹上成熟。在貯藏過程中，一些在較高級階段收獲的果實很快成為后氣候特征。果實成熟后的品質測定結果表明，Mf‘Tropicbeauty’的可溶性固形物含量(SSC)，可滴定酸度(TA)。NMF品種的TA低于MF品種。NMF“Gulfking”始終具有較高的SSC/TA，這是其具有低TA的結果。在成熟過程中，NMF品種保持了比MF品種更堅實的質地。NMF品種的果肉硬度是MF品種的4～5倍。為了研究這一顯著結構差異的原因，對四個品種在成熟后期的細胞壁修飾酶果膠甲基酯酶(PME)和聚半乳糖醛酸酶(PG)的活性進行了定量測定。與PG活性相比，PME活性與桃果實軟化的關系更為直接。

Ethylene production and respiration rate determination

In 2009, an ETH-1010 Postharvest Gas Sensor (Fluid Analytics, Inc., West Linn,OR) was used tomeasure respiration rate and ethylene production. This instrument uses a proprietary nanoporous, electrochemical sensor with a gold electrocatalyst. Ethylene concentration was measured with a resolution of 0.010 ppm and CO2 concentration was measured with a resolution of 0.1%. To obtain the most accurate measurement of CO2 in the headspace, the incubation time (in seconds) was recorded immediay when the concentration increased 0.1% above the initial reading. Fruit were sealed in a 2.735-L Plexiglas container connected to the gas sensor through two Tygon tubes. After measuring each sample, the tubes were disconnected from the container, flushed with air, and connected to the next container. To minimize handling time and better control during the incubation period, the number of containers was reduced by sealing two fruit with matching ground color in one container. Fruit that had no matching counterpart were sealed individually.

乙烯生產和呼吸速率測定
2009年，ETH-1010乙烯檢測儀(Fluid Analytics，Inc.)用于測量呼吸速率和乙烯產量。這臺儀器使用了一種專有的納米多孔電化學傳感器和一種金電催化劑。乙烯濃度以0.010 ppm的分辨率測量，二氧化碳濃度以0.1%的分辨率測量。為了獲得頂空確的二氧化碳測量值，當濃度高于初始讀數0.1%時，立即記錄潛伏期(以秒為單位)。水果被密封在一個2.735升的有機玻璃容器中，通過兩個Tygon管與分析儀相連。在測量每個樣品后，將管子從容器上斷開，用空氣沖洗，并連接到下一個容器上。為了減少孵化期間的處理時間和更好的控制，通過在一個容器中密封兩個具有匹配底色的水果來減少容器的數量。沒有對應物的果實單獨密封。