Studies On Chlorophyll Degradation And Methods For Delaying Green Color Change Of Kiwifruit Puree During Break Processing

The attractive green flesh color of kiwifruit is the important commercial character anddetermined by its chlorophylls, and kiwifruit is also among the very few fruit that are stillgreen when they are ready-to-eat. Chlorophylls which are unsteady and easy to degrade andde-greening in producing and storage, which lead to some of kiwifruit products, appearyellow-brown or light yellow color. It has important realistic meaning and theory value forkiwifruit products with kiwifruit puree as raw materials to study breakdown mechanism andgreen color preserving methods of kiwifruit puree during break processing.Using green-fleshed kiwifruit (Actinidia deliciosa cv. Qinmei) as an experimentalmaterial, this study tested that the effects of ethephon treatment on chlorophylls degradationand quality properties of kiwifruit during ripening, the chlorophylls extraction condition ofkiwifruit flesh and its antioxidant activity in vitro, chrorophylls degradation kinetics andgreen color loss in heated kiwifruit puree and the main degradation derivatives were identified,with a view to preserving green color of puree and to improve the quality of kiwifruitprocessing products. The main results were exhibited as follows:(1) Ethephon treatment could increase respiration rates significantly and decreasefirmness and titratable acidity of kiwifruit, concomitant with higher soluble solidsconcentrations and total phenol contents. Moreover, ethephon treatment had no significanteffects on green color, ascorbic acid contents or chlorophyll contents. The activities ofchlorophyllase, Mgdechelatase, SOD and POD were enhanced gradually during ripeningcompared to the controls, no significant effects on APX. And a significant positive correlationbetween chlorophyll degradation and chlorophyllase activity was also observed. Ripenedkiwifruit can be obtained through ethephon treatment after4d while controls need7d.(2) The optimum extraction conditions for highest recovery of chlorophyll a (Chl a) andchlorophyll b (Chl b) were carried out using central composite design (CCD). The optimumextraction conditions for Chl a were9.93min,8.63﹕1,115min,and Chl b were11.26min,7.83﹕1and114.71min,respectively. Predicted values for extraction of Chl a and Chl bagreed well with the experimental values. Antioxidant capabilities of the optimally obtained chlorophylls extracts from kiwifruit revealed better scavenging abilities on ABTS·+and·OH,and reducing power as compared to BHA, while they were weaker than BHA inO2-· scavenging ability.(3) The chlorophylls and green color of kiwifruit puree were easily influenced bytemperature and pH value. The breakdown of chlorophyll a, chlorophyll b and green colorloss (-a*) values followed a first-order reaction. With the increase of temperature and pHvalue, the rate constant and half-life value of chlorophyll a, chlorophyll b and green color loss(-a*) values decreased. The activation energies ranged from14.69～66.02kJ mol^-1,40.88～54.64kJ mol^-1and48.55～64.14kJ mol-1for chlorophyll a, chlorophyll b and green colorloss (-a*) values, respectively. In addition, significant correlation between chlorophylls andgreen color loss (-a*) values were found for kiwifruit puree at pH3.3. Higher pH value(neutral condition) would benefit for preserving chlorophylls and green color in heatedkiwifruit puree.(4) Chlorophylls and their derivative were separated within35min using a gradientmobile phase of methanol, water and ethyl acetate. During heating treatment, the bright greencolor of kiwifruit puree turn to light yellow-green color, the main degradation derivatives ofchlorophylls were pheophytins. Heating treatment of3min produced complete PODinactivation in puree when93%inactivation of chlorophyllase activity after15min heatingtime.(5) Under heating treatment, chlorophyll b degraded to pheophytin b when chlorophyll adegraded to pyropheophytin a. With the pH value of kiwifruit puree enhanced, the relativepheophytins concentration and pyropheophytins concentration declined gradually, resulting inrelative chlorophylls concentration increased.(6) The has no significant effect on the relative chlorophyll a and chlorophyll bconcentrations when added to the kiwifruit puree with Zn²⁺solution below pH5.0. When pHvalue was5.0for the kiwifruit puree, the relative chlorophyll a and chlorophyll bconcentration were6.44%and11.04%for pulp with Zn²⁺solution, while that of the pulp ofno Zn²⁺solution were5.45%and9.20%respectively, there has significant differencesbetween both. Continue to raise the pH value of the pulp, this significant difference still exists,indicating that the relative chlorophyll a and chlorophyll b concentration can be enhanced atthe high pH value conditions by adding a certain concentration of Zn²⁺solution. Added to thekiwifruit puree with Ca²⁺solution also has the same effect. The addition of Zn²⁺was better fora*value of kiwifruit puree than that of Ca²⁺when the pH value of kiwifruit puree was5.0,but there has no significant difference between both.(7) Compared with kiwifruit puree with no added Zn²⁺or Ca²⁺, there have more relative pheophytins and pyropheophytins concentration were detected in kiwifruit puree with addingZn²⁺or Ca²⁺under the different pH values.. The relative pheophytin a and pheophytin bconcentrations of puree were81%and553%at pH5.0after heating treatment, while theirconcentration of puree with added Ca²⁺significant increased to117%and832%under samepH value, and significant higher than that of added Zn²⁺puree(100%and671%). This may beexplained that there have Zn²⁺-chlorophyll complexes and Ca²⁺-chlorophyll complexformations.