Study on some of biochemical changes during growth and development of taiwanese papaya fruit grown in Quoc Oai, Ha Noi

135 HNUE JOURNAL OF SCIENCE DOI: 10.18173/2354-1059.2018-0081 Natural Sciences 2018, Volume 63, Issue 11, pp. 135-141 This paper is available online at STUDY ON SOME OF BIOCHEMICAL CHANGES DURING GROWTH AND DEVELOPMENT OF TAIWANESE PAPAYA FRUIT GROWN IN QUOC OAI, HANOI Le Thi Thuy, Nguyen Thi Thu Hien, Tran Thi Thanh Huyen and Nguyen Nhu Khanh Faculty of Biology, Hanoi National University of Education Abstract. Some biochemical changes according to the age of Taiwanese papaya fruit were studied. The analytical data showed that, at 13 weeks of age, the fruit reached its maximum size in term of length and diameter. During growth and development of fruit, total carotenoid, reducing sugar and vitamin C content progressively increased and reached a peak at 15 weeks of age. All three parameters declined later, when the fruit turned to overripe stage. Starch content significant of fruit increased up to 12 weeks of age and then decreased during the ripening phase. The total organic acid content in papaya was relatively low and tends to decrease from young fruit stage to ripe fruit stage. Based on this study results, Taiwanese papaya fruit should be harvested after physiological maturity and before ripening completely (from 13 weeks of age to 15 weeks of age) to ensure the nutritional value of the fruit during storage. Keywords: Biochemical changes, papaya fruit, physiological maturity. 1. Introduction The papaya is the fruit of the plant Carica papaya, the only species in the genus Carica of the plant family Caricaceae. It is native to the tropics of the Americas. Nowadays, in the world, there are a lot of papaya varieties which differ in morphology, ripening period, physical and chemical character of fruit [1]. Ripe papaya is a good source of vitamins A, B and especially vitamin C (ascorbic acid). Besides, the extracts of unripe C. papaya contain terpenoids, alkaloids, flavonoids, carbohydrates, glycosides, saponins, and steroids. Due to these characteristics, papaya is not only used for direct nutritional supplementation, it is also used to produce medicinal products and cosmetics [2-4]. Based on a number of studies on the nutritional value and physico-chemical changes in ripe fruit, some researchers pointed out that papaya fruits should be harvested shortly (5-10 days) after physiological maturity [5, 6]. The reason is that most of the indicators related to nutritional value of papaya fruit will decrease during ripening stage. Therefore, the precise determination of harvesting time is especially important in maintaining the quality of papaya fruit during storage. 2. Content 2.1. Materials and methods * Materials: Papaya fruits (F1 Taiwanese variety) collected at the garden of Mr. Nguyen Van Luong, Nghia Huong commune, Quoc Oai district, Hanoi city from September to November in 2017. Received October 14, 2018. Revised November 14, 2018. Accepted November 22, 2018. Contact Le Thi Thuy, e-mail address: hienthuy20@gmail.com Le Thi Thuy, Nguyen Thi Thu Hien, Tran Thi Thanh Huyen and Nguyen Nhu Khanh 136 * Method - Sample collection method Samples were collected by mixed sampling: 40 trees, which were healthy and similar in age, height and number of flowers, were selected from a total of 400 trees. Fruits of the selected trees were marked with age. At sample collected times, fruits were taken early in the morning, after that the fruits were stored cold and transferred to the laboratory for analysis. The number of samples collected and used for the analysis of fruit parameters in one period was 40 (each papaya fruit was collected in a tree). - Parameters studied The fruits were tagged at time of the first appearance. Studies were conducted at different age groups of papaya fruit, including stages: 1 day old fruit (0.14 weeks); 3, 6, 9, 12, 13 weeks of age; 13.5 weeks of age (fruit peel began to appear yellow spot); 14.5, 15 weeks of age (the whole peel turned yellow); 15.5, 16 weeks of age (fruit peel began to appear black spots). Pulp of papaya fruit was used for analysis of study parameters. a B Image of papaya in Taiwan 13.5 weeks of age (a) and 15 weeks of age (b) - Fruit length and diameter were measured by tapeline and were expressed in centimeters. - Total carotenoid content: measured on a UV spectrophotometer VisibleModel SPECORD 200 Plus and calculated according to MacKinney's equation. - Vitamin C content was determined by the iodine titration method. - Reducing sugar content was determined by dinitrosalicylic acid method (DNS). - Starch content was quantified by Bertrand method - Total organic acid content was determined by titration method described by Ermacov. Parameters were analysis at the Laboratory of Department of Plant Physiology and Application, Faculty of Biology, Hanoi National University of Education. - Statistical analysis Using Microsoft Excel 2007 software and SPSS 16.0 software to process statistical data. The data were processed by statistical one-way ANOVA analysis (Turkey’s-b) at the significance level of α = 0.05. Study on some of biochemical changes during growth and development of taiwanese papaya fruit grown 137 2.2. Result and discussion 2.2.1. Changes in fruit length and diameter of fruit Growth in fruit size is a result of cell division and elongation. The changes in Taiwanese papaya length and diameter during growth and development are shown in Figure 1. Figure 1. Changes in fruit length and diameter during growth and development of Taiwanese papaya fruit Figure 1 shows that both the length and diameter of the fruit increase according to the growth and development of the fruit. From the period of 1 day (0.14 weeks) to 16 weeks of age, fruit length increased 6.7 folds while fruit diameter increased 5.2 folds. In particular, the sharply increase in fruit size observed during period from 1 day to 9 weeks of age. This is due to an increase in both the number and size of cells in the papaya fruit. From 9 to 12 weeks old, the fruit reached the maximum value of the cultivar in the study condition (at 13 weeks of age, fruit length was 22.50 cm, fruit diameter was 10.61 cm). After 13 weeks of age, the fruit size increased very slowly and almost unchanged. The ripening process of papaya fruit is marked by the color change on the fruit pods [7]. During the study, we observed that at 13.5 weeks of age, papaya fruit peel began to appear the first yellow spot. Therefore, it can be said that the time of 13 weeks of age is physiological maturity stage of Taiwanese papaya. 2.2.2. Changes in total carotenoid content of fruit Papaya is recommended to be one such pick from the group of yellow and orange fruits, which promises abundant health benefits. Papaya contains high levels of β-carotene, which is the raw material for the synthesis of vitamin C and vitamin A in the human body [2]. 12 µg β- carotene will be equivalent to 1 µg vitamin A. β-carotene is considered to be a very potent antioxidant, which helps to reduce the risk of many serious diseases in humans such as heart disease, colon cancer, lung inflammation, and emphysema [4, 8]. Figure 2. Changes in carotenoid content during growth and development Taiwanese papaya fruit Le Thi Thuy, Nguyen Thi Thu Hien, Tran Thi Thanh Huyen and Nguyen Nhu Khanh 138 Results from the analysis of total carotenoid content of papaya in Figure 2 indicated that carotenoid content of pulp increased up to 15 weeks of age and slightly decreased in overripe fruit (from 15.5 to 16 weeks of age). Carotenoid content increased continuously from young fruit is to physiological maturity. After that, ripening process of the fruit continued to witness an increase in the carotenoid content of pulp. From 13 weeks of age to 15 weeks of age, the total carotenoid content increased 2 folds, from 168.42 to 336.17 mcg/100g of fresh fruit. Therefore, consumption of papaya fruit at appropriate maturity level will help to obtain high levels of carotene. 2.2.3. Changes in starch content of fruit Starch is the most important carbonate reserve in plants. The results of studying the changes of starch content following the growth and development of papaya fruit are shown in Figure 3. Figure 3. Changes in starch content during growth and development of Taiwanese papaya fruit Research results indicated that, during growth and development of papaya fruit, starch content increased with age at green fruit and decreased when fruit begins to ripen. Starch content in papaya was highest at 12 weeks of age. This is the time when fruits tend to accumulate nutrients in preparation for ripening process. After 12 weeks of age, the starch content decreased due to increased starch metabolism. Many studies have shown that the respiratory rate of fruit increases sharply during ripening, so that starch may have been used more in the respiratory tract [5, 9]. This causes the starch content is significantly reduced after 12 weeks of age. Trend in starch content change is consistent with changes in reducing sugars content are presented in the section hereafter. 2.2.4. Changes in reducing sugar content of fruit Reducing sugar is an intermediate metabolite involved in many pathways of synthesis of organic substances in plants from lipids, proteins to nucleic acids. Reducing sugar is considered an important indicator of fruit quality. The reduced sugar content progressively increased during growth and reached a peak at 15 weeks of age (8.6%). From the results shown in Figure 4, the reduced sugar content increased sharply when the fruit started to the ripening process (fruit stage from 13 to 15 weeks). In about 2 weeks, this value increased 1.65 folds. This increase may be due to conversion of starch and sucrose to glucose in the overripe stage and this may account for the sweetness of the fruit at this stage [6]. In addition, glucose is the main source of respiration. The study by Abu-Barks et al. found that the peak of respiration was viewed at ripening stage of papaya fruit and subsequently decreased thereafter [5]. In this study, the reducing sugar content also began to decrease in the overripe fruit. Similar pattern of reducing sugars changes was reported in some different papaya cultivars, mango, purple passion fruit and guava [10, 11]. Study on some of biochemical changes during growth and development of taiwanese papaya fruit grown 139 Figure 4. Changes in reducing sugar content during growth and development of Taiwanese papaya fruit 2.2.5. Changes in total organic acid content of fruit Organic acids are the intermediary of metabolic processes, and they are also the synthesis of many organic substances in the plant. In plant cells, organic acids can exist in free form, ammonium salts or female esters that make up the fruit aroma. In papaya fruit, the two most commonly found organic acids are aspartic and glutamic [2, 3]. The change in the total organic acid content of the fruit according to the growth and development process is shown in Figure 5. Figure 5. Changes in total organic acid content during growth and development of Taiwanese papaya fruit In general, the total organic acid content in papaya was relatively low and tended to decrease from young to ripe fruit. Stage 1 day of age until fruit of 9 weeks of age, total organic acid content ranged from 43.33 to 50.11 mg/100g of fresh fruit. After 9 weeks of age, this value rapidly decreased until the end of the study, when the fruit was in overripe stage (16 weeks). Specifically, at the time of 16 weeks of age, the total organic acid content in fruits was only 16.67 mg/100g fresh fruit. These results explain the view that organic acids can be used as substrates for respiration when sugars have been consumed or participated in the synthesis of phenolic compounds, lipids and volatile aromas and provide in addition, a series of metabolites which are used in many processes that reflect dominance of sweet flavor in papaya fruit [6, 1]. 2.2.6. Changes in vitamin C content of fruit Vitamin C (ascorbic acid) is a water soluble vitamin found in fruits in the form of ascorbic acid L. Vitamin C content is one of the important indicators to assess the nutritional value of many fruits [2]. Le Thi Thuy, Nguyen Thi Thu Hien, Tran Thi Thanh Huyen and Nguyen Nhu Khanh 140 Figure 6. Changes in vitamin C content during growth and development of Taiwanese papaya fruit Analysis of vitamin C content in Taiwanese papaya in Figure 6 showed that the highest values were obtained at 15 weeks of age. The result indicates that the vitamin C content in papaya continues to increase as the fruit moves from physiological maturity to ripeness. This is in agreement with the findings of Abu-Bark et al. (2010) who studied ascorbic acid content of 3 papaya cultivars during different growth and development period. However, the increasing trend of ascorbic acid of papaya fruits is an exception to what is generally demonstrated in many fruits such as: guava, mango, tomato. These fruits reached a maximum value of vitamin C at mature- green stage and then decreased rapidly as fruits ripened [10]. After 15 weeks of age (overripe fruit), vitamin C content began to decline. This result may be related to the activity of certain groups of enzymes involved in ascorbic acid degradation such as ascorbate oxidase, phenolase, cytocrome oxidase, ascorbate peroxidase. Especially, unlike the other antioxidant enzymes, the ascorbate peroxidase activity in the pulp increased continuously during ripening, this is the result have shown in the study by Evellyn et al. [9]. 3. Conclusions Within the scope of this study, the results indicated that: Taiwanese papaya reached physical maturity at 13 weeks of age, at which time the fruit size was maximum and almost unchanged. The ripening process lasted from 13.5 to 15 weeks of age. At 15 weeks of age, the fruit ripened completely with vitamin C, carotenoid, and reducing sugar content reached the maximum value. After 15 weeks of age, nutrients of fruits tended to degraded. 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