EVOLUTION OF QUALITY PARAMETERS IN THE MATURATION STAGE OF TOMATO FRUIT

Transcription

1 EVOLUTON OF QUALTY PARAMETERS N THE MATURATON STAGE OF TOMATO FRUT F.J. López-Andréu, A. Lamela, R.M. Esteban, J.G. Collado Departamento de Química Agrícola, Universidad Autónoma Madrid Spain Abstract n relation to a study of the tomato fruit maturation process, the quality parameters (mineral composition, moisture, sugars, pectic substances, acidity, ascorbic acid and carotenoids) of seven maturation stages of tomato fruits were sudied. On the basis of the results obtained from the analysis of such quality parameters, we can indicate a new maturation diagrams to accurately determine the maturation stage for any fruit of tomato cv. Veinone. 1. ntroduction The tomato has been widely used experimentally because it is easily and rapidly grown, is readily responsive to experimental treatment and is of world-wide importance commercially. Changes in the main constituents during the maturation and senescence of the fruit have attracted considerable attention. This study was carried out in an hydroponic culture of Lycope.n. con cilíesutum Mill, cv Vemone, using the nutrient solution proposed by Hoagland and Arnon, and slightly modified for tomato plants. Said hydroponic culture was grown in a greenhouse controlled by a minicomputer. The increasing adoption of precision growing techniques in the horticultural industry, particularly in the closed and controllable environment of the greenhouse, is necessitating more detailed studies of the tomato with a view to obtaining a better understanding of the factors controlling fruit ripening. 2. Material and methods n this study we have used the species Lycopejiéicon >c.ujlejitum, cultivar Vemone. t was grown under glass, in an hydroponic system, using the nutritive solution proposed by Hoagland and Arnon, adapted to the tomato plant. The various stages of ripeness which were studied were distinguished according to the external colour of the fruit as follows: (mature green); (green-yellow); (yellow-orange); V (orangeyellow); V (orange-red); V (red); V (deep red) Analytical techniques - Reducing sugars: Their extraction was carried out with hot water, and the Bittner-Manning (1966) method was used for their determination. - Ascorbic Acid: Evaluation was carried out with 2,6-Dichloro- Acta Horticulturae, 191, 1986 Solanacea in Mild Winter 387

2 phenol-ndophenol. - Pectic Substances: Protopectins, Pectins and Pectates were extracted and determined by the Rouse-Atkins (1955) method. - Acidity: The ph was measured with a ph-meter at room temperature, directly in the tomato samples. The titratable acidity was obtained with an acid-base volurnetry, using NaOH 0.1N up to ph Carotenoids: For the determination of lycopene and 3-carotene we followed the Zecheille-Porter method used by Sanahuja (1953). - Humidity: t was determined by drying the samples at 60 C for 24 hr, and then raising the temperature up to 105 C for a further 4 hr. - Mineral composition: n order to obtain mineral composition, we used the dry way mineralization method proposed by Lopez-Andreu (1975), and the Kjeldahl mineralization for the case of nitrogen. 3. Results and Discussion 3.1. Redyci[i _sugars The most of carbohydrates in commercial varieties of tomato are reducing sugars (Hobson and Davies, 1971). The results of this study are shown in Figure 1, wherein an upward trend throughout the stages of ripeness, ranging between 26.7 and 33.5 mg/g of fresh weight, can be observed. The reducing sugars decrease at the end of the ripening process due to the fermentation processes present in the senescent fruit. n Figure 1, an increase to a maximum of 31.3 mg/g of fresh weight is initially produced. This maximum can be considered as the point of industrial maturation, coinciding with the minimum respiratory activity of the climateric fruit. From this point, a slight decrease can be observed, which, in our opinion, is due to the consumption of carbohydrates in the synthesis of other substances, such as carotenoids, since the above mentioned maximum coincides with the beginning of the colour change. Following this, sugars content rises again to a second maximum of 34.0 mg/g of fresh weight, coinciding with stage of ripeness of gustative maturity, this then being followed once more by a decrease with the appearance of lycopene Ascorbic_Acid The values for ascorbic acid or vitamina C obtained in this study were somewhat lower than those given in the literature. This can be explained as a result of greenhouse culture, as different authors have observed; with less direct sunlight, the fruit contains less vitamin C tha field cultivated fruit. n Figure 2, it can be seen that initially we obtained low values for the stage (8.4 mg vitamin C/100 g of fresh weight), since at the beginning of ripening, instead of the presence of ascorbic acid, we find dehydroascorbic acid. The evolution of ascorbic acid throughout the ripening process of this variety is abnormal if we compare it to the evolution in other varieties of the bibliography, because in stage we should see a sudden rise due to the change of dehydroascorbic acid to ascorbic acid, because of direct sunlight and the ph of the tomato juice. We justify this abnormality as a consequence of the 388

3 position of the plant in the greenhouse, since they were north facing and covered by other plants, which prevented adequate exposure to sunlight. Nevertheless, the evolution is continuous,reaching a maximum in stage V, the value of which approaches the data of the bibliography. This maximum should have been reached during stage V or the gustative maturity Pectic_Substances Throughout the development and ripening of the fruit, protopectins change to soluble pectins due to the action of pectolytic enzymes. This leads to a crossing over of the two lines of evolution of the different fractions of pectins; we detected this crossover when the fruit reaches maximum development and begins the ripening process (Stage ). Figure 3 represents the evolution of different fractions of pectic substances (pectins, pectates and protopectins). A rise in pectin and pectate contents is observed up to stage V, which reaches values of and mg AGA/100 g fr.wt., respectively, followed by a decrease in both cases, which can be related to enzyme and fermentation processes, which produce their degradation. The protopectins decrease continuously from an initial value of 73.0 mg AGA/100 g fr.wt. to 35.5 mg AGA/100 g fr.wt., which is logical since they are the primary materials of the other fractions Acidity Figure 4 shows the evolution for titratable acidity and ph. The titratable acidity rises at the beginning of the ripening process until stage or envery, with a maximum value of 0.63 g citric acid per 100 g fresh weight, in agreement with Winsor et al. (1962), followed by a slight decrease. This evolution agrees with that to be found in the bibliography (Dalai et al., ). The ph ranges between values of 4 and 4.5, coinciding with the values given by Bradley (1962) and Davies (1964). This small variation is due to the blocking effect of different substances in the tomato juice (Bradley, 1962; Davies and Maw, 1972) Carotenoids The total carotenes amount in the tomato can be considered as the sum of the lycopene and g-carotene (Koskitalo and Ormrod, 1972; Watada et al., 1976). The evolution of total carotenes, lycopene and g-carotene is shown in Figure 5. The total carotenes start with a value of 1.19 Ug/g fr.wt. rising slowly between stages and V, but from stage V there is a sharp rise reaching a maximum value of in stage V. This evolution is in agreement with that described by Sanahuja (1953), and the rise is mainly due to the lycopene content. Lycopene and g-carotene have totally different developments. The evolution of lycopene is similar to that of the total carotenes, beginning with a value of 0.14 yg/g fr.wt. and rising slightly until stage V, followed by a sharp rise in values up to ug/g fr.wt. (3-Carotene has an initial increase from 1.05 ug/g fr.wt. to a value 389

4 of 4.55 g/g fr.wt. in satge, which then decreases to a value of 0.42 g/g fr.wt. This evolution is in agreement with those described in the bibliography (Dalai et al., ). Figure 6 shows the percentage of lycopene in relation to the total carotenes and is considered to be the maturation or ripening index of the tomato (Sanahuja, 1953). t reaches 99.49% of the total carotenes during stage V Humidity The humidity of the tomato shows no clear tendency in its evolution, varying between values of 94.3 and 95.1% according to the degree of ripeness Mineral composition Bearing in mind the diversity of levels between which the bioelements of the fruit vary, we can pick out the high concentration of N, P and K in relation to the other three macroelements, Mg, Ca and Na. The microelements vary within normal values during the ripening period, the values of which are in agreement with those given by Martinez (1985). n a more detailed study, the evolution of N, P and K (Figure 7) throughout ripening is more or less constant, although it is possible to find a slight increase between the initial and final stages for N and K contents (1.95 to 2.82, for N; and 4.49 to 4.92, for K). n the intermediate stages, the values range in both directions. P remains more or less constant, although showing a slight decrease over the different stages. f we compare K with the evolution of titratable acidity, we find that there is a similar evolution between stages and V, due to the blocking system, in which K plays an important role. ts increase in the final stages of ripening is due to the fact that it is the only element which can be constantly absorbed throughout the ripening of the tomato, influencing the composition and quality of the fruit (Hobson and Davies, 1971). The other three macroelements Mg, Ca and Na (Figure 7) show a constant evolution throughout the ripening process. The microelements (Figure 8) show values similar to that found by Martinez (1985). The evolution of Fe shows a slight downward trend with fluctuations in the different stages of ripening. Zn and Mn show a constant evolution with slight downward trend. B began with high values of 38 ppm decreasing constantly,to a value of 11 ppm, throughout the different stages of ripening. References Bittner, D.L., and Manning, J., Automated Neocuproine Glucose method: Critical factors and normal values. Automation in analytical chemistry. Technicon Syrnp. 1:33-36 (White plains, N. Mediad nc.1967) Bradley, D.B., nfluence of K, Ca and Mg application on acid content, composition and yield of tomato fruit. J.Agric. 10: Dalai, K.B., Salunkhe, D.K., Boe, A.A., Olson, L.E., Certain physiological and biochemical changes in the developing tomato fruit. 390

5 J.Food Sci. 30: Dalai, K.B., Salunkhe, D.K., and Olson, L.E., Certain physiological and biochemical changes in greenhouse-grown tomatoes. J.Food Sci. 31: Davies, J.N., Effect of nitrogen, phosphorus and potassium fertilizers on the non-volatile organic acids of tomato fruit. J.Sci.Food Agrie.15(10): Davies, J.N.,and Maw, G.A., Metabolism of citric and acids during ripening of tomato fruit. J.Sci.Food Agrie. 22: Hobson, G.E., and Davies, J.N., The Tomato. n: The Biochemistry of fruits and their products.(ed. A.C. Hulme), Academic Press, New York: Koskitalo, L.N., and Ormrod, D.P., Effects of sub-optimal ripening temperatures on the color quality and pigment composition of tomato fruit. J.Food Sci. 37: López-Andréu, F.J., El boro en el limonero Verna. Doctoral Thesis Facultad de Ciencias, Universidad de Murcia. Martínez, F., Comportamiento de variedades híbridas de tomate en condiciones de fertigación en invernadero. Doctoral Thesis.(Ed. Cebas), Murcia. Rouse, A.H., and Atkins, C., Pectinesterase and pectin in commercial citrus juice as determined by methods used at the citrus experiment. Stn.Tech.Bull.Fia.Agrie.Exp.Stn Sanahuja, J.C., Determinación del contenido de carotenos en el tomate, su relación con el grado de madurez y su aplicación al control analítico de sus extractos. Anal.Bromatol Watada, A.F., Norris, K.H., Worthington, J.T., and Massie, D.R., Estimation of chlorophyll and carotenoid contents of whole tomato by light absorbance technique. J.Food Sci. 41: Winsor, G.W., Davies, J.N., and Massey, D.M., Composition of tomato fruit.. Juices from whole fruit and locules at different stages of ripening. J.Sci.Food Agrie. 13: mg/g fr. wt 35 LSD mg/oog fr wt U 12 LS) b% 27 i n miv v vi vn Figure 1 - Reducing Sugars 10 8 D V V V V Figure 2 - Ascorbic Acid 391

6 mg AGA/lOOgfr.wt i nraw V vi vn i inaiv vvi vii i iiin iv v vi vii PECTNS PECTATES PROTOPECTN Figure 3 - Pectic Substances g citric ac /loog fr wt ph OA 0.3 í n inwv viva 5 LSD 51 mm i n in iv v vi vn Figure 4 - Titratable Acidity and ph

7 /jg/g fr. wt. LSD 5«LSD J -jqjru ' i nrav Vvivii inimvvvivn i n m TV vvi vu TOTAL CAROTENES LCOPENE /3-CAROTENE Figure 5 - Carotenoids % Licopene LSD 5« AO ^ i mv Vvi vn Figure 6 - Maturation ndex

8 g/loogdr. wt. 5 - norm l nin n vvivii P i ilinif vvivii K 0.1 lso51 1 Jim i l i iniv vvivn V VVV V VVV Mg Na Ca Figure 7 - Macroelements p.p.m. Dr. wt } Of 20- i nniivvvivn Fe i nmivvvtvn Zn LSD 51 Hh i nmivvvi vn B LSD 5! nlffii inmivvvrvn Mn Figure 8 - Microelements 394