Effect of Maturity Stage on Ripening and Quality Characters of Four Tomato ( Solanum lycopersicum L . ) Varieties of Sri Lanka

The effect of maturity stage on ripening and quality characters of four tomato (Solanum lycopersicon) varieties was evaluated. The varieties selected were Thilina, Bathiya, Maheshi and Lanka cherry, due to their widespread cultivation and popularity among consumers. Tomato fruits of three maturity stages e.g. colour breaker, 25% maturity and 50% maturity were considered. Maturity stages significantly affected the fruit ripening and quality parameters. The fruits harvested at colour breaker stage had the highest weight loss (22.45%) except in the variety Lanka cherry. Total soluble solid (TSS) content was not significantly different at different maturity stages except in the variety Thilina (P≤0.05). But in the variety Thilina, the highest TSS was recorded in the fruits harvested at 50% maturity (4.07). In varietal comparison, both varieties Lanka cherry and Thilina had the highest TSS values in each maturity stages compared to other two varieties. Titrable acidity in varieties Bathiya (9.95%) and Maheshi(8.4%) was significantly higher at colour breaker stage than the rest of two maturity stages, while in the case of Lanka cherry and Thilina, though titrable acidity was not significant among colour breaker stage and 25% maturity stages, it was significantly lower at 50% maturity stage. As expected, pH had increased with the progression of the maturity except in two varieties, Thilina and Maheshi. The study indicates that identification of effective maturity stage is an important to retain superior fruit quality by maintaining a low rate of weight loss and softening in tomato fruits after harvest for prolong storage and distant markets.


INTRODUCTION
Tomato (Solanum lycopersicum L.), a member of the family Solanaceae, is a most widely cultivated vegetable crop in Sri Lanka.It is native to Central, South and Southern North America from Mexico to Argentina (Rick and Butler, 1956).In worldwide tomato is grown for its edible fruits and it is a good source of minerals (Colla et al., 2002).
Tomato grows well on most mineral soils that have proper water holding capacity and aeration.It prefers deep well drained sandy loam soils.Soil depth of 15 to 20 cm is needed to grow a healthy crop.The optimum temperature for the growth would be in between 21 -27 0 C (Saimbhi et al., 1987).Soil pH should be in between 5.8-6.8 and prefers an elevation of 1,000-2,000 m (Saimbhi et al., 1987).The plants typically grow to 1-3 m in height and have a weak stem that often sprawls over the ground and vines over other plants.
Proper harvesting determines the nutrient contents as well as post harvest life of any fruit.Tomato is normally harvested at different maturity stages, such as green mature stage, half ripen stage and red ripen stage (Alpert et al., 2005).Frary et al., (2000) have reported that tomato is generally harvested at edible maturity, characterized by attaining pink-reddish colour and maximum size.However, edible maturity of tomato fruit is prone to post-harvest losses (Sankar et al., 2002) and quality is also lost due to biochemical changes.
The post harvest life of tomato is largely influenced by the harvest maturity.Fruits and vegetables are living entities and continue to respire for some time after harvest.Kader, (1992) reported that the magnititute of post harvest losses in fresh fruits and vegetables is estimated to be 5-25% in developing countries.Water losses can be one of main causes of determination since it results in not only quantitative losses but also affects the appearance, textural and nutritional quality (Kader, 1992).It was reported that the post harvest losses of tomato in Sri Lanka is around 35-40%.The most important quality criteria for tomatoes are red colour, firm but juicy texture, and good flavor.Tomatoes with high sugar and relatively high acid contents are the best flavored; low sugar and low acid contents result in poor flavored tomatoes (Stern et al., 1994).Therefore, harvesting them at optimum stage of maturity can have tomatoes with better quality and longer marketability.
It has become vital to grow improved varieties and harvest crops at the appropriate physiological maturity stage if postharvest loss in agricultural produce is to be minimized.Department of agriculture in Sri Lanka has recommended several tomato varieties, KWR, T146, T245, Thilina, Ravi, Tharidu, Rashmi, Rajitha, Lanka Sour (GorakaTakkali), Maheshi, Bathiya and Lanka cherry etc., having different varietal characters.The aim of this study therefore was to determine the correct maturity stage of tomato fruit at harvest in selected recommended tomato varieties (Thilina, Bhathiya, Maheshi and Lanka cherry) that will prolong fruit shelf life and quality.

METHODOLOGY
The study was conducted during Maha 2014 at the Horticultural Crop Research and Development Institute (HORDI), Gannoruwa.The experiment was laid out in complete Randomized Design (CRD) having 10 replicates containing five fruits for each four tomato varieties (Thilina, Bhathiya, Maheshi and Lanka cherry) which have high demand in the market.The tomato fruits were harvested at three stages of physiological maturity i.e. colour breaker stage, 25% maturity (yellow) and 50% maturity (greenish red).

Plate1. Harvested three stages of physiological maturity
Colour breaker stage 25% maturity (yellow) 50% maturity (greenish red) (a) Weight Loss% The percent weight loss was calculated by taking five fruits in each replicate and recording the initial weight and weight after storage (one week) under ambient temperature by using electronic balance.The readings of five fruits in each treatment were averaged to represent that treatment.The percent weight loss was calculated as, Percentage weight loss = Weight of fresh fruit -weight after storage *100 Weight of fresh fruit

(b) Total Soluble Solids (TSS)
To determine the total soluble solids (TSS), the juice from tomato fruit was extracted by and few drops could be added onto the prism plate of refractometer.After each test, the prism plate was cleaned with distilled water and wiped with soft cotton.The data were averaged and recorded in percent TSS.

(c) Titrable acidity and pH
The pH of extracted tomato juice was determined using Electronic pH meter by crushing the tomato fruits of about the same weight gently using the laboratory mortar and pestle.To determine total acidity, 10 ml of tomato juice extracted from 100g of peeled fruit sample was transferred to conical flask and volume up to 30 ml and then titrated with 0.1 N NaOH (Sodium hydroxide).The data were analyzed using Analysis of Variance (ANOVA) procedure and mean separation was done using Duncan's multiple range test (DMRT).

(d) Disease Index and Visual Quality Rating Index
Disease index and visual quality rating index was determined by observing fruits according to a scale given in the following table.Both visual quality rating index and disease index values were analyzed by using Krushkal-Wallis test.

RESULTS AND DISCUSSION
Weight Loss (%) Tomato weight was quite variable in variety 'Thilina'; the largest variation was observed in 50 % maturity stage (50.90±18.91g).Tomato weight has increased with maturity, and the most pronounced increase was between the 25% and 50% maturity stages.The largest difference from 25% to 50% stage was observed in variety 'Lanka cherry', exhibiting a 25% increase.
The mean weight loss was significantly different at different maturity stages in all four varieties.Weight loss from harvesing stage to full ripen stage has been given in the results (Table 1).The weight loss was significantly greater in fruits harvested at 25% maturity except in the variety Lanka cherry.Sihag and Mentha (1999) made a statement that water loss increases with increasing periods of storage and it coincides with the result of this study, indicating that fruits harvested at 25% maturity stage have undergone the long storage than fruits harvested at 50% maturity stage.44.14±4.60 5.40b Note: Means followed by similar letters in columns are statistically not significant at α = 0.05.
The weight loss is attributed to the loss of moisture and carbohydrates (Karki, 2005) and causing fruit softening and shriveling (Wilsony., 1999).It is a common but serious problem during storage (Getinet et al., 2008).The intensity of weight loss during storage depends on maturity stage (Moneruzzaman et al., 2009) and same trend was evident with the results of this study as well.Thus, the resistance of the fruit to moisture loss decreases as it advances in maturity to the pink and red stages (Ali et al., 2013).Though, resistance of the fruit to moisture loss is greater at the 25% maturity stage, increasing period of storage may cause rapid water loss.However, the rate at which weight is lost depends on the variety.Comparing among four varieties, the rate of weight loss was greater in variety 'Bathiya' and 'Thilina' at 25% maturity stage, while in the variety 'Maheshi' at 50% maturity stage.The significant factor in water loss is the ratio of the surface area of the type of plant part to its volume.That is, the greater the surface area in relation to the volume the more rapid water is lost.

Total Soluble Solids (%) (TSS)
Total soluble solids content of variety Maheshi, Lanka cherry and Bathiya were not significantly different at the different maturity stages (at P≤0.05).But it was significantly different in variety 'Thilina' (Table 3).Though, there was significant difference in each stage with the 50% maturity stages, The TSS in between colour breaker and 25% maturity stages were not significant at P≤0.05.
In varietal comparison, varieties 'Lanka cherry' and 'Thilina' had given significantly greater values for TSS in each maturity stage with compared to varieties 'Bathiya' and 'Maheshi'.However there was no significant difference in TSS values in between 'Lanka cherry' and 'Thilina' in each maturity stages (Table 3).
The TSS determines the overall taste of the fruit (Baldwin et al., 1998).Getinet et al., 2008 have reported that the total soluble solid was low at the colour breaker stage but increased when tomato fruits were harvested at pink mature stage.Though results of this study have not clearly showed significant difference in TSS at different maturity stages except variety 'Thilina', generally TSS increases with the advancement in maturity and during storage (Karki, 2005;Getinet et al., 2008).The increase in TSS could be attributed to the breakdown of starch into sugars or the hydrolysis of cell wall polysaccharides (Crouch, 2003).
In sauce production, colour and soluble solids content of tomatoes are considered as major attributes of product quality.The flavor of the product is influenced by the balance between sugar content and acidity (Berrett and Garcia, 2006).However based on the results of the study, among the tested four tomato varieties, there is possibility to use 'Lanka cherry' and 'Thilina' for sauce production.3.53±0.31ans 6.73 Note: Means followed by similar letters are statistically not significant at α = 0.05.

Titrable Acidity (%) and pH
Titrable acidity was significantly different (at P≤0.05) at different maturity stages in all varieties.In varieties Bathiya and Maheshi, titrable acidity was significantly higher at colour breaker stage than the rest of two maturity stages (25% and 50% maturities).But acidity was not significant in between those two maturities.In the case of variety Lanka cherry, though titrable acidity was not significant among colour breaker and 25% maturity stages, it was significantly lower at 50% maturity stages.The highest acidity values were exhibited at colour breaker stage and harvesting at colour breaker stage could be used for the purpose of high acidity (tomato juice, tomato paste in all the cultivars.However in the varietal comparison, largest acidity values were exhibited by variety 'Bathiya' followed by variety 'Lanka cherry' at colour breaker stage (Table 6).Titrable acidity has reached its peak at colour breaker stage and then started to decrease with the advancement of the fruit ripening.The vitamin C and titrable acidity content of tomato juice was increased with maturity stages and reached the peak and thereafter started to decreased (Sinaga, 1986).It was found that pH value increased with the advancement of fruit ripening and same trend was evident with the results of varieties Lanka cherry and Bathiya (Table 5).Since, the acidity of the fruit is due to various organic acids, that are consumed during respiration (Albertini et al., 2006), the acidity, thus, decreased with advancing maturity with a corresponding increase in fruit pH (Moneruzzaman et al., 2009).Hence there is an inverse relationship between pH and titrable acidity, though sometimes the relationship is an inaccurate (Stevens, 1972).All the varieties exhibited pH values exceeding 4.6.The pH is an important factor for safe food production during thermal processing to control microbial spoilage and enzyme inactivation in tomato products.As expected, pH has increased with the progression of the maturity except two varieties, 'Thilina' and 'Maheshi'.However tomato pH is dependent on factors including variety, maturity stage, cultural practices, growing location and seasonal variations as well (Gould, 1992).

Fig. 1 .
Fig. 1.The varietal comparison on TSS, TA and fruit pH at different maturity stages

Table 5 . The effect of maturity stage on fruit pH in different Tomato varieties. Lanka cherry Bathiya Thilina Maheshi
Means followed by similar letters are statistically not significant at α = 0.05.