Abstract: This study evaluates the effects of different storage conditions towards improving vegetable intake of Nigerian populace. The experiment was carried out between April through September, 2004 at the Agronomy Department, University of Ibadan, Ibadan, Nigeria using four storage conditions: Deep freezer-DF (0°C; 95% RH), Ambient storage environment-ASE (32°C; 85% RH) (as control), Room refrigerator-RR (12°C; 85% RH), Storage Incubator-SI (8°C; 80% RH), four tomato varieties: NH84/TIL, NH84/TSLN, NH84/TBLN; NH84/TSN) were used. Data was analyzed statistically using the analyses of variance procedure for SAS means were separated using Duncan Multiple Range Test at 5% probability level. Results obtained indicated that cultivars NH84/TSN significantly performed better in terms quality attributes (cracking, yellowing and rottening) than other cultivars. The least quality attributes was obtained in variety NH84/TIL. Deep freezer storage condition ranked best (at 5% level of significance) in terms of quality preservation of tomato among all other treatment combinations. The results revealed that combination of tomato variety NH84/TSN with deep freezer condition gave best result in this study.
INTRODUCTION
Tomato (Lycopersicon esculentum Mill.) is one of the most important vegetables grown for edible fruits consumption in virtually every home in Nigeria. Its production in southwest Nigeria is concentrated occur mainly during the hot rainy season (Akintoye, 2002). However, postharvest storage of tomato fruits is the major cause of seasonal fluctuation in availability, deterioration in quality and other socio-economic inadequacies owing to the fact that an efficient means of storage other than canning is yet to be developed (FAO, 1991).
Deterioration of fresh commodities can result from physiological breakdown due to natural ripening processes, water loss, temperature injury, physical damage, or invasion by microorganisms. All of these factors can interact and all are influenced by temperature. Fresh fruits, vegetables and flowers are highly perishable because they are alive. They breathe (just like humans), release heat from respiration and consequently, lose moisture, which may detract from their appearance, salable weight and nutritional quality. They can become sick, deteriorate and die. Dead fresh fruits and vegetables are not marketable.
Tomato fruits are highly perishable and thus have an inherently short shelf life. High quality fruit have a firm, turgid appearance, uniform and shiny colour, without signs of mechanical injuries, shriveling or decay (Steven and Celso, 2005). Principal causes of post harvest losses are decay, external damages incurred during harvest and handling and harvest at an improper maturity stage (Steven and Celso, 2005). In addition, environmental factors such as soil type, temperature, frost and rainy weather at harvest can have an adverse effect on storage life and quality (Bachmann and Earles, 2000). Management practices can also affect post harvest quality. Produce that has been stressed by too much or too little water, high rate of nitrogen or mechanical injury (scrapes, bruises, abrasion) is particularly susceptible to post harvest diseases (Bachmann and Earles, 2000). The rapid quality loss at relatively short period of 4-7 days calls for an efficient means of storing the fruits to reduce wastage (Thompson et al., 1998) and improve intake and acceptability.
Commercially, preservation of vegetable products is difficult in the tropics because of poor transportation networks and high environmental temperatures that favours decay rather that storage. The challenge now faced by decision makers in many nations of sub-Sahara Africa is how to preserve fresh vegetable produce in order to feed an increasing population. Many attempts have been made in the past. However, very little information exists on the benefits and option of preservative temperature suited to the existing small-scale storage conditions. Present study therefore evaluates the quality of three tomato varieties as affected by four storage conditions.
MATERIALS AND METHODS
Tomato fruits (harvested at mature-green stage) were obtained from experimental field established specifically for the purpose of this experiment at the Department of Agronomy, University of Ibadan, Nigeria (7°30’N, 4°03’E, 218 m asl) from April through September 2004. As at the time of experiment, University of Ibadan had average annual rainfall of 1049.2 mm, mean temperature range of 20.1-28.3°C and mean relative humidity range of 46-89°C. The land had been under maize and cassava cultivation in the previous year 1999.
Four tomato varieties: NH84/TIL, NH84/TSLN, NH84/TBLN and NH84/TSN were cultivated. The soil of the area had nitrogen 0.03%, pH (1:1H20) 3.9, potassium 0.14%, available P 0.24 g kg-1, calcium 0.52% and sandy loam texture. Fruits from four replicates containing each of the cultivars were bulked, washed thoroughly in distilled water at 23°C and then packed in cardboard boxes containing 10 kg of each of the produce sample. Excess water was allowed to drain freely under ambient temperature 23.8°C. They were then divided into samples of 2 kg and sealed in commercially available ZiplocTM bags with micro perforations.
Storage treatments: After normal pre-cooling of the tomato fruits, four traditionally available storage conditions were used: Deep freezer (0°C; 95% RH), Room refrigerator (12°C; 85% RH), Storage Incubator (8°C; 80% RH) and ambient storage environment (32°C; 85% RH). Each storage condition had three replicates of bags of 50 samples from where treatments were randomly selected for each cultivar. Each group of bags was held separately in a 580x720x155 mm vented plastic container and the containers were stacked in the appropriate storage condition in the dark. No free water accumulated in the bags during storage.
Quality evaluation: Tomato fruit quality was accessed at weekly intervals of storage. Overall freshness comprises greenness, cracking, shriveling and decay was evaluated using a scale of 0 to 4 (Table 1) in line with the method of IPGRI/IITA 1998. Disease severity was determined as a percentage of the degree of deterioration of the original sample.
| Table 1: | Rating scales used for measuring overall freshness of tomato fruits |
| Overall freshness in terms of pod shelf life, yellowing cracking, shriveling and rottening qualities | |
Field layout and statistical analyses: This was done using completely randomized design with three replicates per treatment. There were 16 combinations of four storage conditions for the four cultivars. Data were analyzed using the general Linear Models Procedures of SAS (SAS Institute, 1998) and Duncan Multiple Range Test (DMRT) was used to compare the means at 5% level of probability.
RESULTS AND DISCUSSION
Table 1 reflects the scale of rating. Considering cracking rate (CR) in storage conditions among tomato cultivars, NH84/TSN were best (3.0) followed by NH84/TBLN and NH84/TSN (Table 2). Deep freezer (DF) storage ranked best among storage condition used in term of cracking rate. Combination of NH84/TSN with DF storage was observed to be the best in terms of preservation against cracking among all treatment combination (Table 2). This might be attributed to the thick rind of NH84/TSN and the low temperature storage among treatment combination.
Rate of yellowing generally increased with increased weeks of storage. Similar pattern of yellowing rate were observed to increase from one week of storage (Table 3). Firmness decreased with time of storage except under Deep Freezer (DF) condition (Table 4). Deep freezer condition recorded no disease incidence and severity compared to other storage condition (Table 5 and 6). This was attributed to the sub-optimally low temperature used.
| Table 2: | Influence of variety X storage condition on Cracking Rate (CR) |
| Mean followed by the same letter are not significantly different at p = 0.05. NH84/TIL = Tomato Ibadan Local; NH84/TSLN = Tomato Small Local NIHORT; NH84/TBLN = Tomato Big Local NIHORT; NH84/TSN = Tomato Serry NIHORT; ASE = Ambient Storage Environment; RR = Room Refrigerator; DF = Deep Freezer; NSR = NIHORT Storage Room | |
| Table 3: | Influence of variety X storage condition on Colour Change (CC+) |
| Mean followed by the same letter are not significantly different at p = 0.05. NH84/TIL = Tomato Ibadan Local; NH84/TSLN = Tomato Small Local NIHORT; NH84/TBLN = Tomato Big Local NIHORT; NH84/TSN = Tomato Serry NIHORT; ASE = Ambient Storage Environment; RR = Room Refrigerator; DF = Deep Freezer; NSR = NIHORT Storage Room | |
| Table 4: | Influence of variety X storage condition on Firmness of Fruits (FF) |
| Mean followed by the same letter are not significantly different at p = 0.05. NH84/TIL = Tomato Ibadan Local; NH84/TSLN = Tomato Small Local NIHORT; NH84/TBLN = Tomato Big Local NIHORT; NH84/TSN = Tomato Serry NIHORT; ASE = Ambient Storage Environment; RR = Room Refrigerator; DF = Deep Freezer; NSR = NIHORT Storage Room | |
| Table 5: | Influence of variety X storage condition on Disease Incidence (DI) |
| Mean followed by the same letter are not significantly different at p = 0.05. NH84/TIL = Tomato Ibadan Local; NH84/TSLN = Tomato Small Local NIHORT; NH84/TBLN = Tomato Big Local NIHORT; NH84/TSN = Tomato Serry NIHORT; ASE = Ambient Storage Environment; RR = Room Refrigerator; DF = Deep Freezer; NSR = NIHORT Storage Room +NS = Not Significant | |
| Table 6: | Influence of variety X storage condition on Disease Severity (DS) percent |
| Mean followed by the same letter are not significantly different at p = 0.05. NH84/TIL = Tomato Ibadan Local; NH84/TSLN = Tomato Small Local NIHORT; NH84/TBLN = Tomato Big Local NIHORT; NH84/TSN = Tomato Serry NIHORT; ASE = Ambient Storage Environment; RR = Room Refrigerator; DF = Deep Freezer; NSR = NIHORT Storage Room. +NS = Not Significant | |
These observations agree with the findings of Bachmann and Earles (2000), when they observed that fruit storage at extremely low temperature preserves quality better at increased storage period. They also affirmed that temperature is the single most important factor in maintaining quality after harvest. In a similar development Wilson et al. (1995) in their report on post harvest handling and Cooling of Fresh Fruits, vegetables and flowers for small farms, asserted that deterioration of fresh commodities can result from physiological breakdown due to natural ripening processes, water loss, temperature injury, physical damage, or invasion by microorganisms and that all of these factors can interact and all are influenced by temperature.
CONCLUSION
It is concluded that deep freezer ranked best among storage conditions employed, while NH84/TSN tomato variety ranked best in terms of quality and shelf life in storage compared to other tomato varieties. Combination of deep freezer condition with tomatoes varieties NH84/TSN ranked best compared with other treatment conditions.