Studies on Respiration Rates in Coccinia grandis (Ivy Gourd) at Different Temperatures

Ivy gourd (Coccinia grandis) is a unique tropical plant that is a member of Cucurbitaceae family. The common names for Coccinia grandis fruit are ivy gourd, scarlet fruited gourd, Tindori, tindola and Kovaikai [1]. It grows well in India, Thailand and in tropical areas such as Hawaii. The edible parts of plant ivy gourd are differing from place to place due to variation in food habit. In Thailand leaves are edible, in Hawaii both fruits and leaves and in India, raw fruits are mostly consumed as a vegetable. Two varieties of C. grandis are recognized; tender fruits are bitter in one variety and not bitter in another, and the latter is used in Asian cooking [2-4].


Introduction
Ivy gourd (Coccinia grandis) is a unique tropical plant that is a member of Cucurbitaceae family. The common names for Coccinia grandis fruit are ivy gourd, scarlet fruited gourd, Tindori, tindola and Kovaikai [1]. It grows well in India, Thailand and in tropical areas such as Hawaii. The edible parts of plant ivy gourd are differing from place to place due to variation in food habit. In Thailand leaves are edible, in Hawaii both fruits and leaves and in India, raw fruits are mostly consumed as a vegetable. Two varieties of C. grandis are recognized; tender fruits are bitter in one variety and not bitter in another, and the latter is used in Asian cooking [2][3][4].
The raw fruits are used to prepare an array of delicious dishes like stir fries, stuffed curries, stews, pickles and salads [3]. The tender green fruits are nutritious and are good source of protein, calcium, fiber and beta-carotene-vitamin A as precursor. The harvesting maturity of ivy gourd is determined by the fruit colour which changes from green to light green. The normal storage life is 3 to 4 days and 7 to 10 days at room and refrigerated temperature conditions respectively. The Ivy gourd turns to a pink color due to initiation of ripening and loses its weight due to rapid wilting during storage [5]. The ripened pink colour fruits are not suitable for culinary preparations. The quality deterioration with less shelf life of ivy gourd is primarily due to continuous respiration resulting in the process of ripening after harvest. The control of respiration maintains of freshness and keeping qualities on the shelves.
Ripening is a complex physiological process that increases the softening, coloring, sweetening and aromatic compounds in most of the fruits and vegetables. The respiration is a metabolic process by which organic material in living cells are continuously broken down by utilizing O 2 and evolving CO 2, H 2 O and energy [6]. The metabolic reaction during respirations is shown below:

Abstract
Ivy gourd is one of the indigenous vegetable grown in India. The edible part of the ivy gourd is fruit and are mostly used for culinary purposes and also consider as a nutritious vegetable. Though it is a nutritious vegetable, the shelf life of ivy gourd is only 3-4 days in room temperature and 7-8 days in refrigerated conditions. The research maturity index and respiration rate are important in designing a packaging material for extending the shelf life at different storage conditions. Measurement of Respiration rates were carried out by conducting experiments at different temperatures of 10, 15, 20, 30 and 40°C. The respiration rates were calculated as the rate of release of CO 2 relevant to the rate of O 2 consumption of ivy gourd. The CO 2 production and O 2 consumption is maximum at higher temperature of 40°C. The O 2 concentration decreased from 19.5 to 10.41 percentages and the rate CO 2 release increased from 0.60 to 19.33%. The predictive models were developed for calculating the CO 2 release rate and O 2 consumption rates. substrates. In all respiration, due to the biochemical reaction the stored food substrate like glucose will be converted into energy in the presence of oxygen. The loss of water is small during respiration compared to the very high water content of most harvested commodities especially fruits and vegetables. The increased carbon dioxide and decreased oxygen cause a reduction of the respiration rate of the fruit tissue. This reduces the energy available for chemical changes that occur in fruits and vegetables, resulting in lower rates of ripening and prolonged preripening storability of produce i.e. lesser the respiration rate longer is the shelf life of the fruit [7].

Studies on Respiration Rates in Coccinia grandis (Ivy Gourd) at Different Temperatures
Respiration is affected by a wide range of environmental factors that include light, chemical stress (e.g. fumigants), radiation stress, water stress, growth regulators, and pathogen attack. The most important post harvest factors are temperature, atmospheric gas composition, and physical stress. Temperature has a profound effect on the rate of biological reactions like metabolism and respiration. For the potential benefits during storage and packaging optimization, the effects of these gases at particular temperature on respiration must be quantified for the selection of packaging and storage conditions. Measurements of respiration provide an easy, non-destructive means of monitoring the metabolic and physiological state of tissues.
To retain the harvest quality of the vegetable and for extending the shelf life, the research on determination of respiration rates at different temperature is conducted with the following objectives: 1. To determine the changes in the gas concentration for a particular time interval.
2. Determine the effect of temperature on the respiration rate of Ivy gourd.
3. To develop mathematical models to predict respiration rate of Ivy gourd.

Materials
The raw materials, ivy gourd are procured from the local farmer's field located at Vallam, Thanjavur. The ivy gourds are plucked from the plants after 120 to 140 days of planting. Ivy gourd samples were harvested in the morning at typical commercial maturity (dark greencolored firm fruit) and transported within one hour under ambient conditions to the laboratory. The physical dimensions like size, average weight and bulk density are measured for the samples selected for the respiration studies. The glass bottle of known (700 ml) volume is taken as container for filling with ivy gourds, along with closure lid. The closure lid has a small hole which is covered with an air tight rubber holder to draw the gas samples from the container. M-Type seal is used for sealing the container lid outside to make airtight.

Equipments
The environmental chamber (Model HTC-3003, LiBratherm Instrument Private Limited, temperature range-0.1 to 60°C with an accuracy of ± 1°C and relative humidity range from 0 to 99%) for different selected temperatures is used for respiratory studies. The PBI dansensor gas analyzer of model TYP83090138, head space analyzer is used for measuring the oxygen and carbondioxide gas concentrations of the respiratory samples.

Experimental set up
A sample lot of 350 g selected with uniform size and color free from defects were filled in 700 ml glass containers. The glass containers were closed with the metal lid having airtight rubber septum for drawing gas samples using needles. The glazy type seal was used for sealing the bottle. The glass containers were placed in the environmental chamber for different selected temperatures of 40, 30, 20, 15 and 10°C for the respiratory studies. The gas samples were drawn from zero th hour and at every 30min intervals till the O 2 concentration in the bottles fell below 1%. All experiments were replicated for three times and the mean values were obtained ( Figure 1).

Respiration rates:
The respiration rate of fresh ivy gourds stored at different temperatures is calculated using the following formulae given by Susana C. Fonseca [8] in terms of the O 2 consumption rates and/or CO 2 production rates: Where V is the partial volume occupied by the ivy gourd sample inside the glass bottle pack (ml) R is the respiration rate of ivy gourd sample, which expressed as volume of O 2 consumed/CO 2 produced (ml/kg-hr).
M is weight of the product (kg).
T is enclosed time of product in a container (hour).
Modeling: Considering the respiration rate as a function of the four factors influencing the respiratory kinetics (i=4) namely, O 2 and CO 2 gas concentrations and, time and temperature of storage, a model based on an exponential growth or decay function was proposed. A similar relation was also used to express the respiration rate in terms of CO 2 evolution. The values of gas concentrations collected from all temperatures were analyzed by multiple regression analysis using SYSTAT 10.0 for determining the value of the model coefficients.

Physical dimensions
The sizes of ivy gourd vegetables varied from 2.5 to 7 cm. The average weight of one ivy gourd fruit is 1.5 to 3 g. The bulk density per kg of fruit is about 0.02345 m 3 /kg.

Changes in the concentration of gases with respect to time and temperature
The ivy gourd in the airtight glass container undergoes the metabolic reaction due to the respiration, shows the variation in the O 2 concentration and CO 2 concentration. The O 2 concentration decreased and CO 2 concentration increased with time. The changes in O 2 and CO 2 concentrations with time in a jar at 40, 30, 20, 15 and 10°C are presented in the table 1.

CO 2 production rate
The CO 2 production rate increased significantly with increase in temperature. There was a gradual increased concentration of CO 2 with respect to increased time from 0 to 400min at same temperature due to the respiration of ivy gourd samples. The CO 2 production was high at elevated temperatures compared to the low temperature. From the figure 1 the increase in CO 2 production rate at 40°C compared with gradual reduction at 30, 20 and 10°C respectively was observed. According to R. Lakakul, [9] the rise in CO 2 content in the package or inside the jar will increase the heat where there will be a chance of enhancing the rate of respiration and ripening for further time. Similar observations were noted in the respiration studies with increase in the temperature for increase in the respiration rate of ivy guard fruit-let ( Figure 2).

O 2 Consumption rate
The O 2 consumption rate increased significantly with increase in the storage temperature inside the jar with ivy guard fruit let. As the time increased from 0 to 400 min of storage at same temperature, there was a gradual decrease in O 2 concentration inside the glass jar environment. The loss of O 2 and gain in the CO 2 will spoil the product quality due to the internal heat evolved from the tissues by the process of respiration [10]. From the figure 3 and the results obtained shows that the high O 2 consumption rate at 40°C and the gradual decrease of O 2 consumption rate at 30, 20 and 10°C respectively.

Modeling of respiration rate
The rate of decrease of O 2 was found to follow an exponential pattern and observed to fit to a following empirical equation: Where Goodness of fit is indicated by the R 2 value, R = the multiple correlation Coefficient and a and b are constants.

Respiration rates
The O 2 and CO 2 concentrations were predicted from 0 to 360 min for all experimental combinations. Using the equations (2) and (3) the predicted rate of respiration for the obtained gas concentrations was calculated. From the values, it was observed that the respiration rates for CO 2 gas concentration at any temperature with increase in the time interval decreased. The CO 2 production rate was faster at 40°C than the other temperatures. The reduction of respiration rates was noted at 15°C and 10°C. At 15°C there was a significant decrease of CO 2 production rate and at 10°C there were fluctuations in the CO 2 values which may be due to the occurrence of chilling injury of tissues (Table 3, Figure 4).

Conclusion
From the results of this study the following major conclusions can be drawn: 1. The CO 2 release and O 2 consumption rates were faster during the initial hours of packing. The CO 2 release rate was influenced by the O 2 concentration prevailed inside the air-tight glass bottles.

2.
The respiration rate was faster at higher temperatures (40°C) but remained stable at lower temperature (10°C). This shows that the respiration rate was less at lower temperature, which in turn increases the shelf life of the ivy gourd fruit.
a and b are constants.
Similarly the changes in the CO 2 concentration with time were found to fit to an following empirical model: