Effect of Fruit Size and Temperature on the Shelf Life and Quality of Ripe Banana Fruit

The research was carried out to investigate the effect of fruit size, ripening temperature on the shelf life and quality of ripe banana fruit of two sizes, small (14 cm) and large (20cm). It is concluded that ethylene treatment with 1000 ppm for 24 hours is sufficient to initiate the ripening in both sizes of bananas. It was also observed that there was no difference between the shelf life of small or large size bananas of similar maturity. There was no significant variation in the speed of ripening between small and larger one but total soluble solids were greater (18.8% and 19.3 %) in smaller bananas than larger ones (17.2% and 17.7%) . Temperature showed significant effect on ripening so bananas of both sizes took 4 and 2 days to reach colour stage 6 which were transferred at 20C from 16C and 18C respectively. The interaction between fruit size and colour stage indicated that small bananas showed quicker and greater response to higher temperature at colour stage 3 than larger ones. The difference in ripening temperature used in Britain and other countries of Europe is due to the variations in preference. Panelists preferred longer fingers due to their external appearance rather than internal quality. INTRODUCTION Banana is an important fruit crop in the world. It is estimated that 100 million people subsist on bananas and plantain (Seymour, 1993). Banana fruits have a special place in human diet. They are chiefly eaten raw as a dessert fruit, because in the ripe stage they are sweet and easily digestible (Robinson, 1996). They are useful for patients with peptic ulcers, for treatment of infant diarrhea, in celiac disease and in colitis (Robinson, 1996). They are also ideal for patients with gout or arthritis, kidney disease, blood pressure and heart disease (Robinson, 1996). They are low in fats, cholesterol and salts (Stover and Simmonds, 1987). They can make a useful contribution to the vitamin A, C and B6 contents of the diet, and are an important and immediate source of energy, being often eaten by sportsman and women during competition (Robinson, 1996). A medium sized banana contains 280 kilojoules, which is significantly more than deciduous or citrus fruits (Robinson, 1996). The size of individual units of a product can significantly affect consumer appeal, handling practices, storage potential, and market selection (Kays, 1991). It has also been shown that moisture loss of fruit depends upon size, maturity, storage temperature and humidity (Salunkhe et al., 1991). The best commercial ripening temperature in Britain is considered to be 16C (Thompson, 1996). In other countries of Europe, recommended commercial ripening temperature is 18C. The question arises as to why there is variation in the recommended ripening temperature. The control of the ripening temperature is important to obtain the best quality fruit within in specific marketable life. Temperature influences the ripening changes in banana. Therefore this experiment was started to find out the best temperatures for the ripening and differences between small and large bananas quality wise. MATERIAL AND METHODS This research was conducted in post harvest laboratory of Canfield University, at Silso College UK in 1999. Pre climacteric Cavendish Bananas of two sizes 14 cm and 20 cm at colour stage 1 were obtained from C.t Wilkinson in Belford UK. Undamaged bananas of uniform colour were selected and cut into fingers. The cut portions were dipped in 500 ppm thiabendazol (fungicide) and then allowed to air dry. Bananas were treated with 1000 ppm ethylene for 24 hours. Ten fingers each of small and large bananas were kept at 16C and 18C both and 80-85% relative humidity. When fruits of both temperatures reached colour Saeed Ahmad, et al. Effect of fruit size and temperature in Banana fruit.... 46 stage 3, two fingers from each replication in each treatment were analyzed and the remaining fruits transferred to 20C for ripening. Two fingers were randomly selected from each replication in each treatment for daily analysis. These were earmarked at the start of the experiment. During this period (at 20C) two fingers of each replication in each treatment were again analyzed daily until they reached colour stage 6. Sensory evaluation data were only collected when fruits were fully ripen (colour stage-6). The experiment was conducted to Factorial Design with four replications. Assessment of Fruit Ripening (Assessment of Colour Stage) Ripening of banana fruit was assessed according to peel color compared with a color chart as described by Stover and Simmond, (1987). The peel of banana fruits changes colour from dark green to bright yellow during ripening. The ripening process has been divided into seven stages by colour changes. These are as follows: 1,green; 2,green with a trace of yellow; 3, more green than yellow; 4,more yellow than green; 5,only green tips remaining; 6, all yellow; 7, yellow flecked with brown. Assessment of Fruit Quality Two methods i.e. objective method and subjective method were used for the assessment of quality. Objective Methods The peel color was measured by colorimeter A positive (a*) values corresponding to the degree of redness while a negative value corresponding to the degree of greenness. The positive values (b*) represents the degree of yellowness and negative (b) one represents the blueness. Peel firmness was measured using an Instron universal testing machine (model 2211) with an 8mm cylindrical probe. Total soluble solids were measured using refractometer. Starch percentage was measured by using the technique recommended by Blankenship et al., (1993). Individual fruit was weighed using a digital balance (precise 60000 ) cumulative weight loss a percentage was calculated as follows. Weight loss% = Wo-Wi x100 Wo Where Wo = original weight Wi = Weight at sampling (when Banana reached at color score 6). Weight loss percentage per day was calculated as follows: Weight loss percentage per day = TWP SC Where TWP=Total weight loss percentage at color stage 6 SC = Storage life (total days when Banana reached color store 6 from pre-climacteric stage). Subjective Assessments (Sensory Evaluation) The fruits were removed from storage when they were at color score 6. Panel of eight assessors was selected from the college and the tests involved individual assessment in isolated testing condition under a standard light source. The Judges were asked to assess pulp flavor, sweetness, and acceptance on life point’s sale as follows: 1. Low 2. Moderate 3. Moderate high 4. Good / high 5. Very good / high The scores marked by panelists were collected and an average was calculated for each parameter and sub parameter. There averages were used for statistical analysis. Means of treatments were calculated and presented in the form of Tables. Statistical Analysis Data were processed and analysis of variance (ANOVA) was carried out based on Factorial Design using MSTATC, a P.C based programming with four replications. LSD at P=0.05 was used to test for significant difference of results where applicable. RESULTS AND DISCUSSION Storage Life (Speed of Ripening) It is evident from Table I that there was no significant difference in the speed of ripening between smaller and large size fruit. Bananas kept at 18C reached colour stage 3 earlier than those which were kept at 16C. Bananas at both temperatures took four days to reach colour stages 3 to 6. The total time needed for fruit to reach Sarhad J. Agric. Vol. 23, No. 1, 2007 47 colour stage 6 was significantly longer for those, which were transferred from 16C to 20C than those transferred from 18C to 20C. There was no significant interaction between these factors. It is well established and confirmed, that high temperature accelerates the ripening of banana fruit. There was no difference between the speed of ripening in small and large bananas which could be due to the exogenous ethylene treatment. Marriott, (1980) found that ethylene at 1-ppm for 24 hours was enough to induce prompt initiation of ripening. No evidence could be found in the literature which suggests that either small or large size bananas of similar maturity have any variability in response to exogenous ethylene. Therefore, it can be concluded that ethylene treatment with 1000 PPM for 24 hours was sufficient to initiate the ripening in either sizes of banana fruits. Table I Effect of fruit size and temperature on the storage life (days) of banana at different stages. Temperatures and fruit sizes (days to reach colour stage) 16C 18C Days required to attain colour stage Small Large Small Large Mean