Preharvest Changes in the Physical and Chemical Properties of Plantains

A study was conducted to determine the preharvest changes in the physical and chemical characteristics of plantains of the Guayamero and Maricongo cultivars. The average weight of the fruit, the length of the fruit, the cross-sectional dimensions, pulp texture, and pulp:peel ratios were determined for each hand of the bunch at several time intervals after flowering. Starch, total and reducing-sugar content, total acidity, and pH were also measured in fruit from the third hand. Statistical analysis of the data on the measurements taken from fruit from the third hand shows significant correlations between age and pulp:peel ratios. A highly significant correlation was also found between age and texture, the fruit becoming softer as it matured. A significant correlation at the 5-percent level was found between age and average fruit-weight in the Maricongo cultivar, but no similar correlation was found in plantains of the Guayamero cultivar. The fruit becomes more plump and round with age, but wide variations in the cross-sectional area in fruit harvested at any age made it impossible to correlate cross-sectional dimensions with age. Analysis indicated that no changes in the chemical composition of the fruit took place. The quality and appearance ratings of fried-plantain slices prepared from frozen green plantains were affected by the age at which the fruit was harvested. Higher quality products were prepared from the more mature fruit. Since not only the quality of processed products, but also the yields are affected by the stage of maturity at which the fruit is harvested, fruit for processing should be harvested when as mature as possible, but still in the green stage.

Storage of Green Plantains

Studies were made of green plantain behavior when stored under various conditions to develop the best method of prolonging their shelf life without affecting their overall quality and processing characteristics. Freshly harvested green plantains start to ripen in about 7 days, reaching full ripeness 2 days later, when kept under room conditions at temperature of about 85° F. When stored in refrigerated chambers, plantains from the Guayamero and Maricongo cultivara remain green for 12 days, at which time signs of chilling damage begin to appear. However, the quality of plantains stored in these refrigerated chambers at 45° and 55° F. with relative humidities of 86 to 88 percent are definitely affected. At 45° F. a marked hardening of the fruits was observed and at 55° F., signs of false ripening appeared, impairing the quality of the produce. Shelf life of green plantains may be successfully prolonged, however, when thiobendazole-treated fruits are stored in sealed polyethylene bags containing an ethylene absorbent (about 200 g. of Purafil). TBZ was used in a 200-p.p.m. concentration to control mold growth. By using these combined techniques plantains were kept perfectly green for 25 days at room temperature (85° F.) and for 55 days under refrigeration (55° F.). This method had no detrimental effect on the stored fruit, as shown by the sensory evaluations of two processed products prepared from the stored green plantains at various intervals throughout the study. Tasters rated the samples as good or superior to similar products prepared from freshly harvested green fruit.

Lye-Peeling of Green Papaya (Carica papaya L.)

A good lye-peeling operation may be obtained when whole green papayas are peeled under any of the following three combined treatments: 6 minutes in a 10-percent boiling lye solution, 4 minutes in a 15-percent boiling lye solution, and 3 minutes in a 20-percent boiling lye solution. The average weight lost as peel for each of the above treatments was 14.2, 11.6, and 11.5 percent, respectively. Changes in the titrable acidity and hardness of the pulp in lye-peeled papayas fell within the values obtained in hand-peeled papayas. In the lye peeling of whole green papayas, best results were obtained when the papayas were used at the rate of 1 pound for each gallon of lye solution used. It also was found that the average loss in weight of papayas as stems and seeds was 9 percent.

Ripening of Montecristo Bananas

Studies were conducted to determine the optimum conditions under which to ripen the Montecristo bananas grown in Puerto Rico to obtain fruit of high quality for the fresh market and for processing. When harvested at a thin grade like "three-quarters" the fruit generally ripens unevenly or may not ripen at all. The fruit must be harvested at a more developed stage like "light three-quarters" or "full three-quarters". The following ripening treatment gave the best results: The fruit is placed in the ripening room as soon after harvest as possible. The room controls are set to 68° F. and 95 percent relative humidity, and the fruit cooled to a pulp temperature of 68° F., which, in a room with adequate refrigeration capacity, takes about 12 to 24 hours. Two dosages of ethylene at the rate of 1 cubic foot per 1,000 cubic feet of room volume are applied within a period of 2 hours keeping the room tightly closed. The next day after the ethylene application, the room is ventilated for about 15 minutes, after turning, the temperature is lowered to 66° F. and 85 percent relative humidity, ventilating every day as previously indicated until cutting color is reached. The fruit ripens to color 4 in about 6 days. Higher ripening temperatures resulted in excessive finger drop after the fruit was removed from the ripening rooms. The ripening behavior of the bananas was found to vary with the time of the year when harvested and with the geographical zone in which they were produced. Fruit produced on the Southern Coast of Puerto Rico ripened uniformly the year around, while fruit produced in the Mountainous Area was more difficult to ripen, particularly during the winter months. Data are given on the changes in carbohydrates, moisture, acidity, and pH, which take place during ripening of the Montecristo bananas.

Studies on the Freezing of Green Plantains (Musa paradisiaca) II. Sulfitation to Control Browning

The SO2 content of green plantain slices sulfited in metabisulfite solutions increases with dipping time, but not in direct linear relationship. Increasing the concentration of the dipping solution resulted in a proportional increase in the SO2 content. Lowering the pH of the sulfiting solution resulted in higher SO2 uptake. Sulfurous acid solutions at pH 2.2 gave the higher SO2 content at a given clipping time. When sulfiting plantain slices in K2S2O5 solutions at pH 3.3, blanching increases the bisulfite absorption. Sulfiting in sulfurous acid solutions resulted in higher levels of SO2 in hand peeled unblanched slices and lowest in steam peeled and blanched slices. The SO2 content increased with the length of the blanching treatment for both water and steam blanching. Increasing the temperature during water blanching from 71.1° C (160° F) to 93.3° C 200° F) had no appreciable effect on the SO2 content. When slices were sulfited in K2S2O5 solutions, the loss of SO2 during frying was greater in blanched fruit, either hand- or steam-peeled. When the slices were sulfited in sulfurous acid solutions, the greater loss of SO2 during frying occurred in steam peeled fruit and neither the blanching method used nor the temperature had any effect on the SO2 loss. Sulfiting to levels of 100-150 p/m SO2 proved effective in controlling browning. The loss at this level during frying amounted to 50-60 percent, leaving a residue of SO2 which could not be detected by tasters, and did not affect the flavor of the product.

Studies on the Ripening of Plantains Under Controlled Conditions

Studies were conducted to determine the proper conditions for ripening plantains for processing. The plantains ripened evenly in 4-5 days at 72° F., 95-100 percent relative humidity, and with ethylene applied once at the rate of 1 cubic foot per 1,000 cubic feet of room space. Complete conversion of starch to sugars took place by the sixth day in the ripening room. At lower temperatures of 60° to 66° F., ripening proceeded at a much slower rate than at 72° F., only very mature fruit ripening under these conditions. The physical and chemical characteristics of fruit ripening at 72° F., are given for day-intervals from 1 to 12 days. A color chart is presented showing the peel color corresponding to the stage of ripeness at which the physical and chemical characteristics were measured. When ripe fruit was stored at 56° F., the ripening process continued at a very slow rate with the remaining starch being converted to sugars. At the end of 6 days in the ripening room, the fruit was still adequate for processing.