Handling and Physiological Studies with the Carambola1

Carambola fruits have a typical climacteric type of respiration in contrast to the nonclimacteric citrus fruits. The peak height of the climacteric curve is reduced both by low storage temperatures and by waxing of the fruits. Green-mature fruits have about equal amounts of oxalic and tartaric acids (40% and 35% of total acids, respectively); however, in yellow-mature fruits, oxalic acid comprises 74% of the total acids of which aj-ketoglutaric acid accounts for a surprisingly large 17%. Citric, malic, and succinic acids, which are present in the green-mature fruits, were not detected in the yellow-mature fruits. However, the total acids, on a fresh weight basis, did not change materially during ripening. Various amino acids were identified, their concentrations being typical of those in plant tissues. A consistent decrease in amino acids during ripening, coupled with an increase in oj-ketoglutaric acid, suggests utilization of amino acids as respiratory substrate. Waxing tended to reduce weight loss and to retard the green to yellow color change. If carefully handled, to avoid mechanical damage, waxed carambolas stored at 50° F can be expected to remain in good condition for 3 to 4 weeks. Introduction A previous paper (3) reviewed the rather limited literature on the culture and composilFlorida Agricultural Experiment Stations Journal Ser ies No. 2518. 2Associate Biochemist, Florida Citrus Commission and Horticulturist, Florida Citrus Experiment Station, Lake Alfred. Cooperative research by the Florida Citrus Experiment Station and the Florida Citrus Commission. tion of the carambola (Averrhoa carambola L.) and reported on initial tests indicating that this unusual and exotic fruit might be well suited to serve as a "conversation piece" in high qual ity citrus gift fruit packages. Holding tests at various temperatures indi cated a potential storage life of several weeks at cold storage temperatures with no indication of chilling injury and remarkable immunity to fungal invasion. Little was known, however, of the carambola's type of metabolic activity, com position, or reaction to normal marketing meas ures such as waxing and packaging. A matter of considerable interest was the composition of the organic acid component of the fruit. Winton and Winton (10) quoted per vious accounts that the acids were largely oxa lic and expressed doubt that an edible fruit could have such high levels of oxalic acid with out being toxic. The amino acid content was of interest since there appears to be no published data on carambolas. Materials and Methods Source of Fruit Carambolas were obtained from the SubTropical Experiment Station grove at Home stead and were of the 'Golden Star* variety, a Homestead selection. The shipment of over 300 miles was either by private car or by bus, the carambolas being at first jumble packed in car tons which inevitably caused some damage to the frail "wings" or ribs of the fruit. A second shipment, more carefully packed, received al most no damage. Undamaged fruit were selected for respiration and holding tests, damaged fruit being utilized for immmediate analyses. Storage Tests Temperatures of 50° and 60° F were in con stant temperature rooms without humidity conVINES AND GRIERSON: CARAMBOLA 351 ti*o\. The carambolas were stored in 5-pound, 1.5 ml polyethylene bags with seventy-two 1/4inch holes in each and having drawstring clos ures. Waxing was with Johnson's "Primafresh" wax emulsion No 7230 in which the carambolas were dipped and then air-dried. Color was judged subjectively using an em pirical scale of: 0 for deep amber; 1, pale yel low; 2, green-yellow; 3, light green; and 4, dark green. The colors of the individual fruit were averaged to give a representative color for the sample. (A typical sample was 8 fruit.) Treatments at each of 2 picking consisted of storing waxed and unwaxed fruits at 50° and 60° F for 4 weeks. Sample weights and colors were recorded weekly. Respiration Studies Respiration equipment for the determination of CO2 evolution from single fruit samples was used and has been described in a previous report to this Society (9). Individual fruits were left in the respiration chambers for 17 days at either 60° or 70° F to determine the type of respira tory drift—climacteric or non-climacteric. The respiration rates of waxed and unwaxed ripe fruit and green fruit were observed. Organic Acids Organic acids were extracted from homogen ized carambola fruit tissue and measured ac cording to a modification of the method des cribed by Ting and Vines (8). The extraction was made with ethyl alcohol and an aliquot was adsorbed on a double column. Dowex 1X8 (for amino acids) was in the upper column and Dowex 5 X 12 (for organic acids) was in the lower column. The organic acids were eluted as 3 fractions from the lower column using first 25 ml of 2 N acetic acid, then 25 ml of 6 N acetic acid, and finally 50 ml of 6 N formic acid. The 3 fractions were concentrated to dryness, then water added to make 1 ml from which an appropriate aliquot (1 to 5 ^,1) was spotted on Whatman No. 1 paper for chromatographic identification. Development was with 5 M formic acid and amyl alcohol, 1:1 (v/v). The best de tection spray was found to be 0.1 N silver nitrate and 0.1 N ammonium hydroxide, 1:1 (v/v). A separate chromatogram was prepared for detection of the keto-acids. The spray used for this was o-phenylenediamine (0.1 g) in a mixture of 0.1 N H.2SO4 (50 ml) and 95% ethyl alcohol (50 ml). Fluorescence of the ketoacids was observed under UV light (5). Ketoacids have not been the subject of widespread inquiry (1) and, hence, were of particular inter est here. Oxalic acid was determined on a separate aliquot of the same sample according to the method of Baker, as modified by Palmer (4). The carambola extract was first deproteinized with heat and with phosphotungstate, followed by centrifuging. The oxalic acid was precipi tated as calcium oxalate and the precipitate titrated with standard potassium permanganate. Ascorbic acid (Vitamin C) was determined by the method of Deszyck and Ting (2). Amino Acids Amino acids were determined according to the method described by Piez and Morris (6) using a Technicon Instrument Corp. Auto Ana lyzer. With this instrument, amino acids are separated on an ion exchange column. The ef fluent flow is treated continuously with ninhydrin and passed through a series of colorimeters, the output of which are fed into a multipoint recorder. The amino acids are identified by comparing the resulting peaks with those of standard acids. The qualities of each are calcu lated from the area under their respective curves. Results and Discussion Respiration Respiration curves are shown for carambola fruits stored at 60° and 70° F temperatures (Figure 1). These curves show the climacteric type of respiration that is similar to that ob served for the apple, pear, banana, or avocado, rather than the flat non-climacteric respiration typical of citrus fruits. The average preclimacteric rate of respiration was 20 mg CO2/kg/hr at 60° F. This is considerably higher than respiration rates of citrus fruits at the same temperature which vary from 3 to 6 mg CO2/kg/ hr (9). The climacteric rise in respiration rate of carambola fruits stored at 70° F occurred earli er and was higher than those of fruits stored at 60° F. Both waxing and lower storage tem perature tended to reduce the height of the climacteric peak, but extended the climacteric over a longer period, thus delaying senescence. 352 Florida state horticultural society, 1966