Respiration & Internal Atmosphere of Avocado Fruit

Abstract

Tlle relationship hetwveen respiration, ripeening. and the comilpositioni of tlle internal atmlosplhere has heen studied in several fruits. In the case of the banana (M.tsa sapientum) and the papaya (Carica Papaya). Wardlaw and Leonard (24, 25) observedl the coiici(lenice of the onset of the clilmiacteric rise with the peak in oxygen concentration insi(le these fruits. WVith the respirator-rise the oxygen level (lroppe(l reaching very low values of 1 at late stages of senescence. Imnlpresse(l with the miarked changes in the gaseous comllpositioll, they suggestedl thlat the ititer-nlal oxy(gen concentration is the conitrol-ling mleclhaniislmi of the clilmiacteric pattern. Trout et al. (22) reporte(d that in mature apples oxygen (deficiencv dlepresse(l respiration anld retarded ripeni-ing. Observations onl the epidermal layers as tlle tissue that offers nmajor resistance to gaseous (liffu-sioln ere nla(le b-TIrout et al. (22) for the apple ali(l 1bv Cleil(leninillg (7) for the tomiiato. Biale (4) inlcl(le(I inlhis review-a brief accounit of the studies dealing witlh the internal atmospheres of fruits. The avocado fruit is (listiniguislhe(l froimi other-frulits by-its low fermentative cal)acitv, shown b1 (le-pression of CO., evolution and ripening un(ler anaero-bic coniditionis (3). This study was undertakeni. thierefore, w\ithi the purpose of fiidinig an explanation for the physiological behavior of the avocadlo in termis of clianges in the composition of the internal atnioS-pjhere. Materials & Methods Fruit of the Hass and Fuerte varieties of avocado (Prsca americana-, Afiller) w ere obtained fronm the orchiard of the Horticultural Science Department for tliis w\vork. In descril)ing the stages in the respiratory-pattern of the fruit the following termiinology is used: pre-leak period, fronl pickilng to the respiratory peak: lag leriod, froml picking until the oniset of the respiratory rise; climlactel-ic rise, fronm onset of the respiratory rise until its peak: and postclimacteric. from 194 the climlacter-ic l)eak unitil final breakdown of the fruit. 1'ruit respiration was measuredl 1w CO., absorption in alkali asI descril)e(l !1 Biale and Shepherd (5 and moldified by Biale (3). by the Beckman oxygen anaIlyzer (lescribe(l bh Young and Biale (26). anid by simultaneous anialysis of CO., evolutioni and O. uptake in a closed system using the miiethod of Haller an(l Rosie (11). as mo(lified 1w Platenius (16). Fruit saml)les vere peele(l in each phase of the climilactel-ic history. Precautions against conitain ma-tioni wN-ere sufficielit wh-len the exlperiments were car-rie(l out un(ler sanitalry conditions. The inter-nial atmoslphere of the frutit was studiedl 1v aw aiethio(ldescril)e(l 1v \Wardlaw ani(l ILeoliar (24) aln(d milodifie(d 1b Trout et al. (22). A siall area nieal-the stemii end(of the fruit was sterilized 1w alcolhol. A sterilized cork borer 0.5 cim inl diameter was inserte(l thl-otighi the milesocarp up to the see(l. This cylinder of tissue was rel)lace(l 1w a tube 0.5 cimi ill (liamileter and(3 cimi long iliserte(d to a (lis-tanice of 0.5 cmii froImi the seed. The cavity and g]lss tube disl)laced a volumile of 0.5 to 1.0mliì. The taper-e(l glass tutbe was sealed by valve tubing 0.2 cim in dianleter. Sampling of the inter-nial atmosphere fronil thle cavit xvxas (lone 1w the Bonnier and MNfagnin ap-plaratus (lescribe(l 1w Thodav (21). The error of leterminiatioln was no iiiore than-+ 0.5 , of the volume of the gas. The resistanice of fruits to gaseous diffusioni was calculated with the forimiulae (le-scribed by Trout et al. (22): Re C,'R. in which Re resistance of fruit to (liffusion of CO., C volulimetric concentration of CO.. in the internal atmosphere of the fruit, and R = respirationi rate: Ro = (8O + 0.2 8N) /R. in which Ro = resistanlce of fruit to (liffusioni of O.. oO = O., percentage in air imiinus O. percentage in interinal atmosphere, and(8N =_ N., percentage in air less N2 percentage in internal atmosphere. The formiulae assumiie that the respiratory activity in fruit is independlent of Cc or CO (volumietric concentration of CO., & O., respectively) an(l is always inversely proportional to the resistance to gaseous exchange. In the case of in-hibitorv CO., concentration in the intercellular atimlos-phere, the r-esistanice values would be lower than calculated. However, on the basis of the results obtained by Biale (3) aind('oung et al. (27) the forilltu-laCe give rough approximmation's of fruit resist'ance.