1 PHYSIOLOGY AND POSTHARVEST BEHAVIOUR OF MANGO (Mngifer indic L. cv. TOMMY ATKINS) FRUIT GROWN UNDER WATER STRESS NANCY ONJEMO MADIGU MASTER OF SCIENCE (Food Science nd Posthrvest Technology) JOMO KENYATTA UNIVERSITY OF AGRICULTURE AND TECHNOLOGY 2007 i
2 PHYSIOLOGY AND POSTHARVEST BEHAVIOUR OF MANGO (Mngifer indic L. cv. TOMMY ATKINS) FRUIT GROWN UNDER WATER STRESS Nncy Onjemo Mdigu A thesis sumitted in prtil fulfillment for the Degree of Mster of Science in Food Science nd Posthrvest Technology in the Jomo Kenytt University of Agriculture nd Technology 2007
3 DECLARATION This thesis is my own originl work nd hs not een presented for degree in ny other university. Signture. Dte... Nncy Onjemo Mdigu This thesis hs een sumitted for exmintion with our pprovl s University supervisors Signture. Dte Prof. Frncis M. Mthooko JKUAT, Keny Signture. Dte Dr. Christine A. Onyngo JKUAT, Keny Signture. Dte Dr. Willis O. Owino JKUAT, Keny 2
4 DEDICATION I dedicte this work to my fther Joseph Mdigu, my mother Ann Mdigu, my fincée Osorn, my rothers Godfrey nd Alln nd my sisters, Mrgret, Lydi nd Evelyn for their persistent support nd encourgement s I pursued this tsk. 3
5 ACKNOWLEDGEMENTS I express my sincere grtitude to my supervisors, Professor Frncis Mutiso Mthooko for his guidnce nd dedicted support, to Dr. Christine Onyngo nd Dr. Wills Owino for continuing cdemic dvice. Thnks for elieving in me. I m grteful to Mr. Pul Krnj nd Mr. Dvid Voth for ssisting me with the running of the equipment especilly the high performnce liquid chromtogrphy nd the tomic sorption spectrophotometer. I thnk my fther for his finncil support throughout my study, Jomo Kenytt University of Agriculture nd Technology for sponsoring the reserch work through reserch grnt to Prof. F.M Mthooko, Prof. E.M. Khngi nd Dr. C.A Onyngo nd the Mngus s, Ytt for llowing me to use their frm s n experimentl field. It ws not possile to mention y nme ll the orgnistions or individuls who helped to mke this study success ut to ll of you I sy Asnte Sn Finlly, I thnk the lmighty God for giving me strength nd determintion in pursuing this course. 4
6 TABLE OF CONTENTS DECLARATION.і DEDICATION...ii ACKNOWLEDGEMENT.iii TABLE OF CONTENTS...iv LIST OF TABLES...vіі LIST OF FIGURES.viii ABSTRACT...xi CHAPTER ONE: GENERAL INTRODUCTION Introduction Prolem Sttement Rtionle nd Justifiction Reserch Ojectives Hypothesis CHAPTER TWO: LITERATURE REVIEW Fruit development Fruit mturtion Determintion of mturity stge Fruit ripening Posthrvest chnges in mngoes Prehrvest wter deficit...18 CHAPTER THREE: MATERIALS AND METHODS Plnt Mterils Anlyses
7 3.2.1 Determintion of fruit, length nd weight Determintion of glucose, fructose nd sucrose Determintion of strch content Determintion of totl solule solids nd totl titrtle cidity Determintion of respirtion nd ethylene rtes Determintion of β-crotene content Determintion of totl nthocynin content Determintion of chlorophyll content Colour ssessment Determintion of minerl content Determintion of firmness Determintion of vitmin C content Sttisticl nlysis...26 CHAPTER FOUR: RESULT AND DISCUSSION Influence of wter deficit on the physiologicl nd physico-chemicl chrcteristics of mngo fruit during growth nd development Length, dimeter nd weight Sugr content Strch content Totl solule solids nd totl titrtle cidity content Respirtory nd ethylene rtes Crotenoid nd nthocynins content Chlorophyll content Colour
8 4.1.9.Minerls content Firmness Vitmin C content Influence of wter deficit on the physiologicl nd iochemistry of mngo (Mngifer L.) fruit during posthrvest hndling Percentge weight loss Sugr content Strch content Totl solule solids nd totl titrtle cidity content Respirtory nd ethylene rtes Crotenoid nd nthocynins content Chlorophyll content Colour Firmness Vitmin C content..90 CHAPTER FIVE: CONCLUSION AND RECOMMEDATIONS 92 REFERENCES
9 LIST OF TABLES Tle 1. L vlue in the peel nd pulp during growth nd development of mngo fruits from irrigted nd non-irrigted trees...51 Tle 2. Hue ngle in the peel nd pulp during growth nd development of mngo fruits from irrigted nd non-irrigted trees 52 Tle 3. Clcium content in the peel nd pulp during growth nd development of mngo fruits from irrigted nd non-irrigted tree...55 Tle 4. Mgnesium content in the peel nd pulp during growth nd development of mngo fruits from irrigted nd non-irrigted tree...56 Tle 5. Potssium content in the peel nd pulp during growth nd development of mngo fruits from irrigted nd non-irrigted tree...57 Tle 6. Phosphorus content in the peel nd pulp during growth nd development of mngo fruits from irrigted nd non-irrigted tree...58 Tle 7. Pulp sugr content during posthrvest storge t mient temperture of mngo fruits from irrigted nd non-irrigted trees...68 Tle 8. L vlue in the peel nd pulp during growth nd development of mngo fruits from irrigted nd non-irrigted tree..84 Tle 9. Hue ngle content in the peel nd pulp during posthrvest storge of mngo fruits from irrigted nd non-irrigted trees 85 8
10 LIST OF FIGURES Figure 1. Length nd dimeter during growth nd development of mngo fruits from irrigted nd non-irrigted trees.28 Figure 2. Weight during growth nd development of mngo fruits from irrigted nd non-irrigted trees...30 Figure 3. The correltion of length verses dimeter of mngo fruits from irrigted (A) nd non-irrigted (B) trees during the growth nd development period..32 Figure 4. Glucose nd fructose content during growth nd development of mngo fruits from irrigted nd non-irrigted trees.34 Figure 5. Sucrose content during growth nd development of mngo fruits from irrigted nd non-irrigted trees...35 Figure 6. Strch content during growth nd development of mngo fruits from irrigted nd non-irrigted trees...38 Figure 7. Totl titrtle cidity nd totl solule solids content during growth nd development of mngo fruits from irrigted nd nonirrigted trees 41 Figure 8. Respirtion rte during growth nd development of mngo fruits from irrigted nd non-irrigted trees...43 Figure 9. β-crotene nd nthocynins content during growth nd development of mngo fruits from irrigted nd non-irrigted trees..46 9
11 Figure 10. Chlorophyll nd chlorophyll content during growth nd development of mngo fruits from irrigted nd non-irrigted trees..48 Figure 11. Totl chlorophyll content during growth nd development of fruits mngo from irrigted nd non-irrigted trees...49 Figure 12. Firmness during growth nd development of mngo fruits from irrigted nd non-irrigted trees...61 Figure 13. Vitmin C content during growth nd development of mngo fruits from irrigted nd non-irrigted trees.63 Figure 14. Weight loss during posthrvest storge of mngo fruits from irrigted nd non-irrigted trees...66 Figure 15. Strch content during posthrvest storge of mngo fruits from irrigted nd non-irrigted trees...71 Figure 16. Totl solule solids nd totl titrtle cidity content during posthrvest storge of mngo fruits from irrigted nd nonirrigted trees 74 Figure 17. Respirtion rtes during posthrvest storge of mngo fruits from irrigted nd non-irrigted trees...76 Figure 18. β-crotene nd nthocynins content during posthrvest storge of mngo fruits from irrigted nd non-irrigted trees.79 Figure 19. Chlorophyll nd chlorophyll content during posthrvest storge of mngo fruits from irrigted nd non-irrigted trees
12 Figure 20. Totl chlorophyll during posthrvest storge of mngo fruits from irrigted nd non-irrigted trees...82 Figure 21. Firmness during posthrvest storge of mngo fruits from irrigted nd non-irrigted trees..88 Figure 22. Vitmin C during posthrvest storge of mngo fruits from irrigted nd non-irrigted trees
13 ABSTRACT The study minly ims to estlish proper mturity indices nd posthrvest ehvior of mngo fruit of Tommy Akins vriety, the effects of irrigted nd wter-stress on the development, mturity indices nd posthvest ehvior of this fruits. The fruits were smpled from frm in Ytt Division, Mchkos district. Chnges in vrious physicl, physiologicl nd iochemicl were monitored during fruit development from fruit set to mturity. Among the mesured prmeters include chnges in size nd weight, sugr, titrtle cidity, totl solule solids, nd β-crotene pulp content, nthocynin nd chlorophyll peel content, minerl peel nd pulp content, respirtion nd ethylene production rtes. In ddition, posthrvest chnges in these prmeters were determined. Fruit weight, dimeter, length, sugrs (sucrose, fructose nd glucose), strch showed stedy increse with time declining towrds fruit mturity. Totl titrtle cidity incresed just efore mturity nd decresed t mturity. Totl solule solids incresed s the fruit pproched mturity irrespective of the tretment. β-crotene content incresed with growth of the mngo fruit. Anthocynins content showed vrince ut lter decresed towrds fruit mturity, no ethylene ws detected lthough respirtion rtes showed true climcteric curve. There ws high correltion oserved etween the increse in firmness nd strch r 2 = 0.86 nd 0.96 for fruits from irrigted nd nonirrigted, respectively. Vitmin C content vried t different stges of growth nd development. 12
14 Fruits from irrigted nd non-irrigted were hrvested t 168 DAB (Dys fter loom). Fruits from non-irrigted trees hd higher percentge weight loss thn those from irrigted trees. Individul sugrs (sucrose, fructose nd glucose) might hve incresed stedy with fruit ripening while strch content, totl titrtle cidity ll decresed with increse in storge dys. Totl solule solids incresed in oth tretments. Respirtion rtes showed true climcteric curve. β-crotene incresed stedily decresing t 9 dys in storge while the nthocynin content, firmness nd scoric cid content decresed with time. A high correltion ws oserved etween the increse in length nd dimeter r 2 = nd in the fruits from irrigted nd non-irrigted trees, respectively. The formul of the eqution cn e clculted nd therefore used y frmers. This is ccompnied y n increse in glucose, totl solule solids nd decrese in strch content nd firmness. Fruits from irrigted trees mtured erlier thn those from non-irrigted trees. The mngo fruits from nonirrigted trees hd longer shelf life thn those from irrigted trees most proly due to lte mximum climcteric pek nd higher degree of firmness, chrcteristic tht mkes them good for dessert nd export mrket. The fruit from irrigted trees were higher in totl solule content nd β- crotene ut hd short shelf life nd reduced firmness tht mkes them suitle for juice production industry nd locl mrket. 13
15 CHAPTER ONE GENERAL INTRODUCTION 1.1. Introduction Mngo (Mngifer indic L.) is one of the most importnt fruit crops in the tropicl nd sutropicl lowlnds. It is ntive to Indi, Bngldesh, Mynmr nd Mlysi, ut cn e found growing in more thn 60 other countries throughout the world (Slim et l., 2002). The mngo is est dpted to wrm tropicl monsoon climte with pronounced dry seson (>3 months) followed y rins. However, informtion from other countries indictes tht crops cultivted for long time over n extended re show high degree of diversity due to vried environmentl influences. This chrcteristic is likely lso true for mngo seedlings first introduced in Keny which were ll polyemryonic (Griesch, 2003). Over, 20 cultivrs of mngoes re grown in Keny, mong them re: Alphonso, Apple, Cro, Dodo, Hden, Hert, Irwin, Kent, Keit, Kensington, Ngowe, Nimrod, Pech, Senstion, Tommy Atkins nd Vn Dyke. Of these, few hve stedily lost ground to genertion of cultivrs introduced in the 1970s nd 1980s like Tommy Atkins. Tommy Atkins originted from Florid nd elongs to the Ancrdicee fmily memer of Mngifer indic L. (Griesch, 2003). Tommy Atkins is distinguished y greter resistnce to diseses such s 1
16 nthrcnose (cused y Colletotrichum spp) nd powdery mildew (cused y Oidium spp), very ttrctive colour, excellent shipping nd shelf-life qulities. Worldwide mngo cultivtion now covers pproximtely 2.9 million hectres (FAO, 2001) nd erns nerly US$ 500 million in export revenues. The production hs incresed prtly due to incresed lnd under cultivtion nd improved vrieties. In Keny the re under mngo cultivtion rose from 500 h in 1970 to pproximtely 15,000 h in 2005 (Mumero, 2005). Despite the increse in production of mngoes, 40-60% of this crop is lost through poor posthrvest hndling systems (HCDA) (Horticulture Crop Development Authority, 2003). Depending on cultivrs nd environmentl conditions it tkes 90 to 160 dys fter flowering for Kenyn mngos to rech mturity. Not ll fruits on one tree ripen t the sme time. A mjor prolem is to determine precisely the stge t which the fruit is ripe for picking. Fruits hrvested too erly will e of inferior qulity fter storge nd will shrivel during posthrvest storge; however, fruits picked when too ripe cnnot e stored for ny length of time nd my give rise to prolems such s jelly seed (Griesch, 2003). The fruit will hve its est flvour if llowed to ripen on the tree. The tests currently used to determine ripeness of mngo, such s cid, sugr content or specific grvity re not fully relile (Griesch, 2003). For frmers to produce fruits tht re of good qulity oth for export nd locl mrkets they need mturity index tht re ffordle nd tht cn e esily determined in the field. 2
17 Irrigtion hs een reported to ffect the fruit composition nd qulity in vrious climcteric fruits such s grpes (Willims nd Mtthews, 1990), reurn pples (Mills et l., 1996), stone fruits (Crisostol et l., 1997), mngo cv. Lirf, grfted on Mison Rouge (Lechudel et l., 2005), ut little hs een done on mngo fruit. This project imed t estlishing mturity index nd qulity of Tommy Atkins sujected to irrigtion nd wter stress during growth nd development nd its effect t posthrvest storge Prolem Sttement In Keny, the ulk of mngoes re produced y smll-scle frmers. These fruits experience sesonl gluts leding to high percentge of posthrvest wstge. This is ecuse of senescent deteriortion, pests nd diseses, poor hndling prctices nd lck of storge fcilities (Joseph nd Aworh, 1991). Advnced culturl prctices coupled with improved fruit cultivrs, hve in recent yers contriuted to superior qulity of mngo t hrvest nd incresed yields. Unfortuntely, the impct of these horticulturl nd technologicl improvements hve not fully een relised s high percentge of this commodity is lost fter hrvest due to poor posthrvest hndling prctices (Mthooko, 1995), therey ffecting food security. The prolem is mde worse y lck of proper hrvestle mturity indices. Mngo fruits re hrvested commercilly within rnge of mturities including immture green, mture green nd tree ripe (Mitr nd Bldwin, 1997) stges tht hve different impct 3
18 on fruit qulity. When the fruits re hrvested immture they tend to hve inferior qulity, shrivelling on storge. On other hnd when the fruits re picked when too ripe, the fruits develop the est flvour ut they do not store for considerle length of time. This mens the stge of hrvest is very importnt ecuse posthrvest chrcteristics re ffected y stge of mturity t hrvest. With incresing production, nd the fct tht this commodity forms the ulk of fruits for locl nd export mrkets, then proper posthrvest hndling is importnt in order to expnd mrket opportunities. This will increse generted income nd hence llevite poverty Rtionle nd Justifiction Mngoes re the most populr nd choicest of the commercil fruits produced in the tropics due to their extremely excellent flvor, ttrctive frgrnce, eutiful colour, delicious tste nd helth-giving properties (Tsneem, 2004). However, these fruits re delicte nd mny cultivrs cnnot withstnd long distnce trnsporttion, often reching the mrket in mushy, overripe stte. Storge nd mturity indices of mngoes continue to e chllenging prolems tht need more ttention. Indeed poor posthrvest hndling hs een identified s one of the constrints in the mngo industry in Keny. Therefore, development of mturity indices for hrvesting mngoes will result in sound mngo industry in Keny especilly during mrketing nd distriution. 4
19 A numer of frmers in the rid nd semi-rid lnds irrigte their mngo trees. The influence of this on fruit development, qulity nd posthrvest ehviour hs not een well documented. Hrvest time represents compromise etween leving the fruit on the tree long enough to mximize yield (qulity) ut hrvesting erly enough when it still hs sufficient green life is est for effective mrketing. It is, therefore, importnt to hrvest the fruit t n optimum mture stge, which cn only e chieved y the determintion of proper mturity indices. Furthermore, mngo growing cn ecome more vile when one is le to predict the hrvestle mturity, ecuse this helps to seek mrkets efore hnd, thus reducing the posthrvest losses while mintining product qulity during retil/export distriution. This will reduce mngoes price fluctutions therey enling frmers to otin etter profits Reserch Ojectives The min ojective of this study ws to estlish the proper hrvestle mturity indices nd posthrvest ehviour of mngo (Mngifer indic L.) fruit. The specific ojectives of this study were to: ) Estlish fruit growth nd development ptterns of mngo (Mngifer indic L. cv. Tommy Atkins) fruit in irrigted nd non-irrigted trees. ) Identify physicl, physiologicl nd iochemicl prmeters tht correlte well with hrvestle mturity nd qulity, nd therefore, estlish optimum hrvestle mturity indices for mngo fruit. 5
20 c) Determine the effects of irrigtion nd wter stress on the growth nd development nd their effect on potentil hrvestle mturity indices. d) Study the posthrvest ehvior of the fruits from irrigted nd nonirrigted trees fter hrvesting t potentil hrvestle mturity indices Hypothesis () Estlishment of cler mturity indices will improve posthrvest fruit qulity nd reduce posthrvest loss. () Pre-hrvest wter stress ffects the qulity nd posthrvest ehvior of mngo fruit. 6
21 CHAPTER TWO LITERATURE REVIEW 2.1. Fruit growth nd Development Plnts nd plnt prts progress through dynmic series of geneticlly controlled developmentl processes terminting in their eventul senescence nd deth. Their development is the comintion of oth growth (n irreversile increse in size) or volume (ccompnied y the iosynthesis of new protoplsmic constituents) nd differentition (qulittive chnges in the cells) nd cn e viewed t either the whole plnt or individul orgn level. During the developmentl period, plnts disply remrkle degree of vriility in form tht is strongly influenced y the environment in which they re grown (Kys, 1991). Environment hs pronounced influence on the development of plnts nd plnt prts, nd this influence crries over into the posthrvest period. Vritions in composition nd structure cn significntly lter the wy product responds fter hrvest nd s consequence how it must e hndled. If the physicl nd chemicl chnges occurring during the posthrvest period re to e understood, it is essentil tht first there is n understnding of how the posthrvest period fits in to the entire developmentl cycle of the plnt (Kys, 1991). The ility to reproduce is unifying nd essentil chrcteristic of ll orgnisms. In the plnt kingdom, sexul reproduction y wy of flower nd seed production is one of the most common (Kys, 1991). Flowering represents 7
22 distinct stge in the overll developmentl cycle of most plnts. Flowering in mngo trees cn e induced y wter/drought stress. Dry wether preceding nd during the loom period is considered optimum for good fruit production (Crne et l., 1994). Older trees respond etter thn young ones (Griesch, 2003). For optimum growth nd productivity, C is elieved to e idel temperture during flowering nd ripening. Tempertures exceeding 40 C my, especilly in hot/dry res, led to sunurn of fruits nd stunting of tree growth. Different uthors hve found the developmentl pttern of mngoes to vry. For instnce, Suhdr nd Surmnym, (1970) found Alphonso mngo to tke out 16 weeks to rech complete development with the physicl increse in size nd weight slcking etween 9-14 weeks fter fruit set. Leley et l. (1943) nd Mukerjee (1959) found the mngo fruit to tke 21 weeks to mturity while the increse in size nd weight stopped 4-5 weeks efore hrvest. A respirtory climcteric during the erly stges of fruit development hs lso een reported in mngo (Singh et l., 1937), peches nd plums (Roux, 1940) nd pples (Kidd nd West, 1945). Ascoric cid nd cidity reched pek round the 5 th nd 7 th week, respectively ut decresed towrds fruit mturity. Sugr content declined throughout the period of growth while strch continued to increse with growth nd development (Suhdr nd Surmnym, 1970). The wide vrition in physicl, physiologicl nd iochemicl developmentl 8
23 ptterns necessittes more systemtic studies to otin cler understnding. It is lso importnt to correlte the physicl, physiologicl nd iochemicl prmeters if relile results re to e found Fruit Mturtion Mturity descries the stge of internl fruit development. Mturity my e defined in terms of either physiologicl or horticulturl mturity nd is sed on the mesurements of vrious qulittive nd quntittive fctors. Mturity is stge of development superimposed on the plnt or plnt prt reltive to humn needs. The fruit is considered mture when it meets the requirements for hrvest (hrvestle mturity) (Kys, 1991). Mturity t hrvest is the most importnt fctor tht determines storge-life nd finl fruit qulity (Kder, 2002). Immture fruits re more suject to shriveling nd mechnicl dmge nd re of inferior qulity when ripe. Overripe fruits re likely to ecome soft nd mely with insipid flvor soon fter hrvest. Any fruit picked either too erly or too lte in its seson is more susceptile to physiologicl disorders nd hs short-life thn fruit picked t proper mturity (Kder, 1999). Fruits hve to e picked mture ut unripe so tht they cn withstnd the posthvest hndling system when shipped long-distnce (Kder, 2002). During on-tree mturtion of mngoes, neither firmness nor the sugr-cid rtio chnges significntly (Ngle et l., 2005). As descried for other mngo cultivrs (Leshem et l., 1986), respirtory rise is stimulted y detchment from the prent tree, thus inducing posthrvest ripening. Fruit softening nd 9
24 prllel increse in the sugr-cid rtio, chrcteristic of cid degrdtion nd initil sugr ccumultion occurs t fruit ripening. Hence, the post-hrvest ripening index (RPI) tht specifies fruit ripeness sed on these chnges (Vsquez-Cicedo et l., 2005) cnnot e used in detection of picking mturity. Thus there is need for suitle method tht cn e esily dopted y smll scle frmers in Keny. This will increse income erned y the frmers thus erdicting poverty Determintion of Mturity Stge Mny methods exist for determining the hrvest time of mngo tht require set of mturity-relted physiologicl or qulity ttriutes. Most currently used mturity indices re sed on compromise etween those indices tht would ensure the est eting qulity to the consumer nd those tht provide the needed flexiility in mrketing (Kder, 2002). Producers nd trders commonly use destructive methods tht re inexpensive for determintion of hrvest time. Such methods re sed on pit hrdening nd the mesocrp color chnge round endocrp (Crne nd Cmpell, 1994). Thresholds of cidity nd contents of solule solids, crohydrtes nd phenolics hve lso een used (Lkshminryn, 1980). However, differences exist etween mngo vrieties. In some cses, ccess to technologicl resources, such s lortory, nd considerle expertise re needed. Most producers re illequipped to ccurtely determine the est time for hrvest nd remin using unsophisticted methods sed on experience with no rel stndrdiztion. 10
25 Mturity indices for vrious horticulturl crops hve relied on different fetures of the commodity, such s durtion of development, size, density, strch or sugr content, color nd firmness (Shewfelt, 1993). Firmness nd color re good indices used to determine overripe peches during processing (Tyson et l., 1975; Horton, 1992). Fruit showing some yellow colour on the tree hs shelf life of only few dys nd must e sold in the locl mrket. For export mrket, the fruit re picked when firm nd t the mture-green colour stge. A fruit hrvested t the mture green stge ripen quite rpidly fter hrvest nd egin to turn yellow within 3 to 5 dys t mient temperture. A fruit hrvested immture green does not ripen properly, tste poorly, nd shrivels (Medlicott et l., 1986). Although color chnges when the mngo mtures, it is n unrelile mturity index more so ecuse it vries with vriety nd light exposure (Hller, 1952; Lott, 1965). Color mesurements cn lso e ffected y the condition of the fruit surfce nd the mount of trichomes. Moisture on the fruit surfce cn decrese the L* vlue (Delwiche nd Bumgrdner, 1983). Pectic sustnces re structurl polyscchrides responsile for the firmness of fruits. Softening of fruit occurs when these polymers ecome less tightly ound in the cell wlls during ripening. Therefore, firmness could lso e used s n index for fixing optimum stge of mturity for hrvest (Kudchikr et l., 2001). Reduction in firmness my lso e due to ccelerted ripening process in free tmospheric conditions of storge temperture. Similr findings hve 11
26 een reported in mngoes of other vrieties (Doreypp-Gowd nd Huddr, 2001; Opr et l., 2000). Since firmness is ffected y mny conditions, it is importnt to use firmness together with other mturity indices in order to get relile results. Some technologies like ner-infrred (NIR) spectroscopy offer relile tool to specify posthrvest ripeness of mngoes (Mhyothee et l., 2004) or their fruit qulity (Schmilovitch et l., 2000). Ner-infrred quntifiction of strch nd dry mtter contents hs een suggested to determine picking mturity of mngoes (Srnwong et l., 2003). Although NIR mesurements hve een integrted in lrge-scle utomted sorting of vrious fruits (Schmilovitch et l., 1999), such technologies re still not widely ville for use in the mngo orchrd. Moreover, they require comprehensive clirtion sed on precise knowledge of the mturtion kinetics, of suitle thresholds for picking mturity nd re expensive for developing country like Keny Fruit Ripening Fruit ripening is the composite of the processes tht occur from the ltter stges of growth nd development through the erly stges of senescence. Ripening results in chrcteristic esthetic nd /or food qulity, s evidenced y chnges in composition, colour, texture or other sensory ttriutes (Kder, 2002). The ripening process of fruit involves series of iochemicl rections or metolic ctivities. The chnges cuse chemicl chnges, incresed respirtion, ethylene production, chnge in structurl polyscchrides cusing softening, chnges in 12
27 crohydrtes or strch conversion into sugrs, orgnic cids, lipids, phenolics nd voltile compounds. Others includes degrdtion of chlorophyll nd unmsking of preexisting pigments such s nthocynins nd crotenoids, thus leding to ripening of fruit with softening of texture to cceptle qulity (Herinus et l., 2003). Softening is one of the most significnt qulity ltertions consistently ssocited with the ripening of fleshy fruits. Altertions in texture ffect oth the ediility of the fruit nd the length of time the fruit my e held. Once the softening process is initited, the rte of texturl chnge is function of the type of fruit nd the conditions under which the product is held. Often cceptle flesh texture represents very nrrow rnge tht cn e rpidly exceeded, diminishing the qulity of the product (Kys, 1991). During ripening, the tste of mny fruits chnges due to ltertions in sugrs tht enhnce pltility of the fruit. With fruits tht must ripen while ttched to the prent plnt, sugrs increse vi trnsloction of sucrose from the leves. For instnce, upon rrivl, sucrose in grpes is hydrolyzed y invertse, forming glucose nd fructose. In some climcteric fruits such s mngoes, chnges in internl sugrs represent products derived from hydrolysis of strch reserves y α- mylse nd β- mylse nd/or strch phosphorylse. The ctivity of these enzymes increses mrkedly during the ripening of mny fruits (Kys, 1991). 13
28 Chnges in cidity re lso importnt in the development of the chrcteristic tste in mny fruits. During ripening, there is decrese in orgnic cids in most fruits. This loss is due lrgely to the utiliztion of these compounds s respirtory sustrtes nd s cron skeletons for the synthesis of new compounds during ripening. The decrese in totl cidity in the grpes tends to coincide with the onset of ripening nd the ccumultion of sugrs. The concentrtion of orgnic cids does not, however, decline in ll fruit during ripening. In the nns, there is significnt increse in the concentrtion of mlic cid nd decrese in ph (Kys, 1991). Arom of fruit is extremely importnt qulity criterion nd s fruits ripen there is n increse in the rte of synthesis of these voltile compounds. Over 200 different compounds hve een identified in vriety of other fruits (Nursten, 1970). Only reltively smll numer of the totl complement of voltile compounds, however, tends to mke up the chrcteristic rom perceived for specific fruit (Kys, 1991). Chnges in fruit colour my or my not coincide with the development of the other qulity criteri ssocited with ripening. With pples, colour development does not closely prllel the respirtory climcteric. Colour, therefore, is not generlly n cceptle mens of ssessing ripeness of this fruit. There is, however, reltively close ssocition etween colour chnges nd ripening in climcteric fruits such s the nn nd itter melon nd non- 14
29 climcteric fruits such s the cherry, lue cherry (Vccinium spp.), nd strwerry (Kys, 1991). Mngoes exhiit climcteric ripening ehvior chrcterized y decrese fruit respirtion during development (preclimcteric minimum) followed y rise in respirtion levels (the climcteric pek) until full ripeness nd susequent respirtory decline (postclimteric) during fruit senescence (Bile nd Young, 1980). The climcteric rise is ssocited with shrp increse in ethylene production in fruit like mngoes which induces ripening. Ethylene levels t hrvest influence the mgnitude of the climcteric curve, nd therefore, the finl product qulity (Llel et l., 2003). Fruits hrvested too erly do not undergo the desired ripening chnges nd lte hrvest will led to off-flvor nd reduced shelf life. Fruit softening occurs very rpidly nd is one of the min cuses of qulity deteriortion during posthrvest hndling. This includes chnges in scoric cid content, loss of voltile rom components nd texturl properties (Slni et l., 2006). This poses ig chllenge during trnsporttion nd distriution, nd results in considerle posthrvest loss. For mngoes, in order to void the excessive dmge of fully ripe fruits, the fruits re hrvested t erlier stges, resulting in firmer fruits ut with inevitle negtive effects on finl fruit qulity. In the sence of cler hrvest indices, this prolem will continue to persist. 15
30 Light exposure ffects fruits qulity nd storge period. For exmple lrge differences in solule solid concentrtion, cidity, nd fruit size were detected etween fruit otined from the outside nd inside cnopy positions of open vse trined peches trees (Mrini, 1991; Senz, 1991). During the seson it ws oserved tht fruit grown under high-light environment (outside cnopy) hs longer shelf life (storge nd mrket) thn fruit grown under low-light environment (inside cnopy). Investigtion tht re sed on improving the qulity of mngo t prehrvest re of importnce more so ecuse most prehrvest fctors ffect post hrvest storge of fruits Posthrvest Chnges in Mngoes The shelf life of mngo vries mong its vrieties depending on storge conditions. It rnges from 4 to 8 dys t room temperture nd 2-3 weeks in cold storge t 13 º C (Crrillo et l., 2000). A difference mong vrieties exhiits 4 dys of shelf life for Bneshn, Tommy Atkins nd Kit (Nryn et l., 1996; Rodov et l., 1997) s compred to 8-9 dys of Alphonso (Rje et l., 1997; Srinivs et l., 2002). Usully fter hrvest the ripening process in mture green mngo tkes etween 9-12 dys (Herinus et l., 2003) or dys (Mnzno et l., 1997) with good flvor, texture nd colour chrcteristic t mient conditions. Spoilge of mngo due to stem end rot nd nthrcnose limits its storge potentil nd the shelf life is decided on the sis of spoilge (10%) during storge (Nryn et l., 1996). Most posthrvest pthogens re present on the 16
31 fruit surfce t hrvest nd cuse decy where the tissues re wounded or soften sufficiently in storge to permit pthogen penetrtion nd infection (Willim nd Whitker, 1997). The stge t hrvest ffects the qulity of mngoes nd their posthrvest life. Fruits hrvested too erly will e immture with inferior qulity fter storge; however, fruits picked when too ripe cnnot e stored for ny length of time nd my give rise to prolems such s jelly seed. Shriveling of immture fruit occurs t room temperture due to excessive loss of wter from fruit due to skin evportion (trnspirtion) nd to some extent respirtion. This mkes the fruit ppernce to deteriorte thus reducing its mrket vlue. Reduction of post hrvest losses increses food vilility to the growing humn popultion, decreses re needed for production nd conserves nturl resources (Kder, 2003). Mny methods exist for extending fruits shelf life of mngoes such s Modified tmosphere pckging (MAP) nd the use of low-temperture storge. MAP hs een suggested ut it requires creful hndling to prevent dmge to gs nd loss of the modified tmosphere. The min fctor, tht mintin mngo qulity in vrious film pckging re incresed CO 2 nd decresed O 2 levels, which reduce respirtion rtes nd prevent wter loss (Chplin et l., 1982; Miller et l., 1983; Yuen et l., 1993; Rodov et l., 1997). However despite its success t the lortory level (Chplin et l., 1982; Miller et l., 1983; Yuen et l., 1993; Rodov et l., 1997), MAP is still not commercil technique. 17
32 The low-temperture storge hs een use in n ttempt to prolong storge life (Medlicott et l., 1990). In prctice, the minimum temperture for storge of most tropicl fruits is determined y their susceptiility to chilling injury (CI). Between 12 nd 13 º C generlly is considered s optimum for mngo storge (Klr nd Tndon, 1983 nd Medlicott et l., 1987) lthough suitle temperture hs een given s 10 º C (Thoms, 1975) nd 5 º C (Aou Aziz et l., 1976; Thomson, 1977). The vrition in reported optimum temperture my e cultivr s effect, nd my lso e relted to the stge of hrvest mturity nd ripeness of the mngos when plced in storge (Medlicott, 1990). The technology is not widely spred in Keny ecuse of the difference tht exists etween cultivrs, lck of proper hrvestle mturity indices nd high cost of refrigertors Prehrvest Wter Deficit Wter stress is universl prolem in the production of griculturl plnt products. Severe wter stress results in incresed sunurns of fruits, irregulr ripening of pers, tough lethery texture in peches nd incomplete kernel development in nuts (Kder, 2002). Excess wter results to crcking of fruits (such s cherries nd prunes), excessive turgidity leding to incresed susceptiility to physicl dmge, reduced firmness, delyed mturity nd reduced solule solids content (Kder, 2002). Wter deficits hve een found to enhnce red color development t prehrvest nd increses totl solule solids (TSS) nd totl titritle cidity (TTA) in 18
33 reurn pples during posthrvest storge (Mills et l., 1996). This, improved consumers cceptnce of the fruits. Wter deficits lso hs een found to modify tree nutrition tht in turn influences mrket life, qulity nd internl rekdown of fruits like pples (Brmlge, 1993) nd stone fruits (Crisostol et l., 1997). It is, therefore, importnt to estlish the effects of wter deficit nd irrigtion with the im of improving mrket vlue of mngo (Mngifer indic L. cv. Tommy Atkins) fruit. Despite the importnt role of wter in fruit growth nd development, no specific studies hve een done on the influence of the mount of wter pplied on mngo qulity t hrvest nd post hrvest performnce. Therefore, this study seeks to understnd the posthrvest ehvior of Tommy Akins, n importnt Kenyn mngo cultivr. 19
34 CHAPTER THREE MATERIALS AND METHODS 3.1. Plnt mteril Mngo (Mngifer indic L. cv. Tommy Atkins) fruit were smpled of growth, development nd posthrvest storge dt. The fruits were smpled from frm in Ytt Division, Mchkos district. One set of trees ws irrigted throughout the experiment while the other set ws sujected to wter stress until 42 dys fter loom (DAB). This is ecuse of the rinfll tht ws experienced in this region. Fruits were smpled for lortory nlysis from oth sets of trees t intervls of 1 dy for posthrvest storge nd 14 dys for growth development dt. For posthrvest storge fruits were kept t mient temperture. Dt ws nlyzed using Genstt (13 th version) pckge (t-test; pired two smples for mens) Anlyses nd Physicl Mesurements Fruit Hrvestle Mturity-Length, Weight nd Dimeter Chnges in fruit weight were determined using scientific lnce (Model Liror AEG-220, Shimdzu Kyoto, Jpn). Flowers were tgged nd the time tken to develop to hrvestle mturity determined. During the sme period, the chnges in length nd dimeter were determined using cliper (Model Mitutoyo, Jpn).
35 Pulp Sucrose, Fructose nd Glucose Contents Ten grms of fruit pulp ws refluxed in ethnol for one hour. The smple ws then concentrted y rotry evportion nd diluted with 75% cetonitrile. These individul sugrs were nlyzed using high performnce liquid chromtogrph (HPLC) (Model LC-10AS, Shimdzu Corp., Kyoto, Jpn) using refrctive index (RI) detector. The conditions were: oven temperture, 35 o C, recorder speed: 3, ttenution: 4, rnge: 4 flow rte: 0.5 ml/min, column: Reverse phse, NH 2 P 250 Χ 4.6 mm, 5µm nd 75% cetonitrile s n elution solvent Strch Content This ws done y the Strch stining method. A slice from the equtoril region of the fruit ws dipped in I/KI (2g/10g) solution nd rting ws reported s percentge using the Cornell Strch Chrt, wherey 100% flesh colortion is equivlent to 3 while 0% is equivlent to no color chnge. This chrt hs scle of 1-8 with 1, ll strch nd 8, no strch Pulp Totl Solule Solids Content nd Totl Titrtle Acidity Totl solule solids (TSS) content ws determined using n Atgo hnd refrctometer (Type 500, Atgo, Tokyo, Jpn) nd expressed s º Brix while totl titrtle cidity (TTA) ws determined y titrtion with 0.1N NOH in the presence of phenolphthlein indictor. TTA results were expressed s % citric cid.
36 Ethylene Production nd Respirtion Depending on the size of determined weight, mngo fruits were plced in plstic jrs rnging in volume from 100ml to12lt whose covers ws fitted with self-seling ruer septum for gs smpling. The fruits were incuted for one hour t room temperture. Gs smples from the hedspce gs were removed using n irtight syringe nd injected into gs chromtogrph (Model GC-8A, Shimdzu Corp., Kyoto, Jpn). The gs chromtogrph for cron dioxide determintion ws fitted with therml conductivity detector nd Poropk Q nd tht for ethylene determintion fitted with n ctivted lumin column nd flme ioniztion detector. Rtes of cron dioxide production were clculted s ml per kg per hr t stndrd tmospheric pressure while, the rtes of ethylene production clculted s ήl per kg per hr Pulp β-crotene Content β-crotene content ws determined y modified chromtogrphic procedure (Heionen, 1990). Twenty grms of fruit pulp ws crushed in pestle with mortr fter dding sptul of hydroflorosupercel. The smple ws extrcted with 50ml cetone until the residue ws white. Prtitioning ws done using 25ml of petroleum ether in seprting funnel to otin the β-crotene rich upper lyer. Sponifiction ws crried out y dding n equl mount of upper lyer extrct in to 3ml of 10% KOH in methnol, nd few drops of 0.1% utyrtehydrotoluene in petroleum ether. The mixture ws kept in the drk for 16 hours fter which it wshed with wter in seprting funnel until
37 it ws cler. Sodium sulphte (nhydrous) ws dded to remove wter nd further concentrtion ws done using rotry evportor. β-crotene content ws determined using HPLC (Model LC-10AS, Shimdzu Corp., Kyoto, Jpn). The conditions were s follows: the moile phse ws cetonitrile: methnol: dichloromethne in the rtio of 70: 10: 20, flow rte: 1.0 ml/min, column: ODS150, injection volume: 10µl, oven temperture, 35 º C nd UV- Visile detector Totl Peel Anthocynin Content Three grms of the peel ws ground nd diluted with 100ml of distilled wter. Sediment ws removed y centrifugtion. The smple ws diluted with the sme mount of uffers ph 1.0 (0.2M KCL nd 0.2M HCL) nd ph 4.5 (1M of sodium cette nd HCL) nd the sornce mesured t 510nm nd 700nm using UV-Vis spectrophotometer (Model UV mini 1240, Kyoto Shimdzu). Smples diluted with the ph 1.0 uffer were left t rest for 15 minutes efore mesurements, wheres the smples diluted with the ph 4.5 uffer were redy for mesurement fter 5 minutes. The corresponding pure uffer solution ws used s reference smple in the spectrophotometer. To correct for turidity (hze) the sornce t 700nm is sutrcted from the sornce t 510nm (the wvelength of mximum sorption). To clculte the difference in sornce etween the smples the following formul ws used: Asornce = (A 510nm ph 1.0 A 700nm ph 1.0 ) (A 510nm ph A 700nm ph 4.5 ) Determintion of nthocynin content ws sed on Lmert- Beer s Lw:
38 A = CL A is the sornce, which is mesured with spectrophotometer. L is the pth length in cm of the spectrophotometer cell. is the molr sornce, physicl constnt for moleculr species in given solvent system t given wvelength. Molr sornce vlues for purified pigments tken from the literture cn e used, mking it unnecessry to determine them. Molr sornce is lso referred to s the molr extinction coefficient. C is the molr concentrtion nd rerrnging the Lmert- Beer s Lw eqution nd multiplying y the moleculr weight (m) of the pigment, the concentrtion in milligrms per liter is determined y: C (mg/l) = A/ L x M x 10 3 x D Where D is the dilution fctor, nd A is the difference in sornce of the smple t mximum sorption (510nm) in the ph 1.0 nd ph 4.5 uffers Chlorophyll Content Chlorophyll content ws determined using the method of Arnon (1949) using UV-Vis spectrophotometer (Model UV mini 1240, Shimdzu corp, Kyoto, Jpn). Totl chlorophyll ws extrcted with 80% cetone, nd totl chlorophyll, chlorophyll nd contents were clculted using McKinney s coefficients fter mesuring sornce t 645nm nd 663 nm in which: Totl chlorophyll content ( g/g) = 20.2A A 663
39 Chlorophyll content ( g/g) = 12.7A A 645 nd Chlorophyll content ( g/g) = 22.9A A Color Assessment Color of oth the pulp nd peel were mesured using Minolt color difference meter (Model CR-200, Osk, Jpn) tht ws clirted with white nd lck stndrd tile. The L*, * nd * coordintes were recorded nd, * nd * vlues converted to hue ngle (H ), where H = [(tn -1 */*)] (McGuire, 1992; Mclelln et l., 1995) Minerl Content Three grms of the pulp nd peel were ech dried in the oven, shed in the muffle furnce nd diluted with 1% HCL. The minerls determined included Mg, K nd C. Anlysis ws done y tomic sorption spectrophotometry (AOAC (Assocition of Officil Anlyticl Chemists)., 1996) method. Phosphorus content ws determined using scoric cid method with the UV- Vis spectrophotometer (Model UV mini 1240, Kyoto Shimdzu) Fruit Firmness The firmness long the equtoril region of the fruit ws determined using rheometer (Model NRM-2010J-CW, Jpn) fitted with n 8 mm proe. Firmness ws expressed s Newton (N) (Joyce et l., 1993; Jing et l., 1999).
40 Ascoric Acid Content Five grms of the pulp ws ground nd diluted to 100ml using 10% trichlorocetic cid (TCA). The indictor (2, 6-Dichlophenolindophenol) ws titrted to 10ml of the fruit pulp filtrte till color chnged. Ascoric cid content ws determined y visul titrtion ccording to AOAC methods (1996) Sttisticl Anlysis Vlues for the vrious tretments were compred using t-test; pired two smples for mens. Genstt (13 th version) sttisticl nlysis ws used.
41 CHAPTER FOUR RESULTS AND DISCUSSION 4.1. Influence of Wter Deficit on the Physiology nd Physico- Chemicl Chrcteristics of Mngo Fruit during Growth nd Development The irrigted mngoes trees flowered one week erlier thn non-irrigted ones. This suggests tht wter stress suppresses flowering in mngoes. Non-irrigted trees were supplied with wter t 42 DAB Length, Dimeter nd Weight Chnges in the size (length nd dimeter) during the growth nd development of fruits from irrigted nd non-irrigted trees re shown in Fig.1. The length incresed lmost linerly nd ws proportionl to DAB till 112 DAB when the reltionship ws roken in oth fruits from irrigted nd non-irrigted trees. After the termintion of the wter stress in 42 DAB, the fruits incresed in length to 110 mm t 112 DAB, the length eing greter thn the length of 107 mm oserved in the fruits from irrigted trees during the sme period. The length nd dimeter of the fruit growth mesured displyed single sigmoid curve nd reched mximum t 140 DAB for oth the fruits from nonirrigted nd irrigted trees. Single sigmoid curve were lso reported during growth nd development of Alphonso mngo (Suhdr nd Surmnym, 1970) nd red fruit (Worrell et l., 1998).
42 Length (mm) Fruits from irrigted trees Fruits from nonirrigted trees A Dimeter (mm) Fruits from the irrigted trees Fruits from the nonirrigted trees Dys fter loom B Figure 1. Length (A) nd dimeter (B) during growth nd development of mngo fruits from irrigted nd non-irrigted trees. The rrows indicte the end of wter stress period. Verticl rs represent SE of the men of 18 replictions. When sent, the SE fll within the dimensions of the symol. denotes period of no significnce difference while denotes period of difference etween the fruits from irrigted nd non-irrigted trees (P<0.05).
43 The chnge in fruit weight during growth followed the typicl sigmoid curve (Fig. 2). The weight chnges of the fruits were miniml etween 0-42 DAB. A similr trend hs een reported during the erly stges of growth nd development of other fruits like Alphonso mngo (Suhdr nd Surmnym, 1970), redfruit (Worrell et l., 1998) nd per (Mwniki et l., 2005). After 42 DAB there ws stedy increse in weights tht ws lmost liner to the increse in DAB, nd the chnges occurred in oth fruits from irrigted nd non-irrigted trees. A similr experiment crried out on fresh weight of mngo fruit cv. Lirf, showed tht weight incresed lmost linerly until 100 DAB nd then tended to slow down (Lechudel et l., 2005). Bollrd (1970) reported tht the mjor increse in fruit fresh weight towrds mturity my e due to n increse in oth cell size nd intercellulr spcing, thus llowing the mximum possile ccumultion of ssimiltes. Mngo fruits from non-irrigted trees hd less weight thn mngo fruits from irrigted trees. Lechudel et l. (2005) found similr results when they studied irrigtion mngement on Kensington fruit. The reduced weight in the nonirrigted tretment is rought out y decrese in wter supply which gretly decreses growth (Tezr et l., 2002). In the long term, wter deficits decreses growth y slowing down the rtes of cell division nd expnsion due to loss of turgor nd incresed synthesis of scisic cid (Lwlor nd Cornic, 2002).
44 Fruits from irrigted trees Fruits from nonirrigted trees 500 Weight (g) Dys fter loom Figure 2. Weight during growth nd development of mngo fruits from irrigted nd non-irrigted trees. The rrow indictes the end of wter stress period. Verticl rs represent SE of the men of 18 replictions. When sent, the SE fll within the dimensions of the symol. denotes period of no significnce difference while denotes period of difference etween the fruits from irrigted nd non-irrigted trees (P<0.05).
45 A deficit in wter supply ffects mny key metolic nd physiologicl processes in plnts, the mechnisms which re still uncler (Tezr et l., 2002). In generl, there ws significnt reduction in fruit size nd weight under wter stress (Hlil et l., 2001). The termintion of wter stress hd very little effect on the weight nd size of the fruits. A high correltion ws oserved etween the increse in length nd dimeter r 2 = nd in the fruits from irrigted nd non-irrigted trees, respectively (Fig. 3). The length correlted to the rise of shoulders while the dimeter correlted to swelling of the cheeks. The correltion shows the fruits ttined hrvestle mturity t 140 to 154 DAB for the fruits from the irrigted trees nd 154 to 168 DAB for the fruits from the non-irrigted trees (Fig 3). This mens tht the fruits re redy for hrvest t length of mm nd dimeter of 85 to 95 mm for the fruits from the irrigted nd length of mm nd dimeter of 92 to 94 mm for the fruits from the non-irrigted. Length nd dimeter re mturity indices mostly used to ssess mturity of mngoes y frmers. The formul of the eqution cn e esily clculted nd therefore used y frmers in determining hrvestle mturity of the mngo fruit. This is definite good mturity index ecuse it is esily crried out, chep nd nondestructive.
46 A Length (mm) y = x R 2 = Length (mm) B y = 1.332x R 2 = Dimeter (mm) Figure 3. The correltion of length verses dimeter of mngo fruits from irrigted (A) nd non-irrigted (B) trees during the growth nd development period.
47 Pulp sugr content The chnges in the reducing sugrs (glucose nd fructose) nd sucrose during the growth nd development of fruits from irrigted nd non-irrigted trees is shown in Fig. 4 nd 5. Glucose decresed etween 70 to 140 DAB ut lter incresed s the fruits pproched mturity. The initil decline in glucose my reflect the high sugr requirements for metolism during the erly developmentl phse or the chnnelling of crohydrtes into strch, s hs een found to occur in redfruit (Worrell et l., 1998). Similr results were oserved in Alphonso mngoes, with the glucose content reching mximum t out 21 dys fter fruit set with slight fll eing oserved fterwrds during fruit growth (Suhdr nd Surmnym, 1970). The eginning of strch hydrolysis t the ltter stges of fruit development could lso explin the high glucose concentrtion oserved in lrger fruit (Lechudel et l., 2005). A sudden increse in glucose corresponds to the ttinment of hrvestle mturity in these mngoes. Fructose incresed throughout the growth nd development period with significnt difference etween the fruits from irrigted nd non-irrigted eing oserved t 140 DAB. A mximum fructose content ( 52 nd 54mg/100g) ws oserved s the fruits from irrigted nd non-irrigted trees pproched mturity where s mximum glucose content of 14 mg/100g ws found for the former nd 16 mg/100g for the ltter.