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Apple is one of the most valuable fruit consumed worldwide due to its excellent quality features and high degree of acceptation by consumers. However, apples are susceptible to various postharvest disorders, leading to significant economic losses. To slow down food decay and provide constant fresh food to the market, postharvest strategies including decreasing the temperature can slows down the metabolism of fruits, but in parallel can also trigger the occurrence of typical chilling injury related disorders. Among all the physiological disorders, superficial scald is one of the most challenging, causing discoloration and skin browning triggering therefore consumers unacceptance. The development of superficial scald in apple fruit is a complex process influenced by various factors, including genetic background, storage conditions and preharvest management practices. Recent research partially disclosed the molecular mechanisms underlying the development of superficial scald in apple fruit. It has been shown that this disorder is associated with the accumulation of reactive oxygen species (ROS) and the oxidation of alfa-farnesene, a sesquiterpene largely considered as a major actor in the onset of this disorder. Various postharvest treatments have been used to control the development of superficial scald in apple fruit, such as including the application of the ethylene competitor 1-methylcyclopropene (1-MCP) or controlled atmosphere storage. This thesis aimed to identify and characterize the genetic factors involved in symptoms development and to disclose the regulation of this phenomenon. To this end, a comparative multidisciplinary study integrating transcriptomics and metabolomics analysis have been performed in a wide range of storage conditions and across different genetic background. The mechanism of action and effectiveness of two preventing strategies, such as the exogenous application of 1-MCP and storage at low oxygen concentration were assessed in two apple cultivars, ‘Granny Smith’ and ‘Ladina’. The metabolite and transcriptomic profiles revealed that 1-MCP treatment actively stimulated the production of unsaturated fatty acids such as oleic acid (C18:1), linoleic acid (C18:2) and linolenic acid (C18:3), thereby successfully preventing the development of superficial scald in ‘Granny Smith’. ‘Ladina’, on the other hand, was less responsive to these strategies and was characterized by a higher accumulation of very long chain fatty acids (VLCFAs), together with an increased level of fatty acid saturation. Additionally, the integration of the transcriptomic survey and VOCs assessment underlined that storage at low oxygen concentration stimulated the expression of genes involved in anaerobic respiration, such as malate, alcohol dehydrogenase, and pyruvate decarboxylase, leading to the accumulation of ethanol and acetaldehyde in both cultivars. The expression of three members of the VII subgroups of ERF genes was also observed in ‘Granny Smith’, which coordinate the acclimation process to hypoxia in plants. The effect of controlled atmosphere in the prevention of superficial scald was furthermore investigated in fruit of ‘Granny Smith’ stored for different time and employing both a static and dynamic controlled atmosphere approach. The transcriptome analysis found that the duration of storage had an important effect on the coordination of gene expression, and the expression patterns of DEGs identified a distinct networks and types of transcriptomic hubs. Samples that developed superficial scald were characterized by higher concentration of chlorogenic acid and a time-specific increase in the expression of PAL and PPO genes. Prevention of superficial scald was related to a peculiar realigning episodes that involved the accumulation of specific antioxidant metabolites, very long chain fatty acids, and the expression of genes that coordinate the hypoxia acclimation process, such as RAP2-like and PCO. A complementary research was conducted to investigate the connection between the application of 1-MCP, low oxygen, and superficial scald. The study highlighted the possible application of genes involved in key fruit ripening pathways, including ethylene-related pathways and sugar/fermentation metabolism, as potential biomarkers for molecular characterization of the major changes that occur during fruit storage. The specific expression of polyphenol oxidase, along with sorbitol-6-phosphate dehydrogenase, were also used to investigate the onset of superficial scald in apples and correlated with the accumulation of the sugar alcohol sorbitol, which plays a protective role against chilling injuries. Assessing the transcriptional signature of these biomarkers can contribute to the development of new tools for a more informed understanding of the physiological progression of postharvest ripening in apples. Overall, these studies provide insights into the genetic and metabolic mechanisms underlying the development and prevention of superficial scald in apple cultivars during storage. The results obtained here paved the way for the identification of a core set of genes to be used as functional marker suitable to better comprehend this phenomenon and to select new accession characterized by a superior fruit quality and postharvest performance.

The purpose of this study was to determine the quality and microbial load of blueberries at different maturity stages, to develop the effective microbial recovery method and to compare sanitation postharvest treatments on microbial counts of blueberries. The soluble solids and the sugar to acid ratio increased, while pH and TA decreased with maturity. Ripe berries had lower yeast and mold counts (YMC) at other maturity stages, but there were no differences on aerobic plate counts (APC). The medium pH was lower for stomaching and blending than hand massaged samples. This leads to higher recovery of microorganisms by massaging. Sodium hypochlorite at 400 ppm was effective in reducing APC but not YMC. Acidified sodium chloride was very effective, lowering APC and YMC below detectable level. All sanitation treatment did not influence sensory attributes of blueberries.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Apples are an important export commodity for the South African market, and postharvest losses that occur as a result of decay due to infection with pathogenic fungi such as Botrytis cinerea Pers., Penicillium expansum (Link) Thom. and Neofabraea alba (E.J. Guthrie) are of major concern for all parties concerned with fruit production and distribution. Decay control of these fungi is primarily managed through the use of synthetic fungicides; however, pathogen development of resistance to these fungicides and recent worldwide concern over healthier living and a greener environment has called for the discriminate use of synthetic chemicals. This has opened up an avenue for the development of safer and more environmentally friendly alternatives to control postharvest decays. The use of plant extracts and essential oils are favoured as natural sources of antimicrobials whilst still being safe for human consumption and having no negative impact on the environment. Allium sativum (garlic) is one such plant species that is well documented for its value in improving human health and is readily available for consumption not just as a flavour component of food but also to be taken as a daily herbal diet supplement. Given the antimicrobial effectiveness of garlic against human pathogens and ailments, its value as an antifungal agent against postharvest pathogens causing grey mould, blue mould and bull’s eye rot of apples was investigated in vitro and in vivo within this study. Furthermore, an attempt was made to elucidate the chemical components of garlic extracts by gas chromatography-mass spectrometry (GC-MS). All experiments in this study were carried out with garlic extracts prepared from fresh garlic bulbs. For the in vitro experiments, two extract preparations of garlic, one containing ethanol (Extract 1) and one where ethanol had been removed by evaporation (Extract 2), was tested for antifungal action within an amended media experimental design. Both extract preparations were each subjected to two dilution series (0-80% garlic extract) with water and ethanol as diluents. Both extract preparations were successful at retarding pathogen mycelial growth and spore germination; however, concentrations of Extract 2 (ethanol evaporated) and diluted with distilled water provided markedly better inhibition of B. cinerea and P. expansum than the ethanolic dilutions of extract 2. Both extract preparations yielded similar inhibitory results when tested against N. alba. Due to the results achieved in the amended media experiments, the use of a crude garlic extract without ethanol and diluted in water was considered to be the best option for further tests throughout the remainder of the study. In vitro volatile effects of crude garlic extracts at concentrations between 0 and 40% garlic extract were subsequently tested. Garlic volatiles were effective in inhibiting pathogen mycelial growth and spore germination of all three pathogens, at lower concentrations compared to the amended media experiments. In vitro volatile exposure with garlic extracts was more effective at inhibiting N. alba than direct application of the extracts. Curative and protective application of garlic extracts and clove oil for increased fungal inhibition through synergism was tested by direct and volatile exposure to the pathogens in vivo on three economically important apple cultivars; ‘Granny Smith’, ‘Golden Delicious’, and ‘Pink Lady’. Direct exposure of artificially wounded and inoculated fruit to the garlic extract and clove oil revealed that garlic extracts applied curatively but not protectively effectively controlled decay caused by B. cinerea and P. expansum on all apple cultivars. Both curative and protective applications were ineffective in controlling N. alba. In vivo volatile exposure to the garlic extracts and clove oil did not inhibit decay on any of the cultivars and was not effective against any of the three pathogens investigated. A full chemical profile analysis was done by GC-MS analysis of garlic extract samples. The compounds diallyl disulphide, allyl methyl trisulphide, allyl methyl disulphide and dimethyl trisulphide were detected in relatively high amounts. This result suggests that the abundance of sulphur and sulphur related compounds detected may be responsible for the antifungal action noted in the experimental studies. In conclusion, garlic was shown to have antifungal activity against B. cinerea, P. expansum and N. alba. The pathogens used in this study were not compared with each other, but undoubtedly each pathogens reacts differently to exposure to the garlic extracts. It would therefore be advisable to investigate the effects of the extracts on each of the pathogens in a more in-depth study. More investigations into the application of the garlic extracts is required before it may be recommended for use; however, results for the use of garlic extracts against these postharvest pathogens and the postharvest decay they cause are promising. / AFRIKAANSE OPSOMMING: Appels is ‘n belangrike uitvoerproduk vir die Suid-Afrikaanse vrugtebedryf, maar noemenswaardige na-oes verliese word weens bederf deur patogeniese swamme soos Botrytis cinerea Pers., Penicillium expansum (Link) Thom. en Neofabraea alba (E.J. Guthrie) ervaar. Dit raak alle partye betrokke met die produksie en verspreiding van hierdie vrugsoort. Hierdie swamme word hoofsaaklik met behulp van kunsmatige swamdoders beheer, alhoewel weerstand-ontwikkeling en wêreldwye bewusmaking van ‘n gesonder leefstyl en omgewing die gebruik van kunsmatige middels streng aanspreek en die ontwikkeling van veiliger en meer omgewingsvriendelike alternatiewe middels verlang. Plant-ekstrakte en essensiële olies kan dien as sulke middels en is natuurlike bronne van anti-mikrobiese aktiwiteit, is veilig vir menslike verbruik en het ook geen negatiewe invloed op die omgewing nie. Allium sativum (knoffel) is so ‘n plantspesie wat as alternatiewe middel gebruik kan word. Dit is bekend vir sy waarde in die verbetering van menslike gesondheid, is maklik bekombaar en word nie net as ‘n geurmiddel vir voedsel gebruik nie, maar ook as ‘n daaglikse krui-aanvulling. Gegewe die anti-mikrobiese doeltreffendheid van knoffel teenoor menslike patogene en kwale, is die werking (in vitro en in vivo) teen na-oes patogene wat grys skimmel, blou skimmel en teikenvrot in appels veroorsaak, in hierdie studie ondersoek. Bepaling van die chemiese samestelling van die knoffel-ekstrak is ook met behulp van gaschromatografie massa spektrometrie (GK-MS) onderneem.Vars knoffelbolle is vir elke eksperiment in hierdie studie gebruik met die voorbereiding van die knoffel-ekstrak. Vir die in vitro eksperiment is twee knoffel-ekstrakte voorberei, naamlik: ‘n ekstrak wat etanol bevat (Ekstrak 1) en een waarvan die etanol verwyder is met verdamping (Ekstrak 2). Die ekstrakte is getoets vir werking teen fungi in kultuur-medium.. Albei ekstrakte is verdun tot twee konsentrasie reekse (0-80%) met water en etanol as verdunningsmiddels. Albei ekstrakte het suksesvolle werking getoon teenoor die patogene ten opsigte van vertraging van miseliumgroei en spoor-ontkieming, alhoewel konsentrasies van Ekstrak 2, verdun met gesuiwerede water, patogene B. cinerea en P. expansum beter onderdruk het as Ekstrak 2 verdunnings met etanol.. Beide ekstrakte en hul afsonderlike verdunnings met etanol en water het soortgelyke resultate gelewer met onderdrukking van N. alba. Volgens resultate wat verkry is van die kultuur-medium eksperimente, is Ekstrak 2 verdun met gesuiwerde water beskou as die geskikste vir verdere toetse in hierdie studie. Die vlugtige effek van Ekstrak 2 is in vitro getoets by konsentrasies tussen 0 tot 40%. Die vlugtige stowwe van knoffel het al drie patogene se groei en spoor-ontkieming effektief onderdrukby laer konsentrasies as wat gebruik is in die kultuur-medium eksperiment. Dus is in vitro blootstelling van N. alba aan die vlugtige stowwe meer effektief as direkte toediening van die ekstrakte. Die voorkomende en beskermende effek van die knoffel-ekstrak, asook naeltjie-olie, is in vivo ondersoek om te bepaal of die stowwe saam sterker onderdrukking van die patogene kon bewerkstellig. Direkte en vlugtige blootstelling is op drie ekonomies-belangrike appel-kultivars getoets, naamlik: ‘Granny Smith’, ‘Golden Delicious’ en ‘Pink Lady’. Direkte blootstelling met die knoffel-ekstrak en naeltjie-olie aan gewonde en ge-inokuleerde vrugte het aangedui dat B. cinerea- en P. Expansum-bederf net beheer kon word indien knoffel voorkomend toegedien is vir al die ondersoekte appel-variëteite. Voorkomende en beskermende toediening was onsuksesvolle om N. alba te beheer. In vivo blootstelling van die drie patogene aan die knoffel-ekstrak en naeltjie-olie se vlugtige stowwe kon nie enige van die patogene effektief onderdruk nie en was onsuksesvol in bederf-beheer. ‘n Volledige chemiese profiel is saamgestel deur GK-MS ontleding van die knoffelekstrakte. Hoë vlakke van verbindings dialliel disulfied, alliel-metiel-tri-sulfied, alliel-metieldisulfied en dimetiel-trisulfied is bespeur. Die aantal vrye sulfied en sulfied-verwante verbindings in die ekstrak kan moontlik ‘n verduideliking bied vir die anti-swam werking waargeneem gedurende hierdie studie. Ten slotte: knoffel toon ‘n anti-swam werking teenoor B. cinerea, P. expansum en N. alba. Die patogene in hierdie studie is nie met mekaar vergelyk nie, omdat elkeen uniek en uiteenlopend op knoffel reageer het. Alhoewel die huidige studie alreeds belowende resultate gelewer het, moet die ekstrak se effek op elke patogeen onderskeidelik nog in diepte ondersoek word, asook die wyse van die toediening in die na-oes praktyk voordat hierdie middel aanbeveel kan word vir gebruik.

Thesis (PhD(Agric))--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Postharvest decay of stone fruit in the Western Cape province of South Africa is caused primarily by Botrytis cinerea (grey mould) and Monilinia laxa (brown rot). Little is known about the relative importance and seasonal occurrence of the two pathogens in nectarine and plum orchards, the mode of penetration of fruits by M laxa, latency and subsequent disease expression by the latter pathogen. These aspects were investigated in this study. By sampling from the Unifruco Quality Evaluation Scheme and from 11 stone fruit orchards, observations were made over a 3-year period of the occurrence of grey mould and brown rot in the major stone fruit regions. Botrytis cinerea was found to be the most important pathogen causing blossom blight and postharvest decay on stone fruit. The pathogen was most prominent on early- and mid-season culti~ars. Brown rot was exclusively caused by M laxa and no evidence was found that M fructicoZa had been introduced into the region. Monilina laxa was most prominent on the later maturing cultivars. Botrytis cinerea blossom infection did not contribute directly to postharvest decay. Both surface inoculum and latent infection consistently occurred on fruit in each orchard, although at fluctuating levels. Disease expression on developing fruit was not governed by the amount of B. cinerea occurring on fruit surfaces, but by the ability of fruit to resist disease expression. The amount of B. cinerea on fruits was generally higher during spring than during summer. Monilinia laxa occurred sporadically on the blossoms of late-maturing cultivars. Immature fruit were generally pathogen-free and disease expression occurred on maturing fruit only. These findings suggest that conidia of M laxa are generally produced in orchards when fruits are approaching maturity and can penetrate and infect maturing fruit only. The behaviour of airborne M laxa conidia was subsequently studied on nectarine (cultivar Flamekist) and plum (cultivar Laetitia) fruit. For these studies, an inoculation method that simulates natural infection by airborne conidia was used. Fruit at pit hardening, 2 wk before harvest, harvest stage and after cold storage (nectarines 4 wk at -o.soC followed by 1 wk at 23°C at ±56% RH; plums 10 days at .....().5°C,18 days at 7.5°C followed by 1 wk at 23°C at ±56% RH) were dusted with dry conidia of M laxa in a settling tower. The fruits were incubated for periods ranging from 3 to 48 h at high relative humidity (2':93%, humid fruit) or covered with a film of water (wet fruit). Behaviour of the solitary conidia was examined with an epifluorescence microscope on skin segments stained in a differential stain containing fluorescein diacetate, aniline blue and blankophor. The ability of solitary conidia to colonise the fruit surface, penetrate fruit skins and to induce disease expression was determined by using a differential set of tests. For these tests, fruit were surface-sterilised (30 s in 70% ethanol) or left Unsterile. From each group, fruit were selected for isolation (skin segment test), immersed in a 3% paraquat solution (paraquat-treated fruit test) or left untreated (sound fruit test). 1be findings demonstrated that solitary conidia of M laxa behaved consistently on plum and nectarine fruit surfaces: appressorium formation and direct penetration was not observed on any of the fruit surfaces and germ tubes penetrated fruit predominantly through stomata, lenticels and microfissures in the fruit skin. The monitoring of airborne conidia revealed subtle effects of the fruits on the behaviour of solitary germlings, which could not be seen when using conidial suspensions. On both fruit types, no deleterious effect was seen on conidial and germling survival when fruit were kept humid at pit hardening, 2 wk before harvest and harvest. However, conidial and germling survival were drastically reduced by prolonged wet incubation of fruits. The findings on disease expression in the skin segment, paraquat-treated fruit and sound fruit tests clearly showed that the skin of both nectarine and plum fruits were not penetrated at the pit hardening stage, latent infections were not established and fruitsreacted resistant to disease expression. These facets on both fruit types were furthermore unaffected by wetness. The barrier capacity of the fruit skin of the two stone fruit types however differed drastically later in the season. On nectarine, fruit skins were more readily penetrated and disease expression became more pronounced when fruit approached maturity. Penetration and disease expression on ripening nectarine fruit were furthermore greatly influenced by wetness. Maturing plum fruit, on the other hand, did not display the drastic change in the barrier capacity of fruit skins as observed on nectarine. The influence of wetness on infection and disease expression was also less pronounced than on nectarine. In fact, plum fruit remained asymptomatic in the sound fruit test after inoculation and humid incubation at the 2 wk before harvest stage, harvest stage and after cold storage. Plum fruit at these stages only developed disease after a prolonged period (~12 h) of wet incubation. The paraquat fruit test revealed that these fruits became more susceptible to latent infection, but they were not as susceptible as nectarine. Collectively, these findings indicate that M. laxa fruit rot epidemics on plum and nectarine are driven by inoculum levels on fruit approaching maturity and by weather conditions prevailing during the preharvest and harvest period. However, the barrier capacity of plum skins is considerably more effective than that of nectarine fruit. Wounds would therefore play an important role in the epidemiology of M. laxa on plum fruit. Infection of fresh wounds by airborne M. laxa conidia, and by conidia and germlings that have established on fruits, was therefore investigated. Plum fruit (cultivar Laetitia) at pit hardening, 2 wk before harvest, harvest stage and after cold storage were dusted with dry conidia of M. laxa in a settling tower.- Infection of rionwounded fruit and of fresh wounds by \ the airborne conidia on dry, humid and wet plum fruit surfaces, and by conidia and germlings that have been established on fruits under the wetness regimes was then investigated. Nonwounded immature and mature fruit remained mostly asymptomatic, whereas nonwounded cold stored fruit decayed readily. Wounding drastically increased infection by airborne conidia. Immature fruits were less susceptible to wound infection by the airborne conidia than mature fruits. Conidia dispersed freshly were more successful in infecting fresh wounds than conidia that were deposited, or germlings that established, on fruit surfaces 4 days prior to wounding. This decrease in infectivity was especially pronounced on humid and even more on wet incubated fruit. This study clearly showed that in order to reduce. the incidence of brown rot, inoculum levels on fruit approaching maturity should be reduced by sanitation practices and fungicide applications. Furthermore, it is essential to protect fruits, especially. near-mature fruits, from being wounded. / AFRIKAANSE OPSOMMING: EPIDEMIOLOGIE VAN MONILINIA LAXA OP NEKTARIEN EN PRUIM: INFEKSIE VAN VRUGTE DEUR KONIDIA OPSOMMING Naoesverrotting van steenvrugte in die Wes-Kaap provinsie van Suid-Afrika word hoofsaaklik veroorsaak deur Botrytis cinerea (vaalvrot) en Monilinia laxa (bruinvrot). Min is bekend oor die relatiewe belang en seisoenale voorkoms van hierdie patogene in nektarienen pruimboorde, asook oor die infeksieweg, latensie en daaropvolgende siekte-uitdrukking van M laxa. Hierdie aspekte is in dié studie nagevors. \ \ Monsters IS oor 'n 3-jaar periode van die Unifruco Kwaliteitsevalueringskema, en ook van 11 steenvrugboorde verkry. Die voorkoms van vaalvrot en bruinvrot in die hoof steenvrugareas is so bepaal. Botrytis cinerea was die belangrikste patogeen wat betref bloeiselversenging en naoesverrotting. Verder was hierdie patogeen ook meer prominent op die vroeë- en middel-seisoen kultivars. Bruinvrot is uitsluitlik deur M Iaxa veroorsaak en geen aanduiding omtrent die moontlike voorkoms van M fructicola in Suid-Afrika is waargeneem nie. Monilinia laxa was meer prominent op die laat-seisoen kultivars. Botrytis cinerea bloeiselinfeksie het nie direk bygedra tot naoesverrotting nie. Beide oppervlakkige inokulum en latente infeksie het deurgaans, maar wel teen wisselende hoeveelhede, op vrugte in die onderskeie boorde voorgekom. Siekte-uitdrukking op ontwikkelende vrugte is egter nie beinvloed deur die hoeveelheid B. cinerea op die vrug nie, maar eerder deur die vermoë van die vrug om siekte-uitdrukking te onderdruk. Die hoeveelheid B. cinerea op vrugte was verder hoër gedurende lente as gedurende somer. Monilinia laxa het slegs sporadies op die bloeisels van laat-seisoen kultivars voorgekom. Groen vrugte was in die algemeen vry van die patogeen en siekte-uitdrukking het slegs op ryp vrugte plaasgevind. Hierdie bevindinge dui daarop dat M laxa in boorde hoofsaaklik op ryper vrugte geproduseer word. Hierdie swam infekteer ook net ryp vrugte. Die gedrag van luggedraagde M laxa conidia is bestudeer op nektarien- (kultivar Flamekist) en pruimvrugte (kultivar Laetitia). 'n Inokulasie-metode wat natuurlike infeksie deur luggedraagde konidia simuleer, is vir hierdie studies gebruik. Vrugte van die pitverharding-, twee weke voor oes-, oesstadium, asook koud-opgebergde vrugte (nektariene, 4 weke by -o.soe gevolg met 1 week by 23°C en ±56% RH; pruime, 10 dae by -O.5°e, 18 dae by 7.Soe gevolg deur 1 week by 23°C en ±56% RH), is met droë konidia in 'n inokulasietoring geïnokuleer. Die vrugte is vir periodes wat gewissel het van 3 tot 48 h geïnkubeer by hoë relatiewe humiditeit (~93% RH, vogtige vrugte), of dit is bedek met'n film water (nat vrugte). Die gedrag van die enkelspore (konidia) op die vrugoppervlak is met 'n epifluorisensiemikroskoop bestudeer. Skilsegmente is gekleur in 'n kleurstof, bevattende fluorisein diasetaat, analien-blou en blankofor. Die vermoë van die enkelspore om die vrugoppervlak te koloniseer, te penetreer en om siekte-uitdrukking te induseer, is met 'n differensiële stel toetse bepaal. Vir hierdie toetse is die vrugte oppervlakkig gesteriliseer (30 s in 70% etanol), of nie-steriel gelaat. In elke groep is vrugte geneem vir isolasie (skilsegment-to\~ts), of gedoop in "n 3% parakwat-oplossing (parakwat vrugtoets), of\, onbehandeld gelaat (onbehandelde vrugtoets ). Die. bevindinge het op die soortgelyke gedrag van M laxa enkelspore op die verskillende vrugsoorte gedui: appressoria en direkte penetrasie is nie waargeneem nie, en kiembuise het die vrugte hoofsaaklik deur huidmondjies, lentiselle en mikro-krakies .in die vrugskil gepenetreer. Deur luggedraagde spore te bestudeer, is sekere subtiele effekte van die vrug op die gedrag van enkelspore op die vrugoppervlak waargeneem. Op beide vrugtipes is geen nadelige effek op konidiurn- en kiembuisoorlewing opgemerk wanneer die vrugte onder hoë vogtoestande geïnkubeer is. Konidiurn- en kiembuisoorlewing is egter drasties verlaag hoe langer die vrugte onder nat toestande geïnkubeer is. Die bevindinge van die skilsegment-, parakwat en onbehandelde vrugtoetse het duidelik daarop gewys dat die vrugskil van nektarien en pruim nie gepenetreer is tydens die pitverhardingstadium nie, latente infeksies is nie gevorm nie, en die vrugte was bestand teen siekte-uitdrukking. Hierdie fasette op beide vrugtipes is ook nie beinvloed deur inkubasie-natheid nie. Die beskermingskapasiteit van die vrugskil van hierdie steenvrugtipes het egter drasties verskil later in die seisoen. Nektarien-vrugskille is meer geredelik gepenetreer en siekte-uitdrukking het toegeneem met rypwording. Penetrasie en siekteuitdrukking is verder in 'n groot mate deur inkubasie-natheid bevoordeel. Rypwordende pruime het egter nie so In drasties verandering in die beskermingskapasiteit van die vrugskil getoon nie. Die invloed van inkubasie-natheid op infeksie en siekte-uitdrukking was ook minder opsigtelik as op nektarien. Pruimvrugte van die twee weke voor oes-, oesstadium, en , koud-opgebergde pruime, wat onder hoë vog geïnkubeer is, het simptoomloos in die onbehandelde vrugtoets gebly. Vrugte van hierdie stadia het slegs simptome ontwikkel na periodes van langer as 12 h onder nat toestande. Die parakwat-behandelde vrugtoets het egter gewys dat die pruimvrugte meer vatbaar vir latente infeksies raak, maar steeds nie so vatbaar soos die nektarienvrugte nie. Gesamentlik dui hierdie bevindinge daarop <41tM laxa bruinvrot epidemies op pruim en nektarien afhanklik is van inokulumvlakke op rypwordende vrugte, asook die weerstoestande gedurende die vooroes- en oesstadia. Die beskermingskapasiteit van pruim vrugskille was egter aansienlik meer effektief as dié van nektarien vrugte. Wonde op vrugte sal dus 'n groter rol speel in die epidemiologic van M laxa op pruim. Infeksie van vars wonde deur luggedraagde M laxa konidia, en deur konidia en kiembuise wat reeds op die vrugoppervlak gevestig is, is gevolglik bestudeer. Pruimvrugte (kultivar Laetitia) van die pitverharding-, twee weke voor oes-, oesstadium, asook koud- \ \ opgebergde vrugte is in 'n inokulasie-toring geïnokuleer met droë M laxa konidia. .Infeksie , , van nie-gewonde vrugte en van vars wonde deur luggedraagde konidia op droë, vogtige en nat pruim vrugoppervlaktes, asook deur konidia en kiembuise wat reeds op die vrugoppervlak onder hierdie toestande gevestig is, is bepaal. Nie-gewonde groen tot ryp vrugte het meestal simptoomloos gebly, terwyl koud-opgebergde ryp vrugte wel verrot het. Wonde .het die hoeveelheid infeksie deur luggedraagde spore drasties vermeerder. Konidia wat geïnokuleer is op vrugte met vars wonde, was meer in staat om hierdie wonde te infekteer as konidia en kiembuise wat 4 dae voor wonding gevestig is. Hierdie afname in infektiwiteit was meer sigbaar op die vogtige, maar veral die nat vrugte. Hierdie studie het duidelik gewys dat inokulumvlakke op rypwordende vrugte verlaag moet word deur sanitasie-praktyke en fungisiedtoedienings. Dit is verder belangrik om vrugte, veral rypwordende vrugte, teen wonding te beskerm.

The influence of uniformity of heat transfer with respect to the effect of heat treatment was investigated by correlating engineering parameters with the quantified heat treatment effects. Differences in treatment effect in terms of quality, anti-pathogen and chilling injury (CI) control properties among commodities was studied by exposing them to different target temperatures. Similar effects were also evaluated and quantified within an individual commodity by a custom-designed device. This device, whose design parameters were based on a heat transfer simulation, insured that one hemisphere of a tomato was exposed to air at 39&deg;C and 0.24 m s-1; while the other hemisphere was exposed to air at a lower temperature with a velocity of0.24 m s-1 or 0.12 m s-1. / Single-temperature heat treatment was most effective in limiting pathogen development and varied according to the parameter measured: 38&deg;C for hypersensitive response (HR), 36&deg;C for tissue breakdown, 36&deg;C, 38&deg;C or 39&deg;C for mycelium abundance, and 38&deg;C or 39&deg;C for lesion size. Bilateral differences in temperature across the fruit significantly affected disease control: decreasing temperature differences significantly improved the uniformity of disease control. / Some of the effects of heat treatment on tomato quality, such as color development and resistance to CI, appear to be localized. A significant difference in redness was identified between heated parts and unheated parts of tomato fruits immediately after treatment; and the differences persisted during storage. Differences in lightness and chroma were noted on day 4. Delay in ripening caused by heat treatment was confirmed through the higher TA and TSS values of heated tomatoes or heated portion of partially heated tomatoes. / The heated parts of tomatoes showed a stronger resistance to chilling injury. The effective temperature control range for CI was wide, but temperatures higher than 39.5&deg;C for 23 h hot air treatment could lead to adverse effects. / Differences in physiological effects between hemispheres in two chambers was reduced by directly decreasing the temperature difference between upper and lower chambers or relatively increasing the heating air flow rate, highlighting the importance of improving the uniformity of air flow around each individual treated fruit.

Post-harvest cane deterioration in the South African sugar industry results in significant revenue loss that is estimated to be in the region of ZAR 60 million per annum. Despite these large losses, precise biological data relating to the process of cane deterioration under South African conditions is limited. Severity of deterioration is influenced by a number of factors, including the length of the harvest-to-crush delay (HTCD), ambient temperature and harvesting practices. For example, burning of cane prior to harvest may result in rind splitting, which provides entry for microbes, particularly Leuconostoc mesenteroides that may exacerbate deterioration. The effect of these factors on deterioration was examined by quantifying the biochemical and microbiological changes that occur in sugarcane stalks after harvest, with the influence of length of HTCD, degree of L. mesenteroides infection and ambient temperature receiving attention. The primary novelty of the work resides in the analysis of deterioration under tightly regulated temperatures, which were designed to reflect diurnal variations typically experienced during summer and winter in the South African sugar belt. In addition, inoculation of mature internodes with a consistent titre of L. mesenteroides was used as a means to mimic a consistent level of infection of harvested stalks by the bacterium. Metabolites selected for analysis were those both native to the stalk and produced as by-products of microbial metabolism, viz. sucrose, glucose, fructose, ethanol, lactic acid, dextran and mannitol. Simulated HTCDs under summer temperatures resulted in increasing glucose and fructose levels with time, which contrasted to the approximately constant levels of these hexose sugars under winter conditions. Commonly referred to as ‘purity’ in an industrial context, precise determination of the concentration of these hexoses in cane consignments could potentially indicate the extent of deterioration. Despite the detection of a basal concentration of lactic acid in unspoiled cane, the observed increase in concentration of this organic acid over the simulated summer HTCD suggests that this metabolite could also potentially serve as an indicator for postharvest deterioration. In contrast, the investigation indicated that ethanol was an unsuitable biochemical marker for deterioration of L. mesenteroides infected cane. An inability to detect dextran and mannitol in the samples, combined with consistent sucrose levels and variable mill room data, suggest that extreme proliferation of L. mesenteroides is facilitated primarily by in-field practices, particularly the manner in which cane is prepared prior to harvest and transport to the mill. Bacterial proliferation and infection by L. mesenteroides of inoculated stalks were monitored by standard selective culturing techniques. Despite the limited detection of L. mesenteroides-associated metabolites, culture-based analyses revealed that the bacterium was the dominant bacterial species within the samples. A number of other bacterial species were isolated and identified, however the extent to which the total number of microorganisms proliferated was limited to a maximum of 1 x 105 colony forming units per gram of fresh tissue. In conjunction with these analyses, a molecular approach known as Polymerase Chain Reaction-Mediated Denaturing Gradient Gel Electrophoresis (PCR-DGGE) was undertaken to investigate the bacterial diversity patterns associated with deteriorating sugarcane stalks throughout the delay period. In contrast to the results obtained by means of the culture-based assays, PCR-DGGE revealed that L. mesenteroides was not the dominant bacterial population, and showed that the level of bacterial diversity was relatively consistent across the differing treatments and with time. The use of complimentary culture-dependent and cultureindependent analyses thus permitted the detection of this discrepancy and indicated the utility of PCR-DGGE in the determination of bacterial community structure of postharvest sugarcane tissue. The biology of post-harvest deterioration of green sugarcane stalks is highly complex, even under rigorously controlled temperature and infection regimens. The results of this study emphasize the important effects that harvest method and environmental conditions have on post-harvest sugarcane deterioration. Towards the formulation of industry-relevant recommendations for combating post-harvest deterioration, future work will strive to mimic the effects that harsh harvesting and transport practices have on the severity of the problem. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

Thesis (MScFoodSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Postharvest fruit loss is a major challenge in addressing food security, sustainable management of resources and profitability of agribusiness. The incidence of postharvest loss and changes in physico-chemical properties of three types of fruit (peaches, pears and oranges) were evaluated at retail and during post-purchase storage. The amount of physical loss at the three retail outlets studied ranged from 3.61% to 18.09% among the fruit types, with the highest incidence occurring in peaches. The estimated annual national physical loss at retail was 418 tons for pears, 1000 tons for oranges, and 7 240 tons for peaches. Based on the WHO recommended 146 kg per capita per year consumption of fruit, the total loss of the three types of fruit was sufficient to meet the dietary fruit requirements of 50 000 people per annum. Similarly, based on the recommended daily allowance of 50 mg of ascorbic acid, these losses could meet the annual vitamin C needs of 82 000 people. The estimated monetary value of the losses at retail ranged from R2.2 million to R96.87 million per annum depending on fruit type and retail outlet. The land wasted to produce lost fruits was 1965 ha while energy wasted was 32.77 x 106 MJ. Greenhouse gas emission of the losses was 2870 tons CO2eq and total water footprint 68 0000 m3. Losses were mainly due to the presence of severe physical damage, rots and physiological disorders. There were significant variations in physico-chemical properties of fruit of the same type from different retail outlet. Although ambient temperature storage improved fruit colour and some chemical constituents responsible for palatability, it was associated with high physical and nutritional (vitamin C) losses. Results from this study show that appropriate harvesting maturity, packaging and maximum care in fruit handling is essential in reducing postharvest losses. Efficient cold chain management and fruit inspection for rots and damages could help to reduce subsequent spoilage at retail and during post-purchase storage. Given that the incidence of postharvest fruit loss observed at retail is the result of cumulative effects along the supply chain, further studies are warranted to map fruit history and magnitude of losses along the value chain. / AFRIKAANSE OPSOMMING: Naoesvrugteverlies is ‟n groot uitdaging in die strewe na voedselsekerheid, volhoubare hulpbronbestuur en winsgewende landbousake. Die voorkoms van naoesverlies sowel as fisiko-chemiese naoesveranderinge by drie vrugtesoorte (perskes, pere en lemoene) is gevolglik by kleinhandelsafsetpunte én gedurende berging ná aankoop beoordeel. Die graad van fisiese verlies by die drie betrokke kleinhandelspunte het gewissel van 3,61% tot 18,09% tussen die vrugtesoorte, met die hoogste verlies by perskes. Die geraamde jaarlikse nasionale fisiese verlies by die kleinhandelspunte was 418 ton pere, 1 000 ton lemoene en 7 240 ton perskes. Op grond van die Wêreldgesondheidsorganisasie se aanbevole jaarlikse vrugte-inname van 146 kg per persoon, was die totale verlies van die drie vrugtesoorte genoeg om aan die vrugtedieetvereistes van 50 000 mense per jaar te voldoen. Op grond van die aanbevole daaglikse inname van 50 mg askorbiensuur, kan hierdie verlies eweneens in die jaarlikse vitamien C-behoeftes van 82 000 mense voorsien. Die geraamde geldwaarde van die verlies by die kleinhandelspunte strek van R2,2 miljoen tot R96,87 miljoen per jaar, na gelang van die vrugtesoort en bepaalde kleinhandelspunt. Die vermorste grond om die verlore vrugte te produseer, was 1 965 ha, terwyl energievermorsing op 32,77 x 106 MJ te staan gekom het. Kweekhuisgasvrystellings met betrekking tot die verlies was 2 870 ton CO2e, en die totale watervoetspoor 68 0000 m3. Vrugteverlies kon hoofsaaklik aan ernstige fisiese skade, verrotting en fisiologiese afwykings toegeskryf word. Daar was beduidende variasies in die fisiko-chemiese eienskappe van dieselfde vrugtesoort by verskillende kleinhandelaars. Hoewel berging by omgewingstemperatuur vrugtekleur en bepaalde chemiese komponente vir smaaklikheid verbeter, word dit ook met groot fisiese en voedingstof- (vitamien C-) verliese verbind. Die resultate van hierdie studie toon dat toepaslike oesrypheid, die regte verpakking en maksimum sorg in vrugtehantering noodsaaklik is om naoesverlies te verminder. Doeltreffende koelkettingbestuur en vrugte-inspeksie vir verrotting en skade kan latere bederf by kleinhandelsafsetpunte sowel as gedurende berging ná aankoop help beperk. Aangesien die naoesvrugteverlies wat by die kleinhandelspunte waargeneem is uit kumulatiewe faktore in die verskaffingsketting spruit, is verdere studies nodig om vrugtegeskiedenis na te spoor en die omvang van die verlies in die algehele waardeketting te bepaal.

Thesis (MScAgric)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Shrivelling and friction discolouration (FD), as postharvest disorders, negatively influence the marketability and potential shelf life of pears. By investigating the contributing factors in each of the disorders, the potential involvement of handling and storage variables were determined. This allowed for a better understanding of the responsible factors that create susceptible environments for these disorders to occur. From the moment that pears are harvested they lose weight by means of transpiration and, to a lesser extent, respiration. When excessive losses are experienced, the fruit will appear shrivelled and the marketability and shelf life are negatively influenced. By minimizing the rates of weight loss, the occurrence of shrivelling among pears during the postharvest handling can be lessened. The periods that proved to be most conducive to shrivelling (during a simulated postharvest handling duration) were where temperatures above 0 °C were experienced. These short periods proved more perilous for shrivelling than lengthy storage durations at low temperatures. This influenced the transpiration rate in such a way that the driving force accelerated the rate of weight loss in all the cultivars that were studied. Removing field heat from fresh produce and maintaining the cold chain reduces the driving force behind the transpiration of the pears. In all the cultivars studied, ‘Packham’s Triumph’, ‘Beurrè Bosc’ and ‘Forelle’, smaller and less mature fruit were more inclined to appear shrivelled. The surface area to volume ratio is fundamental in determining the rate of weight loss. This was most evident in ‘Beurrè Bosc’. Although no reproducible results could be obtained from the morphological studies, literature has attributed this phenomenon to the composition and quantity of the cuticle layer. Reduction of weight loss was obtained by sealing of the fruit stem. This obstructed water movement from the fruit through the xylem conducting tissue to the surrounding atmosphere. Not only did the stem appear greener and fresher, but less weight loss and subsequent shrivel was noticeable in the treated fruit. This effect was most evident in ‘Packham’s Triumph’ and ‘Beurrè Bosc’, but not in ‘Forelle’. ‘Forelle’ typically has a very short, thin stem in comparison to the other two cultivars.All the cultivars showed visual shrivel symptoms after 11 days at 18 °C. Rate of weight loss was the lowest in ‘Packham’s Triumph’, but due to its prominent dimensions, it appeared shrivelled before any of the other cultivars. ‘Beurrè Bosc’ lost weight at the highest rate (0.42%.day-1). As fruit injury, in the presence of oxygen, is inevitable, the oxidative enzymatic browning of pears will always be troublesome. This defensive mechanism partially prevents the infection of the fruit where epidermal cells are injured. To minimize FD, impact and frictional forces need to be lower during both harvesting and handling practices. A laboratory scale method was developed through which reproduceable treatments could be performed, thereby subjecting the fruit to industry related friction, rather than impact, injury. By assessing the discolouration in terms of both extent and intensity, the influence of variables could be determined on both ‘Packham’s Triumph’ and ‘Doyenne du Comice’ pears. As also found in practice, ‘Doyenne du Comice’ proved to be far more susceptible to FD than ‘Packham’s Triumph’, although the activity of the enzyme, polyphenol oxidase (PPO) was found to be higher in the latter. Although no significant difference was found between the FD encountered at fruit temperature of 3 °C and 15 °C, discolouration was greater at the higher temperature. This might be attributed to a greater degree of water loss, lower cell turgidity or higher enzyme activity. Thus, fruit taken from storage and sorted directly thereafter will exhibit less FD. The contribution of condensation forming on the fruit, acting as lubrication, cannot be ignored. Such fruit, with high turgor pressure, might again be more susceptible to bruising which will only be revealed well after the injury. Since enzymes, which include PPO, catalyse biochemical reactions, the availability of sufficient substrate most probably regulates the extent of this biochemical discolouration. Harvesting at optimum maturity and preventing any unnecessary friction will most definitely reduce the occurrence of FD. The ultimate challenge remains to optimize sorting and packing conditions without compromising on fruit quality. / AFRIKAANSE OPSOMMING: Verrimpeling en friksie verbruining (FV), as na-oes defekte, het ’n negatiewe invloed op die bemarkbaarheid en potensiële raklewe van pere. Hierdie studie het die bydraende faktore vir elkeen van die defekte ondersoek. Daar is gepoog om die effek van verskillende hanteringsen opbergingsmetodes op bogenoemde defekte te bepaal. ‘n Beter begrip is verkry van die oorsaaklike faktore wat bydra tot die ontstaan van die betrokke defekte. Direk na die oes van pere, begin die vrug gewig verloor as gevolg van veral transpirasie. Oormatige verliese sal lei tot ’n vrug wat verrimpeld voorkom, met ‘n negatiewe invloed op die bemarkbaarheid en raklewe daarvan. Die voorkoms van die verrimpeling van pere tydens die na-oes hantering van die vrugte, kan verminder word deur vermindering van die tempo van gewigsverlies. Die periodes waartydens die verrimpeling veral voorgekom het, (soos gevind in ’n gesimuleerde na-oes hanteringsmodel) was wanneer temperature bo 0 °C ondervind is. Sulke kort periodes was meer geneig om aanleiding te gee tot verrimpeling as die verlengde periodes van opberging by lae temperature. Sulke periodes van hoër temperature het gelei tot versnelde transpirasie en ’n versnelde tempo van gewigsverlies in al die kultivars wat ondersoek is. Die transpirasietempo van pere kan verlaag word deur die verwydering van veld-hitte en deur die streng behoud van die koue-ketting. In al die kultivars wat ondersoek is, ‘Packham’s Triumph’, ‘Beurrè Bosc’ en ‘Forelle’, is gevind dat die kleiner en minder volwasse vrugte meer geneig was tot verrimpeling. Die oppervlak area tot volume verhouding is krities in die bepaling van die tempo van gewigsverlies. Hierdie bevinding was die prominentste in ‘Beurrè Bosc’. Alhoewel geen beduidende resultate verkry kon word van die morfologiese studies nie, is daar verskeie verwysings in die literatuur wat hierdie verskynsel toeskryf aan die samestelling en hoeveelheid van die kutikula laag. Vermindering van gewigsverlies is verkry deur verseëling van die vrugtestingel. Hierdie tegniek het gelei tot ’n blokkering van die watervloei van die vrug na die omgewing deur die xileem weefsel. Verseëling van die stingel het dit groener en varser laat voorkom, en het ook ’n merkbare vermindering in gewigsverlies en die daaropvolgende verrimpeling tot gevolg gehad. Die effek van stingel-verseëling was die prominentste in ‘Packham’s Triumph’ en‘Beurrè Bosc’. Dit was minder duidelik in ‘Forelle’ wat tipies gekenmerk word deur ‘n baie korter, dun stingel in vergelyking met die ander twee kultivars. Al die kultivars het makroskopiese verrimpeling getoon na ‘n opbergingperiode van 11 dae by 18 °C. Die tempo van gewigsverlies was die laagste in ‘Packham’s Triumph’ alhoewel dit eerste verrimpeld voorgekom het. Dit kan toegeskryf word aan die spesifieke afmetings van hierdie betrokke kultivar. ‘Beurrè Bosc’ het vinnigste gewig verloor (0.42%.dag-1). Aangesien die besering van vrugte, in die aanwesigheid van suurstof, onvermydelik is, sal oksidatiewe, ensiematiese verbruining van pere altyd problematies wees. Hierdie verdedigingsmeganisme voorkom tot ’n mate die infeksie van die vrug wanneer epidermale selle beskadig word. FV kan beperk word deur die vrugte tydens oes en hanteringsprosedures so min as moontlik bloot te stel aan impak en friksie kragte. ’n Laboratorium-model is ontwikkel ter nabootsing van die omstandighede in die industrie. Die vrugte is aan friksie, eerder as impak, onderwerp, soos ondervind in die industrie. Die omvang asook die intensiteit van die verbruining is gemeet in beide ‘Packham’s Triumph’ en ‘Doyenne du Comice’ pere. Op hierdie wyse kon die invloed van die onderskeie veranderlikes in elke kultivar bepaal word. Alhoewel die ensiematiese aktiwiteit van die polifenol oksidase ensiem (PFO) die hoogste in ‘Packham’s Triumph’ was, is gevind dat ‘Doyenne du Comice’ veel meer geneig was tot FV as ‘Packham’s Triumph’. Hierdie bevinding bevestig die verskynsel soos in die praktyk gevind. Alhoewel geen betekenisvolle verskil gevind is tussen FV by vrug temperatuur van 3 °C en 15 °C nie, was daar meer verbruining by die hoër temperatuur. Hierdie verskynsel kan toegeskryf word aan ’n groter mate van waterverlies, laer sel turgiditeit en hoër ensiem aktiwiteit. Dus sal vrugte wat direk na opberging gesorteer word, minder FV toon. Die bydrae van die kondensasie wat op die vrug vorm, en as ’n smeermiddel dien, kan nie geïgnoreer word nie. Sulke vrugte met hoër turgiditeit, mag egter meer vatbaar wees vir kneusing, wat egter eers ’n geruime tyd na die kneusing tevoorverskyn mag kom. Aangesien ensieme, wat PFO insluit, as katalis dien in biochemiese reaksies, sal die beskikbaarheid van voldoende substraat, na alle waarskynlikheid die omvang van die biochemiese verkleuring reguleer.Die oes van pere tydens optimum volwassenheid, en die voorkoming van onnodige friksie sal definitief die voorkoms van FV verminder. Die uitdaging is steeds om sortering- en verpakkingstegnieke verder te verfyn sonder om ’n negatiewe invloed op vrugtekwaliteit te hê.

Thesis (MSc (Horticulture))--University of Stellenbosch, 2006. / Rind breakdown of ‘Nules Clementine’ mandarin (Citrus reticulata Blanco) is a physiological rind disorder that develops during storage. The disorder appears following leakage of essential oil from oil glands in the flavedo, which then leaks into and oxidises the albedo. Oxidised tissue appears as brown spots in the rind. Occurrence of this disorder over the years has caused high financial losses to ‘Clementine’ mandarin producers and exporting companies. Therefore, research aimed at solving this problem was identified as a priority by the citrus industry. Several factors have been reported to be associated with rind breakdown of ‘Clementine’ mandarin fruit, and include environmental factors, fruit maturity at harvest, ethylene gas degreening, storage temperature and storage duration, canopy position where fruit are borne, plant growth regulators, and differences in susceptibility among selections. Practical information has been generated on rind breakdown, but the basic physiology of the disorder is still unresolved. The objective of this study was, therefore, to quantify the effects of various factors on the development of rind breakdown of ‘Nules Clementine’ mandarin fruit, as well as to establish an association between rind pigments and rind antioxidant capacity on the development of this disorder. In this study a series of five experiments was conducted, and included quantifying the differences in susceptibility to rind breakdown between ‘Nules’ and ‘Oroval Clementine’ mandarin fruit, investigating the effects of fruit canopy position, harvest date, ethylene gas degreening, storage temperature and duration on the development of rind breakdown. The effect of these factors on rind pigments and antioxidant capacity was also reported. Generally, ‘Nules’ and ‘Oroval Clementine’ mandarin fruit exhibited similar characteristics at harvest, in terms of maturity and antioxidant capacity. After storage, ‘Nules Clementine’ mandarin developed higher levels of rind breakdown than ‘Oroval Clementine’ mandarin. However, the difference in susceptibility to rind breakdown of ‘Nules’ and ‘Oroval Clementine’ mandarin fruit could not be associated with the antioxidant capacity measured at harvest...