The focus of this thesis is to develop pectin-based edible films for application of fruits and vegetables to extend their post harvest shelf life. Preliminary research demonstrated that edible coatings could effectively extend the shelf life of based avocado and peach. The respiration rate, moisture loss, firmness, chemical parameters and color changed in a lower rate in coated fruits as compared with the control. Pectin-based film formulations were then evaluated to identify the proper type and concentration of pectin, lipids and plasticizers in the film. The effects of pectin, beeswax and sorbitol concentration on water vapor permeability, mechanical properties and opacity of the films were then evaluated using response surface methodology to identify appropriate levels of different components. Results of studies on film structure revealed that water vapor permeability increased by pectin and sorbitol concentration and was decreased by beeswax concentration. Mechanical properties were mainly affected by pectin and sorbitol concentration. Beeswax was the most influential factor that affected opacity which increased with increasing beeswax concentration. / In order to successfully employ these films, their adsorption behavior, thermal and thermomechanical properties were evaluated as a function of moisture content and sorbitol concentration. The adsorption behavior was strongly influenced by sorbitol concentration. Moisture content and sorbitol concentration increased the films elongation at break, but decreased tensile strength, modulus of elasticity and Tg, and increased water vapor permeability of the films. Finally, avocado was coated with a pectin-based film and the associated quality changes were evaluated during storage. From storage studies, kinetic parameters (rate constants) and activation energy were quantified to help model the quality changes in avocado quality as function of storage temperature and time. Pectin-based coating resulted in slowing down the rate of quality changes in avocado at each storage temperature. In general, most changes were well described by some form of zero or first order rate. Temperature sensitivity of rate constant was adequately described by the Arrhenius model. / A hyperspectral imaging technique was also used to gather additional tools for following quality changes associated with stored avocados. Artificial neural network (ANN) concepts were evaluated as alternated models for predicting quality changes in coated and non-coated avocados during storage at different temperature. Modeling of quality changes in avocado indicated that compared to conventional mathematical models, ANN has more feasibility to predict of these changes. Models developed for firmness, weight loss and total color difference had better fitness than respiration rate. / Finally, the effect of coating on disease severity and different properties of avocados infected by Lasiodiplodia theobromae was studied. The coated fruits demonstrated slower rate of disease progress, respiration rate, softening and color changes. Respiration rate, firmness and color parameters were sensitive to coating and disease severity, and thus these parameters could successfully used to predict fruit quality from disease in coated and uncoated avocados.

Thesis (Ph. D.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 120-148). / Also available by subscription via World Wide Web / xv, 148 leaves, bound col. ill., col. charts 29 cm

Thesis (MScFoodSc )--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The development of science-based management tools and appropriate postharvest handling protocols are required for the determination of optimal storage performance of pomegranate fruit. The South African pomegranate industry experiences considerable fruit quality losses due to the lack of knowledge on optimal storage and handling practices. The cultivar ‘Wonderful’ is the widely grown in South Africa; however, to date there is currently limited scientific knowledge on the storage requirements. To develop quality standards for the export market, knowledge of optimum storage conditions are required to provide an understanding of postharvest quality attributes and consumer organoleptic perceptions. The overall aim of this research was to provide science-based management tools for the storage performance of pomegranate fruit (cv. Wonderful). The research reported in Chapter 3 focused on the physiological responses of pomegranate fruit at different storage temperatures. Commercially harvested fruit were stored at 5±0.7°C, 7.5±0.3°C and 10±0.5°C with 92±2% RH and at room temperature (21±3°C, 65±6% RH) for 5 months. Fruit respiration and physiological disorders during long term storage were investigated. During storage, low temperatures evidently resulted in lower respiration rates; however, respiration rate increased gradually after 2 months resulting in higher respiration rates at 5°C than 7.5°C after 3 month storage period. Overall, fruit became more susceptible to internal and external disorders as storage period progressed. Storage of fruit longer than 2 months at 5°C resulted in chilling injury and this was observed over the 5 month storage period. Fruit stored at 21°C and 10°C were discarded after 1 and 4 months, respectively, due to complete fruit loss to decay and peel shrinkage. Furthermore, the severity of browning increased with storage temperatures, although this became more severe at 5°C after 3 months. Therefore, to maintain a relatively low respiration rate and minimize physiological disorders, the cv. Wonderful should be stored at 5°C and >92% RH for storage period up to 3 months. In Chapter 4, the effects of temperature and storage duration on pomegranate fruit quality and mechanical properties were conducted. This study revealed that weight loss increased with rise in temperature and storage duration with the primary source of moisture loss being the fruit skin (peel), which resulted in significant reduction in peel thickness with prolonged storage period. The CIE (L*, a*, b* and C*) colour parameters of fruit and arils decreased during storage. However, the hue (hº) for whole fruit increased as a result of browning incidence, and decreased in arils suggesting an increase in redness. Significant increases in total soluble solids (TSS), pH, TSS:TA and BrimA were observed with significant decreases in titratable acidity (TA) occurring throughout the storage period. Storage temperature and duration significantly affected majority of the investigated mechanical properties. Puncture resistance, fruit and aril compression strength decreased with storage temperature and duration. These findings showed that fruit may be stored between 2 to 3 months at 5°C to ensure the best internal and external quality attributes. The studies in Chapter 5 investigated the effects of storage temperature and duration on phytochemical and antioxidant properties. Fresh pomegranate juice was assessed for concentrations of total phenolic compounds, total anthocyanin and ascorbic acid. The antioxidant property of the fruit juice was tested against 2, 2-diphenyl–1–picryl hydrazyl (DPPH). The results showed that total phenolic and total anthocyanin concentration increased up to 3 months of storage at 5°C, 7.5°C, 10°C and 21°C and decreased gradually over time. For antioxidant activity, storage of fruit at 5°C, 7.5°C and 10°C significantly (p< 0.05) reduced the radical scavenging activity of juice by more than 56% when stored beyond 2 months. Furthermore, ascorbic acid concentration gradually declined with increasing storage duration, resulting in reduced juice antioxidant capacity. These findings are beneficial to pomegranate export industries, especially where fruit are stored for long for use in health-promoting purposes. The research conducted in Chapter 6 focused on determining suitable storage conditions based on the combination of instrumental measurements and sensory attributes. During storage, individual fruit were evaluated by trained sensory panel based on the overall appearance, taste and aril texture. Discriminant analysis at different storage temperatures was used to distinguish fruit from each other at 2 months of storage with sensory attributes such as overall pomegranate flavour (R2 = 0.56), total anthocyanin (R2 = 0.46) and Chroma (C*) colour index (R2 = 0.37). Discriminant analysis further showed that storage time rather than storage temperature led to the reduction in overall quality when storing fruit beyond 2 months. Based on sensory attributes, suitable storage temperature and duration were found to be 5°C and 2 months when overall flavor were highly rated; thereafter, significant reductions in overall appearance, aril and kernel texture were observed. Furthermore, the proposed storage conditions were supported with instrumental measurements, which revealed a decline in important fruit attributes such as total phenolics, total anthocyanin, aril colour and aril texture after 2 months of storage. Overall, this study provides science-based tools required for developing cold chain handling protocols needed to manage the long supply chain of ‘Wonderful’ pomegranate fruit grown in South Africa. / AFRIKAANSE OPSOMMING: Die ontwikkeling van wetenskap-baseerde beheerinstrumente en toepaslike na-oes hanteringsmetodes is nodig vir die vasstelling van die optimale stoorprestasie van granate. Die Suid-Afrikaanse granaatindustrie ondervind groot vrug kwaliteit verliese as gevolg van die gebrek aan kennis oor optimale stoor en hantering praktyke. Die kultivar Wonderful is die wyd gegroei in Suid-Afrika, maar tot hede daar is tans beperk wetenskaplike kennis oor die stoor vereistes. Om gehaltestandaarde vir die uitvoermark te ontwikkel word kennis van die optimale stoortoestande benodig sodat ’n begrip van die na-oes gehalte-kenmerke en verbruiker se organoleptiese persepsies gevorm kan word. Die oorhoofse doelwit van die navorsing is om wetenskap-baseerde beheerinstrumente vir die stoor van granate (bv. Wonderful) te verskaf. Die navorsing wat in Hoofstuk 3 beskryf word is gerig op die fisiologiese respons van granate op verskillende bergingtemperatuur. Kommersieel-gekweekte vrugte is by 5±0.7°C, 7.5±0.3°C en 10±0.5°C met 92±2% RH en by kamertemperatuur by (21±3°C, 65±6% RH) vir 5 maande gestoor. Die respirasie van die vrugte en die fisiologiese ongesteldhede gedurende langtermyn stoor word ondersoek. Gedurende stoor het die laer temperature gelei tot laer respirasie koerse; maar respirasie koers het geleidelik na 2 maande verhoog wat lei tot hoër respirasie koerse by 5°C as teen 7.5°C na ’n 3-maande stoorperiode. Algehele, vrugte het egter meer vatbaar geword vir interne en eksterne ongesteldhede hoe langer die stoortydperk geduur het. Die stoor van vrugte langer as 2 maande teen 5°C lei tot skade as gevolg van verkoeling en dit is oor die 5 maande stoor tydperk waargeneem. Vrugte wat teen 21°C en 10°C gestoor is moes na onderskeidelik 1 tot 4 maande as gevolg van verlies wat die gevolg was van swam skade en skil krimping, weggegooi word. Die erns van die verbruining het verhoog toe die stoortemperature verhoog, alhoewel dit meer geraak het teen 5°C na 3 maande. Om dus ’n betreklik lae respirasie koers en min fisiologiese probleme te verseker, moet die kultivaar Wonderful teen 5°C en >92% RH vir 3 maande gestoor word. In Hoofstuk 4 word die effek van temperatuur en die duur van stoor op die gehalte van die granate en die meganiese eienskappe gemeet. Daar is bevind dat gewigsverlies met verhoogte toename in temperatuur en langer stoorperiodes toeneem en dat die hoofbron van verlies aan vog die skil van die vrug is. Die gevolg hiervan is ’n betekenisvolle reduksie in die dikte van die skil na ’n lang stoorperiode. Die CIE (L*, a*, b* and C*) kleur parameters van vrugte en granaatpitte het tydens stoor verminder. Die tint, (hº) van die hele vrug het as gevolg van verbruining, verhoog en het verminder in granaatpitte wat daarop dui vermeerdering in rooiheid. Daar was betekenisvolle verhogings in die totale oplosbare vaste stowwe (TSS), pH, TSS:TA en BrimA is opgemerk met betekenisvolle vermindering in asiditeit waarvan die waarde bepaal kan word (TA) en wat tydens die stoortydperk plaasvind. Stoortemperatuur en die duur van die stoor het ’n groot invloed gehad op die meganiese kenmerke wat ondersoek is. Weerstand teen priken die kompressie krag van die vrugte en die granaatpitte het met verhoogde temperatuur en duur van stoor afgeneem. Hierdie bevindinge het getoon dat vrugte kan gestoor word tussen 2 tot 3 maande by 5°C die beste interne en eksterne kwaliteit eienskappe om te verseker. In hoofstuk 5 is die effek van stoortemperatuur en duur op die fitochemiese en antioksidant kenmerke ondersoek. Vars granaatsap is ondersoek en ramings is gemaak t.o.v. totale konsentrasies van fenoliese samestellings, totale antosianiene en askorbinesuur. Die antioksidant kenmerke van die vrugtesap is getoets vir met 2, 2-diphenyl–1–picryl hydrazyl (DPPH). Daar is bevind dat die totale fenoliese en totale antosianiene konsentrasies tot by 3 maandemaande van stoor teen 5°C, 7.5°C, 10°C and 21°C toegeneem het en toe mettertyd afgeneem het. Wat betref antioksidant aktiwiteit, is daar gevind dat die stoor van vrugte teen 5°C, 7.5°C en 10°C die radikale reinigingsaktiviteite van die sap betekenisvol (p< 0.05) met meer as 56% verminder as dit vir meer as 2 maande gestoor word. Verder, askorbiensuur konsentrasie geleidelik afgeneem met toenemende stoor duur, wat lei tot verlaagde sap antioksidant kapasiteit. Hierdie bevindings is van belang vir die granaatuitvoerindustrie, veral waar vrugte vir 'n lang tydperk gestoor vir gebruik in gesondheids-bevordering doeleindes. Die navorsing wat in hoofstuk 6 beskryf is, het gefokus op die vasstelling van geskikte stoortoestande baseer op ’n kombinasie van instrumentale meting en sensoriese kenmerke. Gedurende stoor word individuele vrugte deur ’n opgeleide panel evalueer t.o.v. voorkoms, smaak en tekstuur van die granaatpitte. Diskriminantontleding teen verskillende stoor temperature is gebruik om vrugte na 2 maande stoor vrugte t.o.v sensoriese kenmerke soos algehele granaat smaak. (R2 = 0.56), totale antosianiene (R2 = 0.46) en Chroma (C*) kleur indeks (R2 = 0.37) te onderskei. Diskriminantontleding het verder getoon dat die duur van die stoor en nie die stoortemperatuur nie, gelei het tot die reduksie in algehele gehalte as die vrugte vir langer as 2 maande gestoor word. Gegrond op sensoriese eienskappe is geskik stoor temperatuur en duur gevind word by 5°C en 2 maande wanneer algehele geur was as hoog beoordeel; en daarna, is aansienlike vermindering in die algehele voorkoms, en die tekstuur van die granaatpitte afgeneem. Hierdie voorgestelde stoortoestande word ook ondersteun deur instrumentele meting, wat ’n afname in belangrike kenmerke soos totale fenologie, totale antosianiene en die kleur en tekstuur van die granaatpitte na ’n 2 maande stoorperiode toon. In die geheel verskaf die bevindinge van hierdie studie wetenskap-baseerde instrumente vir die ontwikkel van koue-ketting hantering protokol vir die bestuur van die lang verskaffingsketting van Wonderful granate wat in Suid-Afrika gekweek word.

El procesamiento post cosecha en maca (Lepidium meyenii) es clave en la generación del perfil metabólico que resulta en sus propiedades nutracéuticas tan conocidas. En este artículo se describe los distintos procesos metabólicos responsables de la generación de productos bioactivos clave. / Maca’s (Lepidium  meyenii) post harvest processing is key in generating a metabolic profile that will result in its well reported nutraceutical properties. This article presents how different metabolic processes generate these changes.

M.Sc. / Loss of quality occurs when tomatoes are stored for more than approximately 3-5 weeks at 12 °C. The most common disorders found in tomatoes during storage are colour development to an unacceptable shade of red, softening, shrivelling due to moisture loss, loss of flavour and fungal infections. Storage life of tomatoes is generally extended by storage under refrigeration. Further, extension of shelf life can be achieved by modified atmosphere packaging (MAP). This is done by sealing actively respiring produce in polymeric film packages to modify the 0, and CO, levels within the package atmosphere. Also, 1-methylcyclopropene (1-MCP) has been proven to be an effective postharvest treatment to prolong the storage life of tomatoes. In the present study four trails were conducted. In the first trial the effects of 1-MCP dosage rate and the colour stage of harvest on the quality of `Santa' tomatoes stored for 4 weeks at 12 °C were investigated. The results indicated that ripening related changes were delayed following 1-MCP treatment. 1-MCP treated fruit were firmer, had reduced TA losses, slower colour development, and reduced physiological disorders associated with long term storage. The stage of ripeness influenced the efficacy of 1-MCP on slowing down the tomato ripening process. 1-MCP was of little benefit for fruit treated at stage 4 of ripeness. In contrast, particularly when the 1-MCP dosage was high, 1-MCP markedly delayed ripening in fruit harvested at colour stage 2 and 3, but the quality attributes such as SSC were better in treated fruits harvested at stage 3. Relatively little difference was observed between 250 and 500 nL.L -I 1-MCP and thus 500 nL.Con fruit harvested at stage 3 of ripeness was used in the remaining experiments. Effects of MAP, 1-MCP and imazalil either as combined treatments or as single treatments were studied for their effect on the quality of tomatoes. Ripening related changes were delayed and loss of weight was significantly reduced following 1-MCP treatment and MA packaging in 17 gm thickness bags. Elevated CO, in MAP after a long storage period induced anaerobic metabolism with the generation of off-odurs and the proliferation of anaerobic microbes. Selected doses of imazalil (0, 0.5, 0.05, 0.005 and 0.0005 g.L.1 ) were evaluated for their effect on the fungal infections on tomato fruits. Imazalil at a rate of 0.005 g.L"' was found to reduce fungal infections by 50% when used in combination with MAP and 1-MCP. The combination of imazalil and MAP therefore appears to be the best treatment combination to facilitate export of 'Santa' tomatoes by sea. However, with regards to reducing the loss of TA, treatment with 1-MCP would be beneficial.

Seasonal variations had a great influence on the ripening patterns of banana fruit. Normal ripening was enhanced or delayed by the effect of the maturing season on the fruit. Fruit maturing in summer (harvested in autumn) showed an increase in the rate of ripening, while fruit harvested in winter and spring showed a decrease in the rate of ripening. The banana fruit are sensitive to temperatures outside of their acclimated range. Due to ineffective storage and faulty handling procedures, cold and heat stress is a universal problem in bananas. Large amounts of fruit are lost due to heat and cold stress. Chilling injury occurs when bananas experience or are stored at temperatures below 13C, for a few hours to a few days. Temperatures slightly above 30C may cause extensive heat damage. The three main mechanisms suggested for the prevention of chilling and heat injury are the synthesis of small heat shock proteins, changes in the saturation of fatty acids of the membranes and suppression of the ethylene production and respiration rates. The prevention of cold and heat stress is investigated by monitoring the effect of short-term heat treatment and treatment with ethylene inhibitors on the ripening of the fruit. To determine changes in ripening the following eight ripening parameters are monitored: Yellowing, firmness of the pulp, sugar concentration, starch content, ethylene synthesis, respiration rate, rate of moisture loss and ion leakage. It was found that 1-methylcyclopropene (1-MCP) alleviates the symptoms of heat injury up to a point, but the symptoms of chilling injury were not affected. The effects of the three temperatures investigated: 35°C, 40°C and 45°C for different times. A short pre-heat treatment of 35˚C for 20 minutes proved successful to delay the ripening of the banana fruit, but did not protect the fruit against heat or chilling injury. The results of this study clearly indicate that both chilling and heat injury involve the action of ethylene and suggested that longer exposures to 1-MCP may be effective in preventing both types of injury. / Prof. C.S. Whitehead

Tomatoes (Lycopersicon esculentum cv. Santa) are climacteric fruit that continue to ripen after harvest. Once the fruit are separated from the plant, the physiological reactions that control the ripening process are altered, so that tomato quality is altered. The earlier the stage of ripening at harvest, the larger the discrepancy between the tomatoes left to ripen on the plant and those harvested while still unripe. Quality is lost as the tomatoes lose moisture, firmness, nutrients and stored carbohydrates. Other aspects such as colour and flavour development and cell wall modifications also affect the quality of unripe harvested tomatoes. Environmental factors that affect the postharvest quality include the temperature, humidity and atmospheric conditions in which the tomatoes are stored. Hormonal manipulation (introducing or blocking ethylene) also has an effect on the final fruit quality. This research project concentrated on the changes that occur in quality during post harvest ripening. Comparisons were made on how different post harvest treatments and storage protocols influenced the quality and longevity of tomato fruit. The purpose of this study was to determine storage conditions that would prolong the shelflife of tomatoes so that they can be acceptable for consumption for up to 40 days after harvest. The best results were obtained from tomatoes that had not completely turned red at time of harvest. These tomatoes could maintain their acceptability best when they were stored at 12°C under controlled atmosphere conditions. 1-MCP treatment was also effective in limiting quality losses for up to a week after harvest, and avoiding exposure to ethylene gas can also be recommended. Heat treatment was not at all successful in improving the longevity of the fruit. / Prof. C.S. Whitehead

Please read the abstract in the section 06resume.pdf of this document / Dissertation (MSc (Plant Pathology))--University of Pretoria, 2007. / Microbiology and Plant Pathology / unrestricted

Avocados are an economically important crop in South Africa and are mainly exported to Europe. As with any other tropical and subtropical crop, avocados are prone to pre- and postharvest diseases. Until recently, chemical control was the only effective measure to control fungal avocado pathogens In 1987, a Bacillus subtilis isolate was found that showed promise as a biocontrol agent in both pre- and postharvest applications to control postharvest diseases. However, over time variable results has been obtained in semi commercial trials. From the original B. subtilis isolate several subcultures have been made and used over a 15 year period in various experimental trials. The dual culture technique was used to compare the biocontrol activity of the subcultures against postharvest pathogens (Colletotrichum gloeosporioides, Phomopsis perseae, Dothiorella aromatica and Lasiodiplodia theobromae). The subcultures differed significantly in their effectiveness and genetic stability. No difference between the subcultures could be found when DNA fingerprinting using RISA PCR was used. The most effective subculture, MI-14, was used in further studies. The mode of action employed by a biocontrol agent is of utmost importance and can be used to enhance its efficacy. In a previous study it was hypothesized that antibiosis as well as competition for nutrients and space is the modes of action involved in biocontrol of B. subtilis against postharvest pathogens of avocado. The direct interaction between B. subtilis and C. gloeosporioides on avocado fruit were observed using scanning electron microscopy. Cells of B. subtilis were observed to colonize the hyphae of C gloeosporioides. In some instances, hyphal walls were lysed in the presence of B. subtilis and may be due to the presence of enzymes or antibiotic substances. Conidia of C. gloeosporioides did not germinate in the presence of B. subtilis. Diffusible inhibitory metabolites active against C. gloeosporioides were produced in vitro by B. subtilis. Inhibitory volatile substances were also produced by B. subtilis and were found to be active against P. perseae, D. aromatica and L. theobromae but not C. gloeosporioides. Siderophores production as well as chitinase, amylase, lipase and proteinase activity were also observed and may play a role in antagonism. Antibiotic production by B. subtilis is a well-known phenomenon. Most antibiotics are polypeptides and lipopeptides. The involvement of phenolic metabilites in biocontrol by B subtilis is less known. A seven-day-old culture of B. subtilis in a minimal medium was analyzed for the presence of free acid phenolic compounds active against fungi. Free acid phenolic metabolites were found and separated using layer chromatography. TLC plates containing the separated spots were sprayed with Clasdosporium cladosporioides and plates were observed for inhibition zones. The phenolic substances were present at 7.06 ± 0.95 mg gallic acid ml-1. The phenolic substances fall in the hydroxycinamic acid group due to their fluorescent coloring under UV at 350 nm. The mode of action involved is also influenced by environmental factors. The effect of temperature and carbon- and nitrogen sources of the in vitro inhibitory activity of B. subtilis against C. gloeosporioides, P. perseae, D. aromatica and L. theobromae were investigated using the dual culture technique. The most effective temperature range for B. subtilis was found to be between 20 and 37°C. At temperatures lower than 15°C, B. subtilis was found to be not very effective, suggesting why postharvest applications followed directly by cold storage do not always work effectively. D-arabinose and D-(+)-mannitol evaluated as carbon source as well as L-glutamic acid, L-glutamine and L-(+)-asparagine used as nitrogen sources support in vitro antagonism against the pathogens most effectively. They also do not support the growth of C. gloeosporioides, P. perseae, D. aromatica and L. theobromae. These nutrients can potentially be the most effective ones to incorporate in commercial B. subtilis formulations. The study showed the potential role of antagonistic free acid phenolic substances, volatiles and siderophores on inhibition of fungal avocado pathogens. Further studies to confirm their in situ activity are required. In conclusion, various factors affect the efficacy of B. subtilis against postharvest pathogens of avocado. These factors should be kept in mind when applying the commercial product in order to achieve the best results. / Dissertation (MSc (Microbiology))--University of Pretoria, 2011. / Microbiology and Plant Pathology / unrestricted

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