Past research conducted by our lab demonstrated that potatoes contain significant levels of phytochemicals important to human health. However, since potatoes are not consumed raw, it is important to determine the effects of processing on these levels. Therefore, the changes in carotenoid content, antioxidant activity, and phenolic content were investigated using combinations of cultivars, cooking methods, storage treatments, and low-dose ionizing irradiation. Carotenoid content was measured via absorbance at 445 nm, 450 nm, and HPLC identification. Antioxidant activity was measured initially and at stabilization via the DPPH method and phenolic content was measured via the Folin method and HPLC identification. Microwaved, baked, fried, and raw potato samples contained more carotenoids than boiled samples. The samples microwaved, baked, and fried contained higher antioxidant activity and phenolics than the boiled or raw samples. However, the compound quercetin dihydrate appeared to decrease with cooking. Carotenoids, antioxidant activity, and phenolics appeared to decrease with storage; however, high storage temperatures and long storage times were believed to cause a dehydration and concentration of compounds, which caused levels to be equal to or greater than before storage. However, this decreasing trend was not linear and there were multiple significant interactions. The compound chlorogenic acid appeared to be quite sensitive to high temperature storage. Irradiation dose appeared to have only a minor, if any, effect on carotenoid levels. The interaction between storage time and irradiation dose was very influential on antioxidant activity. In early stages of storage, higher doses of irradiation had greater antioxidant activity, while, with continued storage, low doses had higher antioxidant activity. Exposure to irradiation appeared to cause an increase in phenolic content, determined by the Folin method. There may be a stimulation, induction, or release of some compounds due to processing; however, its magnitude is not believed to be as great as genetic control. The effects of processing can not be denied and should continue to be investigated. Future studies investigating the health properties of fruits and vegetables, particularly potatoes should include processing effects.

Simple technologies are required for reducing the post harvest losses of horticultural produce. Edible films are being studied extensively for application on fresh and cut fruits and vegetables. Tomato, being a very nutritious and important food and a highly perishable climacteric fruit, this study was planned to investigate the application of chitosan films. Chitosan is a biodegradable waste product from sea food and is safe for consumption. With a view to broaden its antimicrobial activity it was combined with lysozyme, a lytic enzyme. Since the edible films are sensitive to changes in temperature and humidity, they were studied under ambient and optimal conditions of storage. / This study showed that 1% chitosan was more suitable for tomatoes for storage at both conditions of ambient and low temperature. Respiration study showed that 1% chitosan treatments resulted in more favorable levels of CO 2 production and internal O2. This was reflected in the quality of tomatoes held under these conditions. Two per cent chitosan films were unsuitable due to their high CO2 production and low internal O 2 levels. Spoilage was more apparent in this treatment. Lysozyme addition did not show any additional benefit. / The research in this study has demonstrated that the selection of edible films for horticultural produce needs to be integrated with the requirement of storage conditions of the produce.

Sweet corn is classified among highly perishable horticultural commodities. Thus, it can be deteriorated rapidly after harvest resulting in high loss and poorer produce quality. Sweet corn's sugar loss is about four times higher at 10°C compared to 0°C. Precooling, immediately after harvest, has shown to be an effective method to maintain the quality for a wide range of fresh fruits and vegetables during storage. Further, this method leads to reduction in metabolism and respiration rate of the produce, retardation of its senescence, and inhibition of growth of pathogens. In addition to diminishing postharvest losses of the produce, efficient precooling is required for increasing the length of duration of marketing time for better profitability. / Precooling of sweet corn was accomplished by three main methods including forced-air, water and vacuum cooling. Operating parameters such as temperature, pressure, orientation of corn cobs, air flow rate and water flow pattern were defined and studied for optimization. The assessment and comparison of the performance of precooling systems was achieved by determining the effect of these parameters on half cooling time and quality of the produce during storage for 7 and 21 days at 1°C and 90-95% RH. In addition, room cooling method was also tested and compared to the three precooling systems. The use of three sweet corn cultivars was important to compare their quality response to different cooling methods. / Experiments were performed on a lab-scale vacuum cooler and modified forced-air and water cooler systems. The results showed that changing the cob orientation perpendicular to the direction of flow medium, using higher air flow rate in forced-air cooling and immersed water flow pattern in water cooling, can significantly reduce the half cooling time of the produce. Finally, the best method to be recommended for precooling sweet corn is by using hydrocooling which results in superior quality produce and minimum time.

The market life of many fruits and vegetables can be extended through storage at low temperatures. Chilling injury (CI) is a major postharvest storage problem for tropical commodities. Storing these products at temperatures below their critical temperature may result in severe physiological disorders known as CI symptoms. Mangoes (Mangifera indica. L) are susceptible to CI when stored below 12 °C. Visual CI symptoms include uneven ripening, surface pitting, discoloration, shriveling and scalding. Research has been conducted to overcome these serious problems using various postharvest treatments such as hot water, methyl jasmonate (MJ) or diphenylamine (DPA) with some reduction of the incidence of CI symptoms in fruits and vegetables. / Experiments were performed to assess and compare the potential of the above-mentioned postharvest treatments to reduce the CI symptoms on mango cv. Kent. The obtained results indicated that MJ- and DPA-treatments gave significantly greater percentage of marketable fruits. / Experiments were also conducted with mangoes cv. Tommy Atkins treated with MJ and DPA before storing at low temperatures (1, 4, 7 and 10°C). The chemical treatments were successful at reducing CI symptoms of mangoes. Fruit decay was reduced during subsequent ripening. MJ-treated fruits had lower mass loss and higher total soluble solids (TSS) than the control treatment. The overall quality of MJ- and DPA-treated fruits was good with lower surface pitting and scalding compared with the control treatment. The best results were obtained at storage temperatures of 7 and 10°C. Both MJ and DPA postharvest treatments can reduce CI symptoms in mangoes cvs. Kent and Tommy Atkins when the mangoes are stored at below critical temperature.

A replacement for silver thiosulphate as a commercial post-harvest treatment needs to be found. The longevity of cut carnation flowers is extended by all concentrations of ethanol tested. Compared to a water control, the vase-life of ethanol-treated flowers is between 150 and 250% longer. The greatest longevity increases are recorded with 3% ethanol. The use of ethanol as a post-harvest treatment was tested. The longevity increase as a result of ethanol application only occurs if the ethanol is applied as a holding solution. Pulse treatments are not effective at delaying the senescence of the flowers. The sooner the ethanol is applied, the greater the increase in vase life. If ethanol treatment is halted at any point during the experiment, the longevity of the flowers is reduced. It was observed that the longer the stems of ethanol-treated flowers, the greater the longevity increases. The ethanol holding solution does not prevent the action of external ethylene, thereby restricting the potential of ethanol as a commercial post-harvest treatment. Physiologically, flowers treated with ethanol exhibit a different senescence process to control flowers. The typical in-rolling of the petals of carnation flowers is not seen, instead the petals appear burnt. The ovaries are also notably effected by ethanol, being smaller and more yellow in colour. Ethanol treatment results in longevity increases by inhibiting the formation of ethylene, the plant hormone responsible for senescence. The concentration of the direct precursor to ethylene, ACC, as well as the activity of the enzyme that converts ACC to ethylene, ACC oxidase, is reduced to almost zero in the tissues of treated flowers. Another physiological factor affected by ethanol treatment is the carbohydrate status of the flowers. The normal sink activity of the ovary is inhibited by ethanol treatment. Although the carbohydrate content of the petals is found to decrease sharply in ethanol-treated flowers, these carbohydrates are not relocated to the ovary. The ovary does not increase in dry matter or chlorophyll content. The carbohydrate content decreases as a result of ethanol treatment, and when ¹⁴C sucrose was applied to petals, no radioactivity was recovered in the ovary. The petals and ovary are the organs most effect by ethanol activity, as when ¹⁴C ethanol was applied to cut carnation flowers as a pulse, the majority of the radioactivity was discovered here. The protein content of cells of both organs decreases significantly compared to control flowers. This is a total protein loss, rather than the destruction of specific systems. If the activity of alcohol dehydrogenase is prevented in ethanol-treated flowers, inhibiting the conversion of ethanol to acetaldehyde, no longevity increases are seen. The airspace surrounding treated flowers was found to contain ethanol and small amounts of acetaldehyde. The tissues of flowers treated with ethanol show an increase in the acetaldehyde content, as well as the ethanol content, especially in the ovary. The application of acetaldehyde directly to cut carnation flowers as a holding solution resulted in the vase life of the flowers increased by 150%. To determine the effectiveness of acetaldehyde as a post-harvest treatment, various concentrations of acetaldehyde were applied to cut carnation ftowers as a pulse treatment and a holding solution. Pulse treatments did not increase the vase life of flowers, and resulted in a number of negative effects in the flower. A holding solution of acetaldehyde does increase the longevity of cut carnation flowers, provided it is above a certain concentration. Treatments at concentrations below 1% acetaldehyde appear to promote flower senescence. The use of acetaldehyde as a post-harvest treatment has many of the same disadvantages as ethanol treatment. Acetaldehyde must also be applied as a holding solution for as long as possible. If removed from this solution, death of the organ occurred quickly. Acetaldehyde is also ineffective against external ethylene. A negative effect of acetaldehyde not found in ethanol-treated flowers, is that the longer the stem of cut carnation flowers, the shorter the resultant vase life. Physiologically the responses in cut carnation flowers were very similar to those seen in ethanol-treated flowers. Acetaldehyde inhibited the formation of ethylene completely. Almost no ACC can be found in treated tissues, and the action of ACC oxidase is completely reduced. The petals of acetaldehyde-treated flowers suffer from severe petal browning, rather than in rolling. The ovaries are particularly badly effected by treatment. There are large scale losses in fresh weight and chlorophyll content. The latter results in the ovaries appearing yellow in colour. They also show a loss in structure. The sink activity of these ovaries is destroyed. Like ethanol-treated flowers, the carbohydrate content of both the petals and ovaries are dramatically reduced. When ¹⁴C sucrose was applied to one of the. petals, almost no radioactivity was recorded in the ovary. There. is also a major loss in general protein content, slightly more severe than in ethanol-treated flowers. The conversion of ethanol to acetaldehyde is necessary in order to achieve longevity increases in ethanol-treated flowers. If the conversion of this acetaldehyde to ethanol is prevented in acetaldehyde-treated flower there is once again no longevity increase. Both ethanol and acetaldehyde are required within the system to result in increased longevity. Although ethanol and acetaldehyde treatments result in decreases in the total protein content of the flowers, certain enzymes remain active. Alcohol dehydrogenase is a bi-directional enzyme, capable of converting ethanol to acetaldehyde and then back to ethanol again. The activity of this enzyme, in both orientations, is increased in ethanol and acetaldehyde-treated flowers. The activity of pyruvate decarboxylase, which converts pyruvate to acetaldehyde, is also increased as a result of both treatments. The similarities of the physiological response of cut carnation flowers to ethanol and acetaldehyde post-harvest treatments, and the increased activity of these enzymes, indicate that the effect of both compounds on longevity is closely linked. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2000.

The South African Citrus Industry is the second largest exporter of citrus, after Spain. The industry is under pressure to supply high quality fruit as well as to expand into new, high paying markets. However, high paying markets such as Japan and the USA require cold sterilised fruit as obligatory quarantine treatments against Mediterranean fruit fly (Ceratitis capitata) in order to reduce any possible spread of the pest. Citrus fruit originated from tropical climates and hence are chilling susceptible. Chilling injury symptoms appear as dark brown spots, pitting and/or decay when fruit are transferred to shelf temperatures; thus reducing the marketability of citrus fruit. Therefore, there is need for methods to mitigate chilling injury. Previous studies have shown silicon to mitigate many forms of stress without any hazardous effect on human health. Thus, the aim of the study was to investigate the potential of post-harvest silicon dips in mitigating chilling symptoms in citrus fruit. Briefly, fruit from two sources (Ukulinga Research Farm and Ithala Farm) were dipped in different silicon concentrations (0, 50, 150, and 250 mg ℓ-1) for 30 minutes and thereafter stored at -0.5 or 2⁰C for up to 28 days with weekly evaluation for chilling injury symptoms. Total antioxidants were determined using FRAP, ABTS, and DPPH assays under spectrophotometer. In addition, sugars, ascorbic acid, phenolics and flavonoids were analysed using High Performance Liquid Chromatography (HPLC). Fruit from Ukulinga Research Farm showed significantly higher total antioxidants (ascorbic acid total phenolics and specific flavonoids hesperidin and naringin) and sugars relative to fruit from Ithala Farm. Low concentrations of silicon dips significantly reduced the appearance of chilling injury symptoms by inducing an enzymatic conversion of glucose to ascorbic acid, thereby increasing the antioxidant capacity of chilling susceptible fruit. Moreover, silicon increased the concentration of total antioxidants, total phenolics and total flavonoids. High silicon concentrations had a negative effect on post-harvest quality of lemons by increasing fruit weight loss and electrolyte leakage, resulting in appearance of chilling symptoms. In conclusion, the study showed that silicon had potential to reduce chilling injury. However, high silicon concentrations raised concern, in particularly, on fruit appearance. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

The use of a direct method for measuring respiration and transpiration rates may lead to better storage control systems and closer observation of storage losses. A laboratory scale environmental chamber was constructed and provided with a fan and adjustable louver to obtain variable ventilation flow rates. Flow rates were determined using a pressure sensor and fan characteristic curves which were determined experimentally. A regression equation representing the flow rate versus pressure relation was derived and used for estimating the flow rates throughout the study. / Respiration and transpiration were simulated using precision heat sources ranging from 15 to 105W in 15W interval and an evaporative pad. Measured wet and dry bulb temperatures and ventilation flow rates were used for the estimation of heat and moisture generated inside the chamber. The work was performed in two parts. In the first, precision heat sources were used and the heat balance equation components were solved. / In the second part, heat and moisture were generated inside the chamber, heat and moisture balance equations as well as psychrometric equations were solved. (Abstract shortened by UMI.)

Bibliography: leaves 204-211. / v, 211 leaves : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This study investigates the effects of a number of petroleum and vegetable oils against citrus pests. / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied and Molecular Ecology, 2000

Doctor of Philosophy (PhD) / The Flesh Browning (FB) disorder of ‘Cripps Pink’ apples presents a significant threat to the established market identity of the ‘Cripps Pink’ apple in Australian and export markets. Climatic conditions during fruit growth and development predispose ‘Cripps Pink’ apples to developing the FB disorder during storage. The FB disorder can be classified into two distinct disorders based on their physiological and structural differences and by seasonal climatic conditions. The diffuse type of FB (DFB) is a chilling injury, occurring in districts or seasons accumulating less than 1100 growing degree days (GDD) above 10oC between full bloom and harvest. In these climatic conditions, ‘Cripps Pink’ apples have delayed postharvest ethylene production. Diffuse FB effects fruit cortex tissue and is characterised as cellular collapse. Storing fruit at 3oC can reduce the incidence of DFB. The radial type of FB (RFB) is primarily a senescent disorder, occurring in districts or seasons accumulating greater than 1400 GDD above 10oC between full bloom and harvest. In these climatic conditions, postharvest ethylene production is not delayed. Radial FB affects the cells adjacent to the vascular tissue of the fruit and is characterised by damaged cell walls. Storing fruit at 1oC can reduce the incidence of RFB. Harvest maturity and the level of CO2 in the storage atmosphere are additive influences on the development of RFB. Seasons or districts accumulating more than 1700 GDD have a very low risk for developing RFB. Seasonal climatic conditions can provide a guide for predicting the risk of developing RFB and DFB during storage.

Thesis (MScAgric)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Internal breakdown (internal browning - IB and gel breakdown - GB), over maturity and immaturity are the main factors adversely affecting the quality of exported South African plums. Maturity problems occur when plums are strip harvested, i.e., all the fruit in a block or orchard are harvested once, when the majority of the fruit are at optimum maturity. This results in both ovennature and immature fruit being harvested and contributes to a high percentage of fruit being rejected for export. In general, internal browning occurs when plums are exported under a single 10\,,, temperature regime and gel breakdown occurs when plums are exported under a dual temperature regime. However, GB can also occur at harvest in fruit that are very ripe and may occur at single low temperatures, where it would be masked by lB. While it is known that some cultivars, like 'Angeleno', can withstand a single temperature regime, others cannot. To the best of our knowledge, the reason for this difference is not understood. Many factors affect the quality of plums, including light incidence in the canopy, mineral nutrition and harvest maturity. Plums that were grown on high density training systems such as 'a V- or spindle system yielded consistently high quality fruit with low incidences of gel breakdown. This was in contrast to earlier findings where low-density training systems produced high levels of GB, especially in the lower part of the tree canopy. Branches that were shaded with 80% shade netting yielded fruit with high levels of GB, indicating that the main effect of improved canopy structure on quality was improved light management. A postharvest boron application on 'Songold' plums prior to storage had no effect on the incidence of intemal breakdown in the fruit, but did damage the cuticle, resulting in severe shrivel. However, internal conductivity and firmness measurements indicated that there was some effect of the boron on cell membranes. A more thorough investigation of pre- and postharvest application of boron is recommended in order to determine whether there could be a positive effect of boron in improving fruit quality in plums. Four cultivars of plums ('Pioneer', 'Sapphire', "Songold ' and 'Angeleno') were harvested throughout, and extending beyond, the commercial harvesting period. In all cultivars, the drop in firmness between harvests was not as great as expected and the later harvested fruit were of a similar, if not superior, quality as compared to the earlier harvested fruit. Later harvested plums tended to have higher TSS and better colour development. Contrary to what was expected, later harvested fruit did not have more internal disorders than earlier harvested fruit. This indicates the importance of harvesting at optimum maturity. 'Angeleno' plums had no internal disorders, even after five weeks of cold storage at a single low temperature. 'Pioneer' and 'Sapphire' plums were classified as climacteric and 'Songold' and 'Angeleno' were classified as suppressed climacteric based on ethylene production. The climacteric plums respired and produced ethylene at a higher rate than the suppressed climacteric plums. Climacteric plums ripened faster during shelf life than suppressed climacteric plums. Furthermore, while climacteric plums did not need a cold storage period prior to ripening, suppressed climacteric plums needed a cold storage period in order to ripen normally. The longer the cold storage period prior to transfer to higher temperatures, the faster the plums ripened and the higher the ethylene production at the higher temperature. The suppressed climacteric genotype could possibly be incorporated into plum breeding programs in order to extend the storage period and shelflife of new plum cultivars. The long storage times required to ship plums from South Africa to the export markets has necessitated research on postharvest physiology and quality of this fruit. The use of the climacteric and suppressed climacteric system to classify fruit is expected to assist in understanding the different physiological responses of the cultivars and assist in developing handling protocols. Preharvest factors, particularly light and nutrition, also playa role in postharvest quality. / AFRIKAANSE OPSOMMING: Interne verval (interne verbruining en gelverval), oorrypheid en onryp vrugte, is die hoof faktore wat die uitvoer van Suid Afrikaanse pruime negatief beïnvloed. Rypheidsprobleme ontstaan wanneer pruime gestroop-oes word, met ander woorde, al die vrugte in 'n blok of boord word geoes wanneer die meerderheid vrugte optimum rypheid bereik het. As gevolg hiervan word 'n groot persentasie vrugte vir uitvoer afgekeur, omdat hulle te ryp of nie ryp genoeg is nie. Oor die algemeen vind interne verbruining plaas wanneer vrugte onder 'n enkel lae temperatuur uitgevoer word en gelvervel vind plaas wanneer vrugte onder 'n dubbele temperatuur regime vervoer word. Gel verval kan egter in baie ryp vrugte by oes voorkom en mag by enkel lae temperature voorkom .waar dit deur interne verbruining gemaskeer sal word. Kultivars soos 'Angeleno' kan onder enkel lae temperatuur uitgevoer word sonder interne probleme, terwyl ander pruimkultivars me so uitgevoer kan word nie. So ver ons weet, word die rede hiervoor nie goed verstaan nie. Daar is baie faktore wat die kwaliteit van pruime beïnvloed, onder meer lighuishouding, minerale voeding en die rypheid waarby die pruime geoes word. Pruime wat in hoë-digtheid sisteme soos 'n V- of "spindle" groei het goeie kwaliteit vrugte met 'n lae persentasie gelverval gelewer. Dit is in teenstelling met vroeër bevindinge, waar vrugte van lae digtheid boorde hoë persentasies geverval gelewer het, veral in die onderste gedeeltes van die boom. Takke wat met 80% skadunet bedek is het hoër persentasies gelverval as die kontrole gelewer, wat aandui dat die hoof effek van die verbeterde boom struktuur op kwaliteit, verbeterde lighuishouding was. 'n Na-oes aanwending van boor op 'Songold' pruime het geen effek op die voorkoms van gelverval gehad nie, maar het die kutikula beskadig en tot hoë persentasies verrimpeling gelei. Fermheid en inteme weerstand lesings het egter getoon dat daar wel 'n effek van die boor op die selmembrane en selwande was. 'n Meer omvattende ondersoek van voor- en na-oes aanwending van boor word aanbeveel om vas te stelof daar wel 'n positiewe effek van boor in die verbetering van pruim kwaliteit is. Vier pruim kultivars, ('Pioneer', 'Sapphire', 'Songold' en 'Angeleno'), is gedurende, sowel as later as die kommersiële oesperiode geoes. In al die kultivars was die afname in fermheid kleiner as wat verwag is, en vrugte wat later geoes is het dieselfde, en soms beter, kwaliteit as die vrugte wat vroeër geoes is gehad. Pruime wat later geoes is het beter kleur en gewoonlik hoër suikers gehad. In teenstelling met wat verwag is, het pruime wat later geoes is nie meer interne verval gehad as die pruime wat vroeër geoes is nie. Dit dui die belangrikheid van optimale oesrypheid aan. 'Angeleno' het geen interne verval gehad nie, selfs na vyfweke opberging by -0.5°C. 'Pioneer' en 'Sapphire' pruirne is as klimakteries en 'Songold' en 'Angeleno' as onderdrukte klimakteries geklassifiseer, gebaseer op etileen produksie. Die klimakteriese pruime het teen 'n hoër tempo gerespireer en etileen geproduseer as die onderdrukte klimakteriese pruime. Gedurende raklewe het klimakteriese vrugte vinniger as onderdrukte klimakteriese vrugte ryp geword. Verder, terwyl klimakteriese pruime nie opbgerging by 'n lae temperatuur nodig gehad het nie, het onderdrukte klimakteriese vrugte welopberging by 'n lae temperatuur nodig gehad om normaal ryp te word. Hoe langer die koel opbergingsperiode was, hoe vinniger het die pruime ryp geword by raklewe en hoe hoër was hulle etileen produksie. Die onderdrukte klimakteriese genotipe kan moontlik in teelprogramme geïnkorporeer word om kultivars met verlengde opbergings- en raklewe te teel. Die lang vervoer tye wat benodig word om Suid Afrikaanse pruime by die uitvoer markte te kry het dit nodig gemaak om navorsing oor die na-oes fisiologie en kwaliteit van pruime te doen. Die klassifisering van pruime as klimakteries of onderdrukte klimakteries kan ons in staat stelom die verskillende fisiologiese reaksies van die kultivars te verstaan en om hanterings prosedures te ontwikkel. Voor-oes faktore, veral lighuishouding en mineraalvoecling speelook 'n rol in na-oes kwaliteit van pruime.