Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The chicken meat has characteristics that has currently attracted the consumer, leading to increased industrial production, which seeks better production conditions. Ultrasound (US) and the electrolyzed water (EW) are technologies that enable improvements in traditional processes employed by slaughter houses. Its features allow it to have a reduction in water consumption and improvements in features such as the microbiological safety and tenderness. However, further studies are briefly describing possible oxidative effects on meat, especially chicken. Descriptions of the application of US pre-chilling showed improvements compared to applications without this technology. US demonstrated assist heat transfer, resulting in a more homogeneous and rapid cooling, especially in frequencies of 130 kHz. Combinations with EW and US have shown an intensification of cooling. These applications have a limit of time, and observed a reduction in the ability to cool the parts analyzed when this limit is exceeded. The US and EW applications also reported reductions in the initial microbial load, without that there was the initiation of oxidative processes, changes in glycolysis and the beginning of the muscle of the conversion process in the meat. In this pieces were not analyzed changes in its tenderness. Characterizing a prospective use of both technologies in larger and industrial scales. / A carne de frango possui características que atualmente tem atraído o consumidor, acarretando em uma crescente produção industrial, que busca melhores condições produtivas. O ultrassom (US) e a água eletrolisada (AE) são tecnologias que possibilitam melhorias em processos tradicionais empregados por indústrias frigoríficas. Suas características permitem que haja uma redução do consumo de água e melhorias em atributos como a segurança microbiológica e a maciez. No entanto, ainda são poucos os estudos que descrevam possíveis efeitos oxidativos na carne, especialmente na de frango. As descrições da aplicação de US no pré-resfriamento demonstraram melhorias em comparação com aplicações sem esta tecnologia. O US demonstrou auxiliar as transferências de calor, resultando em um resfriamento homogêneo e mais rápido, principalmente em frequências de 130 kHz. As combinações com AE e US demonstraram uma intensificação do resfriamento. Essas aplicações possuem um limiar de tempo, sendo observada uma redução na capacidade de resfriar as peças analisadas quando este limite é ultrapassado. As aplicações de US e AE também apresentaram reduções na carga microbiológica inicial, sem que houvesse a iniciação de processos oxidativos, alterações na glicólise e no início do processo de conversão do músculo em carne. Contudo, os pedaços analisados não tiveram alterações na sua maciez. Caracteriza-se uma prospectiva utilização de ambas as tecnologias em escalas industriais.

<p>Cilj ovog rada je bio de se utvrdi uticaj brzog vazdu&scaron;nog hlađenja polutki (na &ndash;31&deg;C do cca 4 sata, a zatim na 2 do 4&deg;C do 8, odnosno do 24 sata post mortem), vremena otko&scaron;tavanja post mortem (8 i 24 sata post mortem), nakon brzog hlađenja, i postupka salamurenja (bez ili sa vakuumom) proizvedenog svinjskog mesa (M. semimembranosus) na kvalitet i bezbednost kuvane &scaron;unke (konzervi od mesa u komadima), odnosno postavljen je zadatak razvoja novog proizvodnog procesa kuvane &scaron;unke koji će počivati na značajnoj racionalizaciji tehnolo&scaron;kog postupka, a čime bi se ostvarila i određena ekonomska dobit, uz postizanje vrhunskog kvaliteta proizvoda.<br />Da bi ovako postavljeni zadatak dao očekivane rezultate najpre je ispitan uticaj brzog hlađenja polutki i vremena otko&scaron;tavanja post mortem, nakon brzog hlađenja, na tehnolo&scaron;ki, nutritivni i senzorni kvalitet i bezbednost svinjskog mesa (M. semimembranosus), namenjenog proizvodnji ovog proizvoda. Analizom dobijenih rezultata zaključeno je da se brzim hlađenjem može obezbediti otko&scaron;tavanje polutki 8 sati post mortem, sa internom temperaturom manjom od 7&deg;C, uz značajno smanjenje tro&scaron;kova rada, kala hlađenja i udela mesa (M. semimembranosus) blede boje, odnosno zaključeno je da su brzo hlađeni mi&scaron;ići već do 8 sati post mortem prevedeni u stanje podesno za salamurenje, čime je dobijena sirovina potrebnih svojstava za izradu kuvane &scaron;unke.<br />Od ovako proizvedenog mesa (M. semimembranosus), nezavisno od postupka salamurenja (sa ili bez vakuuma), može se proizvesti kuvana &scaron;unka vrhunskog kvaliteta, &scaron;to potvrđuju rezultati ispitivanja kvaliteta kuvanih &scaron;unki proizvedenih od ove sirovine, pri čemu treba istaći da su utvrđene izvesne razlike kod pojedinih faktora kvaliteta kuvanih &scaron;unki prvenstveno rezultat faktora proizvodnje (na primer, operacije salamurenja), odnosno jo&scaron; uvek nestandardnog postupka proizvodnje ovih proizvoda (na primer, neujednačeno ubrizgavanje salamure). Dodatnim izmenama u tehnologiji salamurenja proizvedena je kvalitetna konzerva od mesa u komadima od ostataka mesa buta, uključujući i izdvojeno meso slabijeg kvaliteta (M. semimembranosus), i na taj način je samo jo&scaron; dodatno potvrđeno da je moguće značajno racionalizovati proizvodnju kuvane &scaron;unke uz valorizaciju celokupne muskulature buta.</p> / <p>The aim of the work was to determine the effect of rapid chilling of carcasses (at -31&deg;C up to cca.<br />4 hours, and at 2 to 4&deg;C til 8 i.e. 24 hours post mortem), time of deboning post mortem (8 and 24<br />hours post mortem), after rapid chilling, and way of curing (with and without vacuum) of processed<br />pork (M. semimembranosus) on quality and safety of cooked ham i.e. a task was set to develop a new<br />process of cooked ham production based on significant rationalization of the technological procedure,<br />enabling a certain economic profit, and achieving first class product quality.<br />The effect of rapid chilling of carcasses and time of deboning post mortem, after rapid chilling, on<br />technological, nutritive and sensory quality and safety of pork (M. semimembranosus) intended for the<br />production of cooked ham was investigated. The analysis of obtained results showed that deboning of<br />carcasses is possible up to 8 hours post mortem due to rapid chilling, achieving internal temperatures<br />lower than 7&deg;C, with significantly lower working co sts, weight loss and share of pale meat (M.<br />semimembranosus), i.e. the conclusion is that rapid chilled muscles 8 hours post mortem were in state<br />convenient for curing, obtaining the raw material of required characteristics for cooked ham<br />production.<br />First class quality cooked ham can be produced from pork (M. semimembranosus) obtained in<br />this way, irrespective of curing process (with or without vacuum), as supported by the results of quality<br />investigation of the obtained final product. Some differences found between certain quality factors of<br />cooked ham are the result of processing factors (curing processes, for example), i.e. of still nonstandard<br />production way of this product (for example, uneven injecting of brine). Certain changes of<br />curing technology enabled the production of quality cooked ham from rest ham meat and the<br />separated lower quality meat (M. semimembranosus). These results additionally confirm the possibility<br />of significant rationalization of cooked ham production i.e. possible valorization of the whole amount of<br />ham meat.</p>

M.Sc.(Agric) / Department of Horticultural Sciences

No description available.

Penstemon gibbensii and Penstemon haydenii are two rare, perennial forbs inhabiting remote areas of the western United States. P. gibbensii is listed as a sensitive species by the Bureau of Land Management (BLM) in Colorado, Utah, and Wyoming (Heidel, 2009). P. haydenii was designated as Endangered by the U.S. Fish and Wildlife Service in 1987 (Heidel, 2012). This thesis research was geared toward helping land managers in their efforts to protect and rehabilitate these species by providing understanding on different aspects of their seed ecology. My first study was a laboratory experiment performed on P. gibbensii and P. haydenii seed germination response to moist chilling and dry after-ripening. Wild harvested seeds were subjected to moist chilling at 2-4 °C for 0, 4, 8, 12, and 16 weeks and held in dry storage for approximately 2 years to determine effective methods for breaking primary dormancy. P. gibbensii seed germination increased consistently with increased length of chilling up to 16 weeks and exhibited habitat-correlated variation in this response. P. haydenii seed germination increased from 1 to 100% germination with 4 weeks of chilling. P. haydenii germination was greatest (96%) when incubated under a cool, diurnally-fluctuating temperature regime (10-20 °C) and responded positively to dry storage, increasing germination from 0 to 15%. My second study was an in situ field study designed to characterize the active seed bank of P. haydenii. We set up a transect line across a P. haydenii population and measured the number of seeds entering the seed bank, lost to predation post-dispersal, and persisting in the seed bank. P. haydenii does not appear to form an ecologically significant seed bank. Approximately 140 seeds/ 10m2 could potentially enter the seed bank but only 1 seed in the upper 10cm of sand persisted. Heavy post-dispersal insect predation resulted in a decrease in viability of nearly 30% in exposed P. haydenii seeds after just 12 hours. My third study explored the effects of burial by sand on P. haydenii. Wild-harvested seeds were planted in pots at 1, 2, 4, 6, 8, and 10cm deep in sand and incubated at 10-20 °C. Seed germination and mortality and seedling emergence were measured. The response of dormant seeds to post-burial incubation was determined. Burial depth decreased seedling emergence and seed germination. Shallow burial appears to induce secondary dormancy for seeds that don't germinate quickly, whereas deep burial appears to impose enforced dormancy in burial.

Thesis (M.Sc. (Horticulture)) -- University of Limpopo, 2022 / The South African Avocado Industry has recently announced plans to expand exports into new markets, such as the United States (US). As a requirement for these markets, fruit of high quality must be stored at ultra-low temperature to mitigate phytosanitary risks. However, ‘Hass’ avocado fruit are susceptible to chilling injury when stored at temperatures below 3°C. Moreover, CI development resulted in uneven ripening and disease infestation due to damaged cell membranes. Therefore, the objective of this study was to evaluate the potential of methyl jasmonate (MeJA) and salicylic acid (SA) on quality maintenance of 'Hass' avocado fruit during ultra-low cold storage. Matured ‘Hass’ avocado fruit were harvested at commercial dry matter (22%). The experiment was conducted using a completely randomized design (CRD) with eight replications per treatment. Treatment concentrations for methyl jasmonate (MeJA) were 0 (control), 10 and 100 μmol•L−1 , while those for salicylic acid (SA) were 0 (control), 1.0, 2.0 and 3.0 mM. After treatments, fruit were stored at 2°C for 31 days and thereafter, ripened at ambient temperature (±25°C) until fully ripe. During ripening, fruit were evaluated for weight loss, exocarp colour, firmness, chilling injury, as well as physiological (vascular browning) and pathological disorders (fruit rot). In this study, dipping fruit in MeJA solution significantly (P < 0.05) reduced ‘Hass’ avocado fruit firmness loss. Moreover, MeJA showed a significant effect (P < 0.05) on hue angle (h°) but did not significantly affect (P > 0.05) visual colour rating, chroma (C*), lightness (L*) and weight loss. The results showed that ‘Hass’ avocado fruit treated with 10 μmol•L−1 MeJA reduced weight loss when compared with 100 μmol•L−1 MeJA from day 2 to day 8 of ripening. Overall results showed a visual change in ‘Hass’ avocado fruit exocarp colour, with eye colour changing from rating 1 (emerald-green) to 3 (olive- green) for control and fruit treated with MeJA throughout the ripening days. Furthermore, MeJA reduced ‘Hass’ avocado fruit external chilling injury, physiological and pathological disorders. With respect to SA treatments, the result showed that dipping fruit at 1.0 and 2.0 mM SA had a significant effect (P < 0.05) on reducing firmness loss during ripening. Salicylic acid (1.0 mM) reduced and alleviated ‘Hass’ avocado fruit external chilling injury during ultra-low cold storage. Furthermore, result showed that 1.0 and 2.0 mM SA treatments had significant affect (P < 0.05) on firmness loss. Moreover, a significant effect was observed on visual colour and C* but did not affect (P > 0.05) L* and h°. Fruit treated with SA showed poor exocarp colour development with extended exposure to ultra-low cold storage, as a result, developed chilling symptoms. The treatment of ‘Hass’ avocado fruit with 1.0 mM SA inhibited the incidence of fruit rot and vascular browning when compared with control and fruit treated with 2.0 and 3.0 mM SA. In conclusion, 10 and 100 μmol•L−1 MeJA and 1.0, 2.0 and 3.0 mM SA effectively preserved ‘Hass’ avocado fruit quality during storage at ultra-low temperature. / Agricultural Sector Education Training Authority (AgriSeta) and National Research Foundation (NRF)

Thesis (M.Sc.( Agriculture (Horticulture)) -- University of Limpopo, 2022 / Avocado fruit ‘Hass’ exocarp changes colour from green to purple and black during ripening. However, uniform purple or black exocarp colour is not achieved during ripening, leading to consumers' rejection of fruit for not meeting quality standards. Avocado ‘Hass’ fruit harvested early remain green or develop a multicoloured appearance, concurrently devaluing their commercial value; and, therefore, unattractive to consumers. Therefore, this study aimed to investigate the role of sucrose and calcium postharvest pulsing on early matured ‘Hass’ avocado exocarp colour change during ripening. In this study, early matured ‘Hass’ avocado fruit were harvested from Halls and Sons, Mataffin farm (25°25’39.13” S, 30°55’52.84” E), Nelspruit, South Africa with 10 cm pedicel at commercial dry matter content (22%). Thereafter, the fruit were transported to the University of Mpumalanga laboratory. In the laboratory, the study was divided into two experiments: Experiment 1 ‘Hass’ fruit were continuously infused through the pedicel with different sucrose concentrations; 0 (control), 0.2 and 0.5 mM L-1. Experiment 2 fruit were infused with different calcium chloride (CaCl2) concentrations; 0 (control), 2 and 3 mM L-1. In both experiments, treated and untreated fruit were stored at 5.5°C for 28 days. After removal from cold storage, fruit were ripened at room temperature (±25°C) and evaluated every other day for firmness, subjective colour (visual colour), objective colour parameters (lightness-L*, chroma-C* and hue angle- h°), external chilling injury and ripening percentage. The results showed that Su (0.2 mM L-1) pulsing extended the ripening period by one day, corresponding with maintained fruit firmness. Furthermore, Su (0.2 mM L-1) treated fruit reduced the ‘Hass’ avocado fruit chilling injury index (CII) during cold storage. With respect to colour change, Su (0.5 mM L-1) treated fruit developed purple colour when compared with Su (0.2 mM L-1), which only developed to olive colour on the final ripening day (day 6). In addition, the results showed that all sucrose concentrations had a significant decreasing effect (P < 0.05) on objective colour parameters (L*, C* and h°) and increasing visual colour rating. With respect to CaCl2 treatments, fruit firmness decline was significantly delayed, which resulted in extended ripening time. Moreover, CaCl2 (2 and 3 mM L-1) significantly decreased (P < 0.05) pericarp objective colour parameters (L*, C* and h°) and increased visual colour rating and developed purple colour on the final ripening day (days 6 and 8, respectively). In addition, pulsing with CaCl2 (2 and 3 mM L-1) concentration reduced chilling injury during storage compared with control fruit. In conclusion, the results of this study indicated that Su and CaCl2 applied as postharvest treatments may contribute to avocado colour development by increasing anthocyanin accumulation. However, future research is required to investigate whether these treatments affect anthocyanin biosynthesis at the gene level.

Thesis (M.Sc. Agriculture (Horticulture)) -- University of Limpopo, 2017 / Avocado ‘Hass’ fruit characteristically change skin colour from green to deep purple or black during ripening. However, there is an ongoing debate about the use of ‘Hass’ avocado fruit skin colour change as an indicator for ripening and whether pre- and post-harvest factors can alter this relationship. Thus, the aim of the study was to investigate the effect of harvest season, harvest time, ripening temperature and ripening days on ‘Hass’ avocado fruit skin colour change during ripening. The experiment was carried out as 2 x 3 x 3 x 5 factorial with three replicates. The experiment consisted of four treatment factors: 2 x harvest season (2014 and 2015), 3 x harvest time (May-early, June-mid and July-late), 3 x ripening temperature (16, 21 and 25°C) and 5 x ripening days (0, 2, 4, 6 and 8). Fruit were stored at industry recommended temperature of 5.5°C. After storage, fruit were ripened at 16, 21 and 25°C, therefore, evaluated at 0, 2, 4, 6 and 8 days for subjective and objective skin colour, fruit firmness, ripening percentage and chilling injury. Harvest season, harvest time, ripening temperature and ripening days had a significant effect (P<0.001) on ‘Hass’ avocado fruit skin subjective colour development during ripening. However, amongst the treatment factors; harvest time, ripening temperature and ripening days were the predominant factors in skin subjective colour development variation. Hence, late harvest fruit showed an improved skin colour development at higher temperature (25°C) at day 4 to ripening when compared with early and mid-harvest fruit. Moreover, skin lightness showed a decreasing trend during all harvest time and ripening temperature throughout days to ripening during 2014 and 2015 harvest season. Furthermore, ripening at higher temperature (25°C) resulted in rapid decrease on fruit firmness when compared with lower temperature (16°C), irrespective of harvest season and harvest time. In addition, mid-season fruit showed significantly higher chilling damage during the 2014 harvest season. In conclusion, the study showed that harvest season, harvest time, ripening temperature and ripening days factors had a significant influence on ‘Hass’ avocado fruit skin colour development, firmness and susceptibility to chilling injury. / Agricultural Sector Education Training Authority (AgriSeta) and Postharvest Innovation Programme (PHI)

ENGLISH ABSTRACT: The export of Japanese plums from South Africa is challenging, since most cultivars are prone to develop chilling injury (CI) when stored at low temperatures. This injury manifests as gel breakdown or internal browning in the mesocarp tissue of the fruit on removal from low storage temperature conditions, i.e. in the consumer’s fruit basket, who subsequently does not buy plums again. Loss of cell membrane integrity and oxidative stress are, respectively, the primary and secondary physiological responses to CI. The main aim of this study was to investigate changes in cell membrane composition and levels of antioxidants in plums throughout fruit development and maturation, during forced air cooling (FAC) and storage under different temperature regimes. ‘Sapphire’ (a chilling susceptible cultivar) accumulated high levels of glutathione and polyunsaturated fatty acids (PUFAs) during fruit development. Therefore, the cultivar is protected against lipid peroxidation while developing on the tree, but the high levels of PUFAs, which are easily oxidised, may cause this cultivar to be chilling susceptible when stored at low temperatures. It is suggested that the high levels of monounsaturated fatty acids (MUFAs), which are not easily oxidised, and ascorbic acid that accumulated in ‘Angeleno’ (a chilling resistant cultivar) during fruit development, render this cultivar CI resistant during long-term cold-storage. When stored at -0.5 °C, CI development increased at a higher rate, ethylene evolution rates were higher and water soluble antioxidant activity (HAA), ascorbic acid and glutathione levels, and the MUFA:PUFA ratio were lower in H2 (more mature) ‘Sapphire’ plums than H1 fruit (less mature). Therefore, concurrent with H2 fruit having lower levels of antioxidants to quench free radicals caused by chilling stress, their cell membranes were more vulnerable to oxidation due to their phospholipid fatty acid composition. H2 fruit also had higher levels of saturated fatty acids, and hence less fluid cell membranes than H1 fruit when stored at -0.5 °C. An intermittent warming (IW) regime delayed symptom appearance and reduced CI severity in plums significantly compared to storage at -0.5 °C. Fruit stored under the IW regime had a more optimal phospholipid fatty acid composition and lower membrane sterol levels under shelf-life conditions to keep the membranes fluid. It also had higher levels of HAA and lipid soluble antioxidant activity, ascorbic acid and glutathione, which rendered fruit better protected against oxidation. Elevated storage temperatures (2.5 °C to 7.5 °C) caused higher levels of lipid peroxidation or low ascorbic acid levels and poor fruit quality compared to the IW regime in ‘Sapphire’ plums. ‘Laetitia’ plums stored at 5 °C and 7.5 °C had significantly less CI than under the IW regime, but softened quicker due to higher ethylene evolution rates. ‘Sapphire’ tolerated both long and short FAC durations, but a slower initial FAC rate prevented CI manifestation and caused a higher HAA after cold-storage in this fruit. ‘Laetitia’ cooled with a slower initial FAC rate and for a longer duration resulted in the best fruit quality and had higher HAA, total phenolic, phospholipid and saturated phospholipid fatty acid concentrations during storage. / AFRIKAANSE OPSOMMING: Die uitvoer van Japanese pruime vanaf Suid-Afrika hou talle uitdagings in, want die meeste van die kultivars ontwikkel koueskade wanneer hulle by lae temperature opgeberg word. Koueskade manifesteer as gelverval of interne verbruining in die mesokarpweefsel van die vrugte wanneer die vrugte verwyder word uit die lae opbergingstemperatuuromstandighede, m.a.w. in die verbruiker se vrugtemandjie, wat nie weer pruime koop nie. Verlies aan selmembraanintegriteit en oksidatiewe druk is, respektiewelik, die primêre and sekondêre fisiologiese reaksies op koueskade. Die hoofdoel van hierdie studie was om die veranderinge in selmembraansamestelling en antioksidantkonsentrasie in pruime te ondersoek tydens vrugontwikkeling en volwassewording, tydens geforseerde lugverkoeling (GLV) en tydens opberging onder verskillende temperatuurregimes. ‘Sapphire’ (‘n koueskade sensitiewe kultivar) het hoër konsentrasies van glutatioon en polionversadigde vetsure (POV) tydens vrugontwikkeling geakkumuleer. Dié kultivar is dus voldoende beskerm teen lipiedperoksidasie tydens vrugontwikkeling aan die boom, maar die hoë konsentrasies van POVs, wat maklik oksideer, mag veroorsaak dat hierdie kultivar meer koueskadesensitief is wanneer dit by lae temperature opgeberg word. Die hoë konsentrasies van mono-onversadigde vetsure (MOV), wat nie maklik oksideer nie, en askorbiensuur wat in ‘Angeleno’ (‘n koueskade weerstandbiedende kultivar) geakkumuleer het tydens vrugontwikkeling, verleen moontlik weerstandbiedendheid teen koueskade aan hierdie kultivar tydens langtermyn koelkopbering. Tydens opberging by -0.5 °C het koueskade ontwikkeling vinniger toegeneem, was etileenvrystellingstempos hoër en die wateroplosbare antioksidantaktiwiteit (HAA), askorbiensuuren glutatioonkonsentrasies en die MOV:POV verhouding laer in H2 (meer volwasse) ‘Sapphire’ pruime as in die H1 vrugte (minder volwasse). Dus, tesame met die laer antioksidantkonsentrasies in die H2 vrugte om die vry radikale veroorsaak deur koelopbering te verminder, was hul selmembrane ook meer vatbaar vir oksidasie a.g.v. die vetsuursamestellling van hul membraanfosfolipiede. Die H2 vrugte het ook ‘n hoër konsentrasie van versadigde vetsure, en dus minder vloeibare membrane as die H1 vrugte gehad tydens opberging by -0.5 °C. Die dubbeltemperatuurregime (DT) het simptoomontwikkeling vertraag en koueskade-intensiteit betekenisvol verminder in vergelyking met pruime wat by -0.5 °C opgeberg is. Vrugte wat met die DT regime opgeberg is, het ‘n meer optimale fosfolipiedvetsuursamestelling en laer konsentrasie van membraansterole tydens gesimuleerde raklewe gehad wat meer vloeibare membrane verseker het. Hierdie behandeling het ook hoër HAA en lipiedoplosbare antioksidantaktiwiteit (LAA), askorbiensuur- en glutatioonkonsentrasies gehad wat die vrugte beskerm het teen oksidatiewe druk. Verhoogde opbergingstemperature het hoër vlakke van lipiedperoksidasie of lae askorbiensuurkonsentrasies asook swak vrugkwaliteit in ‘Sapphire’ pruime veroorsaak in vergelyking met die DT regime. ‘Laetitia’ pruime wat by 5 °C en 7.5 °C opgeberg is, het betekenisvol minder koueskade gehad in vergelyking met die DT regime, maar het vinniger sag geword a.g.v. hoër etileenvrystellingstempos. ‘Sapphire’ kon lang en kort GLV tye weerstaan, maar ‘n stadiger inisiële GLV spoed het die manifestasie van koueskade voorkom en het ‘n hoër HAA in die vrugte tot gevolg gehad na koelopberging. ‘Laetitia’ wat met ‘n stadiger inisiële GLV spoed en oor ‘n langer tyd verkoel is, het die beste vrugkwaliteit, en hoër HAA, totale fenool-, fosfolipied- en versadigde fosfolipiedvetsuurkonsentrasies as die ander behandelings tydens koelopberging gehad

Le traitement au froid en post-récolte (TPR) des ananas (Ananas comosus. (L). M) destiné à ralentir la sénescence des fruits, induit « le brunissement interne de l'ananas » (BI). Afin d'étudier des gènes susceptibles de discriminer les variétés tolérantes, une comparaison entre des fruits frais ou soumis au TPR a été réalisée pour 4 variétés d'ananas différant par leur tolérance au BI. D'après les résultats, en réponse au TPR l'absence de symptômes de BI est associée à une « tolérance membranaire » et à une faible activité de la polyphenol oxydase. L'étude de l'activité de la phenylalanine ammonia-lyase et de l'ascorbate peroxidase a révélé que le froid induit une stimulation de l'activité de ces enzymes chez une variété sensible au BI. L'étude du catabolisme protéique a montré que la tolérance des fruits au BI était liée : à la sous-expression du gène d'une protéase à cystéine, et à une sur-expression de gènes codant une cystatine et une protéase à acide aspartique, dont l'ADNc a été caractérisé et cloné pour la première fois chez l'ananas. L'expression différentielle de ces gènes indique qu'ils pourraient être utilisés pour le criblage par PCR de variétés dans les programmes d'améliorations de l'ananas pour la résistance au BI / Pineapple fruits (Ananas comosus. (L). M) require postharvest chilling treatment (PCT) in order to extend the postharvest fruit quality during shipping exportation. However PCT induces an injury known as blackheart (BH), or fruit browning, which is characterized by the appearance of brown spots in the flesh. This work has focused on the study of the development of BH physiopathy in the context of postharvest treatment in 4 pineapple varieties differing in their resistance to BH. Results showed that BH was associated with high membrane tolerance, low activity of polyphenol oxidase and absence of the related isoforms. Under chilling stress, the activities of both phenylalanine ammonia-lyase and ascorbate peroxidase were enhanced in the BH susceptible variety. Various genes involved in protein catabolism under abiotic stress were also studied. BH resistance was shown to be linked to the down-regulation of a major cystein protease and to the up-regulation of cystatin, the natural inhibitor of cystein protease. An aspartic acid protease, isolated and sequenced for the first time in pineapple, was also studied. Opposed to cystein protease, the expression and activity of the aspartic acid protease was directly related to BH resistance. Taken together, the results gathered by this work suggest that these genes could provide useful molecular markers for PCR variety screening in breeding programs aimed at improving pineapple BH resistance