Stability, substrate and inhibitor specificity and electrophoretic properties of a crude polyphenol oxidase (PPO) preparation extracted from d'Anjou pears (Pyrus communis L.) were investigated. Levels of polyvinylpyrrolidone and pH of buffer for extraction were found to affect the specific activity of the extracted enzyme. An extract prepared with 1.5 g insoluble PVP per 15 g fresh tissue in acetate buffer (pH 5.6) resulted in the highest PPO specific activity of the crude extract. Addition of PVP did not affect the electrophoretic patterns of PPO isozymes. The pH optimum of PPO occurs at 7.0. Heat inactivation of PPO followed first order kinetics and approximately 50% of PPO activity was inactivated after heating for 11.7, 6.25, 2.25 and 1.1 min at temperature of 70°,75°,80° and 85°C, respectively. The crude PPO enzyme was active towards o-dihydroxyphenols, but inactive towards monophenols. Disc electrophoresis on 7% polyacrylamide gels revealed eight active isozymes towards catechol, 4-methylcatechol, chlorogenic acid, caffeic acid, dopamine, d-catechin and DL-dopa. Similar electrophoretic patterns were observed with all substrates. No differences in the band patterns were observed between a fresh crude PPO preparation, a frozen crude extract and a dialyzed extract when catechol was used as substrate. L-cysteine, diethyldithiocarbamate, thiourea, metabisulfite, cyanide, mercaptoethanol and ascorbic acid inhibited the enzyme activity. L-cysteine and diethyldithiocarbamate were the most effective inhibitors. / Graduation date: 1977

Graduation date: 1955

Graduation date: 1979

No description available.

The retention of pigments in processed raspberries is a function of the process method and conditions of subsequent storage. The presence of sucrose and the nature of the headspace gas also influences the retention of the pigment. The effect of some of the above variables on the pigments was investigated. Variables imposed were: (1) concentration of syrup, (2) headspace gas atmosphere, (3) temperature, and (4) time of storage. Separation of the pigment of Willamette red raspberries and black raspberries was made by column chromatography and the pigments were analyzed. spectrophotometrically. The results showed the following: 1. The pigments of Willamette red raspberries consisted of four separate cyanins as based on the R [subscript f] values and characteristic wavelengths of maximum absorption. The pigments of black raspberries consisted of three fractions. 2. On the basis of R [subscript f] values and wavelengths of maximum absorption only two of the constituent fractions were the same. 3. The wavelength of maximum absorption of all the anthocyanins shifted towards shorter wavelengths after the first month of storage. 4. Time and temperature of storage and their interaction each contributed significantly to the destruction of the cyanin pigments. An increase in either variable resulted in a greater destruction of the pigments. 5. As the concentration of the ingoing syrup was increased, the amount of individual cyanins decreased. 6. Oxygen in the headspace gas was shown to be detrimental to the retention of the cyanins I, II, and IV of the Willamette raspberries and to cyanins II and III of the black raspberries. 7. Changes in the total pigment concentration were greatly influenced by the cyanin in greatest concentration in the species. 8. Heat processing destroyed approximately 20 percent of the pigments of the raspberries. / Graduation date: 1963

Graduation date: 1958

Graduation date: 1951

Graduation date: 1962

Graduation date: 1953

Thesis (MScAgric (Horticulture))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: In order to develop a novel pink- or red-fleshed apple for the fresh consumer market,the red-fleshed genotype, ‘KAZ 91’ (Malus niedzwetzkyana Dieck.), was crossed with ‘Meran’ (M. domestica Borkh) at the Agricultural Research Council (ARC) apple breeding programme in South Africa. The objective of this study was to evaluate and quantify colour variability in the flesh and peel of this progeny (Family 1), to assess quality traits (i.e., acidity and total soluble solids) and phenolic levels in fruit peel and flesh, and to investigate consumer preference for the taste and appearance of redfleshed apples. All data, except for consumer preference, were also collected on two white-fleshed M. domestica Borkh families, i.e., ‘Reinette Burchardt’ x ‘Treco Red Gala’ (Family 2) and ‘Meran’ x ‘Treco Red Gala’ (Family 3). Fruit of Family 1 seedlings were on average darker red with greater blush coverage and higher anthocyanin and phenolic levels compared to fruits of Family 2 and 3. The proportion of bearing trees with red-fleshed fruits in Family 1 increased from 25% in 2007 to 35% in 2008. The intensity and distribution of red pigmentation in the flesh varied considerably between seedlings and even between individual apples from the same tree. A high intraclass correlation coefficient was found for red-flesh coverage within Family 1, indicating a high level of genetic determination that can be used in breeding. When only red-fleshed seedlings were considered, an intermediate repeatability coefficient (0.54) for red-flesh coverage indicates that the extent of red flesh coverage varies to some extent between seasons. The effect of environmental factors on red flesh colour needs to be assessed and breeders need to take care to select for genotypes with stable flesh colour intensity and coverage. Small intraclass correlations were found between families for other traits. No correlation was found for anthocyanin and total phenolics in both peel and flesh or between anthocyanin levels in the peel and flesh of Family 1 fruit. This suggests that red-fleshed fruit will not necessarily be high in antioxidants – since phenolics is by far the greatest contributor to fruit antioxidant capacity. The lack of a correlation between peel and flesh anthocyanin levels also suggest that fruit with dark red flesh will not necessarily have a dark red skin colour. Family 1 fruit were more prone to flesh browning and were more acidic compared to fruit of Families 2 and 3. With regard to consumer preference for flesh colour, 74% of South African consumers preferred white flesh while 64% preferred an attractive “floral” pattern created by the combination of a red cortex and white core. Consumers indicated a much lower liking for other distribution patterns and lower intensities of red flesh colour. Consumers preferred the taste of apples that were crisp, crunchy and high in apple flavour irrespective of flesh colour. Red-fleshed fruit were generally acidic or had poor texture, and some were also astringent. However, despite a general dislike in acidic fruit, consumers showed a preference for acidic fruit if that fruit also had high red-flesh coverage. / AFRIKAANSE OPSOMMING: Appeltelers van die Suid-Afrikaanse Landbounavorsingsraad (LNR) Infruitec- Nietvoorbij poog om unieke appelkultivars met ‘n pienk of rooi vleiskleur te ontwikkel. Vir hierdie doel het hulle die rooivleis genotipe, ‘KAZ 91’ (Malus niedzwetzkyana Dieck), gekruis met ‘Meran’ (M. domestica Borkh). Hierdie studie is uitgevoer ten einde kleurvariasie, interne kwaliteitseienskappe (i.e., suurheid en totale oplosbare vastestowwe) en vlakke van fenole in die vleis en skil van bogenoemde kruisingkombinasie se nageslag (Familie 1) te evalueer en te kwantifiseer asook om verbruikersvoorkeure vir die smaak en voorkoms van rooivleis appels te bestudeer. Buiten vir verbruikersvoorkeure, is alle data ook ingesamel vir twee witvleis M. domestica families, naamlik ‘Reinette Burchardt’ x ‘Treco Red Gala’ (Familie 2) en ‘Meran’ x ‘Treco Red Gala’ (Familie 3). Familie 1 saailinge se vrugte was gemiddeld donkerder rooi met ‘n groter rooi blos en hoër antosianien- en fenoolvlakke in vergeleke met vrugte van Families 2 en 3. Van die Familie 1 saailinge wat wel vrugte gedra het, het 25% en 35% in onderskeidelik 2007 en 2008 vrugte met rooi vleis gehad. Die intensiteit en verspreiding van rooi pigmentasie in die vleis het aansienlik varieer tussen saailinge en selfs tussen individuele appels van dieselfde boom. ‘n Hoë intraklas korrelasie koëffisiënt is gevind vir die proporsie van die vleis met rooi pigmentasie in Familie 1 nageslag. Dit dui op ‘n hoë vlak van genetiese determinasie en vinnige vordering met teling vir hierdie eienskap. Indien net rooi-vleis saailinge egter oorweeg word, word ‘n intermediêre herhaalbaarheid koëffisiënt (0.54) vir die proporsie van die vleis wat rooi is verkry, wat dui op aansienlike variasie tussen seisoene in die omvang van rooi pigmentasie. Die effek van omgewingsfaktore op rooi vleiskleur behoort dus bestudeer te word en telers moet let daarop om te selekteer vir genotipes met stabiele vleiskleur intensiteit en bedekking. Die intraklas korrelasies tussen families vir ander vrugeienskappe was klein. Antosianienvlakke en totale fenole in die skil en vleis van Familie 1 vrugte het nie gekorreleer nie. Dit dui daarop dat rooivleis appels nie noodwendig ‘n hoër antioksidantkapasiteit het nie – fenole maak by verre die grootste bydrae tot die antioksidantkapisiteit van vrugte. Antosianienvlakke in die skil en vleis van Familie 1 vrugte het ook nie gekorreleer nie wat daarop dui dat vrugte met ‘n donker rooi vleis nie noodwendig ook ‘n donker skilkleur sal hê nie. Familie 1 vrugte was gemiddeld suurder as vrugte van Families 2 en 3 en Familie 1 vrugte se vleis het gemiddeld ook meer verbruining ondergaan. Ten opsigte van verbruikersvoorkeur vir vleiskleur is gevind dat 74% van verbruikers ‘n wit vleiskleur verkies het terwyl 64% gehou het van die aantreklike “blom” patroon gevorm deur ‘n rooi korteks en wit kern. Verbruikers het aansienlik minder gehou van enige ander verspreiding van rooi pigment in die vleis of van ‘n laer intensiteit rooi kleur. In terme van smaak is geurige appels met ‘n bros tekstuur verkies ongeag hul vleiskleur. Rooivleisappels was oor die algemeen suur met ‘n swak tekstuur. Sommige rooivleisappels was ook frank. Tog, ten spyte van ‘n algemene afkeur in suur appels, het verbruikers ‘n voorkeur getoon vir vrugte met ‘n kombinasie van hoë suur en ‘n hoë proporsie vleis met rooi pigmentasie.