Browsing by Author "Coetzee, Gerhardt"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Evaluation of commercial enzymes for the bioprocessing of Rooibos tea
    (Stellenbosch : Stellenbosch University, 2005-04) Coetzee, Gerhardt; Bloom, M.; Van Zyl, Willem Heber; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: The Rooibos tea plant (Aspalathus linearis) is indigenous to South Africa and occurs only in the Western Cape's Cedarberg region. Rooibos tea is produced from the leaves and fine stems of the plant. The tea is normally prepared by brewing the leaves and consuming the liquor. However, the Rooibos plant is not only used to prepare tea; the plant extracts are also used in various neutraceutical and pharmaceutical products, including health drinks, iced tea, soaps and moisturising creams. Although the tea plant contains native enzymes responsible for the colour and aroma development of Rooibos tea, the disruption and maceration of the plant material during processing is insufficient to allow these enzymes proper access to the substrates responsible for Rooibos tea's characteristics. The current processing of Rooibos tea is also time consuming and is done under uncontrolled conditions, leading to unnecessary loss in aroma and antioxidant content. The addition of enzymes could improve the maceration of the plant material, shorten the processing time and improve the extraction of aroma, colour and antioxidant components. During this study, 16 commercially available microbial enzymes were evaluated on three different Rooibos substrates for the improvement of aroma and colour development, as well as the extraction of soluble solids (SS) and total polyphenols (TP). Thirteen enzymes were evaluated on spent tea for the enhanced extraction of soluble solids and to determine the best candidates for further evaluation on fermented and green Rooibos tea. Seven of the enzymes improved the yield in SS from spent tea. Up to 232% improvement was obtained, depending on the type of enzyme and dosage applied. The best six enzyme preparations were further evaluated on fermented Rooibos tea. For Depol™ 670L at 20 ul/g tea, the laboratory treatment increased the yield in SS by 44%, while small-scale industrial simulations increased the SS by 26%. However, an increase in the yield in SS was usually accompanied by a decrease in the %TP/SS ratio, indicating that mainly inactive compounds were extracted. Based on the results with the commercial enzymes, twelve "synthetic" enzyme cocktails, consisting of different combinations of commercial enzymes were designed, of which three cocktails released increased amounts of SS without decreasing the %TP/SS ratio significantly. Thirteen enzymes were evaluated on dried and freshly cut green Rooibos tea, with three enzymes (Depol™ 670L, Pectinex Ultra SP-L and Depol™ 692L) increasing the yield in SS between 21% and 66%, and the TP content between 11% and 47%. Laccase was the best candidate in improving colour development from green tea, with the improvement being slightly better at 50°C than at 40°C. All the "synthetic" cocktails containing laccase improved the colour extract of all three substrates evaluated, but also significantly decreased the TP and antioxidant content. However, lower dosages of laccase resulted in colour development with little loss in the antioxidant content. Due to the promising results obtained with the treatments of Rooibos tea with laccases, it was decided to clone and express the laccase gene (lacA) of Pleurotus ostreatus into Aspergillus niger. The gene was successfully transformed into A. niger, but the expression of the recombinant gene was not effective.
  • Thumbnail Image
    Item
    Optimization of Aspergillus fijiensis β-fructofuranosidase expression and production using Pichia pastoris, for the production of fructooligosaccharides from sucrose
    (Stellenbosch : Stellenbosch University, 2019-04) Coetzee, Gerhardt; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: The South African sugar industry faces challenges affecting its profitability such as low international market price and the implementation of tax legislation by the South African National Treasury on sugar-sweetened beverages (SSBs). To alleviate these effects, the industry could produce alternative high-value, low-calorie products from sucrose such as short-chain fructooligosaccharides (scFOS). This product diversification may increase the industry’s revenue while addressing the sugar tax legislation. In this study, the β-fructofuranosidase from Aspergillus fijiensis ATCC 20611 was selected to produce scFOS from sucrose. Native (fopA) and protein-engineered (fopA_V1) versions of the enzymes were produced recombinantly in Pichia pastoris. Factors influencing heterologous protein production require empiric evaluation for each protein and thus the aim was to optimize the yeast expression system and cultivation processes to maximize β-fructofuranosidase production. On the genetic level, different yeast strains, promoters and gene codon-optimization techniques were compared. Dissolved oxygen controlled (DO-stat) and constant feeding strategies were compared in bioreactor cultivations to investigate the influence of yeast growth on volumetric enzyme titers. The application of the two enzymes to produce scFOS from industrial sugar streams were optimized using response surface methodology (RSM). In shake flask experiments the P. pastoris DSMZ 70382 strain proved superior to X-33 when expressing Geneart® codon-optimized fopA under control of the AOX1 and GAP promoters (12.1 U/ml and 3.2 U/ml for AOX1 and 12.0 U/ml and 11.3 U/ml for GAP, respectively). Further bioreactor studies with P. pastoris DSMZ 70382 native fopA transformants showed that the AOX1 promoter was superior to GAP while ATUM codon-optimization produced higher titers than Geneart® (13 702 U/ml and 2 718 U/ml for AOX1 and 6 057 U/ml and 1 790 U/ml for GAP, respectively). Constant feed cultivations produced higher growth rates for strains expressing the ATUM genes under the GAP promoter, but lower volumetric enzyme activities compared to DO-stat cultivations (2 129.25 and 1686.91 U/ml for GAPfopA and GAPfopA_V1, respectively, with DO-stat and 1413.36 and 1222.70 U/ml for GAPfopA and GAPfopA_V1, respectively, with constant feed). The GAPfopA strain produced higher enzyme activities than the GAPfopA_V1 for the constant feed and DO-stat method. Due to the shorter cultivation time, the constant feed method exhibited higher volumetric productivity for both strains (23.96 x 103 and 20.72 x 103 U/L/h for GAPfopA and GAPfopA_V1, respectively). In scFOS production, the native and engineered enzymes were compared to evaluate whether the protein engineering afforded advantages in enzyme performance on non-ideal substrates (industrial sugar). RSM indicated optimum conditions to produce a target scFOS composition were 62 ⁰C and 10 U/g sucrose using pure sugar. These conditions were applied to A-molasses and refinery molasses, however the desired scFOS composition was only successfully attained using A-molasses. In conclusion, P. pastoris proved to be a suitable host for the high-level expression and production of functional codon-optimized native (GAPfopA) and engineered (GAPfopA_V1) versions of the fopA enzyme and that these enzymes can be applied for the batch production of scFOS from a selection of industrial sugar streams for the purpose of reducing process cost.