1,721,177 research outputs found
Understanding problem fermentations – a review
Full text linkCITATION: Malherbe, S., Bauer, F. F. & Du Toit, M. 2007. Understanding problem fermentations – a review. South African Journal of Enology & Viticulture, 28(2):169-186, doi:10.21548/28-2-1471.The original publication is available at http://www.journals.ac.za/index.php/sajevDespite advances in winemaking technology and improvements in fermentation control, problem alcoholic and
malolactic fermentations remain a major oenological concern worldwide. This is due to possible depreciation of
product quality and its consequent negative economic impact. Various factors have been identified and studied overv the years, yet the occurrence of fermentation problems persists. The synergistic effect of the various factors amongst each other provides additional challenges for the study of such fermentations. This literature review summarises the most frequently studied causes of problematic alcoholic and malolactic fermentations and in addition provides a summary of established and some potential new analytical technologies to monitor and investigate the phenomenon of stuck and sluggish fermentations.http://www.journals.ac.za/index.php/sajev/article/view/1471Publisher's versio
Microbial spoilage and preservation of wine : using weapons for nature's own arsenal
Full text linkCITATION: Du Toit, M. & Pretorius, I. S. 2000. Microbial spoilage and preservation of wine : using weapons for nature's own arsenal. South African Journal of Enology and Viticulture, 21(1):74-96, doi:10.21548/21-1-3559.The original publication is available at http://www.journals.ac.za/index.php/sajevThe winemaking process includes multiple stages at which microbial spoilage can occur, altering the quality and hygienic status of the wine and rendering it unacceptable. The major spoilage organisms include species and strains of the yeast genera Brettanomyces, Candida, Hanseniaspora, Pichia, Zygosaccharomyces etc., the lactic acid bacterial genera Lactobacillus, Leuconostoc, Pediococcus, etc. and the acetic acid bacterial genera Acetobacter and Gluconobacter. The faults caused include bitterness and off.flavours (mousiness, ester taint, phenolic, vinegary, buttery, geranium tone), and cosmetic problems such as turbidity, viscosity, sediment and film formation. These spoilage organisms can also affect the wholesomeness of wine by producing biogenic amines and precursors of ethyl carbamate. The judicious use of chemical preservatives such as sulphur dioxide (S02) during the winemaking process decreases the risk of microbial spoilage, but strains vary considerably in their S02 sensitivity. There is,
moreover, mounting consumer bias against chemical preservatives, and this review focuses on the possible use of biopreservatives in complying with the consumers' demand for "clean and green" products.https://www.journals.ac.za/index.php/sajev/article/view/3559Publisher's versio
Selection and characterisation of Oenococcus oeni and Lactobacillus plantarum South African wine isolates for use as malolactic fermentation starter cultures
Full text linkCITATION: Lerm, E., Engelbrecht, L. & Du Toit, M. 2011. Selection and characterisation of Oenococcus oeni and Lactobacillus plantarum South African wine isolates for use as malolactic fermentation starter cultures. South African Journal of Enology and Viticulture, 32(2):280-295, doi:10.21548/32-2-1388.The original publication is available at http://www.journals.ac.za/index.php/sajevThis study focused on characterising 23 Oenococcus oeni and 19 Lactobacillus plantarum strains isolated from the South African wine environment for the development of potential commercial malolactic fermentation (MLF) starter cultures. These strains were characterised with regards to oenological important characteristics, including the genetic screening for enzyme-encoding genes (enzymes that are involved/implicated in wine aroma modification, as well as enzymes pertaining to the wholesomeness of the final wine product), their fermentation capabilities, the ability to maintain viability during MLF, as well as the volatile acidity production. A total of three O. oeni and three L. plantarum strains were selected at the completion of this study. These six strains showed the most potential during the characterisation stages of the study and were able to successfully complete MLF in Pinotage wine. It was also found that L. plantarum strains displayed a more diverse enzyme profile than O. oeni strains, particularly with regards to the presence of the aroma-modifying enzymes β-glucosidase and phenolic acid decarboxylase (PAD), which implies the future use of this species in the modification of the wine aroma profile and use as commercial starter culture.http://www.journals.ac.za/index.php/sajev/article/view/1388Publisher's versio
Optimisation of the quantification of total soluble solids, ph and titratable acidity in South African grape must using Fourier transform mid-infrared spectroscopy
Full text linkCITATION: Swanepoel, M., Du Toit, M. & Nieuwoudt, H. H. 2007. Optimisation of the quantification of total soluble solids, ph and titratable acidity in South African grape must using Fourier transform mid-infrared spectroscopy. South African Journal of Enology & Viticulture, 28(2):140-149, doi:10.21548/28-2-1467.The original publication is available at http://www.journals.ac.za/index.php/sajevCalibration models for Fourier transform mid-infrared (FT-MIR) spectroscopy were developed for the simultaneous quantification of total soluble solids (TSS, measured as °Brix), pH and titratable acidity (TA, expressed as g/L tartaric acid) in South African (SA) grape must. An exploratory data analysis of the FT-MIR spectra of 1170 grape must samples (647 for °Brix, 252 for pH and 271 for TA) was done by principal component analysis, and partial least squares regression was used for the computation of the regression models. The prediction errors for TSS (0.34°Brix), pH (0.04 units) and TA (0.51 g/L) provided analytical data of satisfactory accuracy. The evaluation of readyto-use global calibrations to quantify these three parameters in SA samples presented standard error of prediction (SEP) values of 0.46°Brix, 0.10 pH units and 3.13 g/L for TA. After slope and intercept adjustments of the original global calibration algorithms, the SEP values were reduced to 0.38 °Brix, 0.05 pH units and 0.49 g/L for TA. These results show the necessity for optimisation of the global FT-MIR WineScan calibrations to provide a better fit to samples of South African origin. The results demonstrate that FT-MIR spectroscopy is a useful technique for the rapid quantification of major grape must parameters and for quality control purposes in an industrial cellar.http://www.journals.ac.za/index.php/sajev/article/view/1467Publisher's versio
Preliminary expression analysis of stress related genes in Lactobacillus paracasei strains under winemaking conditions.
No full textEarly fermentation characteristics of non-Saccharomyces yeasts in red and white grape must, a targeted approach
No full text
Designation of ATCC 334 in place of ATCC 393 (NCDO 161) as the neotype strain of Lactobacillus casei subsp. casei and rejection of the name Lactobacillus paracasei (collins et al., 1989) request for an opinion
No full textStrain ATCC 393 (= NCDO 161) was selected as the neotype strain of Lactobacillus casei subsp. casei by Hansen and Lessel in 1971 and was confirmed as such on the Approved Lists of Bacterial Names in 1980. However, two independent DNA-DNA homology studies have shown that strains belonging to the subspecies of L. casei are not genetically closely related to strain ATCC 393(T) (T = type strain). In 1989 Collins et al. found high levels of DNA homology between strains belonging to the subspecies of L. casei and L. casei NCDO 151 and reclassified L. casei subsp. casei (the majority of the strains), L. casei subsp. alactosus, L. casei subsp. pseudoplantarium, and L. casei subsp. tolerans as Lactobacillus paracasei. However, results obtained from DNA-DNA hybridization experiments and a computerized numerical analysis of total soluble cell proteins indicated that authentic strains belonging to the subspecies of L. casei are genotypically closely related to L. casei subsp. casei ATCC 334. According to Rules 18g and 18i of the International Code of Nomenclature of Bacteria, replacement of a neotype strain can be requested if ''an original strain that should constitute the type of a species is discovered subsequent to the final proposal or establishment of a neotype for that species'' or if the neotype has become ''unsuitable due to changes in its characters or for other reasons.'' We request that the Judical Commission designate strain ATCC 334 in place of ATCC 393 as the neotype strain of L. casei subsp. casei. Furthermore, we request that the species name L. paracasei be rejected
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
