Browsing by Author "Gouws, Pieter A."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Effect of colony age on near infrared hyperspectral images of foodborne bacteria
    (IM Publications, 2019-01-30) Williams, Paul J.; Kammies, Terri-Lee; Gouws, Pieter A.; Manley, Marena
    Near infrared hyperspectral imaging (NIR-HSI) and multivariate image analysis were used to distinguish between foodborne pathogenic bacteria, Bacillus cereus, Escherichia coli, Salmonella Enteritidis, Staphylococcus aureus and a non-pathogenic bacterium, Staphylococcus epidermidis. Hyperspectral images of bacteria, streaked out on Luria—Bertani agar, were acquired after 20 h, 40 h and 60 h growth at 37 °C using a SisuCHEMA hyperspectral pushbroom imaging system with a spectral range of 920–2514 nm. Three different pre-processing methods: standard normal variate (SNV), Savitzky—Golay (1stderivative, 2nd order polynomial, 15-point smoothing) and Savitzky—Golay (2nd derivative, 3rd order polynomial, 15-point smoothing) were evaluated. SNV provided the most distinct clustering in the principal component score plots and was thus used as the sole pre-processing method. Partial least squares discriminant analysis (PLS-DA) models were developed for each growth period and was tested on a second set of plates, to determine the effect the age of the colony has on classification accuracies. The highest overall prediction accuracies where test plates required the least amount of growth time, was found with models built after 60 h growth and tested on plates after 20 h growth. Predictions for bacteria differentiation within these models ranged from 83.1 % to 98.8 % correctly predicted pixels.
  • Thumbnail Image
    Item
    Food preservative capabilities of grape (vitis vinifera) and clementinemandarin (citrus reticulata) by-products extracts in South Africa
    (MDPI, 2019-03-22) Pfukwa, Trust M.; Fawole, Olaniyi A.; Manley, Marena; Gouws, Pieter A.; Opara, Umezuruike Linus; Mapiye, Cletos
    The drive towards sustainable food systems coupled with increased consumer sophistication have prompted innovation in waste valorization. Grape and citrus processing by-products, abundant in the Mediterranean and tropical regions, respectively, are expanding and are sustainable sources of bioactive phytochemicals that can be used as natural preservatives for foods. Phytochemical composition, antioxidant, and antimicrobial properties of extracts from grape pomace (GPE), seeds (GSE), and clementine mandarin peel and pulp (MPE) grown in South Africa were analyzed. Total phenols and carotenoids were highest in GPE followed by GSE and MPE (p ≤ 0.05). Flavonoids and anthocyanins were higher (p ≤ 0.05) in GPE and GSE compared to MPE. The GSE had the highest proanthocyanidins content followed by GPE and MPE (p ≤ 0.05). Ascorbic acid was only detected in MPE, which also had the highest titratable acidity and lowest pH values (p ≤ 0.05). The GSE had the highest antioxidant potency composite index followed by GPE and MPE (p ≤ 0.05). The order of antimicrobial activity of the extracts was MPE > GSE > GPE (p ≤ 0.05). Current findings show that GSE is a potential antioxidant while MPE holds promise as an antimicrobial for the food industry.