Masters Degrees (Food Science)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/538

Browse

Browsing Masters Degrees (Food Science) by Author "Arendse, Garron Mark"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Selection and metabolic characterization of mesophylic starter cultures for optimizing the sensory attributes of fruit flavoured Maas
    (Stellenbosch : Stellenbosch University, 2000-03) Arendse, Garron Mark; Britz, T. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science .
    ENGLISH ABSTRACT: Maas is a traditional fermented milk drink of the indigenous people of Southern Africa and can thus be used to uplift the nutritional status of the South African population, especially for the lower income groups. Furthermore, the problem of lactose intolerance among the Black population can also be addressed by the consumption of Maas. The objective of this study was to screen mesophylic lactic acid bacterial strains (25 in total) from the University of Stellenbosch Food Science Culture Collection for suitable metabolite production and then to produce traditional Maas with a starter culture combination that produces a distinctive acid and traditional flavour. The representative 25 single lactic acid starter strains were identified as Lactococcus lactis subsp. leetis biovar diacetylactis (12 strains), L. leetis subsp. leetis (four strains) and L. leetis subsp. cremoris (nine strains). These strains were inoculated into pasteurised full cream milk and activated for 8 h at 22°C. Pasteurised full cream milk was then inoculated with each of the activated starter strains, incubated at 22°C for 16 h and assessed for acid production abilities (pH = 4.6) under controlled time-temperature conditions. The results of this study showed that nine of the single strains, L. lactis subsp. leetis biovar diacetylactis (S1, S2, S3 and S5), L. teetis subsp. lactis (S13, S15 and S16) and two L. leetis subsp. cremoris strains (S17 and S22), produced sufficient acid, rendering them suitable for the use as starters in the production of traditional Maas. A pH range of 4.3 - 5.1 was reached by the nine single strains after 16 h at 22°C. Two-strain starter combinations were then formed by combining the most suitable single L. leetis subsp. leetis biovar diacetylactis, L. lactis subsp. lactis and L. lactis subsp. cremoris strains, respectively. From the data, it was concluded that acceptable Maas could be produced with four two-strain combinations (S3S 17, S3S22, S5S17 and S5S22). This selection was again based on suitable acid and metabolite production, as well as on sensory evaluation of the final product. These four two-strain combinations produced sufficient acid to reach a pH in the 4.6 - 4.8 range, and showed a high metabolite concentration for the most suitable compounds and formed a thick, smooth and creamy body texture after 16 h at 22°C. Three-strain combinations formed between the two-strain starter combinations and L. leetis subsp. teetis strains (813, 815 and 816), were also evaluated. With these combinations a lack of a pronounced Maas flavour was found. Thus, it was decided to add aroma producing strains of the species Leuconostoc mesenteroides subsp. dextranicum (strain L1) and L. mesenteroides subsp. citrovorum (strain L2) to the three-strain combinations. Four culture combinations (A, B, C and D) were then formed by combining the selected Leuconostoc strains (L1 and L2) with the most suitable Lactococcus strains (83,817,813 and 822). These combinations produced sufficient acid to reach the pH 4.5 - 4.6 range after 14 h at 22°C. Acetaldehyde was the major flavour metabolite formed in the Maas made with these four combinations, with concentrations ranging between 26.6 - 89.3 mg.l ̄ ¹, while other flavour metabolites (ethanol, acetone, diacetyl and 2-butanone) were present at lower concentrations. It was found that three of the four culture combinations (A, C and D) were characterised by a superior, but delicate flavour and a typical characteristic Maas body texture. Fruit flavoured Maas was subsequently prepared with the three most suitable culture combinations (A, C and D) using 11 flavours and a sensory evaluation performed. The statistically evaluated data showed that the appearance, smoothness, flavour intensity, sweetness and overall acceptability were influenced by the type of fruit flavour and the culture combination. Fruit flavour 4 (banana) was the most preferred flavour. The sensory panellists also indicated that the culture combination C gave the best overall acceptability over a three week study period. Data on the shelf-life study of natural unflavoured Maas, prepared with the three culture combinations (A, C and D), showed that the Maas still had an acceptable appearance, taste and good microbiological quality after 15 d at refrigerated temperatures.