Food & Nutrition

Arab Journal of Food & Nutrition
List A: English Abstracts of Master Student Theses in Jordan in
Food Science and Technology until December,2010.
1. Effect of Yeasts on the Quality and Shelf Life of Labaneh (1990)
Maha M. Abu – Jaber\ University of Jordan
Supervisor: Dr. Mohammed Isam Yamani
Labaneh samples from 19 producers were examined for the presence of yeasts,
and for their effect on its shelf life and sensoric properties.
Directly after packaging, the mean yeast counts were 2.6 x 10 6 /g, 4.4 x 10 6 /g
and 2.6 x 10 5 /g for psychrotrophic , mesophilic and facultative thermophilic yeasts,
respectively. The percentages of samples showing yeast counts above 10 6 /g were 45,
50 and 5 for psychrotrophic, mesophilic and facultative thermophilic yeasts,
respectively. Signs of spoilage were observed in 25 % of the labaneh samples at the
same day of packaging. This indicates high initial contamination with yeasts that could
be attributed to poor hygienic practices through any of the steps of labaneh production.
At expiry date (14 d at 7 °C) the mean yeast counts increased to 1.1 x 10 7 /g, 1.4 x
10 7 /g and 2.3 x 10 6 /g for psychrotrophic mesophilic and facultative thermophilic,
respectively. The percentages of samples that showed yeast counts above 10 6 /g
increased to 70, 75 and 35 for psychrotrophic, mesophilic, and facultative
thermophilic, respectively. All labaneh samples produced by the traditional method
were spoiled at expiry, while the labaneh samples produced by the mechanized method
showed yeast count < 10/g directly after packaging and at expiry. This was proved to
be due to the addition of mycostatic agents.
Isolated yeasts were identified to species level Saccharomyces cerevisiae biovars
were the most frequently isolated yeasts found in all the samples containing yeasts.
Trichosporon brassicae, Cryptococcus curvatus and Kluyveromyces marxianus (var.
lactis and bulgaricus) followed Sacch. cerevisiae with an occurrence of 33.34%,
27.78% and 16.67 %, respectively. Trichosporon cutaneum, Debaromyces hansenii
Pichia farinosa var. lodderi, Geotrichum candidum and Candida blankii were the least
frequent yeasts with an occurrence of 5.56 % for each species. The predominance and
growth of these species in labaneh could be attributed to their ability to utilize the
available carbon sources (glucose, galactose, lactose, lactic acid ) in labaneh, grow at
different temperatures of labaneh processing (25°C, 43°C) and storage (7°C) and to
produce lipolytic and proteolytic enzymes.
The effect of yeast growth on the sensoric quality of labaneh was carried out
using six yeast species K. marxianus var. lactis, Tr, cutaneum, G. candidum and
Sacch. cerevisiae biovar 1 and 4 by inoculating these yeasts into pasteurized labaneh.
Pasteurized labaneh without yeasts was used as a control sample.
Paired preference test was used to investigate which samples in each pair (control
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Volume 11, No. 25, 2011