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Isolation and Identification of Indigenous Bakers’ Yeast

Nasrin Jahan

Nafisa Azmuda

Anisur Rahman Khan

Abstract/ Executive Summary:

This investigation was performed to isolate and identify indigenous bakers’ yeast. Initially, 75 yeast isolates were collected from different sources such as decomposed fruits, fermented rice and fermented fruit juices. Twenty five isolates were selected by primary screening; among them, ten isolates were considered as potential bakers’ yeasts on the basis of their ability to produce high amount of biomass and leavening action. Two isolates were identified as Saccharomyces cerevisiae, seven as Saccharomyces species and only one as Kluyveromyces species. These isolates have sufficient potential to be produced commercially after evaluation of some baking parameters like texture and organoleptic properties.

Keywords: Bakers’ yeast, Saccharomyces cerevisiae, Cell mass, Leavening action

Location: Department of Microbiology, University of Dhaka

Start Date:

End Date:

Program Area: Resource Development and Management

Commodity: Fermenters

Objectives:

To isolate and identify indigenous bakers’ yeast in this study.

Methodology:

Malt extract yeast extract glucose peptone (MYGP) medium, urease test broth, bromocresol purple broth, nitrate broth, yeast extract agar media and actidione agar media were used to isolate and identify indigenous yeast isolates. Indigenous yeasts were isolated from different decomposed fruits such as mango, banana peel, apple, grape, lichi, black berry, date fruit, jack fruit, orange, pine apples as well as fermented sugar cane juice and fermented rice. The isolation and identification of yeasts were carried out as described by Perkins12. Biomass mass production was carried out according to standard procedure13. Dough was prepared by mixing 0.5 g yeast cells, 50 g wheat flour, 4.0 g sugar, 1.0 g salt, 10 ml fresh milk, 1 ml soybean oil, 1 tea spoon of egg, 1 tea spoon of butter and 60 ml water. All the ingredients were homogeneously mixed and incubated at 30°C for fermentation. The dough volume was recorded at every 60 min interval. The initial and final dough volumes were recorded from the graduated surface of the beaker and the net increased volume was calculated according to the standard procedure13. Initially, 75 yeast isolates were recovered from various sources. Among them 25 potential isolates were screened out on the basis of cell mass production and leavening action.The cell mass production ranged from 9 to 24 mg/ml. Among the isolates, FSC-1, FSC-2, DP-2, DP-4, DG-4, DG-6, FR-1, DM-1, DB-1 and DA-2 exhibited relatively higher cell mass yield ranging from 13 to 24 mg/ml. These isolates were then used to check their leavening action. The leavening action of these ten isolates was found to be superior to the remaining other isolates that showed 80.00 to 105.00% increase of dough volume after fermentation. These indigenous isolates were considered as potential for baking purposes.

Source of Information: Bangladesh J Microbiol, Volume 24, Number 1, June 2007, pp 65-66

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The present study showed that some indigenous yeast isolates could be considered as potential sources of bakers’ yeasts considering the biomass yield and leavening action. However, dough fermented with indigenous bakers’ yeasts should be evaluated for bakery products with respect to texture taste and aroma. In addition, bread content of the essential amino acids lysine, methionine and threonine should be evaluated and pilot plant scale study for mass production of the isolates should be carried out in future for their industrial use.

Knowledge Management: Journal