Summary

Acetic acid bacteria (AAB) are Gram-negative aerobic bacteria, and used for the commercial production of vinegar and other industrially important materials, such as L-sorbose for vitamin C production, and D- gluconic acid from D- glucose.

Studies on AAB from Sri Lanka have been done very limitedly. Thus, during current research project isolation, identification and characterization of AAB from various sources from Sri Lanka will be done. In current fermentation industry, mesophilic AAB strains that perform at temperatures around 30˚C are been used. But, during fermentation, a heat is generated, and this will badly affects the efficiency of fermentation. Thus, throughout the study, screening of thermotolerant and thermo-adaptive AAB strains which could grow and perform oxidative fermentation at higher temperatures will be also attempted. Moreover, in Sri Lanka, there are many kinds of fruits which are underutilized, and also with high post harvest losses due to poor handling. Such fruits could be utilized through development of fermented healthy nonalcoholic beverages such as fruit vinegar and gluconic acid beverages. Furthermore, these developed products would be a good source of functional food for people who are suffering from non-communicable diseases such as diabetic, cholesterol, high blood pressure, and cancer as well as for healthy people due to the presence of antioxidants and secondary metabolite with health benefits produced during the fermentation process. Also, development of such healthy beverages will be beneficial for the uplift of traditional AAB fermentation industry in the country because to local market on AAB fermentation is dominated by traditional coconut water vinegar that used only for culinary purposes.

In order to achieve the above mentioned goals, AAB (both Acetobacter type and Gluconobacter type strains) will be isolated from different sources in Sri Lanka with using appropriate isolations media. Species level identification of the isolated strains will be done with using morphological, biochemical and molecular biological techniques. Then, the strains showing high performance in oxidative fermentation at higher temperatures will be selected, and the relevant thermo-adapted strains will be developed by repeated breeding of the thermotolerant strains. Subsequently oxidative fermentation by isolated thermotolerant strains and the developed thermo-adapted strains will be attempted with using underutilized fruits and fruits with high post harvest losses to produce healthy non-alcoholic beverages. Finally, the effect of the developed products on selected non-communicable diseases will be examined with using appropriate cell line assays together with antioxidant assay.

Since, studies on AAB from Sri Lanka is limited, this research would be a good scientific source about diversity of AAB in Sri Lanka. Furthermore, isolation of thermotolerant AAB and development of thermo-adapted strains would be beneficial for the fermentation industry in tropical countries such as Sri Lanka. The development of value added non-alcoholic beverages would be helpful to strengthen the fermentation industry as well as improving the product diversification in the local market. These products would be a good source of functional food for non-communicable diseases as diabetic, cholesterol, high blood pressure, and etc. Moreover, as a result of this research project, a student will be graduated with a M.Phil degree, and the research finding will be presented in national and international forums together with at least two peer reviewed journal publications.

Objectives

To develop value added fermented beverages (fruit vinegar and beverage rich in gluconic acid) from underutilized fruit crops with using AAB isolated from Sri Lanka

Specific Objectives:

1. To isolate, identify, and characterize AAB from various sources in Sri Lanka

2. To screen thermotolerant AAB (Acetobacter type) that showing high acetic acid production from ethanol at 40˚C or higher temperatures, and Gluconobacter type strains which show high ability to produce L-sorbose from D-sorbitol and D-gluconic acid from glucose

3. To perform oxidative fermentation from the selected strains in order to produce different types of fruit vinegar and beverages rich in D-gluconic acid with using localy available underutilized and wasted fruit and vegetable sources

4. To evaluate the health benefits (antidiabetic effect, antiobesity effect, and cholesterol reduction ability) given by the developed fermented beverages

Major Equipment Facilitated by Grant