Utilisation of Dates in Biotechnology II
Biotechnological Ethanol Production using Juice Raw Dates in a Fixed Cell Process
Abstract
Dates juice is one of the richest foodstuff in neutral compounds such as carbohydrates, minerals, salts and vitamins .These substances considered as essential elements for the growth of microorganisms especially yeast. The ability of two strains of Saccharomyces Cerevisia and Candida utilis to utilize the dates juice had been studied .The results showed that S.cerevisia has a high ability to metabolize dates juice for ethanol production .The data on optimization of physiological conditions of fermentation (pH, temperature and carbohydrates concentration )showed similar effects on immobilized and free cells of S.cerevisia and C.utilis, in batch and immobilized fermentation of S.cerevisia .A maximum yield of 12.8%,13.4% w/v ethanol obtained respectively from 200 g/L dates juice when fermentation was carried at pH 4.5 and 30° C using s.cerevisiae ,these result suggests that dates juice can be metabolized effectively for ethanol production using immobilized S.cerevisiae cells.
INTRODUCTION
The Immobilized yeast technologies present a relatively new method for sugar fermentation and ethanol production (Ntagasetal, 2005). Dates juice ingredients are considered as essential elements for the growth of micro-organisms especially yeasts. Raw date juice used for the production of ethanol Alogaidi, 1987). Finding the best method and optimum conditions for fermentation is required in the process of producing ethanol. From raw date juice Several methods were used for fermentation such as immobilized cell method for Saccharomyces cerevisia by using different carriers like sodium alginate, Calcium alginate, polyacrylamide, collagen and Agar ( Cheryan and Mehaia, 1985; Freer and Detroy,1983 ;Hahn,1985 ; Mehaia and Cheryan,1984).
They found that the productivity of ethanol by immobilized cells method is higher and economically better than free cells method.
The concentration was 76-78% in Brix unit and serial concentrations were prepared from the main concentration. More over we used to complete the fermentation process under the same conditions from Saccharomyces cerevisai and Candida utilis. Two different methods where used, immobilized cells and free cells methods after determination the optimum conditions for fermentation (Temperature, pH, sugar concentration).
Material and methods
- Isolates of yeast strains Saccharomyces cerevisia and Candida utilis were obtained and kept in 2% sucrose, 1 % yeast extract, 2% peptone, 2% Agar, and re-culturing of these strains was done every 15 days.
- Date's juice was obtained from local sayer date's syrup, the following concentration were prepared 50, 100, 200, 300 g/l. pH was ad justified to 4.5 by using HCL N.
- Fermentation was done by using 250 ml glass flask containing 100 ml of the media in anaerobic conditions at 30ْ C for 48 hours. Cells were collected by centrifugation at 4500 rpm for 15 min. Then they were used for immobilization by carriers of sodium alginate according to (Marwaha and Kennedy, 1984). That was by putting them in glass tube of 50cm in length and 2 cm in radius, the flow rate of the liquid reached 6ml/hours.
- Analytical methods: total and residual sugars were calculated according to (Nickerson et al., 1975) and (Remington, 1940) methods respectively. While the measuring of ethanol was done by GLC according to (Marwaha and Kennedy, 1984) or by pyrometer method of (Nanba et. al, 1987).
Results and Discussion
This study determines the optimum condition for fermentation by free cell method. Initial experiments were designed to find out the optimum time to produce ethanol.
Results showed that the production of ethanol by S.cerevisiae reached 8.4% after 36 hours. Whereas the ethanol by C.utilis reached 6.8% after 48 hours. Which mean that Saccharomyces cerevisiae is better than Candid utilis in the metabolism of monosaccharides and disaccharides found in date's juice and converting it to ethanol.
The results of conditions effect found that the optimum temperature for fermentation process by the two methods free and immobilized cells was 30ْ C for both Saccharomyces cerevisiae and Candid utilis. The residual sugars percentage reached 0% in this temperature and the metabolism to ethanol to reached 100%. As shown in figures (1, 2, 3, 4). We can also conclude that S.cerevisiae was the best in the production of ethanol, thus it gave 10.6% at 30ْC by free cells method with presence of 0.4g/l residual sugar by this yeast. While the immobilized cells gave 11.4% ethanol with complete consumption of the residual sugar found in the media. Figures (5.7) showed the effect of pH on the fermentation other conditions and the productivity of ethanol. The productivity increase at pH4.5 by fixing the temperature at 30ْ C. Figures (6.8) shows that S.cerevisiae strain is the best in the production of ethanol and its metabolism of sugars found in date's juice was 100%.
It is noticed from the figures (9.10.11.12) that 20% was the best to produce 12.8% of ethanol when using S.cerevisiae in free cells method, and 13.4% ethanol when those cells were immobilized by Sodium alginate (optimum conditions for fermentation were used: temperature 30ْ C, pH 4.5).
The reason for the descent of ethanol production rate at high concentrations 30% to the inhibition that occurred when the atom of carbon hydrolyze. As a result of losing off activity of enzymes especially invertase enzyme due to raising ethanol percentage in the media.
From the experiment mentioned above that immobilized can be used in the production of ethanol and from inexpensive sources, presented by date's juice, thus the productivity reached almost 13.4% when using immobilized cell method by yeast of S.cerevisiae . In addition to that this method has large economical advantages (Ntagas et al., 2005). Thus yeast cells keep their activity and fermentation affectivity for more than 3 months (Mohite and sivaraman, 1984).
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