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To investigate the effect of cellulase on fruit juice extaction.

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Introduction

AS LEVEL BIOLOGY COURSEWORK TO INVESTIGATE THE EFFECT OF CELLULASE ON FRUIT JUICE EXTRACTION A METHOD An amendment was made to the suggested method for practical reasons. Instead of leaving the apple puree in the enzyme solution for twenty four hours at room temperature, beakers containing the samples were immersed for one and a half hours at 40oC in a thermostatically controlled water bath. B RESULTS Table of Results See over for table prepared for results and observations and completed during the experiment. Since the 0% enzyme immersion solution would not be expected to change fruit juice extraction, this datum was used as a control and fruit juice volume produced calculated by subtracting this baseline volume from the total observed at each enzyme concentration (see table below). The percentage of cellulase is the independent variable and the increased or decreased volume of juice produced is the dependent variable. % cellulase solution Total volume of apple juice (+ enzyme solution) produced cm3 Change in volume cm3 due to enzyme activity 0 10.3 + 0.0 0.5 15.2 + 4.9 1.0 15.8 + 5.5 1.5 10.1 - 0.2 2.0 17.2 + 6.9 C GRAPH (see graph paper over) ...read more.

Middle

and increasing enzyme availability. Increased concentration of enzyme provides more active sites for substrate binding. So long as excess substrate is available, the reaction rate increases in proportion to enzyme concentration (see over). If substrate is limited, an increase in enzyme availability does not result in increased reaction rate because active sites have no substrate to bind and the reaction rate plateaus. The experimental graph shows a tendency towards a plateau of the reaction rate with increasing enzyme concentration indicating that substrate concentration (i.e. apple cell wall cellulose) was limiting. However, a plateau was not actually reached as high enough enzyme concentrations were not used (see D 1 g below). D EVALUATION 1) Limitations of the Experimental Method a) Replicates No replicates were carried out. At least 3 sets of data should have been obtained in order to be certain that results are meaningful, to identify the trends and to identify anomalous results. b) Even Puree? The apple pulp could not be evenly pureed with the blender because the volume was too small. There were some lumps. This could have resulted in variation in the total surface area of apple presented to the different enzyme solutions and therefore in cellulose available for reaction. ...read more.

Conclusion

Pectins bind water tightly and therefore prevent loss of cell sap. c) Varying sources of substrate Different varieties of apple could be used using the same weight and consistency of puree for each experiment. The effect of storage and age of the fruit could also be investigated. d) Rate of extraction of juice This could be established by immobilising the cellulase - for instance in alginate beads mixed with the substrate in a column with an outlet at the bottom - and measuring the liquid produced per unit time under different conditions. The initial reaction rate could be measured by plotting volume produced against time and measuring the gradient of the asymptote at zero time. Initial reaction rates at different substrate concentrations could be plotted against substrate concentration to investigate Michaelis-Menten kinetics of the enzyme. A Lineweaver Burk plot of the reciprocal of initial velocity against the reciprocal of substrate concentration would give the Michaelis constant which gives an indication of the turnover rate of the enzyme. e) Conditions for optimum fruit juice extraction The experiment could be repeated with differing incubation times at the optimum temperature and pH (see a) above) to find the conditions under which maximum fruit juice extraction occurs. This would be the pilot stage of a design to produce apple juice commercially. ...read more.

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