In the field of biotechnology, now days the most concentrating point in order to reduce pollution is the production of ethanol and other value added product from agriculture waste. The fruit wastes are highly biodegradable; therefore they could be preserved by drying and may well be used for further processing for a long time. Pakistan is at number 30 in the production of water melons. The water melons are usually consumed throughout the summer. The usage of water melon in summer produced huge amount of waste every year. There is dire need to manage this waste because of easy degradation and causing pollution in environment.
The study investigated the potential of yeast isolate to convert the water melon hydrolysate to ethanol and optimization of hydrolysis condition by Response surface methodology using central composite design at 23factorial level.In optimization variable factors were acid concentration (X1), hydrolysis temperature (X2) and hydrolysis time (X3) whereas the reponses were reducing sugars, total carbohydrates, weight loss, extractive, hemicellulose, lignin and cellulose contents. Different acids i.e sulphuric acid, hydrochloric acid and nitric acid were used to hydrolyse water melon peels.
In sulphuric acid hydrolysate the observed optimum values for reducing sugars, total carbohydrates, weight loss, extractive, hemicellulose, lignin and cellulose contents (%) were 4.56±0.05, 19.45±0.16, 24.35±0.37,32.14±0.07, 28.46±0.013, 14.48±0.04 and 24.92±0.04 respectively at 6% acid concentration,50˚C for 60 minutes. The experimental values were more than the predicted values for all responses except extractive. The model is significant for weight loss only and non-significant for all other responses with F value less than 4 and R2values varied from 0.5-0.7. On the basic of results 4.56% reducing sugar were recorded with 24.35% weight loss.
In hydrochloric acid hydrolysate the optimum values (%) were 6.34±0.05, 19±0.07, 18.94±0.26, 38.28±0.07, 24.62±0.04, 10.14±0.05, 26.96±0.08 for reducing sugars, total carbohydrates, weight loss, extractive, hemicellulose, lignin and cellulose contents at 6% acid concentration, 100 ˚C for 60 minutes. The experimental values for reducing sugar, lignin and cellulose were less than the predicted values while total carbohydrate, extractive weight loss showed more experimental values than the predicted values. The model is non significant for all responses with F value less than 4 and R2 valued varied
xi from 0.5-0.7. On the basis of results 6.34% reducing sugar were recorded with18.84% weight loss.
In nitric acid hydrolysate the optimum values (%) were 28.45±0.25, 21.94±0.18, 10.94±0.44, 317.03±0.18, 21.35±0.02, 25.37±0.05, 23.25±0.04 for reducing sugars, total carbohydrates, weight loss, extractive, hemicellulose, lignin and cellulose contents at 3.5% acid concentration, 66 ˚C for 60 minutes. The experimental values for reducing sugars, weight loss, hemicellulose, lignin and cellulose were less than the predicted values but total carbohydrates, extractive showed more values. The model is non significant for all responses with F value less than 4 and R2 valued varied from 0.5-0.7. On the basis of results 28.45% reducing sugar were recorded with10.94% weight loss.
In the present study the detoxification was done with 2.5% charcoal treatment for improving the quality of fermentation. The reduction in phenol contents can be seen by investigating untreated hydrolyzate and treated dilute sulphuric acid, nitric acid and hydrochloric acid hydrolyzates. The phenolic were reduced to 19% in sulphuric acid hydrolysate. After detoxification and neutralization, fermentation was carried out using yeast strains Metschnikowia sp. Y31 and Metschnikowia cibodasenesis Y34. While Saccharomyces cerevisiae K7was used as standard yeast in fermentation experiment.
The reducing sugar (%) after H2SO4, HCl and HNO3 hydrolysis yield 3.56±0.02 (on day 8), 2.32±0.004 (on day 9) and 2.90±0.05 (on day 5) % ethanol respectively by Metschnikowia sp. Y31 and 3.29±0.013(on day 4), 2.77±0.002 (on day 5) and 2.66±0.05 (on day 8) % ethanol correspondingly by Metschnikowia cibodasenesis Y34. While with Saccharomyces cerevisiae K7the ethanol yield(%v/v) was 3.28±0.03 (on day 5), 3.51± 0.06 (on day 6) and 3.23±0.06 (on day 9).