SALAK FRUIT (SALACCA ZALACCA) POTENTIAL FOR CITRIC ACID PRODUCTION USING ASPERGILLUS NIGER

• Main Author: Ayu Mungkashi, Galuh
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/46393
• Institution: Institut Teknologi Bandung

The most commonly known species of salak is Salacca zalacca. In Tasikmalaya area, this variety is known as Salak Manonjaya. Its popularity progressively decreased compared to the other type of salak fruit. This condition is very worrying and will cause the loss of this variety in the future. Carbohydrate content of salak fruit reaching 20.90% and its productivity reaching 105,321 quintals / year in Tasikmalaya, making it suitable to be substrate in the process of citric acid fermentation. The use of salak as a substrate for citric acid production will be one of new alternatives in the use of salak fruit which comes from Tasikmalaya area. Aspergillus niger is known to produce citric acid with glucose as the main substrate. Glucose can be obtained from carbohydrates hydrolysis by amylase enzyme. This research aims to determine the potential of salak fruit with rice bran to produce citric acid using A. niger with Solid State Fermentation (SFF) method. In this study, the selection of two A. niger isolates obtained from the culture collection of Microbiology SITH (A. nigera) and Chemical Engineering ITB (A. nigerb) laboratories based on their ability to produce amylase was conducted. The isolate which has the highest amylase activity would be used for further experiment. The inoculum was prepared by determining the optimum time of cell growth based on biomass or time using a mixture medium of PDB and salak fruit (25:75 %). Citric acid fermentation was carried out for 144 hours using salak and rice bran with different substrate ratio namely of F1 = 100: 0 b/b (control), F2 = 90:10 b/b, F3 = 85:15 b/b, and F4 = 80:20 b/b. In addition, the optimization of initial pH fermentation with different variations of pH 2.75, 3.00, 3.25, and 4.52 (control) was also carried out. The parameters analyzed were citric acid, amylase enzyme activity, pH, and total acid. Citric acid analysis was carried out through qualitative (chemical reaction) and quantitative (UV-Vis spectrophotometer by measuring the absorbance level at ? = 420 nm) analysis based on Murray and Denstedt method. Analysis of amylase activity was determined using a UV-Vis spectrophotometer by measuring the absorbance level at ? = 540 nm based on Miller method. The results showed that A. nigerb isolate had higher amylase activity than A. nigera isolate with ratio value of 1.65. Therefore, A. nigerb isolate was used on further study. Cell productivity at the optimum growth time gave the best fermentation results. The results of A. nigerb growth curve analysis showed a growth rate (?) of 0.066 / hour, a doubling time of 10.48 hours, and optimum inoculum age at 42 hours. These conditions were used for optimizing of citric acid production. Optimization results of the salak fruit and rice bran showed that F3 ratio (85:15 w/w) produced the highest citric acid (29.44% after 60 hours) and the highest amylase activity reaching 425, 73 U/mL (after 24 hours). The optimization results of initial pH variations showed that the highest citric acid was produced at pH 2.75 (45.88% after 48 hours) and the highest amylase activity reaching 432.33 U/mL (after 24 hours). Based on these results, it can be concluded that variations ratio of subtrate and pH variations significantly influenced the citric acid production (P <0.05), especially in the treatment of F3 (85:15 w/w) and pH 2.75.