POST-HARVEST PROCESSING OF COCOA BEANS (THEOBROMA CACAO L.) USING SOLID STATE FERMENTOR AND METABOLOMIC APPROACH TO DETERMINE THE QUALITY OF COCOA BEANS

• Main Author: Putri Kumalasari, Ditta
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/69545
• Institution: Institut Teknologi Bandung

In Indonesia, cocoa is one of the mainstay commodities of plantations and quite important for the national economy. However, the quality of Indonesian cocoa beans is still at grade 3. This is because most of the cocoa bean production comes from smallholder plantation (98.38%), while those owned by the government and private sector are only 0.75% and 0.87%, respectively. Nearly 80% of the cocoa produced by smallholders has not been processed properly. One source of cocoa plantations is in the Senara Chocolate Village area, Genggelang Village, Gangga District, North Lombok Regency, West Nusa Tenggara (NTB). In these areas cocoa beans processing is still simple by doing natural fermentation or the beans are sold directly (without fermentation). This causes the taste and aroma of cocoa beans to be inconsistent. Therefore, it is necessary to do controlled fermentation to standardize the fermentation process. The aims of this study were (1) to determine the dynamics of the microbial population that occurred during the natural fermentation process using a 20 kg wooden box for 5 days; (2) knowing the microbial species used as inoculum in controlled fermentation; (3) optimizing controlled fermentation with a single inoculum variation (lactic acid bacteria), and a consortium (lactic acid bacteria: yeast) (1:1) with an inoculum concentration of 10% (v/w) and a cell density of 109 CFU/mL at a temperature of 37°C for 5 days using a 2 kg scale bamboo basket; (4) scale up controlled fermentation with the addition of variations in inoculum and the best fermentation time on a scale of 20 kg using a wood fermenter equipped with IoT (Internet of Things) at 37°C; and (5) examine the precursor metabolites that affect the taste of cocoa at optimum conditions. The characteristics of the cocoa fermentation process were determined by parameters of temperature, pH, weight loss, fermentation index, moisture content, and number of cocoa beans per 100 grams, as well as organoleptic tests. The results of microbial isolation obtained during the natural fermentation process were also screened using enzymatic tests (pectinolytic, proteolytic, amylolytic, cellulolytic, lipolytic), sugar fermentation tests (glucose, fructose, sucrose), and total alcohol production. Furthermore, the selected isolates from the results of the enzymatic test were added to a controlled fermentation process using a 2 kg scale bamboo container at 37 °C, and data were collected every 24 hours for 5 days. Next, scale up with the best inoculum treatment using an IoT-based wood fermentor with a scale of 20 kg at 37 °C. Cocoa beans were fermented at the optimum conditions, then analyzed for metabolites using GC-MS. Statistical analysis to determine the correlation of metabolite content during the fermentation process used multivariate Principal Component Analysis (PCA) on Minitab® software. Results from this study showed that during natural cocoa fermentation process, the microbial population dynamics was dominated by three groups of microbes (yeast, lactic acid bacteria, and acetic acid bacteria) with temperature changes starting from 28 °C to 43 °C. On day 0, the microbial population was dominated by yeast with a cell density of log 7.88 CFU/gram, but decreased by log 0.46 CFU/gram in day 2, and increased again by log 1.53 CFU /gram on the 5th day. Then, the microbial population was continued by lactic acid bacteria, which tended to increase from day 0 to day 5 with an increase in the log cell number of 1.20 CFU/gram. While acetic acid bacteria showed the lowest population during the fermentation process, the log value of the number of cells on day 0 was 6.72 CFU/gram, and day 5 was 8.57 CFU/gram. This change in microbial dynamics was followed by a change in the degree of acidity (pH) with the lowest pH value of 3.30 on the 3rd day and the highest pH of 6.45 on the 5th day. The characteristics of natural fermentation have a fermentation index value of 50%, water content of 4.90%, and quality of beans per 100 grams included in category B. From the results of natural fermentation, 14 isolates of yeast, 15 isolates of lactic acid bacteria, and 8 isolates of acetic acid bacteria were also isolated. Based on the results of the enzymatic test, 2 superior isolates were selected, namely H5B7-1 (lactic acid bacteria) and H1Y4-1 (yeast). The H5B7-1 isolate (Lactiplantibacillus plantarum) had a high amylolytic ability, while the H1Y4-1 isolate (Candida tropicalis) had the highest alcohol production ability and showed a positive (+) value in the fermentation test. The two isolates were added to a controlled fermentation process with a single inoculum variation of lactic acid bacteria (H5B7-1) and a consortium inoculum (lactic acid bacteria-H5B7-1 : yeast-H1Y4-1) (1:1) with a initial microbial concentration of 10% (v/w), and the cell density of H5B7-1 was 3.4 x 109 CFU/mL and H1Y4-1 was 1.1 x 109 CFU/mL. The results of controlled fermentation showed that the addition of a single inoculum of lactic acid bacteria (H5B7-1) on day 4 was better with the fermentation index parameter showing the highest value reaching 75% compared to the addition of a consortium inoculum of 70%. The results of the scale-up are also able to improve the quality of cocoa beans with a fermentation index value reaching 90% of well fermented cocoa beans, and are included in category A (88 beans) for the number of beans per 100 grams. The metabolite content of cocoa beans in the best controlled fermentation (day 4) was positively correlated with the aroma precursor metabolites in the form of amino acid leucine (sweet chocolate), threonine (chocolate), phenylalanine (almond, floral/honey), and 2,3-butanediol (buttery). In addition, there are also precursor metabolites of bitter taste (bitterness-cocoa flavor) with a high content of glutamic acid. This is also correlated with the results of organoleptic tests, which show the aroma of chocolate is quite strong, with a bitter taste and a slightly dark brown color.