Biochemical changes in fermented durian (Durio zibethinus Murr)

Reports on microbial and biochemical process responsible for the fermentation of durian (tempoyak) are limited. This study was conducted to evaluate the biochemical changes during fermentation of tempoyak. Biochemical changes of fermented durian revealed that there were significant changes at 4-days fermentation in pH, acidity, and total lipid. Changes in pH and acidity were highly significant at 4-days fermentation, where a rapid decrease in pH from pH 6.9-7.0 to 4.0-4.2 and increases in acidity were observed. Samples inoculated with Pediococcus had the highest total acidity and non-volatile acidity but lowest in volatile acidity. Total lipid decreased with longer fermentation time for all treatments (7.99-5.14%) but only slower reduction for non-starter treatment (7.99-6.60%). In terms of reducing sugar, Weissella and mixed starter treatments showed an increasing trend after day-8 fermentation (2.36-4.54%). Meanwhile, Pediococcus and no starter treatments showed an increasing pattern from day-0 to day-12 (2.82-5.79%). Organic acids found in tempoyak were malic acid, followed by lactic acid, and small amounts of acetic acid. The flavor examination showed that there were 24 sulfur compounds and 31 non-sulfur compounds found in fresh durian. In fermented durian, 20 sulfur compounds and 36 non-sulfur compounds were found. Of the sulfur compounds, diethyl trisulfide had the highest concentration in fresh durian, while the concentration of 3,5-dimethyl-1, 2,4 trithiolane was the highest in fermented durian. Among the non-sulfur compounds present in both fresh and fermented samples, butanoic acid, 2-methyl ethyl ester was found in the highest amounts. Flavor examination of tempoyak inoculated with different LAB starters showed that no starter, Weissella, Pediococcus and mixed starter treatments had 22, 25, 50 and 56 compounds, respectively. These compounds were thiol, ester, alcohols, aldehyde, alkane, ketone, and unknown compounds. The sulfur compounds, diethyl trisulfide and diethyl disulfide, were the major components followed by ethane, 1-1-bis ethyl thio. Identification of microflora revealed that bacterial populations in tempoyak consisted mainly of lactic acid bacteria: Lactobacillus plantarum, Lactobacillus sp., Pediococcus acidilactici, and Weissella paramesentoreides. Sensory evaluation of tempoyak inoculated by different LAB starters showed that Pediococcus and mixed starter treatment gave the highest acceptability.