การแยกและคัดเลือกแบคทีเรียแลคติกและการหาสภาวะที่เหมาะสมสำหรับการผลิตกรดแลคติกไอโซมอร์ดีและแอลจากน้ำคั้นและกากลำต้นปาล์มน้ำมันด้วยระบบการย่อยพร้อมการหมัก

Abstract

Lactic acid (LA) is an organic acid produced by lactic acid bacteria (LAB) and can be used as a monomer feedstock for biodegradable plastic. There are two optical isomers of lactic acid, L(+) and D(-)-lactic acid. This study investigated the process integration strategy for LA production from oil palm sap (OPS) and oil palm trunk (OPT) as mixed substrates through simultaneous saccharification and fermentation (SSF). OPS contained high sugar concentration of 38-40 g/L (26.90±0.06 g/L glucose, 9.18+0.25 g/L fructose, 4.39+0.25 g/L sucrose, 3.04±0.06 g/L xylose) and nitrogen concentration of 0.6-0.7 g/L. It can be used as both carbon and nitrogen source. OPS at sugar concentration of 30 g/L was used as a sole medium for screening of LAB with high LA production. The cultivation was performed at 37°C, 100 rpm for 72 h under condition with and without pH control at 5.5. LAB produced higher LA under pH control condition than uncontrolled pH condition. Lactobacillus acidophilus TISTR 1338 and Lactobacillus kefiri KF1 could grow well in OPS and gave the highest LA production of 21.98±3.36 g/L (L-isomer 62.7%) and 19.31±1.11 g/L (D-isomer 75.4%), respectively, with LA yield of 0.80±0.12 and 0.75±0.04 g/g-available sugar, respectively under condition with pH control. The OPT residues could be separated in to vascular bundle (OPT-VB) (0.75-2.0 mm) and parenchyma (OPT-PA) (<0.75 mm). As OTP-VB contained 56.60% cellulose, 23.44% hemicellulose, 13.70% lignin and 4.76% starch. OPT-PA contained 37.1% cellulose, 29.8% hemicellulose, 18.4% lignin and 25.09% starch. OPS added with OTP were used as a sole medium for LA production. The cultivation was performed at 37°C, 200 rpm and pH 5.5 for 120 h. The optimal conditions for LA production by L. acidophilus TISTR 1338 and L. kefiri KF1 through SSF were OPT loading at 10% w/v in OPS and cellulase loading at 15 FPU/g-OPT. The highest LA production obtained were 64.94±0.51 g/L and 23.45±0.35g/L, respectively, with LA yield of 0.68+0.01 and 0.30±0.01 g/g-available sugar, respectively. The medium cost of LA production