American Journal of Chemistry 2018, 8(2): 45-50 DOI: 10.5923/j.chemistry.20180802.04 Thermal-Acid Hydrolysis of Sisal Boles Juice for Lactic Acid Production N. Msuya * , J. H. Y. Katima, R. J. A. Minja, E. Masanja, A. K. Temu Department of Chemical and Mining Engineering, University of Dar es Salaam, Dar es Salaam, Tanzania Abstract The effect of reaction temperature, time and pH on the maximum total sugar concentration during thermal-acid hydrolysis of sisal boles juice was investigated. The Minitab software (V. 17) was used to design a 2 n full factorial design for sisal juice hydrolysis and analyse the effects of the variables on the response. Thermal-acid hydrolysis can be carried out at a moderate temperature of 60°C with a concentrated hydrochloric acid at pH of one within a period of 30 minutes to achieve a sugar yield of 39%. The breakdown of complex sugars to simple sugars of sisal bole juice is basically a function of acid concentration in sugar solution. Lowering pH of the juice contributed to increase in hydrolysis rate. The use of ANOVA analyses gave evidence that linear, 2- way interactions and 3-way interactions of all the variables: temperature (60-100°C), time (30-60 min) and pH (1-5) significantly affected the sugar yield. This amount of sugar yield from sisal boles juice is higher than the yield of 26% which has been reported. The hydrolysed juice was also subjected into fermentation for lactic acid and results showed favourable LA yield was obtained with the recommended thermal-acid hydrolysis in this study. Keywords Thermal-acid hydrolysis, Sisal bole juice, Complex sugars breakdown, Lactic acid production 1. Introduction Sisal is a semiarid and marginal land crop of the tropics whose leaves are used for extraction of fibres. In a typical sisal production process, a very small portion, about 2% of sisal plant (sisal fibres) is used to produce twines, packaging’s, carpets, marts, threads, fine yarns, ropes and roofing tiles. The remaining bulk (98%) which include leaves decortications residue and sisal postharvest remaining (sisal poles, sisal boles with leave stubs) is discarded as waste [1-3]. Sisal fibres have also been used in the automotive sector and for specialist paper manufacturing [4]. Generally, production of one tonne of fibre generate waste amounting to 24 tonnes of leaf residues, 100 m 3 of wastewater and 4.7 tonnes of sisal boles [4]. On average a sisal bole weighs 40 kg and contains juice which consist of hydrolysable sugars (mostly fructose) that can be fermented to produce different bio-products such as citric acid, lactic acid and ethanol [1, 2, 5]. Extraction of juice from sisal boles is discussed in earlier study by Msuya et al, [5]. Before fermentation to other bio-products the extracted sisal bole juice need to be hydrolysed to break down the total sugars into simple monomer sugars that can be assimilated into microbial cells. Various researchers have worked on different methods for * Corresponding author: nmsuya@udsm.ac.tz (N. Msuya) Published online at http://journal.sapub.org/chemistry Copyright © 2018 Scientific & Academic Publishing. All Rights Reserved breaking down the complex sugars in sisal boles into simple sugars [2, 6, 7]. Conversion process of polysaccharides (mainly fructans) to fermentable sugars from sisal juice can be done either by thermal, enzymatic or chemical hydrolysis. Enzymatic hydrolysis leads to high purity fructose yield but requires commercial hydrolytic enzymes such as fructanase which are expensive considering high volume production [2]. The enzymatic hydrolysis is also very slow [8]. In addition, some hydrolysis products such as glucose tend to inhibit the process and thus need to be removed, this increases complexity of the process [2]. Thermal hydrolysis involves heating the chopped boles to temperatures above 100°C by autoclaving or oven cooking. The boles are cooked or autoclaved to hydrolyze the fructans and release fermentable sugars, principally fructose [2, 9]. Here the hydrolysis is done before extraction of juice. Thermal hydrolysis has the advantage of ease of controlling, acceptable processing time and relatively low capital investments costs [2, 10]. The resulting fructose syrup has a relatively low purity and can form Maillard reactions due to high temperatures (above 100°C) used [1, 2]. A Maillard reaction is a non-enzymatic reaction between sugars and proteins that occurs upon heating and that produces browning colour into the product. These are fermentation inhibitors which reduces the microorganism activities hence low product yield [10-12]. Acid hydrolysis (dilute or concentrated) involves use of large quantities of mineral acids, which has to be recovered,