Abstract:
Out of fifty-two genera of micro-organisms isolated from different sources, only the following were shown to hydrlyse linamarin - two bacteria Leuconostoc mesenteroides and Alcaligences faecalia both isolated from fermenting cassava pulp, two yeasts, Saccharomyces cerovisiae from refuse dump, and Rhodotorule minuta, and three fungi, Aspergillus niger, A, flavus and Fusarium oxysporium from the rhizosphere of cassava.
Linamarases extracted from four of the organisms, A. faecalis, L. mesentercides, S. cerevisiae and R. minuta were studied further. Their kinetics showed activity in the temperature range of 160 C - 400 C, with optimum at 280 +20 C. They functioned over PH range of 2.5 - 7.5, with optimum at 5.0 - 6.0. Their optimal substrate concentration was 0.15 - 0.25 mg/g. Partial purification on diethyl amino ethyl (DEAE) cellulose chromatography and further by Sephadex G -200 gel filtration produced two peaks of activity. The specific activities of linamarasae from A. faecalis L. mesenteroides, S. cerevisae and R Minuta were respectively 356.94, 883.80, 869.70 and 526.18 units/g with 17.60%, 10.20%, 9.18% and 9.10% yields at 12.9, 38.06, 23.36 and 20.18 folds of purification. Their PH of stability were at 5.0-7.0, 5.5 -7.5, 5.0 -7.5 and 4.5 - 7.0 respectively, while at 600 C it took about 18 minutes to produce 90% inactivation. Their molecular weights were estimated to be 162000, 145000, 178000 and 166000 Daltons respectively, using aldolase, catalase and cytochrome C as reference markers. Addition of Na+, Ca++ ,K+, NH4+, Mg++, Fe+++ and Zn++ up to 1x10-1 M produced no significant inhibitory effect which was recorded when 1 x 10-3 M Cu++, Hg++ and Fe++ were incorporated in their growth media. Linamarases from the four micro-organisms readily hydrolysed other glucosides, namely lactose, cellobiose and p - Nitropheny1-B-D-glucoside, but not maltose and sucrose. The organisms grew well in fresh cassava pulp and hydrolysed linamarin therein, reeasing between 0.090 - 0.102 mg HCN/g whereas the endogenous cassava linamarase released only 0.045 mg HCN/g of pulp. It is concluded from the above findings that the four micro-organisms can be used commercially in the detoxication of cassava pulp during the production of gari or other fermented cassava- based meals.
