Extraction of cassava (Manihot Esculenta Cranz) starch with the aid of pectolytic enzymes from Saccharomyces cerevisiae (ATCC 52712): Effects of cassava varietal differences on the process.
This work sought to study and compare the effects of various dosages of pectolytic enzymes from S. cerevisiae ATCC 52712 on yield and physicochemical parameters of starch fromfive cassava varieties (‘Nkabom’, ‘Afisiafi’, ‘Dokuduade’, ‘Bankyehemaa’ and ‘Esambankye’) and to explore feasibility for scale-up production with the variety that gives the best response to enzyme treatment. Generally, application of pectolytic enzymes significantly (P<0.05) increased starch yield and recovery rates in all selected cassava varieties.However, optimization of both yield and recovery rate was dependent on variety,enzyme dosage and holding time for enzyme action. An enzyme dosage of 0.02% was found to significantly (P<0.05) peak starch yield in ‘Esambankye’ and ‘Nkabom’varieties at 0.5 hrs and 1 hour in the ‘Afisiafi’ variety; 0.025% enzyme dosage at 0.5 hours holding time was the optimum treatment combination for starch yield in both ‘Bankyehemaa’ and ‘Dokuduade’ varieties. Enzyme treatment significantly enhanced the release of larger starch granules thus subsequently enhancing water binding capacity, solubility and swelling power of starches from most varieties; starches from the treated samples were also significantly(P<0.05) lighter in colour;crude fibre, crude protein and ash contents were however not affected by enzyme treatment.Enzyme treatment also significantly (P<0.05) reduced the time and temperature required for starch gelatinization without affecting the starch’s viscosities. Time required for attainment of peak viscosity was significantly (P<0.05) reduced in starches from the ‘Afisiafi’ and ‘Esambankye’ butdid not have any significant effect (P>0.05) on peak viscosities of starches from the ‘Bankyehemaa’. Apart from starches from the ‘Afisiafi’, all other starches from enzyme treated mashes were significantly less stable at 95OC. Hot paste viscosity of ‘Bankyehemaa’ starches were also significantly (P<0.05) enhanced by enzyme application. The technology did not also affect the stability of starches from the ‘Nkabom’ and ‘Bankyehemaa’ varieties when their starches were held at 50OC. ‘Esambankye’ and ‘Nkabom’ recorded highest values for setback viscosity due to enzyme treatment. Given the good responses of ‘Bankyehemaa’ to enzyme treatment, its adoption for feasibility studies at the industrial scale gave an overall enhanced yield and flow rates of 44.45% and 46.15% respectively over the control. The study therefore showed that although application of pectolytic enzymes to starch extraction enhances yield, the technology is affected by varietal difference. It also enhances many physicochemical properties of starches for application to industry. Given the heavy dependence of most of Ghana’s industries on starch, the technology if made available would greatly boost the productivity of these sectors at relatively lower cost.
Thesis submitted to the Department of Biochemistry and Biotechnology in partial fulfillment for the Master of Science (MSc.) degree in Biotechnology, 2013