Syrups Two processes are followed to produce glucose syrup, namely enzymatic and acid hydrolysis. For the enzymatic approach, the process consists of five stages. The flour is mixed with water into slurry at 105 °C. Next is conversion of starch in HQCF to dextrin by addition of α-amylase enzyme. After this, dextrin is hydrolyzed to glucose by adding glucoamylase at 60 °C at 1 atm. The glucose syrup is then purified by removing color pigments and ions with the aid of activated carbon and ion exchange, respectively. Additional filtration is required when HQCF is used as a raw material instead of cassava starch. The final process is evaporation to concentrate the syrup. The proportion of glucose, maltose and maltodextrins present in the hydrolysate determines whether it will be called maltodextrin, high maltose syrup or high dextrose glucose syrup. High fructose syrup (HFS) is produced by passing glucose syrup over columns packed with immobilized glucose isomerase.
Thai and Vietnamese glucose syrup production technologies are widely adopted internationally. There is evidence also that small-scale industries in Nigeria and Ghana exist directly by using HQCF for glucose syrup production. Ekha Agro Nigerian Limited is one of the foremost private initiatives in Nigeria that established an ultramodern glucose syrup factory capable of processing 400 tons of fresh cassava root to produce 100 tons of glucose syrup per day at full capacity. It is the second largest glucose syrup factory in Africa.
The development of membrane reactor technologies developed for the improvement of traditional batch processes to overcome the limitations of conventional processes (i.e. product inhibition, cofactor regeneration, biocatalysis in non-conventional media) is a task of growing interest with potential industrial applications. Lopez-Ulibarri and Hall (1997) studied the enzymatic saccharification of CF starch with glucoamylase from Aspergillus niger in a hollow-fiber enzymatic membrane reactor (HF-EMR). The saccharification was enhanced by pre-gelatinizing the flour via extrusion.
Adhesives Adhesives mainly used by the paper, textile and packaging industries are originally made from corn starch and imported to many developing economies. In the past two decades, attention has been shifted to using alternative sources of starch such as HQCF. Cassava-based adhesives have the unique advantages of being smooth, clear, fine in texture, non-staining, more viscous, stable and neutral (Gunorubon, 2012). The non-poisonous nature makes it a desirable choice, particularly for many domestic and food applications (Masamba et al., 2003). The major drawback in the use of starch as an adhesive is the stability of the product over time.
The native starch present in HQCF does not yield good adhesive properties. Moreover, the presence of other components such as fiber, fat and protein in HQCF can also reduce its adhesive function (Derkyi et al., 2008). Therefore, when a strong adhesive property is required, attention is shifted to cassava starch. Variables that affect the adhesive properties of starch are formulation, molar mass of starch, starch modification (Emengoa et al., 2002), and so on.
Bioethanol Biodiesel is planned to be a community energy product in certain areas, whereas the bioethanol is recognized as environmentally-friendly energy due to less greenhouse gas (GHG) emission (Nguyen et al., 2007; 2008; Nguyen and Gheewala, 2008).
Co-culture of Bacillus subtilis with Clostridium butylicum enhanced acetone-butanol-ethanol (ABE) fermentation process. The benefits of using this high amylase producing aerobic Bacillus in a co-culture with anaerobic Clostridium were not only increasing substrate utilization and ABE production, but there was also no requirement to add any costly reducing agent to the medium or flushing with N2 to ensure anaerobic conditions. This may contribute greatly to developing industrialized ABE production (Tran et al., 2010). Another energy saving approach to make bioethanol directly from cassava chips, by boiling and enzymatically liquefying cassava root, is being taken up in Thailand (Nguyen et al., 2010).
10.1.3 Cassava Starch
Starch is the major food reserve of cassava. It is approximately 21.5 % of fresh cassava tuber (IITA, 1990). Like CF, cassava starch (CS) is prepared from either wet mash or dry chips. Starch extraction is easier and economical with wet mash. It also gives consistent and better-quality starch. Particle size from dry milling of chips are highly variable with very fine and coarse materials resulting in constant clogging of the sieve aperture during washing of flour to obtain starch. Also, large quantity of water is necessary to drive the material through the sieve. Since quality is of paramount importance in starch trading, extraction from wet mash is often preferred in commercial starch extraction, because of control over product quality.
10.1.3.1 Cassava Starch Production Technology
While CF is the main commercial product from cassava roots in sub-Saharan Africa, CS is an important export commodity of cassava producing countries of Asia and Latin America. Cassava starch extraction follows a similar pattern with production of CF, except that starch milk is passed through a screen of 150 microns aperture size to separate starch from fibers and other impurities. Typical starch extraction process from cassava roots is shown in Figure 10.1.7.
Figure 10.1.7 Starch extraction process from cassava roots.
Washing Cassava starch production is on a larger scale than CF production. Its technology has undergone major transformation from subsistence to commercial production. This is in order to meet global starch demand and compete favorably with starch from other sources such as maize and potato. The technological transformation is more pronounced in Asia and Latin America, especially Thailand and Brazil. After initial quality checks on the roots with the estimation of root starch content through the determination of root apparent density using a Reiman balance, roots are fed through a hopper into mechanized rotary washers fitted with overhead water sprays. Roots are transported through the system by chain conveyors. The tumbling action in the system removes the peel alongside soil and dirt. Soil, sand, peel and other impurities are removed as the roots pass through a rotating cylindrical sieve. Thereafter, peeled roots are moved to a water chamber where these are washed as they are moved by a paddle blade. Capacity of washing in most large CS production factories in Asia is 15–20 t of roots per h (Sriroth et al., 2000).
Cutting and Rasping Rasping is done to enhance starch extraction from cassava roots. The technology is as discussed in Section 11.1.2. Most Asian CS factories rely on locally made motorized raspers. The most commonly-used locally made saw-tooth raspers in Thailand consist of a drum with 144 blades on its surface, with 201 teeth distributed along the length of each blade (Sriroth et al., 2000). This equipment can process 5–6 t of chopped roots per h. Rasping efficiency is measured by the amount of unextracted starch in the pressed pulp, so high starch content in the pulp indicates lower efficiency.