Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
application of either 10 or 15 mm hydrocyclones from the fourth to the eleventh
stage. Extra washing of fine starch is not performed.
8.4.3.5 Starch Dewatering and Drying
Because of the excellent filtering characteristics of potato starch, rotating vacuum
drum filters that use filter cloth are standard equipment in dewatering. 22,24 They make
available a minimum water content of 38%. The water content is further reduced to
equilibrium relative moisture content of approximately 20% by flash drying. Drying
of starch granules is performed rapidly without much damage in functionality.
Maximum moisture level of commercially available potato starch is 21%.
8.4.3.6 Protein Recovery — By-Products
As stated previously, approximately 50% of the crude proteins solved in potato fruit
water are high-molecular-weight proteins. This fraction can be separated by isoelectric
precipitation and heat coagulation. The desired efficiency of these measures
depends on concentration of the respective solute components. A process developed
by GEA Westfalia Separator Industries GmbH, a machinery supplier, uses undiluted
fruit water with a dry substance content of 4.5 to 5.2% or even diluted fruit water
with 4% dry substance. Potential tuber protein recoveries range from 83 to 85%.
Technically, fruit water effluents are adjusted to a pH of 4.8 to 5.2 after preheating.
Then, optimized precipitation is supported by steam injection and an induced
heat shock of 110 to 120°C. The coagulated proteins are then separated by decanting
and result in protein cakes with 38 to 43% dry matter. Dry and stable proteins having
a protein content of 83 to 85% are recovered from air drying in ring dryers. For
utilization, for example, as animal feed, the content of potato glycoalkaloids, solanines
and chaconines, is critical. Provided suitable extraction or washing measures
are applied, potato protein isolates with considerably reduced content of glycoalkaloids
and of improved sensorial quality might serve valuable and palatable protein
sources for human consumption. 25,26
After removing the high-molecular-weight protein fraction, the remaining deproteinized
fruit water contains a considerable amount of low-molecular-weight organic
compounds such as amino acids, organic acids, and sugars, as well as minerals,
predominantly potassium. The effluents produced mainly in a period of reduced
plant growth get concentrated and as such are well-accepted storable fertilizers
providing nitrogen, phosphorous, and potassium. Evaporation or membrane filtration
is a suitable technique to prepare residual fruit water concentrates for future farm
uses. 21,27–29
8.5 CASSAVA (TAPIOCA, MANIOC) STARCH
8.5.1 GENERAL REMARKS
Cassava, also known as tapioca or manioc, is a major tuber crop of tropical countries.
Cultivation is reported in more than 80 countries, with a diversity of species belonging
botanically to Manihot utilissima Pohl or Manihot esculenta Crantz and divers