Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.10 Food industry 943
ticle size was more influential when the seed grit was being extracted. When oilseed flakes
were being extracted, the flake thickness would be a more important factor instead of size of
the flakes. Moisture content in oilseed can affect the extraction results. 93-95 Optimum moisture
content of cottonseed meats for extraction was first reported by Reuther et at. 94 to be
from 9 to 10%. Work by Arnold and Patel 95 indicated 7 to 10% to be the optimum moisture
for cottonseed flakes and very little variation in extraction rate for soybean with moisture
content between 8 and 12%.
Wingard and Phillips 96 developed a mathematical model to describe the effect of temperature
on extraction rate using a percolation extractor as follows:
o
( time ) n ( Temp F) k or time k( Temp)
n
log ,min = log ., + log = . [14.10.1]
where time is defined as the number of minutes required to reach 1% residual oil in the oilseed
flakes. For all practical purpose, they concluded that the time in minutes required to reduce
the oilseed to 1% residual oil content on a dry basis varied inversely with the square of
the extraction temperature in degrees Fahrenheit.
Evaluation methods: Except for the pilot plant batch or counter-current extraction described
by various labs, 54,74,78 most of the solvent extraction evaluation work found in the literature
was done in one or several of the lab scale devices. The percolation batch-extraction
apparatus of the Soxhlet type has often been used to evaluate the rate of extraction of hydrocarbon
solvents such as the one described by Bull and Hopper. 89 Wingard and Shand 97 described
a percolation type of extractor and a co-current batch extractor and claimed to be
useful to study the factors influencing equipment design and plant operation as well as fundamental
studies contributing to a general understanding of extraction. Wan, et al. modified
the design of percolation type extractor to closely simulate a single stage counter current
miscella extraction conditions as practiced in the factory. 85 Co-current batch extractor with
numerous variations was also frequently applied for the extraction properties of selected
solvents which were often operated at room temperature. 75,97 Soxhlet extraction 84,85 and
Soxtec System HT6 (Perstorp Analytical, Herndon, VA) were also frequently used to evaluate
solvents. 98 Soxhlet extractor allows vaporized and condensed pure solvent to percolate
through oilseed sample. The temperature of the condensed solvent is normally lower than
its boiling point. Depending upon the cooling efficiency of the condenser and the room temperature,
the temperature of the condensed solvent and the temperature of the extracting solvent
in the extractor largely varied from lab to lab. This extraction temperature variability
was minimized with the Soxtec method by refluxing the oilseed sample in the boiling solvent
for 15 minutes followed by Soxhlet type of rinsing for 35 minutes. In theory the Soxtec
method is more efficient and better reproduced. However, the Soxtec method only utilized a
3 g oilseed sample. The heterogeneity of an oilseed sample could be a significant source of
variation.
Flakes of oilseeds were most frequently used for the solvent extraction studies. Sometimes,
ground oilseed kernels through a specified sieve size was used. 98 Residual oil content
in the extracted flakes after a certain specified extraction condition or oil content in miscella
(mixture of oil and solvent) was examined and the percentage of total oil extracted was
calculated. 89-97 The total extractable oil of flakes was determined by four hours Soxhlet extraction.
Wan et al. 85 used a precision densitometer to determine the miscella concentration
(percent of oil in miscella by weight) after a given time of extraction from which the per-