Dates - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 187

addition, two by-products of potential economic value are
produced, namely, carbon dioxide, which can be used in
the food industry, and stillage, which can be used as ani-
mal feed. Commercial alcohol contains about 90% of pure
ethyl alcohol, the remainder being water. A solution of 70-
85% of ethyl alcohol is commonly used as a disinfectant; it
kills organisms by denaturing their proteins and dissolving
their lipids. It is effective against most bacteria and fungi,
and many viruses, but is ineffective against bacterial spores
(CAG, 2004).
The optimum temperature of fermentation for S.
cerevisiae is about 30 ◦ C (Hettenhaus, 1998). The overall
yield on substrate must be above 90% of the theoretical
yield, and the minimum ethanol concentration in the mash
must be at least 10% v/v so that the process can be eco-
nomically feasible. The theoretical yield equals therefore
0.51 g ethanol and 0.49 g carbon dioxide per gram sugar
assimilated. An ethanol yield of 90% of the theoretical is
considered satisfactory from the economical point of view
(Cot et al., 2007).
When fermentation was carried at pH 4.5 and 30 ◦ Cus-
ing S. cerevisiae and a substrate of 22 g/l of monosac-
charides and disaccharides found in date's juice, there
was a maximum yield of 12.8% of ethanol when using
S. cerevisiae in free cell method, and 13.4% w/v ethanol
when those cells were immobilized by sodium alginate,
respectively (Al-Bassam, 2001).

Table 10.4. Comparing date syrup and molasses
as substrates for baker's yeast production.

Date
Syrup

Beet
Molasses

Cane
Molasses Nutrient

Sugars (%) 80 50 50

Nitrogen (%) 0.13 0.5 0.1

Phosphorus (%) 0.11 0.03 0.09

Potassium (%) 1.5 3.0 3.0

Magnesium (%) 0.08 0.01 0.3

Biotin (ppm) 2.73 0.05 2.0

Pantothenic acid (ppm) 240 80 25

m-Inositol (ppm) 0 6,500 4,000

Source: Aleid et al. (2009), Bronn (1990).

as carbon and energy source will yield 325-435 kg ac-
tive dry yeast (Aleid et al., 2009). Table 10.4 shows the
comparison of different substrates for baker's yeast pro-
duction. Date syrup contains higher amount of sugars,
biotin and pantothenic acid than molasses, about simi-
lar contents from nitrogen, phosphorus and magnesium,
about half the content of potassium (but still enough for
baker's yeast production) and much less m-inositol (Aleid
et al., 2009).
Nancib et al. (1997) used waste products from dates in
the production of baker's yeast from strains of S. cerevisiae.
They used a semisynthetic fermentation medium contain-
ing sugars extracted from the date coat (freshly part), ni-
trogenous compounds extracted from seed hydrolysate,
6.0 g/l KH 2 PO 4 , 1.0 g/l date seed lipid, 0.6 g/l date seed
ash, and 1.0 g/l ammonium nitrate. Their yield was very
low, i.e., 0.6 g/l biomass concentration in the fermentation
medium compared to the optimum of about 40 g/l for an
economical production. Aleid et al. (2009) used substrates
from pure date syrup and pure molasses for the propaga-
tion of the baker's yeast strain S. cerevisiae. All runs were
fed-batch processes, at pH 4.5, 30 ◦ C, 8 g/l inoculum size,
and sugar concentration in all substrates was 200 g/l. The
overall biomass yield from pure date syrup substrate was
significantly lower than the yields from pure molasses sub-
strates. The reduced yields could be attributed to the effect
of yeast toxic organic acids contained in date syrup at high
concentrations.

Machine vision in date processing
In the date industry, grading is based on color, size, surface
defects, and texture. Color is an important factor in dis-
tinguishing between acceptable date fruits and damaged or
immature dates. The color of acceptable dates is relatively
uniform and predominantly light amber in color (Al-Janobi,
2000). Few research papers focused on applying machine
vision technique on dates; most of them studied each vari-
ety solely. It was necessary to study different varieties of
dates to lay the foundation for a machine vision system,
which has the capability to differentiate between various
date varieties as well as estimating sugar content of each
variety (Fadel et al., 2001).
Wulfson et al. (1989) used a color camera to capture
date fruit images to determine the relative reflectance in
the range of 400-1,000 nm for good and defective dates.
Furthermore, they used an infrared cutoff filter. They noted
that the red band image was most effective for detecting
defective 'Majhul' dates, and the green band image
performed best for 'Zahidi' dates. The system showed an
average classification error of 1.8% using features from the
red color band. A machine vision system to grade date fruits
('Deglet Nour' variety) into quality classes based on color

Ethanol production from dates
If dates, which contain about 60-80% w/w sugar, are used
as a substrate for medical and industrial ethanol produc-
tion, 1 ton of dates should produce an amount in the range
of 300-400 kg ethanol, that is, about 380-500 liters. In