The role of the yeast in bread making is the rising of the dough to produce the
characteristic loaf preferred by consumers. Dough rising occurs as a result of the
gases produced by the yeast as it grows within the dough. During growth, the yeast
metabolizes sugars in the dough with the help of a special enzyme system and produces
alcohol and CO2. The leavening power of the yeast depends on its activity and
viability; hence the yeast used must be fully active with a high viable cell count.
Furthermore, the leavening power of any yeast strain depends on its genetic makeup
and on the process of production, and also on the storage conditions before use
(Pyler 1988). The most important function of bakery yeast in bread making is to
leaven the dough during the fermentation process by producing CO2 via the alcoholic
fermentation of sugars. Furthermore, the yeast produces desirable flavor and
aroma compounds as products of secondary metabolism (Evans 1990), thus enhancing
the characteristic flavor and aroma of baked products.
32.2.1 Dates as a Substrate for Bakery Yeast Production
Bakery yeast can be produced from substrates that contain suitable sources of carbon,
energy, nitrogen, minerals and essential vitamins. Dates are said to be a good
substrate for bakery yeast production. Their carbohydrate content is mainly sugars
amounting to 65–87% of their dry matter. Date sugars are mainly glucose and fructose,
which are easily assimilable to most microorganisms (Sawaya 1986). The protein
content of dates is 1–3%. This is a low amount and hence a suitable source of
nitrogen, in the form of inorganic salts, has to be added to the date substrate for
bakery yeast production. Dates also contain vitamins important for yeast growth
such as B1 (0.75 mg/100 g), B2 (0.2 mg/100 g) and nicotinic acid (0.33–2.2 ml/100 g).
Also, the important minerals in 100 g dates are: potassium (650–750 mg), magnesium
(50–58 mg), sulfur (43–51 mg), phosphorus (59–64 mg), iron (1.3–2 mg), calcium
(58–68 mg) and chloride (268–290 mg) (Aleid et al. 2009). Commercial bakery
yeasts produced from strains of Saccharomyces cerevisiae have the following average
chemical composition: 47% C; 32% O2; 6% H2; 7.7% N2; 2% K; 1.2% P; 1% S;
0.2% Mg; 0.1% Na and other trace elements. In addition, the yeast cells contain
small amounts of vitamin B complex, of which D-Pantothenic acid, D-Biotin and
m-Inositol are essential because the yeast cells cannot synthesize them (Bronn
1990). To produce 1 kg of yeast about 3 mg D-Biotin, 150 mg D-Pantothenic acid
and 2 g m-Inositol are needed. These elements and compounds must be provided in
the production medium in sufficient quantities and in metabolizable forms. If dates are used as a substrate for production, their sugars will act as a source of carbon and
energy. According to the date fruit chemical composition given above, 1 mt of dates
used as a carbon and energy source will yield about 325–435 kg of active dry yeast.
The nitrogen content of dates is insufficient to produce such quantities of yeast and
a suitable nitrogen source has to be added. The contents of dates in terms of other
elements and essential vitamins must be determined and any deficiencies remedied
(Aleid et al. 2009).
When comparing date and molasses as substrates for bakery yeast production,
with regard to its nutrient contents, date syrup compares favorably with molasses
which is the conventional substrate for bakery yeast production worldwide
(Table 32.1). Date syrup contains much more sugar, biotin and pantothenic acid than
molasses, about similar content of nitrogen, phosphorus and magnesium, about half
the content of potassium (but still enough for bakery yeast production) and much
less m-inositol. Compounds toxic to bakery yeast detected in date syrup include
formic acid at 3.06%, acetic acid at 2.38% and propionic acid at 0.68% (total acids
6.12%), but no detectable amounts of the toxicants nitrite, sulfite and butyric acid.
Formic acid becomes toxic to the yeast when its concentration in the medium
exceeds 0.25%, whereas the toxicity level of the other two acids is in excess of 3.0%
for the sum of the two (Aleid et al. 2009).

32.2.2 Production Process of Bakery Yeast
Bakery yeast is propagated under optimal conditions of temperature, pH, aeration and
nutrient supply to give maximum yields of time, space and raw materials. The best
fermentation process for bakery yeast production from strains of Saccharomyces
cerevisiae is the fed-batch process, so that the Crabtree effect is avoided. Usually, part
of the mineral medium and a small amount of the substrate is added to the fermentor,
then the inoculum is added and the process started. The rest of the mineral medium
and the substrate are fed to the fermentor at such a rate that the concentration of sugar
in the fermentor does not exceed about 0.1 g/l. Continuous aeration and stirring is necessary to ensure the transfer of sufficient quantities of oxygen and nutrients to the
growing yeast cells. Also, cooling is necessary to remove heat generated by the metabolic
activity of the growing yeast culture and to maintain the fermentation temperature
at about 30°C. When the fermentation process is completed, the final cell
concentration in the fermentor is 4–5% by weight. Yeast cells are harvested by filtration
or centrifugation and processed to the final product (Aleid et al. 2009).
32.2.3 Bakery Yeast Production from Dates
A few investigations into the production of bakery yeast from date extracts have
been conducted (AlObaidi et al. 1985, 1987; Bassat 1971; Mohammed et al. 1986;
Mudhaffer 1978). Comparisons were made between date extract and molasses.
Positive findings were reported and claims were made that there are no technological
constraints to using date extract for bakery yeast production. Nancib et al. (1997)
used waste products from date in the production of bakery yeast from strains of
Saccharomyces cerevisiae. They used a semi-synthetic fermentation medium containing
sugars extracted from the date coat (freshly part), nitrogenous compounds
extracted from seed hydrolysate, 6.0 g/l KH2PO4; 1.0 g/l date seed lipid; 0.6 g/l date
seed ash and 1.0 g/l ammonium nitrate. Although they described this medium as
satisfactory for bakery yeast production, yields obtained were very low with a maximum
of 0.6 g/l biomass concentration in the fermentation medium compared to the
optimum of about 40 g/l expected for an economical production. Khan et al. (1995)
used Saudi Arabian dates in the production of bakery yeast. They propagated six
different strains of S. cerevisiae in fermentation media containing Sefry Beesha cv.
date extract (with 60% sugars) in place of molasses, in addition to 2 g/l ammonium
sulfate and 50 mg/l biotin. Yields were also meager with a maximum of 10.7 g/l
biomass concentration in the fermentation medium from 50 g/l sugar, representing
a yield of only 42.8% of the theoretical. Date extract as a carbon and energy source
for the propagation of bakery yeast on a pilot-plant scale, in comparison with molasses,
was investigated by AlObaidi et al. (1986). Results showed that higher productivity
of bakery yeast was observed when date extract was used. It was concluded
from their study that date extract holds promise as a source of carbon and energy for
the production of bakery yeast, although the average yields were only 47%. None of
the authors discussed the Crabtree effect as a major technological problem encountered
with bakery yeast propagation.
Aleid et al. (2009) used substrates from pure date syrup and pure molasses for the
propagation of the bakery yeast strain Saccharomyces cerevisiae. All runs were fedbatch
processes, at pH 4.5, 30°C, 8 g/l inoculum size and sugar concentration in all
substrates of 200 g/l. The overall biomass yield from pure date syrup substrate was
significantly lower than the yields from pure molasses substrates. Reduced yields
could be attributed to the effect of yeast toxic organic acids contained in date syrup
at high concentrations. The performance of the bakery yeast, propagated on date
syrup as a fermentation substrate, in an Arabic bread test was excellent (Fig. 32.2).

32.3 Single Cell-Protein Production from Dates
The technology of single-cell protein (SCP) production was established in the
1970s (Martin 1997). SCP is produced from bacteria, yeasts, molds and algae
using different substrates as sources of carbon and energy such as food crops,
by-products of agriculture and industry, wastes and also sunlight and atmospheric
CO2 (Israelidis 1987). Abduljabbar et al. (2008) reported about a yeast
and a bacterium used for the production of SCP from ethanol, kerosene and gas
oil. They found that optimum substrate concentrations during propagation were
0.5–4%. These are very low concentrations and will not yield more than about
2% biomass concentration in the bioreactor, hence the economic feasibility of
the process is doubtful. No citations on SCP production from dates were found
in the literature.
SCP is mainly considered a protein source and hence it is used to replace protein
concentrates in animal feeds. SCP contains 50–70% protein, about 30% carbohydrates,
6% lipids and 8% minerals. In addition SCP is rich in vitamins, especially
the B-complex group (Hamad 1986; Herbert 1976; Robinson 1986). Other advantages
that support the use of SCP as animal feed include short production time
(a few days compared to months for crops; years for animals), small land areas, no
seasonality and use of cheap raw materials which are usually wastes that contaminate the environment.

32.3.1 Organisms Used for SCP Production
Desirable characteristics of the production organism include freedom from toxicity
and pathogenicity, high content of protein with a well-balanced amino acid composition,
thermo-tolerance, no growth factors needed, high yields and high growth rate
(Hamad 1986).
32.3.1.1 Bacteria
Bacteria can be used for SCP production. The advantages are many e.g. they have
high growth rates; are more stable in adverse growth conditions such as high temperatures;
can utilize a wide range of substrates as sources of carbon, energy and
nitrogen; and have high protein content. However, the main disadvantages of bacteria
are: the cell wall makes digestion difficult, the high content of nucleic acids and
the small size makes separation difficult (Holts 1994; Madigan et al. 1997).
32.3.1.2 Yeasts
Yeasts like Candida utilis, Kluyveromyces marxianus and Saccharomyces cerevisiae
are used for SCP production. Yeasts used in SCP production have the advantages
of better digestibility, lower nucleic acid content and easier handling during
harvest (Hamad 1986; Ray 1996). On the other hand they have lower protein content
than bacteria, lower growth rates and are less thermo-tolerant.
32.3.1.3 Algae
Algae are also used for SCP production, but less frequently. Algae are produced in
bonds exposed to sun where they perform photosynthesis. Production costs are low,
but much water and sunshine are needed.
32.3.2 Substrates for SCP Production
SCP can be produced from substrates that contain suitable sources of carbon, energy,
nitrogen, minerals and vitamins Substrates range from food materials like grains
and dates; by-products like molasses; alkanes, whey and wastes like sulfite liquor;
residues of foods, plants and animals; and waste water. Some substrates contain
easily-metabolized carbon and energy sources such as mono and disaccharides in
molasses, dates and whey. Others contain complex carbohydrates such as starches
in grains and cellulose in plant residues. Only a limited number of microorganisms
are able to metabolize complex carbohydrates. In most cases such substrates need some treatments before use for SCP production. The use of wastes for SCP production
serves two goals. First, it is possible to get rid of these environment-polluting wastes
and, second, the process results in obtaining valuable products of commercial use
(Allison 1975; Einsele 1975; Oura 1983). The yields on substrates are about 0.5 mt
dry biomass per 1 mt carbohydrate (Allison 1975; Einsele 1975; Oura 1983). In
most cases the substrates used for SCP production are low in nitrogen content and a
suitable nitrogen source must be added. Usually inorganic nitrogen salts are added
e.g. ammonia, ammonium salts, nitrates, etc.; sometimes urea is used. The process
is therefore an upgrading of such inorganic nitrogenous compounds to the highly
valuable organic nitrogen, the proteins.
32.3.2.1 Dates as a Substrate for SCP
Dates are a good potential substrate for SCP production. Their carbohydrate content
is mainly sugars, amounting to 65–87% dry matter. The sugars are sucrose, glucose
and fructose, which are easily assailable to most microorganisms (Aleid 2006; Sawaya
1986). This means that 1 mt of dates dry matter can produce up to 435 kg dry SCP.
The protein content of dates is 1–3%; a low amount and hence inorganic nitrogen has
to be added to the date substrate for SCP production (70 kg ammonium phosphate per
mt of dates). The vitamin content of dates includes: thiamine (B1), 0.75 mg/100 g;
riboflavin (B2), 0.2 mg/100 g and nicotinic acid (niacin, B5), 0.33–2.2. The content of
some important minerals (in 100 g dates) is: K, 650–750 mg; Mg, 50–58 mg; S,
43–51 mg; P, 59–64 mg; Fe, 1.3–2 mg; Ca, 58–68 mg and CI 268–290 mg).
32.3.2.2 Chemical Composition of Date Substrate
Date syrup for the production substrate should contain nutrients needed by yeasts
such as sugars, protein, minerals, D-Biotin, D-Pantothenic acid and m-Inositol. As
shown in Table 32.2, date syrup is deficient in P, K, Mg and proteins, it serves
mainly as carbon and energy source. As a result, the deficient minerals need to be
supplied to the yeast in the mineral medium in form of (NH4)2SO4, KH2PO4, and
MgSO4 salts, and in case of the Saccharomyces cerevisiae strain, inositol needs to
be added to the medium (Aleid et al. 2010).
32.3.3 Process of SCP Production SCP is produced in fermentors using the fed-batch or continuous fermentation processes
(Brauer 1985; Bronn 1990; Roels 1983). At first the substrate and the media
are prepared by dilution, mixing, sterilization and purification if needed. Also the
fermentor is cleaned and sterilized as needed. The process begins with the addition
of a starter culture of the production organism to the fermentor containing some
medium and substrate. The rest of the medium and substrate are then fed to the

fermentor. In the continuous fermentation process, feeding and harvest continue
simultaneously and the process goes on as long as it is in a steady-state and no contamination
of foreign microorganisms occurs. In the fed batch-process, feeding continues
until a certain broth volume in the fermentor is reached, after which the
process is stopped and the biomass harvested. Continuous aeration is needed because
the process is mostly aerobic. Also cooling is necessary because large amounts of
heat are produced during microbial growth. Stirring is needed to intensify cooling
and air transport to the microorganisms. The final biomass concentration in the
fermentor is about 4% on a dry weight basis. The biomass is harvested by filtration,
centrifugation or sedimentation. The biomass is then dried to about 95% dry matter
in dryers or under the sun. Drying increases the shelf-life by killing the cells of the
production organism and preventing the growth of contaminants. According to use,
the product is dried into powder, granules or flakes. Finally the product is packed in
suitable containers and sent to the market.
For the assessment of the safety and nutritional value of SCP, factors such as
nutrient composition, amino acid profile, vitamin and nucleic acid content as well
as palatability, allergies and gastrointestinal effects should be taken into consideration
(Litchfield 1968). Also, long-term feeding trials should be undertaken for
toxicological effects and carcinogenesis.
32.3.4 SCP Production from Dates
Aleid et al. (2010) described using date syrup as the production substrate for singlecell
protein and steps taken to formulate a suitable substrate from it. Fermentation
process optimization experiments for both Candida utilis and Saccharomyces 32.3.5 The Problem of Nucleic Acids
About 70–80% of the total cell nitrogen is represented by amino acids while the
remainder occurs as nucleic acids. This concentration of nucleic acids is higher
than other conventional proteins and is characteristic of all fast-growing organisms.
This has two implications for the nutritional value of SCP. For use of SCP
in animal feeds the major implication is simply that nucleic acid is not protein and
essentially dilutes the protein, although there are at least some possibilities of
physiological effects (Bull et al. 1997). As far as the potential use of SCP in
human food is concerned, nucleic acids are undesirable because their digestion
leads to unacceptably high levels of uric acid in the blood, sometimes resulting in
gout disease (Edozien et al. 1970; White et al. 1964). Uric acid is a product of
purine metabolism.
The bulk of the nucleic acid in microorganisms is RNA, which has a critical role
in protein synthesis. Thus, it may be anticipated that the faster the rate of protein
synthesis in a particular cell, the higher the nucleic acid content (Bull et al. 1997).
The removal or reduction of nucleic acid content of various SCPs is achieved with
one of the following treatments (Zee and Simard 1974): (a) chemical treatment with
NaOH; (b) treatment of cells with 10% NaCl; (c) thermal shock. These methods aim
to reduce the RNA content from about 7% to 1%, which is considered within acceptable
levels. Thus SCP is treated with various methods in order to kill the cells,
improve digestibility and reduce the nucleic acid content

• Rabbi date
• Zahedi date
• Piarom date
• Chopped dates
• Khasouyeh date
• Mazafati dates
• Maryami date
• Dates paste
• Sayer Dates

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Dates can be utilized as a substrate for fermentation processes to manufacture
different
products such as alcohol, bakery yeast, organic acids, antibiotics and others.
Date palm fruits are found to contain carbohydrates (44–88%), fats (0.2–0.4%),
protein (2.3–5.6%), fiber (6.4–11.5%), minerals and vitamins (Al-Shahib and
Marshall 2003). Carbohydrates in dates are mostly in the form of fructose and glucose,
which are easily absorbed by the human body (Al-Farsi et al. 2005).
Interestingly, dates contain higher concentrations of protein as compared to other
major cultivated fruits such as apples, oranges, bananas and grapes (containing
0.3%, 0.7%, 1.0% and 1.0% protein, respectively) (Al-Showiman 1998). Twentythree
different amino acids are found in date protein, many of which are not contained
in the most popular fruits. Several studies in the literature concluded that the
aqueous extracts of dates have potent antioxidant and antimutagenic activity
(Mansouri et al. 2005; Mohamed and Al-Okabi 2004). Dates are reported to have
the second highest antioxidant activity among fruits commonly consumed in China
(Guo et al. 2003). Al-Farsi et al. (2005) found that dates are a high source of antioxidants,
anthocyanins, carotenoids and phenols. Antioxidants have received increased
attention by nutritionists and medical researchers for their potential effects in the
prevention of chronic and degenerative diseases such as cancer, cardiovascular diseases
and to slow aging (Kaur and Kapoor 2001; Young and Woodside 2001). The
most effective antioxidants in this respect appear to be the flavonoids and phenols.
Because of their metal-chelating and radical-scavenging properties, phenols were
considered effective inhibitors of lipid peroxidation (Mansouri et al. 2005).
Furthermore, Al-Shahib and Marshall (2003) concluded that, in many ways, dates
may be considered an almost ideal food, providing a wide range of essential nutrients
and potential health benefits.
Based on the above compositional properties of date fruits, they are considered
one of the most appropriate substances for production of value-added products
through fermentation technology such as bakery yeast, single-cell protein as a fodder
yeast, medical and industrial ethanol, and date flavored probiotic fermented
dairy products, all of which are addressed in this chapter.
32.1.1 Date Fruit Production and Consumption
Dates are cultivated mainly in warmer regions of Asia and Africa. The fruit is also
grown in some parts of Europe and the USA. It is now estimated that annually
about seven million mt of dates are produced worldwide. The production period
of the main supplying countries including Egypt, Iran, Saudi Arabia, UAE, Iraq
and Tunisia etc. is from July to November. Dates are harvested and marketed at
three stages of their development. The choice of harvesting at one or another stage
depends on cultivar characteristics, climatic conditions and market demand

(Pakistan Horticulture Development and Export Board 2008). The world date
fruit export market is about 0.42 million mt per annum (2005). Iran is on the top
of the list with a 28% share, while Pakistan with 20% occupies second of the
world’s top ten exporting countries. Saudi Arabia and Tunisia both with almost
12% share are at par in their export performance securing third position in the
year 2005. The world date imports are about 0.63 million mt per annum (2005).
India is the largest importer with market share of about 38% while France and UK
are the second and third largest importers with shares of 4% and 2.5%, respectively,
in 2005 (FAOSTAT 2005).
The edible stages of ripening of date fruit can be divided into three main stages:
khalal stage – physiological mature, hard and crisp, moisture contents 50–85%,
yellowish in color; rutab stage – partially browned, reduced moisture contents
30–35%, softened; tamar stage – color from amber to dark brown, moisture contents
reduced below 25–10%, texture soft pliable to firm. In conventional date processing,
dry or soft dates are eaten as whole fruit, pitted and stuffed, or chopped
and used in a great variety of ways: as ingredients in cereals, puddings, breads,
cakes, cookies, ice cream and confectionaries. The pitting may be done by crushing
and sieving the fruit or, more sophisticatedly, by piercing the seed out of the
whole fruit. The calyces may also be mechanically removed. Surplus dates are
processed into cubes, paste, spread, powder (date sugar), jam, jelly, juice, syrup,
vinegar or alcohol. De-coloured and filtered date juice yields a clear invert sugar
solution (Morton 1987).
32.1.2 Date Fruits as Raw Materials
Good quality raw material in volume is important to the development and modernization
of the date industry. An important element is the formation of rural
collection centers located in the main date-production areas. The purpose of the
collection center is twofold. It provides a central location to create a buying hub
and initial grading and processing of dates that have export potential and can be
shipped to the central processing facilities for processing of lower-grade fruit
and inferior-quality dates into value-added products such as syrup, paste, alcohol,
vinegar etc. Secondly, it is a site from which agricultural extension agents
can work to educate and assist farmers with improved practices in the care and
harvesting of dates (Agland Investment Services Inc. 2008). Date fruits usually
are fumigated and placed into cold storage. Dates are washed, graded for size and
quality on belts, and then channeled to conveyor lines for further processing. The
machines should have the advantage of being able to handle different date cultivars.
A large area of the plant floor will be devoted to heavy usage of hand labor
and fruit will again pass through an inspection belt prior to bulk packing End-products may include pressed date blocks, pitted dates, chopped dates and date paste

In the season of tamar stage date harvest, some industries receive the fruits in
amounts that far exceed immediate market capacity. Thus, most tamar dates are
stored and then released into the market according to demand. Since quality parameters
are affected by storage, it is very important to understand the effect of storage
conditions on the different characteristics and acceptability of the date fruit to consumers
(Ismail et al. 2008). There are several inherent constituents of dates, each of
which in its own way takes part in the formation of the fruit. Due to genetic differences and growth conditions dates exhibit, perhaps more than other fruits, a wide
variation in their final appearance and quality as one can perceive. Moreover, fruit
quality, apart from these inherent properties, is also determined by exterior influences.
Dates are classified in terms of the degree of insect infestation, defects,
presence of foreign matter (sand, dust, debris) and pesticide residue (Saleem
2005). A quality profile of dates involves an evaluation of four aspects. First, color,
shape, size, taste, texture, pit/flesh ratio and uniformity in color and size of the fruit.
Second, moisture, sugar and fiber content. Third, defects of the fruits, which may
include discoloration, broken skin, sunburn, blemishes, shrivel deformity etc. and
fourth, presence of insect infestation, foreign matter, pesticide residues, molds and
decay. A number of countries have formulated and applied date standards at the
national level for both locally produced and imported dates. In an effort to arrive at
global standards for dates the Codex Alimentarius Commission of the joint FAO/
WHO Food Standards Program formulated a proposal for date standards intended to
be the basis for worldwide application, subject to acceptance by the respective

governments
(Saleem 2005). Design of machines and the processes to harvest,
handle
and store agricultural materials and to convert these materials into food and
feed requires an understanding of their physical properties (Keramat et al. 2008).
Dry dates are attacked by moths and beetles. Dates usually are subject to insect
infestation during storage, resulting in high economic loss if disinfestation treatments
are not applied. In order to store dates for a long period (several months to
1 year), the fruits must be thoroughly cleaned of any pests (eggs, pupas, larva or
adults). This is done by fumigation, either in the field under various kinds of plastic
sheets, or at the packaging warehouse in special sealed rooms. Infestation of dates
with moths (almond moth, meal moth), beetles (sap beetle, saw-toothed grain beetle,
flour beetle), rats, mice and ants leads to contamination and loss of volume. To
comply with USA and European standards, for example, European markets require
that the growers document the quality control processes used; especially a report
concerning treatment against insects. Such a report must include a list of the materials
permitted for use and approved by an official agent, in addition to the timetable
of spraying with details of materials used, the date, concentration, number of days
before harvesting and the level of residue of pesticides (Glasner et al. 2002).
32.1.4 Industrial Uses of Dates
Industrialization of dates has focused mainly on conventional processes, such as
pitting, packaging, date pastes and animal feed. Biotechnological industrial processes
using dates as raw materials are highly flexible and can accept most date
cultivars. However, the most important factors to be considered in selecting date
cultivars suitable for the production process are the sugar content, price per ton and
storage life of the dates. As yet, there is no integrated date-processing industry,
despite the early realization of the importance of dates as a source of many useful
value-added products (Capital Advisory group 2004a). Even though date fruit is
marketed all over the world as a high-value confectionery and fruit crop (Zaid 2006)
and the production of dates has been increased many fold with modern biotechnological
approaches, the processing industries have not been developed to keep pace.
There is enormous industrial potential for fresh dates and date products with better
quality attributes. Date processing industries are producing various date products like
date paste, date syrup, date honey, date jam, date vinegar, etc. (Ahmed et al. 2005).
The industrialization of dates is a highly demanding need (Capital Advisory group
2004a). The following are the advantages listed therefore:
• Availability of a consistent supply of raw materials (dates), taking into consideration
adequate storage.
• Socioeconomic changes in date producing countries such as shifts in food habits
and consumption patterns, which have led to a substantial surplus of fresh dates.
• Producing new products from dates will generate economic value and improve
return.

Date processing industries could use second- or third-grade dates that are not
easily marketable.
• Generate more income for farmers by utilizing their production in manufacturing.
32.1.5 Economic Feasibility for Industrial Uses
Industrial projects utilizing dates as raw materials should focus on buying the less
expensive cultivars that are not generally preferred for direct local consumption. To
further control pricing and availability issues, annual supply contracts with date
farmers are essential. Dates of an industrial processing grade (off-grade) could be
purchased in bulk at low price. However, prices are relevant to the immediate postharvest
months and fluctuate at other seasons. Therefore, it is very important for
industrial date processing projects to establish an efficient date collection and procurement
mechanism. The trend of higher supply and declining demand will cause
a downturn in date prices which might favor the industrial processor (Capital
Advisory group 2004a).
32.2 Bakery Yeast Production from Dates
Dates are reputed to make a good potential substrate for bakery yeast production,
serving mainly as a source of carbon and energy for the yeast. Molasses now is
the dominant raw material for bakery yeast production worldwide. It is mainly
used as a source of carbon and energy for the yeast in addition to providing some
essential vitamins and minerals. Currently all bakery yeasts produced and used
commercially in the world are strains of the species Saccharomyces cerevisiae
(Barnett et al. 2000). The dry matter of the yeast cell is mainly composed of
40–54% raw protein (proteins, amino acids, nucleic acids and nucleotides), 39%
carbohydrates (glycogen, trehalose, mannans and glycans), 7% lipids (neutral
fats, sterines and phospholipids) and 6–10% (potassium, phosphorus, magnesium,
sulfur, magnesium, sodium; smaller amounts of silicon, calcium, chlorine
and iron and other trace elements) and ash (P2O5 and K2O). In addition the yeast
cell contains other components in smaller amounts such as vitamins, especially
the B complex group, (about 480 mg/100 g yeast dry matter), of which D-biotin,
D-pantothenic acid and m-Inositol are essential growth factors. The optimum
growth temperature and pH for S. cerevisiae are 30°C and 4.5, respectively. It is
facultatively anaerobic, i.e. it is able to grow aerobically and anaerobically.
Under aerobic conditions, the yeast completely oxidizes sugars to CO2 and produces
38 moles ATP (adenosine triphosphate) from 1 mole of glucose used for
energy production. In this way a yield of about 0.5 g yeast/g sugar consumed is
obtained. If the yeast grows anaerobically, it produces only 2 ATP moles from 1
mole glucose used for energy production. Hence the amount of biomass
produced

is much lower (maximum of 0.1 g yeast/g sugar), and the yeast produces high
amounts of ethanol
(about 0.5 g ethanol/g sugar consumed). A phenomenon
unique to S. cerevisiae is the condition termed aerobic respiration which is the
result of metabolic regulation known as the Crabtree Effect (Bailey and Ollis
1986). Due to this effect, if the sugar concentration in the growth medium exceeds
0.1 g/l, the yeast will start to ferment the sugars and produce ethanol, hence
greatly reducing the biomass yield.

 

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