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.