Apart from sizeable quantities of dates being consumed at perishable immature stages (khalal and rutab), the majority of date fruits are consumed in the dry tamer stage with moisture content of less than 20% (Sabbri et al., 1982). These tamer date fruits are bulk packed in bags, metal tins, or baskets without fumigation or even without normal washing and are offered for marketing. To maintain the high quality expected by the consumers, the date producing and exporting countries have established a number of bulk-packing houses with modern facilities.
The Government of Saudi Arabia has initiated an ambitious project to modernize the date processing industry and to establish modern date-packing plants. To conform to the Saudi date standards for quality, the dates are fumigated with MB to kill all insects, if present (Anon, 1983). MB is used at a concentration of 1.0 lb/1000 ft3 for an exposure time of 24 h. Chloropicrin may also be added to the MB at a rate of 2%. After fumigation, the dates are transferred to a shaker for preliminary washing with water sprayers to remove dust or other coarse foreign materials. The washed dates are then graded and sorted to remove the defective and inferior dates.
The dates are finally washed using freshwater containing a food-grade detergent superchlore (sodium salt of dodecylbenzene sulfonic acid) and dubois 317 (sodium mono- and dimethyl naphthalene sulfonate) as a disinfectant. Excess water is removed from the dates by blowing hot air before packing in 20-kg corrugated cartons, which are then pressed, sealed, and wrapped (Mikki et al., 1986). If they are not sent for immediate shipping and marketing, the packed dates are transferred to cold storage (5 ± 2◦C) to maintain better shelf life up to 6 months with minimal changes in their original texture and flavor (Hegazi et al., 1986b). Preserved Products Anumber of preserved products such as pickles, chutney, jam, date butter, dates-in-syrup, paste, candy, and confectionery items have been prepared from date fruits (USDA, 1973). For preparing pickles and chutney, date fruits at the kimri and khalal stages of maturity are suitable. Pickles-in-oil and chutney prepared from kimri date fruits (Al-Hooti et al., 1997b, c) can substitute the extremely popular products being commercially prepared from raw mango fruit (Das- Thakur et al., 1976).
Typical hard texture and the ample amounts of sugars present at kimri stage are conducive for producing good-quality pickles and chutney. The shape, size, and green color of kimri stage date fruits make them look similar to olives. Except for their lower acidity values, the sweetness and textural characteristics of kimri -stage date fruits are similar to rawmango fruit, thus suitable for preparing pickles-in-oil and sweet chutney for local consumption and export purposes. Brine and salt-stock pickles are other popular products that could be prepared from kimri date fruits (Hamad and Yousif, 1986). These pickles are microbiologically safe as coliforms were absent, and the products had acceptable sensory quality even after 3 months of storage.
The duration of the pickling process varies from prolonged fermentation for brine pickles to very limited fermentation for fresh-pack pickles or no fermentation as for mango and other fruit pickles (Das-Thakur et al., 1976). Detailed information on the most important factors for pickling, such as brine concentration, use of antimold additives like sorbic acid and acetic acid, thermal processing requirements, and shelf life is available (Yousif et al., 1985; Al-Ogaidi et al., 1982; Khatchadourian et al., 1986).
Some of the processed products prepared from date fruits are presented in Figure 22.2. Traditionally, jam is defined as a self-preserved, cooked mixture of fruit and sugar (honey is often qualified as a sugar), with a total soluble solid content of 68.5% or higher (Al-Hooti et al., 1997d). For preparing a good jam, 65% of sugar, 1% of pectin, and a pH of about 3.0–3.2 are required. If the fruit is low in acidity, citric acid is often added. The basis of jam preservation is related to the water activity of the product. Mainly the sugar and pectin present in jam are responsible for attaining the desired water activity. Usually a sugar–date pulp ratio of 55:45 is used for jam making. Date fruits, having high sugar contents, are suitable for jam manufacture (Khatchadourian et al., 1986). The rutab stage date fruits have a reasonable quantity of sugar as well as the pectin required for jam preparation. Certain date fruit cultivars, such as Khalas, Sukkary, and Ruzeiz, have been shown to possess the desirable sugar and pectin contents and are highly suitable for jam making (Yousif et al., 1993a).
For making date butter (a product similar to peanut butter in usage), tamer fruits having the highest sugar content are used. All the steps are similar to jam making, except the pH of the pulp and sugar mixture is adjusted to 4.5–4.7, and the total soluble solid content at finishing stage is 74–75 Brix. Usually a sugar–date pulp ratio of 40:60 is used in date butter making.
For the preparation of dates-in-syrup, peeled, pitted whole date fruits at the khalal stage of maturity are used (Al-Hooti et al., 1997e).
After adjusting the pH of sugar syrup (50 Brix) to 2.8–3.0, it is boiled to reach a concentration of about 75–80 Brix. The hot syrup is poured into glass jars containing peeled, pitted date fruits, and the jars are capped immediately. The minimum drained weight of processed fruit should be kept at 55%. To achieve microbial sterility, the capped jars are processed in hot water (95◦C) for 30 min, then cooled to room temperature and labeled. Date syrup (dibs) is another useful product that can be prepared from tamer stage fruits. Recently,Al-Hooti et al. (2002) made use of pectinase and cellulase enzymes to obtain almost double the recovery of soluble solids than were obtained with the conventional hot water and autoclaving extraction methods.
The date syrup extracted with pectinase and cellulase can be used as a good substitute for sucrose in bakery products (Sidhu et al., 2002). Compared with the traditional heating methods, the use of microwave heating is another alternative to obtain better uniformity in product temperature, in a comparatively shorter time period that leads to better quality and yield of syrup (Ali et al., 1993).
Date syrup produced by these methods is used in a variety of food products, such as cakes (El-Samahi et al., 1993), carbonated beverages (Hamad and Al-Beshr, 1993), soft frozen yogurt (Hamad et al., 1993), milk-based drinks (Alhamdan, 2002; Yousif et al., 1986a, 1996), nutritious creamy foods (Alemzadeh et al., 1997), and ready-to-serve date juice beverages (Godara and Pareek, 1985; Yousif et al., 1993b).
Based on date syrup, butter, hazelnuts, dried skim milk, cocoa, starch, lecithin, and baking powder, a food can be formulated to have 6.13% protein, 19.86% fat, 47.8% total sugars, and a good amount of minerals (Alemzadeh et al., 1997).
The hot weather prevailing in this part of the world for most of the year offers a very good potential for the commercial production of these date juice or syrup-based drinks. Traditionally, a number of fruits, such as apple, apricot, mango, raisin, and strawberry, are converted into paste on a commercial scale for use in baby foods, baked goods, and confectionery (Ziemke, 1977; Anon, 1981), but so far date fruit has not been exploited to its full potential. Date fruit is not only the richest source of sugars but also contains various vitamins, minerals, and phytochemicals.
The production of date paste is, therefore, of particular interest to the food industry as it also results in reduced transportation and storage costs, since the stones (10–20% of the whole fruit weight) are removed in the process. This will also ensure the availability of date fruit paste for the food industry throughout the year.
For the preparation of date paste, pitted tamer date fruits are either soaked in hotwater at 95◦C for 5–15 s or steamed at 10 psig for about 3 min. To maintain the desirable color and good shelf life, citric acid or ascorbic acid (0.2% on a fruit basis) is added to lower the pH of date paste.
Thewater activity (aw) and pH of date paste prepared by this method are kept within the safe limits of 0.57 and 5.4, respectively (Yousif et al., 1986b, c). Date paste offers an opportunity to convert even the lower grade date fruits into an intermediate value-added product by the date processing industry (Mikki et al., 1983). Date paste and date fruit chunks can also be added to a number of food products such as baked goods and ice cream.
Up to 50% of the sucrose in ice cream can easily be replaced with date paste without adversely affecting its quality (Hamad et al., 1986).
Addition of date pieces (10%) to ice cream reduces the overrun slightly. Use of 4– 8% date paste in bread formulation results in marked improvements in the dough rheological properties, delays gelatinization, improves gas production and retention, prolongs the shelf life, retards staling, and improves the crumb and crust characteristics (Yousif et al., 1991). Date fruits serve mainly as a source of calories as these are rich in carbohydrates (about 78%) but low in proteins (2–3%) and fat (1%). To convert date fruits into nearly a complete food would, therefore, require supplementation with proteins, dietary fiber, and fats. Recently, the trend is shifting toward the use of blends of vegetable and dairy proteins to formulate a variety of candies, energy bars, and confectionery, which are becoming popular among children and adolescents.
One similar product made with tamer date pulp, sesame seeds, almonds, and oat flakes has been found to be quite acceptable to consumers (Al-Hooti et al., 1997e). The average ash, fat, and protein contents of 1.78%, 6.09%, and 7.83% in the control date bars (containing date paste and almonds) changed to 2.60%, 3.90%, and 9.56% in these date bars fortified with sesame seeds, almonds, skim milk powder, and rolled oats, respectively.
In another type of date bars fortified with soy protein isolate, single-cell proteins, almonds, and skim milk powder, the protein content was increased from 4.9– 5.3% in the control to about 10.7–12.1% (dry basis) in samples containing the high-protein ingredients.
Such formulated bars not only supply calories but can also provide a reasonable amount of fat, fiber, and minerals. These supplemented date bars not only have increased protein content but also possess significantly higher chemical scores of essential amino acids (Khalil, 1986). A variety of candied or glace fruits are being prepared from a number of fruits for use in new food product development by the dairy and bakery industries. To enhance the penetration of sugars, the fruit is pierced and is also dipped in dilute calcium chloride solution to toughen the texture.
Use of citric acid and ascorbic acid is also commonly used in the preparation of invert sugar syrup (about 30–45 Brix) required for cooking such fruit. During the preparation of candied fruit, the cooking of fruit with sugar syrup is repeated for short intervals over a period of many days until the soluble solids content of the cooked fruit reaches 70 Brix or higher.
This higher sugar content enhances the shelf life of candied fruit even when stored for many months at room temperature. Khalal stage fruits can be used for the preparation of glace dates (Sawaya et al., 1986b).
Khalal fruits from two varieties, Hallaw (red) and Khuwaildi (yellow), werewashed, air-dried, and pricked to facilitate sugar penetration. Sugar syrup of 35 Brix was prepared from 4.25 kg each of sucrose and glucose in 20 l of water.
To the syrup, 10 g each of calcium chloride and potassium sorbate are added, and the pH is adjusted to 2.8 with a solution made from a 4:1 mixture of citric acid and ascorbic acid. The fruit and syrup are cooked slowly over a period of time (with intermittent overnight rests) till the fruit gets to 75 Brix.
The glace fruit can be flavored or coated with milk chocolate for improved acceptability.