Most of the date fruits atkhalal, rutab, andtamerstages of maturity are consumed directly with little or no processing.
However, a number of value-added date products are now available in the local market throughout the year. For a more detailed description of value-added functional foods prepared from date fruits, the reader should refer to Sidhu and Al-Hooti (2005). A brief discussion about some of the important value- added food products prepared from date fruits is presented here.
Commercially Packed Dates
Besides, sizeable quantities of dates being consumed at per- ishable immature stages (khalalandrutab), the majority of date fruits are consumed in the drytamerstage with moisture content of less than 20% (Sabbri et al. 1982). Thesetamer 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 mod- ern facilities. The Government of Saudi Arabia has initiated an ambitious project to modernize the date-processing indus- try and to establish modern date-packing plants. To conform to the Saudi date standards for quality, the dates are fumi- gated 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 hours. 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 fresh water 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 shelf life of up to 6 months with minimal changes in their original texture and flavor (Hegazi et al. 1986b).
Preserved Products
A number of preserved products such as pickles, chutney, jam, date butter, dates-in-syrup, paste, candy, and confec- tionery items have been prepared from date fruits (USDA 1973). For preparing pickles and chutney, date fruits at the kimriandkhalalstages of maturity are suitable. Pickles-in- oil and chutney prepared from kimridate fruits (Al-Hooti
et al. 1997b, 1997c) can substitute the popular products com- mercially 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 ofkimristage date fruits make them look similar to olives.
Except for their lower acidity values, the sweetness and textu- ral characteristics ofkimri-stage date fruits are similar to raw mango 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 fromkimridate 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 fer- mentation as for mango and other fruit pickles (Das-Thakur et al. 1976). Detailed information on the most important fac- tors for pickling, such as brine concentration, use of antimold additives like sorbic acid and acetic acid, thermal processing, etc. is reported by several researchers (Al-Ogaidi et al. 1982;
Yousif et al. 1985; Khatchadourian et al. 1986). Some of the processed products prepared from date fruits are presented in Figure 34.3.
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, hav- ing high sugar contents, are suitable for jam manufacture (Khatchadourian et al. 1986; Besbes et al. 2009). Therutab stage date fruits have a reasonable quantity of sugar as well as the pectin required for jam preparation. Certain date-fruit cultivars, such asKhalas,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 (similar to peanut butter),tamerfruits hav- ing 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 fin- ishing 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 thekhalal stage of maturity are used (Al-Hooti et al. 1997e). After ad- justing 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 minutes, then cooled to room temperature and labeled.
Date syrup (dibs) is another useful product that can be prepared fromtamer stage fruits. Sidhu et al. (2002) used pectinase and cellulase enzymes to obtain almost double the recovery of soluble solids than were obtained with the con- ventional 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. 2003). 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). Sonication of date fruit/water mixture has been used for the extraction of date syrup in higher yield and with better microbial quality (Entezari et al. 2004). 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 (Yousif et al. 1996;
Yousif et al. 1986a; Alhamdan 2002), nutritious creamy foods (Alemzadeh et al. 1997), and ready-to-serve date juice bever- ages (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 in- dustry 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 avail- ability of date-fruit paste for the food industry throughout the year. For the preparation of date paste, pittedtamerdate fruits are either soaked in hot water at 95◦C for 5–15 seconds or steamed at 10 psig for about 3 minutes. 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. The water 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, 1986c). 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
Date jam
Date butter
Dates-in-syrup
Date relish
Pickle-in-oil Pickle-in-vinegar
Kimri
Date bars
Chutney
Figure 34.3. Selected processed date fruit products. (Photo source: Prof. Jiwan S. Sidhu.)
goods and ice cream. Up to 50% of the sucrose in ice cream can easily be replaced with date paste without adversely af- fecting 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 improve- ments in the dough rheological properties, delays gelatiniza- tion, improves gas production and retention, prolongs the
shelf life, retards staling, and improves the crumb and crust characteristics (Yousif et al. 1991). Ahmed and Ramaswamy (2006) investigated various physicochemical properties (total solids, color, rheology, texture, melting point, and glass tran- sition) of commercial date pastes made from three cultivars (Khalas, Bumaan, Lulu). Paste made from Bumaan exhib- ited elastic and viscous modulus compared to other cultivars.
Texture Profile Analysis data onLulu date paste exhibited the least hardness, gumminess, chewiness, and springiness but moderate cohesiveness when compared with date paste made from other cultivars. Sablani et al. (2008) have de- veloped a technique to produce non sticky and free flowing powder granules from date paste and measured its water ac- tivity, bulk density, color, hygroscopicity, and glass transition temperature.
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 withtamerdate pulp, sesame seeds, almonds, and oat flakes has been found to be quite accept- able 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 for- tified 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% to 5.3% in the control to about 10.7–12.1% (dry basis) in samples containing the high-protein ingredients. Such for- mulated bars not only supply calories but can also provide a reasonable amount of fat, fiber, and minerals. These supple- mented 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 devel- opment 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 re- peated 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.
Khalalstage fruits can be used for the preparation of glace dates (Sawaya et al. 1986).Khalalfruits from two varieties, Hallaw(red) andKhuwaildi(yellow), were washed, air-dried, and pricked to facilitate sugar penetration. Sugar syrup of 35◦Brix was prepared from 4.25 kg each of sucrose and glu- cose in 20 L of water. To the syrup, 10 g each of calcium chloride and potassium sorbate are added, and the pH is ad- justed 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. Dehy- drated dates from immature date fruits have been prepared by Kulkarni et al. (2008). These dried dates when packaged in 75 low-density polyethylene maintained an acceptable qual- ity for 6 months at room temperature.