CHAPTER 4:
BY-PRODUCTS OF DATE  PACKING AND PROCESSING

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Intro immage

 

In date packing and processing operations a number of by-products are becoming available, for which a use should be found in order to improve the economics of the operation as a whole and to decrease disposal problems and costs. The main byproducts are cull dates and date pits from packing operations, and pits and presscakes from date processing:

4.1 Cull Dates

Whether on the household, small or large scale level of whole date use there is bound to be a selection of the fruit which will leave, proportionally to the quality standards set, a percentage of cull dates, which are not considered suitable for the main envisaged use. Consequently the definition of a cull date is rather flexible but is generally connected with "too hard, too small, blemished, poor appearance, foreign matter, infested" etc. In Chapters I to III the end use possibilities for the date have been described proportional to an increasing prominency of these defects with probably alcohol making as the least demanding product with regard to the quality of the raw material. But products based on date extraction like alcohol and syrup require substantial additional industrial set up. A more direct use, also very suitable for the rural level is the use in, or as animal feed. This heading on cull dates will therefore be used to look into the value of dates as an animal feed with the understanding that it will also include the use of low quality or surplus dates which otherwise would have been suitable for the product range described in Chapter 3.

Making good use of the (cull) date as an animal feed source requires not only consideration of its chemical composition but also the physical form in which the date is fed to the animal. Although whole dates will be eaten by camels, cattle, goats and sheep it is not uncommon to see the pit coming out the other end, undigested, thus losing its effect as a feed source (see 2.). Furthermore, the date, especially without considering the pit, is an unbalanced feed, i.e. high in carbohydrates and low in protein and fat, and for best feed efficiency has to be supplemented. Apart from feeding dates as is, which surely is the cheapest but not the nutritionally most optimal method, several techniques can help to improve the feed value, but this goes at a cost, which has to be recovered from the gain in nutritional worth of the feed. One of them is size reduction and mixing with other feeds. However, technologically, whole dates, especially the wetter ones, are an awkward material because they are composed of a soft and sticky, and a very hard component.

Unless they are very hard and dry when ground on their own, dates tend to smear and clog the sieves of the commonly used hammermills in feed plants. It is therefore necessary to make a premix with a dry material such as barley or maize or soybean meal, which normally forms part of the feed anyway, and then grind. It was found that incorporation of dates up to 30% of the mix is possible without fear of caking in the machinery (170). At this level also the compressing of the mix resulted in an excellent pellet and the beneficial effect of the use of dates in this case is that it can take the place of molasses as a lubricant and binder (170). Date ratios of 20% also gave this result but at lower levels the resulting pellets are poor and molasses would have to be added in compensation (170).

A second point in size reduction and incorporation of whole dates in feed mixes is the presence of the pits. In grinding tests, curiously, it was found, that grinding whole dates costs more energy (about 30%) than the sum of grinding the components, of the mix, separately (170). As can be expected the pits are the highest energy consumer in grinding (a factor 10:1 compared with the energy required for the rest of the mix). To reduce the cost of energy some thought has been given to separate the pits from the flesh first and treat them on their own (see 2) or discard them. When the dates are rather soft date maceration as described in Chapter I could be considered, which also leaves the date flesh already broken up for more easy mixing with other materials.

However, because for animal feed purposes usually the lower quality and drier dates are used, the available mechnical date pitters will not perform efficiently. Therefore a date mash was made by adding about 50% water and thorough mixing after which the pits are removed from the pulp in a rotary screen. The date mash was mixed with flaked barley (1:1) and dried in a rotary dryer to be used as a feed component (251). Apart from some technological limitations of mashing, screening and mixing, this process is however rather energy intensive too. On the other hand it produces a semi-finished product which does not necessarily have to pass through the grinder in the feed mill before final mixing. By and large, however, it would seem that the above process will not offset the alternative energy costs for grinding the whole date, but it leads to another possibility: could not a date mash from which the pits have been removed, replace molasses? This would simplify the preparatory operation to a (heated) mixing vessel for making a date pulp and a rotary screen for removing the pits. A possible limiting factor could be the moisture content of the mash, which cannot be expected to be lower than 50% at best (molasses 20-25%). It will not be a serious handicap when a fresh ration is made up for daily supplement feeding to the animals, but to produce storable compound mixes or pellets the final moisture content should not be more than 12-15% in the final mix. A compound mix of components averaging 7% moisture would not allow more than 13-16 kgs of date mash (corresponding to 6.5-8 kg of date flesh) to be added to 100 kgs of mix (molasses are normally added in the range of 5-10%).

If above "wet" additions of dates do not fit the requirements of the feed to be produced, one has to resort to passing the whole dates through the grinder and accept the extra energy costs or investigate the efficiency of a specially designed whole date/barley groats mixer which by its action breaks up the date flesh but leaves the pit intact, and which is separated in a following operation (286).

Grinding whole dates into a paste without premix has also been proposed and demonstrated in a reinforced powerful meat grinder with double plate and knife set (247).

With regard to the nutritional acceptability and value of dates for different target animals, a few pertinent examples are cited:

i. Chickens:

- whole ground dates replacing maize at respectively 5, 10 and 30% of a diet for broilers supported growth as efficiently as the control, but 47.7% as a total replacement of the maize resulted in growth depression and reduced feed utilization (263)

ii. Pigs:

- high digestibility coefficients for carbohydrates, but low if any for the protein and fat. Intake of whole dates up to 2500 gms daily for 120 kgs pigs. No stones found in faeces (457, 458). (Plinius, incidentally, already refers to the use of dates in fattening pigs in Egypt (128))

- Fed on an equal based ration of 1 kg cereals and vegetable and animal protein, substitution of potatoes (up to 2 kgs daily) for dates did not affect rate of gain and efficicency of feed conversion in the control and 2 experimental groups fed (partially) on dates (458)

iii. Sheep:

- replacing barley by whole dates at the rate of 25, 40 and 60% in rations containing 20% soybean meal and supplemented with roughage, lamb performance was similar, also with the control, fed on 85% barley and 15% soybean meal (592)

- Lambs fed ad lib alfalfa hay with incorporated respectively 10, 20, and 30% date flesh and ground pits showed for the 30% date level faster weight gain, highest feed intake with similar feed conversion rate, but a tendency to deposit fat. Date-fed lambs all showed highest in organoleptic testing of the loin chops for tenderness, juiciness and flavour (168)

iv. Cattle:

- for weaned male Jersey calves the average growth rate was 20% less when fed on fresh alfalfa and hay plus 1 kg dates than on alfalfa alone, though the diets were palatable (462). For young bulls on 3 kg alfalfa hay plus 3 kgs concentrate or alternatively 2.8 kg dates + 0.2 kg fishmeal, the date fed animals gained less and ate more dry matter per kg live weight gain (463)

- Macerated dates can successfully replace barley up to 50% in rations for cattle fattening (161)

- 25% of macerated dates incorporated in a ration for lactating dairy cows and replacing barley/oats by half with total protein kept constant, did not lower the milk yields (24).

More information on the value of feeding whole dates and date flesh to animals can be found in literature (463, 22, 231, 230, 494, 23, 112, 492).

In conclusion it can be stated that dates have a value as a carbohydrate feed but that its feed efficiency depends on suitable administration and supplementation to reach the best feeding results.

4.2 Date Pits

Date pits, also called pips, stones, kernels, or seeds form part of the integral date fruit in the order of, depending on variety and quality grade, 6-12% of its total weight in the tamr stage (Fig. 85). They become available in concentrated quantities when pitted dates are produced in packing plants or in industrial date processing plants based on juice extraction. In the latter case they may still be mixed with the exhausted presscake or they have been screened out in the process. At the rural level one may find some accumulation of date pits when immature dates are pitted before sundrying (e.g. on the coast of Libya) or countries where dates are pitted and preserved as a paste (agwa). For the rest, date pits follow the dispersed ways of distribution routes of the whole fruit and have no importance as an individual raw material.

Figure 85: Date Pits

Figure 85: Date Pits


Adapted from a number of literature references (554, 503, 536, 559, 139, 167, 146, 509) an indicative picture of the chemical composition of the date seed has been collated in the following table:

Table 19
Approximate composition of date pits

Moisture 5-10%
Protein (N x 6.25) 5-7%
Oil 7-10%
Crude fibre 10-20%
Carbohydrates 55-65%
Ash 1-2%

Information on the amino acid pattern of date seed protein is scarce but from a study on 2 Saudi varieties (503) it appears that glutamic acid, aspartic acid and arginine account for nearly half of total amino acids whilst tryptophan is the most limiting essential amino acid followed by isoleucine, and lysine as a border case in reference to the FAO/WHO reference pattern of essential amino acids (for human consumption).

The oil extracted from date pits is pale yellowish-green with a pleasant odour (146). Its main median characteristics are: spec weight, 0.9207 (15.5 C); 0.9174 (20 C), refr index, 1.4580 (40 C); 1.4633 (25 C); iodine value: (a measure for the degree of unsaturation of a fat): 50-55; saponification value: 205-210. Two independent analyses (i. (139); ii. (503)) on fatty acids show that oleic acid (i. 44.3%; ii. 52.2% including linoleic acid), lauric acid (17.4%; 24.2%), myristic acid (11.5%; 9.3%), palmitic acid (10.3%; 9.9%), and linoleic acid (8.5%; included with oleic acid) form by far the bulk of the total fatty acids. Stearic, capric and caprylic acid are present in minor amounts.

In the above analyses (Table 19) "carbohydrates", the largest component, is found as the rest value (i.e. 100 minus the other main components). Only a small part, in order of a few percentage points, consists of sugar, the remainder of carbohydrates being of a more complex nature. With a special eye for use as an animal feed and together with crude fibre content this part can be further split up in cellulose, hemicellulose, lignin and ash. For date pits this gave the following results (608):

Table 20
Composition date pit carbohydrates (excl. sugars)   (% of dry weight)

NDF 75.0 (neutral detergent fibre, total cell wall content)
ADF 57.5 (acid detergent fibre, NDF less hemicellulose)
Hemicellulose 17.5 (NDF minus ADG; hemicellulose is a long-chain carbohydrate composed of pentoses. It is readily hydrolyzed by dilute acids into mainly xylose)
Lignin 11.0 (determined by potassium lignin procedure on ADF residue, oxydixing the lignin)
Cellulose 42.5 (burning above residue)
Ash 4.0 (what remains upon burning)

With regard to mineral content date pits show appreciable amounts of K followed by P, Mg and Ca and a low Na content. Of the micro elements Fe, Mn, Zn and Cu are the more important ones (503; 536; 355).

On the basis of the above indicative composition figures a first prognosis can now be made on the possible use of date pits. For human consumption there seems to be little scope, though there are early reports of elaborate processes of pounding and boiling with the use of salt and vinegar, finally arriving at a soft paste, drying and grinding it into flour to be used for making a sort of pancake (445). Date seed oil is an edible oil but its low extraction for this purpose is no competitive match for the many other oil bearing crops. Date oil does not have any characteristic that would make it suitable for specific end uses, thus raising its value and compensating for its low extraction rate. Similar arguments apply also to the protein content.

There remains therefore the use of the whole seed as an animal feed which apart from the value of the protein and fat is favoured by the rather high hemicellulose content. However, feed value is not only determined by composition but also by accessibility and digestibility of the components. The hard, enclosed structure of the seed is a real obstacle to optimize the feed value, although it is also claimed that pits are an excellent slow release energy feed for camels during long desert journeys. Traditionally, especially at the rural level one has resorted to soaking the pits after which they are fed whole to ruminants. Date pits submerged in water for 72 hours will gain 25% in weight, but may increase by 50% after a week or so. But even then they are not readily ingested by the animals.

A second improvement is grinding which, again in view of the hard structure of the pit, is costly on energy and wear and tear of the machinery. Experimentally it was established that in a 40 HP swinging hammermill fitted with a 2 mm sieve the grinding of date pits consumed over 100 Kwh/ton whilst for barley or maize these figures are 19 and 15 Kwh respectively in the same mill. The energy consumption can be reduced by first crushing the pits and then grinding, but it requires more investment. The question is easily raised but only to be answered when all details are known, whether the high cost of size reduction is justified vis--vis the improved feed value resulting from it.

With regard to the acceptability and feed value of date pits a number of research trials have been carried out over the last decennia, a sampling of which is summarized below:

i. date stone meal can successfully replace a 10% barley content in chick rations, though the increased live weight gain over the control is related to more feed intake (9)

ii. ground date seeds can be used from 20 to 75% in ruminant rations if a good protein supplement (e.g. cotton seed cake) or urea is added (178, 28)

iii. except for its protein, date seeds have a high digestibility coefficient for ruminants and somewhat less for pigs (34)

iv. a wheat bran/barley mixture for carp feed could be replaced by up to 75% by date seed meal, whilst complete replacement would reduce daily growth rate but increase fat content in carp flesh (37).

Further references on the use of date pits in or as animal feed are found in (151, 598, 450, 451, 347, 348, 281, 45, 28, 252, 263).

Next to physical pretreatment of the raw material to improve the accessibility of the feed, some chemical treatments are known to increase digestibility. For instance, alkali treated straw has a linearly higher digestibility coefficient (from 45% to 71% for respectively 0 to 120 g NaOH per kg of treated straw). The mechanism of alkali treatment is not known exactly but is most likely based on displacement of intra-fibril hydrogen linkeages by much larger Na-ions, and breakage of bonds between lignin and cellulose. The result is a material with more accessible nutritive compounds and which is physically more attractive for the animal to ingest because the material becomes softer. The disadvantage is the high lye intake (average 6% of the straw) and the animal's water intake is greatly increased to remove excess sodium. Ammonia and urea in decreasing rates of efficiencies are also used for the purpose of upgrading ligno-cellulosic materials. Sodium hydroxide treatment of date pits has been experimented with (608). Ground date pits were treated with respectively 2.4, 4.8 and 9.6% NaOH solution, which resulted in increased in vitro digestion rates.

In another attempt to avoid costly size reduction of date pits to make them more valuable as a feed source, date seeds were germinated (over a period of 74 days). It could be concluded that without appreciable loss in nutrients (based on chemical analysis) the pits gained in softness to the point of possible direct consumption by the animals (560). A nutritional evaluation, if proven positive, might be interesting for village application of seeds for animal feed, in spite of the time factor involved for germination.

The use of date pits for animal feed in the traditional way is still likely the most common practice but there are reports on other uses of date pits, both traditionally and experimentally. In remote parts of the desert a coffee like beverage is sometimes prepared from date pits by roasting and grinding in a similar way as for coffee beans. The result must have been promising because the method has been used to adulterate coffee powder. A research article devoted to possible toxic effects of this adulterant, states "date seeds are roasted by dry heat, then ground to a similar powder as for coffee. The colour is a little lighter, the odour is fairly agreeable, and when mixed with coffee is difficult to detect". (226)

In Tibesti and other remote desert areas date pits are heated in closed pots and the tar thus formed is used as a preserving agent for wood. In a slightly modified form of dry distillation date pits can be turned into charcoal. In a test on making charcoal (554) the following results were obtained. Whole dates were carbonized (main reactions took place between 300-400 C) and the major formed products analysed:

Table 21
Dry distillation of date pits

Carbon 27%
Tar, crude 13-14%
Acetic acid 2-3%
Methanol 2%

The characteristics of the carbon were:

Table 22
Composition of date pit carbon

Moisture 0%
Volatiles 8.8%
Ash 4.0%
Apparent spec.grav. 0.67%
Real spec. grav. 1.36%
Porosity 51%
Ion-absorption 1.8% mgaeq iodine/g carbon

On the basis of these results it was concluded that pit carbon is not likely suitable as active carbon for use in metallurgy (ash content), though it has been quoted as a fine charcoal used by silversmiths (445). It does not exclude, however, the use as fire carbon which is still very common for small cooking stoves in the Arab World.

Dates pits, cleaned and polished have been used in necklaces and as earrings by women (445).

Some attention has been given to investigate microbial conversion of date seeds such as utilization of date pits and cheese whey for the production of citric acid by Candida lipolytica (7), the production of protein from date stone by Apergillus oryzae (421), and Candida Utilis (427) but practical follow-up to these investigations is unlikely in view of the type and composition of the raw material.

A perhaps more interesting potential use already referred to in the fifties in animal feed literature is the presence of a growth stimulating hormone, identified as estrone at the rate of 1.9 mg per kg of date seeds (212). The synthetically produced sisters of this female sex hormone have been used in chemical caponization of young cocks, but are more known for their growth promoting effect in animals. Their use in most countries is strictly regulated or totally forbidden for fear of the continuing effects of the hormone by consumption of the animal products by humans.

Chickens given 10 g daily of ground date seeds with the normal diet gained weight at a faster rate than the control as the following average figures (for 10 birds each) show (522).

Table 23
Weight gain of chickens fed on date pit meal (grams)

  Start After 1 week After 2 weeks After 3 weeks Total increase
Chickens (control) 858 900 919 1 067 212
Chickens (fed on date pit meal) 858 976 986 1 199 345

In this experiment no mention is made of the total feed intake of the two groups. In another similar experiment (9) the same accelerated growth in chickens fed on (partly) date stone meal is reported, but it was also measured that this increased weight is proportional to increased feed intake, which does not exclude the effect of a growth promoting substance in date seeds.

However, increased weight gain was not attained but did not change significantly in an experiment on broilers fed on rations replacing wheat bran/maize/lucerne at the rate of 5, 10 and 15% by date pit meal (263). And even a negative effect on growth rate of broilers by the feeding of date stones was reported (252).

The feed value of date pit meal for chickens is therefore not quite clear as is shown from the various contrasting reports referred to (9, 522, 263, 252).

The matter of purported hormonal effect of date stone meal was further pursued in tests measuring sperm output and concentration in rams (253, 349) but no conclusive results were obtained. Neither could any significant influence of incorporating date stone meal in the diet of Awassi ewes be detected on their reproductive performances (350).

The search for minor components with a specific activity has not limited itself to the effects related to animal feeding: an ethanolic extract of date pits showed, albeit weak, antimicrobial activity on several strains of microorganisms and increased motor activity in mice (355). Date seed extract lowered blood pressure in dogs when administered intravenously (522). Some flavonoids were analyzed in date seeds (372).

4.3 Presscakes

Presscakes are the result of processes where dates are extracted such as for syrup and alcohol. It is the exhausted date flesh with some residual sugar with or without the pits incorporated, depending on the type of extraction. It is wet (up to 70% moisture) and therefore bulky (from Appendix III it can be seen that presscake constitutes about 30% of the weight of ingoing dates) and will deteriorate quickly and become a disposal problem. The composition of dried presscake (excluding the pits) varies but on average will be about:

Table 24
Composition of dried date press cakes

Dry matter 87.7 92.8 95.2
Crude protein 5.3 4.4 8.1
Crude fibre 21.8 11.6 9.1
Crude fat 2.7 2.1 1.8
Ash 2.6 2.0 3.5
Nitrogen free extr. (NFE) 55.3 72.7 -
Sugar (part of NFE) 15.6
(458)
-
(554)
-
(215)

The feed value is estimated somewhat lower than dried beet pulp (458) but no references on tests on ensiling date pulp have been traced. This method has been very successful for beet pulp and avoids the prohibitive costs of drying these wet pulps. Date waste in broiler diets partially replacing cereals at the rate of respectively 50, 100 and 150 g per kg of feed gave higher weight gains, but at the cost of higher feed intake per kg gained, as shown in the following table (215):

Table 25
Weight gain, food consumption and conversion efficiency during fattening period (49 days) of broilers

Treatments Weight gain, g. (mean) Food consumption (g/bird) Food cons./ weight gained
I. Date waste (50) 1411 3310 2.22
II. Date waste (100) 1472 3324 2.26
III. Date waste (150) 1472 3323 2.26
IV. (Control) 1371 2861 2.07

It can be concluded that date waste can be used in broiler diets and that its inclusion will relate to practicality and relative cost of the waste and the replaced grains.

Further work on nutritional value has been reported (215, 439. 616) as well as a few attempts on microbial conversion of date presscakes (232, 611, 20, 420).

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