Pods as a resource

Fruit of the P. juliflora - P. pallida complex is sweet, nutritious, has low concentrations of tannins and other unpalatable chemicals, and has moderate to high digestibility. Natural selection favoured these characters as they are attractive to foraging animals and thus help in dispersal of seed. Prosopis pods and seeds are consumed by a wide variety of animals, both in their native range and where introduced, and are often an important part of mammalian diets when trees are present in large numbers. Insects, reptiles and birds are minor disseminators of seed, but pods may play an important role as a source of nutrition of such animals (e.g. Mooney et al 1977).

P. juliflora - P. pallida pods are used as a feed mainly for cattle but also for sheep, goats, camels, pigs and poultry. Pods are mainly used as a forage, browsed directly from the tree or the ground below, rather than as a fodder, where the pods are collected and fed to stalled stock. As a part of extensive grazing systems, livestock was introduced into native Prosopis woodlands in the Americas and still browse in natural woodland today. Many introductions of P. juliflora and P.

pallida were made in arid and semi-arid zones around the world primarily because of a perceived need for additional sources of forage. Livestock is often allowed access to naturalised stands and plantations of P. juliflora and P. pallida where introduced. These species are especially suitable for extensive grazing systems as the leaves are unpalatable and pods are produced either towards the end of the dry season

Table 27. Composition of P. pallida pulp and endocarps (Cruz et al 1987, Cruz 1990, Saura et al 1991, Salazar 1993, Bravo et al 1994, Grados and Cruz 1994).

Main components Pulp Endocarp

(g/100 g dry matter)

Soluble sugars 48.5 1.6

Total sucrose 46.1

-Total fructose 1.26

-Total glucose 1.02

-Total xylose 0.27

-Dietary fibre 32.2 92.3

Total insoluble dietary fibre 30.6 88.9

Total soluble dietary fibre 1.6 3.4

Protein (NX6.25) 8.1 2.3

Sum of amino acids 7.1

-Resistant 2.2

-Fat 0.8 1.3

Ash 3.6 1.3

Condensed tannins 0.4

-Total soluble polyphenols 0.81 0.7

Table 28. Mineral and vitamin composition of pulp from P. pallida pods (Cruz et al 1987).

Minerals (g/kg dry matter) Vitamins (mg/kg sample)

Potassium 26.5 Vitamin A not detected

Sodium 1.1 Vitamin E 5

Calcium 0.8 Vitamin B1 1.9

Magnesium 0.9 Vitamin B2 0.6

Copper trace Vitamin B6 2.35

Zinc trace Nicotinic acid 31

Manganese trace Vitamin C 60

Iron 0.3 Folic acid 0.18

Calcium pantothenate 10.5

Table 29. Amino acid composition of P. pallida pulp and seed cotyledon (Cruz et al 1987).

Amino acids Pulp Seed Amino acids Pulp Seed

(g/100 g DM) cotyledon (g/100 g DM) cotyledon

Aspartic acid 8.51 8.30 Isoleucine 3.26 3.09

Throenine 4.68 2.42 Leucine 7.94 7.51

Serine 4.96 4.87 Tyrosine 2.84 1.84

Glutamic acid 10.07 21.31 Phenylalanine 2.98 4.29

Proline 23.40 7.49 Lysine 4.26 4.09

Glycine 4.68 4.59 Histidine 1.99 3.10

Alanine 4.26 4.34 Arginine 4.82 14.63

Cysteine 0.43 1.31 Tryptophan 0.89 1.37

Methionine 0.57 0.88 Hydroxyproline 2.13

-Valine 7.80 7.80

or are easily stored until then, coinciding with the period when alternative sources of forage are lacking.

Collected pods are fed to stalled livestock, whole or processed, alone or as part of a ration and fresh or after storage. Processing involves the pounding, grinding or milling of pods, either as a single process producing a whole pod extract, or with some separation of pod parts and further processing of each fraction. Processing usually involves milling of whole pods into a homogeneous, coarse flour, although in some cases exocarp and mesocarp (pulp) are separated from the endocarp and seed. Considerable research has been undertaken on the use of milled pods in livestock rations, particularly in Brazil and India. Pods must be ground or milled to secure the full nutritive value as most of the protein rich seeds would otherwise pass undigested through the digestive tract of livestock.

Whole pods P. juliflora were found to provide 7% digestible crude protein and 75% total digestible nutrients on a dry matter basis (Shukla et al 1984). The digestibility of crude protein from P. juliflora pods was 50-60%, with the average digestibility of ether extract being 70%, crude fibre 80%, nitrogen free extract 79% and organic matter 74% (Shukla et al 1984). The in vitro digestibility of P. pallida pulp protein has been determined to be 73% (Bravo et al 1994), similar to the value for P. juliflora pulp from Ecuador (Marangoni and Alli 1988). These figures are comparable with other results for P. juliflora, P. pallida and other Prosopis species.

Nitrogen and calcium balances were positive, but the phosphorus balance was negative suggesting that pods should be fed with a phosphorus rich feed supplement. Levels of anti-nutritional chemicals are not significant in pods of Prosopis species, and the tannin content of pods is low (0.7-1.5%) (Shukla et al 1984). Makkar et al (1990) found low levels of total phenols and condensed tannins in pods of P.

juliflora with no protein-precipitation capacity, as a measure of biological activity.

Consumption of rations containing up to 45% P. juliflora pods was 1.5% of cattle body weight in India, with acceptable liveweight gains (Shukla et al 1984). Other studies have indicated that cattle rations containing less than 50% P.

juliflora pods lead to no adverse effects on consumption, digestibility, nutrient balance and animal health. However, there are several records of pods causing ill effects in livestock when used alone as a feed. Alder (1949) observed 1% of cattle becoming ill when P. pallida pods were used as a sole ration. This was assumed to be due to the regression of rumen bacterial cellulase activity due to the high sugar content of the pods. Rations containing Prosopis pods have been recommended for lactating animals, with milk production often said to improve following inclusion of pods in the ration. No effects on milk flavour were noted at less than 50% pods in the ration, though as a sole feed some taste change has been suggested (e.g. Silva 1990b). It may be seen that pods have a valuable role either as a forage for grazing animals, or as part of milled rations for stalled livestock.

Considerable work has also been undertaken in Brazil (e.g.

Habit and Saavedra 1990).

Pod collection in the Americas is done manually, by children and women and sometimes by the whole rural family, as an activity marginal to their home and agricultural tasks.

Considering that bearing trees are often widely dispersed and there may be no means of transport, one person can collect no more than 150 kg of pods per day (see 4.1.1).

Collectors in Peru earn an equivalent of less than US$5/

day, as during the production season pods fetch a very low price because of their abundance (e.g. US$27/t in February 1995). People use the pods for feeding their small livestock or sell them to merchants. In Peru, most of the merchants have storage facilities, allowing them to supply ranchers in other regions of the country throughout the year. They profit from the fact that the price for Prosopis pods can quadruple by the end of the dry season in September, when other forages are lacking.

Commercial production of Prosopis pods is not well documented in government statistics and the merchants do not usually declare the real amounts. A compilation of records shows that 12635 t of pods were collected in northern Peru in 1996, of which 60% were transported to Lima. This figure is, however, thought to be only a very small part of the total (Asencio Díaz 1997). An estimation based on sampling studies and forestry maps suggests 400000 t of pods are available annually in the northern region of Peru, more than 50% of which may not be collected (Jara and Otivo 1989, INRENA 1998).

Storage must protect pods from the rain and livestock, and avoid infestations such as those by insects of the family Bruchidae and Pyralidae (Domínguez 1982, Núñez-Sacarías 1994) Traditional pod stores in North America tended to consist of large baskets made from natural fibres, with a rain-proof roof, and raised off the ground to prevent predation and to keep the pods dry (Felger 1977). In Brazil, standard agricultural barns used for storing other dried animal feeds or special rooms with wooden floors and walls are used (e.g.

da Silva 1996). In Peru, rustic closed rooms were used, made from mud bricks. These have largely been replaced with block buildings (Grados and Cruz 1996). Special storage units for P. pallida pods are built, 5 m x 5 m x 4 m high, which are capable of storing 40 t of pods (Díaz Celis 1995).

In India, layers of dry pods are laid down alternately with layers of sand. This is said to increase storage time up to three years. Periodic checking of the pods in the store is recommended to assess any damage due to fungal infections, high moisture or pests. Removal of infected pods should be carried out immediately. In Peru, however, once a pod store is filled, it is sealed with clay and opened only when the whole batch is to be sold. Chemicals are not often used for insect control during storage. Fumigants and dusting with insecticide powders have been reported to be effective, but the use of natural repellent plants such as neem is preferred and recommended (Tewari et al 2000). Another suggested

Figure 20. Fractions and potential uses from processing and separation of P. juliflora - P. pallida pods.

Prosopis pods

Episperm (seed coat) Coffee substitute

Pulp flour Syrup

Alcohol by fermentation

Protein enriched flour Bakery and extrusion-cooking product Animal feed

Fuel Additive for dietetic foods

(35%) (9%)

Gum Protein

concentrate Seed

Endosperm Cotyledon

(20%) (32%) (48%)

Endocarp (hull) Exo and mesocarp

(pulp) (56%)

use is as a binding agent in preparing compact roughage blocks from agricultural waste (Shukla et al 1984).

Human food

Being nutritious and readily available, pods from the P.

juliflora - P. pallida complex can be used to supplement human diets. Pods can be sucked, chewed or eaten raw but for processing into human food, separation of pod parts is generally undertaken, with the mesocarp (pulp) fraction undergoing further processing. Traditionally, dried pods are pounded in a pestle and mortar to produce a coarse flour, or ground using a variety of stone mills. Mills made of two stones, suitable for grinding cereals have been used, while a special rotary mill was used to grind Prosopis pods in North America and Asia (Felger 1977, Fisher 1977). This consisted of a larger basal stone with a conical shaped hole in the centre and a smaller conical stone that was rotated in the hole. Other methods of manual grinding and milling require hand turned rollers or corkscrew mills with perforated end plates. For hand processing in particular, adequate drying is essential to reduce the problems caused by sticking of moist mesocarps. Small hand-fed mechanical threshers and mills

such as a disc mill (Flynt and Morton 1969) or a meat grinder (Pasiecznik and Felker 1992) have proved successful for processing small quantities of Prosopis pods.

Several large, semi-industrial sized processing units have been adapted or designed specifically for processing Prosopis pods (Grados and Cruz 1996). In Peru, a mill prototype was constructed specifically for processing P. pallida pods by improving the design of a cereal thresher (Cruz 1986), having several hammers fixed to a rotating shaft and short hammers mounted on the screening housing (Coronado 1988). Mills for processing pods are in use through the native range of Prosopis species in the Americas. In Brazil, facilities are being built in various locations specifically for drying and milling P. juliflora pods. These provide a good example of small scale pod processing for communal use by local farmers and land owners. Processing involves the drying of pods with a wood burning drier in large open bins at approximately 80°C for four hours immediately before milling. ‘Micro-mills’ are adapted rotating mills with meshed screens of various sizes. Several types of mill that are used for grinding cereals and animal feeds are also used for P.

juliflora pods (Kanzaria and Varshney 1998).

There have been several detailed studies on the milling and separation of pod parts of the North American P. glandulosa (Meyer et al 1982, Meyer 1984, Saunders et al 1986). Pulp flour, seeds and endocarp hulls were obtained, and techniques were proposed for further separation of the seed into endosperm, cotyledon and seed coat. The integral grinding of pods including seeds was investigated by Del Valle et al (1986, 1987) for the production of high-protein, low-fibre flours, recoverable by sieving. A pilot plant in Peru allows the separation of pods into four fractions and the recovery of entire seeds (Grados and Cruz 1996). The fractions from the separation and processing of P. juliflora and P. pallida pods and their end uses are presented in Figure 20, with flour and syrup the most commonly used.

A syrup, or concentrated sugary extract from Prosopis pods, called ‘algarrobina’, is commonly made from P. pallida in rural areas of northern Peru. This syrup is made from whole or crushed pods which are soaked in water for two hours before pressing and filtering the resulting liquid, and finally concentrating the liquid by evaporation. The dark brown syrup obtained is more viscous than honey and exhibits a peculiar brightness. The process is carried out on a household level in rural Peru using very simple kitchen equipment, and the ‘algarrobina’ produced is sold in reusable glass bottles.

No quality standards exist for this product (Estrada 1974, Alza et al 1998). Modern processes are much quicker and require no heating as they use a finely ground flour from the pulp (Bravo et al 1998). The solid residue that remains following extraction is called the filter cake which can be washed and dried and could be used to enrich food products with dietary fibre. Such syrups and dietary fibres, made using different conditions and processes, have slight differences, which have been characterised (Bravo et al 1998).

‘Algarrobina’ is consumed in different ways. In Peru, some people recommend taking a spoon daily as a health food. It is consumed directly or added to fruit juices or milk, where it acts as both sweetener and flavouring agent. It is often given in this way to children and elderly people in Peru because it is believed that the syrup has fortifying and revitalising properties. In urban zones, the syrup is used as an ingredient in home confectionery and to prepare a tasty drink, the ‘cocktail de algarrobina’, which is a mixture of a small quantity of ‘algarrobina’ with brandy and milk (Cruz 1999).

Another food product from Prosopis is ‘yupisín’, a beverage which is obtained by water extraction of the sugars from the pod. In contrast to ‘algarrobina’ it is consumed directly without concentration or used to prepare desserts with sweet potato flour. ‘yupisín’ is presently consumed only in rural zones , and it is not bottled. A very similar beverage is known in Argentina as ‘añapa’. A fermented beverage, ‘aloja’ can be obtained from ‘añapa’ and is a substitute for beer or wine (Cruz 1986, Ochoa 1996). In Peru, no fermented beverages are prepared commercially from the sugary pulp of P. pallida.

Prosopis pods played an important role in the Sonoran Desert in North America, where Indian tribes made flour and dough with the dried or toasted pulp from ripe pods. A kind of durable cake was prepared by drying dough balls (Simpson 1977, Meyer 1984). In Northern Argentina, flour made from the sugary pulp of several Prosopis species is known as ‘patay’

and is still consumed today (Ochoa 1996). The flour can be incorporated into a variety of food products including bread, biscuits and cakes. These are sometimes consumed in the native range of P. juliflora and P. pallida in Peru but rarely elsewhere and not at all where the species have been introduced. The absence of starch is, however, a limitation to Prosopis flour levels in bread formulations. Mixing 5-25%

Prosopis flour with wheat flour produces products which have acceptable taste. The rheological behaviour of P. pallida-wheat composite flours has been studied (Cruz 1986), and P. pallida flour causes dough resistance to decrease and dough elasticity to increase resulting in softer leavened bread. Sweet bread containing 5% P. pallida flour is acceptable in texture and taste. Up to 25% P. pallida flour has been used in making biscuits, which reduced the amount of additional sugar required. There is a slightly bitter aftertaste reported by some after consuming these products, but which some people, however, find pleasant (Cruz 1999). In Brazil, the production of a protein isolate (Baião et al 1987) and a protein-enriched flour (Ruiz 1997) from P. juliflora seeds and its application in bread making have been reported. P. pallida pulp flour can also be used as an ingredient in many other food preparations, such as cakes, ice creams and other desserts.

P. pallida pulp flour has been converted into an instantly soluble powder, and could be used as a cocoa powder substitute. A similar ‘instant’ soluble powder derived from carob (Ceratonia siliqua) pulp is currently commercialised.

A preliminary study has shown that a soluble powder can be obtained from the fine Prosopis pulp flour by re-milling and sieving through a 100-mesh screen (La Torre 1990). In order to improve the dispersability in milk, yoghurt and juices, the agglomeration of the fine powder should be studied.

Improvements to the nutritional or sensorial properties of Prosopis pulp flour have been achieved by mixing with other cereal flours and with cocoa (Grados and Cruz 1996). New food products from Prosopis pods are being developed in Peru by adapting processing technologies to rural situations. A powder called ‘garrofina’ is produced from finely ground whole fruits with small, rural pod processing mills.

Coffee substitute has been made from P. juliflora in Brazil (e.g. Azevedo Rocha 1987), with the roasting of just the coarse pulp flour giving a better flavour than roasting the whole pods (Carrión 1988). Flour is roasted at 120°C until it becomes dark brown, during which time it agglomerates into larger granules requiring further grinding. The final product is used in the same way as filter coffee granules.

Compared with other coffee substitutes such as roasted beans or cereals, it is generally well accepted by consumers and has an acceptable flavour. Prosopis coffee substitutes are caffeine free (Vieira et al 1995). Coffee substitutes or ‘café de algarroba’ are produced and successfully commercialised

from P. pallida pods in Peru, packed in 250 g plastic bags at a convenient price under the manufacturers’ own trade names (Cruz 1999).

Fuel

The uses of P. juliflora - P. pallida pods other than for food or feed have often been based on the high percentage of sugars primarily to produce liquid fuel. Attention has been paid to the potential of pods as a source of biofuels by processing the carbohydrates into ethanol. In the USA, Avgerinos and Wang (1980) assessed the potential for the direct fermentative production of ethanol from the pods of P.

glandulosa and a P. alba X P. velutina hybrid. They used a mixed culture of Clostridium thermocellum and C.

thermosaccharolyticum, able to break down both the sugars and celluloses in the pods. Up to 80% of the total carbohydrates present in the hybrid pods were utilised, with ethanol produced at 80% of theoretical yield (Avgerinos and Wang 1980).

Felker et al (1986b) estimated that in native stands of Prosopis, pods were a significant and unrecognised alcohol fuel resource. Potential ethanol production was estimated at 1100 l/ha/yr if only the sugars were utilised, or 1900 l/

ha/yr if starch hydrolysis was also employed. The use of by-products from industrial processing of Prosopis pods for human food has also been suggested, such as using pod endocarps as fuel (Cruz 1999). P. juliflora pods have been suggested for use in the formulation of substrates and media for laboratory use (Bohra et al 1998).