Plant extracts

3.4.1 Honey and wax

Flowers of P. juliflora - P. pallida are small, yellow and gathered on long inflorescences producing pollen and nectar that is high in protein and sugars. The proximate composition of the flower parts have not, however, been ascertained. Flowers of North American Prosopis species were eaten directly as a human food but this was only ever a minor use. The overwhelming use of flowers is for the supply of nectar and pollen as a bee forage for the production of honey. Honey from P. juliflora and P. pallida can also be processed into other products, or fermented into mead (honey beer). Wax is a by-product, used as an industrial and pharmaceutical raw material for the production of candles, furniture polish, creams and balms.

Production can be from wild bees’ nests collected from the branches of trees (Varshney 1996) but is more often from commercial hives in organised apiaries (Esbenshade 1980).

P. juliflora and P. pallida are the main source of pollen and nectar in many regions. Their ability to produce profuse numbers of flowers and flower regularly, even in drought years, often twice a year or almost continually, means that large bee populations can be maintained where woodlands or plantations are present. In Mexico, India and Hawaii particularly, commercial production of honey from P. juliflora and P. pallida has been developed. These industries are important to local economies, with the additional advantage that pod production is improved where hives are present (Esbenshade 1980, Varshney 1996). An often overlooked constraint to increased honey production in arid zones is water availability for bees, with a need to provide adequate quantities of fresh water near to each colony (Esbenshade 1980).

Many bee species visit the flowers (Simpson et al 1977) but only a few are of economic importance as honey producers.

Apis mellifera, the common honey bee, is widely kept. In Gujarat, India, nests of the bee Apis florea are collected (Varshney 1996), while in Andhra Pradesh, P. juliflora is a nectar and pollen source for Apis florea and Apis cerana (Kalpana and Ramanujam 1990). In Brazil, the Africanized honey bee is domesticated. The foraging behaviour of bees has been studied. P. pallida was one of the three most visited tree species in Peru (Zevallos and Higaonna 1988), while in Brazil, P. juliflora was the second most important source of pollen for bees (Freitas 1994). In India, 52-95% of the pollen collected by Apis florea was from P. juliflora (Kalpana and Ramanujam 1990) while in another state, P. juliflora accounted for 90% of the honey produced (Varshney 1996).

In Pakistan, Muzaffar and Ahmad (1991) noted P. juliflora as a major source of bee forage.

Honey is separated from the wax by straining through a cloth.

Honeycombs are, however, sometimes heated in which case

attention must be given to the possible production of toxic chemicals during heating. The honey produced by the various species of bee is noted as having excellent quality, being light in colour and flavour. In India, honey from P.

juliflora was given an ‘A’ grade, and classed as one of the finest medicinal honeys (Varshney 1996), while in Hawaii, honey from P. pallida earns a price premium over honey from other species because of the high quality (Esbenshade 1980).

In Brazil, however, the honey was said to be of an inferior grade. Prosopis honeys were declared adulterated in the USA, based on delta ¹³C values being outside the range accepted there, but detailed analysis found that such high values are typical of Prosopis species, including P. pallida (White et al 1991). Furfural, a toxic chemical which can be produced during inadequate heat processing of honey, was detected in P. juliflora (Rocha 1990). The potential hazards of introducing new honey plants such as P. juliflora is discussed by Eisikowitch and Dafni (1988), suggesting that besides potential invasiveness, such species may attract native pollinators away from the native flora. Profuse production of pollen from P. juliflora has other potential drawbacks, being blamed for allergic reactions in the Middle East, India, the USA and elsewhere (see 3.5.2).

Limited information is available on the honey production per tree or per unit area. However, Burkart (1943, in Silva 1990b) estimated that bees may extract enough nectar and pollen from a single flowering tree to produce over 1 kg honey, which could yield an equivalent of 100-400 kg/ha/yr depending on tree density. Other data are more general, only relating to production over unspecified areas. Hawaii was estimated to be the largest honey producer in the world in 1930, producing over 225 t of honey/yr, primarily from P.

pallida, with mean production (surplus) per colony estimated at 50-70 kg/colony/yr, and other estimates as high as 225-360 kg/colony/yr (Esbenshade 1980). Approximately 60 t of honey are produced annually from the collection of wild nests in Gujarat, India and 3 t/yr of wax has been produced and sold as a by-product (Varshney 1996), illustrating the great potential of honey production where woodlands and plantations are present.

3.4.2 Exudate gums

The exudate gum from P. juliflora and P. pallida appears as a viscous liquid exuding from the trunk or branches of the tree, before drying and becoming solid. The colour can vary from translucent to yellowish, generally amber, becoming darker with age. Prosopis gums are soluble in water with a low viscosity. They are odourless and have little taste, are non-crystalline and non-soluble in alcohol or ether (Rangel 1943, in Lima 1994). Where referring to Prosopis gums in the literature, it is important to differentiate exudate gums from seed (galactomannan) gums (see 3.2.1). The most important physical properties of exudate gum are light colour, solubility in water and high viscosity. The composition of Prosopis gum collected in Mexico was 11% moisture, 3.4%

ash, 0.2% nitrogen, 0.6% methoxyl and 18% uronic acid (Anderson and Farquhar 1982). Sugar composition after hydrolysis was 3.8% 4-0-methylglucuronic acid, 14%

glucuronic acid, 45% galactose, 24% arabinose and 13%

rhamnose. The intrinsic viscosity of P. juliflora was assessed as 14 ml/g (Anderson and Farquhar 1982).

The sample of P. juliflora analysed by Anderson and Farquhar (1982) was found to differ considerably from exudates of other Prosopis species tested, by having a lower methoxyl content, a negative optical rotation, smaller nitrogen and arabinose contents and a higher proportion of rhamnose.

While amino acid composition of exudates from five Prosopis species was analysed by Anderson et al (1985), neither P.

pallida or P. juliflora was included. However, overall, amino acid composition was similar amongst species, and also to commercial gum arabic (from Acacia senegal). Commercial

‘gum mesquite’ from North American Prosopis species has also been analysed and found to be very similar to gum arabic (e.g. Anderson and Farquhar 1982, Anderson et al 1985).

The samples analysed by Anderson and Farquhar (1982) and subsequently by Jurasek and Phillips (1993) showed that the sample of gum mesquite was probably from P. glandulosa.

Commercial production of Prosopis exudate gum from South Asia and Africa could be assumed to be predominantly from P. juliflora.

Exudate gums have a wide variety of uses in the food, pharmaceutical, chemical and manufacturing industries. The gum of P. juliflora is used for sizing cloth and as a paper adhesive in India (Vimal and Tyagi 1986). The use of P.

juliflora gum has been evaluated for use as a binder in tablet manufacture (Khanna et al 1997) and other pharmaceutical preparations. The gum has also been used as a stabilising agent for spray-dried encapsulated orange peel oil. Compared with gum arabic, P. juliflora emulsions were more stable but had a lower encapsulation capacity (80%), with no difference in flavour intensity (Beristain and Vernoncarter 1994).

However, commercial gum mesquite or exudates from any Prosopis species are not permitted food additives in any of the regulatory listings (Anderson 1989). No toxicological study has been undertaken on the exudate gum of Prosopis species, but the mandatory tests required take 5-7 years and would cost over US$1 million. Considering the low present volume of trade, the chances of gum mesquite being accepted for food use are extremely slight (Anderson 1989).

The collection of the gum exudate is very time consuming and harvesting costs are a major constraint. A single person has been estimated to be able to collect 1-2 kg of P. juliflora gum/day in India (Tewari 1998). The trade in exudate gum has been increasing in India, with Gujarat state recording a total annual production of 850 t in 1989, with P. juliflora gum estimated to make up approximately 80% of that total (Tewari 1998). Seasonality of gum production was noted by Lima (1994) and Tewari (1998). P. juliflora gum exudation increased at higher temperatures and ceased completely at the beginning of the rainy season. Peak production occurred in India in April and May, extending to June where rains

were later (Tewari 1998). In Brazil, gum production was also higher in the dry season, peaking from August to October (Lima 1994).

Total gum production per tree varies greatly, generally being very low in young trees and increasing with tree age. Lima (1994) found exudate gum production of P. juliflora and P.

pallida began after the third year but was much lower than that of the other Prosopis species investigated, with a maximum annual yield of only 9 g and 49 g, respectively.

The average annual gum yield from a mature P. juliflora tree was estimated to be 1 kg/tree/yr, with a range of 0.25-2.5 kg/

tree/yr (Tewari 1998). There were large variations in yield between years, and a large difference in gum yields was also noted between provenances of P. alba and P. chilensis (Lima 1994). Annual variations were assumed to be associated with water availability, gum production increasing with increasing water deficit (Lima 1994), though Espejel (1980) found no correlation between climate and yield. Natural yields can often be quite low, with increases expected from artificially inflicted wounds. Gummosis has also been observed, that is thought to be related to fungal infections. Chemical treatments of trees are possible to improve gum output, and a method has been developed in India that has substantially increased production from a number of gum yielding tree species (Tewari and Harsh 1998).

3.4.3 Tannins and dyes

The tannins of P. juliflora and P. pallida are complex organic structures, comprising of phytogallotannins and pyrocatecollic tannins (Rocha 1990). Tannins of tropical woods tend to be of a cathetic nature rather than of the gallic type present in temperate woods (Doat 1978). Malhotra and Misra (1983, in Alves et al 1990) reported a new tannin in P. juliflora roots.

Tannin content of the pods and leaves of P. juliflora and P.

pallida have been assessed in relation to the food and feed value (see 3.2.1, 3.3.1), but it is the bark, stem wood and root wood that are generally used for extracting tannins primarily for use in curing leather. Tannin is generally obtained by boiling the macerated bark or wood but can also obtained as a by-product from the processing of timber for other chemical extractives (Parker 1982b).

The percentage of tannins in plant parts is variable but is generally highest in roots and bark. Tannins are present in the wood in various quantities (e.g. Gowda and Ramaswamy 1960). With P. juliflora, Kazmi and Singh (1992) found 3-8% tannin in bark and root wood, Patel (1986) found 3-3-8%

tannin in bark and up to 9% in wood, while Vimal and Tyagi (1986) found 6-7% tannin tannin in root wood. Tannin contents increase as the tree gets older with considerable accumulations possible in dead tissue. Tan extract from all plant parts of P. juliflora is yellowish but generally of poor quality, possibly due to the presence of alkaloids. Tannin in P. juliflora roots was found to be unsuitable for tanning purposes by Vimal and Tyagi (1986). Tannins are also used in the petroleum industry, mixed with sodium hydroxide,

to reduce the viscosity of drill mud, and also for making ink and conserving the fibres used in fishing nets.

There are a few references to the use of dyes specifically from P. juliflora and P. pallida, although dyes are prepared from other American Prosopis species. Several species of Prosopis have been used historically in the preparation of dyes, including the use of bark and gums in the USA (Felger 1977), roots to make a purple dye for cotton in Mexico (Martínez 1970, in Díaz Celis 1995) and a dye made from Prosopis branch wood of economic importance in Argentina.

In India, Mohan (1940) and Vimal and Tyagi (1986) noted the use of P. juliflora pods to make a black dye used in the preparation of ink. The exact chemicals from P. juliflora and P. pallida involved as dyes are not fully understood but are thought to relate to the tannins and associated organic compounds with gums occasionally dissolved as a fixing agent. However, in areas where P. juliflora and P. pallida are found, there are often other species which have a higher percentage of better quality tannins which are used in preference.

3.4.4 Medicines

All parts of P. juliflora and P. pallida are used in the preparation of medicinal products to treat human ailments.

There are many records of the use of these products from historical literature where Prosopis species are native and from recent descriptions where they have been introduced.

In India, for example, an astringent decoction is made from boiling wood chips, a bark extract is used as an antiseptic on wounds, and gum is used to treat eye infections (Vimal and Tyagi 1986). In Brazil, P. juliflora flour is used as an aphrodisiac, syrup as an expectorant and tea infusion against digestive disturbances and skin lesions (Rocha 1990).

Because of their noted bactericidal and fungicidal effects, Prosopis extracts are widely used to treat four main groups of affliction; eye infections, stomach disorders, skin ailments and superficial wounds. Against optical and dermatological ailments, Prosopis extracts form a protecting antiseptic coat over lesions allowing tissues below to regenerate (Rocha 1990). Against diarrhoea and stomach disorders, there is a constipating action and the formation of a protective coat over inflamed mucous membrane, preventing the action of irritants and decreasing toxin absorption (Rocha 1990). In Guatemala, P. juliflora is used to treat sexually transmitted diseases (Caceres et al 1995). Anticarcinogenic effects have also been reported.

Of the many chemicals with effects on human health that have been isolated from P. juliflora and P. pallida, most work has concentrated on alkaloids, flavonoids and tannins.

Several groups of piperidine alkaloids have been isolated from Prosopis species. Full analysis of the alkaloids has been carried out for several Prosopis species, including P. africana (Neuwinger 1996) and P. cineraria (Jewers et al 1976). The alkaloids juliflorine, juliprosine, juliprosopine, julifloricine

and julifloridine have been isolated from P. juliflora (Vimal and Tyagi 1986). A diketone, prosopidione was isolated from P. juliflora leaves by Ahmad and Sultana (1989), and a cytotoxin patulitrin was found by Merzabani et al (1979, in Ahmad and Sultana 1989). Many flavonoids and tannins have also been isolated (Rocha 1990). An extensive list of other chemical compounds that have been isolated from P. juliflora bark, pods and roots is given by Vimal and Tyagi (1986).

A mixture of alkaloids from P. juliflora has significant inhibitory effects on gram positive bacteria (Ahmad et al 1988, Aqeel et al 1989). The minimum inhibitory concentration (MIC) of julifloricine for the gram positive bacteria was 1 µg/ml for Staphylococcus aureus, S. epidermidis, S. citreus, Streptoccus pyogenes and Sarcina letea; 5 µg/ml for S. faecalis, S. pneumoniae, S. lactis, Cornynebacterium diphtheriae, C. hofmanii and Bacillus subtilis 5 µg/ml, but there was an almost insignificant effect on gram negative bacteria such as Aeromonas, Enterobacter, Klebsiella, Proteus, Pseudomonas, Salmonella, Shigella and Vibrio spp. (Ahmad et al 1988, Zainal et al 1988, Aqeel et al 1989). A water-soluble mixture of alkaloids from P. juliflora leaves was more active against gram-positive bacteria than three commercial antibiotics bacitracin, chlormycetin, gentamicin or trimethoprim (Ahmad et al 1988).

As a fungicide, julifloricine was more effective than miconazole but less effective than econozole, two commercially available fungicides, against Candida albicans and C. tropicalis but not effective against dermatophytic fungi and viruses (Zainal et al 1988, Aqeel et al 1989). Water soluble alkaloids, mainly juliprosine and isoprosine were less active than econazole against Allescheria boydii, Aspergillus (three spp.) and Candida (two spp.) but more active than griseofluvin against Allescheria boydii, Aspergillus (three spp.), Trichophyton violaceum, T. simii, T. tonsurans and Microsporum ferrugineum (Ahmad et al 1989).

Alcohol extracts of P. juliflora leaves inhibited Neisseria gonorrhoea (Caceres et al 1995). The fruits of P. juliflora contain patulitrin, which is effective against lung carcinomas (Ahmad et al 1988). P. juliflora extracts had a low antigiardiasic activity against trophozoites of Giardia duodenalis (Ponce-Macotela et al 1994).

The antifungal, antibacterial and general antimicrobial activity of plant extracts of P. juliflora is well established, but there are concerns as to their toxic effects. An immune response was induced in mice injected by two plant protein extracts of P. juliflora (Lima et al 1990). Julifloricine was non-lethal to mice in doses up to 1000 µg/25 g of mouse (Aqeel et al 1989). Topical 1% juliflorine was non-lethal to rabbits at a concentration of 2.5% but produced irritation and inflammation, lethargy, prostration and weakness (Aqeel et al 1991). The LD₅₀ of julifloricine was 33 mg/kg in rabbits and 17 mg/kg in mice (Aqeel et al 1991). Cytotoxic effects were also observed with extracts of P. juliflora by Merzabani et al (1979 in Ahmed and Sultana 1989), and alkaloids were reported to cause haemolysis of rat and human erythrocytes (Kandaswamy et al 1989).

Crushed leaves of P. juliflora are known to be used as a suicidal agent in India (Srivasankar et al 1991) and the incidence of poisoning is common in rural areas reflecting its abundance (Kandaswamy et al 1989). Rocha (1990) also identified the presence of the toxic chemical furfural. Tannins present are irritants of internal organs and can also bind proteins making them indigestible (Rocha 1990). Constraints to the use of P. juliflora extracts as a source of medicinal compounds are the presence of such irritant and potentially toxic chemicals, and further work would be required before making any recommendations for the use of Prosopis plant extracts for medicinal use.