CHAPTER TWO
LITERATURE REVIEW
2.1 Introduction
In a natural environment the
establishment of a microbial population in the digestive tract of all warm
blooded animals, soon after birth, is inevitable (Jernigan and Miles, 2012).
Efforts to improve livestock
productivity by manipulating digestion and the gut ecosystem have occupied
scientist and farmers since the beginning of settled agriculture, and
especially, the introduction of commercial livestock production, (Uguru 2004).
The ban on the use of antibiotics as growth promoters in the poultry industry
necessitated the introduction of probiotics as natural alternative. However,
according to (Kannan et al, 2005) it
has some constraints like lack of viability, stability and inability to be
established in the intestinal eco-system due to barriers like gastric acid, and
bile acid, during its transit, etc. Alternatively, prebiotics have been
suggested to achieve all the probiotic benefits while overcoming all its
constraints Kannan et al (2005).
Prebiotics have been defined according to
Kannan et al (2005) as non digestible
feed ingredients, which are grown substrates, specifically directed towards
potentially beneficial bacteria already existing in the caecum and colon. Xu et al, (2003), Spring et al, (2000) and Pelicano et al, (2004) reported that the addition
of prebiotics to the diet of broilers, layers and pigs led to improved
performance by improving gut microflora.
2.2 Origin, Distribution and Morphology of
Papaya leaf.
The papaya tree belongs to a small family- Caricaceae consisting
of four genera. The genus Carica Linn
is represented by four species in India, of which Carica papaya Linn is the
most widely cultivated and best known species. Among other species are, C. cauliflora, C. pubescens Lenns and K.
Knocb, C. quercifolia Krishna et
al, (2008).
Papaya probably originated in Southern Mexico and
Costa Rica. Subsequently it was introduced as a plantation crop in Australia,
Hawaii, Phillipines, Sri Lanka, South Africa, India, and in all tropical and
subtropical regions Krishna et al
(2008). It is grown both commercially and in in home gardens. Papaya is a
polygamous species and it is difficult to identify whether a plant is male, female or hermaphrodite. It is a
tree reaching 3-10m in height. The
flowers are, trimorphous and have frangrance
usually unisexual-dioecious, densely pubescent cymes at the tips of the
pendulous, fistular rachis, female flowers large, solitary or in few flowered
racemes with a short thick rachis (Krishna et
al, 2008). It also has large berry, varying in size, elongate to globose
with a large central cavity, seeds black, and enclosed in a transparent aril. The tree
starts to bear fruits in 18 months of age or less. The leaves and unripe fruit
contain milky juice in which the protein present is fermented papain , (Krishna
et al, 2008).
2.3 Nutritional Value of Papaya
Papaya is a common man’s fruit,
which is reasonably priced and has a high nutritive value. It is low in
calories and rich in natural vitamins and minerals (Krishna et al, 2008). Papaya is placed first
among the fruits for vitamin C, vitamin A, riboflavin, folate, calcium,
thiamine, iron, niacin, potassium and fibre (Krishna et al, 2008). The comparatively low calories content (32 kcal/100g
of ripe fruit) makes this a favourite fruit of obese people who are running a
weight loss programme (Onyimonyi and Onu, 2009). Papaya has more carotene
compared to other fruits such as apples, guavas, sitaphal and plaintains, which
are anti-oxidants that help to prevent damage by free radicals. Unripe green
papaya is used as vegetable, it does not contain carotene but all other
nutrients are present (Krishna et al,
2008). The fruit is a rich source for different types of enzymes. Papain,
vegetable pepsin, present in good amounts in unripe fruit is an excellent aid
to digestion, which helps to digest the protein in food at acid, alkaline or
neutral media (Krishna et al, 2008).
Thus, it can be prescribed for dyspeptic patients, as papain may help in the digestion
of proteins. Papaya has the property of tenderizing meat. This knowledge is
being put to use in cooking meat with raw pawpaw to make it tender and more
digestible, (Onyimonyi and Onu, 2009).
The fermented papaya fruit is a
promising nutraceutical as an antioxidant. It improves the antioxidant defense
in elderly patients even without any overt antioxidant deficiency state at the
dose of 9 g/day orally, (Krishna et al,
2008). The papaya lipase, an enzyme tightly bonded to the water insoluble
fraction of crude papin, is considered as a “naturally immobilized
biocatalyst”.
The dried fruit skin is a potential
source as dietary ingredient for broiler chickens. It gives similar food
consumption, food conversion efficiency, survivability and meat yields to a
control diet when used up to 120 g/kg of diet, (Fouzder et al,
1999).
Fouzder et al,
(1999) also reported that dried papaya skin could safely be used up to 90g/kg
in the diet of growing pullets. It is also used in ethno veterinary practices.
2.4 Medicinal
and Pharmocological Properties
Many biologically active
phytochemical(s) have been isolated from papaya and studied for their action.
Recently an antifungal chitinase has
been gene cloned and characterized from papaya fruit, (Krishna et al 2008). These chitinases have
antibacterial activity. The purified chymopapein from commercially available
spray dried latex of the fruit has shown immunological properties. (Fouzder et al,
1999). The anthelmintic activity of papaya seed has been variously ascribed to
carpaine (an alkaloid) and carpasemino (later identified as benzyl thiorea) and
benzylisothiocyanate. Cysteine proteinases from papaya fruit have also been
reported,(Krishna et al, 2008).
2.4.1 Medicinal Uses of Papaya Plant.
Parts : Uses
Latex: Anthelmintic, relieves
dyspepsia, cures diarrhea, pain
of burns and topical use, bleeding hemorrhoids.
Ripe fruit: stomachic, digestive,
carminative, relieves obesity,
bleeding
pites, wounds of urinary tract, skin diseases.
Unripe fruit: laxative, diuretic, dried fruit reduces
enlarged spleen
and liver,
antibacterial activity.
Seeds:
carminative,
emmenagogue, vermifuge, abortifacient, counter irritant, as paste in the
treatment of ringworm and psoriasis, anti-fertility agents in males.
Seed juice: bleeding piles and enlarged
liver and spleen.
Root: Abortifacient, diuretic, checking
irregular bleeding
from
the uterus, piles, anti-fungal activity.
Leaves: Young leaves as vegetable,
jaundice (fine paste),
urinary
complaints and gonorrhea (infusion), dressing wounds (fresh leaves).
Flowers: Jaundice,
emmenagogue, febrifuge and pectoral
properties
Stem bark: Jaundice, anti-haemolytic
activity, STD, sore teeth
(inner
bark), anti-fungal activity.
Source: Krishna et
al (2008).
Papaya seed also contain some
alkaloids in their endosperm (Bolu et al,
2009). The leaves of papaya also contain magnesium, iron and potassium, which
are essential nutrients and play an important role in the synthesis of aminoacids
and proteins (Malik and Srivastava, 1982).
2.5 Antimicrobial properties/uses of papaya.
The seeds of papaya has
antimicrobial activity against Trichomonas
vaginalis trophoziotes, ( Krishna et al, 2008). The seeds and pulp of
papaya was shown to be bacteriostatic
against several enteropathogens such as Bacillus
subtilis Enterobacter cloacae, Escherichia coli, Salmonella typhi, Staphylococcus aureus, Proteus vulgaris, Pseudomonas aeruginosa and Klebsiella pneumonia. Purified
extracts from ripe and unripe fruits also produce very significant
antibacterial activity on S. aureus, Bacillus cereus, E. coli,
P. aeruginos and Shigella flexneri
( Nwofia et al, 2002).
The aqueous extract of papaya fruit
exhibits anti-microbial activity and promotes significant wound healing ability
in diabetic rats. The seeds of papaya irrespective of stage of maturity have
bacteriostatic activity on gram positive and gram negative organisms, which
could be useful in treating chronic skin ulcers, (Marotta et al, 2006). The papaya seeds macerate has clinical potential on conjugal and plasmid
transfer from Salmonella typhimurium to Escherichia coli , both invitro and in the digestive tract of
genotobiotic mice, (Dominquez et al,
2008).
Herbal containing papaya leaves and
root or leaves alone as one of the constituents has antibacterial activity
against Salmonella tyhii, S. paratyphi and S. paratyphi
and S. typhii murium. However, water, acetone and ethanol extract of papaya
leaves showed no microbiadal activity. (Krishna et al., 2008).
2.6 Organic
Acid (orgacid)
An organic acid is an organic
compound with acidic properties The most common organic acids are the
carboxylic acids, whose acidity is associated with their carboxy1 group [-COOH-]
(Dibner and Buttin 2002). Organic acids
are used in food preservation because of their effects on bacteria. The basic
principle of the mode of action of organic acids on bacteria is that,
non-dissociated (non-ionized) organic acids can penetrate the bacteria cell
wall and disrupt the normal physiology of certain types of bacteria that refer
to as pH sensitive” meaning that they cannot tolerate a wide range of internal
and external pH gradient, (Dibner and Buttin 2002).
2.6.1 The
Effect of Organic Acid on Gut Microflora of Broilers
The antibacterial effect of orgacid was
observed in the study in which
significant (P<0.05) reduction in the caecal population viability and
coliform counts in birds fed organic based diet was recorded (Adil et al., 2011). Similar effects were
observed by (Owens et al, 2008) and (Pirgozliev
et al, 2008) reporting significantly
(P<0.05) reduced total viable coliform numbers in the ileum and caecum of
boiler chicken due to organic acid supplementation. (Gunal et al, 2006) also reported that the use of organic acid mixture
significantly decreased the total bacterial and gram negative bacterial counts
in broiler chicken. Mohanery and Mahzorieh (2005) recorded a decrease in E. coli
population in the intestines of broiler chicken with malic acid.
Apart from antimicrobial properties,
organic acids have been shown to have beneficial effect on the intestinal mucosa
of boiler chicken as well (Adil et al,
2011). Nutrient absorption in the gut
occurs from the intestinal mucosa and hence, manipulation there may improve the nutrient utilization (Bradley et al, 1994, Savage et al, 1996, Pelicano et al,
2005) and consequently growth performance.
2.7 Understanding
the Gut Microbial Ecology of Broilers
The microflora
in the gastrointestinal tract of boiler chickens influences digestions, health,
and well being. Analysis of chicken gut microflora has been mainly by
culture-based methods (Amit-Romach et al,
2004). Studies using these technique have been useful for the identification
and analysis of specific groups of bacteria. However, the use of enrichment
medium precludes even relative quantitation of bacterial species, (Amit-Romach,
et al., 2004). Soumaya et al, (2011) reported that the use of
ribosomal DNA-based molecular techniques make it possible to identify different
bacterial populations in environmental samples without culturing.
Anti-Romach et al., (2011) evaluated six bacterial species present in chicken gut: Lactobacillus, Bifidobacterium,
Salmonella, Campylobacter, E.coli and Clostridium. The authors reported that the major species present in
the small intestines and caecum was Lactobacillus
with a Bifidobacterium population becoming
more dominant in the caecum of older birds. A review dedicated to the bacterial
population in the digestive tract of chickens reported a predominance of Lactobacillus strains (68.7%) in the
ileum and and jejunum followed by
strains of Streptococcus (6.6%) and Enterococcus (6.4%) (Soumaya
et al., 2011). They also reported that these proportions are statistically
different in the cecum with Lactobacillus strains contributing only 8.2%, Streptotoccus 0.7%, and Enterococcus
strains 1% of the bacterial population. However, different author reported
different findings regarding the composition of the microbiota in the chicken
digestive tract. Bjernum(2006) noted that Lactobacillus
composed of only a small proportion (5 to 6%) while Domonceaux et al, (2006)
reported a large number of Lactobacillus
strains (25%) with a high degree of diversity. In addition, two studies also,
indentified different species, with Bjerrum et
al., (2006) reporting the presence of L.
salvarius, L. agilis and L. ketasatonis
and Dormonceaux et al., (2006), L. salivarius
sub sp. Salivarus. However, Soumaya et al.,( 2011) reported that the predominant caecal isolates
of LAB were L.sakai, L. salivarius sub sp. Salivarus.
However, Soumaya et al, (2011), reported the predominant Lactobacillus spp population isolated were; L.
sakai, L. salivarius , L. reteri,
L.
curvatus. Other species included Weisella spp (16.6%) and Enterococcus
spp (5.5%). The presence in the
caecum of chickens of Weissella spp and Lactobacillus strains such as L. acidophilus,
L. crispatus, L. reuteri and L. avianus has been
reported by Lu et al, (2003).
Amit-Romach et al (2004) reported that Clostridium
was detected in some segments of the small intestine in young chicks. In older
chickens, Salmonella, Campylobacter, E.coli species were found
in the caeca.
2.8 Microbial Diversity along the digestive tract
Analysis of the
microbial luminal contents of the different sites in the small intestine
examined indicated that among the six bacterial species examined, only Lactobacillus was consistently detected
in all intestinal regions (Amit-Romach et
al, 2004). They also reported that
at day four, most of the bacterial species were not detectable in the
small intestines. Proportions of Lactobacillus changed little along the
intestine at a young age. However, at 35 days of age the posterior segments
exhibited lower levels of lactobacillus
compared with the anterior segment of the intestine. In addition, at Day 25, E.coli
and Clostridium were detected in the
duodenum and ileum.
However, the exact composition of
the microbiota differs depends on the age, rearing environment, and diet of
chickens (Soumaya et al, 2011). The
authors also showed that the antagonism against Camphylobacter by the lactobacilli strains isolated from the
chicken caecum could be attributed to the production of bacteriocin-like
substances.
Lactobacillus was the major species
present in the duodenum of young chickens. Some clostridium species were found
in the jejunum and ileum, as has been described previously in older chicks
using culture methods (Amit-Romach et al,
2004). The population in the caecum was more varied, with some Salmonella and E. coli species
occurring, as has been previously observed using culture and molecular methods (Mead and Adams, 1977, Zhu et al, 2002). With advancing age, the
small intenstine bacterial population still remained predominantly Lactobacillus, whereas in the caecum, Bifidobacterium began to develop and
reached a stable proportion between 14 and 25 days (Amit-Romach et al, 2004).
2.9 The use of probiotics in Broilers Production
The bacterial flora of the digestive
tract is the first barrier that protects the host organism against pathogen
colonization. The beneficial effect of lactic acid bacteria (LAB) exerted from
probiotics on birds involves the colonization of the mucous membrane of
different parts of the digestive tract, and protection of the mucous membrane
against pathogenic bacteria (Brzoskol et
al, 2007). It was found that some
species of lactic acid bacteria (e.g Enterococeus
faecium) inhibit the growth of Salmonella pullorum, thus reducing the mortality of experimentally infected
chickens (Audisio et al, 2000).
Mulder et al, (1997) showed that at 19 weeks of age, birds fed corn-soya
bean diets viable Lactobacillus (lacto) kg-1 diet (rccms-lacto diets) had
better (P < 0.05) feed intake and body weight gain than those not receiving
the treatment. Lactic acid bacteria produce a wide range of bacteriocins with
antagonism against gram-negative and gram-positive bacteria including Campylobacter (Soumaya et al, 2011). Tortureo (1973), and
Jernigan (2012) showed prebiotics addition in broilers diets to stimulate
appetite, body weight gain and reduction in bacterial load on the gut of the
birds.
Tortureo (1973) reported results
from a study in which broilers were fed a culture of L. acidophilus. Data
collected were weight gain, feed conversion ratio, fat digestibility, nitrogen
retention, caeca and faeces weight and
levels of the lactic acid bacteria flora and Enterococcus up to 15 days of age. The results indicated that implantation of Lactobacillus, resulted in an effect
similar to that observed in chicks fed probiotics and antibiotics.
The implantation of L. acidophilus resulted
in lower caeca and excreta weights. A distinct change in the bacterial flora in
the caeca and small intestine also occurred. By nine days of age the population
of Enterococcus had almost completely
disappeared.
Microbiology analyses of the small
intestine digesta showed that lactic acid bacteria increased the intestinal
counts of Enterococcus Streptococcus
and Lactobacillus compared with the unsupplemented control group
and with the antibiotic supplemented
group (Brzokal et al, 2007). In the
caecum, the Streptococcus, Escherichia coli and Clostridium
counts were considerably reduced. No Salmeonella,
Shigella, Campylobacter or clostridium were found in the small instestine or in the
caecum. These results corroborate those of earlier studies (Barnes et al, 1972) on the bacterial composition
of the digestive tract of birds including birds receiving probiotic bacteria (Brzoska
et al, 2007).