INTRODUCTION
Family: Myrtaceae Genus: Psidium
Species: guajava
Common names: Guava, goiaba, guayaba, djamboe, djambu, goavier,
gouyave, goyave, goyavier, perala, bayawas, dipajaya jambu, petokal,
tokal, guave, guavenbaum, guayave, banjiro, goiabeiro, guayabo,
guyaba, goeajaaba, guave, goejaba, kuawa, abas, jambu batu,
bayabas, pichi, posh, enandi
Part Used: Fruit, leaf, bark
Guava is a common shade tree or shrub in dooryard gardens in the
tropics. It provides shade while the guava fruits are eaten fresh and
made into drinks, ice cream, and preserves. In the richness of the
Amazon, guava fruits often grow well beyond the size of tennis balls
on well-branched trees or shrubs reaching up to 20 m high. Cultivated
varieties average about 10 meters in height and produce lemon-sized
fruits. The tree is easily identified by its distinctive thin, smooth,
copper-colored bark that flakes off, showing a greenish layer beneath.
Guava fruit today is considered minor in terms of commercial world
trade but is widely grown in the tropics, enriching the diet of
hundreds of millions of people in the tropics of the world. Guava has
spread widely throughout the tropics because it thrives in a variety of
soils, propagates easily, and bears fruit relatively quickly. The fruits
contain numerous seeds that can produce a mature fruit-bearing plant
within four years.
PLANT CHEMICALS
Guava is rich in tannins, phenols, triterpenes, flavonoids, essential
oils, saponins, carotenoids, lectins, vitamins, fiber and fatty acids.
Guava fruit is higher in vitamin C than citrus (80 mg of vitamin C in
100 g of fruit) and contains appreciable amounts of vitamin A as well.
Guava fruits are also a good source of pectin - a dietary fiber. The
leaves of guava are rich in flavonoids, in particular, quercetin. Much
of guava's therapeutic activity is attributed to these flavonoids. The
flavonoids have demonstrated antibacterial activity. Quercetin is
thought to contribute to the anti-diarrhea effect of guava; it is able to
relax intestinal smooth muscle and inhibit bowel contractions. In
addition, other flavonoids and triterpenes in guava leaves show
antispasmodic activity. Guava also has antioxidant properties, which
is attributed to the polyphenols found in the leaves.
Guava's main plant chemicals include: alanine, alpha-humulene,
alpha-hydroxyursolic acid, alpha-linolenic acid, alpha-selinene,
amritoside, araban, arabinose, arabopyranosides, arjunolic acid,
aromadendrene, ascorbic acid, ascorbigen, asiatic acid, aspartic acid,
avicularin, benzaldehyde, butanal, carotenoids, caryophyllene,
catechol- tannins, crataegolic acid, D-galactose, D-galacturonic acid,
ellagic acid, ethyl octanoate, essential oils, flavonoids, gallic acid,
glutamic acid, goreishic acid, guafine, guavacoumaric acid,
guaijavarin, guajiverine, guajivolic acid, guajavolide, guavenoic acid,
guajavanoic acid, histidine, hyperin, ilelatifol isoneriucoumaric acid,
isoquercetin, jacoumaric acid, lectins, leucocyanidins, limonene,
linoleic acid, linolenic acid, lysine, mecocyanin, myricetin, myristic
acid, nerolidiol, obtusinin, octanol, oleanolic acid, oleic acid, oxalic
acid, palmitic acid, palmitoleic acid, pectin, polyphenols, psidiolic
acid, quercetin, quercitrin, serine, sesquiguavene, tannins, terpenes,
and ursolic acid.
OXALIC ACID
IT is the chemical compound formula H C O . This dicarboxylic
224 acid is better described with the formula HO CCO H. It is a
22relatively strong organic a cid, being about 10,000 times stronger
than acetic acid. The dianion, known as oxalate, is also a reducing
agent and a ligand in coordination chemistry. Oxalic acid and
oxalates are abundantly present in many plants, most notably in sour
grass, and sorrel (including Oxalis), roots and leaves of rhubarb and
buckwheat.
At high concentrations, it is a dangerous poison, but such
immediately toxic levels are not found in foodstuffs but rather in
manufactures, such as some bleaches, some anti-rust products, and
some metal cleaners (among other things). It is also a naturally
occurring component of plants, and is found in relatively high levels
in dark-green leafy foods
In the human body, ingested oxalic acid is not a useful nutrient; so,
like all such unneeded components of diet, it is processed by the body
to a convenient form and that byproduct is then excreted-- in this
case, in the urine. In the course of being processed by the body, oxalic
acid combines with other substances to form various salts, called
oxalates; usually, those salts are in solution, but in high concentration
some may precipitate out in crystalline form. Such tiny crystals can
cause damage to human tissue, especially to the stomach, the kidneys,
and the bladder. It is commonly believed that oxalates contribute to
the formation of kidney and bladder stones; one common nutrient
with which oxalic acid combines is calcium, making the salt calcium
oxalate, and calcium oxalate is found in kidney stone
To study the presence of Oxalate Ion
content in Guava Fruit at different
stages of ripening
Requirements:100 ml measuring flask, pestle and mortar, beaker,
titration flask, funnel, burette, weight box, pipette, filter paper,
dilute H SO , KMnO , and guava fruits at different stages of
ripening.
Theory:Oxalate ions are extracted from the fruit by boiling pulp
with dil. H SO . Then Oxalate ions are estimated volumetrically
by titrating the solution with standard KMnO4 solution.
End Point: Appearance of permanent pink colour. Procedure:
1. 50.0g of fresh guava was weighed and crushed to a fine pulp using
pestle-mortar.
2. The crushed pulp was transferred to a beaker and about 50ml dil.
H SO was added. The contents were boiled for about 10 minutes.
3. The contents were filtered and cooled in 100ml measuring flask.
The volume was made up to 100ml by adding distilled water.
4. 20ml of this solution was taken into a titerating flask and 20ml of
dil. H SO was added to it. The mixture was heated to about
60C and titerated against the standard KMnO solution taken in
a burette
5. The process was repeated with different samples of guava.
OBSERVATION
Weight of guava taken = 50.0 g
Volume of guava extract taken = 20.0 ml
Normality of KMnO4 solution = (1 / 10).
Calculations
N1V1 = N2V2
(guava extract) (KMnO4 solution)
N1 x 20 = xV
Normality of oxalate, N1 =
Strength of oxalate = Normality x Eq. mass of oxalate ion
= x 44 g/litre of the diluted extract.
= 1.32/100 x 44g/litreof diluted extract
=0.581 GL'1
2)For semi ripened guava
(1 day old)
Strength of oxalate in one day old guava extract
= (1.37/100) x 44g/litre of diluted extract
=0.603 GL-1
3) For ripened guava
Strength of oxalate in fresh guava extract
= 1.39 /100 x 44g / litre of diluted extract
= 0.612 g L1
Conclusion
Oxalic acid and oxalates are abundantly present in many
plants, most notably in sour grass, and sorrel (including Oxalis),
roots and leaves of rhubarb and buckwheat.
After doing this experiment we can conclude that unripe guava
has a high content of Oxalate ions. The concentration of
oxalate ions decreases with the ripening of fruit.
BIBLIOGRAPHY
In order to complete this project, I took help from:
My chemistry teacher
Comprehensive Practical Chemistry
(Lab Manual) of Laxmi Publication
Different internet sites:
www.google.com
www.rain-tree.com
www.wikipedia.com
INDEX
S.NO. TOPIC PAGE
1 Acknowledgement
2 Introduction
3 Plant Chemicals
4 Oxalic Acid
5 Experiment
6 Observations
7 Calculations
8 Conclusion
9 Bibliography
