Biology and Potential of <i>Psidium guajava</i>

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Biology and Potential of Psidium guajava

S21tyawati Sharma, Kirti Rajat, Rajendra Prasad and Padma Vasudevan Centre for Rural Development and Technology, Indian Institute of Technology

New Delhi 110016

This review paper deals with the biology and potential of PsidiulIl guajava relating to its food value, medicinal v<\lue and various types of chemicals obtained from it. Guava is a mycorrhizotrophic and mUltipurpose plant highly suited to tropical and subtropical climates. Evaluation of high yielding and short duration varieties of guava with tissue culture techniques ranks its porcntial. Further, auava is rich in Vit-A and a number of carotenoids namely Iycopene, a-carotene, y-carotene, Zeinoxanthium, 5-6, 5·, 6· - diepoxy -13-

~arotene and 5-8-epoxy 3, 3' 4'-trihydroxy l3-carotene. Lycopene is a principal pigment in this plant. The medicinal propcl1ies of guava for certain types of diseases covering cancer are attributed to the presence of carotenoids and other bioactive components and Vit-A in different parts of it. It is rich in 116 types of volatile compounds. Its multipurpose economic use need to be applied in rural and urban areas.

Biological Aspects

Guava (Psidium guajava) member of family Myrtaceae, is an important small fruit tree native to tropical America, now distributed in all tropical and SUbtropical areas of the world (Martin 1984). India ranks fourth in guava production (Singh, 1992). Although it is cultivated in almost all parts of the country, Allahabad is famous for production of best quality in India as well as in the world (Mitra and Bose, 1985). Its total production area in In- dia is 30,000 hectares. V.P. covers largest area, i.e. 9,840 ha followed by Bihar 4,800 ha (Jaiswal, 1980). It grows well in light sandy loam to clay soils in a pH range of 4.5-8.3 and can also be grown in poor soils.

Varieties

There are a number of varieties of guava.

Lucknow 49 (roundish Ovate), Allahabad Safeda (roundish) and seedless fruits are known to be excellent varieties while Banarsi (round), Chitridar (Sub-globose), Apple colour (spherical), Behat coconut (round), Hafshi (spherical), Safed jam (roundish), etc. are considered to be good. The variety red tleshed (roundish ovate) is known as poor quality fruit.

Propagation

Guava is propagated by freshly extracted seeds, layering (both air and pot), grafting, budding, root sprouts,

tissue culture and cuttings (Soule, 1976). Propagation of guava by cuttings under ordinary conditions may not be done; however, the propagation with cuttings has been found very successful (93.3 per cent rooling) under mist condition, i.e., with the use of p-hydrobenzoic acid (200 ppm) and IBA (5000 ppm) (Dhua et al., 1992).

Pot layering method was highly successful for raising guava plant from the old and unproductive guava trees which are head back very near to the ground level. The new shoots formed are placed in the rich rooting medium pots. A cut is made in bent shoot and this portion is buried in the soil. This method is carried out during Dec.- Mar, and can also be followed during rainy season. Regu- lar watering of pot is a must. The best result is seen with IBA treatment (6000 ppm) in lanolin paste (Singh, 1992).

Air layering is done in the rainy season. In this process old plant shoots of about \-1.5 cm dia are taken and a ring of bark 2.5-3.0 cm is removed and a black polythene is wrapped. After 6-7 weeks the polythene is removed and the ring is covered by sphagnum moss followed by polythene strip wrapping for rooting. Now these layers can be removed in 30-45 days and planted in pots containing almost equal parts of soil and compost.

However, guava plants raised from seeds show great variability and, therefore, vegetative propagation of se- lected clones has been recommended (Purseglove, 1974).

During last two decades the technique of

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SHARMA el al. : BIOLOGY AND POTENTIAL OF PSIDIUM GUAJAVA 415

micropropagation has been used for the rapid clonal mul- tiplication of many fruit plants including guava. In India work on propagation of guava through tissue culture was initiated by laiswal and Amin (1987). They found that shoot tip explants from mature trees were capable of form- ing multiple shoots. Proliferation of shoot tip was obtained on Murashige and Skoog's (MS) basal medium containing different combinations and concentrations of auxins and cytokinins. Highest number of shoots per explant was obtained from cultures grown on medium supplemented with I mg per litre 6-benzylamino-purine (BAP) only. Rooting was achieved by transferring the individual shoots to half strength MS medium having 0.1- 0.5 mg per litre Indole-3-Butyric acid (IBA) and a- Napthalene acetic acid (NAA). Addition of activated charchoal showed beneficial effects on rooting percent- ages and plantlet growth. Papadatou et al. (1990) established proliferated shoot cultures from shoot tips from seedling grown in a growth chamber and cultured on rugini olive medium (OM) supplemented with benzyladenine (BA). Maximum proliferation was achieved with 2 mg per litre BA. Blackening of medium which is a serious problem in chittidar guava and shoot- tip necrosis did not occur in the cultures. Shoot explants were easily rooted in vitro using Olive medium (OM) with NAA and IBA at 0.5 and I mg per litre for both auxins. Rooted shoots can readily be established in peat- based medium.

Similarly different parts of guava seedlings and the nodal segments of grafted plants were used as explants for in vitro culture. A high frequency (75-100 per cent) at shoot generation was obtained from seedling hypocotyl, shoot tip and nodal segments cultured in Murashige and Skoog's (MS) medium with or without G-Benzyl amino purine (BA~he advantages of using grafted plants as a source of explants over explants from mature trees are:

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2.

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Elite fruiting trees from distant places could be grafted onto root stocks and the grafted plants brought to the lab.

Growing them in an enclosed area would reduce problems of contamination.

Plants maintained under controlled condition minimize seasonal variations in response and cultures can be raised round the year (Loh and Rao,

1989). Morc work on callus formation and clonal

propagation of guava was reported by different workers. (Amin and Jaiswal, 1987; 1988; Babbar and Gupta, 1986).

Babbar and Gupta (1986) worked with the anthers of guava cultivated on either Murashige-Skoog's or Nitsch Basal medium (BM) supplemented with 10" Benzyl amino Purine (BAP) which were observed to contain micro spores undergoing androgenic segmentations as well as a few multicellular microscopic embryoids. How- ever final morphogenic response from such cultured anthers was the development of calli. These calli had re- stricted growth accompanied by their early browning.

Suspecting the browning to be due to accumulation of polyphenols, the culture medium was fortified with poly- vinyl pyrolidone (PVP). The PVP increased sucrose con- centration in the medium and the cold pretreatment of anthers decreased the proportion of anthers turning brown as well as delayed the browning of calli. But it was not possible to maintain the calli for differentiation. Cold pre-treatment significantly increased the percentage of callusing anthers and also resulted in the early emergence of calli.

The guava crop varies in requirement of manure and fertilizers with varieties grown, climatic conditions, soil status, management practices, etc. Wagh and Maliazas ( 1985) reported the general doses of manure and ferti I iz- ers in various states ofIndia for better and high fruit yield. Young guava trees require pruning several year to avoid long, slender branches. Also, heavy pruning in guava helps fruiting. Guava trees produce fruits twice in a year in northern India and thrice in western and southern In- dia. When flowering is in June-July, the fruits that ripe from November-January are of excellent quality but the yield is very low. Fruits produced from July-September are of poor quality.

Menzel and Paxton (1986) studied the pattern of development in seven guava varieties grown in subtropical coastal southern Queensland to test the hypothesis that the growth pattern of some varieties is more suited to that environment. Guava fruit yield ranged from 68.8-

138.7 kg/tree.

Tiwari and Upadhyaya (1996) studied the effect of add- ing phosphorus and boron in combination and separately.

The positive effect was observed maximum with 30 g phosphorus and 10 ppm boron per plant, in terms of plant growth, nutrient status and intensity of bronzing decrease.

Bronzing is a complex nutritional disorder due to potassium, phosphorus and zinc deficiencies.

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Nagar and Rao (1986) studied the early changes in growth regulator content of pollinated guava fruits and observed that endogenous auxins, gibberellins and cytokinins are associated with fruit set in guava. In the pollinated ovaries of both cultivars the activity of these factors increased during fruit set and in the unpollinated ovaries it decreased after anthesis. Harrnonal activity disappeared when the unpollinated overies dropped off the branches on the 3rd or 4th day after anthesis. The result also showed that there may be an overlap of func- tions and synergistic relationships between these hormo- nal factors in fruit set, which may be a function of their combined action.

The plant raised by seedling starts bearing fruits in 4- 5 years while from vegetative methods it starts at the age of 2-4 y. However guava fruits require nearly 5 months to mature (Welgemoed and Preez,. 1986). A yield of 80- 90 kg per grown up seedling tree and 150-200 kg per grown up tree raised from vegetative method such as grafted or layered trees is reported. The yield is very low under waste lands (30-50 kg/grown up tree) (Singh, 1992).

Fruit Yield and Storage

The guava tree begins to bear small crops from its

• fourth year. It reaches full maturity and starts bearing large crops in its eighth year and may continue to bear heavily for 30 years or more. The guava tree takes nearly 5 months from flowering time to maturation of fruits. Attaining maturity shows signs of changing the colour of the fruits from dark green ~o yellowish green. This is the right stage for harvesting them for the market. Though the guava acquires the finest eating quality when allowed to tum perfectly yellow and to ripen fully on the tree, it is not advisable to keep it so long on the tree, since it either drops or is eaten away by birds and squirrels. Also, such ripe fruits become soft and over-ripe and unfit for con- sumption by the time they reach the consumer. The guava fruit does not keep in wholesome condition for more than a couple of days after it is fully ripe.

A seedling tree of 8-1 0 years and above may bear 400- 500 fruits, weighing about 60-80 kg. and a grafted or layered tree of the same age may bear as many as I ,000- 2,000 fruits weighing about 180-310 kg. In Allahabad, a yield up to 35 tonnes per hectare has been reported. Guava is highly perishable fruit. It can be cold stored at II "C for a week but tends to lose its lusture and deteriorates once it is removed from the storage. Allahabad Safeda type of guava can be stored for 4 weeks at a temperature

of 9-1 0" and R.H. of 85-90 percent. Bigger fruits should be chosen for cold storage in preference to smaller ones.

The approximate post-storage life at 25-30" is three days.

Storage life of the fruits coated with 3 per cent wax emul- sion can be extended by 8 per cent at room temperature (22-28") and by 50 percent at low temperature (8-10").

Diseases

The common diseases observed in guava are Anthrac- nose (Gleosporium psidu) in whi~h the growing tip turns dark brown and black necrotic ca~sing dieback of plants, Guava wilt (Fusarium solani, Macrophomina phascolina), Guava fruit canker (Pestalotia psidii) and stem canker (Psysalospora psidii). Ullasa (1985) dis- covered a new fruit rot of guava caused by Sclerotium rolfsii. Infected fruits were kept under lab conditions and the viability of the sclerotia were tested periodically by inoculating the healthy fruits of guava. It was observed that sclerotia were viable and caused infection even after one year. In a heap, infection spreads very fast from fruit to fruit during storage.

Guava fruit fly (Dacus dorsalis Hendal), Mealy Bug.

Bark eating caterpillar (Inderbela tetranois) and Carribean fruit fly (Nigg and Mallory; 1994) are commonly known insect pest. Chloropulvinaria psidii, com- monly called the guava soft is one of the commonest scale insects in southern India and is a serious pest of guava and sapota. (Gopalakrishnan and Narayanan, 1989).

Willers and Grech (1986) studied the pathenogenicity of the spiral nematode Helicotylenchus dihystera to guava. Potential Aspects

Food Value

Guava fruits, rich in vitamin C, vitamin A, pectins and other nutrients (Wilson, 1980), are best known for making pickles, jelly, jams, squashes, sherbets and icecreams in the most countries of tropics. The process products of guava are important in international trade (Martin, 1984). Fruit taste is best at the edible ripe stage when it is still slightly hard. Mature guavas can only be stored for a limited period at room temperature. The maturity of the fruit at the time of harvest detennines its quality and storage life (Chundawat et al., 1978). It is reported that with the advancement of fruit growth, specific gravity (sp. gr.) decreases and reaches - 1.0 at the mature harvest stage (Kumar and Hoda, 1974). Tandon et al. (1989) concluded that guava fruits with asp. gr. <

1.00 are of the best quality but a slightly shorter life due

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SHARMA el al. : BIOLOGY AND POTENTIAL OF PSIDIUM GUAJAVA 417

to dull appearance, loose texture and overripe taste with poor flavour at later stages. The quality of fruits of sp.

gr. between 1.00 and 1.02 was marginally inferior to the former at earlier stages but they had a slightly longer shelf life having glossy appearance, optimum ripe taste and good texture. The fruits of this group withstand han- dling and transport better. The fruits with asp. gr. of

> 1.02 should not be harvested as they are relatively im-

mature and may not develop proper colour, texture, flavour, and inferior in nutrient quality, especially in vitamin C content, aroma and taste. Yusof and Mohamed (1987) studied the physico chemical changes in guava during development and maturation. They found that soluble pectin increase during development and maturity. Insoluble pectin (NaOH soluble) increased during development but was converted to soluble pectin during maturity after 14 weeks, after which the fru its can be considered to have attained maturity. They also found that moisture content is a better index of maturity to be used along with fruit size, colour, texture and the chemical indices of tannin and sugar content. Studies were conducted to observe the changes in sugar, ash and min- erals in four guava cultivars during ripening (Buluk and Babiker, 1996). When guava fruits were picked 106-126 days after fruit set, it ensures sufficient amount of miner- als. Cell wall materials (CWM) were extracted separately from the endocarp and mesocarp portions of guava fruit by the sodium deoxycholate extraction procedure and further fractionated by enzymic and physical means into parenchymatous and hard stone cell wall. Mesocarp contained approximately 90 per cent of total CWM of the edible part of guava. Approximately 74 per cent of which were stone cells while endocarp was relatively richer in parenchymatous tissue. Parenchymatous cell wall had similar compound in both endocarp and mesocarp and were made up of - 55760 per cent of neu- tral polysaccharides (Marcelin et al., 1993). The carotenoid composition of guava fruit was studied by different workers. Nakasone et at. (1976) quantified only the lycopene fraction while Nougueria et al. (1978) and Fonseca et al. (1969) determined the B-carotene content.

Holdsworth (1979) cited a-carotene and B-carotene as the principal pigments of guava. Padula and Rodriguez Amaya (1986) dealt with the characterisation of the carotenoids and assessment of Vit-A value of Brasilian guava fruits. The carotenoids of guava cultivar IAC-4 from the state of SaO Paulo (south eastern Brasil) were identified as B-carotene C-carotene, Y -carotene, Zeinoxanthin, Iycopene, 5-6, 5'6' - diepoxy-B-carotene

and 5,8-epoxy - 3,3,4'-trihydroxy B-carotene. The principal pigment was Iycopene, corresponding to 86 per cent of the total carotenoid content (62 flg/g). B-carotene was present at 3.7 flg/g, consequently, the vitamin-A was relatively low (617 IU/IOOg). The same carotenoids were encountered in guavas from the states of Ceara and Pernambuco (north eastern Brasil).

Cis-'t-carotene and 5,8-epoxy-zeino xanthin were also found in the samples from pernambuco. While the Iycopene contents of the north eastern fruits were equal to, or, lower than that found in guava IAC-4. The B- carotene level (5.5-11.9 flg/g) was higher, corresponding to higher vitamin A values (914-1983 lUll OOg). With respect to vitamin C, the amount detected in guava cultivar IAC-4 was much higher (97.7 mgl I OOg) than that encountered in the north eastern guavas (9.2-52.2 mgll OOg).

The need for the re-evaluation of Vit-A values of food has been emphasized by Klaui and Bauernfeind (1981).

This is especially important in developing countries where vitamin A deficiency is considered a serious nutritional problem. The efforts were made for the better yield of juice by enzymic treatment and was found that the con- jugated extract on method (mech/enzymic) was more effective than the conventional one (mech) since it yielded

27 .84 per cent more juice based on guava weight after

enzymic action that is very significant for industry (Brasil and Maia, 1996). Ahmed Maqbool et al. (1993) evalu- ated the quality and storage stability of pure and mixed fruit squashes. Combination of citrus or mango enhanced the ascorbic acid content. Chen Meiling Lee et al. (1994) made efforts for some possible mechanisms for non- enzymatic browning in guava nectar during storage. Yung and Huang (1992) used different methods for producing clarified guava nectar. Quality deterioration of dehydrated or candied guava fruits is due to a number of factors including flavour changes, microbial spoilage, non- enzymic browning and ascorbic acid loss during storage.

Mehta and Tomar (1980) reported the production of good quality dehydrated guava by steeping in 70" Brix syrup containing I g/kg sulphur dioxide with 6 per cent retention of ascorbic acid.

Mohamed et al. (1993) concluded that dehydrated pickled/candied guava pretreated with 0.24 g/kg cysteine hy- drochloride (cys-HCI) increased ascorbic acid retention and reduced colour change during storage. Candied dehydrated guava showed less colour change and higher ascorbic acid retention (about 57 per cent) than pickled guava (ascorbic acid retention about 30 per cent). Sen- sory evaluation showed that candied guava pretreated

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with 0.24g/kg cys-HCI was generally preferred over the other dehydrated guava products. EI-zoghbi (1994) studied changes during ripening in alc insoluble solid and dietary fibre and found that alc insoluble solid and texture declined rapidly during ripening. The dietary fibre decreased as the fruits lost their firmness and became soft.

A typical analysis ofIndian guava is as follows. Mois- ture 81.7 per cent, protein, 0.9 per cent, fat 0.3 per cent, fibre 5.2 per cent, other carbohydrates 11.2 per cent and mineral matter 0.7 per cent which includes calcium 10, magnesium 8, Oxalic acid 14, Phosphorus 28, Iron 1.4, Sodium 5.5, Potassium 91, Copper 0.3, Sulphur 14, Chlo- rine 4, Thiamine 0.03, Riboflavin 0.03 and vitamin (212 mg/lOOg). Vitamin C is found to be highest in skin and the percentage of it decreases in the inner portion. Its value increases with maturity but declines when the fruit is overripe (The wealth of India, 1969). The dietary fibre (OF) is present in the outer peel and seeds have 28 per cent cellulose, 46.3 per cent hemicellulose and 25.7 per cent lignin.

Since guava can be cultivated on a variety of soils under varied agro-c1imatic conditions, efforts can be made to propagate guava cultivation on waste lands or marginal lands. On waste lands it can be planted as sole planta- tion or under silvipastoral system. Farmers in the vil- lages and people in the cities should be encouraged to plant guava in their courtyards/homesteads as a nutrient

garden. .

Guava Food Products

Guava is used in the preparation of guava cheese, canned guava and guava jelly. Processes have also been developed for drying guavas as such as and as pulp in the form of sheets, and also for the preparation of products such as guava juice and juice powder, guava concentrate, and guava nectar.

Guava Cheese

Guava cheese is prepared from ripe and firm fruits.

The fruits are washed and cut into small pieces, boiled in water and the pulp after straining to remove seeds and peels, is mixed with sugar and butter and heated until the mass becomes sufficiently thick. Citric acid, common salt and colouring matter are added. The whole product is allowed to set and then cut into pieces of attractive shape. It is wrapped in butter paper and stored in a dry clean place. A cold process has also been developed for the preparation of guava cheese using the pulp along with the seeds and peelings.

Guava Jelly

For the preparation of guava jelly, healthy, and rather tart fruits are preferred; they are washed, cut into small pieces, and after the addition of citric acid, boiled in water for about half an hour. The juice is pressed out with a muslin cloth, and examined for the degree of richness in pectin content. It is cooked with an equal quantity of sugar till the resulting jelly boils at 105" C.

Canned Guava

Fully ripe and firm fruits preferably with white flesh and few seeds are chosen for canning. The fruits are peeled with a knife, cut into halves, and the seeds present are scooped out. The peeled cored fruits are kept im- mersed in 1-2 percent common salt solution to prevent browning, and canned in hot sugar syrup containing citric acid. Canned guavas often have a taste and aroma better than those of the fresh fruits. Loss of ascorbic acid during canning amounts to 19.4 per ent. During storage at room temperature (25-30") for 6, 12, and 24 months, the ascorbic acid losses have been recorded to be 10.0, 18.3, and 39.5 per cent, respecti "ely. Effects of blanching and canning by different procedures on ascorbic acid content of the fruits have also been studied.

Guava Nectar

Pink-fleshed fruits are found particularly suitable for the preparation of guava nectar. The inner pulp is sieved and blended with sugar syrup of IS" Brix and 0.25 per cent acidity, when a nectar type of beverage, having a delicious taste and aroma, is obtained. The yield of guava juice is 65-80 percent on the weight of the whole fruit.

The juice can be processed into a powder of high quality.

The products are likely to find application in syrups, aer- ated water industry and large scale feeding programmes.

Guava paste can be prepared by boiling down the juice until it forms a gel on cooling.

Although a number of food products can be prepared from guava, there is no report on availability of guava products in the market on commercial basis. However, the possibilities of commercialization of guava products can be explored.

Medicinal Value

Guava has a number of medicinal properties. The leaves of guava plant were found to be effective in diabetic problems (Maruyama et ai., 1985). The narcotic like principle extracted from guava (Psidiwn guajava) leaves was found to effect mice locomotor activity

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SHARMA el al. : BIOLOGY AND POTENTIAL OF PSIDIUM CUAJAVA 419

(Lutterodt and Maleque, 1988). A SOper cent ethanolic extract (G-ext) from guava leaves was used in Japan and subtropical zones as a remedy for diabetes (Maruyama et. al. 1985). G-ext (200 mg/kg PO.) was found to inhibit the increase in plasma level of insulin alloxan induced diabetic rats. In the glucose tolerence test, G-ext was shown to inhibit the increase in plasma sugar level in such diabetic rats at a dose of 100 mg/kg P.O. An- BuOH soluble fraction prepared from G-ext also inhibited the increase in plasma sugar level in alloxan-induced diabetic rats (25 or 100 mg/kg PO.). In the glucose tolerence test this fraction inhibited the increase in plasma sugar level in alloxan induced diabetic rats (100 mg/kg).

A number of workers studied antidiarrhoeal properties of guava. Luttterodt (1989) tested guava leaf extract in the treatment of acute diarrhoeal disease inhibiting gastrointestinal release of acetylcholine by quercetin as a possible mode of action of guava. The antidiarrhoeal activity of the methanolic fraction of extract of the unripe fruits of Psidium guajava was studied by Ghosh ef al.(1993). The guava leaves are utilized in traditional medicine of the several latin American countries for the treatment of the acute diarrhoeic syndrome. The histo- logical description of the mature leaves of guava was reported by Luna el al. (1986).

On the other hand Kochar and Sharma (1992) found the effect of dietary fibre (OF) present in outer peel and seeds of guava causing non-infective degenerative diseases such as ischaemic heart diseases, diabetes, diver- ticular diseases of colon, cancer of colon and other gastrointestinal tract. The dietary fibres along with a cabbage and isabgol adversely affected the activities of sucrose, maltase, alk phosphatase which further decreased significantly with an increase in level of dietary fibre from cabbage and guava when fed to rats (Khokhar, 1994). The leaves both complete or ground, can be rapidly identified, in order to prevent adulterations or to detect any contamination of medicinal product. C/P ratio in serum is one of the reliable predictors of subject's risk to hyperlipidemia ischaemic heart diseases and arterial/

myocardial damage, a decrease in C/P ratio as evidenced during guava pulp treatment indicated that dietary fibres of guava pulp are good hypocholesterolemic and/or phos- pholipid lowering agents, whereas isabgol husk fibre were very effective in lowering serum triglyceride level (Bssumilk, 1994). Effects of guava intake on serum total and high density lipoprotein, cholesterol levels and on systemic blood pressure was reported by Singh ef al.

(1992). Studies on the neuropharmacological effects of

essential oils extracted from Psidium. guyanensis and Psidium pohlianuol! were also conducted by Santosh et al. (1996). Guava was found effective in tooth diseases (Touyz and Boutsias, 1985). Santosh ef al. (1997) studied the antibacterial activity of essential oils from guava species against certain bacterial strains.

Chemicals from Guava

The guava pulp is light yellow or pink. The aroma impression of the fruit is described due to the presence of cinnamyl derivatives, other ester and sulphur containing component with aldehydes, alcohols, terpenoids and C derivatives (Hermann, 1994). Several publications aBout guava fruit volatiles have already been provided. (Nishimura, 1989; Binder and Flath, 1996; Idstein ef al., 1985). Fresh guava (Psidium guajllva ) fruit pulp was found to contain 154 volatile substances (Idstein and Schreier, 1995). Of which 116 compounds could be described for the first time as guava fruit constituents. The compounds were identified by capillary gas chromatography (HRGC) and capillary gas chromatography mass spectrometry (HRGC-MS). In these fractions as well as in the concentrates obtained by liquid-liquid extraction of the disti lIation residues were 41 carbony Is, 35 esters, 25 alcohols, 22 hydrocarbons 13 acids, 9 sulphur containing compounds and9 substances with miscellaneous structures. Qualitatively and quantitatively the carbonyls occupy a special place among guava fruit volatiles. Fifty percent of the total amount consists of aldehydes. Most of them are typical products of pre-ox idation of unsatu- rated fatty acids.

The second important class of volati les consists of esters. Among the esters some "exotic" methyl derivatives have been found remarkable, c g., methyl nicotinooatc, a compound that is not very common among fruit volatiles.

The aliphatic alcohols detected in guava fruit pulp origi- nate from fatty acid metabolism. Another groups of ho- mogenous biogenetic origin consists of non-carotenoids, e.g., hypothetical biodegradation products of higher terpenes. A further interesting group, of guava aroma substances, is 3 (2H) -furanones. Their occurrence and importance in various fruit aromas are well known. Fur- thennore, a certain amount of N-and S-heteroatomic compounds seems to be characteristics for the guava aroma.

A polyphenol oxidase was extracted from guava Psidium guajava by Augustin el al. (1985). Also six new complex tannins. i.e., guajavins A and B, Psidinins A, Band C and psiguajavins together with a variety of condensed, hydrolyzable and complex tannins were isolated from the

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bark of Psidium guajava (Tanaka et ai. 1992). On the basis of chemical and spectroscopic evidence, the structures of guajavins and psidinins were established. Simi- larly guavin A, guavin C and guavin D, a complex tannins were isolated (Okuda et 01., 1987). The biochemical substances, i.e., pectinesterase were also extracted from guava (Fayyaz and Asbi, 1993). They extracted pectinesterase (PE) from guava fruit and assayed it NaCI con- centration and pH influenced the extraction processes of PE from this fruit. The highest PE extraction value at pH 8.0 with 1.75 M NaCI solution was 2.5 micro equiva- lent COOH/min/ml crude extraction. Work had also been done on the changes of concentrations of different hor- mones like gibberllins, cytokinins and auxins during different growth stages of guava. (Nagar and Rao, 1981 a;

198! b; 1982; 1983; 1986). Marcelin et al. (1992, 1993) extracted water soluble pectic substances from guava.

Acknowledgement

Authors are grateful to Departmenr of Science and Technology (DST), Government of India for finan- cial assistance.

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