Peitanikali(l),45-50(1988)

Post-harvest Storage of Guava (Psidium guajava, L, var. Taiwan)

M.A. AUGUSTIN AND AZIZAH OSMANDepartment of Food Science

Faculty of Food Science dan BiotechnologyUniversiti Pertanian Malaysia

43400 Serdang, Selangor, Malaysia.

Key words: Guava; psidium guajava; total soluble solids; sugar content; titratable acidity.

ABSTRAKBuah jambu batu (jenis Taiwan) telah disimpan pada suhu bilik (26°C), 20°C dan 5°C, dan ciri-

ciri buah semasa penyimpanan telah dinilai. Jangka masa penstoran buah jambu batu pada suhu bilikadalah lebih kurang 1 minggu dan jangka masa penstoran dilanjutkan beberapa hari pada 20°C. Pada26°C dan 20°C, jangka masa penstoran dihadkan oleh kewujudan kulat. Pada 5°C, pemerangan ('bron-zing1) kulit buah jambu batu berlaku lebih kurang selepas 2 minggu penstoran. Kulat tidak merupakansuatu masalah semasa penstoran pada 5°C. Purata pH, jumlah pepejal terlarut dan keasidan tertitrat buahjambu batu pada masa dituai, masing-masing 3.5, 5.4° Brix dan 62.8 ml 0.1NNaOH/lOOg. Parasgula ter-larut individu adalah: fruktosa 1.60g/100g, glukosa 1.06g/100g dan sukrosa 0.78g/100g pada permulaankajian. Peningkatan pepejal terlarut yang bererti didapati semasa penyimpanan pada semua suhu pen-storan. Perubahan keasidan tertitrat didapati tidak bererti semasa penstoran selama 10 hari pada suhubilik, dan 20°C dan semasa penstoran selama 4 minggu pada 5°C. Terdapat peningkatan yang berertibagi paras fruktosa, glukosa dan jumlah pepejal terlarut tetapi tidak terdapat perbezaan yang bererti bagiparas sukrosa semasa penstoran pada suhu bilik Terdapat peningkatan yang bererti pada paras fruktosadan paras jumlah pepejal terlarut semasa penstoran pada 20°C dan 5°C. Nisbah fruktosa/glukosa mening-kat dengan bererti semasa penstoran pada semua suhu penstoran.

ABSTRACTGuava fruit (var. Taiwan) were stored at room temperature (26°C), 20°C and 5°C and the

characteristics of the fruits during storage were evaluated. Guava fruit has a post-harvest life of about 1week during room temperature storage and post-harvest life can be extended by a few days during storageat 20° C. At 26° Cand 20° C, post-harvest life is limited by the occurrence of rots. At5°C, bronzing of theguava skin occurs at about 2 weeks of storage. Rots were not evident during storage at 5°C. The averagepH, total soluble solids and titratable acidity ofguava at harvest was 3.5, 5.4°Brix and 62.8 ml O.lNaOH/WOg respectively. The levels of individual soluble sugars were: fructose 1.60 g/1 OOg, glucose L06g/100gand sucrose 0.78g/100g at the commencement of the study. There were significant increases in totalsoluble solids during storage at all temperatures. Titratable acidity did not change significantly duringstorage for 10 days at room temperature and 20°C and during storage for 4 weeks at 5° C. There weresignificant increases in fructose, glucose and total soluble sugars but no significant differences in sucroselevels during storage at room temperature. Significant increase in fructose levels and total soluble sugarlevels were also obtained during storage at 20°C and 5UC. The fructose/glucose ratios significantly in-creased during storage at all temperatures.

INTRODUCTION known and important commercial CTOP of theGuava (Psidium guajava, L) is the most widely Myrtaceae family. It is native to tropical America

M.A. AUGUSTIN AND AZIZAH OSMAN

and is widely distributed throughout the tropics(Kennard and Winters, 1960).

The characteristics of different varieties ofguava vary considerably. Fruit shape ranges fromround to pear shape. Skin colour of mature ripefruit can be various shades of green or yellow. Theflesh colour can range from white to yellow topink and red. Texture and taste of different guavaas well as the seed content also vary (Brown andPaxton, 1983). The guava is rich in vitamin C andlevels of 200 mg/lOOg are generally found (Tho-mas and Corden, 1970).

The guava is a soft thin-skinned fruit. It isvery susceptible to mechanical damage, insectattack and fungal rots and has a short post-harvestlife (Brown and Paxton, 1983). Cool storage ofthe fruit can prolong the post-harvest life of theguava (Broughton and Leong, 1979; Singh andMathur, 1954, Wills et al, 1983). Different varie-ties respond differently to cool storage and shelf-life extension obtained upon cool storage varies.Work on the 'Safeda' guava showed that optimumstorage conditions for cool storage were 8 — 10°Cand 85-90% relative humidity (Singh and Mathur,1954). Broughton and Leong (1979) suggestedthat the optimum temperature of storage forgreen, mature but unripe guava (var. GU 3 and GU4) was 20°C. Wills et al. (1983) found that theoptimum cool storage temperature of guava (var.41O5O' and 'GA 11-56') was 5°C. In their work,guava was packed on a fiber-board tray fitted witha polyethylene cover.

This paper reports the changes in guava (var.Taiwan) during post-harvest storage at differenttemperatures.

MATERIALS AND METHODSFruitsGuava fruits (var, Taiwan) were obtained from afarm in Slim River, Perak. The fruits of commer-cial maturity (about 15 weeks after fruit set)were used in the study. The fruits used for theassessment of post-harvest storage life was ob-tained at a different season from those used forstudy of the compositional changes and weightloss of the fruits during storage.

Sampling and Storage of FruitFruits of commercial maturity were brought tothe laboratory on the day of harvest. The fruits

were washed and left to dry in the air. Onlyacceptable fruit of firm texture which were free Ifrom mechanical injury were used in the study,The fruits were randomly sampled, placed in;plastic trays and put in rooms set at room tempera-ture (26 ± 2°C), 20°C and 5°C on the next day. i

At intervals during the storage period, sixfruits were randomly sampled and taken out foranalysis of compositional changes. Twenty fruitsat each storage temperature were randomlysampled and set aside for assessment of weightloss.

For evaluation of storage life, the fruits weredistributed into replicates of 10 fruits, placed inplastic trays, with five replicates for each tempera-ture. At various storage intervals, the fruits wereindividually scored for incidence of rots (where1 = no rots, 2 = slight rots, 3 = medium rots and 4= severe rots). The degree of surface bronzing (dis-colouration of the skin) of fruits stored at 5°Cwas also assessed (where 1 = no bronzing, 2 =|slight bronzing, 3 = medium bronzing and 4 =severe bronzing).

Analysis of Compositional Changes in the FruitsA representative portion of each fruit was homo-genized. Samples of each homogenate were usedfor analysis of pH, titratable acidity, total solublesolids and soluble sugars.

For the measurement of pH, 25g of the homo-genized pulp was mixed with 100 ml distilledwater. The slurry was filtered and the pH of thefiltrate was measured.

The AOAC (1980) method was used for thedetermination of titratable acidity. 25 g of thehomogenized sample was put into a 100 ml jvolumetric flask and the volume was made up tothe mark with distilled water. A 10 ml portionof this solution was used for titration with 0.1 N;NaOH using phenolphthalein as indicator. Thetotal soluble solids content of the expressed juicefrom the pulp was measured using an Erma handrefractometer.

The method for determination of solublesugars was based on that of Wills et al (1980).5 g of the homogenized pulp was extracted withhot 85% methanol for 20 min. The mixture wasfiltered and the residue was re-extracted twicewith 25 ml volumes of hot 85% methanol. Theextracts were combined and methanol was re-

46 PERTANIKA VOL. 11 NO. 1, 1988

POST-HARVEST STORAGE OF GUAVA

moved by rotary evaporation. Portions of theextract were filtered through C-18 Sep-pak car-tridges and analysed by HPLC using conditionsdescribed before (Augustin and Khor, 1986).The column used was NH2 polar bonded phase.The mobile phase was acetonitrile: water (85:15).Quantification of sugars was obtained by com-paring peak areas of samples to peak areas of sugarstandards of fructose, glucose and sucrose. Re-covery studies showed that there was between 9 4 -97% recovery of sugars using the extraction pro-cedure described and HPLC analysis.

RESULTS AND DISCUSSION

Storage Life of GuavaThe storage life of guava stored at room tempera-ture was about 1 week. Storage at 20°C extendedthe post-harvest life by a few days compared toroom temperature. At room temperature andat 20°C storage, the post-harvest life of guavawas limited by the occurrence of rots and soften-ing of fruits (Table 1). The incidence of rots

TABLE 1Rots score of guava during storagea

Trial Days of

•storage

I 147

101417

II 148

1115182225

5°

1.0a1.0a1.0a1.0a1.0a1.0a

1.0a1.0a1.0a1.0a1.0a1.0a1.0a1.0a

Storage Temperature

20°

Rots Score

1.0a1.0a1.2a1.7b2.4b3.1b

1.0a1.0a1.1a1.2a1.9b2.1b2.5b2.9b

RoomTemperature

1.0a1.2b2.2b3.1c3.6c4.0c

1.0a1.0a1.4b1.9b2.9c3.3c3.9c4.0c

during storage at room temperature was signifi-cantly greater (p < 0.05) than during storage at20°C. It was noted that the skin colour of guavachanged from light green to greenish yellow onstorage at 20°C. Rots were not a problem whenguava was stored at 5°C but the major factorlimiting the acceptability was the bronzing of theguava skin (Table 2). Bronzing was observed atabout 2 weeks of storage at 5°C. After 5 weeks'storage at 5°C, there was severe bronzing of theguava but there was no obvious sign of pulpinjury. It may be noted that the mean rots andbronzing scores for guava from two differentharvests are different but nevertheless similartrends were observed.

TABLE 2Bronzing scores of guava during storage at 5°Ca

Week of storage

0

0.51

I J22.5

33.5

4

4.5

5

Trial I

1.0a1.0a1.0a1.4b2.5c3.0d3.2d3.6e3.8f3.9f4.0f

Bronzing Score

Trial II

1.0a1.0a1.0a1.1a1.6b

-

3.1c3.3d3.6e3.7f3.9f

Mean Scores for 5 replicates of 10 fruit each. Numbers in,each row followed by the same alphabet are notsignificantly different (p <0.05). Trials I and II refer tostudies on fruits of commercial maturity of a different

harvest.

aMean Scores for 5 replicates of 10 fruits each. Numbersin each column followed by the same alphabet are notsignificantly different (p<0.05).Trials I and II refer to studies on fruits of commercialmaturity of a different harvest.

The short post-havest life of guava (var. Tai-wan) obtained in this study is in line with theobservations of other workers on different varie-ties of guava. Wills et al (1983) reported thatguava (var. '1050' and 'GA 11-56') had a storagelife of about a week at 20°C. Broughton andYoung (1979) found that green, mature but unripeguava (var. GU3 and GU4) took 8-9 days toripen at 20°C and remained in good condition foranother 5 days. Wills et al (1983) found that

PERTANIKA VOL. 11 NO. 1, 1988 47

M.A. AUGUSTIN AND AZIZAH OSMAN

storing guava fruits at 0°C reduces rotting consi-derably but that darkening of the flesh of theguava during storage at 0°C and 5°C became evi-dent after 3 weeks and 4 weeks respectively.Broughton and Leong (1979) found that whenguava (var. GU3 and GU4) was stored at 4°Cand transferred to 20°C, the fruits developedbrown blemishes and had a flat taste. Brown andPaxton (1983) reported that common guavashowed pulp injury symptoms on cool storage.Differences in the responses of the various varie-ties of guava stored under similar temperatureconditions may be expected. Commodities grownin different areas as well as varieties of the samecrop can differ in their susceptibility to chillinginjury and development of chilling injury symp-toms.

Weight LossThe weight loss from the fruit is dependent onboth the temperature and duration of storage(Table 3). The rate of water loss from the fruit

was higher at higher temperatures. This wasobserved for fruits stored at room temperature,where there is a 35.6% weight loss after storage for17 days whereas fruits stored at 20°C experienceda weight loss of 18.4%. Weight loss for fruitsstored at 5°C was 11.4% after 17 days of storage.Excessive loss of moisture from fruits is undesi-rable as it lowers the overall acceptability of thefruit. The effects of dehydration are noticeablevisually. In the case of guava, fruits acquired adehydrated appearance and the skin of the fruitsbecame tougher. Work on the guava of the Kampu-chean variety (Azizah Osman et al., 1987) alsoshowed that the guava was susceptible to dehydra-tion during storage and weight losses of 20%, 14%,9% and 8% were recorded after 8 days of storageat 26°C, 20°C, 12.5°C and 5°C respectively.

Compositional Changes in Fruits during StorageThe changes in total soluble solids, titratableacidity and soluble sugars are given in Table 4.

The average initial pH, total soluble solids

TABLE 3Moisture loss from guava (var. Taiwan) during storage8

Days after harvest RoomTemperature(26 ± 2°C)

4.7 ± 0.89.9 ± 1.2

13.8 ± 1.518.7 ± 1.226.3 ± 2.735.6 ± 3.3

----

Storage temperature

20°C

Moisture Loss (%)

2.2 ± 0.44.5 ± 0.67.0 ± 1.09^ ± 1.4

13.4 ± 1.918.4 ± 2.9

-———

5°C

1.7 ± 0.43 9 ±0 .85.7 ± 1.27.0 ± 1.49.0 ± 1.8

11.4 ± 3.214.6 ± 2.916.6 ± 3.418.6 ± 3.820.1 ± 4.221.8 ± 4.3

368

1013172124272932

aResults are the average weight loss from 20 fruits ±S.D.

Fruits used in this study was obtained at a different season from those used for the evaluation of rots and bronzing scores.

Analysis of moisture loss for fruits stored at room temperature and 20°C were terminated on day 17 of storage as most ofthe fruits were bad on day 21.

48 PERTANIKA VOL. 11 NO. 1, 1988

POST-HARVEST STORAGE OF GUAVA

TABLE 4Physico-chemical characteristics of guava (var. Taiwan) during storagea

Temperature

RoomTemperature(26 ± 2°c)

20°C

5°C

Daysafterharvest

136

1013

137

101417

17

132127

Totalsolublesolids°Brix

5.4a6.8bc7.3cd8.0cde9.5f

5.4a5.6ab6.7bc6.9bc7.3cd8.8ef

5.4a6.5abc7.0bcd7.7cde8.4def

TitratableaciditymlO.lNNaOH/lOQg

62.8a67.2a72.4abc76.8abcd86.8d

62.8a68.3a66.4a68.8ab85.2cd84.8bcd

62.8a79.2abcd72.4abc70.4ab76.3abcd

Fructoseg/100g

1.60a1.68ab1.83abcd2.25e2.73f

1.60a1.76abc1.73ab2.09cde2.11de2.16de

1.60aL89abcd1.96bcde2.12de1.97bcde

Glucoseg/lOOg

1.06abcd1.18bcde1.16bcde1.33ef1.51f

1.06abcd1.08abcd1.0 2ab1.18bcde1.04abe0.91a

1.06abcd1.30def1.26cde1.18bcde1.05abc

Sucroseg/lOOg

0.78abc0.60b0.53a0.86abcde0.83abcd

0.78abc0.68ab0.77 abc0.98bcdef0.80abc1.24ef

0.78abc1.26f1.15cdef1.18cdef1.20def

Totalsolublesugarg/lOOg

3.44a3.46a3.52ab4.44cd5.07d

3.44a3.52ab3.52ab4.28bcd3.84abc4.11abc

3.44a4.45cd4.37cd4.46cd4.22abc

Fructose

Glucose

1.54abcL46a1.51ab1.69cde.1.83ef

1^4abc1.64 bed1.70cde1.79def2.05g236h

1.54 abc1.47ab1.56abc1.83ef1.91fg

aMean of 5 - 6 fruits. Values in the same column followed by the same alphabet are not significantly different (p ^0.05) .

Fruits used for these analysis were obtained at a different season from those used for evaluation of rots and bronzing scores.

and titratable acidity of guava used in this studywere 3.5, 5.4° Brix and 62.8 ml 0.1N NaOH/lOOg respectively. The fructose, glucose, sucroseand total soluble sugar levels of the freshly har-vested guava were 1.60 g/100 g, 1.06 g/100 g,0.78 g/100 g and 3.44 g/100 g fruit respectively.The % distribution of soluble sugars were 46.5%fructose, 30.8% glucose and 22.7% sucrose. Chan

; and Kwok (1975) reported that fructose is thepredominant sugar in guava constituting 58.9% ofthe sugar followed by glucose at 35.7% and sucroseat 5.3%. Wills et al (1983) found that the guavaused in their study had fructose, glucose andsucrose levels of 1.60 g/100 g, 0.5 g/100 g and°-5 g/100 g-respectively i.e. the % distribution ofsoluble sugars were 61.5% fructose, 19.2% glucoseand 19.2% sucrose. Differences in sugar contentand % distribution of sugars in different varietiesmay be expected. Even within the same variety,differences in total soluble solids, titratableacidity and sugars may occur in different seasons.Work done on guava (var. Kampuchea) showed

that the distribution of the relative amounts ofsoluble sugars were different at different stagesof maturity (Salmah Yusof and Suhaila Mohamed,1987).

With respect to the changes in compositionduring storage it was noted that there were signifi-cant increases in total soluble solids of the fruitduring storage. The rate of increase in total solublesolids was dependent on temperature, with gieaterrates of increase at higher temperatures of storage(Table 4). Increases in total soluble solids afterharvest were also found in other varieties of guava(var. Kampuchea) (Azizah Osman et al, 1987)and guava (var. GU3) (Tung and Nair, 1980).However, Wills et al (1983) found that the levelsof soluble solids of fruits did not change signifi-cantly during storage of fruits in fiber-board trayswith a polyethylene wrap at 2-8°C.

There were no significant differences in thetitratable acidity of the fruits during storage for4 weeks at 5°C and during the first 10 days ofstorage at room temperature and 20°C. Significant

PERTANIKA VOL. 11 NO. 1, 1988 49

M.A. AUGUSTIN AND AZIZAH OSMAN

increases in titratable acidity were observed after10 days of storage at room temperature and 20°C(Table 4). Wills et al. (1983) found that titratableacidity of gua*a (var. '1050' and 'GA 11-56'did not change significantly during storage at2-8°C.

The levels of individual sugars and total solu-ble sugars in the guava (var. Taiwan) change duringstorage (Table 4). There were significant increasesin fructose, glucose and total soluble sugars offruits stored at room temperature but there wasno significant changes in the level of sucrose.Significant increases in fructose and total solublesugar levels were also found during storage at 20 Cand 5°C. Levels of glucose remained relativelyconstant at 20°C and 5°C storage whereas sucroselevels were between 0.78 and 1.26g sucrose/lOOgduring the storage period. It was noted that theglucose/ fructose ratios increased significantlyduring storage. In their work on guava (var. GU 3),Tung and Nair (1980) found that the concentra-tion of sugars as well as sucrose increased withthe onset of the climacteric and decreased whenthe fruit entered the post-climacteric storage.Studies on the storage of guava (var. '1050' and*GA 11 -56') showed that the levels of all solublesugar in guava (placed in fibre-board trays witha polyethylene wrap) declined during storageat 2--8°C and that the relative proportions of eachsugar remained the same (Wills et al., 1983).

CONCLUSION

Guava (var. Taiwan) stored at 26°C has a post-harvest life of about 1 week. Storage at 20°Cextended the post-harvest life by a few days.Storage at 5°C resulted in bronzing of the fruitsbut there was no obvious injury to the pulp.However, bronzing may reduce consumer accep-tance when the fruit is marketed for fresh con-sumption.

ACKNOWLEDGEMENTS

This research was funded by Universiti PertanianMalaysia. The authors would like to thank AzmanAbu Yamin, Abdul Halim Abdul Rahman, MartiniKatimin and Chua Beng Chee for their help in theproject.

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50 PERTANIKA VOL. 11 NO. 1, 1988