Effect of Chemical Treatments on the Shelf Life of ... PAPERS/PERT Vol. 11 (3) Dec...Effect of Chemical Treatments on the Shelf Life of Rambutans (Nephelium lappaceum )—II ... chemicals

Pertanika 11(3), 407-417 (1988)

Effect of Chemical Treatments on the Shelf Life of Rambutans(Nephelium lappaceum )—II

SUHAILA MOHAMED, ESHAH OTHMAN and FAUZIAH ABDULLAHDepartment of Food Science

Faculty of Food Science and BiotechnologyUniversiti Pertanian Malaysia

43400 Serdang, Selangor, Malaysia.

Key words: Rambutans; calcium chloride; sodium metabisulphite; benomyl dips and sulfur dioxidetreatment.

ABSTRAK

Mencelup rambutan selama 5 minit dalam larutan sodium metabisulfit, calcium chloride dan meta-bisulfit atau calcium chloride dan asid askorbik dapat mengurangkan % buah-buah rosak sehingga 30%.Perlakuan sulfur dioxide didapati kurang berkesan untuk mengekalkan kesegaran rambutan bila diban-dingkan dengan penyimpanan di bawah udara terubah suai Teknik-teknik yang dapat menukar kadarpernafasan dan kadar kehilangan kelembapan adalah lebih berkesan dalam mengekalkan kesegaran ram-butan dari cara-cara yang menghalang keperangan enzim. Buah-buah yang telah dicelup dengan sodiummetabisulphite + calcium chloride selama 5-10 min, dalam bungkusan PE pada suhu simpanan 8 C,masih manis dan mantap pada hari yang ke 17. Buah-buah yang disimpan pada suhu bilik tidak menun-jukkan perbezaan bererti antara yang telah dicelup dan yang tidak melalui perlakuan kimia.

ABSTRACT

Dipping rambutans for 5 minutes in sodium metabisulphite, calcium chloride and metabisulphiteor calcium chloride and ascorbic acid solutions helped reduce % unacceptable fruits by up to 30% whenfruits were stored packaged at 8 C. Chemical dipping of rambutans and sulfur dioxide treatments werefound to be less effective in prolonging the shelf life compared to low temperature storage. Techniqueswhich slow down respiration rafe and dehydration rate were found to be more effective in prolongingthe shelf life of rambutans than methods to inhibit enzymic browning. Fruits treated with sodium meta-bisulphite + calcium chloride in PE at 8 C with soaking time of 5-10 minutes, remained sweet and firmon the 17th day. Shelf life of treated fruits stored at room temperature is not significantly differentfrom untreated fruits.

INTRODUCTIONChemical control of post harvest wastage hasbecome an integral part of the handling andsuccessful marketing of fruit. A wide range ofchemicals has been used for the control of post-harvest wastage of fruits.

Lieberman and Mapson (1962), Liebermanet alf (1964) and Ayres et al, (1964) reportedthat treatment on tomatoes with ethylene oxideshowed a definite delay in ripening, developedattractive skin colours with firm texture. Whereasusage of potassium permanganate as ethyleneabsorbent (Scott et aL, 1970) in film bags package

of bananas showed firmer texture than fruitssealed with calcium hydroxide to removed carbondioxide.

Usage of mold fumigant, methyl bromide,gave the maximum inhibition of mango ripeningthroughout the storage period of 20 days atambient temperature (Subramanyam etaL, 1969).Benomyl, a fungicide used to control spoilageduring storage was observed to delay ripeningof Alphonso mango (Shanta Krishnamurthy andRao, 1983). Sulfur dioxide as a gas or in solutionas the acid or salt has been in use for centuriesespecially in the preservation of dried fruit and

SUHAILA MOHAMED, ESHAH OTHMAN AND FAUZIAH ABDULLAH

wine to maintain their light, natural colour duringextended storage. It is also being used for theextension of shelf-life of raw grape and preser-vation of raw crushed grapes or wine (USDA,1977).

The objective of this research is to determinewhether chemical treatments can be used toprolong the shelf life of fresh rambutans.

MATERIALS AND METHODSRambutans of the red variety (R7) were harvestedin bulk from the University Orchards (Ladang 5).They were sorted, weighed and subjected tovarious treatment and storage conditions on thesame day.

Each result is an average reading fromanalysis of 6 fruits.

Chemical TreatmentsThe rambutans were dipped for 5, 10, 15 and 20mins. in the following solutions:

i) 1000 ppm sodium metabisulphite.ii) 1000 ppm sodium metabisulphite+300

ppm calcium chloride,iii) 500 ppm benomyl at 50 C.iv) 1000 ppm calcium chloride + 1%

ascorbic acid.

Results were compared to that of untreatedfruits. The chemical treatments were also studiedin combination with the following storage con-ditions:a. Stored unwrapped at ambient temperature.

b. Sealed in low density polyethylene bags atambient temperature.

c. Sealed in low density polyethylene bags at8 ± 2°C.

d. Packed in nitrogen gas, sealed in low densitypolyethylene bags at ambient temperature.

The effect of leaving the fruit stalks attachedto the fruits, on shelf life of rambutans wereobserved. Fruit stalks of different lengths (0 cm,15cm and 30cm) were left attached to the fruits.The colour and texture of the fruits were com-pared to that of the control (fruits with no stalks).

Treatments with Sulfur DioxideFruits were exposed to dense sulfur dioxidefumes from burning sulphur in a closed dessicatorfor 1 min, 5 min, 10 min, 15 min, 120 min and240 min respectively. Care was taken to ensurethat neither the flame nor the hot crucibletouched any part of the fruit. Fruits were weighed,packed and sealed in LDPE bags after exposure-.

RESULTS AND DISCUSSION

Chemical TreatmentsThe effect of chemical dips on rambutan storedunwrapped at ambient temperatures and in LDPEbags at ambient and 8 ± 2 C are shown in Figs. 1,2 and J respectively.

For fruits kept unwrapped at ambeinttemperatures, all the chemical treatments (exceptwith benomyl) reduced the percentage unaccep-table fruits by 20-30%. However, the storage

LEGEND

* CONTROL

o NAMET

o NAMETCACL

* BENOMYL

Figure 1. Effect of chemical treatments on % un-acceptable fruits (unwrapped ambient temp)

408 PERTANJKA VOL. 11 NO. 3, 1988

EFFECT OF CHEMICAL TREATMENTS ON THE SHELF LIFE OF RAMBUTANS

100% unacceptable fruits (ambient in LDPE)

doyia benomyl + control 0 NoMetCaCI A NoMet X CoClAacA

Figure 2. Effect of chemical treatments on % unacceptablefruits (ambient in LDPE).

life could not be extended beyond four days. By was present in all except those treated withthe 14th day all the samples have turned black sodium metabisulphite. The skins was beginningaccompanied by an unfavourable fermented smell to rot.and softening of the skin and flesh. At this stagediscolouration of the flesh had occurred and the

Rambutans sealed in LDPE, both at 8 C andambient temperature, have reduced % unaccep-

fruit was inedible. By the fifth day fungal growth table fruits only with sodium metabisulphite,

on % unacceptable fruits (LDPE at 8°C)

1 3

+ NoMetCcC!

19days

• Control o NaMat A CaCL AscAcid * benomyl

Figure 3. Effect of chemical treatments on % unacceptablefruits (LDPE at BC).

PERTANIKA VOL. II NO 3, M9W

21

40V


calcium chloride + sodium metabisulphite andcalcium chloride + ascorbic acid treatmentscompared to the control (chemically untreatedfruits under the same storage condition). Benomyltreatments increased the percentage of unaccep-table fruits showing that the degradation is physio-logical, i.e. not due to microbes or fungus. Hotwater treatment at 50°C increased the rate ofbrowning, causing drying of the skin tissue and afaster drying rate.

The best chemical treatments appeared tobe sodium metabisulphite + calcium chloridewhich reduced the % unacceptable fruits by10-20% of the control. Metabisulphite acts bothas an enzymic browning inhibitor and preservative.Sulphites acts as a reducing agent and also gradual-ly reduces the effectiveness of the enzyme (Embs&Markakisl965).

Calcium acts synergistically with eithersulphites or ascorbic acid to prevent browningin apple slices (Ponting etaly 1972). Faust & Klein(1973) and Faust & Shear (1972) have shownan inverse relation between respiration and the Caconcentration in the flesh of fruit. In this experi-ment the Ca may have done the same to the peri-carp. Calcium has been shown to be able topreserve cellular organisation and at deficiencylevels, to induce disintegration of cytoplasmicmembranes. One function of Ca may be to main-

100

tain protein synthesis which may supplement itseffect in preserving cell membranes as a factor inthe preservation of cellular organisation. (Faust& Klein 1973, Faust & Shear, 1972).

The chloride present can also inhibit theactivity of phenol .oxidase enzymes and will retarddevelopment of brown color for a limited time.Poix Ade et alM (1980) showed an exponentialrelation existing between reaction speed andamount of added chloride. Ascorbic acid is alsoknown to delay browning in fruits, possibly byreducing the oxidized intemediate of phenoliccompounds. In addition, it is believed to act onsome functional group in the enzyme (Baruahand Swain, 1952). For fruits sealed in LDPE, thedifferences between treatments with sodiummetabisulphite and sodium metabisulphite +calcium chloride is not much at ambient tem-perature but is quite significant at 8°C.

The effect of varying the soaking time forthe chemical treatments are seen in Fig. 4. Theoptimum time appears to be 5-10 minutes andsoaking at 20 minutes adversely affects the storagequality of the fruits. The fruits became too moistand decayed faster. A similar trend is seen for allthe chemical dipping treatments. By the 17th day,fruits treated with sodium metabisulphite +calcium chloride in LDPE at 8 C, remained sweetand firm at soaking time of 5 to 10 minutes.

on shelf life of rambutans (8°C in LDPE)

CD

410

a control + 5 mln $ 10 min A 15 mm

Figure 4. Effect of NaMetCaO soaking time on shelflife of rambutans BC in LDPE).

PERTANIKA VOL. 11 NO. 3, 1988


Brown patches were observed in the inner layerof the skin for samples soaked at 15 and 20minutes.

Mendoza et al (1972) study on Seematjanand Maharlika rambutans showed that storagedecay could be controlled effectively by treatmentwith 1000 ppm benlate (l-butylcarbonyl-2-benzi-midazol carbonic acid) but wax coating reducedmoisture loss for 2 days only.

Sulfur Dioxide TreatmentsSince sodium metabisulphite dips in the presenceor absence of calcium ions were able to slightlyextend the shelf life of wrapped rambutans at 8°C,a further experiment was carried out using sulfurdioxide gas exposure. Sulfur dioxide gives betterpenetration into the skin, and like metabisulphite,it behaves both as a preservative, and anti brown-ing agent. When fruits were exposed for differentdurations, 15 minutes sulfur dioxide exposureextended the shelf by 2 -3 days but had a higher% unacceptable fruit at anytime until the 16th

1 0 0 .

60

SO -

unacceptable level

D.ys

Figures.3 T 11 15 19

% unacceptable fruits with time storedat l(Pc (SO2 treatments).

day compared to that of the control at 8 C(wrapped in LDPE), (Fig. 5). For ambeint tem-perature storage, sulfur dioxide treatment wasdetrimental to the fruits (Fig. 6).

Although sulfur dioxide inhibits enzymicbrowning it does not slow down the respirationrate, hence the physiological deterioration thatoccurs in the fruits during storage. Fruits treatedwith excess sulfur dioxide for 120 minutes and240 minutes have the lowest shelf life. The fruits

unacceptable level

Days

0 1 3 3 7

Figure 6. % unacceptable fruits with time storedat ambient temperature (SO2 treatments).

suffered from excessive bleaching and injury, withthe skin turning bright pink and browningoccurring on the inner side of the skin. The fleshalso suffered injury - had turned slightly brownand gave off a strong acidic, sulfurous odour thusmaking it inedible.

Treatment with sulfur dioxide gas canprovide satisfactory quality maintenance for otherfruits. However, the limiting parameter is usuallythe acid-sulfurous odour and taste, and also itscorrosivity. It is necessary to promptly and vigo-rously sweep out excess sulfur dioxide to avoida sulfurous off-flavour. A recent comprehensive

PERTANIKA VOL. 11 NO. 3, 1988 411


review of sulfur dioxide application to foodrevealed no deleterious effects with the exceptionof a reduction in thiamine (Post, 1979a). Anycondition that accelerates sulfur dioxide loss willin turn accelerate the darkening of the product(Schrader and Thompson, 1947; Bolin and Boyle,1972).

Weight LossSulfur dioxide treated fruits showed a slightincrease in dehydration compared to untreatedfruits sealed in LDPE. Maximum weight loss forsulfur dioxide treated fruits was 0.8% at 8 C and1.3% at ambient (Fig. 7). Sulfur dioxide may havecaused some changes in the cells and decreasedthe ability of the cells to retain moisture.

Ambient temperature

8-c

1.4-

1.3-

1.2 -

1.1 -

1.0-

0.9 _

0.8-

0 .7-

0.6 H

0.5 .

0 . 4 -

0.3 ,

0.2 _

o.i -

Ah

ill

"9t><>

1

N•*•

i'1

bw$iit'iu

»'!'ni ii inJtmilS:

m

w^

X

•

V

Control

lmin

S mins

10 mins

IS mins

120 mins

240 mins

r . . • V•> Days0 1 3 5 7 9 11 12 15 17 19

Figure 7. % weight loss with time (SO2 treatments).

ColourSulfur dioxide treatments helped retain thehighest L values (lightness) and b values (yellow-ness) but gave the lowest a values (redness) (Table1). This showed that sulfur dioxide preserved thecolour by a bleaching effect i.e. sulfur dioxideinhibits browning, but is detrimental to thenatural red pigment present in the fruit skin.Discolouration to yellowish brown could be seenin fruits which were exposed for short durations(1-15 mins) while a pink discolouration was seen

in fruits which underwent longer exposure (120-240 mins).

TextureFruits stored at 8 C, and which had undergone 15mins of exposure to sulfur dioxide gas, showedfirmer skin texture than those of the control fruitsat the end of its shelf life (Fig. 8). Fruits exposedto sulfur dioxide for 10 and 15 mins showedsignificantly firmer skin texture, compered tothe control up till the 9th day of storage.Exposure of fruits to sulfur dioxide for 1 min,120 mins and 240 mins decreased the skin firm-ness. Too long an exposure to sulfur dioxide mayhave caused injury to the fruits. Storage atambient temperature showed a similar trend, butwith a shorter storage life of 4 days, hence asteeper slope of decline is obtained. Sulfur dioxidetreatments for any duration adversely affect thepulp firmness (Fig. 9).

Days0 1 3 5

Figure 8. Pulp firmness with time (SO2 treatments).

412 PERTANIKA VOL. 11 NO. 3, 1988

fj

TABLE 1Effect of various SO2 treatment on colour of the skin

for rambutans stored in LDPE BAGS (0.05 mm thickness)

Day

Control

L

(8°C)1

357

9111517

19

19.918.218.517.716.7

15.915.013.5

(Ambient)1

3

5

20.118.615.5

a

13.010.910.4

9.08.57.8

7.0

6.2

11.911.39.7

b

6.96.4

6.05.75.4

5.24.1

3.9

7.05.8

3.9

L

27.4'

26.924.721.3

20.016.116.4

25.4

20.1

18.2

1 min

a

1.6

4.96.3

7.58.07.6

3.9

3.7

4.53.5

b

3.45.6

6.67.8

7.95.95.8

4.1

6.35.4

L

27.320.7

25.020.5

19.916.4

15.1

14.3

26.1

21.817.4

5 mins

a

2.33.74.65.96.74.6

5.8

4.9

1.74.03.0

b

4.14.6

5.96.4

6.95.8

4.94.5

4.05.6

3.7

10 mins

L

25.724.523.622.3

21.717.416.6

14.5

26.221.818.7

a

4.35.97.78.4

3.67.4

4.0

4.0

2.14.9

2.9

b

5.45.6

6.97.5

9.56.3

5.75.3

1.5

5.94.0

15 mins

L

26.4

25.724.3

23.922.6

19.917.8

16.715.3

28.3

25.021.5

a

1.23.94.5

5.25.35.6

6.25.4

4.5

1.94.8

3.4

b

2.5

5.26.06.8

6.9

7.06.7

6.3

5,2

3.8

5.64.0

120 mins

L

28.5

26.124.3

21.019.8

24.019.3

16.9

a

6.3S.4

5.3

5.24.9

4,05.43.5

b

10.09.7

9.18.06.8

8.6

7.97.5

240 mins

L

29.025.623.824.620.4

22.920.918.7

a

4.93.6

2.15.14.4

3.72.8

2.0

b

11.810.4

10.18.07.6

9.8

8.1

6.2

O

offlSn

>Hm

OzHmXrfl*1

mO

>DO

a*SD values ranges from 0.1 - 0.3


kv. \\\

V

11 13 IS 17 18

Ambient temperature

8-cControl1 min5 mliw10 mini

ItnfM

UOminr

240 mini

i 1 r~> Days0 1 3 5

Figure 9. Skin firmness with time (SO2 treatments).

Chemical Treatment together with Storage inNitrogen at Ambient TemperatureThe result of treating fruits with various dips andthen storing them under nitrogen in sealed LDPEbags are shown in Table 2. Storage in nitrogenshow some potential in prolonging the shelf lifeof rambutans treated with calcium and a reducingagent which reduced the respiration and oxidationrate of the fruit. The effect of storing rambutanstreated with calcium chloride and Na met undernitrogen at 8 C could very well prolong the shelflife of the fruit further but this was not inves-tigated because it would mean a costly post-harvest handling of the fruit.

Norman and Craft (1971) found thatoranges held in nitrogen produced increasingamounts of ethanol, acetaldehyde and methanolas the duration of the anaerobic treatment wasprolonged. Volatile emission fell upon transferof fruits to normal air. Rind injury, howeverdeveloped in air preceeding an exposure period of3 or more days in N. The high oxygen uptake orcarbon dioxide production as a result of exposureto nitrogen may be reversed if low oxygen levelsare used. Craft et al (1968) observed that theanaerobic carbon dioxide output initiated bylemon fruits in the nitrogen atmosphere wassuppressed by adding 2 or 5% oxygen. Orangesand lemons were compared to rambutans becausethey all fall under the category of non-climatericfruits (Mendoza et al., 1972).

Effect of Leaving Fruit Stalks Attached to theFruitLeaving the fruits stalks on the fruit, did notsignificantly prolong the shelf life of the fruitswhen compared to the control. (Table 2) This iscontrary to the general belief that the presence offruit stalk can prolong the shelf life of the freshfruits but is in agreement with the fact that themajor moisture loss occured through the softspines (hairs) of the pericarp (Mendoza et al1972).

Correlations between Weight Loss, Texture andColourThere appears to be a good correlation betweenskin firmness and L value for all the treatmentsboth at 8 C and ambient temperature (Table 3).However, the correlation of a and b values totexture is poor with sulfur dioxide treatments.There is a good correlation between firmnessof the skin and pulp with weight loss in sulfurdioxide treated fruits.

ACKNOWLEDGEMENTThe authors thank the Universiti farm personnelfor making available the fruits for research(especially Wan Jaharah Wan Ngah and HajiMahmood Jaafar), Encik Abdullah Hassan (BTM,MARDI) for useful suggestions at the start of theresearch, and Norhayati Salamuddin for typingthe manuscript.

4J4 PERTANIKA VOL. 11 NO. 3, 1988


TABLE 2

Effect of varying stalk length and storage

in Nitrogen on % unacceptable fruits

% Unacceptable trulti

Stalk length/days

U n wrapped/ KT

0

IS

30

LDPL/RT

0

15

30

0

0

0

0

0

0

0

LDPE/RT Namct + Cacl2

0

15

30

0

0

0

LDPE/RT (Namet + Asc. Acid)

0

15

30

Unwrapped/8 C

0

15

30

LDPE/8 C

0

15

30

0

0

0

0

0

0

0

0

0

LDPE/8 C (Namct + Cacl2)

0

15

30

0

0

0

LDPE/8 C (Namet + Asc. Acid)

0

15

30

0

0

0

Chemically treated fruits stored in nitr

LDPE

Na Benz/sorbate

Hot benomyl

NaMet + CaC12

CaQ2 + Asc. Acid

0

0

0

0

0

2

40

50

50

20

20

20

20

20

20

30

30

30

15

15

15

5

5

5

5

5

5

5

5

5

OQ«n/

33

37

63

27

23

10 12

90

90

90

65

65

65

60

60

60

75

75

75

30

30

30

15

15

15

15

15

15

20

20

20

57

93

93

40

60

100

100

100

95

95

95

90

90

90

90

90

90

60

60

60

20

20

20

20

20

20

30

30

30

90

100

100

50

73

100

100

100

100

100

100

100

100

100

80

80

80

35

35

35

30

30

30

35

35

35

100

73

100

90

90

90

45

45

45

40

40

40

40

40

40

90

100

100

100

50

50

50

50

55

55

50

45

45

100


TABLE 3Correlation between skin and pulp firmness with weight loss

and between skin firmness with colour

m

o

o

TRFATMFNTS

1.

2.

SO2

a)b)c)d)c)0g)

a)b)c)d)e)0g)

(8°C)Control1 min5 minslOmins15 mins120 mins240 mins

(Ambient)ControlI min5 minslOmins15 mins120 mins240 mins

TREATMENTS

1.

2.

S0 2

a)b)c)d)e)08)

a)b)c)d)e)

0g)

(Ambient)Control1 min5 minslOmins15 mins120 mins240 mins

(8°C)Control1 min5 minslOmins15 mins120 mins240 mins

N

16141616181010

6666666

N

6666666

16121616181010

Correlation CoefficientSkin Texture vs W|

-0.903-0.969-0.976-0.931-0.972-0.942-0.965

-0.943-0.983-0.945-0.955-0.981-0.909-0.948

Correlation Coefficient

Texture vs Colour

L

0.9190.9920.9400.9970.9900.9950.997

0.893-0.938

0.9620.9700.9280.9840.985

a

0.8940.051

-0.243-0.439-0.500-0.027

0.989

0.9480.930

-0.8170.402

-0.7500.893

-0.059

:. Loss Pulp Texture vs Wt. Loss

b

0.944-0.694

0.480-0.700-0.081

0.9920.976

0.9220.994

-0.5870.075

-0.6140.9430.987

-0.918-0.907-0.967-0.895-0.981-0.961-0.896

-0.880-0.998-0.918-9.995-0.932-0.945-0.988

L

y - 0.997 xy * 1.876 xy * 0.638 xy - 1.513 xy = 1.335 xy = 1.771 xy * 2.708 x

y « 1.815 xy * 0.850 xy * 0.441 xy * 1.275 xy * 1.017 xy - 1.264 xy « 1.691 x

+11.502-9.189+ 9.666-3.089

-1.602-8.558

-31.310

-0.422+ 10.642+ 13.749+ 6.445

9.621-1.44912.447

Best Fitted

Sicin Texture vs Wt. Loss

yyyyyyy

yyyyyyy

yyyyyyy

yyyyyyy

= -23.261 x +36.502= -20.740 x +38.257= -10.310 x +28.022= -20,537 x +42.746= -20.041 x +41.304= -51.517 x +40.455= -60.567 x +43.261

- - 6.097 x +32.433= -17.777 x +41.135= - 6.723 x +27.594= -12.735 x +39.370= -10.890 x +38.227= -11.334 x +35.436= -11.501 x +33.358

Best Fitted Line

Texture vs Colour

a

2.001 x +7.5680.686 x +27.972

= -0.622 x +25.363= - 1.740 x +36.283* -1.564 x +36.960- -0.173 x +27.718

6.765 x +5.934

1.778 x +13.925= -1,525 x +39.097- -1.225 x +29.128

1.117 x +26.617- -2.302 x +42.078

7.808 x -13.505= -0.271 x +29.694

Line

Pulp Texr-ire vs Wt. Loss

y =

y =y =

y -y -y =y s

y s

y -y* ~y =y =

y =y *

y *y K

y *y =y =y *

y =

y =y =y *y •y • •y •y =

-15.137- -.968- *\5O7-15.536-11.338-;o.O96-40.155

- >J96-T.276- 3.224-10.919- 7.057-5.972-10.543

1.5364.4281388

-1.814-0.37311.4483.155

3.7165.710

-1.2990.283

-1.9283.2193*. 137

X

X

X

X

X

X

X

XXX

X

X

X

X

b

X

X

X

X

X

X

X

X

X

X

X

X

X

X

+30.149+23.428+23.986+30.609+25.437+32.156+34.126

+32.070+36.693+ 19.068+31.271+25.474+26.839+31.538

+20.956+53.966+ 17.407+ 37.432+33.361-64.614

-0 .248

+ 10.025-3.821

+30.412+31.093+42.653+ 0.872-1 .445

COCX>>

5>mf—i

monX>XoX>

* z5 >a

i Tl•• >

* N>X>sr>X


REFERENCES

AYRES. J.C, A.A. KRAFT, and L.C PIERCE. (1964):Delaying spoilage of tomatoes. Food Tech. 18(8):1210.

BARUAH, P. and T. SWAIN. (1925): The effect of1-ascorbic acid on the in vitro of polyphenoloxidasefrom potato. Biochem. J. 55: 392-399.

BOLIN, H.P and F.P. BOYLE. (1972): Effect of storageand processing on sulfur dioxide in preserved fruits.Food Prod. Dev. 6(7): 82.

EMBS, R.J. and P. MARKIKIS. (1965): The mechanismof sulfite inhibition of browning caused by poly-phenol oxidase. J. Food Sci 30: 753-758.

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(Received 19 June 1987)


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