J Sci Food Agric 1994,66,9-11

Effects of Various Surface Treatments on the Storage Life of Guava (Psidium Guajava L) at 10°C Suhaila Mohamed,* Khin Ma Ma Kyi and Salmah Yusof

Faculty of Food Science and Biotechnology, University Pertanian, 43400 Serdang, Malaysia

(Received 1 September 1993; revised version 31 Januray 1994; accepted 12 April 1994)

Abstract: The use of various surface treatments to prolong storage life of guavas at 10°C was examined. LDPE shrinkwrap was most effective in reducing weight loss and maintaining the firmness of guava (most likely indicating its effectiveness in alleviating water stress), followed by clingwrap packaging and 200 g litre- ’ palm oil emulsion coating. The skin colour of guava was most effectively pre- served by LDPE packaging, sucrose-ester and 200 g litre-’ palm oil emulsion dips. Paraffin treatment caused the skin to turn brown after 2 weeks storage. The ascorbic acid content was highest in control followed by clingwrapped guava. Clingwrapped guava also received the highest organoleptic scores followed by shrinkwrapping and 200 g litre- ’ palm oil treated guava.

Key words : guava, shrinkwrap, clingwrap, starch, parafin, palm oil, sucrose- ester.

The storage life of guava is approximately 3 days at room temperature (27-33°C); 1 week at 20°C; and about 2 weeks at 0-10°C (Gupta et a1 1979; Wills et al 1983). Singh and Mathur (1954) reported that ‘Safeda’ guava could be stored for about 4 weeks at 8-10°C under 85-95% relative humidity. A 60 g litre-’ wax emulsion retarded the rate of ripening and prolonged the storage life of ‘Safeda’ guava (Bhullar and Farm- ahan 1980). This study was conducted to compare the effect of various suface treatments (palm oil, parafin, sucrose-ester, starch or LDPE wrappings) for main- taining the freshness of guava, stored at 10°C.

‘Vietnamese’ guavas from Semenyih, Malaysia, of 15-16 weeks maturity, were washed, dried and given fungicide treatment (100 mg litre-’ perchloraz: Scher- ring Agrochemicals, Hauxton, Cambridge, UK) together with the following treatments followed by air drying and storage at 10°C. The solvent in each case was water and 1% vfv monoglycerides were added where necessary as emulsifier. Treatments were as follows:

* To whom correspondence should be addressed.

100 g and 200 g litre-’ refined, bleached and deodorised (RBD) palm olein; 7.5 g and 10 g litre-’ fatty acid sucroseesters (semperfresh@) ; 10 g, 50 g, 100 g and 200 g litre- ’ liquid parafin (BDH, Poole, UK); 20 g and 30 g litre-’ soluble starch (BDH, Poole, UK) previously gelatinised in 90°C water; shrinkwrapped (0.025 mm low-density poly- ethylene (LDPE) under a hot air tunnel (model WF12 at 170°C for 10 s); and clingwrapped (0.01 mm LDPE, twisted both sides).

Four guavas from each treatment were individually analysed weekly for weight loss; skin colour change (HunterLab colorimeter model D25 L-2 expressed as 6 colour = J(~L’ + 6a’ + 6b’); firmness (Instron Univer- sal Testing Machine model 1140 with 8 mm plunger); soluble solids (Otago hand refractometer 0-32”B); ascorbic acid (dichlorophenol indophenol titration); titratable acidity (with 0.1 M NaOH); and pH. In addi- tion fruits were tasted by 10 semi-trained panellists and

9 J Sci Food Agric 0022-5142/94/$09.00 0 1994 SCI. Printed in Great Britain

10 S Mohamed, K M M Kyi , S Yusof

examined by scanning electron microscope (SEM). Data were subjected to analysis of variance.

Analysis of data showed that the best concentrations for the various dips were (a) 200 g litre-' palm oil, (b) 7.5 g litre-' sucrose-esters, (c) 10 g litre-' parafin, (d) 30 g litre- soluble starch (only these data are shown in Table 1 to simplify the discussion).

The weight loss increased significantly with increased duration of storage (P = 0-05) (Table 1). LDPE shrink- wrapping had the lowest weight loss over the 9 weeks storage period followed by clingwrap and 200 g litre-' palm oil. Paraffin (10 g litre-') was as effective as 200 g litre-' palm oil in preventing weight loss for the first 5 weeks, after which lesions on the skin as indicated by brown discoloration, caused the fruits to lose as much moisture as the control. Sucrose-esters were less effec- tive in preventing weight loss probably because of the low concentration used. Starch treated fruits lost more moisture than untreated fruits.

Palm oil (200 g litre-') was the best treatment for maintaining the green colour of guava at 10°C until

about 8 weeks, followed by clingwrap, shrinkwrap pack- aging, and sucrose-esters (Table 1). Maintenance of the fruit colour is most likely dependent on the gaseous per- meability of the surface coatings. Paraffin appeared to be incompatible with the epidermal layer causing brown lesions during storage. Colour change was found to be correlated with weight loss (r2 = 0.86; n = 117), prob- ably because moisture loss hastened ripening or chlo- rophyll loss in the guava. Colour was also correlated with hardness (r2 = 0-80; n = 117) for most treatments.

LDPE shrinkwrapped fruits were firmer than the other fruits over the 9 weeks storage period followed by 200 g litre-' palm oil and clingwrapped fruits (Table 1). Paraffin-treated fruits maintained firmness for up to 5 weeks of storage. The general decrease in firmness of the guava during storage was primarily due to the loss of moisture from the surface causing the cells to lose tur- gidity. Thus weight loss and firmness were highly corre- lated (r2 = 0.82; n = 117) for most treatments. Ben-Yehoshua et a1 (1983) showed that softening was highly correlated with declining water potential of fruit

TABLE 1 Effects of various surface treatments on the physico-chemical characteristics of guava stored at 10°C

Storage Treatment Weight Colour Hardness SSC pH T A Ascorbic duration loss change (ks) ("B) (Yo) acid (weeks) ("/.I (ms Per 100 9)

3 Control 200 g litre-' palm oil 7.5 g litre- ' semperfresh 30 g litre- ' starch 10 g litre-' parafin Shrinkwrap Clingwrap

200 g litre-' palm oil 7.5 g litre- ' semperfresh 30 g litre-' starch 10 g litre-' paraffin Shrinkwrap Clingwrap

200 g Iitre- ' palm oil 7.5 g litre-' semperfresh 30 g litre- ' starch 10 g litre- ' parafin Shrinkwrap Clingwrap

200 g litre-' palm oil 7-5 g litre- ' semperfresh 30 g litre- ' starch 10 g litre- ' paraffin Shrink w r a p Clingwrap

5 Control

7 Control

9 Control

Least significant difference (LSD)

11.72 4.91 7.87

12.52 5.82 0.49 2.34

14.92 8.08

14.82 18.22 7.12 0.78 4.46

20.65 11.86 19.16 23.48 20.04

1.31 6.02

31-82 14-79 24-03 32.40 30-00

1 -90 8.22

1.50

5.05 1.54 3.47 3.84 5.39 3.21 2.81

10.91 2.83 6.55 8.79 7.36 5.97 7.70

1.99 4.10 8.77

10.66 11.78 6.32 5.74

14.46 6.54 7.76

11.96 14-79 6.60 7.15

2.67

17.83 19.13 17.73 19.22 17.00 17.19 14.88

5.04 18.33 13-64 7.03

10.14 15.25 12.96

1.99 8.52 3.49 1.71 1.43

1 1.93 7.83

1.24 4.13 1.75 1.41 0.76 9.17 4.12

2.25

9.55 8.27 8.70 9.97 8.50 7.55 7.90

10.85 8.53 9.03 9.75 7.78 7.25 8.95

11.00 8.88 9.45

10.80 10.53 6.98 8.13

8.08 7.05 9.43

10.18 8-25 6.45 6-38

1.23

4-0 1 3.99 3.84 3.92 4.09 4.10 4.04

4.03 3.98 3.95 3.98 3.91 4.12 4.04

4.10 4.10 4.04 4.09 4.28 4.25 4.11

4.07 4.07 4-01 4.34 4.00 4.10 4.06

0.2 1

0.50 137.17 0.47 79.28 0.54 107-97 0.54 111.88 0.55 111.72 0.4 1 105.36 0.42 115.68

0.58 167.02 0.50 75.99 0.57 109.45 0.54 152.37 0.57 102.19 0.48 92.90 0.51 131.12

0.55 121.90 0.52 74.99 0.58 113.71 0.58 107.93 0.52 87.22 0.38 98.94 0.43 140.29

0.48 24.48 0.42 45.95 0.53 55.93 0.46 26.94 0.44 13.61 0.31 29.85 0.39 49.26

0.14 18.10

Storage of guava 11

TABLE 2 Mean score values of sensory evaluation of various surface treated guava"

Treatments Colour Taste Texture Flavour Overall accept

Week 3 Control 4.7bc 4.3cde 4.4cd 4.8cd 4-0cd Shrinkwrap 543a 4.9c 5-3abc 5.0bc 5-2ab Clingwrap 6.1a 6.2a 6-3a 6.1a 54a 10 g litre- parafin 1.9f 4.7cd 5.lbcd 4.2cdef 2.2e

7.5 g litre-' semperfresh 543a 5-9ab 58ab 5.9ab 5-6a 30 g litre-' starch 3.8de 3.5efg 3.lf 3.9defg 4-0cd

Control 2.9d 2.2cd 2.0de 2.8cd 2 4 Shrinkwrap 5.7ab 3.2b 3-lc 3.7bc 4.8ab Clingwrap 5.9a 5.4a 5.5a 5.7a 5.1a 10 g litre-' paraffin 1.6e 2.0cde 2.2de 2.6d 1.5f 200 g litre-' palm oil 5.lab 3.9b 4.6b 4.4b 4.lbc 7.5 g litre-' semperfresh 3.2d 1.6de 1.7e 2 4 3.3cd 30 g litre-' starch 2.8d 1.9cde 2.1de 2.8cd 1.5f

200 g litre-' palm oil 44cd 4.4cde 46cd 4.8cd 4-3bc

Week 7

Means for each storage duration followed by the same letter are not significantly different at P = 0.05. Scale: 1, dislike very much; 7, like very much.

which adversely affected membrane function and increased polygalacturonase activity.

LDPE shrinkwrapped fruits had lower soluble solids content (SSC) compared with other treatments while higher SSC was observed in control, semperfresh and starch-treated fruits (Table 1). The general increase fol- lowed by decrease in SSC during storage (Table 1) could result from breakdown of insoluble poly- saccharides, followed by utilisation of the soluble solids (sugars, etc.) for respiration. SSC was found to be corre- lated (r2 = 0.51 ; n = 117) to titratable acids (TA).

pH increased slightly during storage (Table 1) but was not significantly different between treatments (P = 0.05). pH was correlated to colour (ripeness) (r2 = 0.86; n = 117). Starch coatings caused the most TA changes while 200 g litre-' palm oil coating caused the last TA change. The poor correlation between TA and pH showed that guava had high buffering capacity.

Ascorbic acid content increased during ripening and decreased during senescence. Control guava had the highest ascorbic acid content until 8 weeks storage, fol- lowed by clingwrapped and sucrose-ester treated fruits (Table 1).

Under SEM the guava skin at week 0 was found to be smooth and a little shrinkage was observed after 3 weeks storage of the untreated guava. Guava skin treated with paraffin appeared rough (like scars) after 3 weeks storage. The lesions were more pronounced at the higher parafin concentrations. The stomata appeared to be completely blocked by 200 g litre-' palm oil and the skins remained smooth. The skin of 10 g litre-' semperfresh treated guava was similar to controls.

At 3 weeks storage, sensory panellists preferred the skin colour, taste, texture and flavour of clingwrapped guava, followed by sucrose-ester treated and shrink- wrapped guava (Table 2). Parafin treated guava received the lowest scores in colour due to the browning of the skin. After 3 weeks storage, starch treated fruits received the lowest scores in texture. After 7 weeks storage, panellists preferred the taste, texture and flavour of clingwrapped guava followed by palm oil treated guava. For colour and overall acceptability, clingwrapped guava had the highest scores followed by shrinkwrap, 200 g litre-' palm oil and 10 g litre-' semperfresh-treated guava. Clingwrapped guava received the highest mean scores in all attributes at both 3 and 7 weeks storage.

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Gupta 0 P, Singh, B P, Gupta, A K 1979 Studies on the shelf life of different guava cultivars. Haryana Agric Univ J Res 9

Singh K K, Mathur P E 1954 Cold storage of guava. Ind J Hort 11 1-5.

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