Pertanika 10(2), 143-149 (1987)

Prevention of Browning in Canned Langsat(Lansium domesticum)

SUHAILA MOHAMED and S.H. LEONGDepartment of Food Science,

Faculty of Food Science and Biotechnology,Universiti Pertanian Malaysia,

43400 Serdang, Selangor, Malaysia.

Key words: Browning; canned langsat (Lansium domesticum).

ABSTRAK

Langsat mengalami keperangan oleh enzim semasa penyediaan dan keperangan bukan enzimsemasa penyimpanan hasil dalam tin. Kesan NaCI, asid askorbik, sistin HCl dan asid sitrik he ataspemerangan telah dikaji. Pemerangan enzim semasa penyediaan dapat dikurangkan dengan meren-dahkan pH tetapi penggunaan asid sitrik tidak disyorkan kerana ia akan meningkat keperanganbukan enzim semasa penyimpanan. Asid askorbik melengahkan keperangan enzim tetapi menghasil-kan banyak keperangan bukan enzim semasa penyimpanan. Walau bagaimanapun hasil asid aminodehidroaskorbik bukanlah pigmen terbanyak dalam langsat terkaleng yang tidak ditambah bahankimia. Antara perlakuan-perlakuan yang dikaji, penambah sistin HCl adalah yang paling berkesanuntuk menghalang keperangan dan memberi hasil yang boleh diterima dari segi rasa dan rupa.Walau bagaimanapun, kajian menggunakan sistem contoh menunjukkan bahawa sistin HCl tiadamemberi kesan ke atas keperangan bukan enzim. Cara ia menghalang keperangan dalam langsat ter-kaleng dijangka dengan menurunkan O-quinon yang terbentuk sebagai bahan perantaraan semasakeperangan enzim, sebelum pemprosesan haba, kepada sebatian-sebatian tiada warna, yang menjadibahan pelopor pembentukan pigmen keperangan bukan enzim. NaCI tidak mempunyai kesan yangsama se per ti sistin HCl ke atas hasil dalam tin itu. Kepekatan NaCI yang tinggiyang diperlukan untukmenghalang kegiatan polifenoloksidas akan menjejas rasa dan penerimaan langsat dalam tin.

ABSTRACT

Langsat undergo both enzymic browning during preparation and non-enzymic browningduring storage of the canned product. Effects of sodium chloride, ascorbic acid, cysteine HCl andcitric acid on browning of the product were studied. Enzymic browning during preparation could bereduced by lowering of pH, but the use of citric acid is not recommended because it increases non-enzymic browning during storage. Ascorbic acid delays enzymic browning but produces intense non-enzymic browning on storage. However, amine-dehydroascorbic acid products are not the majorpigments in chemically untreated, canned langsat. Amongst the treatments studied, addition ofcysteine HCl was most effective in preventing browning and giving an acceptable product with regardsto taste and appearance. However, studies using model systems showed that cysteine HCl has no effecton non-enzymic browning. It probably prevents browning of canned langsat, therefore, by the reduc-tion of the O-quinones, formed as intermediates in enzymic browning prior to canning to stablecolourless compounds, thus eliminating their activity as precursors for non-enzymic brown pigmentformation. NaCI does not have the same effect on the canned product as cysteine HCL The fairly highconcentration of NaCI needed to totally inhibit PPO activity would adversely affect the taste andacceptability oj the canned langsat.

SUHAILA MOHAMED AND S.H. LEONG

INTRODUCTIONLangsat (Lansium domesticum) is a fruit withgood prospects for canning, not only because it ishighly perishable but also because its percentageof edible portion is high (65%) compared to thatof other seasonal tropical fruits (Leong, 1982).Unfortunately, langsat undergo both enzymicbrowning during preparation for canning andnon-enzymic browning during storage of thecanned product. Chemicals used to inhibitbrowning in other products include cysteine(Montgomery, 1983); NaCl, CaCli;, ascorbicacid (De Poix et ai, 1980); cinnamic acid(Garzago, Vamosa & Sumeghyne 1981); citricacid (Me Cord & Kilara, 1983); metabisulphideand thiosulphite (Fuster, et aL, 1982); glutamicand aspartic acids (Nafisi and Markikis, 1983).In this worl̂ the non-enzymic browning oflangsat under aerobic and anaerobic conditionsand its inhibition by NaCl, ascorbic acid,cysteine hydrochloride and citric acid (to reducepH) were studied to determine the conditionswhich give the most acceptable product.

MATERIALS AND METHODSCommercial samples of langsat were obtainedfrom the local markets of Seri Kembangan,Sungei Besi and Kajang. The fruits were mixedtogether and randomly selected for chemicalanalysis and treatments.

Samples of 20 fruits were used for pro-ximate analysis. Langsat juice was prepared byhomogenising the edible portion of the fruit.The effect of pH on the rate of non-enzymicbrowning was studied by adjusting the pH of thejuice in the range of 2 - 7 with HC1 and NaOh.The heat treated or unheated juices were thenstored under aerobic or anaerobic conditions atvarious temperatures (0 - 4 ° C , 28°C & 35°C) forup to 150 days. Optimum concentrations ofNaCl, ascorbic acid and cysteine HC1 needed toreduce browning were determined by addingvarious levels of the chemicals to the juice. Thebrowning of langsat juice under various condi-tions and treatments was monitored by takingthe absorbance at 400nm of the juice clarified bycentrifuging. Ascorbic acid was determined bytitrating with 2,6 dichlorophenol indophenol(AOAC, 1980).

The final product, canned langsat, was pre-pared by soaking the peeled langsat duringpreparation and blanching the peeled fruit for 3minutes in solutions of sodium chloride, ascorbicacid or cysteine HC1 at previously determinedoptimum concentrations. The fruits were drain-ed and filled into sterilised AI cans, to which wasadded 40% sucrose syrup whose pH had beenadjusted to 3 .7-3 .8 with citric acid, allowing0.5cm head space. The cans were exhausted at98°C for 5 minutes, sealed and processed for 12minutes in boiling water. The effect of storage atvarious temperatures on colour, flavour andascorbic acid content was monitored.

To study non-enzymic browning in modelsystems, stoppered 20ml bottles containingsimulated solutions were incubated at 37°C. Theintensity of browning was measured at 400nm inlem cells in a Pye Unicam Spectrophotometer,diluting when necessary, and the change in pHnoted.

The basic model system (bottle a) had thefollowing composition (Table III): 0.8% aminoacid mixture, 0.008% ascorbic acid, 40%sucrose and HC1 to adjust pH to 3.15, i.e. theoriginal pH of langsat juice. Bottles b and c con-tained the basic system, plus 1.0% NaCl and0.024% cysteine HC1 respectively. Bottles d ande contained 0.6% hydrogen peroxide. Bottles fand g contained no ascorbic acid at all. To bothbottles e and g were added 0.024% cysteine HC1.Bottles h, i and j had the same composition asbottles a, b and c but their pH was adjusted withcitric acid. Bottle k had a similar composition tobottle h but had 0.2% ascorbic acid added.

RESULTS AND DISCUSSIONThere was a correlation between pH and opticaldensity at 400nm for unheated langsat juicebetween the pH range of 2 - 7 . This browningwas almost certainly enzymic in origin since itincreased with increasing pH during preparationof the fruit and it could be reduced by loweringthe pH in the holding tank. Below pH 3.0, thejuice remained relatively clear even after 3hours. Browning occured very rapidly as soon asthe skin was broken and the interior exposed toair, indicating that the enzyme involved is mostlikely polyphenol oxidase (PPO). However,studies of the enzymic browning activity, the pH

144 PERTANIKA VOL. 10 NO. 2, 1987

PREVENTION OF BROWNING IN CANNED LANGSAT (LANSIUM DOMESTICUM)

profile, and the temperature profiles of theenzyme, etc., were not within the scope of thiswork.

Heat treatment (3 minutes at 100°C) andvacuum sealing, either singly or in combination,were not effective in controlling browning oflangsat juice (initial pH 3.15) stored for morethan 35 days at 35°C. Rapid enzymic browningwas eliminated by the heat treatment andvacuum sealing but a slower non-enzymicbrowning was observed. Deterioration of thejuice was faster in those cans sealed in the pre-sence of air.

The effect of various chemical treatmentson acceptability, colour, taste and flavour of thefinal product is summarised in Table 1. Accept-able canned langsat was only obtained in thecysteine HC1 treated samples. A decrease inascorbic acid content and a correspondingincrease in pH occurred in all cans of processedlangsat juice on storage; the smallest changesoccurred in those cans treated with cysteine HC1.

The results of pre-treating canned langsatwith the optimum concentration of ascorbic acid(0.20%), NaCl (1.0%) and cysteine HC1(0.024%) are summarised in Table II, withrespect to pH, absorbance at 400nm andascorbic acid retention. A good correlation existsbetween pH and ascorbic acid content except insamples treated with cysteine HC1, indicatingthat the change in pH can be used to monitorascorbic acid retention in the canned products.Correlation between pH and O.D. 400nm wereobserved only in samples not treated chemically.In other cases, correlations were not observedbecause the points were scattered and showedlittle variation in pH for the corresponding O.D.readings.

Effects of (i) chlorides, (ii) ascorbic acid and(iii) cysteine HC1 on enzymic browning havebeen reported by several researchers, (i) Chlorideanions inhibit and delay the onset of enzymicbrowning. An exponential relation appears toexist between reaction speed and amount ofadded chloride (De Poix et ai} 1980). (ii)Ascorbic acid delays the onset of browning with-out inhibiting the enzymic activity (De Poix etai, 1980). Ascorbic acid is consumed in brown-ing reaction systems to reduce 0-quinone back tothe parent 0-diphenol, itself being oxidised to

dehydroascorbic acid (DHA). Reactions betweenDHA and amino acids then lead to formationof a red pigment, the oxidised form ofbis-(2-deoxy-2-L-ascorbyl)-amine. Furtherreactions, variously involving ascorbic acid,DHA and ascorbamic acid yield 3 different freeradicals and production of a yellow pigmentthought to be a key intermediate in the browningreaction (Hayashi & Namiki, 1983). (iii) CysteineHC1 prevents enzymic browning by reducing0-quinone to a colourless complex. Unlikemetabisulphite or thiosulphite, cysteine does notcause any deleterious changes to flavour(Montgomery, 1983).

In the present studies, ascorbic acid reten-tion was highest in the cysteine-HCl-treatedlangsat. The reduction of 0-quinones by cysteineHC1 to colourless complex would have forestalledreactions between quinones and ascorbic acid,thus eliminating one cause of the oxidation ofascorbic acid.

Model SystemsNon-enzymic browning could be due to (a)sugar -amine condensation products, (b)furfuraldehydes (sugar-sugar) type compoundsor (c) amine-dehydroascorbic acid products.Effects of NaCl, ascorbic acid and cysteine HC1on non-enzymic browning in model systems aresummarised in Table III.

The darkest colours were observed in bottlek containing a high concentration of ascorbicacid and in bottles d and e containing hydrogenperoxide and the standard concentration ofascorbic acid, where oxidation of ascorbic acidled to greater pigment formation with amines.Although ascorbic acid delays PPO activityduring fruit preparation, it itself undergoes oxida-tion leading to the formation of brown amine-dehydroascorbic acid products during processingand storage. Cysteine HC1 has no capacity toreduce or prevent this pigment formation (bottlee), and ascorbic acid should therefore not beused to prevent browning of canned acidicproducts.

Systems acidified with citric acid (bottlesh - j) were darker in colour then similar compo-sitions acidified with HC1 (bottles a - c). The useof citric acid to lower the pH values should beavoided (if possible), when light coloured pro-

PERTANIKAVOL. 10 NO. 2, 1987 145

3

o

o

o

Treatment

Control(None)

1.00% NaCl

0.200%Ascorbic acid

0.024%Cysteine HC1

TABLE 1Acceptability of canned langsat (in 40% sugar solution, heated and vacuum sealed)

stored for 150 days, given various chemical pretreatments

Storagetemperature

Colour Taste Langsat Acceptability Ascorbic acid pHflavour % retention

0-4°C

28°C

35°C

0-4°C

28°C

35°C

0-4°C

28 °C

35°C

0-4°C

28°C

35°C

Slightbrown

Brown

Brown

Brown

Brown

Brown

Brown

Brown

Brown

Original

Original

Original

Retains acidityand sweetness

Slightly acid withsweet tinge

Slightly bitterand acidic

Acidity and sweetnessretained

Slightly acid withsweet tinge

Slightly bitter

Acidity and sweetnessretained

Slightly acid withsweet tinge

Slightly bitter

Acidity and sweetnessretained

Slightly acidic

Slightly acidic

Mild

Mild

Absent

Mild

Mild

Absent

Good

Mild

Absent

Good

Mild

Mild

Nil

Nil

Nil

Nil

Nil

Nil

Nil

Nil

Nil

Good

Fair

Fair

90.1

35.5

25.0

97.3

92.5

90.0

97.5

95.2

94.0

97.9

97.5

97.1

3.33

4.42

4.50

3.60

3.83

4.10

3.55

3.76

4.01

3.55

3.65

3.70

IO

5

>a

c

with mild bitterness

o

S

TABLE 2Correlationships between optical density at 400nm, ascorbic acid

Each correlationship was calculated from an average

Treatments

Unheated/A

H / A

H/A/NaCl

H/A/asc. acid

H/A/cyst. HC1

H/V/NaCl

H/V/asc. acid

H/V/cyst. HC1

H / V

Unheated/vacuum

p.c. — poor correlationshipn.d. — not determinedunheated — enzymic browningA — aerobic conditionsV — vacuum sealedH — heat treated samples

Correlation coefficient

pH vs O.D. pH vs ascorbic acid

0.972

0.955

p.c.

p.c.

p.c.

n.d.

n.d.

n.d.

0.992

0.917

(non-enzymic browning).

-0.987

-0.976

-0.943

-0.881

-0.817

-0.966

-0.958

p.c.

-0.950

-0.960

retained and pH in canned langsat.of 12 pairs of readings.

y

y

y

y

pH vs OD

= 735x - 1

= 1.408x -

p.c.

p.c.

p.c.

n.d.

n.d.

n.d.

= ,637x -

= .6475x -

Best fitted line

.84

4.18

1.92

1.88

pH vs ascorbic acid ;

y =

y =

y =

y =

y =

y =

y =

y =

y =

29.7x +

-30.1x

-68.5x

-41.7x

- 11.7x

-14.1x

-7.51x

p.c.

-73x +

-17.2x

189 I+ 191 |

+ 331

+ 238

+ 135

+ 148

+ 124

368

+ 152

RE

VE

NT

K

; °v 0

Q•WN

I

Z: O

znzir

1>

too

1

SUHAILA MOHAMED AND S.H. LEONG

Bottle

a

b

c

d

e

f

g

h

i

j

k

TABLE 3Non-enzymic browning of model

Contents

0.8% amino acid, .008% asc. acid, surcose + HC1

comp. a + 1.0% NaCl

comp. a + 0.024% cysteine HC1

comp. a + 0.6% hydrogen peroxide

comp. d + 0.024% cysteine HC1

comp. a but ascorbic acid omitted

comp. f + 0.024% cysteine HC1

comp, a, replace HC1 with citric

comp. h + 1.0% NaCl

comp. h + 0.24% cysteine HC1

comp. h + 0.2% ascorbic acid

systems

Optical density

42 days

0.57

0.44

0.53

1.53

1.86

0.38

0.46

0.67

0.60

0.71

2.97

at 400nm

95 days

1.65

1.75

2.04

3.41

3.49

1.53

1.93

2.27

2.33

2.37

3.43

Each optical density is an average of readings from triplicate experiments; average standard deviations were approximately 8%of the readings.

ducts are required. CJegg (1966) detected aspecific brown pigment when citric acid andascorbic acid were present in acidic productscontaining amino acids.

A slight increase in colour could be seen inall treatments containing cysteine HC1 (bottles c,e & g) when compared with similar systems with-out this component (bottles a, d, f), and can beattributed to the slight increase in aminocontent. Since cysteine HC1 has no inhibitingeffect on non-enzymic browning, the mechanismby which it inhibits browning in canned langsatis probably by reducing 0-quinones, the enzymicbrowning intermediates formed during the pre-paration of the product, which otherwisebecome non-enzymic browning precursors incanned langsat. Studies on the optimum cysteineHC1 concentration needed in prevention ofbrowning in fruits demonstrates the importanceof using sufficient cysteine HC1 as a quinonecoupler; the concentration of cysteine HC1 in themodel systems may have been insufficient toinhibit browning in these systems. The chloridecomponent of cysteine HC1 in unlikely to haveany effect in inhibiting PPO since its concentra-tion is very small compared to the concentration

of NaCl effective in inhibition of enzymic brown-ing.

Elimination of ascorbic acid from the modelsystem reduced non-enzymic browning onlyslightly (bottle a compared with bottle f),indicating that amine-dehydroascorbic acidinteraction was not the major origin of chromo-phores in non-enzymic browning of cannedlangsat.

Like cysteine HC1, NaCl has no significanteffect on non-enzymic browning but inhibitsenzymic browning. However, on storage thebrowning of canned langsat treated with NaClwas much greater than in samples treated withcysteine HC1. This effect could be due to insuffi-cient NaCl concentration to totally inhibit PPO,leading to the development of enzymic browningintermediates which became the non-enzymicbrowning precursors. Higher NaCl concentra-tion treatments could not be used because theywould adversely affect the taste and acceptabilityof the canned langsat.

CONCLUSIONThe use of cysteine HC1 to prevent browning canbe applied to canned langsat in the same way as

148 PERTANIKA VOL. 10 NO. 2, 1987

PREVENTION OF BROWNING IN CANNED LANGSAT (LANSIUM DOMESTICUM)

it has been used in other canned fruits whichundergo rapid browning. It is important that theaddition of citric acid or ascorbic acid is avoidedin heat processed fruits, as they promote ratherthan inhibit browning. This finding may beapplicable to other Malaysian canned fruits, butfor fruits with high ascorbic acid and citric acidcontent, other procedures may be needed toprevent non-enzymic browning of the processedproduct.

ACKNOWLEDGEMENTSThe authors thank Fuan Norhayati Salamudinfor typing and Universiti Pertanian Malaysia forfunding the research.

REFERENCES

AOAC. (1980): Official Methods of Analysis 13th ed.The association: Washington D.C.

CLEGG, K.M. (1966): Citric acid and the browning ofsolutions containing ascorbic acid. J. Sci. Fd.Ague. 17: Dec.

DEPOIX, A., M.A. ROVET MAYER and J. PHILIPPON.(1980): Combined action of chlorides andascorbic acid on inhibition of enzymic browningin apples puree. Lebensmittel-wissenschaft und-Technologie, 13(2): 10110.

FUSTER. C , G. PRESTANO, a n d j . ESPINOSA. (1982):Choice of optimum treatment to prevent brown-ing of Frozen mushrooms. Alimentaria 131: 33 -35.

GARZAGO, I., V.L. VAMOSNE, and K.N. SUMEGHYNE.(1981): Effect of polyphenol oxidase inhibitors onthe enzymic browning of apples. Edel miszer-vizsgaiati Kozlemenyek 27(4): 173- 178.

HAYASH1, L.T. and M. NAMIKI. (1983): The mecha-nism of the browning reaction of dehydroascorbicacid with amino acid involving the free radicaland yellow product. Proceedings of the 6th Inter-national Congress of Food Science and Techno-logy. 2 :55 -56 .

LEONG. S.M. (1982): A study on nutritional and pro-cessing behaviour of some Malaysian Fruits.Universiti Pertanian Malaysia. (1982 — B.Sc.Thesis).

Me CORD, J.D. and A. KILARA. (1983): Control ofenzymic browning in processed mushrooms. J. ofFood Science 48(5): 1479 - 1483.

MONTGOMERY, M.W. (1983): Cysteine as an inhibitorof browning in pear juice concentrate. J. of Fd.Science 48(3): 957-952.

NARFISA, K. and P. MARKIKIS. (1983): Inhibition ofsugar amine browning by aspartic acid andglutamic acid. J. of Agricultural and Food andFood Chemistry 31(5): 1 1 1 5 - 1 1 1 7 .

(Received 22 May, 1986)

PERTANIKA VOL. 10 NO. 2, 1987 149