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Chlorophyll and color of green chilli puree as affected by mesh size andtemperatureJasim Ahmeda; U. S. Shivharea; G. D. Singha

a Department of Food Science and Technology, Guru Nanak Dev University, Amritsar, INDIA

To cite this Article Ahmed, Jasim , Shivhare, U. S. and Singh, G. D.(2000) 'Chlorophyll and color of green chilli puree asaffected by mesh size and temperature', International Journal of Food Properties, 3: 2, 305 — 315To link to this Article: DOI: 10.1080/10942910009524636URL: http://dx.doi.org/10.1080/10942910009524636

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INTERNATIONAL JOURNAL OF FOOD PROPERTIES, 3(2), 305-315 (2000)

CHLOROPHYLL AND COLOR OF GREEN CHILLI PUREEAS AFFECTED BY MESH SIZE AND TEMPERATURE

Jasim Ahmed*, U.S. Shivhare, and G. D. Singh

Department of Food Science and TechnologyGuru Nanak Dev University, Amritsar-143005 INDIA

*Corresponding author (Tel: 91 0183 220667, Fax: 91 0183 258820, and E-mail:fst@gndu.ernet.in)

ABSTRACT

Chlorophyll content and total color were studied at selected mesh size (# 10, 12 and 14)and temperature (0 to 100° C) of green chilli puree. Results indicated that bothchlorophyll and color varied significantly (p 0.05) with temperature and the mesh sizethrough which the chillies were pureed. Chlorophyll content of green chilli pureeincreased with increased fineness but decreased linearly with process temperature. Upto 60% loss of chlorophyll was observed while the puree was heated for 15 min at 100°C. The Hunter color values combination -La/b described closely the linear variation ofthe total color of green chilli puree with temperature. Relationship between total colorwith the chlorophyll content of green chilli puree was described using a linearrelationship. Storage of puree at room temperature for a period of six months resultedin color degradation as evidenced by decreased Hunter color values.

INTRODUCTION

Chilli (Capsicum annuum L), the most widely consumed spice, is used in the cuisine ofboth the developing and developed countries. The wide popularity of chilli is due to itswide range of shapes and sizes and sensory attributes such as color, pungency anddistinctive aroma that make generally insipid bulk nutritive flesh and cereals foodsmore appetizing (Govindarajan et al., 1987). Although chilli can be used afresh, thenormal way to use it is in the dried form either whole, ground or crushed. The freshfruit is also used in salad, pickle and canned product (Govindarajan et al., 1987).Annual trade of chilli in the world is 0.055-0.065 MT which is 16.7% of total spicetrade in the world (Peter, 1994). India ranks first in the production (0.691MT) as wellas in the export (0.033 MT) of chilli in the world.

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306 AHMED, SHIVHARE, AND SINGH

The maintenance of naturally colored pigments in thermally processed andstored foods has been a major challenge in food processing. Many attempts have beenmade to stabilize the color with limited success (Clydesdale et al., 1970; Dil et al.,1998). The most common change that occurs during thermal processing of greenvegetables and spices is the conversion of chlorophyll to pheophytins, causing a changefrom bright green to olive-brown (Rocha et al., 1993; Ihl et al., 1998). The chlorophylldegradation involves the loss of phytol to form chlorophyllide, loss of Mg2+ to formpheophytin, the loss of Mg2+ and phytol to form pheophorbide, and the loss of Mg2+

and carbomethoxy group to form pyropheophytin (von Elbe, 1986). Generally, thecolor measurement is carried out by spectrophotometric measurement of acetoneextract of chlorophyll which is time consuming and thermally decomposed pheophytinscause interference in chlorophyll concentration measurements (Eheart and Gott, 1965).On the other hand, colour, which is an indicator of chlorophyll, can be measuredinstantaneously for on-line quality control (Rocha et al., 1993). Hunter colourparameters L, a and b have been widely used to describe the colour change during heatprocessing of fruit and vegetable products by several research workers (Hoover andMason, 1961; Nagle et al., 1979; Lukes, 1986; Rocha et aL, 1993; Shin and Bhowmik,1994).

In the food processing industry, a large number of food products are subjectedto size reduction. The process results in a range of product particle sizes whose properdescription is with the complete cumulative size distribution (Walas, 1988). Particlesize distribution influences considerably the color (Surak et al., 1979) of pureed foods.Puree is made by passing the fruit or vegetable pulp through a fine finishing screencontaining a large number of circular perforations. The aperture of the finisher screenaffects the particle size and the color of the puree by exposing more surface area andconsequently more scattering of light into the product.

Little has been reported in the literature on the effect of particle size and processtemperature on the chlorophyll and color retention of green chilli puree. A study wastherefore undertaken to determine how the particle size and temperature affect the totalchlorophyll, chlorophyll- a and b and total color of green chilli puree.

MATERIALS

Fresh green chillies {Variety: CH-1) were procured from local market of Amritsar in thestate of Punjab, India.

METHODS

Preparation of Puree

Chillies were washed in running tap water, destalked manually and blanched for 3 minin water at 85° C. Preliminary trials demonstrated that the blanching at 85° C for 3 minresulted in complete inactivation of chlorophyllase and peroxidase enzymes in greenchillies. Chillies were cooled immediately in chilled water and drained. The blanchedchillies were then pureed in a laboratory size grinder (Comitrol, USA) through 10 (1.68mm), 12 (1.41 mm) and 14 (1.19 mm) mesh screens to obtain the puree of different

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GREEN CHILLI PUREE 307

particle sizes. Production of puree hampered considerably while chillies werecomminuted using screens higher than mesh# 14. The puree was stored immediately ata storage temperature of 0° C till further use. Total soluble solids and pH values ofgreen chilli puree were 9.0° Brix and 5.6 respectively.

Chlorophyll and Color Measurement

Approximately 200 g puree was weighed and transferred into 250 ml glass beaker andcovered with a lid. The beakers containing puree were placed in a constant temperaturewater bath maintained at selected temperatures, viz. 0, 25, 50, 75 and 100° C for aretention time of 15 min. The temperature of the sample at its geometric center wasmonitored using a thermometer (±0.5° C). The samples were transferred in an ice waterbath immediately after the thermal treatment.

Color measurement was carried out using a Hunter colorimeter model D25optical sensor (Hunter Associates Laboratory Inc., Reston, VA, USA) on the basis ofthree variables namely L, a and b. The L value signifies the lightness (100 for white and0 for black), a value represents greenness and redness (-80 for green and 100 for red)while b value signifies change from blueness to yellowness (-80 for blue and 70 foryellow). The instrument was calibrated against a standard white reference tile.

Green chilli pureed through 14 mesh screen was stored in glass bottles at roomtemperature (20-25° C) for 6 months and the Hunter color values were measured at aninterval of 3 months.

Total chlorophyll and chlorophyll- a and b were determined following themethod described by Ranganna (1986) using a spectrophotometer (SchmidzuCorporation, Japan). Each experiment was replicated thrice and the average valueswere used in the analysis.

Statistical Analysis

The experimental data was statistically analyzed by the analysis of variance accordingto Steel and Torrie (1960). The significant treatment effects were further evaluated forthe significance of individual treatment factors using the least significant difference(LSD). All the results were inferred on 5% level of significance.

RESULTS

Effect of Temperature on Chlorophyll

Chlorophyll content of green chilli puree decreased significantly (P<0.05) withincreased temperature (Tables lthrough 3). Selected mathematical models (polynomial,exponential, linear) were tested to describe the variation of chlorophyll withtemperature; the criterion of selection of the best model were the standard error andcorrelation coefficient. Variation of chlorophyll content with temperature was found tobe linear and a relationship of the following form was proposed:

ch/cho = kd .T+1 (1)

where, ch is chlorophyll content of green chilli puree at any given temperature T

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308 AHMED, SHIVHARE, AND SINGH

Table 1. Analysis of variance of total chlorophyll (mg/1) of green chilli puree (n=3)

Temperature (°C)0

255075

100Mean

Mesh #101.661.551.260.940.681.22a

Mesh #121.671.591.321.210.801.32a

Mesh #142.132.011.351.221.081.56b

Mean1.82"1.72a

1.31b

1.12C

O.85d

LSD (Temperature) = 0.137LSD (Mesh size) = 0.176

Table 2. Analysis of variance of chlorophyll- a (mg/1) of green chilli puree (n=3)

Temperature (°C)0

255075

100Mean

LSD (Temperature)LSD (Mesh size) =

Mesh #101.000.900.850.560.381.23a

= 0.1030.133

Mesh #121.000.930.800.780.631.38b

Mesh #141.321.250.990.980.941.83°

Mean1.11'1.03a

0.88b

0.77c

0.65d

Table 3. Analysis of variance of chlorophyll- b (mg/1) of green chilli puree (n=3)

Temperature (UC)0

255075

100Mean

Mesh #100.660.650.400.380.310.48

Mesh #120.670.660.520.430.170.49

Mesh #140.810.760.370.230.150.46

Mean0.71a

0.69a

0.43b

0.35b

0.21°

LSD (Temperature) = 0.11

(mg/1), cho is chlorophyll content of green chilli puree at 0° C reference temperature(mg/1), ch/cho is dimensionless chlorophyll ratio, kch is chlorophyll degradationcoefficient (per °C), T is the process temperature (°C)

Linear regression of eq (1) was carried out using the least-squares technique andthe coefficients were computed (Table 4). A typical plot showing the variation of thetotal chlorophyll of green chilli puree with process temperature is shown in Fig. 1. It isobvious from Fig. 1 that eq (1) described adequately the variation of chlorophyll withtemperature at selected mesh sizes. Standard error values were less than 0.0008 while

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GREEN CHILLI PUREE 309

Table 4. Values of the coefficients of Equation 1

Chlorophyll typeTotal

a

b

Mesh#101214101214101214

-0.0056-0.0045-0.0054-0.0056-0.0035-0.0033-0.0057-0.0060-0.0088

Rz

0.970.920.910.910.960.850.890.860.92

Standard error0.00030.00040.00050.00060.00020.00040.00060.00080.0008

25 50 75

Temperature, C

Figure 1. Effect of temperature on total chlorophyll of green chilli pureed throughselected screens

the coefficient of correlation (R2) were greater than 0.85 in all the cases (Table 4). Thesolid lines in Fig 1 represent values computed using Equation 1.Results indicated that variation in thermal degradation of chlorophyll with the meshsize was not systematic (Table 4). Chlorophyll a was found to be more resistant whilechlorophyll b and total chlorophyll were observed to be more susceptible in pureeobtained using #14 mesh screen.

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310 AHMED, SHIVHARE, AND SINGH

Table 5. Analysis of variance of -La/b values of green chilli puree (n=3)

Temperature, °C0255075

100Mean

Mesh# 1016.4815.5013.7412.6611.8214.04"

LSD (Temperature) = 0.624LSD (Mesh size) == 0.806

Mesh# 1217.3216.3716.2615.0014.8215.95b

Mesh# 1417.8116.6216.1214.7714.8616.04b

Mean17.20"16.16b

15.37C

14.14d

13.83d

Effect of Mesh Size on Chlorophyll

Total chlorophyll and chlorophyll- a content of the puree increased significantly (P <0.05) with increase in mesh size (Tables 1 through 3); where as variation ofchlorophyll- b with mesh size was not significant (P > 0.05). Total chlorophyll contentof green chilli pureed through mesh# 10 and 12 were not significantly different (P >0.05) but were significantly lower (P < 0.05) than that of mesh# 14.

Effect of Temperature on Hunter Color Values

Hunter color L, -a and b values decreased significantly (P<0.05) with increasedtemperature at all mesh sizes used in the study (Table 5). Hunter color values changeas the chlorophyll degrades at elevated temperatures. Transformation of the Huntercolor values to specify the color of food products has been successfully attempted byseveral researchers (Nagle et al., 1979; Govindrajan et al., 1987; Shin and Bhowmik,1994). Following these investigations, various combinations of L, -a and b values, viz.,L, -a, b, -La, Lb, -ab, -Lab, -La/b, -Lb/a and -L/ab were tested to describe the variationof color with process temperature. Standard error and correlation coefficient of themodels were used as the criterion to decide the best fit. Among the variouscombinations tested, -La/b described well the linear variation of Hunter color valueswith temperature. The relationship being,

(La/byfLoao/bo) = kc T +1 (2)

where, kc is the color degradation coefficient, per °C, and subscript o refers to therespective color values at 0° C. Values of the coefficients are reported in Table 6. Thestandard error was less than 0.0001 while the coefficient of correlation was greater than0.92 in all the cases. The variation of dimensionless color values with temperature isshown in Figure 2. The solid lines in Figure 2 represent the color values computedusing Equation 2. It is evident from Figure 2 that Equation 2 adequately described thevariation of color of green chilh' puree with temperature at selected mesh sizes.

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GREEN CHILLI PUREE 311

Table 6. Values of the coefficients of Equation 2

Mesh#101214

-oao/b

o)

l)/(

. Q

15i

io, (

1ra

t

<DD

so

8<D

unt

I

k c-0.0030-0.0015-0.0019

1.1

1 i

0.9

0.8

0.7

0.6C

\9

• 10 mesh* 12 mesh• 14 mesh

— eqn(2)

) 25 50

R'0.990.940.92

X

75

Temperature, C

Standard error0.00010.00010.0001

^ v #

100

Figure 2. Effect of temperature on Hunter iLa/b" value of green chilli pureedthrough selected screens

Effect of Mesh Size on Hunter Color Values

The -a and L values increased with increase in mesh size while the variation of b withmesh size was not systematic. The variation of -La/b with mesh size was significant at0.05 level (Table 5). The difference between the -La/b values corresponding to mesh#12 and 14 were not significant (P > 0.05) but were significantly greater (P < 0.05) thanthat of mesh #10.

Relationship between Color and Chlorophyll

Hunter color L, -a and b values decreased with decrease in chlorophyll content of greenchilli puree. The dependence of the Hunter color values on the chlorophyll content wasdescribed using the linear relationship (Figure 3) as represented by Equation 3:

(La/b) I = k3 (ch/cho) + (3)

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312 AHMED, SHIVHARE, AND SINGH

1.05 -

oa

3 . u - a l

Ooo

3

0.95

0.9

0.85 i

I

0.8

0.75 -

0.7

0.650.6 -f

• 10 mesh

* 12 mesh

• 14 mesh

eqn (3)

0.2 0.4 0.6 0.8 1

Chlorophyll ratio, ch/cho

Figure 3. Relationship between Hunter color value and total chlorophyll content ofgreen chilli puree

Table 7. Values of the coefficients of Equation 3

Mesh# Standard error101214

0.4690.2600.293

0.5090.7160.687

0.9700.8040.854

0.047

0.074

0.070

where k3 and ki are the coefficients. Linear regression of Equation 3 was carried outusing the least-squares technique and the coefficients were determined (Table 7).

Effect of Storage on Hunter Color Values

Hunter color L, -a and b values decreased significantly (P < 0.05) with the duration ofstorage. Variation of -La/b with storage time followed a linear relationship (Figure 4)similar to Equation 2. The standard error was 0.0016 while the coefficient of correlationwas 0.997.

DISCUSSIONS

The present study confirms the results of Tan and Francis (1962), Buckle and Edwards(1970), Schwartz and Lorenzo (1990) and Ihl et al (1998) that chlorophylls degrade

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GREEN CHILLI PUREE 313

0 1 2 3 4 5 6

Storage periods, month

Figure 4. Color degradation of green chilli puree during storage at roomtemperature

during thermal processing. Chlorophyll content of green vegetables is therefore anindicator of the severity of thermal processing. It is now well established that the majorcause of discolouritation in processed green chilli is the conversion of chlorophyll topheophytin and further degradation of pheophytin to pheophorbides and pyrolecompounds. While working on leaf vegetables, Haisman and Clarke (1975) reported thethermal susceptibility of chlorophyll at temperatures above 50-60° C. The data reportedin Table 1 verifies this observation that there was no significant difference betweenchlorophyll content of puree processed at 0 and 25° C. Color degradation was howeversignificant at and above 50° C and the loss was of the order of 50-60% while puree wasprocessed at 100° C for 15 min. Eheart and Gott (1965) reported about 62 and 70%loss of chlorophyll during microwave- and conventional- cooking of broccolirespectively. Aseptic processing of broccoli resulted in reducing the chlorophyll lossesto about 32% however.

The particle size has a pronounced effect on chlorophyll content as well as thecolor of the chilli puree. The fine particles (passed through #14 mesh screen) exhibitedthe higher chlorophyll content and greater -a value as compared to 10 and 12 meshscreen. The higher -a values on Hunter color scale may be attributed to increasedscattering of light in the finely divided puree. In case of chlorophyll, it is probably dueto greater extraction of the green pigment in acetone solvent due to decreased particlesize increased surface area. Mesh# 14 may therefore be recommended for pureeing ofgreen chilli.

Theoretically, thermal resistance of chlorophyll in puree should decrease withdecrease in particle size (increase in mesh size). This behavior was evident in

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314 AHMED, SHIVHARE, AND SINGH

chlorophyll b and total chlorophyll in which the rate of chlorophyll degradation washigher while chillies were pureed through #14 mesh screen. Chlorophyll a exhibitedreverse trend, chlorophyll degradation rate decreased with increase in mesh size, thereason for this trend is not clear however.

The Hunter color values (L, -a and b) of green chilli pureed through 10, 12 and14 mesh screen decreased with temperature. Since the -a value on the Hunter colorscale represent the greenness on the chromaticity dimensions, it may be used todescribe the color change of green chilli puree during thermal processing. However, asthe puree turns brown during thermal processing, L and b values should also beincluded to define the total color change. Therefore, L, -a and b and differentcombinations of these were selected to ascertain their affect on the total color change.These combinations were subjected to linear regression with respect to processtemperature as represented by eq (2). Standard error and correlation coefficient wereused as the basis to select the combination, which described best the variation of colorwith temperature. The analysis revealed that -Lq/b was the most appropriatecombination which described closely the linear variation of color degradation withtemperature for the selected mesh size used in the study.

Good correlation between Hunter color values and chlorophyll content (asmeasured spectrophotometrically) indicated that the Hunter color values may be usedto estimate the loss of chlorophyll in routine quality control purpose in the process line.The chlorophyll extraction is time consuming and thermally decomposed productscause interference in the measurement of chlorophyll concentration (Ehart and Gott,1965).

Results indicated that quality deteriorated during storage of green chilli puree at20-25° C as evidenced by decreased -La/b values (Fig. 4). This observation suggeststhat the product should preferably be stored at near 0° C; the exact level howeverrequire further investigation.

CONCLUSIONS

The effect of temperature and particle size of green chilli puree on total chlorophyll,chlorophyll-a and b and color were studied. Retention of chlorophyll and color found tobe the function of both temperature and screen aperture. Both chlorophyll and colordecreased significantly (P < 0.05) with increased temperature but increased with meshsize. Maximum values of chlorophyll and color were observed while green chilli waspureed through mesh# 14. Screens finer than 14 mesh produced low yield of productindicating their unsuitability to manufacture green chilli puree. Loss in color wasobserved while the puree was stored at room temperature for 6 months.

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(Received June 1, 1999; revised August 8, 1999; accepted Novemberl, 1999)

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