Color and Lycopene Content of Tomato Puree Affected by Electroplasmolysis

Abstract

Tomato puree was produced using three different breaking methods, namely heating by steam injection, by electroplasmolysis, and combination of both steam injection and electroplasmolysis. In electroplasmolysis, the tomato pulp was treated at the electric field strength of 68 V/cm for 1.5 seconds. L, a, b, a/b, tomato color index, total color difference, chroma difference, hue angle, and lycopene content of purees were measured. Puree samples breaked by electroplasmolysis had better color values and the highest lycopene content. The a/b, tomato color index, and lycopene content of these samples were as 2.00; 49.94 and 273.9 mg/kg, respectively.

Keywords:

• Tomato puree
• Electroplasmolysis
• Color
• Lycopene

INTRODUCTION

Concentrated tomato products, including tomato puree, were one of the most important product groups in fruit and vegetable processing industry in Turkey. In conventional tomato puree production, tomatoes were cleaned, sorted, and chopped. Then, the chopped tomatoes were pulped. The pulp was concentrated and then packaged.

One of the important quality parameters of tomato puree was color.[1] Some parameters including “a/b,” TCI, and Hue angle were used to evaluate the color quality. Lycopene, the predominant carotenoid pigment of tomato contributes to its characteristic red color. It functions as an antioxidant and helps in lowering DNA damage. These properties have accelerated research activities to improve processing factors that lead to maintain the nutritional as well as sensory quality of tomato product. Nutritional and sensory quality of tomato products are primarily affected by fruit cultivator, growing conditions, and processing parameters.[2,3] Willcox et al.[4] reported that 78.7% of total color pigments were lycopene.

Electroplasmolysis is the process which is aimed to improve the yield in fruit juice and pulp production by destroying the cell wall. Many researchers reported that the electroplasmolysis increased the yield in juice and pulp production.[5,6] Bologa et al.[7] reported that the electroplasmolysis accelerated the process and improved quality at the electrical current of 0.1-0.2 A/cm² in tomato paste production. Shcheglov et al.[8] reported that the yield was increased up to 12% by using electroplasmolysis in tomato paste production. Moreover, some improvement in quality was also obtained by electroplasmolysis. McLellan et al.[9] reported that the application of electroplasmolysis improved the color of apple juice as compared to that of enzyme application and mechanical extraction. However, no published data were found on the effects of electroplasmolysis treatment on the color of tomato paste and puree. The goal of this study was to evaluate the effects of electroplasmolysis on color quality and lycopene content of tomato puree.

MATERIAL AND METHODS

Tomato Puree Production

Rio Grande variety tomato was used to produce tomato puree. The tomatoes were washed and chopped. The chopped tomato was heated by three different methods: (i) by injection of steam (S), (ii) applying electroplasmolysis (E), and (iii) combination of steam and electroplasmolysis (SE). The heated chopped tomato was then pulped by using double stage pulper and concentrated to 16.8 ± 0.8% of soluble solids content. The tomato puree was packaged in glass jar and pasteurized at 100°C for 35 min. The color and lycopene analyses were done in raw material and pasteurized purees. The breaking temperatures, or preheating temperatures after chopping were measured for S, SE, and E procedures as 89, 93, and 32°C, respectively.

Physical and Chemical Analysis

Total solid content was determined by vacuum oven method.[10] The water soluble solid content was determined by a refractometer (RFM 330 Bellingham+Stanley Limited, UK). The color values of L, a, and b were determined by using Minolta (model 508 D, Germany) color-meter. Tomato color index (TCI),[11] chroma difference (ΔC), total color difference (ΔE), and Hue angle[12] were determined by using L, a, and b values as follows:

(1)

(2)

(3)

(4)

Lycopene content was determined spectrophotometrically.[13] 0.3 g of corn starch and 20 ml of acetone (Riedel de Haen, 24201, Germany) were added to 0.3 g of puree (w) in a centrifuge tube and vortexed for 40 s. After shaking for 20 min., it was vortexed again for 30 s. The sample was centrifuged at 3000 rpm for 3 min. Absorbance of supernatant was determined at 503 nm (A₅₀₃) by using Varian Cary 50 Scan (Australia) model spectrophotometer. Lycopene content of the puree sample was determined as follows:[13]

(5)

Statistical Analysis

Statistical significance was carried out using a computer program (SPSS 11.01, SPSS Inc.)[14] by analysis of variance and means were calculated and separated using the Duncan's test when significant (P < 0.05). The number of replications was 6.

RESULTS AND DISCUSSION

The preheating temperatures during different breaking methods and solids contents of samples were given in Table 1. The temperature in electroplasmolysis method was quite lower than that of the steam used processes. Although it was not significance (p < 0.05), the temperature in combination method (SE) was found higher than that of steam preheating (S). It might be caused by electrical resistance heating. Increasing breaking temperature negatively affected tomato puree color.

Table 1 Breaking temperature and total and soluble solids contents of the puree samples produced by different preheating methods

	Raw material	S	SE	E
Breaking temperature (°C)	—	87.0 ^a	90.5 ^a	26.5 ^b
Total solids content (%)	—	16.66 ^a	16.37 ^a	17.30 ^b
Soluble solids content (%)	4.97 ^a	16.30 ^b	16.02 ^b	16.45 ^b
^a,b,cFor the same parameter, mean values followed by the same letter are not different (p < 0.05). S: Samples heated by steam injection; SE: Samples heated by steam injection and electroplasmolysis; E: Samples heated by electroplasmolysis.

Color values of raw material and puree samples were given in Table 2. As shown in Table 2, “a” values of the samples S and SE were higher than those of sample E. It may be caused by the caramelization of the sugars depends on the high temperatures of steam application during breaking procedure.[15] Porretta and Poli[16] reported that “a” values of the cold and hot breaked purees were 31.18 and 27.43, respectively. Unlike “a” value, “b” value decreases with decrease in breaking temperature. Luh et al.[15] reported that “b” value of tomato pastes having breaking temperatures of 99°C and 27°C were 12.9 and 11.5, respectively.

Table 2 “L,” “a,” “b,” and “a/b” values of raw material and puree samples

	Raw material	S	SE	E
L	34.77 ^a	35.47 ^b	35.45 ^b	34.68 ^a
a	17.48 ^a	22.50 ^b	22.19 ^b	23.52 ^c
b	8.68 ^a	13.31 ^b	12.96 ^b	11.73 ^c
a/b	2.04 ^a	1.69 ^b	1.71 ^c	2.00 ^a
^a,b,cFor the same parameter, mean values followed by the same letter are not different (p < 0.05). S: Samples heated by steam injection; SE: Samples heated by steam injection and electroplasmolysis; E: Samples heated by electroplasmolysis.

The value of “a/b” is the most widely used reference parameter for color quality in commercial practice and scientific publications in concentrated tomato products.[17,18] The puree samples of E had significantly higher “a/b” value than that of S and SE samples (p < 0.05) (Table 2), because of the low temperature during breaking process (Table 1). Although there were no significant differences (p < 0.05) in “a” and “a/b” values of S and SE, the procedure of SE resulted in higher “a” and “a/b” values. The reason of this case might be electrical process. The TCI value of the samples of E had significantly higher than that of the S and SE (p < 0.05). This result agreed with “a/b” values. High linear correlation was observed between TCI and “a/b” (Figure 1).

Figure 1 The relationship between TCI and “a/b.”

ΔC is the parameter of difference in chroma and ΔE is the variation in total color compared to the raw material. The lowest ΔC or ΔE was observed in the sample of SE. However, this result was not in line with the values of “a/b”, TCI, and lycopene contents. It is thought that ΔC and ΔE were insufficient to explain the color changes. Because, as shown in the equations of ΔC and ΔE, the square of the color parameters (a, b, L) was calculated. Therefore, it was thought that the values of ΔC and ΔE do not represent the color changes of purees obtained by different preheating methods. The Hue angle characterizes the color difference. Hue angle values also indicate the degree of browning. In other words increasing yellowness and/or decreasing greenness result in high Hue angles.[12] The lowest Hue angle was observed for the puree produced by the method E (Table 3). The Hue angle values of the samples showed that the puree produced by the procedure E resembled the raw material the most. The Hue angles were not significantly different for the samples S and SE (p < 0.05). But it has to be noted that the changes in color values were probably not only due to browning, but could also be attributed to difference in water content of the puree samples (Table 1).

Table 3 Some color parameters of fresh tomato and tomato purees

	Raw material	S	SE	E
TCI	51.61 ^a	46.79 ^b	47.07 ^b	49.94 ^c
ΔC	—	7.01 ^a	6.48 ^a	6.88 ^a
ΔE	—	7.09 ^a	6.53 ^a	6.93 ^a
Hue angle	—	30.75 ^a	30.32 ^a	26.48 ^b
^a,b,cFor the same parameter, mean values followed by the same letter are not different (p < 0.05).

The relationship between lycopene content and “a/b” was given in Figure 2. Since the lycopene is the main color pigment in tomato and tomato based products, a linear correlation (R² = 0.9997) existed between the lycopene content and “a/b.” Lycopene is a heat sensitive pigment. Akanbi and Oludemi[3] reported that the tomato pulp prior to heating had a bright red color that changed to dark red after heat processing. This change in color intensity may be due to the isomerization of lycopene from the usually all trans form to cis isomers. Because of the breaking temperature of E is quite lower than that of S and SE, the lycopene degradation is low in the puree obtained by breaking procedure E, in our study. There were no significant differences (p < 0.05) between lycopene content of S and SE. However, SE had higher amount of lycopene than that of S. The reason may be electrical process. Mc Lellan et al.[9] reported that browner apple juice was obtained by thermal treatment compared to electroplasmolysis. These results may indicate that the electroplasmolysis inactivated or inhibited expression of the browning enzyme polyphenoloxidase.

Figure 2 “a/b” value and lycopene content of puree samples. (▪): a/b, (○): Lycopene.

Lycopene content of tomato was reported in the range of 90–190 mg/kg fresh weight.[19] Tonucci et al.[20] reported that the lycopene contents of tomato juice, puree, and paste were 107.7, 166.7, and 554.5 mg/kg, respectively. The lycopene contents of tomato purees were 186.0, 186.9, and 273.9 mg/kg for S, SE, and E, respectively (Figure 2). Similar results were found with the literature for the puree samples produced by steam preheating methods. However, the lycopene content of E was higher than that of conventional preheating methods. Although the main effective factor on lycopene content was temperature, Akanbi and Oludemi reported that the lycopene may be associated with the fiber and the insoluble fraction in tomato fruit. The carotenoid-lycopene (red pigment) in tomato is to a great extent linked in the prevention of the onset of cancer. Many of the protective benefits of lycopene were suggested to be a result of its ability to protect against oxidative damage and its free radical scavenging capacity.[3] Bioavailability of lycopene from tomato paste is greater than that of fresh tomatoes.[21] More than 80% of dietary lycopene consumed in the United States comes from tomato products.[4]

CONCLUSION

The results showed that the color quality characteristics of tomato puree differs according to the preheating method used. The color is one of the most important quality parameters of tomato puree. Overall color values of puree samples breaked by electroplasmolysis (E) had better than those of methods in which steam was used. Statistical analysis showed that the effects of electroplasmolysis on “a/b,” TCI, Hue angle and lycopene were significant (P < 0.05). Higher breaking temperature decreases the values of “a/b,” TCI, and lycopene content of tomato puree. Because of the lower breaking temperature by electroplasmolysis application, the color parameters “a/b” and TCI, and lycopene content are higher than that of the application of steam and combination of steam and electroplasmolysis. The “a/b,” TCI, and lycopene content of E samples were as 2.00; 49.94, and 273.9 mg/kg, respectively. On the other hand, although the breaking temperature of SE was higher than that of S, the “a/b,” TCI and lycopene content of SE were higher than those of S. This may be explained by increases in permeability of cell membrane by electroplasmolysis and higher amount of extraction of color pigments. Therefore, it can be concluded that electroplasmolysis may be applied during preheating of tomato puree production due to improved color and lycopene content.

NOMENCLATURE

a	=	Redness-yellowness in tristimulus color scale
aref	=	a value of raw material
A530	=	Absorbance value at 530 nm
B	=	Greeness-blueness in tristimulus color scale
bref	=	b value of raw material
E	=	Sample heated by electrical application at breaking process
L	=	Lightness in tristimulus color scale
Lref	=	L value of raw material
S	=	Sample heated by steam injection at breaking process
SE	=	Sample heated by both steam injection and electrical application at breaking process
TCI	=	Tomato Color Index
W	=	Weigth of sample, g
ΔC	=	Chroma difference
ΔE	=	Total color difference

ACKNOWLEDGMENTS

This project was supported by Research Fund of Celal Bayar University, Manisa, Turkey.

Notes

14. SPSS Statistical Package,. SPSS for Windows, Ver. 11.0.1, Chicago, SPSS Inc. 2001.