African Journal of Food Science Research Vol. 1 (2), pp. 018-020, October, 2013. Available online at www.internationalscholarsjournals.org © International Scholars Journals Full Length Research Paper Incorporation of turmeric-lime mixture during the preparation of tomato puree Chaitali Dutta, Banani Ray Chowdhury*, Runu Chakraborty and Utpal Raychaudhuri Department of Food Technology and Biochemical Engineering Department, Jadavpur University, Kolkata, India. Accepted 19 September, 2013 New types of tomato puree products were developed by blanching matured tomatoes (Lycopersicon esculentum) for 1 min, 2 min and 3 min individually with or without addition of the mixture of turmeric and lime during the blanching time. Soluble solid content and pH of the puree products were in the range of 11 - 12.6 Brix and 4.32 - 4.68 respectively. Total Hunter Lab colour difference (E) of treated sample following 2 min and 3 min blanching significantly (P < 0.05) higher than corresponding control samples. Again, 2 min- and 3 min-blanched treated samples did not have significantly different (P > 0.05) Lab values (L, brightness; a, redness and b, yellowness). Also, yield stress (measure of flow behaviour) of 2 min- blanched samples (both treated and control) were the maximum among other corresponding puree samples. Thus, 2 min blanching time may be preferred for the preparation of this new type of turmeric-lime treated tomato puree product. Key words: Turmeric-lime, Lycopersicon esculentum, tomato puree. INTRODUCTION Tomato (Lycopersicon esculentum) is cultivated in different countries for its edible red fruit. Lycopene is a phytochemical nutrient element found in many fruits and vegetables, but excessively found in tomato that imparts natural red colour (Holden et al., 1999). Gertner et al. (1997) reported that lycopene is the predominant caro- tenoid in tomatoes. Supplementation of tomato products, containing lycopene, has been shown to lower biomar- kers of oxidative stress and carcinogenesis (Basu and Imrhan, 2006). Many factors affect the lycopene concen- tration in raw tomatoes, such as genetics, soil, and plant nutrition, handling, maturity and seasonal variations. The green raw tomato turns into red when it ripens, as the cis- form of lycopene present in tomato gradually changes into transform of lycopene with the maturity (Xianquan et al., 2005). The redness of tomato depends upon the majority concentration of trans-form. Retention of natural pigment is one of the symbols of livelihood. Thermal treatment is one of the most important methods of preservation of vegetables (Lund, 1975). Thermal processing inactivates pathogens and other *Corresponding author. E-mail: brchowdhury1@rediffmail.com. Tele-Fax: 9133-24146822 microorganisms and also improves the bioavailability of lycopenes since it breaks down the cellulose structure and plant cell. However, unfortunately thermal processing is also responsible for the degradation of red coloured lycopene pigment present in tomatoes. Therefore dis- colouration during thermal processing (blanching) ren- ders tomato puree unmarketable and leads to poor consumption. To compensate the reduction of red colour of tomato puree during its preparation, an attempt is made by add- ing equal proportion of turmeric and lime at the time of blanching of tomatoes. The objective of this paper is to intensify the colour of tomato puree for its better use and consumption. Another objective of this research work is to measure the rheological characteristics of fortified tomato puree as fortification of turmeric-lime mixture might be responsible for the appetizing characteristics of tomato puree such as colour and consistency (rheology). MATERIALS AND METHODS Preparation of tomato puree Matured red coloured fresh tomatoes were purchased from the local market in Kolkata. The tomatoes were sorted and washed with clean water. Then it was blanched in hot water at 100 C for 1, 2, and 3 min, separately. In case of pretreated tomato puree prepara- Dutta et al. 018 Table 1. Soluble solid content of different tomato puree samples. Sample Blanching time 1 min 2 min 3 min Control 11ax* 11.2 ax 11.4 ax Treated 12.6 by** 12 bx 12 ax a – b Different letters corresponds to the samples of a particular blanching time differ significantly (P < 0.05). x – y Different letters corresponds to the same type of samples differ significantly (P < 0.05). Table 2. pH of different tomato puree samples. Sample Blanching time 1 min 2 min 3 min Control 4.32 ax 4.46 ax 4.38 ax Treated 4.82 by 4.57 ax 4.68 ax a – b Different letters corresponds to the samples of a particular blanching time differ significantly (P < 0.05). x – y Different letters corresponds to the same type of samples differ significantly (P < 0.05). 27 Control sample b Treated sample u n it ) 26 L a b c o lo u r b a a L ( H u n te r 25 a a 24 0 1 2 3 4 Blanching time (min) Figure 1. L-value colour parameter of tomato puree samples. a – b Different letters corresponds to the samples of a particular blanching time differ significantly (P < 0.05). tion, 4 mg of each of turmeric and lime were added in the blanching water during blanching. After blanching, the tomatoes were taken out of cooking water and deskined by keeping it under running water. Then it was cut into two halves, with the seeds kept out, and ground the pulp in a Food Processor (Inalsa Appliances Ltd., India). The excess water was discarded by a strainer to obtain tomato puree. The puree was stored in a sterile container at 0 o C. Puree prepared by adding no turmeric and lime was considered to be as control sample. Soluble solid content Soluble solid content of the samples were determined by using a Bellingham-Stanley digital refractometer (Model RFM 110) and were expressed in terms of o Brix. pH pH of both treated and control tomato puree samples were determined by using a pH-meter (Model no. 355, Systronics, India). Determination of colour Visual colour was measured by using a Hunter Lab Colour Measurement System Model Color Flex 45/0 (Hunter Associates Laboratory, Inc., USA) in terms of universally accepted Hunter Lab colour scale. The intensity of the colour of both the treated and control tomato puree samples were expressed in L, a and b (brightness, redness and yellowness, respectively). The instrument (10 observer, Illuminant D-65) was calibrated against a standard white reference tile. Determination of rheology Approximately 17 ml of tomato puree was placed in a concentric cylindrical cup in a rotational Rheometer (Anton Paar, Model Physical MCR 51, Germany). Rheological measurements (shear stress and shear rate) of the samples were done and the yield stress (in Pascal unit) readings were obtained directly from the instrument. Flow model The power law model with or without yield term describes the flow behaviour of viscous food over wide ranges of shear rate (Vitali and Rao, 1984). The rheological model that has been generally used for non-Newtonian fluids, especially puree/paste is the Herschel- Bulkley model, as shown in Equation 1 below: y p = a + b.x ………… (1) a, b and p are regression parameters; p is the flow behaviour index. Statistical analysis All the tests were done in triplicate and the samples were subjected to F-test for significant difference (P < 0.05) using Microsoft Excel software. RESULTS AND DISCUSSIONS Soluble solid content of tomato puree samples were observed to be in the range of 11 – 12.6 (Table 1), which followed the conventional rule of tomato puree prepara- tion (Crandall and Nelson, 1975). pH of the treated and control puree were in the range of 4.32 – 4.68 (Table 2). It was observed from Table 2 that the treatment of lime (alkali) along with turmeric during tomato puree prepara- tion did not change significantly (P < 0.05) the acidic pH of the puree sample compared to the control sample with- out any turmeric-lime treatment. This observation indica- ted non- significant (P < 0.05) change in sourness of the puree product from the control sample and the acceptabi- lity of the treated puree product was comparable to the traditional control product. Colour and rheology of tomato puree are important appetizing properties of tomato puree. It was observed from Figures 1 and 2 that the colour parameters; L-and a- 019 Afr. J. Food Sci. Res. 25 Control sample b b Treated sample u n i t ) 24 L a b c o l o u r b 23 a a ( H u n t e r a a 22 0 1 2 3 4 Blanching time (min) Figure 2. a-value colour parameters of tomato puree samples. a – b Different letters corresponds to the samples of a particular blanching time differ significantly (P < 0.05). 13 Control sample Treated sample b u n it) 12 co lo u r b a a a L a b b ( H u n te r 11 a 10 0 1 2 3 4 Blanching time (min) Figure 3. b-value colour parameter of tomato puree samples. a – b Different letters corresponds to the samples of a particular blanching time differ significantly (P < 0.05). 7 Control sample b D if fe re n c e 6 Treated sample 5 b C o lo u r 4 a a L a b 3 a a T o ta l H u n te r 2 1 0 1 min 2 min 3 min Blanching time (min) Figure 4. Changes in Total Colour Difference of the tomato puree samples. a – b Different letters corresponds to the samples of a particular blanching time differ significantly (P < 0.05). values of both the control and treated samples increased with the time of blanching and a-value of the treated samples were significantly (P < 0.05) higher than the cor- responding control samples. However, b (i.e. yellowness of the samples) of the treated samples decreased with increasing of blanching time and was significantly (P < 0.05) lower than the corresponding control samples (Figure 3). This finding indicated that the treatment with turmeric and lime increased the redness of the tomato puree. In alkaline medium (due to presence of lime), the yellow coloured curcumin pigment of turmeric turns into red and the addition of turmeric-lime mixture in the blanching water of tomato puree preparation minimizes the conversion of trans-form of lycopene (red coloured 56 Control sample 55 Treated sample by by 54 u n it) 53 co lo u r 52 ax L a b 51 (H u n te r 50 49 ay L a /b 48 ax 47 ax 46 0 1 2 3 4 Blanching time (min) Figure 5. Lab value Colour Parameter of tomato puree samples. a – b Different letters corresponds to the samples of a particular blanching time differ significantly (P < 0.05). x – y Different letters corresponds to the same type of samples differ significantly (P < 0.05). tomato pigment) into cis- form of lycopene (yellow coloured pigment in tomato) and minimizes the cause of discolouration. The total colour difference ( E) of the tomato puree a product (as shown in Equation 2) were determined and was shown in Figure 4: where E = ( (a) 2 + (b) 2 + (L) 2 ) 1/2 (2) It was observed from Figure 4 that the total colour difference E of treated sample following 2 min and 3 min blanching significantly (P < 0.05) higher than correspond- ing control samples. The colour differences were measu- red with respect to the colour parameters of 0 min blanc- hed tomatoes (a, b and L values were 21.63, 11.62 and 22.31 Hunter Lab colour unit, respectively). However, as b-value of purees increased with blanc- hing time, combination of Hunter Lab parameters (La/b) was found to be increased exponentially with increasing of blanching time up to 2 min and then decreased when Dutta et al. 020 Table 3. Yield stress values and corresponding Model-fitting parameters of different tomato puree products. Sample Blanching time Regression coefficients Regression (%) Yield stress (Pa) (min) a b p 1 102.27 -0.09 0.92 0.93 102.27 b Control 2 90.25 -18.18 0.29 0.94 90.25 ab 3 86.73 -2.36 0.61 0.91 86.73 a 1 132.94 -12.22 0.43 0.95 132.94 b Treated 2 126.84 -0.41 0.91 0.94 126.84 b 3 112.45 -2.68 0.68 0.93 112.45 a a – b Different letters corresponds to the same type of samples differ significantly (P < 0.05). the tomatoes were blanched for 3 min (Figure 5). La/b has also been expressed to colour change of puree products (Avila and Silva, 1999; Shin and Bhowmick, 1995). 2 min-and 3 min-blanched treated samples showed insignificant (P < 0.05) La/b values. Rheology of tomato puree products can be measured in terms of yield stress (in Pascal unit) and data were fitted by Herschel Bulkley model. The yield stress, regres-sion coefficients and corresponding R (percentage of model fitness) of different tomato puree samples were shown in Table 3. It was observed that the yield stress of both the treated and control samples decreased with blanching time. However, of 2 min-blanched puree sho-wed no significant (P < 0.05) difference of yield stress value from 1 min-blanched tomato puree products. Toma-to puree exhibited yield stress, which decreased with the blanching time, due to the reason that the rapture of tomato skin occurred and the food structure becomes weak resulting in the lowering of yield stress (Steffe, 1992). The flow behaviour index (p) was less than unity. This indicated that the puree behaved its pseudoplastic (shear thinning) nature. Treated samples had significantly (P < 0.05) higher yield stress value than corresponding control sample irrespective of blanching time. Conclusion Degradation of lycopene, that is, deterioration of red colour of tomato in tomato puree preparation can be best compensated by using turmeric and lime mixture during the blanching of tomatoes. 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