Flavor of tomato and tomato products

Abstract

The characteristic sweet‐sour taste of tomato and its overall flavor intensity are due to the following components: reducing sugars (fructose and glucose), free acids (mainly citric’ acid), their ratio, as well as some volatile substances, not identified so far, and the interplay between the above‐mentioned groups of compounds. Of the minerals, potassium (by influencing the free acid content) and phosphate (due to its buffering capacity) indirectly affect the taste. The effect of the free amino acids (glutamic acid, glutamine, gamma‐aminobutyric acid, and aspartic acid) is not unambiguously proven.

The characteristic tomatolike flavor is predominantly determined by volatile substances. Volatile substances develop partly during ripening, partly during the comminution of the ripe fruit, as an effect of the enzymes activated. Volatile substances characterizing fresh tomato flavor are derived mainly from fatty acids and amino acids. Differences between the flavors of different varieties, the less characteristic, weaker flavor of hothouse‐grown tomatoes or artificially ripened ones, are explained by the different quantitative proportions of the volatile substances. So far no key substance playing a decisive role in the flavor of tomato has been detected. Of the approximately 400 volatile compounds so far identified, several were found, however, which have an important role in the flavor of fresh tomato (cis‐3‐hexenal, trans‐2‐hexenal, 2‐isobutylthiazole, hex‐anal, cis‐3‐hexen‐1‐ol, 2E,4E‐decadienal, 6‐methyl‐5‐hepten‐2‐one, etc.).

In the course of tomato processing the flavor substances undergo substantial qualitative and quantitative change, which may or may not be favorable. Depending on the extent of heat treatment and its duration, the reducing sugar and amino acid content decreases while the acid content (by the formation of pyrrolidone carboxylic acid) increases. A part of the volatile substances (mainly those providing “green” smell) evaporates and at the same time—traceable back to the breakdown of sugars and carotenoids—new components, among them those which characterize the “cooked” smell of tomato products, are formed (e.g., dimethyl sulphide, acetaldehyde). Although our knowledge as to the qualitative and quantitative composition of tomato flavor, the factors affecting it, and the effect of certain compounds on it has substantially increased, we are still not in the position to consciously develop the flavor during cultivation and processing. To achieve this further systematic research work is necessary.     

Phase stability of concentrated dairy products

The interactions between the two most important colloids in milk, fat globules and casein micelles, were investigated. Mixtures of oil droplets (as a model for fat globules) and casein micelles were prepared, and their phase behavior was studied. It was found that the oil droplets and the casein micelles phase separate as a result of depletion interaction. The experimentally determined phase boundary is consistent with a prediction by theory that involves no adjustable parameters. Furthermore, it is shown that the kinetics of phase separation can be explained by the differences in viscosity of the samples. The results are of relevance to the behavior of concentrated dairy products such as whipping cream and evaporated milk.     

Antioxidative capacity of tomato products

The antioxidative capacity of methanol/water and hexane extracts of five tomato juices, four canned tomatoes and four tomato pastes was measured using two test systems: with 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS⁺) and with linoleic acid emulsion. In both the ABTS assay and the linoleic acid system, most of the antioxidative capacity of analysed products was from the methanol-water fraction, which contained polyphenols and ascorbic acid. On the basis of the wet weight of the tomato products, tomato pastes had the highest activity towards ABTS⁺ (micromoles of Trolox equivalents per gram) followed by tomato juices, and canned tomatoes. The inhibition of formation of thiobarbituric acid-reactive substances in the linoleic acid emulsion was strongly dependent on antioxidant concentration. The results suggest that tomato products, in addition to fresh tomatoes, may also be important in supplying dietary antioxidant, especially polyphenols and carotenoids.     

Nonenzymatic browning of tomato products

The effects of ascorbic, malic, galacturonic, citric and glutamic acids on nonenzymatic heat-induced browning were studied with special reference to formation of HMF and degradation of reducing sugars occurring in tomato (fructose and glucose).

Galacturonic acid was found to slow down browning reactions, which allows the behaviour of tomato products prepared by the hot-break technique to be differentiated from that of cold-break products with regard to nonenzymatic browning.     

Non-linear viscoelasticity modeling of tomato paste products

This paper deals with the characterization and modeling of the non-linear rheological properties of tomato paste samples manufactured under different conditions (sieve pore size and breaking temperature). With this aim, flow measurements, dynamic linear viscoelastic and linear and non-linear stress relaxation tests have been carried out on the above-mentioned tomato paste samples. Different geometries with smooth and serrated surfaces have been used to optimize the viscous flow measurements and avoid wall-depletion phenomena. The viscous flow properties of tomato paste samples depend on water insoluble solids (WIS) content and particle size, which may be highly influenced by processing conditions. In general, viscosity follows a power-law relationship with tomato paste water insoluble content and particle diameter. A factorable non-linear viscoelasticity model, the Wagner integral equation, predicts the non-linear rheological response of these products under shear fairly well. The time-dependent part of this model is described by a continuous linear relaxation spectrum, calculated from regularization techniques. The use of the Soskey–Winter damping function provides the best predictions of the viscous flow curves.     

Microstructure of highly concentrated tomato suspensions on homogenisation and subsequent shearing

The changes in the microstructure of tomato paste suspensions have been investigated during homogenisation and subsequent shearing in suspensions with similar composition, at three tomato paste concentrations 10, 30 and 40%. The suspensions were characterised by the particle size distribution (PSD), volume fraction (ø), and dynamic rheological properties (G′, G″). All suspensions exhibit a solid-like behaviour with G′ > G″. Micrographs indicate that the process of homogenisation creates a smooth network of finer particles, that is easily disrupted by prolonged shearing, giving rise to the formation of densely packed flocs that become clearly oriented in the direction of the shearing. At high concentrations, these changes in the microstructure on homogenisation and subsequent shearing were better reflected by differences in ø than in G′. The rheological behaviour of the suspensions exhibits a power-law dependence on ø, over a large range of PSD and for 0.05 < ø < 0.55. Finally, an experimental equation, including ø and the size of the coarse particles in the surface-weighted PSD, is found to accurately estimate G′ (R² > 99.3%, p < 0.001).     

Linear viscoelasticity of tomato sauce products: influence of previous tomato paste processing

Tomato paste is used as an ingredient for the manufacture of tomato sauce products. This work deals with the influence that some tomato paste processing variables (finisher screen opening and breaking temperature) and tomato variety exert on the linear viscoelastic properties of tomato sauce products. Four tomato varieties (two commercial varieties, one with a lower content of polygalacturonase enzyme, and one with a low content in pectin methylesterase enzyme) have therefore been used. Dynamic viscoelastic tests and particle size distribution (PSD) measurements have been carried out. From the experimental results obtained, we may conclude that the dependence of the linear viscoelastic properties of tomato sauce on the above-mentioned variables is very complex. Nevertheless, the evolution of the viscoelastic characteristics of these products is mainly related to their mean volume diameter and tomato paste water insoluble solids content (WIS). This solid content is mainly controlled by tomato variety and tomato paste processing conditions.     

番茄及其制品中番茄红素反相高效液相色谱法测定

建立了番茄及其制品中番茄红素高效液相色谱法测定方法.样品经丙酮加石油醚(2:1/V:V)(contain 0.1%BHT)提取,色谱柱采用(4.6×250 mm,i.d,5μm),流动相为甲醇-乙腈-二氯甲烷(体积比25:70:5),柱温为室温,检测波长为473 nm,番茄红素的保留时间为6 min.在3～24 mg/kg添加水平,回收率为87.8 %～99.9%,相对标准偏差为2.3%～5.8%.     

酶制剂在番茄制品加工中的应用

果胶酯酶NovoShape在番茄制品加工中的应用明显提高了番茄丁、去皮整番茄的成型率,并赋予成品饱满、光滑的外观,同时又很好地保持了番茄原有的良好风味和色泽,从而提高了番茄制品的品质。      

Lycopene content of tomatoes and tomato products and their contribution to dietary lycopene

Tomatoes are an integral part of diet world wide. Many population studies have established link between dietary intake of tomatoes, a major source of a carotenoid antioxidant lycopene and reduced risk of chronic diseases. This study evaluates the lycopene contents of various commonly consumed tomato products and estimates its daily intake levels. A fast and simple spectrophotometric method for routine analysis of lycopene was developed and validated against HPLC method. Lycopene content in various tomato products ranged from 42 ppm to 365 ppm. Average daily dietary lycopene intake levels were assessed by administering food frequency questionnaire and were estimated to be 25.2 mg day⁻¹. Fresh tomatoes accounted for 50% of total lycopene intake.     

Behavior of Escherichia coli O157:H7 in tomato and processed tomato products

The survival of E. coli O157:H7 in acid foods for weeks and its prolonged survival in refrigerated acid foods are well documented. This prompted the study to evaluate survival of E. coli O157:H7 in tomato and processed tomato products. The pH of the various products ranged from 4.2 to 4.8 and some products contained preservatives such as vinegar. Samples were separately inoculated with a mixture of four E. coli O157:H7 strains previously isolated from hamburger meat at lower and higher initial inoculum levels, incubated at 4 and 25 °C and assayed for survival at regular intervals. In fresh whole tomato, growth was detected until day 4 and complete elimination was observed at day 7 at room temperature incubation. At refrigeration temperature, counts decreased slightly but survival was noted until day 10. In processed whole tomato, similar patterns were seen at room temperature incubation, but elimination was not observed until day 16. At refrigeration temperatures counts at day 16 were higher than the initial inoculum level. In processed tomato juice, the test strains kept on growing for over 20 days at room temperature storage, whereas at refrigeration temperature, the initial number was more or less maintained until day 23. In processed tomato sauce, incubated at room temperature, a sharp decline in number until day 6 was followed by a sharp increase in number until day 16. At refrigeration temperature, the test strain survived until day 16 with slight decrease in number. The test strains were eliminated in ketchup within 2 days at room temperature, whereas elimination was not achieved until day 8 at refrigeration temperature. In pasta sauce and snack sauce, although elimination was observed at days 11 and 7, respectively, at room temperature incubation, the test strains survived for about 22 days at refrigeration temperature without much decrease in count. Patterns were similar at higher levels of initial inoculation, but it took longer to achieve elimination of the test strains. This study demonstrated that E. coli O157:H7 can survive markedly in various tomato products, and the survival is notably prolonged at refrigeration temperatures.     

Evaluation of tomato textural mechanical properties

The texture of fresh tomatoes (Lycopersicum esculentum Mill., ‘Momotaro’) at three different stage of ripeness (mature green, pink, and red) was intensively evaluated. The double-cycle load plate compression test showed that initial firmness, average firmness, energy absorption, deformation ratio, and relaxation ratio were sensitive textural parameters for identifying the maturity stages. From a puncture test, initial firmness, average firmness, apparent modulus of elasticity, rupture force, toughness, and deformation at the rupture point were sensitive to the maturity stages. The mature unripe tomato deformed linearly as a function of force; hence, the firmness was constant. However, the fully ripe tomato firmness increased as a function of applied force. The fruit strain increased during ripening, and it was independent of fruit size. The unripe tomato was more elastic than the ripe one. The peel at the mature green stage contributed approximately 70% of the firmness of the fruit and approximately 90% at the pink stage and red stage. The rupture force by the puncture test (traditionally, peak force) was correlated well with other textural parameters, which indicated that it could be used as a firmness representative parameter, as has been used by many researchers. The degree of elasticity was a better indicator for elasticity than the relaxation ratio.     

Enzyme inactivation of tomato juice by ohmic heating and its effects on physico‐chemical characteristics of concentrated tomato paste

Fresh juice of fully ripe tomato was subjected to ohmic heat (OH) treatment (90°C for 1 min) and the effectiveness of treatment was compared with conventional hot break (CT) treatment (90°C for 5 min). PG (Polygalacturonase) and PME (Pectin methyl esterase) enzyme inactivation achieved by the OH (1 min.) was similar as compared to CT of 5 min. During the kinetic analysis it was observed that the inactivation of PME & PG enzyme and degradation of ascorbic acid followed first order trend in ohmic as well as conventional treatment of tomato juice, however total color change (DE) was found to follow least‐squares non‐linear parameter algorithm behavior. Thermal treatments leads to the increased release of phyto‐chemicals from the matrix which results in a significant (p<0.01) increase in lycopene content during the early phases of the treatments. The Paste (28±0.5 °Brix) obtained after pre‐treatment was analyzed for lycopene, ascorbic acid content and apparent viscosity and color. OH Paste was found more viscous than CT treatment with maximum viscosity of 2.33×103 mPa‐s. The color of OH treated paste was bright red as compared to CT treatment, however the lycopene and ascorbic acid content of paste were found similar in OH and CT. Based on results of present study it is concluded that the ohmic treatment may be applied as an efficient alternative to the conventional method of enzyme inactivation in tomato juice.     

Evaluation of equations to predict dry matter intake of dairy heifers

Daily pen dry matter intakes (DMI, n = 9,275) were collected over a 28-mo period at the University of Wisconsin's Integrated Dairy Research Facility. Heifers were housed in pens containing 8 Holstein or Holstein × Jersey crossbred heifers/pen. Heifer diets were formulated to energy and protein requirement twice monthly, with feed intake, dietary nutrient density, and ambient temperature recorded daily. Heifers were weighed at 60-d intervals, and mean pen body weights (BW) were estimated for each day between the weigh dates using the interval average daily gain as a regression coefficient. Prediction of heifer DMI was evaluated using the equations of NRC (2001), Quigley et al. (1986), or alternative random effects mixed models or nonlinear exponential models. The effects of breed, BW, temperature and neutral detergent fiber deviation (NDFdv) were considered as independent variables. Holstein and crossbred heifer DMI was predicted with reasonable precision [standard error (SE) < 0.86 kg/d], by the NRC (2001) or Quigley et al. (1986) equations, but heifer DMI was over- or underpredicted for heifers >500 kg, respectively. Improved heifer DMI prediction equations were achieved with exponential models. For Holsteins (SE = 0.71 kg/d), the prediction equation was: DMI (kg/d) = 15.79 × [1 - e^{(−0.00210 × BW)}] − 0.0820 × NDFdv, where NDFdv = (dietary neutral detergent fiber as a % of dry matter) - {22.07 + [0.08714 × BW] - [0.00007383 × (BW)²]}. For crossbred heifers (SE = 0.60 kg/d), the prediction equation was: DMI (kg/d) = 13.48 × [1 - e^{(−0.00271 × BW)}] - 0.0824 × NDFdv where NDFdv = (dietary neutral detergent fiber as a % of dry matter) - {23.11 + [0.07968 × BW] - [0.00006252 × (BW)²]}. Alternative exponential DMI model equations when dietary neutral detergent fiber is unknown were also developed. The Holstein DMI equation (SE = 0.73 kg/d) was: DMI (kg/d) = 15.36 × [1 - e^{(−0.00220 × BW)}], and the crossbred DMI equation (SE = 0.81 kg/d) was: DMI (kg/d) = 12.91 × [1 - e^{(−0.00295 × BW)}].     

Dielectric spectroscopy of osmotic solutions and osmotically dehydrated tomato products

Complex permittivity is the physical property that describes the interaction between matter and an electromagnetic field. This property is related to the structural and physico-chemical properties such as water and soluble solids content or water activity of the material.

The complex permittivity of different aqueous solutions, fresh and osmotically dehydrated cherry tomatoes was measured and related to the products’ composition. Results showed that fruits osmotically dehydrated with sucrose solutions reached the lowest loss factors but the maximum penetration depth (D_p). On the other hand, fruits immersed in binary salt solutions showed the inverse tendency. For products impregnated with ternary solutions an intermediate behaviour was observed. Calcium lactate addition had no significant effects on complex permittivity at 2.45 GHz, but its presence increased the effective loss factor at low frequency.

The dielectric properties of fruits and vegetables can be modified by controlling osmotic process variables (time, temperature, pressure and osmotic solution composition) in order to improve their further drying with microwaves.     

Evaluation of heat and oxidative damage during storage of processed tomato products. I. Study of heat damage indices

The evolution of heat damage during storage of tomato pulp, puree and paste was studied by accelerated aging tests. Heat damage indices—5‐hydroxymethyl‐2‐furfural (HMF), furosine and colour changes (ΔE)—were evaluated for tomato products stored at 30, 40 and 50 °C for up to 90 days. Furosine and ΔE values increased following pseudo‐zero‐order kinetics, and the higher the solid content of the products, the higher were the rate constant values. HMF formation followed pseudo‐first‐order kinetics in tomato pulp and pseudo‐zero‐order kinetics in puree and paste samples. Data show that heat damage reactions in tomato products proceed even at room temperature, and the kinetic model provided can be used to predict changes occurring during shelf‐life. © 2002 Society of Chemical Industry     

Evaluation of heat and oxidative damage during storage of processed tomato products. II. Study of oxidative damage indices

Tomato products (pulp, puree and paste) submitted to accelerated aging (30, 40 and 50 °C for 3 months) were studied to evaluate variations in the kinetics of the degradation of antioxidants and antioxidant activity. The carotenoids lycopene and β‐carotene, ascorbic acid, rutin and total phenolics were analysed. The antioxidant activity was measured using (a) the xanthine oxidase (XOD)/xanthine system, which generates superoxide radicals and hydrogen peroxide, and (b) the linoleic acid/CuSO₄ system, which promotes lipid peroxidation. The ascorbic acid content decreased even at 30 °C, following pseudo‐first‐order kinetics, with an activation energy of 105 200 J mol^?1 for tomato pulp and 23 600 J mol^?1 for tomato paste. The lower the initial ascorbic acid content, the higher was the degradation rate. Variations in phenolic compounds occurred at 40 °C and higher, following pseudo‐zero order kinetics. The antioxidant activity of the hydrophilic fraction of the tomato products depended on both antioxidant degradation and the Maillard reaction and could not be described by a kinetic model. The β‐carotene content decreased even at 30 °C, whereas the lycopene content was stable in all samples. The antioxidant activity of the lipophilic fraction of the tomato products decreased following pseudo‐first order kinetics, with an activation energy of 22 200 J mol^?1 for tomato pulp and 20 200 J mol^?1 for tomato paste. It is concluded that significant ‘oxidative damage’ can occur in tomato products during their commercial shelf‐life. Copyright © 2003 Society of Chemical Industry     

Technical note: Effect of low pH preservation on the colour and consistency of tomato juice

The changes in colour and consistency are reported for tomato juice produced by low pH preservation and stored under ambient conditions. The juice preserved under acid conditions showed higher consistency, probably due to the higher concentration of pectin and the presence of low methoxyl pectin. The furfural and hydroxymethyl-furfural which were detected in the juice indicated that darkening of the juice colour was due to non-enzymic browning involving both ascorbic acid and sugars (hexoses). Although the retention of ascorbic acid was higher under low pH conditions, it led to a significant darkening of the juice colour due to non-enzymic browning involving mainly ascorbic acid.     

Investigation of colour changes of some tomato products during frozen storage

The colour changes of frozen tomato pulp were investigated under different conditions of frozen storage (?25°C; in open bags with presence of O₂ and in artificial light or darkness; in closed bags also in artificial light or darkness). In addition the antioxidative effect of tomato seeds and spices (sage, thyme, rosemary, oregano, majoram) was studied. The colour change of tomato pulp was determined with instrumental colour measurement, the carotenoid pigments loss was measured with UV/VIS spectrophotometry. It was found that exposure to light and oxygen accelerated the colour loss and oppositely packaging and storage in darkness had a colour saving effect. The ground tomato seeds (5%) could stabilize the carotenoid pigments after longer time frozen storage (min. 10 weeks). The commercial spices (0.2%), mainly rosemary and marjoram significantly reduced the pigment degradation. The tomato seeds and the spices did not change significantly the taste of tomato pulp.