Essay: Adding tomato and asparagus powders in processed cheese

Abstract: Rheological, chemical and sensory properties of processed cheese fortified with different levels of tomato (1%, 2% and 4% wt/wt) and asparagus (0.5%, 1% and 1.5% wt/wt) powders were analyzed. Both of the powders decreased the pH and lipolysis indexes and increased proteolysis extent of processed cheese. Phenolic and lycopene content and antioxidant activity decreased during storage of 3 month. The frequency sweep test and temperature sweep test showed that all samples had Gʹ > Gʺ, indicating that, solid-type structures were present. Tomato powder decreased the solid like behavior of processed cheeses. However, asparagus powder led to a more elastic structure in the processed cheese. Control sample and processed cheese with low level of tomato powder had highest scores of flavor, color and total acceptance and also processed cheese samples containing asparagus powder were significantly (P < 0.05) more rigid and less spreadable compared with control samples which corresponded to results obtained by dynamic oscillation rheometry. Results showed that low levels of tomato and asparagus powders could be used for fortification of processed cheese.
Keywords: processed cheese, tomato, asparagus, frequency sweep, Temperature sweep
INTRODUCTION
Processed cheeses are stable oil-in-water emulsions made by heating a mixture of cheeses, edible oils/fats and other dairy and nondairy ingredients in the presence of emulsifying salts1. They are being used increasingly because of their cost-effectiveness, attributed to the simplicity in their manufacture and the replacement of selected milk ingredients by cheaper vegetable products. However, processed cheeses are low in functional and bioactive ingredients which should be enhanced by the addition of some valuable ingredients2.
Asparagus contains flavonoids (mainly rutin) and other phenolic compounds, which possess strong antioxidant properties. With abundant cellulose and phytochemicals present, asparagus may be a promising source of new value-added compounds, including phenols, flavonoids, hydroxycinnamic acids, as well as a dietary fiber3.
Tomato is also a good source of carotenes and phenolic compounds and provides a significant proportion of total antioxidants in the diet. Lycopene is the most important carotenoid in tomato and is responsible for the color of tomato fruits and their derived products. The seeds and skin of tomato are rich sources of minerals4.
There are several researches about fortification of different kind of cheeses with functional ingredients such as fish oil emulsion5, spice and herb extracts6 (cinnamon stick, oregano, clove, pomegranate peel, and grape seed), cranberry fruit extract7, peppermint extract8 or replacement of milk fat of cheese with hazelnut oils9 and vegetable oils10.
No attempt has been made so far to study qualitative properties of processed cheese containing tomato powder (PCT) and processed cheese containing asparagus powder (PCA). The aim of this study is improving the health attributes of processed cheese and investigating the effect of adding tomato and asparagus powders on the rheological and physicochemical properties of processed cheese.
MATERIALS AND METHODS
Material: Processed cheese samples containing tomato powder, were prepared in a Stephan Vacuum Vertical Mixer (Stephan Machinery Corp., Mundelein, Ill., U.S.A.) by melting a mix of feta cheese, butter (3%), water (5%), emulsifier salts (2%) (Tri sodium citrate E331 (1%) and di sodium phosphate E339 (1%); Sigma-Aldrich Chemie Gmbh, Munich, Germany) and tomato powder (1%, 2% and 4% wt/wt) at 85°C for 4 min at 1500 rpm. The molten cheese samples were then hot-filled into rectangular molds, cooled to 4 ◦C, and stored at that temperature.
Processed cheese samples containing asparagus powder were prepared in the same way by adding asparagus powder (0.5%, 1% and 1.5% wt/wt). Tomato and asparagus powders were prepared by grinding of dried tomato and asparagus by a grinder (Pars Khazar Grinder Chili, Iran). Qualitative analysis including measurement of dry matter content, fat content, pH, lipolysis, proteolysis, water-soluble phenolic content (WSPC), lycopene content and antioxidant activity (AOA) were carried out on days of (1, 20, 40, 60 and 90). Rheological measurements were analyzed after 20 days of storage.
Chemical Analysis: Dry matter content was determined by drying at 102 °C to a constant weight according to the IDF, 198211. Fat content was determined by the Gerber method described by Marshal12. The pH of the samples was estimated at room temperature with the direct insertion of a glass electrode into the sample, using a previously standardized digital pH meter (PHC3031-9, Radiometer Analytical, Copenhagen, Denmark) according to the method described by Marshal12. Protein concentration was determined by the Kjeldahl method13.
Water-Soluble Phenolic Content: The water-soluble phenolic content was measured via the Folin- Ciocalteu procedure, according to an assay modified by Shetty et al.15. Homogenized water extract, was prepared by the method of Apostolidis et al.16, and 1 ml was transferred into a test tube and mixed with 1 ml of 95 % ethanol and 5 ml of distilled water. To each sample, 0.5 ml of 50 % (V/V) Folin- Ciocalteu’s reagent was added and mixed. After 5 min, 1 ml of 5 % Na2CO3 was added to the reaction mixture and allowed to stand for 60 min. The absorbance was read at 725 nm in a spectrophotometer (Jenway, Model 6305, UV/Vis., England). The absorbance values were converted to water-soluble phenolics and were expressed in mg gallic acid equivalents per gram of dry matter of sample. Standard curves were established using various concentrations of gallic acid in water.
Antioxidant Activity (AOA) by DPPH Radical Scavenging Assay: The capacity to scavenge the 2,2-diphenyl-1- picrylhydrazyl (DPPH) free radical was monitored according to the method reported by Apostolidis et al.16. To 3 ml of 60 μM DPPH in ethanol, 250 μl of each homogenized water extract was added, the decrease in absorbance was monitored at 517 nm in a spectrophotometer (Jenway, Model 6305, UV/Vis., England). DPPH scavenging effect was calculated as percentage of DPPH discoloration using the equation: %scavenging effect = [(ADPPH−AS)/ADPPH] ×100, where AS is the absorbance of the solution when the sample extract has been added at a particular level and ADPPH is the absorbance of the DPPH solution.
Lycopene: Lycopene content of PCT samples was measured by the method of Javanmard17 with slight modifications.
Lipolysis and Proteolysis Assessment: Lipolysis index was determined by the method of Nonez et al.14. Acid Degree Value (ADV) can measure the rancidity of cheese by de-emulsification and separation of free fat, followed by titration of free fatty acid by alcoholic KOH in a weighed portion of fat.
The pH 4.6 soluble nitrogen (SN) of cheese samples was obtained modifying the procedure of Kuchroo and Fox18, as described by Sousa and McSweeney19. pH 4.6-insoluble fraction of the cheese was assessed using a Urea-polyacrylamide gel electrophoresis (PAGE) which performed by Protean II XI vertical slab gel unit (Bio-Rad Laboratories Ltd., Watford, UK) according to the method of Shalabi and Fox20. Gels were stained directly with Coomassie Brillant Blue G250, as described by Blakesley and Boezi21.
Rheological Measurements: The dynamic rheological properties of the processed cheeses were measured after 2 weeks of storage at 4 °C, using a controlled stress rheometer (Anton Paar, MCR301, Austria). Cheese samples were carefully cut to 25 mm diameter discs using a cylindrical cutter. The measurements were carried out at 25°C using a cone and plate system. A strain sweep (0. 1-100%) at 25°C and frequency of 1 Hz were used to determine the limits of linear viscoelastic behavior of the model processed cheese. A frequency sweep test was performed at 5 °C and a strain amplitude of 0.2% with the frequency varied from 1 to 100 Hz. A temperature sweep test was performed at a constant frequency of 10 Hz and a constant strain amplitude of 1%, with the temperature varying from 25 to 80 °C at 5 °C /min. The storage modulus (Gʹ), the loss modulus (Gʺ) and the loss factor (tan d) were determined. All the rheological measurements were made at least in triplicate and the average reported.
Sensory Analysis: Processed cheese samples were evaluated by a panel of 15 selected assessors according to the method described by Macku22. Samples were coded and served at the room temperature. Five-point hedonic scale was used for assessment of cheese appearance (color), rigidity, spreadability, flavor and total acceptance.
Data Analysis: All the formulations were prepared in triplicate. The fortified data were analyzed using spss statistical software (IBM spss statistics 22) by one-way analysis of variance. The level of significance (p) was set at 0.05. Duncan`s HST test at 5% significance level was used as the multiple comparison test on all main effect means.
RESULTS AND DISCUSSION
Chemical Analysis: processed cheese had protein content of 12%, fat content of 23% and moisture content of 56.67%. Samples did not show any significant differences in, protein, fat and moisture and these properties did not change significantly (P > 0.05) during storage (results are not shown). This could be because of low levels of powders added to the samples and did not make significant difference in these properties. In the case of pH, there were significant difference between control and fortified cheeses. Bin Shan et al.6 reported that herbal extracts with high phenolic contents in cheese samples, prevented the increasing of pH, during storage. Results showed that pH has been decreased by increasing asparagus and tomato level in cheese formulation and it was decreased during storage. However, pH changes in cheeses fortified with tomato powder were as control sample during storage (Tables 1 and 2).
Lycopene contents of samples increased with the increasing of tomato powder. Lycopene content decreased during storage which was severe at the beginning of storage, then followed by slow lycopene degradation (Table 3). Lycopene is a carotenoid found in fruits and vegetables which is responsible for the redness of tomato and tomato based products. Lycopene can act as an antioxidant and has many positive effects on prevention of many diseases25. Therefore, cheeses fortified with tomato powders can be as functional and healthier food products in our daily diet.
Lycopene has been added as a functional ingredient in several kinds of cheeses such as Queso Blanco cheese supplemented with powdered microcapsules of tomato extracts26 and other foods such as extruded snacks fortified with lycopene27.
Generally, lycopene level of fortified cheese were decreased by 63% during 90 days of storage (Table 3). It shows that lycopene is preserved in cheese during storage and consumers can get health benefits from their consumption.
Total phenolic compound of tomato is 2.68 mg/ g of DW25 and total phenolics of asparagus is 5 mg catechin equivalent/ g DW28. Also, medium chain peptides produced by rennet, may act as phenolic compound. WSPC of fortified cheeses were higher than those of control at first days of storage. However, WSPC of fortified cheeses decreased during storage. On the other hand, WSPC of control sample did not change significantly (P > 0.05) during storage (Tables 4 and 5). Decrease of WSPC of fortified cheeses during storage may be due to the absorption of phenolic compounds of tomato and asparagus by some peptides (produced by rennet and starter during storage) which neutralizes and deactivates the phenolic compounds presented in cheese8. Fadavi and Beglaryan8, reported that peppermint showed a lower WSPC in UF feta cheese than expected, and rennet had a positive effect on WSPC in UF feta cheese. It has been explained that, this paradox may be due to the absorption of phenolic compounds of peppermint by some peptides. The retention of phenolic compounds in cheese is related to the interactions between phenolic compounds and proteins, which can be induced by hydrogen bonding, hydrophobic, ionic, and covalent interactions. Besides, these interactions can be affected by several factors such as pH, temperature, phenolic structure, molecular weight, and amino acids compositions in that medium29. Apostolidis et al.16 reported that herbal enriched cheese samples, did not have significantly (P > 0.05) higher WSPC, when compared with plain cheese. Also heat treatment of fortified samples could influence the WSPC.
There were no significant difference between AOA levels of PCT samples and control samples at first days of storage. However, AOA level of control sample was significantly (P < 0.05) higher than PCA samples. Generally, AOA levels of samples decreased during storage (Tables 6 and 7). This might be due to interactions occurred between phenolic molecules of tomato and asparagus and proteins, especially whey proteins with active group (-SH). These reactions reduce the influence of antioxidant compounds. So many enzymes such as tyrosinase which can be produced by starters, could convert polyphenols especially luteolin, the important flavones having AOA, to highly active quinines. Quinones can react with amino and sulfhydryl groups of proteins and enzymes as well as with anthocyanins. These secondary reactions can change the physical, chemical, and nutritional characteristics of proteins and may also affect sensory properties of food products30. On the other hand, after 1 month of storage, decreasing in AOA levels in control sample, were more than those of fortified samples and levels of AOA in fortified samples were higher than control sample (Tables 6 and 7). Apostolidis et al.16 reported that the antioxidant activities of the herbal-enriched cheeses were significantly (P < 0.05) higher when compared to the nonenriched samples. Fadavi and Beglaryan8 also, reported that although peppermint has a rich source of antioxidant compounds, it did not have significant effect on AOA of UF cheese. Khalifa and Wahdan7, reported that the addition of dehydrated cranberry fruit extract improved cheeses stability for oxidation. Cranberry fruit extract (containing phenolic compounds) has the ability to act as an antioxidant7. Khalifa and Wahdan7, also reported that cheese samples containing dehydrated cranberry fruit extract had lower acid value, lower proteolysis and lower lipolysis than control. These effects could be due to lower total viable counts, moisture content and titratable acidity7.
Fortified samples had lower lipolysis than control sample (Tables 8 and 9). Lipolysis increased in all samples during storage. However, increasing of lipolysis in fortified cheeses was less than control sample. Heating process that was applied to fortified cheeses, and also asparagus and tomato powders have a negative effect on lipolysis. Driessen23 reported that the thermization of milk (63 °C, 20 s) as well as the cooking of Emmental curd grains (51 °C for 20 min) inactivates the lipase enzymes. The main agents responsible for lipolysis of aged cheese are the intracellular bacterial lipases of cheese fat. Thermoduric bacterial lipases which survive during pasteurization are responsible for increasing of free fatty acid in cheese23.
Soluble nitrogen at pH 4.6 (SN) was used as an index of storage, includes peptides of medium to small molecular weight, proteoso peptones, whey proteins and free amino acids. These nitrogen compounds are the main results of rennet and plasmin proteolytic activity and/or microorganism peptidases31. Levels of SN of control samples did not significantly (P > 0.05) increase during storage (Tables 10 and 11). However, SN of fortified samples significantly increased (P < 0.05) during storage, which indicates that asparagus and tomato powders increased the proteolysis during storage.
Electrophoretic profile indicated that β-casein was hydrolyzed in fortified samples, more than control sample and γ-caseins accumulated as its main degradation products (Fig 1). β-casein was hydrolyzed faster than αs1-casein and intense bands of γ-casein were accumulated (Fig 1). These results were similar to results of Mulvihil and McCarthy32. According to their findings, there was no evidence of accumulation of degradation products of αs1-casein. Since processed cheeses are produced from a high solids molten mass of casein, proteolysis that occured during storage of these cheeses would be primarily due to residual proteolytic activity arising from the casein. Rennet caseins being used in the manufacture of processed cheese, contain a substantial quantity of plasmin which is the main proteolytic agent in processed cheeses made from rennet casein.
SN values and electrophoretic profile of samples showed that asparagus and tomato powders, increased the proteolysis of processed cheese. This could be due to thermoduric micro flora or native vegetable proteolytic enzymes of these plant powders.
Dynamic rheological behavior of processed cheeses: The textural and rheological properties of processed cheese are important determinants of its quality. Factors that are reported to influence these properties including composition, fat, moisture, protein contact, pH, type and level of emulsifying salts and maturity of the natural cheese, in addition to a number of processing parameters, such as time, temperature, and shear rate34.
Cheese is viscoelastic in nature and exhibits both solid (elastic) and liquid (viscous) behavior. Dynamic rheology testing is a fundamental method for determining the rheological properties of viscoelastic materials. This test is rapid and minimum physical and chemical changes occur in the samples. Small deformation (dynamic oscillatory rheometry) techniques is recommended to be used to study the linear viscoelasticity of cheese. These tests include stress or strain sweep, frequency sweep, temperature sweep, and time sweep35.
The dynamic rheological measurements were carried out at the linear viscoelastic region of the processed cheese samples. The frequency sweep test of the processed cheeses showed that all samples had Gʹ > Gʺ, indicating that solid-type structures were present and both parameters increased with frequency (Fig 2). Gʹ and Gʺ of PCT samples were lower than Gʹ and Gʺ of control sample. However, there were no significant difference (p>0.05) between the Gʹ and Gʺ values of PCT samples (Fig 6). These results showed that tomato powder decreased the solid like behavior of PC. One of reasons for this effect of tomato powder could be the effect of stirring and heating of PC while making the samples. On the other hand, Gʹ and Gʺ of PCA increased with increasing of frequency and were higher than those of control sample. However, the changes in Gʺ were not as large as changes in Gʹ (Fig 3). It means that asparagus powder led to a more elastic structure in the PC. One explanation for this behavior of asparagus could be existence of dietary fiber. Dietary fiber consists primarily of carbohydrate polymers (non-starch polysaccharides) that are components of plant cell walls, including cellulose, hemicelluloses and pectins, as well as other polysaccharides of plant or algal origin, such as gums and mucilages and oligosaccharides such as inulin36. Asparagus is a natural sources of fructo-oligosaccharides and inulin37. Dietary fibers have some special properties such as water holding capacity and viscosity, or gel-forming capacity. Water holding capacity is the amount of water that is retained by known weight of dry fibers under specified conditions. In general, the polysaccharide constituents of dietary fibers are strongly hydrophilic. Water is held on the hydrophilic sites of the fiber itself or within void spaces in the molecular structure. Viscosity is a physicochemical property associated with dietary fibers especially soluble dietary fibers such as gums, pectins, psyllium, and β-glucans. Viscosity, or gel-forming capacity, is related to a fiber’s ability to absorb water and form a gelatinous mass. Water soluble fibers are the major component that would increase the viscosity of a solution38. Thus, there is two way for asparagus powder to increase the elastic behavior of PC. One way is by absorbing the moisture of PC and forming a gel like solution and second way could be attributed to the formation of polysaccharide network throughout the casein matrix. With increasing concentration of asparagus, more intensive interactions between its fiber chains take place, leading to the formation of a denser network structure. Similar results were reported with k-carrageenan and ι-carrageenan39. Also, Ribeiro et al.40 reached similar conclusions, i.e. gel hardness and strength rise with increasing concentration of carrageenan. Other research reported that a pectin gel, which acted as a linkage with other ingredients in a processed cheese analogue, made the product more compact with less pores and as a result higher storage modulus41.
Dynamic rheology can provide useful information on the heat-induced changes that occur to imitation cheese viscoelasticity. Temperature sweep test of processed cheeses with different tomato and asparagus powder content from 25 to 80 °C were determined at frequency of 10 1/s and strain of 1%. For all products at 25 °C, the values of Gʹ were significantly (P < 0.05) higher than Gʺ (Figs. 4 and 5), indicating the dominant elastic character of the PC. Gʹ values decreased with increasing temperature from 25 to 80 °C, as has previously been observed in natural cheddar cheese42 and in imitation Mozzarella cheese43. This indicates that the cheese matrix became less elastic with increasing temperature. This may have been caused by liquefaction and deformation of the fat globules which may plasticized the protein matrix and weakening of protein-to-protein interactions within the casein network which, all of these, allowing the protein matrix to flow44. Gʹ and Gʺ of PCT samples at 25 °C was lower than those of control sample and samples with higher concentration of tomato powder, had lower Gʹ and Gʺ (Fig 4). These results showed that adding tomato powder in PC, decreased the firmness of that. Gʹ of PCT samples slightly increased or became liner at more than about 60 °C. It means that after this temperature some kind of solidification occurred in the samples. Imitation cheese containing inulin had similar behavior at 55°C39. Gʹ and Gʺ of PCA samples also decreased with the increasing of temperature and were significantly higher than control sample at less than about 53°C, but above that temperature, Gʹ and Gʺ of PCA were lower than those of control sample (Fig 5). The results indicated that adding asparagus to the processed cheese formulation significantly (P < 0.05) strengthened the cheese structure at low temperatures. Gʹ and Gʺ of PCA samples at more than about 60°C became liner.
Tan d (Gʺ/Gʹ) may be a useful indicator of processed cheese meltability43. The modulus value at tan δ =1(45°phase angle) is known as crossover modulus, where the material is equally solid and liquid like characteristics. It had been studied that if tan δ is less than 1 the material is more elastic, and when tan δ is more than 1 the material is more viscous35. In the temperature sweep test, Gʹ and Gʺ curves of the high concentration of PCT samples crossed each other (Gʹ = Gʺ or tan d = 1) at 60°C (gel-sol transition) and at higher temperatures, viscous behavior of the samples dominated the elastic one. All Gʹ and Gʺ of PCA samples have crossover point at about 62°C which DF=1 (Fig 6). Tan d of the samples containing different concentration of asparagus powder, had little change up to ~60°C and increased after this temperature (fig 6). These results showed that heating of the processed cheese samples more than 60°C increased the viscous behavior, indicating that the elastic component decreased to a greater extent than the viscous component, showing a weakening of the network arrangement. However, the protein-protein and protein-polysaccharide interactions might increase with heating up to 85 °C leading to less viscous behavior of the samples. Similar results have been achieved about model processed cheese containing basil seed gum45. Hennelly et al.44 showed that replacing fat with Inulin in the imitation cheese formula showed no significant effect on meltability. However, Gʹ and Gʺ of the processed cheeses containing the higher level of Inulin increased at temperatures more than 55°C.
Existence of transition temperature in PCA samples proves that asparagus powder is much more effective than tomato powder at increasing the meltability of processed cheese. However, Different between transition temperatures among PCA samples was not Significant.
Sensory analysis. Results obtained by the sensory analysis showed that color and flavor of processed cheese were not significantly (P > 0.05) changed with the increasing of asparagus concentration (P < 0.05) (Fig 7). Highest scores of flavor, color and total acceptance belonged to control processed cheese and processed cheese with 1% wt/wt tomato powder and lowest scores belonged to processed cheese with 4% wt/wt tomato powder. These results showed that low levels of tomato powder in processed cheese was more acceptable. Samples containing asparagus powder received average scores of flavor, color and total acceptance. All processed cheeses with asparagus powder additions were significantly (P < 0.05) more rigid and less spreadable compared with control samples (P < 0.05) and also rigidity increased and spreadability decreased with the growing amount of asparagus (P < 0.05). However, with increasing tomato powder levels, rigidity decreased and spreadability increased compared with control samples (P < 0.05). This finding were similar with results obtained by dynamic oscillation rheometry.
CONCLUSIONS
Adding tomato and asparagus powders in processed cheese did not have significant (P > 0.05)effect on protein, fat and moisture contact of fortified samples. Generally, during storage of 90 days, levels of pH, Lipolysis, SN, increased and lycopene, WSPC, AOA levels of samples, decreased. Among samples, fortified samples generally, had higher levels of lycopene, WSPC, AOA and proteolysis however, they had lower lipolysis and pH. Asparagus due to its high content of phenolic compounds, had more effect on preventing from increasing of pH, comparing with tomato powder. Rheological measurements indicated that solid-type structures were present in processed cheese samples and asparagus powder led to a more elastic structure in fortified samples. However, adding tomato powder in fortified samples, decreased the firmness of that. Sensory analysis showed that control sample and processed cheese with 1% wt/wt tomato powder had highest scores of flavor, color and total acceptance and also PCA samples were significantly (P < 0.05) more rigid and less spreadable compared with control samples which corresponded with results obtained by dynamic oscillation rheometry. Results showed that low levels of tomato and asparagus powders could be used in fortification of processed cheese.
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