Effect of 1-Monoglycerides on Viscoelastic Properties of Processed Cheese

Abstract

This article deals with the influence of selected 1-monoglycerides (1-monocaprylin, 1-monocaprin, 1-monolaurin, 1-monopalmitin, and 1-monostearin) in a concentration of 0.25% w/w on viscoelastic and sensory properties of the processed cheese with 45 and 50% fat in dry matter after 14 days of storage at temperature of 6 ± 2°C. With increasing number of carbons in the molecule of fatty acid, which is ester-bound in 1-monoglycerides, both the storage G′, and the loss G″ moduli increased in whole frequency range. This enhancement was relatively smaller in the group of processed cheeses with 45% fat in dry matter compared to the group of processed cheeses with 50% fat in dry matter. The additions of 1-monocaprylin, 1-monocaprin, and 1-monolaurin were not sensorial acceptable due to the off-flavour. The effect of addition of 1-monopalmitin and 1-monostearin (from 0.1 to 0.5% w/w) has also been presented.

Keywords:

• Processed cheese
• 1-Monoglycerides
• Viscoelasticity
• Sensory evaluation

INTRODUCTION

Processed cheese is produced by blending shredded natural cheese of different types and degrees of maturity with emulsifying agents, followed by heating the blend under a partial vacuum with constant agitation until a homogenous mass is obtained. In addition to natural cheese, other ingredients of both dairy (e.g., butter, cream, skim-milk powder, and whey powder) and non-dairy origin may be included in the blend.[1,2] Processed cheese is an oil-in-water emulsion in which dairy proteins play the important role of emulsifiers. The majority of the proteins are caseins (from cheese, rennet casein, or other milk protein sources), whose emulsification potential is improved by the use of chelating salts. The active ingredients in the chelating salts are monovalent cations (e.g., sodium) and multivalent anions (e.g., citrate or phosphate). The chelating salts chelate calcium. As calcium plays an important role in the three-dimensional structure of cheese, the chelation of calcium disrupts the structural integrity and solubilizes casein. This solubilized casein is able to interact with water and fat under agitation and heating, and forms a gel network structure during subsequent cooling.[3,4]

The consistency is one of the most important organoleptic attributes of processed cheese. In addition to dry matter content, fat content, maturity of natural cheese, and mixture of emulsifying agents, there are many other factors affecting the consistency of processed cheese, e.g.: pH of processed cheese,[5,6] presence of rework (processed cheese that is not packaged for sale, although it meets product specifications, and is mixed with a fresh blend and reprocessed),[1] calcium content,[7] presence of proteins such as casein, Na-caseinate, Ca-caseinate, casein hydrolysate fractions, whey proteins, and so on.[3,8] time and intensity of processing,[9] presence of many substances, e.g., lactose, addition of emulsifiers into raw material, storage conditions (duration, temperature),[10,11] and so on.

Monoglycerides or their derivatives, respectively, are extended emulsifiers in the food industry. Their usage is known, for example, in production of emulsified fats and whipped dairy products.[12] They are widely used in bakery applications, where they increase the durability of bread and also have favourable influence on rheological properties of the dough[13] and on conditions of solubility of the protein fraction.[14] In the available literature, no sufficient information was found about the effect of monoglycerides addition on the quality of processed cheeses and mechanism of their action in these products. Just one notice about monoglycerides in processed cheeses, which was found by the authors, is in the work of Caric and Kaláb.[1] They specified that processed cheese of good quality can be produced using 1% of surface-active monoglycerides in combination with 50% of the usual amount of phosphate.

The aim of this article is to describe the effect of small addition of 1-monoglycerides with different amount of carbon atoms, and the effect of different concentrations of selected 1-monoglycerides on the viscoelastic properties and sensory qualities of processed cheeses with 45 and 50% (w/w) fat in dry matter.

METHODS

Preparation of Processed Cheese

The formulation of processed cheese for this article was based on commercial processed cheese: 41% w/w dry matter; 45 and 50% w/w fat in dry matter. The raw materials and processing conditions were chosen to simulate commercial conditions for processed cheese making: Eidamsky Blok—Dutch type cheese with 30% w/w fat in dry matter and 50% w/w dry matter; Eidamsky Blok—Dutch type cheese with 45% w/w fat in dry matter and 55% w/w dry matter; Madeland—hard cheese with 45% w/w fat in dry matter and 57% w/w dry matter; butter 82% w/w fat and 84% w/w dry matter, water, commercial emulsifying agents (sodium salts of phosphates and polyphosphates—JOHA, Benckiser-Knapsack, Ladenburg, Germany), temperature of processing—above 90°C and moderately long time of preparation.

The model processed cheeses were prepared using 2-L capacity Vorwerk Thermomix TM 21 blender cooker (Vorwerk & Co. Thermomix; GmbH, Wuppertal, Germany). This cooker was the same type as the cooker used by Lee et al.[4] in their work. The cooker had a four-blade chopper rotor (two blades facing upward and two blades facing downward) placed at its base. The speed range was from 100 to 12,000 rpm. There were 10 speed steps: steps 1–3: 100–1 000 rpm; steps 4–9: 2 000–9 100 rpm; and Turbo step that runs at a single speed of 12,000 rpm. The cooker was electrically heated around the base (to about a third of the height of the cooker). The heating scale ranged from 40 to 100°C.

The mixture of the above-mentioned natural cheeses and butter were cut into pieces (approx. 2 × 2 × 2 cm). Cubes of natural cheeses and butter were placed into the blender cooker and the mixture was minced at 40°C for 1.5 min at speed 4 and Turbo step was set three-times for 5 sec in approx. regular intervals. Then 1-monoglycerides were solved in water at 60°C and added into the mixture. Finally, emulsifying agents (2.0% w/w) were added (approx. 2 min after beginning of mincing and heating). Then the cooker temperature was set to 100°C, and the mixture was being processed totally for 10 min. The final temperature of processed cheese melt (92°C) was held for 1 min. Then hot processed cheese was poured into standard 100 g plastic doses with sealable lids and stored at 6 ± 2°C. Total amount of processed cheese was approximately 1 200 g per batch. Total processing time varied in the range of 10–12 min.

In the first stage of this work, processed cheeses with addition of 0.25% w/w saturated 1-monoglycerides (for details of preparation see below) having 8, 10, 12, 16, and 18 carbon atoms in ester-bound fatty acid (1-monocaprylin MAG-C8:0; 1-monocaprin MAG-C10:0; 1-monolaurin MAG-C12:0; 1-monopalmitin MAG-C16:0; 1-monostearin MAG-C18:0) were prepared. All the additions of 1-monoglycerides were realized into two types of processed cheese, 45% w/w and 50% w/w fat in dry matter. The amount of dry matter was kept approximately constant in both cases. Two processed cheeses without 1-monoglycerides were prepared as control samples (with 45% w/w and 50% w/w fat in dry matter). Products were evaluated after 2 weeks of storage at 6 ± 2°C.

For the second stage, only MAG-C16:0 and MAG-C18:0 were chosen and these 1-monoglycerides were added into processed cheeses with 50% w/w fat in dry matter at the target 1-monoglycerides concentrations: 0.1, 0.2, 0.3, 0.4, and 0.5% w/w. The same kind of raw materials as in the first stage was used, but natural cheeses have higher degree of maturity compared to the first stage. A new control sample without 1-monoglycerides was prepared as well.

1-Monoglycerides' Preparation

Saturated 1-monoglycerides MAG-C8:0, MAG-C10:0, MAG-C12:0, MAG-C16:0 and MAG-C18:0 were prepared according to the procedure published earlier by Janiš et al.[15] Crude products were purified by recrystallisation from ethanol in order to remove residual glycidol and reduce the quantity of Cr(III) ions (catalyst of 1-monoglycerides preparation). Purity of 1-monoglycerides determined by HPLC was 99%, and residue of Cr(III) ions determined by AAS was below 50 mg·kg⁻¹.

Dry Matter Content, Fat Content and pH Measurements

The dry-matter content is defined as the residue, which remains when the product is dried under certain conditions and expressed as a percentage by weight. The drying was carried out under normal atmospheric pressure at 102°C until the constant weight was achieved. The fat content was determined by Weibull-Stoldt method.[16] The pH of the samples was measured using a pH-meter GRYF 209 S with combined glass electrode at 22°C. Each sample was measured at least twice.

Rheological Measurements

Viscoelastic properties of processed cheese samples were measured by Bohlin Gemini (Malvern Instruments, UK) rheometer with parallel plate geometry (diameter of 40 mm, gap 1 mm) at temperature of 20°C. All the experiments were performed in the control shear stress mode in frequency range from 0.1 to 50 Hz. Amplitude of shear stress 50 Pa was chosen in region of linear viscoelasticity. The exposed edge of parallel plates geometry was covered with thin layer of silicone oil to prevent dehydration of the samples. Reported results are the mean values of at least three replicates.

Sensory Evaluation

A sensory evaluation of samples was performed by 16 selected assessors (employees from Department of Food Engineering) trained according to ISO standard.[17] Samples of the processed cheese were evaluated in a sensory laboratory with booths consistent with ISO standard.[18] All the samples were coded and served randomly at room temperature (22 ± 2°C). Five sensory descriptors (appearance, rigidity, spreadability, flavour, and off-flavour intensity) were assessed by way of seven points ordinal scale (results were expressed by means of median). For evaluation of the significance of the sensory analysis results Kruskal-Wallis test was used.[19]

RESULTS AND DISCUSSIONS

In the first stage of the work, the samples of processed cheeses with addition of 0.25% (w/w) of chosen 1-monoglycerides (MAG-C8:0, MAG-C10:0, MAG-C12:0, MAG-C16:0, MAG-C18:0) were characterized after 14 days of storage at temperature of 6 ± 2°C by the method of dynamic oscillation rheometry. The group of processed cheeses with 50% w/w fat in dry matter had similar content of the dry matter, content of fat and pH, as follows from Table 1. A similar conformity was found also in the group of products with 45% w/w fat in dry matter. This fact allowed us the comparison of the effect of the addition of 1-monoglycerides in evaluated products because all above mentioned characteristics could considerably influence the consistency of processed cheeses.[4,5] Figure 1 shows the results of dynamic oscillation rheometry for the group of processed cheeses with 50% (w/w) fat in dry matter. With increasing number of carbon atoms in the molecule of fatty acid, which is ester-bound in 1-monoglycerides, both the storage G′ and the loss G″ moduli continuously increased in all the range of tested frequencies. The cross-over point (the point of intersection of the storage modulus G′ curve and the loss modulus G″ curve) was shifted to lower frequencies with increasing number of carbon atoms in the molecule of fatty acid indicating that firmer gel structure was formed.

Figure 1 Influence of type of added 1-monoglycerides with different number of carbon atoms (MAG-8:0, MAG-10:0, MAG-12:0, MAG-16:0, MAG-18:0—concentration 0.25% w/w) on storage modulus G′ and loss modulus G″.

Table 1 Mean content of dry matter (% w/w), fat (% w/w), and pH in processed cheeses produced in the first phase (addition 0.25% w/w saturated 1-monoglycerides in processed cheese)

Type of processedcheese	Type of added 1-monoglyceride	Dry matter content (% w/w)	Fat content (% w/w)	pH
Processed cheese with 50% (w/w) fat in dry matter	None	41.64 ± 0.32	21.18 ± 0.23	5.85 ± 0.01
	C8:0	41.82 ± 0.21	20.84 ± 0.21	5.84 ± 0.02
	C10:0	42.64 ± 0.14	20.55 ± 0.21	5.82 ± 0.01
	C12:0	41.73 ± 0.17	20.30 ± 0.28	5.82 ± 0.02
	C16:0	42.74 ± 0.25	20.24 ± 0.19	5.81 ± 0.03
	C18:0	42.58 ± 0.14	21.20 ± 0.20	5.84 ± 0.01
Processed cheese with 45% (w/w) fat in dry matter	None	42.09 ± 0.25	19.62 ± 0.29	5.82 ± 0.03
	C8:0	43.31 ± 0.23	19.45 ± 0.15	5.78 ± 0.01
	C10:0	42.75 ± 0.15	19.50 ± 0.19	5.77 ± 0.02
	C12:0	43.03 ± 0.22	19.38 ± 0.22	5.80 ± 0.02
	C16:0	43.22 ± 0.18	19.76 ± 0.18	5.77 ± 0.01
	C18:0	42.67 ± 0.10	19.23 ± 0.23	5.76 ± 0.01
(n = 4; mean ± S.D.).

The change in viscoelastic properties, as the result of the addition of different 1-monoglycerides, is more obvious from Fig. 2. Values of the storage modulus G′ and the loss modulus G″ at the reference frequency 1 Hz (arbitrary chosen) for both groups of processed cheeses with 45 and 50% (w/w) fat in dry matter are shown for comparison. There is a remarkable enhancement of both G′ and G″ moduli as a consequence of the additions of 1-monoglycerides with increasing number of carbon atoms in the molecule of fatty acid also in the group of processed cheeses with 45% (w/w) fat in dry matter. However, this enhancement is relatively smaller (in comparison to the control sample) than that for the group of processed cheeses with 50% w/w fat in dry matter.

Figure 2 Influence of type of added 1-monoglycerides with different number of carbon atoms (MAG-8:0, MAG-10:0, MAG-12:0, MAG-16:0, MAG-18:0—concentration 0.25% w/w) on storage modulus G′ and loss modulus G″ of processed cheese with 45 and 50% w/w fat in dry matter. Frequency of 1 Hz was arbitrarily chosen.

The increase of the storage modulus G′, the loss modulus G″, and the shift of the cross-over point to lower frequencies indicated the change in the properties of the gel, which showed increasing rigidity with increasing number of carbon atoms in molecule of fatty acid ester-bound in 1-monoglycerides. This can be explained by the fact, that with the addition of modifiers, which increase the degree of emulsification of the fat the rigidity of processed cheeses also rises.[20] According to Faur[21] and Moonen and Bas,[12] emulsifying ability of 1-monoglycerides increases with the length of the carbon chain in ester-bound fatty acid.

The results of sensory analysis of both groups of processed cheeses are shown in Table 2. The addition of 1-monoglycerides practically did not influence the visual appearance of processed cheeses. The assessors recognized the changes of “rigidity” and “spreadability” only for processed cheeses with 50% (w/w) fat in dry matter with additions of MAG-C16:0 and MAG-C18:0. In the group of processed cheeses with 45% (w/w) fat in dry matter the assessors have not recognized any changes in “rigidity” and “spreadability” at any of 1-monoacylglycerols. During evaluation of “flavour” it was found that processed cheeses in both groups with the additions of 0.25% (w/w) MAG-C8:0, MAG-C10:0, and MAG-C12:0 exhibited an unacceptable off-flavours. A similar problem with sensory acceptability of dairy products with additions of 1-monoacylglycerols with shorter acylate rest was published by Faur[21] and Nair et al.[22]

Table 2 Results of the sensory analysis of processed cheese with addition of 0.25% w/w 1-monoglycerides (expressed as median).∗

Type of processed cheese	Type of added 1-monoglyceride	Sensory evaluation (median)
		Appearance	Rigidity	Spreadability	Flavour	Off-flavour
Processed cheese with 50% (w/w) fat in dry matter	None	2^a	5^a	5^a	2^a	1^a
	C8:0	3^a	5^a	5^a	7^b	7^b
	C10:0	3^a	5^a	5^a	7^b	7^b
	C12:0	3^a	5^a	5^a	7^b	7^b
	C16:0	2^a	4^b	4^b	2^a	2^c
	C18:0	2^a	4^b	4^b	2^a	2^c
Processed cheese with 45% (w/w) fat in dry matter	None	2^a	4^a	4^a	2^a	1^a
	C8:0	3^a	4^a	4^a	7^b	7^b
	C10:0	3^a	4^a	4^a	7^b	7^b
	C12:0	2^a	4^a	4^a	6^c	6^c
	C16:0	2^a	4^a	4^a	2^a	2^a
	C18:0	2^a	4^a	4^a	2^a	2^a
Appearance: 1 – excellent to 7 – very poor, unacceptable; rigidity: 1 – very stiff to 7 – very soft; spreadability: 1 – spreadability is impossible to 4 – optimal spreadability to 7 almost liquid sample; flavour: 1 – excellent to 7 – very poor, unacceptable; and off-flavour: 1 – no recongnizable to 7 – very strong.
∗The values reflecting statistically significant differences in sensory attribute (in columns) are designated with different letters in indexes (P < 0.05); samples with 45 and 50% (w/w) fat in dry matter were evaluated by means of Kruskal-Wallis test separately.

For the second stage of the work, where the effects of different concentrations of 1-monoglycerides (0.1 to 0.5% w/w) on viscoelastic properties of the processed cheese were examined, only MAG-C16:0 and MAG-C18:0 were chosen. These two types of 1-monoglycerides significantly affected the “rigidity” and “spreadability” (evaluated by sensory analysis) and have not shown any off-flavours. The experiments were performed only with the processed cheese with 50% (w/w) fat in dry matter, because in that group of processed cheeses relatively higher changes of the storage modulus G′ and the loss modulus G″, due to the addition of 1-monoglycerides were observed. The prepared processed cheeses had similar content of dry matters and fat, and pH, only the processed cheese with the addition of 0.5% (w/w) MAG-C18:0 had a slightly lower content of the dry matter (see Table 3). Figure 3 shows the effect of different concentrations (0.1 to 0.5% w/w) of MAG-C16:0 and MAG-C18:0 on the storage modulus G′ and the loss modulus G″ at the reference frequency 1 Hz. At all tested concentrations of MAG-C18:0, the storage modulus G′ and the loss modulus G″ increased in comparison to the control sample. The enhancement of storage modulus G′ was relatively higher. The addition of 0.2% w/w MAG-C18:0 shows the highest value of both moduli (G′ and G″) at the reference frequency 1 Hz. With further increase in concentration of MAG-C18:0, G′ and G″ changed slightly. The cheeses with the additions of MAG-C16:0 exhibited different behaviour. After decrease of values of both moduli (G′ and G″) at the addition of 0.1% w/w MAG-C16:0 their gradual increase with rising concentration of MAG-C16:0 is observed. Further addition of MAG-C16:0 (0.5% w/w) caused decrease of the storage modulus G′ and the loss modulus G″, but the values of both moduli remained higher, than those of the control sample. The increased concentration of tested 1-monoglycerides has not affected the rigidity of processed cheeses in one certain direction. Therefore, there exists an optimum concentration of 1-monoglycerides, which depends, besides the kind of 1-monoglycerides, probably also on other factors, such as content of dry matter, fat in dry matter, level of maturity and the kind of natural cheeses, quality of raw materials and other substances (especially surface active), etc. In addition to above mentioned effects, used emulsifying agents should be regarded as a very important factor influencing final consistency of processed cheeses.[23]

Table 3 Mean content of dry matter (% w/w), fat (% w/w), and pH in processed cheeses produced in the second phase (addition of different amount of saturated 1-monoglycerides with 16 and 18 carbons)

Type of processed cheese	Type of added 1-monoglyceride	Amount of added 1-monoglycerides (% w/w)	Dry matter content (% w/w)	Fat content (% w/w)	pH
Processed cheese with 50% (w/w) fat in dry matter	C16:0	None	41.99 ± 0.36	21.36 ± 0.21	5.77 ± 0.01
		0.1	41.52 ± 0.21	21.16 ± 0.12	5.83 ± 0.01
		0.2	41.71 ± 0.18	21.25 ± 0.14	5.90 ± 0.02
		0.3	41.88 ± 0.11	21.27 ± 0.15	5.88 ± 0.01
		0.4	42.02 ± 0.15	21.58 ± 0.15	5.87 ± 0.02
		0.5	41.78 ± 0.15	21.22 ± 0.22	5.88 ± 0.01
	C18:0	None	41.14 ± 0.18	21.59 ± 0.32	5.87 ± 0.01
		0.1	41.56 ± 0.36	21.78 ± 0.14	5.88 ± 0.02
		0.2	41.25 ± 0.14	21.91 ± 0.12	5.88 ± 0.02
		0.3	41.59 ± 0.16	21.51 ± 0.35	5.89 ± 0.02
		0.4	41.59 ± 0.20	21.28 ± 0.11	5.87 ± 0.01
		0.5	40.88 ± 0.22	20.88 ± 0.32	5.86 ± 0.02
(n = 4; mean ± S.D.).

Figure 3 Influence of different concentration of 1-monoglycerides (MAG-C16:0—1-monopalmitin and MAG-C18:0—1-monostearin) on storage modulus G′ and loss modulus G″of processed cheeses with 50% w/w fat in dry matter. Frequency of 1 Hz was arbitrarily chosen.

In the second stage of the work, the sensory analysis was performed with control samples, processed cheeses with concentrations of 1-monoglycerides which were found as the most efficient (0.2% w/w for MAG-C18:0 and 0.4% w/w MAG-C16:0) by dynamic oscillation rheometry and with the highest concentration of tested 1-monoglycerides (0.5% w/w). The visual appearance was not significantly affected by the additions of 1-monoglycerides. There were recognized no off-flavours for all tested processed cheeses. Processed cheeses with addition of 1-monoglycerides were evaluated as less spreadable and more rigid in comparison with control samples. Neither the difference between the additions of MAG-C18:0 on levels 0.2 and 0.5% w/w, nor between the additions of MAG-C16:0 in concentrations 0.4 and 0.5% w/w was recognized by assessors.

CONCLUSION

In this paper, the influence of addition of 1-monoglycerides on the viscoelastic and organoleptic properties of the processed cheese with 45% and 50% w/w fat in dry matter was evaluated. Influence of 0.25% (w/w) 1-monoglyceride content on the rheological properties was dependent on the number of carbons in a fatty acid molecule, which is ester-bound in 1-monoglycerides. 1-monoglycerides with a very short chain (1-monocaprylin and 1-monocaprin) influenced viscoelastic properties of the processed cheese only to minor extent. Simultaneously, during the sensory evaluation of the product consistency, these changes were not noticed. 1-monopalmitin and 1-monostearin at the same level of addition increased rigidity and decreased spreadability of the final product. Experiments with different concentrations of 1-monopalmitin and 1-monostearin have shown that within the range of 0.1 to 0.5% (w/w), an optimal concentration of 1-monoglyceride exists for each type of processed cheese. This amount was 0.4% w/w for 1-monopalmitin and 0.2% w/w for 1-monostearin. Additions of 0.25% (w/w) 1-monoglycerides with shorter fatty acid chains (1-monocaprylin, 1-monocaprin, and 1-monolaurin) showed unacceptable off-flavours. Additions of 0.5% w/w 1-monopalmitin and 1-monostearin did not negatively influence the flavour of the product.

ACKNOWLEDGMENT

This work was kindly supported by a project of Czech Ministry of Education, Youth and Sports (Grant No. MSM 7088352101).

Notes

17. ISO Standard No. 8586-1:1993 Sensory analysis—General guidance for the selection, training and monitoring of assessors—Part 1: Selected assessors. International Organization for Standardization: Geneva, 1993.

18. ISO Standard No. 8589:1988 Sensory analysis—General guidance for the design of test rooms. International Organization for Standardization: Geneva, 1988.