Die Nahrung 33 (1989) 4,333-337

Institute of Meat Industry, Sofia, Bulgaria

Effects of some technologies of curing uncomminuted meat products on their flavour Part 1. Changes in the contents of fatty acids as meat flavour precursors

E. MITEVA, Z. TRENDAFILOVA and M. CHAKUROV

A study was made of the fatty-acid composition of phospholipids and the fraction of free fatty acids in two uncomminuted pork products, loin and neck, manufactured by three technologies: I, brine curing; 11, dry curing; 111, dry curing using%.6% honey. A higher phospholipid content was found in the loin products. Brine curing caused a more intensive lipid hydrolysis in both types of meat products. The free fatty-acid fraction in the meat products manufactPred by technologies I1 and I11 was richer in unsaturated fatty acids, which are some of the most important meatflavour precursors.

Lipids are of essential importance for flavour formation in meat products. They can play the role of solvents of the volatile components of meat flavour or, through their degradation products, they can be involved directly in the flavour formation process.

A number of authors relate lipids to the appearance of a specific meat flavour [5, 14, 121. Besides, it is not as much adipose tissue, as intramuscular and structural lipids that are the important sources of its formation [9]. During meat processing, they undergo enzymatic and oxidative changes resulting in the formation of low molecular weight products which are involved immediately in meat flavour or are its precursors [l 11. Structural lipids are rich in unsaturated fatty acids. Free unsaturated fatty acids are some of the most important pre- cursors of meat flavour [4,6]. Under definite conditions, they produce volatile aldehydes, ketones, and alcohols, involved directly in meat flavour. Lipid destruction products can also be involved in reactions with some meat flavour precursors derived from proteins and resulting in specific products of meat flavour [lo].

The objective of the present work was to determine the effects of three technologies of curing smoked and cooked uncomminuted meat products on the fatty acid composition of the lipids in them.

Materials and methods

The experiments were made using meat products of uncomminuted pork, loin and neck, each of which were divided into three equal parts. Individual experimental lots were formed of them, cured in the following manner :

I. Brine curing method. For this purpose, the meat was injected in advance with a brine of a density of 1.1 16 g/cm3, at the level of 10 % relative to meat, then it was submerged into a brine of a density of 1.092 g/cm3

334 Die Nahrung 33 (1989) 4

in the ratio of me'at: brine, 2: I . The meat staying time in the brine was 4 days at a temperature of 4 "C, and afterwards, it was strained for two days at the same temperature.

11. Dry curing. The curing mixture was prepared in advance by mixing to homogeneity NaCI, NaNO, and ascorbic acid in the following amounts relative to meat: - NaCI, 2.2 % for loins and 2.6 % for necks; - NaNO,, 0.012%; - ascorbic acid, 0.03 %.

The curing mixture was applied uniformly on the surface and massaged intensively. The aging of the meat products proceeded for 6 days at a temperature of 10-12 "C.

111. Dry curing using 6% honey relative to the amount of meat, the honey being applied on the surface ajier the application offhe curing mixture. Upon curing and aging, the meat was subjected to heat treatment compris- ing: drying at a temperature of 80-90 "C for 30 min, smoking at a temperature of 75-80 "C for 30 min, and cooking at a temperature of 75 "C. Final products were cooled down in an air stream at a temperature of

Lipid extraction was performed using a mixture of chloroform and methanol in the ratio of 2: 1 by the method of BLIGH et al. [3]. In the total lipid extract. phospholipids and free fatty acids were determined. In- dividual fatty-acid composition was determined in the two lipid fractions, phospholipids were isolated from total lipids using a florid column of a diameter of 1.5 cm and a height of 8 cm [I]. Neutral lipids were eluted from the florid with 60 ml of ether, and phospholipids, with 50 ml of chloroform and methanol in the ratio of 1 : 1 and 50 ml of pure methanol.

Free fatty acids were separated from total lipids by thin-layer chromatography on silica gel with the solvents hexane, diethyl ether, and glacial acetic acid in the ratio of 80:20:2 after development with Rhodamine 6G in the U V region.

The levels of phospholipids and free fatty acids were estimated as % total lipids, on the basis of the sum of fatty acids contained in them. The individual fatty acid composition was determined by gas chromatography of their methyl esters obtained by methylation with methanol and BF, as catalyst by the method Of METCALFE [8]. The methylation of the free fatty acids isolated by thin-layer chromatography was performed directly on the silica gel by a method described by us earlier [2].

The identification of fatty acids was performed against pure standards, and quantitative determination against an internal standard, methyl heptadecanoate. The ratio of the sum of unsaturated fatty acids and saturated fatty acids was presented as the R factor. The results are presented as means of five determinations.

8-10 "C.

1

Results and discussion

The amounts of isolated phospholipids and free fatty acids are shown in Table I . Phospho- lipid content is higher in the meat products prepared from loins. We attribute this to the higher level of adipose tissue in the products made of neck where triglycerides predominate. The values of phospholipids in the meat products prepared by the different technologies are similar in the two types of meat products. The differences found, though small, are in favour of technologies I1 and 111.

Table 1 Contents of phospholipids (PHL) and free fatty acids (FFA) [ % of total lipids]

Technology Pork Loin Pork Nedk

PHL FFA PHL FFA

1 12.7 5.2 9.4 6.1 11 11.3 4.1 8.9 5.4 111 10.8 4.2 8.1 5.2

MITEVA/TRENDAFXLOVA et al. : Effects of curing meat products on their flavour. Part 1 3 35

Certain differences were found in the content of the total amount of free fatty acids. A higher level of‘them was found in the products prepared from neck. Further, a larger amount of free fatty acids was found in both types of products prepared using technology I. Clearly, there is a more intensive lipid hydrolysis, favoured by available water during the technological process and the catalytic action of the high salt concentrations present in it [ 131.

The data on the contents of individual fatty acids in the fractions of phospholipids and free fatty acids are shown in Tables 2 and 3, respectively. In the phospholipid fraction, a greater number of acids was identified, compared to the fraction of free fatty acids. The total amount of unsaturated fatty acids in the fraction of phospholipids was greater com- pared to that in the fraction of free fatty acids which is clearly manifested upon the com- parison of the R factor. It is noticeable that the factor is lower in technologies I1 and I11

Table 2 Fatty acid composition of the phospholipid fraction [ %]

Acid Pork Neck Pork Loin

Technology Technology I I1 111 I I1 I11

Cl 2 1.5 1.8 I .9

Cl,:, 6.2 7.4 7.0 ‘18 20.5 21 .o 21.2 CI,:, 20.1 10.8 21.0

C18:3 9.2 8.1 7.9

C20, 3.6 1.6 1.4

CI, 2.6 2.5 2.5 CI, 13.5 14.0 14.0

C18:Z 18.4 18.8 19.0

C*O 4.4 4.0 4.6

1.4 1.9 2.0 2.1 2.8 2.8

13.2 16.0 15.3 6.7 7.6 7.4

19.5 18.5 19.2 21.0 22.1 22.0 19.0 19.2 19.0 10.2 7.8 8.1 2.9 2.6 2.2 4.0 1.5 2.0

R 1.35 1.30 1.28 1.55 1.39 1.40

Table 3 Individual fatty acid composition of the free fatty acid fraction [ %]

Acid Pork Neck Pork Loin

Technology Technology

I I1 . I11 I I1 I11 ______.____

1.8 1.5 1.1 1.2 0.8 1 .o 15.0

3.0 2.8 2.0 4.2 4.1 3.9 27.7 26.1 26.6 26.0 25.5 24.8

46.8 8.2 8.4 8.1 7.5 7.9

0.3 0.5 0.6

C14

%:I

C I S

C,,:,

CI, 16.8 16.2 16.5 15.6 14.8

C I S : , 42.5 45.0 45.2 44.6 46.8

R 1.15 1.28 I .26 I .33 I .42 I .45

336 Die Nahrung 33 (1989) 4

for both types of meat products. In those technologies an appreciable reduction is perceived in C,,:, and CzOz4, better pronounced in technology 111. It is obvious that, under the condi- tions of dry curing, more intensive destructive processes take place, involving, in the first place, the double bonds of polyene fatty acids in structural lipids. The changes found in the contents of fatty acids could be related to the catalytic action of some pigments and to the higher content of haem pigments in them [7]. We found a greater amount of total pigments in those products (data in the press). Probably, the biological activity of the honey used in technology I11 is also important. It contains glucose oxidase, catalase, esterases, which, on the one hand, stabilize meat colour, and, on the other, are directly involved in oxidation- reduction processes, the end products of which may be the initiators of a lipid oxidation affecting double bonds above all. We feel that the presence of a higher level of total pigments and the enzymatic activity of honey in the meat products manufactured by technologies I1 and 111 are responsible for the reduction in the contents of unsaturated fatty acids in the phospholipid fraction due to the occurrence of more intensive destructive oxidation and enzymatic processes in them. Unsaturated fatty acids originating from phospholipids are necessary precursors of the volatile meat flavour [lo]. One may expect that the reduction in their contents in technologies I1 and I11 results from their conversion into low molecular weight, reactive compounds directly involved in flavour formation.

The fraction of free fatty acids in the meat products manufactured by technologies I1 and I11 is richer in unsaturated fatty acids. The difference between the values of the R factor is insignificant, however. Significant differences are only found in the values of oleic acid. Obviously, in those two cases, conditions are created for a specific lipolysis of this acid.

Analysing the data on the individual free fatty-acid composition we can find that, in the products manufactured from loin, the level of unsaturated fatty acids is higher compared to that in the products made of pork neck. For instance, in the latter, we cannot detect C18:3. This could be explained by the higher contents of unsaturated fatty acids in lean meat, due to the higher level of phospholipids in them.

The data we found of the fatty acid composition of lipids in uncomminuted meat pro- ducts and the difference in their values indicate that more intensive oxidative-destruction processes involving lipids, occur upon the application of the dry method of curing, or dry curing using honey. As a result, changes in unsaturated fatty acids take place in the meat products obtained by these technologies. In this way, the processes related to some of the most important meat flavour precursors, are intensified. How far the changes that occurred in fatty-acid composition were favourable for meat-flavour formation was determined in our subsequent work related to the determination of the carbonyl components of meat flavour and the sensory quality of the product.

Zusammenfassung

E. MIPEVA, Z. TRENDAFILOVA und M. CHAKUROV : EinfluB einiger Technologien der Pokelung unzerkleinerter Fleischprodukte auf das Aroma. 1 . Mitt. Veranderungen des Gehalts an Fettsauren als Fleischaroma-Vor- stufen

Es wurden Untersuchungen uber die Fettsaurenzusammensetzung der Phospholipide und der Fraktion der freien Fettsauren in den unzerkleinerten Schweinefleischprodukten Lende und Nacken vorgenommen. Die Herstellung der Erzeugnisse erfolgte nach 3 Technologien: I, Salzpokelung; 11, Trockenpokelung; 111, Trockenpokelung unter Zusatz vori 0,6% Honig. In der Lende wutde ein hoherer Gehalt an Phospholipiden

MITEVA/TRENDAFILOVA et al. : Effects of curing meat products on their flavour. Part 1 331

ermittelt. Die Salzpokelung ver\lrsachte in beiden Fleischarten eine intensivere Fetthydrolyse. Die Fraktionen der freien Fettsauren in den nach den Technologien 11 und 111 hergestellten Erzeugnissen waren reicher an ungesattigten Fettsauren, die einige der wichtigsten Fleischaroma-Vorstufen darstellen.

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References

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[lo] MOTTRAM, D. S., and R. A. EDWARDS, J. Sci. Food Agric. 34 (1983) 517. [ l l ] SCHR~DTER, R., J. SCHLIEMANN and G. WGLM, Nahrung 30 (1986) 753. [I21 SCHR~DTER, R., J. SCHLIEMANN and G. W ~ L M , 2nd Wartburg Aroma Symposium, Eisenach, GDR,

1131 WAITS, B. M., Adv. Food Res. 5 (1954) 1. [I41 WASSERMAN, A. E., and A. M. SPINELLI, J. agric. Food Chem. 20 (1972) 171.

EKATARINA MITEVA, PH. D., Z. TRENDAPILOVA and M. WKUROV, Institute of Meat Industry, 65 Cherni Vrah Blvd., 1407 Sofia, Bulgaria

Received February 24, 1988

1987.