G. Gandemer

Lipids in muscles and adipose tissues, changes during processing and sensory properties of meat products

Dry-cured meat products represent a large part of the meat products on the European market. The technologies develop for these products lead to the production of a large scale of meat products with typical sensory traits. Numerous studies have been devoted to optimise the quality traits of these products which are considered as traditional products by the consumer and provide a high added value to the producer. Among the components of the raw material, lipids play a key role in the final quality of these products. Many sensory traits of dry-cured meat products depend on lipid traits of muscle and adipose tissues of fresh meat and on their degradation through a complex set of lipolytic and oxidative reactions during processing. Lipid traits of both muscle and adipose tissues of fresh meat are strongly related to pig rearing conditions, mainly genotype and feeding strategy. During processing, lipids undergo intense lipid hydrolysis controlled by both lipases and phospholipases, which remain active all along the process. Lipids are also subjected to oxidation, which generates numerous volatile compounds. These volatiles contribute to some typical aroma notes of dry-cured meat products such as rancid, aged ham and dry-cured odours. This paper reviews the recent knowledge on the influence of lipid traits of fresh meat, lipid hydrolysis and oxidation on the development of sensory traits of dry-cured meat products.

Lipid composition of pork muscle in relation to the metabolic type of the fibres

The aim of this study was to investigate the relationships between lipid composition and metabolic type of the muscles in pork. Five muscles (Longissimus dorsi, Biceps femoris, Psoas major, Trapezius and Masseter) were chosen in order to cover a broad range of metabolic type. The results showed that:

Volatile compounds of commercial Milano salami.

The relationship between extracted volatiles of Milano salami, one of the main dry-cured sausages produced in Italy, and their olfactory properties was studied. Volatile compounds were extracted by a purge-and-trap method, quantified using a flame ionisation detector and identified by mass spectrometry. Olfactory analysis was performed by sniffing the gas chromatographic effluent. Nearly 80 compounds were identified and quantified: most came from spices (60.5%), 18.9% from lipid oxidation, 11.8% from amino acid catabolism and 4.9% from fermentation processes. Panellists detected 19 odours by sniffing. These odours were associated with spices, lipid oxidation or fermentation and were in agreement with the contributions of each reaction to the overall aroma of the product.

Effect of dietary lipid on growth performance and body composition of brown trout (Salmo trutta) reared in seawater

Abstract An experiment was carried out with 12 groups of a fast-growing strain of brown trout reared in seawater. Each treatment was fed to triplicate groups of 158 fish of 1.6 kg average body weight reared in 60-m3 floating cages. Four experimental diets corresponding to two levels (21 versus 29%) and two sources of added lipid (corn, i.e. vegetable, versus cod liver, i.e. marine) were tested. Crude protein content was similar (about 52%) in all diets. All fish were fed the same amount of calculated digestible energy. The level of fat had a slight but significant effect on growth rate and feed conversion; the higher dietary lipid level led to a faster daily growth index (+4.8%) and better feed conversion (−12%). Protein utilization, estimated by both protein efficiency ratio and productive protein value, was also improved in the high-lipid compared to low-lipid treatments. The same factor also significantly influenced fat and muscle water content which were higher and lower, respectively, in the high-lipid compared to low-lipid treatments. The source of added lipid did not influence growth rate, feed conversion, or protein efficiency. Lipid source had no effect on body composition except in the case of liver which contained more lipid and less water in the fish fed cod liver oil. The source of lipid had very pronounced effects on the fatty acid (FA) profile of muscle and liver lipids but the variations mainly concerned saturated (in liver only), monounsaturated and 18:2n−6 FAs (in both tissues). On the other hand, n−3 polyunsaturated FAs were significantly but only slightly modified by the source of lipid, corresponding for both tissues to that found in other salmonids. The level of 20:4n−6 remained constant. The elongation product of 18:2n−6, namely 20:2n−6, was incorporated in muscle and liver lipids while the Δ6 desaturation product, 20:3n−6, was only observed in liver.

Time-related changes in intramuscular lipids of French dry-cured ham

The aim of this study was to investigate the changes in intramuscular lipids during the processing of French dry-cured hams. In the fresh biceps femoris muscle, the lipid content was on average, 105 mg/g DM with a large individual variation. Glycerides accounted for about 75% of total lipids. During processing for 273 days, phospholipid content decreased markedly whereas free fatty acid content rose from 1·9 mg/g DM to 9·4 mg/g DM. Little change affected the fatty acid composition of both glycerides and phospholipids during processing. After a decrease in the proportion of polyunsaturated fatty acids during the first 2 months, free fatty acid composition remained stable. The results suggest that lipid alteration during dry-curing of hams is due to lipolysis and that lipid oxidation is limited.

Lipolysis and oxidation in subcutaneous adipose tissue during dry-cured ham processing

Abstract In southern countries where the consumers eat the adipose tissue of ham slices, adipose tissue contributes to the typical flavour of ham. The aim of this study was to investigate the changes in lipids of subcutaneous adipose tissue during dry-cured ham processing. Lipid hydrolysis and oxidation were followed in the adipose tissue of 30 hams (by groups of six) at different stages of processing (green ham, 6, 12, 18 and 24 months). The results showed that: (1) Adipose tissue of the green ham contained 89.7% triacylglycerols, 5.6% water and low amounts of free fatty acids (FFA) (0.1%), diacyl- and monoacylglycerols (traces). The main triacylglycerols were di-oleoyl-palmitoyl glycerol (POO) (36.6%), palmitoyl-stearoyl-oleoyl glycerol (PSO) (19.9%) and palmitoyl-oleoyl-linoleoyl glycerol (POL) (8.0%). Free fatty acids had a higher proportion of polyunsaturated fatty acids than triacylglycerols (17.7% vs 8.3%). (2) An intense lipolysis occurred during the first 6 months and continued at a slow rate up to 24 months. The amount of triacylglycerols decreased from 89.6 to 75.8% while FFA, diacyl- and monoacylglycerol amounts increased to reach 10.5, 4.5 and 1.3%, in the 24 month old hams, respectively. A preferential hydrolysis of triacylglycerols POO, POL and OOL was observed. Free fatty acid composition showed a sharp decrease in linoleic and stearic acids and an increase in palmitic acid. The decrease in linoleic content during the process suggested that this fatty acid acid was oxidised. Both lipolytic and oxidative changes in lipids of adipose tissue could affect its sensory traits, particularly colour and taste.

Lipid characteristics associated with oxidative and glycolytic fibres in rabbit muscles.

The purpose of this study was to specify the intramuscular lipid characteristics which are related to the metabolic type of muscles. Two glycolytic muscles (Longissimus lumborum and Psoas major), two oxidative ones (Soleus and Semimembranosus propriosus) and an intermediate one (Gastrocnemius laterale) were dissected from rabbit carcasses. The results showed that:

Relations between compositional traits and sensory qualities of French dry-cured ham.

The left hams of 20 pig carcasses were processed by dry-curing for either 179 (n = 10) or 273 days (n = 10). The Biceps femoris was taken at the end of the processing and submitted to chemical and sensory analyses. The following chemical traits were determined: pH, moisture, salt content, fatty acid content and composition of lipid classes (triglycerides, phospholipids, free fatty acids), nitrogen fractions (soluble and insoluble protein, non-protein nitrogen, free amino acids) and volatile compounds. Sensory analysis was performed by a panel of 12 trained members, who scored texture traits (firmness, dryness, fibrousness, mellowness), taste (salty, acid), intensity of aromas (typical of dry ham, fresh meat, fat, cured meat, rancid, metal), persistence of dry ham aroma, persistence of taste after deglutition, persistence of astringency, persistence of metallic taste. The sensory qualities of dry-cured ham showed noticeable changes between days 179 and 273. Firmness, dryness and intensities of aromas typical of dry-cured ham and cured meat were enhanced with time. Neither pH, moisture nor salt content played a noticeable role in determining the sensory quality of dry-cured ham. Among the volatile compounds, the levels of several ketones and 1-butanol were significantly correlated with the aromas of dry ham and cured meat, while rancid aroma was related to aldehydes, ethylacetate, 2,3-pentanedione and nonane. Therefore, the aromas of dry ham and cured meat appeared to be determined mainly by the products of lipid oxidation. However, they were related also to unidentified volatile compounds, whose identification would be of particular interest.

Quality of pig adipose tissue: relationship between solid fat content and lipid composition

The dependence of solid fat content at 20°C of adipose tissues on their fatty acid and triacylglycerol compositions was studied on lipids extracted from tissues from 166 pigs. The solid fat content (SFC20) was 20% on average but varied widely (9-35%). The SFC20 variability was closely related to the proportions of disaturated triacylglycerols and more specifically to palmitoyl-stearoyl-oleoyl-glycerol (R(2)=0.92). The SFC20 variability was also related to the proportions of the saturated fatty acids, palmitic and stearic acids (R(2)=0.94). The part of the variance of SFC20 explained by the proportion of polyunsaturated fatty acids was lower (R(2)=0.48). The iodine value showed a high correlation with SFC20 (R(2)=0.81) but carcass lean content was a poor indicator of the solid fat content of adipose tissues (R(2)=0.06).

Reducing salt content of dry-cured ham: effect on lipid composition and sensory attributes

The salt content of dry-cured ham must be reduced to adapt the product to the taste of the consumer and to human health recommendations. This study dealt with the effect of lowering salt content on the lipid composition and sensory attributes of 18-month-old Corsican dry-cured hams. Six were salted according to a long time salting method and six according to a short time method (STS). The latter was lower in both total and free chlorides (4.7% v 7.3% and 1.5% v 2.0%, respectively) and in dry matter (23.8% v 25.2%). The composition of the intramuscular lipids was similar for both salting methods except that the proportion of polyunsaturated fatty acids of the phospholipids was higher in STS hams (42.3% v 34.0%). The salting method had no significant effect on the appearance of the hams (marbling, colour). However, the STS hams were less salty and their aroma notes related to fat such as rancid, fatty and buttery were more pronounced.