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ANIMAL PRODUCTS |
* Laboratory for Animal Nutrition and Animal Product Quality, Department of Animal Production, Ghent University, 9090 Melle, Belgium; and and
Faculty of Biosciences and Landscape Architecture, University College of Ghent, 9000 Ghent, Belgium
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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-linolenic acid and eicosapentaenoic and docosahexaenoic acid (EPA and DHA), respectively, were supplied equivalent to a level of 1.2% oil (as fed), either during the whole fattening period or only during the first (P1; 8 wk) or second (P2; 6 to 9 wk until slaughter) fattening phase. All diets were based on barley, wheat, and soybean meal and were fed ad libitum. Crossbred pigs (n = 154; Topigs 40 x Piétrain) were randomly allotted to the 7 feeding groups. In the basal diet (B), only animal fat was used as the supplementary fat source. Three dietary groups were supplied the same fatty acid source during both fattening phases (i.e., group BB, LL, and FF). For the other 4 dietary groups, the fatty acid source was switched after the first phase (groups BL, BF, LF, and FL; the first and second letter indicating the diet in P1 and P2, respectively). Twelve animals per feeding group were selected based on average live BW. The LT was analyzed for fatty acid composition; lipid stability (thiobarbituric acid-reactive substances) and color stability (a* value, % of myoglobin pigments) were determined on the LT after illuminated chill storage for up to 8 d. The -linolenic acid, EPA, and docosapentaenoic acid incorporation was independent of the duration of linseed feeding (1.24, 0.54, and 0.75% of total fatty acids, respectively, for group LL). Supplying fish oil during both phases resulted in the greatest EPA and DHA proportions (1.37 and 1.02% of total fatty acids; P < 0.05), but the content of docosapentaenoic acid was not affected. The proportion of DHA was greater when fish oil was administered during P2 compared with P1 (P < 0.05). There was no effect of diet on meat ultimate pH and drip loss or on lipid or color oxidation.
Key Words: fish oil • linseed • omega-3 fatty acid • oxidative stability • pork
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Increasing their intake may be most easily achieved by supplementing the human diet with encapsulated fish oil or microalgae or by increasing the consumption of fish. However, because the intake of fatty fish is low in Western societies, the consumption of LC n-3 PUFA from terrestrial animal products (meat, eggs) may be important (Howe et al., 2006). Givens et al. (2006) and De Henauw et al. (2007) argued that enrichment of meat products with n-3 PUFA by dietary means could help bridge the gap between their recommended and actual intake. Hereby, the feed oil source is important and delivers either the LC n-3 PUFA as such as in fish oil or under the form of its precursor fatty acid, -linolenic acid (-LNA), as in linseed oil. Apart from the nature of the oil source, the duration and level of its supplementation are of crucial importance and can be varied to determine the optimal supplementation strategy (Wood et al., 2003; Raes et al., 2004).
A more unsaturated fatty acid profile may limit the shelf-life of meat, because PUFA are more prone to oxidation. This has been identified as a major problem in previous work using -LNA-rich oilseeds or fish oils to enrich pork with n-3 PUFA above certain concentrations (Romans et al., 1995b; Overland et al., 1996; Leskanich et al., 1997; Wood et al., 2003). Oxidation may be manifest as off-odors and flavors resulting from lipid oxidation or as an impaired meat color.
In this experiment, we assessed the importance of the time and duration of linseed and fish oil supplementation to enhance the incorporation of n-3 PUFA in pork. While altering the fatty acid profile, the oxidative stability (color and lipid oxidation) also was measured.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Experimental Setup and Sampling
Crossbred pigs [n = 154; Topigs 40 sow (Helvoirt, the Netherlands) x Piétrain sire] at a mean (SD) live BW of 36.4 (4.5) kg were randomly allotted to 7 feeding groups. Each group was housed in 2 pens of 11 animals and was fully balanced according to sex (barrows and gilts). The trial lasted for 14 to 17 wk and consisted of 2 phases [P1, 8 wk (until approximately 70 kg); P2, 6 to 9 wk (until an approximate slaughter weight of 100 kg)], in which the feed fat source differed depending on the dietary group. Pigs were fed ad libitum. All diets were based on barley, wheat, and soybean meal. The dietary fat was adjusted to 4% (as-fed basis) by the addition of rendered animal fat. Diets were formulated for an equal energy supply (2,225 kcal/kg, as fed) and a minimum linoleic acid (LA) content of 0.9%. In the basal diet (B), only animal fat was used as supplementary fat source. In diets L and F, linseed (L; -LNA supply) or fish oil (F; EPA and DHA supply) was added, respectively, to provide 1.2% oil (as fed) at the expense of animal fat. Three dietary groups were supplied the same fatty acid source during both fattening phases (i.e., groups BB, LL, and FF). For the other 4 dietary groups, the fatty acid source was switched after the first phase (groups BL, BF, LF, and FL; the first and second letter indicating the diet in P1 and P2, respectively). A graphical presentation of the experimental setup is given in Figure 1. The composition and the fatty acid profile of the experimental diets are given in Tables 1 and 2, respectively.
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Carcass and Meat Quality Measurements
At the beginning of each phase and before slaughter, pigs were weighed individually. Carcass lean content was assessed by means of a Giralda Choirometer PG 200 apparatus (Classpro GmbH, Sielenbach, Germany). At 24 h postmortem, pH in the LT [6th- to 7th-rib region; Knick Portamess 654 (Knick Elektronische Messgeräte GmbH, Berlin, Germany) with Schott N5800A electrode (Schott Instruments, Mainz, Germany) and Pork Quality Meter (PQM-I Kombi, Intek GmbH, Aichach, Germany)] and the ham (semimembranosus muscle) was measured.
Percentage drip loss of meat was determined by measuring the amount of fluid lost from a 2.5-cm-thick loin chop that was suspended for 48 h in a chill cabinet at 4° C.
For color measurements, meat samples were overwrapped in an oxygen-permeable polyethylene film (oxygen transmission rate > 1,000 cm3/(m2 x 24 h). On d 0, the measurement was done after 30 min of blooming (in the film at 4° C) and then daily until 8 d of illuminated chill storage (fluorescent light, 900 lx, 4° C). Reflectance spectra (every 10 nm between 400 and 700 nm) and color coordinates (CIE L*a*b* color system) were assessed using a HunterLab Miniscan Minolta XE plus spectrocolorimeter [light source of D65, standard observer of 10° , 45° /0° geometry, 2.54 cm light surface, white standard (Hunterlab Associates Laboratory Inc., Reston, VA)]. The results were expressed as lightness (L*), redness (a*), yellowness (b*), hue value [tan– 1(b*/a*)], and saturation index [(a*2 + b*2)1/2]. By means of reflectance values at specific wavelengths, the percentage of the different forms of myoglobin [oxymyoglobin (OxyMb), deoxymyoglobin, and metmyoglobin (MetMb)] was calculated according to the method of Krzywicki (1979), as modified by Lindahl et al. (2001).
For lipid oxidation analysis, the same samples as for color measurements were used. Lipid oxidation was assessed by thiobarbituric acid-reactive substance measurement (TBARS) using the distillation method, as described by Tarladgis et al. (1960), after adding the strong antioxidant butylated hydroxytoluene, and was expressed as micrograms of malondialdehyde per gram of meat. Lipid oxidation of LT samples was measured in duplicate after 8 d of storage.
Fatty Acid Analysis
Feed and meat samples were extracted using chloroform:methanol (2:1, vol/vol; modified based on the methods of Folch et al., 1957). Fatty acids were methylated as described by Raes et al. (2001) and analyzed by gas chromatography (HP6890, Brussels, Belgium) on a CP-Sil88 column for fatty acid methyl esters (100 m x 0.25 mm x 0.2 µm; Chrompack, Middelburg, the Netherlands). Peaks were identified based on their retention times, corresponding with standards (NuChek Prep., Elysian, MI; Sigma, Bornem, Belgium). Nonadecanoic acid (C19:0) was used as an internal standard to quantify the individual and total i.m. fatty acids.
Statistics
For all analyses performed on the fresh meat, a GLM with fixed factors of feeding group and sex was used. The interaction term was not significant (P > 0.05). In a preliminary statistical analysis, slaughter group was added as a factor, but because it was not significant, it was omitted from the final model. Orthogonal contrast analysis was performed to detect differences between feeding groups. The effect of the fatty acid profile of the diets given during both feeding phases was tested by the contrasts LL vs. BB, LL vs. FF, and BB vs. FF. The effect of duration of supplementation of linseed and fish oil was assessed by the following contrasts, respectively: LL vs. (BL and FL) and FF vs. (BF, LF, and FL). The significance of the time of fish oil supplementation was tested by contrasting LF vs. FL. The analyses were performed using the statistical software package S-Plus for Windows (version 6.0, Insightful, Seattle, WA).
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Fatty Acids
There was no difference for the total i.m. fatty acid content between the feeding groups [mean (SD) 1.41 (0.22) g/100 g of meat] with the lowest and greatest value for groups BL and FF, respectively (Tables 3 to 5).
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shows the effect of supplying a single fatty acid source during the whole fattening period on the fatty acid profile of the LT muscle (groups BB, LL, and FF). The total n-6 PUFA and LA proportion was similar in groups BB and LL. The basal diet gave rise to a greater arachidonic acid (AA; C20:4n-6) proportion as compared with linseed feeding (P < 0.05). The proportion of total as well as individual n-6 PUFA was lower in the FF group as compared with the LL and BB groups (P < 0.05; except for LA being lower, however nonsignificantly (P > 0.05), in FF as compared with LL).
The -LNA proportion was greatest in the meat of group LL (P < 0.05). The supply of -LNA in this group also increased the proportion of EPA and docosapentaenoic acid (DPA, c22:5n-3) as compared with the basal feeding group (P < 0.05). However, the DHA proportion did not differ between BB and LL. The total and LC n-3 PUFA proportion was greatest for group FF (P < 0.05). The fish oil diet resulted in a 6-fold increased deposition of EPA and DHA in the LT as compared with the basal diet and a 3- and 5-fold increase of EPA and DHA, respectively, as compared with the linseed feeding. In the FF group, the DPA level was greater compared with group BB (P < 0.05).
The effect of duration and time of linseed or fish oil supplementation on the fatty acid profile of the LT muscle is shown in Tables 4 and 5. The -LNA incorporation was similar when feeding linseed during both phases or only during P2. For EPA and DPA, there was no difference between feeding the basal or linseed diet in P1 in combination with linseed in P2. Feeding fish oil continuously as compared with fish oil feeding only in 1 phase resulted in greater EPA and DHA proportions (P < 0.05), but the proportion of DPA was not affected. When fish oil was fed either during P1 or P2, only the proportion of DHA was influenced, being greater when fish oil was administered during P2 (P < 0.05).
Barrows had the greatest i.m. fatty acid content, together with the greatest total and individual SFA proportions (C12:0, C14:0, C16:0, and C18:0; P < 0.05). Only the proportion of C17:0 was greater for gilts (data not shown; P < 0.05). The proportions of the major MUFA, C18:1cis-9 and C16:1cis-9, were greater for barrows (data not shown; P < 0.05). Total and individual n-6 (except for C22:4n-6) and n-3 PUFA were greater for gilts (P < 0.001; Table 6).
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For the color of fresh LT expressed as L*, a*, and b* values (and saturation index and hue values calculated from those data), groups were not different throughout the storage period (data not shown). Up to d 3 of chill storage, color stability expressed as MetMb and OxyMb percentage was not different between groups. From d 3 until the end of the chill storage, group LL behaved differently, although not significantly, as compared with the other groups having lower MetMb and greater OxyMb percentages (Figure 2).
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DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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).
Fatty Acids
The lack of effect of dietary fatty acid source on the i.m. fatty acid content accords with other work on pigs receiving diets differing in total fat or fatty acid composition, or both (Allee et al., 1972; St. John et al., 1987; Rhee et al., 1988; Leskanich et al., 1997; Scheeder et al., 2000).
The slightly lower dietary LA supply in the FF group resulted in a significantly lower n-6 PUFA proportion in the meat. In case of similar dietary supply of n-6 fatty acids (groups LL and BB), an increased n-3 PUFA supply in the LL group was not accompanied by a decreased deposition of n-6 fatty acids, except for AA. These results were partly in agreement with Riley et al. (2000), in which an equal amount of LA together with increasing levels of dietary -LNA did not induce differences in total n-6 fatty acids deposited in the LT. However, in contrast to our study, no differences in any of the individual n-6 PUFA were found by Riley et al. (2000). The greater AA proportion in meat of the animals on the basal diet compared with the linseed or fish oil diet confirms the inhibiting effect of greater -LNA proportions on elongation and desaturation of LA to its longer-chain metabolites and the competition between AA and LC n-3 PUFA for incorporation into phospholipids. The increased supply of -LNA in group LL yielded a significant increase in the proportion of EPA and DPA as compared with group BB. However, increasing DHA proportion in meat was only achieved when fish oil was included in the animal diet. Hence, this study supports other literature findings that specific dietary supply of DHA is needed to increase the DHA content of pork (Romans et al., 1995a,b; Ahn et al., 1996; Riley et al., 2000; Raes et al., 2004). The DHA formation seems to be strictly metabolically regulated and cannot be substantially influenced by dietary supply of the precursors. The desaturation and elongation chain of n-3 fatty acids seems to block at the level of DPA. On the other hand, Enser et al. (2000) observed an increased i.m. DHA level in pork by feeding linseed at a level of 4 g of -LNA/kg of feed. However, the increase was small (0.38 and 0.45 g/100 g of total fatty acids for the control and linseed-fed group, respectively). Also, incorporation of -LNA and elongation to EPA and DPA was more efficient in their research compared with our study. Recently, Kralik et al. (2006) found that adding rapeseed oil to the diets of pigs (at a level of 3 and 6%) increased the DHA content in muscle tissue, which in turn supports the fact that pigs can synthesize DHA in vivo.
The total and LC n-3 PUFA proportion was significantly greater for group FF > group LL > group BB. It seems that the incorporation efficiency of EPA and DHA from fish oil into muscle was much greater than the one of -LNA from linseed. A level of 2.31% EPA and 3.53% DHA in the lipid fraction of the fish oil diet resulted in 1.37 and 1.02% of EPA and DHA, respectively, in the muscle lipid fraction, whereas 16% -LNA in the lipid fraction of the linseed diet only resulted in 1.24% -LNA in the muscle lipid fraction. This can be explained by 3 factors. First, there might be an effect of the matrix in which the fatty acids were embedded, leading to a potentially greater digestibility of the fatty acids in the fish oil compared with those in crushed linseed. Second, β-oxidation is faster for -LNA compared with its LC products, which are more selectively incorporated into phospholipids within permanent cell structures (Leyton et al., 1987). When a fatty acid is preferentially oxidized for energy, this could account for low incorporation rates observed with this particular fatty acid. Third, after absorption, -LNA has to compete with LA for incorporation and desaturation and elongation to its longer-chain metabolites in the tissues (Mohrhauer and Holman, 1963).
The increased level of DPA after fish oil supplementation as compared with the basal diet is in accordance with Lauridsen et al. (1999). However, other studies consistently showed an increased EPA and DHA deposition but no effect on the DPA concentration in pigs fed fish oil diets (Irie and Sakimoto, 1992; Morgan et al., 1992; Leskanich et al., 1997). Sprecher et al., 1995 found that DPA can be formed during elongation of EPA or by retroconversion of DHA.
The -LNA incorporation was similar when feeding linseed during both phases or only during P2. This indicates that, in case of linseed supplementation during P2, the -LNA proportion remained unchanged irrespective of the oil source during the previous phase (P1). Also, for EPA and DPA, there was no difference between feeding the basal or linseed diet in P1 in combination with linseed in P2. It seems that by supplying linseed for 6 to 9 wk before slaughter at the level in this experiment, the saturation plateau for the synthesis of the LC metabolites was reached.
The greatest EPA and DHA proportions were obtained when fish oil was fed during both phases. When supplied during either P1 or P2, the proportion of DHA was greatest with fish oil feeding in P2. To our knowledge, the alternating supply of fish oil and linseed (oil) has only been studied in fish (Bell et al., 2004). Feeding fish oil in at least 1 phase caused the n-6:n-3 ratio to conform to the recommendation of < 5 (Hoge Gezondheidsraad, 2006). The n-6:n-3 ratio is known to be highly influenced by the fatty acid composition of the diet. The range of the P:S ratio was narrow (0.27 to 0.4) and for all groups lower than the recommended minimal value of 0.7 (Hoge Gezondheidsraad, 2006).
Meat Quality Traits
Despite the significant effects of dietary fat source on the i.m. fatty acid composition, none of the measured meat quality traits (pH, drip loss, color, lipid oxidation) were significantly different between dietary treatments. The reason for the distinct color stability for group LL from d 3 on is unclear. For monitoring the negative quality effects of high-PUFA diets in pork, several thresholds have been suggested for the maximum level of PUFA in feed. Warnants et al. (1996) proposed the threshold for feed to be 18 g of PUFA/kg of feed. For all the feeds in this experiment, PUFA were below this level. Feeding linseed at a similar level to our trial did not induce negative effects on pork quality as seen by Sheard et al. (2000). However, it should be kept in mind that these threshold levels are dependent on other factors besides the PUFA levels in the feed (e.g., duration of supplementation, dietary antioxidant levels, storage and processing conditions of the meat, muscle and animal differences).
In conclusion, the effects of duration and time of feeding a specific fat source on the muscle fatty acid composition is dependent on the fatty acids considered. For the deposition of -LNA and its conversion to LC metabolites in muscle after the supply of linseed, only the last phase before slaughter was determinant. When supplying fish oil, the greatest EPA and DHA proportions were found in case of a continuous supply throughout the fattening period, and levels of DHA but not EPA were lower when fish oil was fed during the first fattening phase followed by linseed feeding before slaughter. Neither meat quality traits (drip loss, pH, etc.) nor lipid or color oxidation were influenced by dietary oil source or duration of supplementation.
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Footnotes |
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3 Present address: EnBiChem, Department of Industrial Engineering and Technology, University College West-Flanders, 8500 Kortrijk, Belgium.
2 Corresponding author: Stefaan.DeSmet{at}UGent.be
Received for publication January 15, 2007. Accepted for publication February 20, 2008.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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-linolenic acid on the fatty acid composition, storage stability and sensory characteristics of pork loin. Meat Sci. 43:291–299.[CrossRef]This article has been cited by other articles:
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
for the LL group, linseed diet in both phases;- for the mean of the other groups).