Jean-Michel Besle

Phospholipid, Sphingolipid, and Fatty Acid Compositions of the Milk Fat Globule Membrane are Modified by Diet

The phospholipid and sphingolipid composition of milk is of considerable interest regarding their nutritional and functional properties. The objective of this article was to determine the lipid composition of the milk fat globule membrane (MFGM) of milk from cows fed a diet rich in polyunsaturated fatty acids. The experiments were performed with 2 groups of 6 cows feeding on (i) maize silage ad libitum (+ grassland hay, mixture of cereals, soyabean meal) or (ii) the maize silage-based diet supplemented with extruded linseed (bringing a lipid proportion of 5% of dry matter). The phospholipid and sphingolipid composition of the MFGM was determined using HPLC/ELSD. The fatty acid (FA) composition of total lipids and phospholipids was determined using GC. As expected, the linseed-supplemented diet decreased the saturated FA and increased the unsaturated FA content in milk fat. MFGM in milk from cows fed the diet rich in polyunsaturated FA resulted in (i) a higher amount of phospholipids (+ 18%), which was related to a smaller size of milk fat globules (ii) an increase of 30% (w/w) of the concentration in sphingomyelin, (iii) a higher content in stearic acid (1.7-fold), unsaturated FA (1.36-fold), and C18:1 trans FA: 7.2 +/- 0.5% (3.7-fold). The MFGM contained a higher concentration of unsaturated FA (C18:1, C18:2, and C18:3) and very long-chain FA (C22:0, C23:0, C24:0, EPA, DHA) compared with total lipids extracted from milk. The technological, sensorial, and nutritional consequences of these changes in the lipid composition of the MFGM induced by dietary manipulation remain to be elucidated.

Ultraviolet-absorbing compounds in milk are related to forage polyphenols

The aim of this work was to characterize UV-absorbing compounds (UAC) in milk in relation to diet. In winter, 4 groups of cows each received a different diet: concentrate rich containing 35% cocksfoot hay (CCH), maize silage (MS), rye grass silage (RS), or rye grass hay (RH). In summer, 2 additional diets were given: mountain grassland hay (GH) and mountain grassland pasture (GP). Polyphenols were analyzed by HPLC and Folin reaction on forages and UAC were extracted from milks and analyzed by HPLC. In forages, the number of polyphenols was lowest in MS (57) and greatest in GP (85). Twenty-four peaks were identified, accounting for 28 to 47% peak area at 280 nm. Caffeoyl compounds and flavonoid glycosides were mainly found in RH, GH, and GP. Hydrolyzed compounds such as hydroxycinnamic acids and aglycones were found in MS and RS. Estimated amounts of polyphenols were lowest for MS (3.7 g/kg), roughly similar for CH, RS, and RH (about 15 g/kg), and greatest for GH and GP (21.6 and 35.3 g/kg, respectively). About 230 different peaks were separated in milks. Milks from RH and GP contained the lowest (87) and the greatest (127) numbers of peaks, respectively. Only 10 peaks were identified, accounting for 21 to 54% of the total spectra area. In addition to the major compound hippuric acid, phenylacetic acid, benzoic acid, 4-hydroxybenzoic acid benzaldehyde, catechol, and small amounts of ferulic acid were found in varying amounts depending on the diet. Flavonoids such as quercetin, luteolin, and apigenin were also present. Hippuric acid was clearly related to the presence of caffeoylquinic compounds in forages. Other identified UAC may originate essentially from forage simple polyphenols or from cell wall aromatics. Some of the several unknown compounds may also originate from the transformation of other nutrients. Estimated amounts of UAC were widely variable within each animal group. They were surprisingly high in CCH and roughly similar in all milks from preserved forages (about 3.6 mg/L), with generally greater values for GH milks, whereas the greatest amount was found in GP milks (13.3 mg/L). Hierarchical clustering clearly discriminated the 6 diets, showing that there were major differences in GP milks. Some UAC were specific to one or a group of diets. Ultraviolet-absorbing compounds are therefore a potential tool to distinguish between milks according to diet. In addition, they may have a bioactive effect on milk component conservation or on human health.

Selection for nutrients by red deer hinds feeding on a mixed forest edge

We studied the nutritional behaviour of hinds foraging on a mixed-forest edge by direct observation of their choices at each season and by measuring nutrient concentration in the plants. We compared nutrient concentrations in the observed diets with those in the total available vegetation, and with those of 1,000 randomly simulated diets in which we included only those plants that were actually eaten by the animal. Whether the available or the consumed feeds were used as the basis for comparisons had important consequences due to the presence of conifers and ferns, which were high in soluble sugars but were never eaten by the animals (potentially due to their toxicity). The selected diets were lower in sugars than the total available vegetation in summer, but were actually higher in sugars than the random diets generated from consumed forage species only. Hind diets contained more soluble sugars but not more protein than simulated diets in all seasons. Contrary to our prediction, anti-nutritional compounds (ADL and tannins) were avoided only in winter. Compared to simulated diets, hinds consumed more tannins in spring and summer and more ADL in summer and autumn. We suggest that this was a consequence of selection for soluble sugars, because the preferred plant species, which had high soluble sugar concentrations, also contained a large proportion of the anti-nutritional compounds eaten. In winter, the grass-dominated diets contained more fibre (NDF) and less ADL than the simulated diets, indicating that hinds orient their feeding towards digestible fibres. The switch from a browser to a grazer diet was related to a change in the availability of the nutrients, mainly soluble sugars. In our study, grasses contained more soluble sugars and proteins than deciduous browse during winter. This calls into question the dichotomy usually assumed in the literature between grass and browse in terms of nutrient content.

Tissue distribution of isoflavones in ewes after consumption of red clover silage.

When discovered in the 50s, isoflavones were suspected to provoke infertility syndrome in sheep grazing on clover. Many others effects of these phytoestrogens have been documented afterwards. To determine the distribution of isoflavone metabolites in ewe tissues and look for a link with their physiological impact, two ewes were fed a diet containing 50% red clover silage (variety Pawera) for one month with a daily intake of 157.6 mg/kg bw of total isoflavones. Only aglycones were fed due to the fermentation stage of the silage. At the sacrifice, isoflavone metabolites and aglycones were analyzed in blood, liver, kidney, lung, heart, muscle, ovaries, uterus, mammary glands, suprarenal glands, thymus, aorta, thyroid, pituitary gland, cerebellum, olfactory lobes, and brain hemispheres using HPLC-Coularray and LC-MS-MS. The major compounds recovered in tissues were equol and daidzein, present as glucuronides. Kidney concentrations were 10-fold higher than in other tissues. Penetration in brain was very limited. Reproductive organs contained higher concentrations of isoflavones than heart, muscle, or thymus. Distribution of isoflavones in ewe tissues is unequal and may reflect specific impact in some target tissues.

Variation in content and composition of phenolic compounds in permanent pastures according to botanical variation.

Phenolic compounds contribute to the micronutrient composition of pasture, which in turn may affect animal product composition. To assess the importance and variations in content of these compounds, the polyphenolic and botanical compositions of 24 permanent pastures located in one lowland and two upland regions were studied at equivalent stages of growth. Phenolic fractions were characterized and quantified using HPLC-PDA-ESI-QToF, and the total content was determined by colorimetry over each whole pasture. A rise in altitude was accompanied by a marked increase in total phenolic content, linked to changes in botanical composition, but did not have any influence on the distribution according to molecular class. For all of the pastures, significantly different patterns due to qualitative and quantitative differences among the 92 separate peaks were observed with 31 compounds identified. The involvement of certain plants in the variations of content and composition in phenolic compounds of pastures was statistically evaluated.