Nitrogen Oxide-Initiated Cholesterol Oxidation and Carotenoid Degradation in an Egg Lipid Model System

The influence of nitrogen oxide (NO _x ) concentrations on the oxidation of cholesterol and carotenoids in an egg lipid model system was investigated. The effects of dietary α-tocopherol supplementation on cholesterol and carotenoid stability in egg lipids were also evaluated. The rate constants for cholesterol oxidation and carotenoid degradation in egg lipids during storage at 40°C were affected by both the egg treatments and the level of exposure to NO _x before storage. The presence of NO _x greatly promoted the oxidation of cholesterol and carotenoids. Dietary supplementation with α-tocopherol greatly improved the stability of carotenoids and cholesterol in egg lipids exposed to NO _x . The addition of carotenoids to egg lipids also protected cholesterol from NO _x -initiated oxidation. The patterns of cholesterol oxidation and carotenoid loss in this lipid model system were similar to those in egg powders processed by the direct gas-fired spray-dryer.     

Deposition of Carotenoids in Eggs from Hens Fed Diets Containing Saponified and Unsaponified Oleoresin Paprika

Deposition of carotenoids in saponified paprika (SP) and unsaponified oleoresin paprika (OP) in egg yolks as well as the dietary level for desired pigmentation were evaluated. Sixty-four hens on a carotenoid-depletion diet were divided into two replicated groups of each of eight dietary treatments containing from 0 to 16 mg paprika carotenoids per kg feed. Colour and the carotenoid content of egg yolk increased linearly ( P< 0·01) with the amounts of paprika carotenoids in the diets. The colours of egg yolks from hens fed similar concentra-tions of OP or SP were not significantly different ( P< 0·01). A low dose (4 mg kg⁻¹) of OP or SP provided yolk colour equivalent to the colour of eggs in supermarkets. High-performance liquid chromatographic analyses showed that carotenoids deposited in the yolk are in the free alcohol form, regardless of the form of carotenoids in the diet. Capsanthin, the predominant carotenoid in paprika, was deposited in egg yolk less efficiently than zeaxanthin and lutein.     

The relationship between the α-tocopherol content of the yolk and its accumulation in the tissues of the newly hatched chick

The effect of a range of concentrations of α-tocopherol in the initial yolk on the subsequent levels of this vitamin in the tissues of the newly hatched chick was investigated. Four batches of fertile eggs (Ross 1 broiler-breeder type) with mean yolk α-tocopherol concentrations (μg g⁻¹ yolk) of 60·8, 155·3, 272·2 and 376·6 were incubated and the levels of the vitamin in the liver, brain, heart and kidney of the resultant chicks were measured. The liver of the day-old chick contained far higher levels of the vitamin than were found in the other tissues studied. The concentration of α-tocopherol in the liver was directly proportional to the initial level of this vitamin in the yolk. The concentrations of α-tocopherol in the brain were only about 1% of the corresponding liver values but were also directly proportional to the levels initially present in the yolk. The concentrations of α-tocopherol exhibited by the heart and kidney were affected by the initial yolk values but the response was not linear over the range of yolk α-tocopherol concentrations studied. The results indicate that the initial concentration of α-tocopherol in the yolk has a profound effect on the subsequent levels of this vitamin in the tissues of the chick. In a separate experiment, the changes in the concentration of α-tocopherol in the liver were studied over the first 9 days after hatching. The vitamin was found to be rapidly depleted from the liver after hatching. © 1997 SCI.     

Cholesterol Oxides in Commercial Dry Egg Products: Quantitation

Cholesterol α-oxide (5α-cholestan-5,6α-epoxy-3β-ol), a suspected carcinogen and/or atherogen, and its β-isomer are found in varying amounts in commercial dried egg products. The level of total cholesterol oxides in dried eggs ranges from undetectable to 311 parts per million of total lipids. The majority of the samples (64%) had total cholesterol oxides content between 6 – 49 ppm. The level of cholesterol α-oxide ranges from undetectable to 62 ppm. The ratio of α-oxide to its β-isomer is found consistantly to be 1 to 4. The formation of cholesterol oxides is greater in samples dried by hot air heated directly with gas burner than those dried by air heated indirectly with steam. Prolonged storage increases cholesterol oxides content in dried egg products.     

Thermal and light stabilities and antioxidant activity of carotenoids from tomatoes extracted using an ultrasound-assisted completely solvent-free method

The use of petroleum-derived solvents, particularly volatile organic compounds (VOCs), in the chemical industry has increased the contamination and residual effects of these solvents. Ionic liquids (ILs) can potentially replace VOCs, thereby reducing the risks of environmental contamination and toxicity. In this context, the objectives of this study were as follows: 1 — to obtain an ionic liquid for use in extracting carotenoids from tomatoes with ultrasound assistance; and 2 — to determine the stability and antioxidant activity of tomato carotenoid extracts. Ultrasound can also efficiently extract carotenoid compounds with ionic liquids in comparison with conventional VOC solvents (obtained from an all-trans-lycopene 7.5–8.0 μg·g^− 1 tomato sample by IL and 6.2–7.7 μg·g^− 1 by acetone). Similarly, the activation energies (E_a) in aqueous medium were obtained for the IL carotenoid extract (10.8 kJ·mol^− 1) and acetone carotenoid extract (9.4 kJ·mol^− 1). The antioxidant activities of the tomato carotenoid extract were 7.4 and 12.4 relative to α-tocopherol for the ionic liquid extract and acetone extract, respectively. The combination of chromatographic analysis and degradation kinetics provided data for positive assessment similarity of thermal and light stabilities of tomato carotenoids extracted by IL and extracted by acetone.     

Electron spin resonance (ESR) study on free radical transfer in fish lipid–protein interaction

Oxidised lipids interact with proteins causing undersirable changes in the nutritional and functional properties, including a loss of amino acids, cross-linking and damage to proteins and DNA. Proteins including egg lysozyme, egg ovalbumin, fish myosin and amino acids arginine, lysine and histidine were exposed to oxidised lipids methyl linoleate and oil extracted from Atlantic mackerel (Scomber scombrus). A strong central singlet signal was induced in the proteins and amino acids which was detected by ESR spectroscopy and assigned to the carbon radical (g value range 2.0021–2.0049); with ovalbumin and fish myosin a downfield shoulder, attributed to the sulphydryl group (g value 2.014–2.017), was also observed. The above changes in the proteins were accompanied by an increase in fluorescence indicating the formation of cross-links. Synthetic antioxidants such as butyl hydroxytoluene (BHT) and butyl hydroxyanisole (BHA) as well as natural antioxidants ascorbic acid and α-tocopherol inhibited the development of both the free radical signal and fluorescence when added to the proteins prior to incubation with oxidised lipids; the central singlet signal attributed to the carbon radical was reduced by 10–50%. This paper clearly indicates direct free radical transfer from oxidised lipids to amino acids and proteins which results in protein denaturation and the formation of insoluble aggregates in fish flesh on storage. © 1999 Society of Chemical Industry     

Effect of antioxidants in combination of VCO nanoemulsion on gel properties and storage stability of refrigerated sardine surimi gel

Impacts of β-glucan–virgin coconut oil (VCO) nanoemulsion containing epigallocatechin gallate (EGCG) and α-tocopherol at levels of 0–3.0 g kg⁻¹ on properties and storage stability of surimi gel were investigated. Augmented breaking force, deformation and fracture constant were obtained in gels containing 2.0 g kg⁻¹ EGCG or 1.0 g kg⁻¹ α-tocopherol (P < 0.05). Expressible moisture content increased as EGCG levels were more than 2.0 g kg⁻¹. Smoother microstructure was observed in gels containing 2.0 g kg⁻¹ EGCG. Whiter gels were obtained when β-glucan–VCO nanoemulsion was incorporated. No change in protein pattern of gels was observed regardless of antioxidant incorporation. Viscoelastic moduli decreased as β-glucan–VCO nanoemulsion was added; however, incorporation of 2.0 g kg⁻¹ EGCG or 1.0 g kg⁻¹ α-tocopherol lowered the decrease in G'. β-glucan–VCO nanoemulsion containing gels had higher likeness scores than the control (P < 0.05). Gels containing EGCG and α-tocopherol at selected levels had the improved oxidative stability and lowered microbial loads.     

Fatty acid profile and cholesterol content of egg yolk from chickens fed diets supplemented with purslane (Portulaca oleracea L.)

BACKGROUND: The aim of the present study was to evaluate the effects of purslane on egg production, egg weight, feed efficiency, yolk fatty acid composition, and egg cholesterol content in laying hens. MATERIAL AND METHODS: Sixty 80‐week‐old layers were allocated randomly to receive diets supplemented with 0 (control), 10 g kg^?1 or 20 g kg^?1 dried purslane for 84 days. Egg weights and egg production in the groups were recorded daily, whereas feed intake was measured weekly. RESULTS: Diet supplemented with 20 g kg^?1 purslane significantly decreased body weight of the chickens compared to the control. Inclusion of purslane at the level of 10 g kg^?1 or 20 g kg^?1 into the diet significantly (P < 0.05) improved egg weight compared to the control. Chickens fed the diet including 20 g kg^?1 purslane had a significantly (P < 0.05) higher egg production and improved feed efficiency compared to the control. Cholesterol content of eggs from the hens fed 0, 10 or 20 g kg^?1 did not differ and was 10.45, 9.51 or 9.51 mg g^?1 dried egg yolk, respectively. Inclusion of purslane at the level of 20 g kg^?1 into the diet significantly (P < 0.05) increased ω‐3 fatty acids such as C18:3(ω‐3) and C22:6(ω‐3). The ratio of ω‐6 to ω‐3 also was significantly (P < 0.05) lower in the eggs from chickens fed 10 g kg^?1 or 20 g kg^?1 purslane supplemented diets compared to the control. CONCLUSION: This study showed that adding dried purslane to the diet of laying hens significantly increased egg production and egg weights although there was no reduction in the egg cholesterol concentration. This study also showed that inclusion of purslane into diet enriched eggs with ω‐3 fatty acids and decreased the ratio of ω‐6/ω‐3 in the yolk. Copyright © 2010 Society of Chemical Industry     

A new process for preparing transparent alkalised duck egg and its quality

When fresh duck (Anas plotyrhyncus) eggs (pH 8·0–8·5) are heated, their albumen develops a turbid gel. Through appropriate alkalisation (pH 11·5–12·8), the gel's transparency can be increased. The transparency of the heated duck egg-white is affected by pH value, heating temperature, heating rate and salt concentration. This research deals with the process for preparing the transparent alkalised duck egg and the change in its quality when stored. If fresh duck eggs are pickled in a solution of 42 g NaOH+50 g NaCl litre^?1 (25·3°C) for 8 days, removed, put in a water bath and heated at 70°C for 10 min they become transparent, their hardness and penetration increasing with storage. Total bacterial count and volatile basic nitrogen also increase with storage. The total bacterial count and the volatile basic nitrogen were 4·6 × 10⁶ cfu g^?1, 0·32 mg g^?1 when stored at a temperature of under 25°C for 4 weeks, respectively.     

The relationship between the levels of α-tocopherol and carotenoids in the maternal feed,yolk and neonatal tissues: comparison between the chicken,turkey, duck and goose

The relationship between the levels of the lipid-soluble antioxidants, α-tocopherol and carotenoids, in the parental diet, the yolk and the neonatal tissues was investigated for four avian species of commercial importance. The chicken displayed a much greater efficiency in incorporating α-tocopherol from the parental diet into the yolk in comparison with the turkey, duck and goose. Thus, in spite of similar concentrations in the respective diets, the resultant concentration of α-tocopherol in the yolk of the chicken egg was four to five times greater than observed for the other three species. A similar but less dramatic picture was observed for carotenoids: identical dietary provision of carotenoids in the maternal feeds resulted in the chicken eggs displaying between 1·4 and 1·9 times the concentration in the yolk than was observed for the other three species. These differences between the species regarding the levels of α-tocopherol and carotenoids in the yolk were closely reflected in the subsequent concentrations of these components in the livers of the hatchlings. Thus, the concentrations of α-tocopherol and carotenoids in the liver of the day-old chicken were respectively about three and two times greater than in the livers of the other three species. Although the water-soluble antioxidant, ascorbic acid, is synthesised by the embryo as opposed to provision via the maternal diet and the yolk, the concentration of this component in the brain of the day-old chicken was approximately 50% greater than in the brains of the other three species. Thus, it is possible that the antioxidant capacity of the developing turkey, duck and goose may be compromised under conditions of commercial production. All four species displayed a rapid depletion of α-tocopherol and carotenoids from the livers during the first 9 days after hatching. © 1998 SCI.     

Quantification of Cholesterol Oxidation Products In Egg Yolk Powder Spray-dried with Direct Heating

A direct-heated spray dryer with an evaporative capacity of up to 7 kg H₂O/hr was used to identify processing conditions responsible for formation of cholesterol oxidation products (COPS) in spray-dried egg yolk. Outlet air temperature and nitrogen oxides (NO_x) in the combustion gases were the only conditions that affected COPS levels. At outlet temperature 150°C, total COPS concentrations in the spray-dried product were 75 ppm at 5 ppm NO_x and 213 ppm at 300 ppm NO_x. In products dried at 75°C outlet temperature, total COPS concentrations were 21 ppm at 5 ppm NO_x and 58 ppm at 300 ppm NO_x. In general, individual COPS responded to outlet temperature and NO_x in the same manner as total COPS.     

THE EFFECTS OF DIETARY α-TOCOPHEROL AND SURFACE APPLICATION OF OLEORESIN ROSEMARY ON LIPID OXIDATION AND CHOLESTEROL OXIDE FORMATION IN COOKED RAINBOW TROUT (Oncorhynchus mykiss) MUSCLE

The inhibitory effect of dietary α-tocopherol supplementation (100 and 500 mg α-tocopheryl acetate/kg diet) and an oleoresin rosemary dip on lipid and cholesterol oxidation in cooked rainbow trout ( Oncorhynchus mykiss ) during storage at 4C for 48 h was investigated. The 2-thiobarbituric acid-reactive substances (TBARS) values of cooked fish muscle increased during storage for all treatments. Dietary α-tocopherol supplementation partially inhibited lipid oxidation. Surface application of oleoresin rosemary further enhanced this protective effect. Cholesterol oxides were formed in all the samples following cooking and storage. The major cholesterol oxidation products (COPS) were identified as 7 β-hydroxycholesterol, α- and β-epoxides, and 7-ketocholesterol. Formation of COPS was reduced by dietary supplementation with α-tocopherol and surface application of oleoresin rosemary. Statistical analysis revealed a highly significant (p < 0.01) inhibitory effect of oleoresin rosemary on COPS formation.     

Transport properties of liquid egg related to spray drying behaviour

The viscosities, critical moisture contents and effective water diffusivities were determined on samples of fresh and incubated liquid whole eggs at various temperatures. The liquid eggs were pretreated to simulate the possible effects of homogenisation and pasteurisation. The drying characteristics were based on measurements of weight losses against time of liquid egg films formed on glass spheres. The experimental results were used to obtain correlations appropriate for the expected temperature dependence of each property, for convenience in modelling of the spray drying operation. The ranges of the measured values are 5·6–14·5 mPa. s for coefficient of viscosity, 0·73–1·09 kg water kg⁻¹ dry matter for critical moisture content and 10–19 × 10⁻¹² m² s⁻¹ for effective water diffusivity. The results indicate similar magnitudes for the properties of fresh and incubated eggs.     

Glycoalkaloid Concentrations in Aerial Tubers of Potato ( Solanum tuberosumL)

The total glycoalkaloid concentrations in aerial and subterranean tubers of 14 potato genotypes were measured using high-performance liquid chromatography immediately after harvest. Post-harvest, aerial tubers from all genotypes were exposed to 144 h continuous fluorescent light; additionally three genotypes (cvs Home Guard, Kerrs Pink and Desiree) were subjected to mechanical wounding prior to glycoalkaloid analysis. Variations in glycoalkaloid concentrations between aerial tubers taken from a single genotype (cv Kerrs Pink) were determined by analysis of eight aerial tubers formed in the second leaf axil, selected from separate individual plants. Irrespective of genotype, total and individual glycoalkaloid concentrations were higher in aerial than in subterranean tubers. The highest glycoalkaloid concentrations were found in aerial tubers of cv Kerrs Pink (1343·0 mg kg⁻¹ FW) and lowest in cv Lindsey (301·0 mg kg⁻¹ FW). Ratios of α-chaconine: α-solanine in aerial tubers differed significantly ( P< 0·05) from those in subterranean tubers of cv Cara, Golden Wonder, Home Guard, Lindsey, Maris Piper, Record and 8859 indicating that exposure to light during aerial tuber growth enhanced the synthesis of one glycoalkaloid to a greater degree than the other. In all cultivars except cv Maris Piper, exposure of aerial tubers to 144 h continuous fluorescent light post-harvest increased total and individual glycoalkaloids compared with dark-treated controls. However, the ratios of α-chaconine: α-solanine in all genotypes except cv Golden Wonder (decreased α-chaconine: α-solanine, P< 0·05) were not significantly altered in comparison with dark controls, indicating that light exposure of aerial tubers post-harvest fails to enhance selectively synthesis of individual glycoalkaloids in the majority of cultivars. Regardless of cultivar, total glycoalkaloid, α-solanine and α-chaconine concentrations were higher in wounded than unwounded aerial tubers. Wounding stimulated synthesis of α-solanine more than α-chaconine ( P< 0·05) in cv Home Guard and Desiree. Glycoalkaloid concentrations in aerial tubers varied widely from a minimum of 1010 mg kg⁻¹ to a maximum of 2520 mg kg⁻¹ FW when harvested from individual plants of cv Kerrs Pink but selected from equivalent positions on the plant. Throughout the experiments large, non-significant increases in total and individual glycoalkaloid concentrations were recorded following light and wounding treatments. The scientific implications of aerial tuber formation are discussed.     

Time-dependent uptake and antiperoxidative potential of lycopene in multilamellar liposomes

Concentration, time and influence of α-tocopherol on the uptake and antiperoxidative effect of lycopene were assayed using a liposome model. Liposomes prepared from egg yolk phosphatidylcholine that were incubated at 37 °C with 100 μM of lycopene as initial concentration showed a maximum percentage of uptake (21.5%) compared with 16.0% at higher concentration of 200 μM as initial concentration after 4 h of incubation. A decrease of 13% in lycopene absorption was observed in the presence of 50 μM α-tocopherol as initial concentration. Different initial concentrations of lycopene (0.6×10⁻² μM, 1.2×10⁻² μM, 1.8×10⁻² μM) significantly (P<0.001) decreased the formation of TBARS when lipid peroxidation in multilamellar liposomes was induced by 1 mM FeSO₄. The antioxidant effect of lycopene (1.2×10⁻² μM as initial concentration) was greater than α-tocopherol (1.2×10⁻² μM as initial concentration). Multilamellar liposomal system provides an effective model to study the absorption and antioxidant properties of lycopene and other phytonutrients and their role in the prevention of chronic diseases.     

Cholesterol Oxides in Foods of Animal Origin

The earliest discovery of an oxidation product of cholesterol from a natural source was reported in 1940. Additional discoveries of cholesterol oxidation products (COPS) in edible food products accelerated in the 1980s as gas chromatography and high performance liquid chromatography detection methods were improved. COPS have been found in several foods including liquid eggs and dried egg products, milk and milk products, meat and meat products, marine food products, and other processed foods. Compelling evidence demonstrates that several cholesterol oxides are cytotoxic, atherogenic, mutagenic, and carcinogenic. Therefore, the presence of COPS in foods raises questions about the safety of consumption of some products.     

Screening of macro- and bioactive microconstituents of commercial finfish and sea urchin eggs

Crude and lipid composition, tocopherols, carotenoids, sterols and squalene content, together with fatty acids profiles of commercial marine egg products are reported, namely (a) canned eggs of lumpfish (Cyclopteris lumpus), Atlantic salmon (Salmo salar), trout (Oncorhynchus mykiss), smoked herring (Clupea harengus), and sea urchin (Paracentrotus lividus), (b) fresh sea urchin (P. lividus) eggs, and (c) beeswax covered, dried and salted mullet (Mugil cephalus) skeins -Greek “Avgotaracho”. The protein content of marine eggs ranged from 8.7 to 33.7 g/100 g on a fresh weight (fw) basis. Among neutral lipids triacylglycerols predominated, except for mullet roe where wax and steryl esters comprised 75% of neutral lipids. Phosphatidylcholine was the major phospholipid, followed by phosphatidylethanolamine. Marine eggs contained 0.18–2.39 g/100 g fw long chain ω3 polyunsaturated fatty acids (PUFA), mainly docosahexaenoic acid (DHA) in finfish eggs and eicosapentaenoic acid (EPA) in urchin eggs. They also contained 86.2–342.0 mg cholesterol/100 g fw, low amounts of squalene and other sterols and significant amounts of tocopherols (0.45–4.4 mg/100 g) and carotenoids (0.31–11.4 mg/100 g). The commercial finfish and urchin eggs are food of high nutritive value providing significant amounts of protein, ω3 PUFA, phosphatidylcholine, carotenoids, and tocopherols, with fatty acids profiles that exhibit low atherogenic and thrombogenic potential.     

Oxidative stability of Atlantic salmon (Salmo salar,L.) fillet enriched in α-, γ-, and δ-tocopherol through dietary supplementation

The purpose of this study was to examine the effect of dietary tocopherols on the oxidative stability of Atlantic salmon fillet. The fish were fed four diets supplemented with 150mg kg⁻¹ α-tocopherol and different combinations of γ- and δ-tocopherol (50 or 100mgkg⁻¹) for 10 months, slaughtered, and stored for 16 days on ice, or 48 weeks at −30 °C. Fillet concentrations of tocopherols at slaughter were 0.101 ± 0.001, 0.091 ± 0.004 and 0.025 ± 0.002 times feed concentration for α-, γ- and δ-tocopherol, respectively. Fillet α-tocopherol, but not γ- and δ-tocopherol, was moderately lowered during iced and frozen storage. The non-α-tocopherols protected the fillet against lipid oxidation in a dose-dependent manner during frozen storage, but appeared to act as prooxidants during storage on ice. It is concluded that α-tocopherol may be better suited than mixed tocopherols as a tool to optimize the oxidative stability of Atlantic salmon fillet.     

Physicochemical traits and sensory quality of commercial butter produced in the Azores

In the volcanic islands of the Azores archipelago, pasture is available the entire year and affects the composition of bovine milk fat. The composition of cows' milk butter manufactured in this region was evaluated. All brands showed excellent microbiological and oxidative quality. The fatty acid profile range presented a low n-6/n-3 ratio (1.81–3.38), low atherogenic (2.86–3.11) and thrombogenicity (3.27–3.60) indices and reduced cholesterol content (136–143 mg 100 g⁻¹). In addition, Azorean butters have a high content of conjugated linoleic acid (0.44–0.64 mg 100 g⁻¹), β-carotene (0.12–0.17 mg 100 g⁻¹) and α-tocopherol (1.40–2.20 mg 100 g⁻¹). Sensory analysis revealed high scores for appearance, consistency and flavour of all brands. These results indicate that Azorean butters produced from cows’ milk based on grass-feeding have a potentially healthier fat content and a desirable flavour that, associated with its “natural image”, may be promoted for product differentiation.     

Oven drying improves the nutritional value of Calliandra calothyrsus and Gliricidia sepium as supplements for sheep given low-quality straw

Leaves from the tree legumes Gliricidia (Gliricidia sepium) and Calliandra (Calliandra calothyrsus) were fed as supplements (200 g dry matter) to sheep (n=3) given a basal diet of barley straw ad libitum. Tree leaves were fed either freshly harvested (F=fresh) or after drying at 60°C in a forced draught oven (D=dried). Voluntary intakes, digestibility and aspects of nitrogen (N) and phenolic compound metabolism were measured in all sheep. Drying decreased the condensed tannin (CT) content of Calliandra (F 117, D 82 g CT kg⁻¹ DM). Total phenolics (TP) were significantly decreased when Gliricidia was dried (F 39, D 21 g TP kg⁻¹ DM), and CT content was reduced from 20 g CT kg⁻¹ DM to zero. Sheep given Gliricidia had higher rumen ammonia concentrations (73–85 mg N litre⁻¹) than did sheep given Calliandra (37–40 mg N litre⁻¹). For both species, drying significantly increased the voluntary consumption of straw, increased DM digestibility, decreased faecal N excretion and increased N balance. For calliandra, drying decreased the apparent degradability of N in the rumen (DNR) from 0·40 to 0·28 g N g⁻¹ N ingested, and increased the apparent digestibility of N (ADN) in the post-ruminal tract from 0·20 to 0·52 g N absorbed g⁻¹ N flowing into the small intestines. For Gliricidia, DNR decreased from 0·64 to 0·51 and ADN increased from 0·41 to 0·56. There were no significant effects of drying on rates of microbial N synthesis. The above changes were discussed in relation to changes in tannin content and it was concluded that drying facilitates the formation of protein–tannin complexes which protect proteins from degradation in the rumen. These proteins are subsequently released in the small intestines, thereby promoting an increased efficiency of dietary N utilisation. ©1997 SCI