Rumen bypass polyunsaturated fatty acid (PUFA) products to improve the milk fatty acid profile

Even though several health benefits can be ascribed to the consumption of milk FA (Gomez-Cortes et al., 2018), the general perception of dairy fat is negative, as it is high in SFA associated with an increased risk of cardiovascular diseases. Grass-based production systems are an effective dietary strategy to enhance the milk FA profile, with grass as a cheap and easily accessible n-3 FA source for the farmer (Gebreyowhans et al., 2019). As such, grass-based production methods were shown to increase the content of the health-promoting CLAand n-3 FA in milk (Elgersma, 2015). Indeed, the intake of CLA - including human bioconversion from trans-11 18:1 - via milk and dairy products was shown to increase from 350-550 mg per day to 707-1107 mg per day when grass-based production methods (maximum 50% grain-based feed) were applied (van Wijlen and Colombani, 2010). However, often such grass-based production systems are not feasible, because of limited availability of grass land or suboptimal climate.

Supplementation of n-3 or n-6 PUFA in the form of oil or oilseeds could be considered as an alternative, either or not in combination with supplements to modulate the ruminal lipid metabolism. Addition of such modulation agents which could be considered as dietary supplementation of unprotected oils or oilseeds only results in a limited PUFA enrichment of milk due to the extensive ruminal biohydrogenation in the rumen (Gebreyowhans et al., 2019; Shingfield et al„ 2013). As such, plant secondary compounds and direct-fed microbials have been examined in an attempt to enhance the concentration of putative desirable PUFA in ruminal digesta, milk and intramuscular fat.

The compiled information in the recent review by Toral et al. (2018b) indicates only a limited potential of such additives to change the milk PUFA composition in a repeatable manner. Diversity in active components and doses (e.g. a wide variety of plant secondary compounds, including, for example, tannins, essential oils, oxygenated fatty acids and saponins, has been examined) and differences in ruminant species, basal diet composition and timing of treatments are some factors which might have contributed to these inconsistent results. Accordingly, the most efficient way to transfer PUFA towards milk would be to bypass the rumen, through the use of rumen protection technologies.

Given the recent excellent review by Toral et al. (2018b) on the modulation of the ruminal metabolism of unprotected lipid supplements, this chapter will further focus on rumen protection technologies. Two classes of such protection technologies could be determined (Jenkins and Bridges, 2007):

  • 1 modification of the FA structure to inhibit bacterial isomerases
  • 2 encapsulation in a protective matrix

An overview of the most common technologies is presented in Table 2 (adapted from Gadeyne et al., 2017), with the corresponding transfer efficiencies of PUFA from the diet to the milk. By comparison, in post-ruminal infusion studies transfer efficiencies of 18:2n-6 and 18:3n-3 could reach 49% and 50% (Shingfield et al., 2013), and for trans-10, c/s-12 CLA and 22:6n-3, transfer efficiencies as high as 22% (de Veth et al., 2004) and 25% (Shingfield et al., 2013) were reported, respectively.

Rumen lipid protection technologies

This section is based on Gadeyne et al. (2017),where sections 7.1 to 7.5 have been literally cited from Gadeyne et al. (2017), while section 7.6 was adapted from Gadeyne et al. (2017).

7.1 Alterations of the fatty acid structure: calcium salts

Calcium salts of LCFA are soaps formed by the creation of an ionic bond between the free carboxyl group of the FA and calcium ions. The possibility to protect calcium salts of FAagainst ruminal biohydrogenation was first proposed by Palmquist and Jenkins (1987) and suggested that it could be caused by the insoluble character of the calcium salts, permitting an efficient bypass across the rumen without disturbing the rumen microorganisms. As dissociation constants (pKa) of calcium salts range between 4.5 and 6 (Sukhija and Palmquist, 1990), salts dissociate again in the acid environment of the abomasum, which makes the FA available for absorption in the small intestine.

However, a major disadvantage of this technology is that dissociation might already occur, if the pH decreases beneath 6.3 (Chalupa et al., 1986; Van Nevel and Demeyer, 1996), making the FA accessible to bacterial isomerases. Indeed, pKa depends on the unsaturation of the FA in the soap (Sukhija and Palmquist,

1990), meaning more dissociation will occur with increasing concentrations of UFA at a given rumen pH. Finally, a major (economic) disadvantage is that the production of calcium salts requires free FA as precursors. Generally, very inconsistent results are found in literature dealing with calcium salts of UFA, but most of them reported an incomplete protection (Table 2).

Table 2 Protective mechanism, possible disadvantages and literature-extracted transfer of polyunsaturated fatty acids (PUFA) from intake to dairy cow's milk for the most described or promising rumen lipid bypass technologies

Protection

technique

Protective mechanism (+) Disadvantages (-)

Lipid source

Evaluated PUFA"

Transfer6 (%)

Reference

Protected

supplement

Unprotected supplement (control)

Calcium salt

+ Blocking free FA carboxyl end

Linseed oil

18:3*7-3

0.67

-

Chouinard et al. (1998)

Linseed oil

18:3*7-3

1.2

-

Sultana et al. (2008)

-Protection impaired by dissociation

Linseed oil

18:3n-3

1.9

1.5*

Cortes et a I. (2010)

Fish oil

22:6n-3

6.0

3.3d

Castaneda-Gutierrez etal. (2007b)

-Limited protection of PUFA

High-PUFA palm oil

18:2*7-6

13.2

-

Theurer et al. (2009)

CLA oil

t10 c12 18:2

1.9-7.2

-

de Veth et al. (2005)*

-Free FA needed

CLAoil

t10 c12 18:2

3.2

0.0'

de Veth et al. (2005)

Soybean oil

18:2*7-6

6.5

6.9

Lundy et al. (2004)

Fatty acyl amide

+ Blocking carboxyl end

Canola oil

18:2*7-6

17

18

Loor et al. (2002a)

Soybean oil

18:2*7-6

5.5

6.9

Lundy et al. (2004)

CLAoil

t10 c12 18:2

7.1

0.0'

Perfield et al. (2004)

Formaldehyde

+ Encapsulation within formaldehyde-protein matrix

Canola/soybean

18:2*7-6

25-44

-

Gulati et al. (2005)*

Cottonseed

18:2*7-6

43

-

Gulati et al. (2005)*

Soybean/linseed

18:3*7-3

19-24

-

Gulati et al. (2005)*

-Toxic product needed

Soybean/fish oil

22:6*7-3

10-14

-

Gulati et al. (2005)*

-Untargeted reaction

Linseed oil

18:3*7-3

13

3.0 9

Sterk etal. (2012)

-High cost

CLAoil

t10 c12 18:2

7.0

0.0'

de Veth et al. (2005)

CLAoil

t10 c12 18:2

6.9-8.6

-

Gulati et al. (2006)

Protection

technique

Protective mechanism (+) Disadvantages (-)

Lipid source

Evaluated PUFA”

7ransferb(%)

Reference

Protected

supplement

Unprotected supplement (control)

Lipid

composite gels

+ Encapsulation within gelled protein matrix

Soybean oil

18:2n-6

46-69 (16-30)

22-37

Carroll et a I. (2006)

Soybean/linseed oil

18:3*7-3

81-225' (9-43)'

21

Heguy et a I. (2006)

-contains large volume of waters

Soybean/linseed oil

18:3*7-3

13-19

-

van Vuuren et al. (2010)

Rapeseed oil

18:2 *7-6

11-15

13

Kliem et al. (201 6)

Encapsulation within lipid

+ Encapsulation within highermelting point lipid matrix

CLA oil

t10 c12 18:2

7.9

0.0'

Perfield et al. (2004)

CLAoil

t10 c12 18:2

5.1

0.0'

Castaneda-Gutierrez etal. (2007a)

CLA oil

t10 c12 18:2

4.8

-

Moallem et al. (2010)

-low payloads

CLAoil

t10 c12 18:2

6.3

0.0'

Odens et al.(2007)

-low post-ruminal release

CLAoil

t10 c12 18:2

2.4-5.8

-

Pappritz et al. (2011)

CLAoil

t10 c12 18:2

4.9

-

Schwarz et al. (2009)

Algal oil

22:6n-3

1.0

-

Stamey et al. (201 2)

Algal biomass

22:6n-3

2.0-3.4

-

Stamey et al. (201 2)

Echium oil

18:4*7-3

3.2-3.4

-

Bainbridge et al. (2015)

Tyrosinase

cross-linking

+ Encapsulation in phenol- protein matrix

Linseed oil

t10 c12 18:2

4.0

-

Gadeyne et al. (2016)

-Protein extraction

-Phenolic mediator needed

“The most prominent PUFA within the oil was used for evaluation; Transfer was calculated as (g PUFA in milk)/(g PUFA in diet)* 100, whereby fat was assumed to contain 90% (w/w) FA; 'Whole linseed; dRuminal infusion offish oil, no statistical difference with the treatment; “Summary of earlier studies; fNo t10c12 18:2 measured in milk of control treatment; 9Extruded whole linseed; hNo scientific literature describing in vivo milk data available; Net transfer efficiency as reported in reference; Calculation with data from reference results in an unrealistic high transfer.

Source: adapted from Gadeyne et al. (201 7).

7.2 Alterations of the fatty acid structure: fatty acyl amides

Fatty acyl amides consist of a FA chemically linked through an amide bound to an amine. This approach was proven potentially useful to protect UFA against ruminal biohydrogenation, using either amino acids (Fotouhi and Jenkins, 1992), non-acidic primary amines, such as aliphatic amines containing 1-30 carbon atoms (Jenkins, 1996), or ammonia (Cummings and Forrest, 1997). As for theCa salts, the production process of simple amide-protected supplements requires free FA as precursor. However, fatty acyl amides do not seem to be more effective in transferring dietary PUFAto milk than pure oil (Table 2).

7.3 Encapsulation in a microbe-resistant shell: aldehyde treatment

In 1975, Scott and Hills (1975) proposed a method to protect UFA by encapsulation within a protein aldehyde reaction product. Prior to aldehyde addition, lipids first need to be emulsified using proteins such as casein, gelatin or other plant, fish, meat or oilseed proteins to ensure a homogeneous distribution of the lipid within the protein, and can further be processed using spray-drying to obtain a coated particulate solid. However, formaldehyde is a noxious product and its use in the European Union is subject to strict regulations (2011/391/EU). Although formaldehyde treatment is considered to be the most effective technique so far, its application remains limited nowadays due to its high cost, the bad image of chemical treatments of feedstuffs and possible residues in the final animal products (Doreau et al., 2015; Palmquist and Jenkins, 2017). The method proposed by Scott and Hills (1975) effectively prevented ruminal biohydrogenation, both in vitro and in vivo (Table 2).

7.4 Encapsulation in a microbe-resistant shell: encapsulation within lipids

A more recent method describes the potential of composite gels containing amino acids and lipids to bypass the rumen. Rosenberg and DePeters (2010) claimed that dispersions of lipid droplets in an aqueous protein phase can be protected against ruminal degradation by heat-induced gelatinization. In contrast with the aldehyde treatment, the cross-linking of protein is not induced by a divalent linker such as formaldehyde, but by gelation of proteins. Reducing sugars can be present in the matrix to additionally cross-link the proteins by a Maillard reaction. Embedding lipids in a protein matrix of whey or blood proteins has the advantage of upgrading such side streams, while creating rumen bypass lipid. However, it could be assumed that gelled emulsions have a low shelf life as they contain generally large volumes of water, which may cause deterioration of the gels and the enclosed lipids during storage (van Vuuren et al., 2010). Nevertheless, as gels are prepared at elevated temperatures, others consider composite gel's shelf-stable (Weinstein et al., 2015). Carroll et al. (2006) were the first to report on the efficacy of whey protein gel complexes to increase the PUFA content of bovine milk fat (Table 2). Similarly, Heguy et al. (2006) found that feeding whey protein isolate gel complexes of soybean/linseed oil successfully increased the PUFA content and decreased trans FA of plasma and milk lipids. More recent research demonstrated the persistent effect of long-term administration (10 weeks) (van Vuuren et al., 2010).

7.5 Encapsulation in a microbe-resistant shell: lipid composite gels

Technologies described in the former sections relied on different types of protein-cross-linking to achieve rumen protection. In other formulations active compounds are protected in a microcapsule of lipids according to either one of two basic concepts: active compounds are either embedded in a lipid matrix or are formulated in small spheres, which then are coated with lipid (Desai and Jin Park, 2005; Wu and Papas, 1997). Generally, coatings are comprised of fats with a high melting point, that is, at least higher than the matrix it envelops (Lorenzon, 2015; Meade et al., 1999). Despite this common overall principle, the composition of the outer coating particularly differs between described methods, which results in varying protection efficiencies (Table 2).

7.6 Encapsulation in a microbe-resistant shell: tyrosinase cross-linking of emulsions

Another recently explored lipid protection technology involved enzymatic cross-linking of protein-stabilized emulsions by tyrosinase (Gadeyne et al.,

2015). The transfer of trans-10, c/s-12 CLA, encapsulated in tyrosinase-cross- linked emulsions, from the diet to the milk was evidenced in vivo (Gadeyne et al., 2016). However, transfer efficiencies were not higher than those reached for trans-10, c/s-12 CLA in commercially available rumen-protected products (Table 2). Therefore, further research is needed to optimize the current enzyme- based method, which is particularly of interest because of the possibility of solvent-free processing, at ambient temperatures and pressure, and the potential to valorize industrial agri-food side streams.

 
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