Food Structure

Volume 5 Number 2 Article 11

1986

Lipolytic Changes in the Milk Fat of Raw Milk and Their Effects on the Quality of Milk Products

E. Kirst

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Recommended Citation Kirst, E. (1986) "Lipolytic Changes in the Milk Fat of Raw Milk and Their Effects on the Quality of Milk Products," Food Structure: Vol. 5 : No. 2 , Article 11. Available at: https://digitalcommons.usu.edu/foodmicrostructure/vol5/iss2/11

This Article is brought to you for free and open access by the Western Dairy Center at DigitalCommons@USU. It has been accepted for inclusion in Food Structure by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. 0730-5419/86$ I. 00+. OS FOOD MICROSTRUCTURE, Vol. 5 (1986), pp . 265-275 SEM, Inc . , AMF O' Hare (Chicago). I L 60666- 0507 U.S.A.

LIPOLYTIC CHANGES IN THE MILK FAT OF RAW MILK AND THEIR EFFECTS ON THE QUALITY OF MILK PRODUCTS

E. Kirst

VEB Wissenschaftlich-technisch - 6konornisches Zentrum der Milchindustrie Sachsenha usener Strasse 7 DDR 1400 Oranienburg, German De mocratic Republic

Intt·oduction

Lipolytic changes in milk rat affect sensory attri­ The qua I i ty of dairy products is determined by butes and techno logica I properties of milk a nd milk their sensory. chemica-physical and microbiological pt•oc.lucts. They are cream and the rest passes into absorption of a I ien odours and flavours from the barn the skim milk. ln the froth churning process. approxi air. by formation of metabolites of the milk components mate\y 0.15 nunol free fatty acids per 100 g of fat pass etc. Of all t hese factors . ....nich influence the odour and into butlcrmi lk taste of milk, lipolytic changes in the milk fat play one o f the most important roles In addition to t he prope1·ties mentioned abovt~. they affect technological properties of the milk, such as t he sep;u·ation of the milk fat. Lipolytic changes whi ch develop in the milk fat include the aggregation of milk fat globules. the forma ­ tion of free fat, and the hydrolysis of glycerides that PI'Oduces fr·ee fatty acids (Fig. 1) but do not include ox \dative changes Initial paper received September 24, 1985 Fat present in the milk in the form of globules is Manuscript received Oc tober 15, 1986 protected by membranes from lipolytic and oxidative Direct inquiries to E. Kirst effects. Thus, lipolysis occurs only after the disrup­ Telephone number: 37 - 15 - 8536 tion of the membranes and the subsequent formation of free fat (96). Due to incomplete esterification in the udder , a small amount of free fatty acids is present in fresh mi] k (37, 62). Addi tiona}, post- secretory forma­ tion of free fatty acids is influenced by physiological. physical, and b.iochemical factors (Fig. 2) (45- 48, 51, 53, 59). It is estimated that because of an increased effect of t hese factors in the past 10 lo 15 years. t he f1·ee fatty acid content in the raw mi)k has doubled world- wide {67). primarily due to physical handling. KEY I'IURDS. Free fat, Free fatty adds, Heat treatment. Uydro l ysis induced by physiological factors is usually Lipolysis. Mec hanical t1·eatment. Milk. Milk fat. Physiologi cal influence. Quality of mi ]k, Quality of cal led "spontaneous" lipolysis and hydrolysis induced by physical factors i s called "induced" lipolysis milk products :.\echanism of the Formation of Free Fat and Free Fatty Acids in Milk

The stability of milk fat globules is bnsed on an energy barrier formed by equidirectional electric sur­ face charees (93). The stabi 1 ity of disperse systems can

265 E. KIRST

FAT

lipolyt ic action c atalytic or of 1 ipase enzymatic ox i dative effects ACIDS

RANCIDITY

Fig. 1. Me chanism of changes in the milk fat.

be explained by the so- called DLOV theory. [The name prerequisite for t he hydro l ysis of g l ycerides. Influenc­ OLOV is derived f rom the firs t 1 etters of the names of ed by inhe rent or mi crobi al l ipases. lipolysis leads to t he a u thors of the t heory, i.e., Oerjagui n , Landau, t he formation of free fatty acids in the mi lk (82- 85). Overbeek and Ve rwey {9 1)1 . Mechani ca l e ne1-gy, e.g., as provided by foaming, can suppress the energy barrier. Inf luence of Physiological Factors on Milk Fat Under the effect of low energy, hydrate e nvelopes of milk fat globu l es are ruptured. At a higher energy, the Physiological factors affecting the milk fat com­ protein and phosphol i pid layers of the milk fat globule prise. in particular, feeding, stage of lactation. milk me mbrane disintegrate and the fat globules form a W)i ­ output, health of the udder, and exogenous factors form mass, i.e., free fat. Nordlund and Jl eikonen (7 1) These factors contribute the most to the lipolysi s of discussed a t heory on the formation of free fat during milk cooljng of the milk. The theory postulates t hat due to In the case of a reduced milk output , whi ch may be r·adial so lidificat ion of the mi l k fat, l ow- melting, due to the stage of l actation {87) as well as to feed ­ mostly non- solidified triglycerides a r e present in the ing, the level of free fatty acids in the milk is in­ core of the milk fat globulf'!s during coo ling. The non­ creased (13, 41. 63). A particularly marked incr·ease in solidified fat occupies a larger volume t han t he same the f ree fatty acids conte nt occurs when the milk pro­ amount of solidified fat. Thus, the l.iquid glyceride duction is reduced to less than 3 kg of milk per mi !king part in the centre of the milk fat globul es is subjected (4 1). Feeding plays an important role in the stability to a pr essure caused by the inner str ess of the mo l e of the milk fat . Nonruminant- related feeding causes c ules. Compr·essibility of l iquid fat is low, and shifts changes in the protein fractions. This may be reflected in t he crysta l s tr·uctures t hus occur i n the mi lk fat by the c ompos ition of the milk fat globul e membmnes. globul es as well as in t he so lidified fat l ayers. This which may be formed only partly or· incomplete l y (20) may lead to the destruction of the fat g l obule mem­ An excessive supply of feed e nergy (34. 66, 90) branes. i.e.. to the formation of free fat. Therefo1·e. leads to a soft milk fat, which is subsequently subjec t ­ milk fat ha vi ng a higher content of short- chain or ed to I ipolytic a I terations during coo I ing and under unsaturated fa tty acids i s more sensitive to 1 ipolytic me chanical effects. The liiCk of fped ene r·gy causes the changes . formation of a weak milk fat g l obule membrane ""' he!'eas an Milk fat globule membranes rupture during t he foam­ excessi ve supply of raw protein in th£! f eed results in ing o f milk under t he effect of an increased surface an increased incorporation of iong- ch~in, w1satur·ated tension as t he milk fat globu les enter t he boundary fatty acids in t he milk fat. TI)r!Sf'! latter fatty acids layer between air and milk. Thus. free fa t is also are formed due to the decomposition of the body fat of fo rmed by this process. The f orma t ion of free fa t is a t he cows {20, 23. 33, 43). In the case of an energy­ deficient diet. the l ong- c hain unsatUJ·ated fatty acids of the fatty t issues are digested more s.Jow1y t han the s hort-chain saturated fatty acids that at'e used for the energy supply of the cow. A greater nmounl or lo!'l!! c h<1 in PHYSIOLOGICAL fatty acids thus enters the udder. Formation of o leic FACTO RS acid is catalyzed in the udder· by an enzyme called desaturase. Hence, an incr eased o l eic acid content in t he milk fat indicates a lack of energy in t he feed ration (20). Associated with this effect o f feeding is a changed composition of fatty adds and a softer consis ­ tency of t he milk fat. Accord ing to t he t heor y of Nord­ lactation microbial lund a nd Heikonen ( 71), t h e change in the f

266 tiPOLYTIC C HANGES IN J"'ILK FAT

Some enzymes are part of the milk. Lipoprotein extent. Experimental findings by vat·ious authors on the I ipase, which participates in the transfer of fat from effects of possible activators and inhibitors are re­ UH~ blood into the mOk and catalyzes 1 ipolytic reac­ viewed in deta.i l by Olivecrona (72). tions (12). is one of them. It .is l i kely that greate 1· Kuzdzal - Savoie et al. (62) suggested that grass quanti Ucs of this enzyme are secreted along with somat­ fccd.ing may have an inhibitory effect on Upo1ysis due ic cells into the milk in a diseased than in a healthy to the presence of some specific substances present in udder. However, Olivecrona et al. (73) assume that an the grass inactive proenzyme existing in the milk is activated by substances existing in the somatic cel l s. Jellcma (40) Influence of Physicmilking, milk is ~ubjected to the effects of f iow processes. Such processes probably af­ milk Lipolytic problems are mort~ frequent in dairy cat­ fect the milk fat to some extent. tle herds producing medium cell counts in the milk Laminar flow takes place in smooth pipes at low (300 .000 to 500,000 cc 11 s / mL) than in those prorlucj ng flow rates. Turbulent flow develops with the increase of low eel J cowlts (<300,000 cells/ mL). The higher counts the flow rate, due to rapid changes in direction of the Wf"!re found in milk ubtctined by improper machine mi \king flowing Uquid, and .in pipes having rough surfaces and Sal in et a l. (86) reported an additional increase .in the edges {l, 44). free fatty acid values in milk with counts exceeding The nature of the flow is cha1·acte rjzed by the 500,000 cells/ mL. Data obtained in thr:.ir experiments in Reynold's number. It is low fot· laminar flow Wltil the vivo arc 1 istcd .in Table 1. Effects of subc lini cal so- called criticfll Reynold's numbet' (R " 2300) is reach­ symptoms of mnslitis on lipolysis were reported by ed. Beyond it. the flow changes from laminar form into the turbulent form with a considerable increase in re­ Vcl.itok (95), Jngr (36) and others Severa I authot·:; a I so described the effec ts of exo sistance (78). Back {8) and Back and Reuter (9) found genous factors such as acUvators and inhibitors on the liMt with a laminar flow (up to a maximum flow velocity of 2.03 m/ s). fat globules in milk do not agglomerate activity of lipoprotein lipase. It \'lOS found that an add.iUon of bovine blood serum (4, 41. 89), blood frac­ In experiments using a model In m.i lk. Activation of J ipolyt.ic processes .in m/ s .in raw milk passed through the pipes fo1· 15 min. Reuter {80) found similar changes in ndationsh.ip to the the milk by somatic cells may also be a consequence of 2 the effect of activators (15) fr.icUon shear stress T nbove 4 kp/ m . Reuter (79) Downey and J'olurphy {19) found an effect of gjyco­ estimated that flow processes in dairy fat·ming are most ­ macropeptides on the forntat.ion of free fatty a c ids ly turbulent. This is caused, e.g., by pipe bends. by Driessen anll Sl

267 f. KIRST the milk, efficient cooling is requir·ed which wou l d pr imary t.re<-ttment, bacteria formed t.he base of the raw Thf~ ~ffect of hir~h microbiHI counts on the free milk f lor·a but now psychrotrophic bacteria predominate fatty acids content in r·aw milk stor·ed at 5°C is pre­ These microorganisms are more lipolytic thHn lactic acid sented in Table 2 bacteria (75, 98). Lipases formed by the psychrotrophs can intensify lipolytic processes in milk (30, 75) in Table 2. accordance with the mechanisms described by Kirst (47) Changes in the free fatty acid content and Nordlund and Heikonen (71). during the stor·age of raw milk at 5°C In addition to flow-conditioned effects which lead as a function of total ee l l counts to turbulence and to changes in the structure of the lllilk fat. an excessive absorption of a.ir in the rni lk. speto,.r,age f-!-F O're .,_,r,::";c' t'-"y-'a "'c:"i<:... 1 "'co:::n.::te ::;nco.t _,(;:::mm:::o-::'1/ ;-'1-;,00::2'-g,.Cf.,;" t::C);;;-*;;;--; i.e., foaming (39) also stimulates I ipolysis Foaming 00 at 7total counts at total counts in milk can be caused by air· absorpt ion .into the teat (h): of 12,000/ mL of 3,500,000/ mL c ups, leaking pipeline joints, differ·ent pipeline dia meters, or large pipeline diameters through whi ch only a 12 - 16 1.2 1.5 small volume of milk is transported. and by idling of 72 1.4 2. 7 centr ifuga 1 pumps (continuous operaU on of the mi J k pump even in case of insuff i cient milk volume) (96, 97) *rn this study, the fat was obtained by churnlllg the Using model systems, Worstorff et HL (97) studied the cream separated by skimming f1·om the raw milk tested effects of various gases used in the stir'l'ing of milk. The free fatty acid values were reduced by the passage Considerably higher concentrations of free fatty acids of the free fatty acids into the skim milk as well as were produced in the milk in the presence of oxygen than into the buttermilk. Conseqtrently, the ascertained in the presence of air or nitrogen. Aulc and Worstor•f f fatty acid content \Oo'l'I.S lower than the value obtained by (7) found that the free fat concentration irr milk was using the method of Deeth et al. (l8) increased 2.6- fold when air was present in the milk pro­ cessing equipment; the free fatty acid concentr·ation Oxid

268 LIPO IYTfC CHA NGES I N MlLK FAT become s part of the fat phase of chocol a te, !.he v isr:osi ·­ pungent, bitter. and ram-:id. In general, such sensory ty o f t h e chocolate mass is reduced; thi s makes it defects may be noticed at a free fatty acid conte n t IXJSSib l e to limit t he amount of the coconut o il used. In exceeding 4 mmol / 100 g fat, whi c h cor-responds to ap­ contt·ast. other industrial applications r·equir·e a n easi ­ proximately 1.5 mmo l/L of milk. Individual free fatty acids have differe nt e ffects on the flavour: a l ow ly wettable milk powder ~ooili c h has a long shelf life and concentration of a particula r fatty aci d may affect the contains t he fat in a "concealed" form f l avour more severel y than a high concentr ation of a n­ Sepa rability of t he milk fa t i s inf l uenced to a other fatty a cid. The off- flavours me ntioned above are great extent by the s ize of t he fat g I obu I es and by the con tent of free fa tty acids Mechani cal effects are usually caused by short-chain fatty acids, i.e .. butyric part l y t•esponsible for the destruc t ion of t he fat to lauric acids (62). According to Paulet et a I. (74). soapy f J avour is caused mainly by decanoic acid (capric Table 3 acid) and dodecanoic acid (lauric ac id). Connolly et al Threshold values at wh ich single free fatty acids (16) determined the threshold fl avour values of indivi ­ cause rancid flavour in pasteurized milk. According to dua 1 fatty acids present in pasteurized milk (Tabl e 3). Connoll y et al. (]6). Atra.men tov et al. (5) f ound that during t he separa­ tion of fat. about 90% of the free fatty acids passed into the cream and on I y about 10% passed into t he s ki m Fatty acid: Nu mber of C Concentr ation in milk milk. Consequen t ly, t he quality of bu tter was influenced a toms in the mg/kg mmol / kg by the raw milk to a great extent (38). According to mo l ecu le: Ce r·nbutter. A simi !at· finding was made by butanoic 46.1 0.52 .Jamotte (38 ). To inhibit lipolysis. the latter author hexano ic 30.4 0.26 recommended to heat the cream before its storage octanoic 22.5 0.16 Even i n milk products hav ing a low fat con ten t, decano i c 10 28. 1 0.16 high concent r a tions of free f atty acids can have detri­ dOO ecanoic 12 29 .7 0. 15 mental effects on the sensory a ttributes. Supported by tett·adecanoic 14 80.5 0.35 the result of factor ana l ysis, Sonntag (92) showed that hexadecanoic 16 24 4 .5 0.96 the concentration of free fatty acids in raw mi lk has octadecanoic 18 14 2. 1 0.50 t he most i mpor tant inf I uence on the qua 1 i ty of pasteur­ c is- 9- octadecenoi c 18* 221 .1 0. 78 ized m.ilk ; ------One C::C double bond Effects of Energy- Restricted Feeding on Milk Fat globules and for the subsequent. diff.i cul lies encounter ed Feed rations. whi c h allow farmers to r e duce the use when separa t i ng t hem from t he milk (37). For exampl e. an of feed concentrates , have been used extensively at increase in the fret! fatty acids content in t•aw nlilk by pr esen t in variou s countri es. In a dd ition , the crude 0.91 mmol / L during separ·ation l eads to an 1nc t·ease in protein content in grass and i n grass si I age has been the fat con tent in t he s kimmed milk by 0.045% (:J5). increased world-wide. This means lhat dair y cows are fed Sensory attributes of milk and milk pt•ot.lucts are partly energy- deficient yet high- protein rations. To aff ected negatively by the presence of free fatty acids examine the consequences of t he changes in the feeding (11). However, low concent t·ations of fL·ee fatty acids practice. t he effects of e ne t-gy- deficient, high- protein contri bute to the charactel'istic flavours of raw milk, rations on milk fat were studlt.od.. by the author of this c r·eam. butte1·, and yoghul't (27, 94). Also in some c heese review va r ieUes, free fatty ac ids. whi ch are formed durlng The experiments 101ere conducted using one group of l'ipeni ng, produce charactel'istic f l avours (32). On t he cows i n each the first a nd second thirds of lactation othe r hand, Jamotte (38) no t ed that off- flrtvours, whic h (Groups 1 and 2) a nd a group of 6 cows in the last third usua 1 J y deve I op as the resu 1 t of I ipo I yt ic r eact ions, of lactation (57, 70) (Group 3). 'ill1li 1e t he cows in Group C

Ta ble 4 . Effect of energy-deficie nt f eedi ng of cows in the l ast t hird of lactation (Group 3) on the fat and fatty acid contents in milk

Feeding Energy content Crude protein content Fat content Free fatty acids period: of the ration of the ration i n the milk content i n mi lk fat (% of standard) (% of standard)· {%) · (%): (mmol / 100 g)

140 135 4.3 10.6 171 131 5.7 20.9 4 .8 16.1 3 .9 21.6 3 (day 250- 267) 40 64 4.1 14 . 1 2.6 4.1 12. 8 2.4 4 (day 268- 28 1) 62 103 4. 0 13.7 2.2 3.6 16.5 2.9 152 126 4.7 13.7

269 E. KIRST with t he feeding standards suggested by llle Department Table 6. of Agriculture of the German Democrati c Republic (88) Passage of free fatty acids from raw milk into c ream* Cows in Group 2 were fed e nergy-defi c ient rations at the end of the dry phase. Milk obtained from the 6 cows in No Free fattv acids in IMlol in: the last third of lactation wa s t ested weekly, whereas 1 L of 1 L of c ream from milk from t he other two groups of cows wds tested once a raw milk 1 L of raw month. The free fat content was deterrn.ined accordi ng to milk the method of Lagoni and Peters (65) a nd the free fat t y ------f------acid content was determined by the procedure of DeP-th et 1.31 8.96 0.640 48.8 a l. (18). The s uitab.ility of these analytical methods 1.36 8.16 0.646 47.5 for t h e given purpose was confirmed by our own tests 1.22 6. 75 0.541 44.4 (56). In t he examination of cows in the last third of 1.34 8.16 0.637 47.6 lactation (Table 4}, the increase in the fat content in 1.29 7. 20 0.540 41.9 t he milk i s c learly evident immedi ate ly following the 1.38 8.46 0.648 47.0 administration of energy-deficient rations and may be 1.30 8.67 0 .637 49.0 explained by t he degradation of body fat (fat mobiliza­ 1.40 8.00 0.600 42.9 tion syndrome). Later. the fat content in the milk is 9 1.37 5.00 0.668 48.8 decreased. Its concentration rapidly recover s du1·i ng r e­ 10 1.40 7.21 0 .834 59.6 al imentation (5th f eeding period). The onset of e nergy­ 11 1.33 4 .80 0. 737 55.4 defic ie nt feeding in each period induces a temporary 12 1 .37 7.65 0 .815 59.5 jncrease in the free fat content i n the milk but is 13 1.33 8.12 0.824 62.0 follo~o.'Cd by a decrease and stabil i zation of t he free fat 14 1.40 7.50 0 .740 52.8 concentration at the lower leve l . Return to a standard 15 1.49 11.44 1.066 71.5 diet (re- alimentation) r esul ts in the r·ecovery of the 16 1.44 13. 18 1 .263 87.7 free fat concentration. The free fatty acid content in 17 1.41 10. 62 0.947 67.2 the milk remains a pproximately consta nt wi t h cows in the 18 1.46 10 .00 1.041 71 .3 late stages of lactat.ion. 19 1.42 10.92 1.012 71.3 A marked effect of feeding on the free fa tty <~cid 20 1.38 11.71 0.938 68.0 conte nt. however, can be determined at t he beginning of ---- L______------lactation. At that time, lhe fat content of Lhe milk is severely reduced (Table 5). In both groups of cows . the Fat content approximately 50%. effect of the previous energy-deficien t diet on Lhe fat

Table 5 Effect of energy- deficient feeding of cows in the first and second thirds of lactation on the fat and fatty acid contents in the rni lk

Feeding period : Energy conte nt Cr·ude protein Fat content Contents of (duration in of the ration content of t he i n mi l k (%): free fat free fatty acids weeks): (%) r·at ion (% ) : (%of total fat) : (mmo J/ 100 g fat): ------Group 1 1 (4 w of energy- reduced 30- 50% reduced 30- 50% 3.6 20 .0 3.0 deficient feeding) 3.8 20.4 4 .8 2 (8 w of realimen- raised 30% 2.0 14.6 4.0 tation) 2.0 18.0 5.2 2.5 18.6 4.6 3 (5 w) reduced 30% standar·d 3.0 14. 6 3.6 4 (3 w) raised 30% raised 30% 2.8 15.6 6. 2 5 (5 w) standard raised 30% 3.0 11.4 3.0 6 (4 w) reduced 30% standard 1.0 11.0 3.0

Group 2 1 (2 w"' ) reduced >50% reduced >50% 5.0 13.6 2.7 3.0 19.2 4.4 2 (8 w energy- raised 30% standa rd 2.9 17.8 2.6 deficient 1.9 12.8 4.5 feeding) 2.8 17.2 4.5 3 (5 w realimen- standard r aised 30% 2.3 12 .0 6.6 tation) 4 (3 w) raised 30% raised 30% 2.8 12.4 7.0 5 (4 w) reduced 30% standard 3.2 14.0 2.6 6 (5 w) standard raised 30% 3.6 11.2 2.3 ------From 2 weeks before the beg.inning of lactation unt.il the 4th week of lactation.

270 L IPOL ! TIC ClfANGES IN MILK FAT content and the content of free fatty acids i s t: xtended Table 8. even following rea l ime ntation (2nd f eeding period). This Passage of free fatty acids from crcaiA into butter is shown a) so whe n the feeding patterns are vari ed (3rd -----.------to 6th periods). Under t he condi tion of the e nergy­ No.· Free fatty acids (mmol/100 g fat) deficient diet beginning as early as in the dry period in butter difference and by severe underfeeding during t he first l actation period, a marked effect of feeding on milk fat i s found 1.8 1.6 0.2 with t he second gr oup of cows. Pooled milk from t hese 1.7 1.6 0.1 cows contained a maximum of 7.0 mmol free fatty acids 1.6 1.6 0.0 per 100 g of fat and t he rna.ximum content of free fatty 1.5 1.4 0.1 acids in the pooled mi \k obtained from the first group 1. 7 1.5 0 . 2 of cows was 6.2 mmol / 100 g of fat. The fat contents were 1.4 1.2 0.2 reduced to 2.0% and 1.9%, respect i vely. The effect of 1.3 1.4 - 0.1 feeding appears to be even stronger on the mi lk from 1 .7 1.6 0.1 i ndividual cows. In both groups, the increase in the fat 1.2 1.1 0.1 content and t he reduction of the share of free fat as 10 1.3 1.3 0.0 well as of the content of free fatty acids is particu­ 11 2.6 2.2 0.4 larly obvious in the last two f eeding periods. during 12 2.1 1 .9 0.2 \Oohich the cows were fed in accordance with the feeding 13 2.5 2.3 0.2 - 0.3 standar ds 14 2.3 2.6 15 1.6 1 . 7 - 0.1 Passage of Free Fatty Acids into Cr eam and Butter 16 2.1 1.8 0.3 17 2.1 1 .6 0.5 It W'dS found that i n skim milk. the free fatty acid 18 1.9 1.5 0.4 content was highe1· than expected (5). For this reason. 19 2.3 1.8 0.5 the passage of free fatty acids from raw whole milk into 20 2.0 1.6 0.4 skim milk and c t·eam a nd from cream into butter was 21 2.0 1.9 0.1 examined. Free fatty acids in milk and cream were deter­ 22 2.3 1.9 0.4 mined according to Deeth et al. (18) . In butter, the ------free fatty acid content was t i trated <~fter the butte1· had been dissolved in a mi xture of ethanol and d i ethyl ether (1:1). Approx imately 55% of the free fatty acids foam - churning process with the mean difference obtained passed into c r eam obtained from milk in two milk­ by the churning process without separating the butter­ collecting districts (TabJe 6). To check these results. milk .indi cates that 0 . 15 mmo1 of free fatty acids, a compat·ative examination wa s carried out using raw milk related to 100 g of butterfat. passed into the butter­ before it entered the separator and then using the milk. The buttermilk could not be examined for compari­ corresponding ski m milk and cream after separation son because t he method according to Deeth et al. (18) (Table 7). The r esults s how a good agreement between the cannot be appl icd to the determination of free fatty amount of the free fatty acids in the raw milk skimmed milk. technology based on the phase reversa I without separa­ tion of buttermilk (samples 1- 10) and a foam -churning process (samples 1.1 - 22) have been compared with each other. The results s how that when the butter serum Js A 1 though an inquiry by the In terna tiona l Dairy separated, approximately 0.1 mmol free fatty acids. Federation has indicated that Upolysis is not a major related to 100 g butterfat, passes into this serum. A probl em in most cow1tries (2), t he effects of 1 ipolytic comp ar i son of the mean difference between the free fatty changes on the quality of milk products must not be acid conten t of t he cream and that of the butter in the underrated. Special attention should be paid to I ipoly­ tic changes in the fat of raw milk caused by physiologi­ cal factors, in particular by feeding. To reduce 1 ipoly­ Table 7. tic processes in milk. special attention should be paid Comparison of the passage of free fatty acids into skim to milk and c1·earn - ruminant- related feeding practices for cows, - restriction of other physiological factors. No Concentration of free fatty acids Sum of f ree - minimization of mechanical and thermal effects. mmol /Ll fatty acids - prevention of foaming i n the milk, and in raw i n skim in cream and - minimization of t he growt.h of psychrotropic bacteria milk milk skim milk in milk. ------1 1.37 0.605 0 .668 1. 273 Acknowledgments 2 1.40 0.528 0.834 1.362 1.33 0.590 0.737 1.327 The author thanks Prof. DrSc. R. Hansen (Humboldt 1.37 0.568 0.815 1 .383 university of Berlin). DrSc. w. Krause (Technical Uni­ 1.33 0.516 0.824 1.340 versity of Dresden). and Mr . A. T6pel (Engineering 1.40 0.566 0 .740 1. 306 School of the Dairy Indust ry in Hal berstadt) for useful ------suggestions and for reviewing the manuscript.

271 f . KIRST

lipolysis. Austral. .J. Oairy Techno]. 30, 109-111 19. Downey WK. Murphy RF. (1075 ). Class ification of 1. Alfet·jew MJ. (1958). Hydromechanik. [llydromechanics lipolytical P.nzymcs. lnl. Oairy FfXI. Doc. No. 86. - in Ge rman] . B.G. Teubner- Verlagsgcsellschafl. 19-23 Leipzig, German Democ ratic Republic. 226 llP 20. DrP.ws M. GrSweden, 81 - 83 238 4. Astrup liN. Bengtsson G. (1982). Activator proteins 21 Driessen FM, S t ad h o otlt ~rs J . (1975). Lipolytical for lipoprotein lipase from bovine plasma: Prepa­ enzymes and co- factot•s suitable for lhe sponta­ ration by adsorption lo intra1ipid. Comp. Biochem neous rancidi ty in cow milk. lnl. Dairy Fed. Doc Physiol. 72 B. 487- 491. No. 86, 73- 79 5 Atramentov ~ Atramentova VG, Chumakov NJA. (1976). 22. Enge1rud T, Olivecr ona T. (1973). Purifit~d bovine Svobodnye kislot y v moloke. [Free acids in milk - milk (lipoprotein) li]x~s e: Activity against lipid in Russian). Mol och. Prom. 43(3). 26 ·27. substrates in lhe absence of exogenous serum 6. Atramentova VG. (1971). MetodYopredeleniya prigod­ factors. Biochi m. Biophys. Acta 306. 115- 127. nosti mo l oka dlya maslodeliy-d. [Methods used to 23 Farries E. (1983). Die Mi lchzusammense lzung als determ i ne the sui tabi 1 i ty of mJ 1 k in butter· pro­ Hinweis auf Stoffwechse lbelastungen und Fort­ ducti on - i n Russian]. Mo l och. Prom. 38{10). 9 - 10. pf 1 anzungsstfu-ungen. Mo ) kerej Ztg. We 1 t Mi 1 ch ;!_!_, 7 Aule 0. Wor storff H. (1975). Influence ofmechanical 1207-1213. t r eatme n t o f milk on quantities of frcP. fatty 24 Finke II. (1965 ). Handbuch dct· Kakaocrzeugnisse. acids and free fat in the milk, as well as on the [Handbook on cocoa products - in Gennan ]. Sprin­ separabi lity of the mi lk. Int. Dairy FOO. Doc. No. ger- Verlag Berlin, lleideJberg, New York. 579 pp. 86, 116- 120. 25 Fox FF. Stepaniak L. ( 1983). I solat ion a nd some 8 Back WO. ( 1973). Auswirkw1gen turbul en ter Strt'mungen properties of extracellular he<~t. .. stable lipases auf das System Milch. (Effects of tu t·bulence on from Pseudomona s fluorescens str ain AFT 36. Dairy lhe system milk - in German] . Mil chwissenschaft Res . ~Q. 77- 89 ~ . 628-636. 26 Fredriksen B. He rne !\ 0 , Bl~kberg L, Olivecrona T 9. Back WO, Reute r H. {1973). Auswirkungen von Strt'm­ (1978). Bile salt st im ulated lipase in human ungsvorg~nge auf die Xanthinoxydase - Aktivit~t milk: In - vivo activ i ty and i mparlance for lhc i n Rohmi l ch. 1. The or ie und Versuchsanordnung. digestion of mi lk retinolic esters. Pediatric Res ( Effects of flow mechanisms on xant h ine oxidase 12, 1048- 1052 activity in raw milk. I. Theory and experimental 27 Gl'J~er F. (1980) . Aroma von Sauermi lchproduklfm. design - i n German}. Mi lchwissenschaft ~. 137- ( P Iavour of c ultured mi l k products - in German] 141. Nahrung 24, 63- 69. 10. Bakke H, Ask A, Fjeld K. ( 1983). Verknaci av u 1 i kt 28 Gr·iffiths ~- Phi 1 Ups JU, Muir DO. (1981). Thermo ­ lufti nn s l epp i s penekoppsentralen p1i feittspa l ting stahl I i ty of pt·oteases and 1 ipases of vari ous i mjolk. [Effect of increasing air admission at sorts of psychrolt' opi c bacteria f rom mi lk. J the claw on l i pol ys i s in milk - in Norweg ian} . Appl. Bactel"i o l. §Q. 289- 303. Me ieriposten 72, 350-352. 29 Grosserhode J. (1974). Physikal i sch-c hemische Ve r ­ 11. Biallas E. (1982). Qualitlit und Ausbeute bei fett ­ ~nd er un ge n der Milchinhaltsstof fe durch Tief ­ ha1tigen Mil c hprodukte n. [Qual ity and y.leld of ldh1ung der Mi l ch. [Physico - c hf~mical changes in fat- containing milk products - in German}. Otsch. the milk constituents caused by l ow- temperatut·e Mi lchwirtschaft 33, 198, 205- 207. cool ing of mil k - in German]. Dtsch. Mi1chw.i rt­ 12. Castberg HB. (1978)." Quelques mesu r es pratiques 8. schaft 25, 686- 693. prendre pour reduire la tendance du \ait a Ia 30 Grosserh~e J. ( 1975 ). Ch ern i sch - physikalische und lipolyse. [Some practical measures to r educe the technologi sche Vertlnderungen der Rohmi lch durc h susceptibility of milk lo lipolysis - in French]. Tieflcthlw1g. [Physico- chemi ca l changes in raw milk 5 9 2 caused by low- temperatut·e cooli ng - in Ge rman] 13. Ce!~~ h ·E . L~~~72~~ ~joi)~to~ a~1 .t hydrol yUckCho Stepeni Dtsch. Mi1 chwirtschaft 26, 198- 200 tuku v mlece. [Deter·mination of fat hydrolysis in 31 Gudding R. Lorentzen P. (i983). The influence of milk - in Czech]. PrUm. Potravin 23, 139- 141 low- line and high- line milking plants on udder 14. Cerna E. {1983) Senzoricke zmeny-;; mlece vl i vem health and li!X)lysis. Not-disk Vet. Med. ~(4 / 5). lipolYzy. [Sensory changes in mi lk Ci'\used by lipo­ 153- 157. l ys i s). Pn'im. Potravin 34, 198- 201 32 Hanspach J. (1981). Untersuchungen l'lber freie Fett­ 15. Cl egg RA. (1980). Ac t ivati~ of milk lipase by serum s:!uren a I s Ar o masubstanzen verchiedenet• K~se­ pr oteins: Possible r ole at behaviour o f I ipolysis sorten. [Studi es of free fatty acids as flavour ln raw c ow milk. J . Dairy Res. 47, 62- 70. substances in var ious c heeses - i n Get·man}. PhD 16. Conno ll y JF , Murphy JJ , O'Conn;;. CB, il eadon OR. Thesis, Justus- Li e big - Un i ver sity, Giessen, Fede ral (1980). Relationship between free fatty acid Republic o f Germany, 147 pp. levels of milk and butter and li!X)lysed f l avour 33. Henkel H. {1971). Beitr~gc zur Ke nntn i s des Fett­ Int. Dairy Fed. Doc. No. 118. 667- 676 stoffwechsels hochl eistendet· MilchkOhe, insbe­ 17 . Deeth HC, Fitz- Gerald CH. (1975). Factors govern i ng sondere der Mil c hfetlb.i !dung. [Contribution to the the susceptibility of mi 1k to spontaneous l i po­ unde rstanding of the 1 ipid metabol i s m, particular­ lys is. Int. Dairy Fed. Doc . No. 86, 24- 34 ly the fat production, in highl y productive cows ­ 18 . Deeth HC, Fitz-Gerald CH, Wood AF. (1975). Comfort­ in German}. Paul - Pa r ey- Verlag Berlin and Hamburg, able method for the estima tion of extent of Fe deral Republi c o f Germany. 346 pp

272 LIPOLYTIC CIIANGES IN MILK fAT

311. Hoste tter 11. FlUckigP-r E. (1954). Ver:lnderungen due to tP.c hnologicfl1 processf's. 1. The state of des Mi lchfettes durch die Fllttenmg der Kllhe. knowledge and stud ies on t he effects of pumping on [Chl'tnges in the milk fat as re latrd to the fpeding mJ lk and cream - in German] . Nrthrung 24 , 569- 576 of cows - in German]. Schweiz. Milch Ztg. llQ.. 639- '19. Kirst E. (1981). Die lipolytische F.:mpf~d l ichke.it rler Rohmilr:h und ihre Beeinflussung. [Suscf'ptibil ­ 640. ity of raw milk to lipolysis and t he way of af­ 35 Hunter AC. (1970). Free fatty ac.id values of norml'tl and rancid milk in butter manufacture. XVIII lnl fecting it in German]. Milchforscnung- Mil ch­ Dairy Congress. Sydney, Australia, XVIll tnt. praxis 23, 60-62. Dairy Congr ess Co mm ittee, Sydney, N.S.W., Austru·· 50 Kjrst E. {1981}. E.influss l ipolytischer Verl:il.derun­ gell auf die Qual i U\t von Dauerm i l cherzeugnissen. l ia. l E. 508. 36. fngr .J.- (1973) Zus amme nsetzung und Eigenschaften lEffect of Lipolytic changes on the quality of des Kuhmilchfettes bei subklinischen MasUtiden. long she l f - 1 ike milk products - in German]. Mil ch­ [Composition and properties of cow's milk fat in forschlmg·-Mi 1 chpraxi s 23, 140- 141. subclinical masti tis - in German]. Nabrung E.• 51 Kirst E. (1981). Der Einf!Uss 1 ipolytischer VOJ·gt!nge auf die Qualittltsei gensch;:~;fl'f!n von Schli\gsahne. 215 · 232. 37. Tn.ikhov G. (1958). Rol sostavnykh chastei moJok?J pri (Effect of lipolytic p1·ocesses on t he quality of proizvodstve. [Tile ,-ole of milk constituents dur­ whipped cream - in German]. B~cker Konditor g~. ing processing - in Russian]. Moloch. Prom. ~. 4. 282- 281 52. Ki rst E. {1981). Lipolytische Vorgtinge in Mil ch und 41 18 ..htmotlf~ P. (1970). Effect of the use of lipolysed Milchp1·odukten. IV. Untersuchungen zum Einfluss cr·cam on butter quality. XVIII Int. Dairy Con ­ der Schaumbildung auf die Struktur des M.i l ch­ gress, Sytlncy, Australia. XVI I I lnt. Dairy Con­ fettes. [Lipolytic processes in milk and in milk gress Comm ittee. Sydney, N.S.W .. Austrma A. (1!:174). LipoJytical sensitiv i ty of miJk. Milch durch die Pr imti t·bearbe i tung. [ Li po 1 yt.ic Off. Ot·gnn FNZ 66, 334- 341 activity of milk after pr.imS. 44 Ki ermeier F. Lechner E Mil ch und Mi l cherzeuEnisse. forschung-Mi lchpraxis 24, 102- 103. 109. [Mi Jk and milk pt·Ollucts - in German} . Paul Pa,·ey­ 56. Kirst E. Hanse n R. (1983). LJpoJytische Vorg~.nge Ver 1 ag, Der I ing and Hamburg, Federal Repub I ic of in Milch und Milchprodukten. V. Zur Eignung ver­ sch iedener Parameter fllr die Beurteilllilg lipo­ Germany. 1143 pp 45. Kirst E. (1980). L.ipolytische Vorg~ge in Milch und lyt.ischel' VerMderllilgen in der Rohro i lch. [Lipo­ Mi lchprodukten: Lite1·aturber.icht und Untersuchun lytic processes in milk and in milk products. V gen zum Einf 1 u::;s von RUhren und Pumpen auf dal' Suitability of various parameters to induce lipo­ Mil chfett. {Lipolytk processes in milk il!ld in lytic changes in raw milk in German]. Lebens­ milk prorlucts: Literature revie\1.' and studies of mittel industr.ie Leipzig 30, 77 81 the effect of st.i r·ring and pump ing on mi \k fat - 57 Kirst E, Lill R, SchJeusen~ 1, Kre nke1 K, Jacobi U. .in Gf~r·man]. Lebenmittelindustrie Leipzig~. 27 - {1983). Einfluss einer Energiemangelert'\IDlrung lak­ 31; Molkere i Ztg. Welt Milch 34, 1002 -1006. tierender Rinder auf Zusammensetzung und Eigen­ 46 Kirst E. (1980). Lipolyt.ische vOrgtlnge in Milch und schaften der Rohm.i l ch. [Effect of energy- deficient Mil chprodukten: II. Untersuchungen !':Urn Einfluss nutrition in cattle on the composi t .i on and proper­ der Strl'mung auf dils Milr:hfett. [Lipolytic pro­ ties of raw milk - in German]. Mil c hforsc hung­ cesses in milk and in milk products: II. Studies Mi lchpraxis 25, 3- 6 of the effect of flow on milk fat - in German]. 58. Kirst E, Meye-;=- A, Cernci E. Obermaier 0. (1983). Lebensmittelindustrie Leipzig 27. 3 14 - 316 Bee influssung der sensorischen Qualitlkt de1· Milch 47. Kirst E. (1980). Ljpolytische von!~~e .in Milch und du rch lipolytische Verl'!nderw1gen. [Influencing the Milchp!'odukten: III. Untersuchungen zum Einf luss sensm·y property of mi lk t ht·ough lipolytic changes der KlilJune: auf die Mi lchfc ttstruktur. lLipolytic - in German]. Milchforschung- MiJchpra.xis ~. 100- p t•ocesses in milk a nd in milk products: III 102. Studies of t he effect of cool .ing on the structure 59. Kirst E. Westphal G. (1983). Zur Llpolyse der MHch of milk fat - in German]. Lebensmittelindustrie durch technologische Beeinf 1 ussungen. 2. Unter­ Leipzig 27, 464 - 468; Molkerei Zt g . Welt Milch suchungen zum Einfluss der Mi l chfettzusammen­ setzung auf die 1 ipolytischen Vedllderungen bei :J.9.( 1981)' -349- 353. 48 Kirst E. (1980). :Z. ur Upolyse der· Milch durch tech­ der Kljllung der Milch. [Lipolysis in milk induced nologische Bee.influssungen. 1. Stand der Kennt­ by technologi cal pr·ocesses. 2. Studies on the nlsse und Untersuchungen zur Beeinflussung von effect of the milk fat composition on lipolytic Mil ch und Rahm durch Pumpen. [Lipolysis of milk changes during the cooling of milk - .in German]

273 K 1 RST

Nahrung 27, 1~8 in Rohmilch mit llilfe des Kochsche n Plattenver ­ 60. KlostermeYer H, Re.imerdes EM . (1 976 ). C h e lllisc h ~ fahrens. (Attempts to s ho rte n the proof of the physikalische Vorgfulge in gekl.lhl ter Rohmil c h. spores o f psychrotrophic microorganisms in raw [C hemi co ~ phys .i cal processes in cooled r·aw milk ~ milk using t he plate method by Koch - in German]. i n German]. Molkerei Ztg. Welt Mil ch~. 1 35~ 138 Mi lchforschung Mi lchpraxis £!., 39- 41. 61. Kodgev A, Rachev R. (1970). Influe nce of some fwhey products as ingredients feeding on lipolysis in milk - in Dutch] . Bedrijf­ in confectione ry and cocoa prOOucts - in German] . sontwikkeling 5(4), 315- 319. J.ebensmi ttel industri e Lepzjg 26, 211-214 , 269-273 67. Lehmann 11. (1982). Der Einfluss der mechani sche n 82. Saito Z, Harper WJ , Gould IA. (1966). Distribution Behandlw1g der Milch auf ihre Separierf:.Vtigkeit and partia.l pul'ificaUon of m.ilk l ipHse. Bull unter dem Gesichtspunkt der Gehal te an freiem Fett Fac. Agric. llir·osak i Univ. g, 66- 74. und freien F e tts~ur e n . [Effect of mechanical 83. Saito Z, Igarashi V. ( 1971). The milk lipases. VII I. handling of milk on its separability as related t o Separation of lipases by gel filtr a tion by treat­ t he free fat and free acid contents in the mi \k ment wi th sodium chlor ide. Bul l. Fac. Agrlc. Hiro in Ge rman]. Dtsch. Milchwirtschaft ~. 172- 174 saki Univ. 17, 126 135. 68. Lindne r H. (1970). Lehrbuch der Physik. {Bandbook on 84 . Saito z. (1977). Lipases in bovine mi lk . .l a p. J physics - .in German]. VEB Fachbuchverlae: Le i pz ig, Zoo t e ch. Sci. 52, 299- 307. German Democratic Republic, 584 pp. 85 Saito z. Kitrty;-E, Ok

274 LIPOLYJ C CHANGE S IN MILK FAT

t he qualHy of rawmilk - in German]. PhD tesis, S. Saito: Homogenization does not produce free fat but B. Humboldt- Univ .. Berlin , Ge rman Democrat c Re­ ~most effective treatment to .induce 1 ipolys .is. Wi 11 t he a uthor please give his opinion on the e f fect of public. 185 pp. 93. T~pe1 A. (1982). Chemie und Physik d er i l c h . homogenization on the microstructure of fat g lobules? (Chemistry and physics of milk - in German VEB Author: Homogenization results in the disintegration of Fachbuchver l ag, Leipzig, German Democratic .epub- the original (large) fat globules in milk and .in the production of a great number of smaller fat g lobules. 1 ic. 488 pp. 94 Urbach HG , Stark W. Forss DA. (1970). Flavou s and Consequen tly, also the fat globule membra nes are disin­ flavour thresholds of acids, lactones, ph ~ no! ic tegrated and lipase is released. As the total surface and indol ic compounds. XV Ill Int. Dairy Con ;ress, of t he fat globules is increased 5 to 6 fold (101), the Syd ney, Au stralia, XVII I Int. Dairy Congres Com­ newly formed fat surface is rapidly coated with surface­ active materia l such as the fragments of the fat g lobule mittee. Sydney, N.S .W .. Australia, .! ~. 234. 95 Velitok JG. (1973). Vl.iyanie subk l inicheskikh r.asti ­ membranes. casein, and undenatured wh ey proteins from tidov na fiziko- khim.ichesk.ie svoistva mt loka. t he mi lk serum. Liberated lipase participates in lipo­ [Effect of subclinical masti tis on physical and lysis. Lipolysis may be induced by homogenization only chemical properties of milk - in Russian]. M lloch. in raw milk but not in pasteurized or utiT - treated milk. Prom. 40(3). 19- 20. Saito: The effect of energy- deficient feeding on t he 96. \\'h ittles"t~ n e WG. (1968). Influence of machine 'llilk­ z. ing on the milk quality. J . Milk Food Teclmo .... 31. fat content in milk and the projXlrtion of fatty acids 73- 77. - (Table 4) seems to be smalL I s it statistical l y signif­ 97. Worstorff H. Heeschen W, Reichmu t h J, Tolle A. icant? (1972) . Freie Fettsauren in der Milch in Abhlin­ Author: Stati s tical tests were carried out by analysis g i gkeit von str&lungstechnischen Bedingungen der of variance (ANOVA) {to study the interactions between Milkanlagen. [ Free fatty acids in milk as re lated the lactation stages and feeding] and by a multiple to the technological flow conditions .in dairy comparison of the mean values using a Newman- Keuls Test facilities - i n German] . Otsch. Milchwirts c haft (102). The increase in the mi lk fat content at the begin­ £1_, 477- 480. 98. Z.ickrick K. Posur H. (1971). Psychrotrophe Keime in ning of the energy- deficient feedi ng wa s found to be tiefgek\.'j1l ter Rohmi lch. [Spores of psychrotrophic statistically significant (P < 0.05). This effect is mi ci'Oorganisms in low- temperature c ool ed raw mi lk called 'the fat - mobilization syndrome' (103 ). In the - in Germanj . Mil chforschung Milchpraxis 13, 155- subsequent period, the fat conten t i n the mi l k decreas­ e d: this decrease was also significant. However, the 156. 186- 188. - increases in the free fat con tent at t he beginning of each feeding period were statistically not signi fican t Discuss ion with Reviewers Additional References D. E. C'l rpenter: The author refers to protection by t he milk fat g lobul e meMbra nes of the fat from lipolytic and 99. Shimizu M. Yamaguchi K, Kanno C. ( 1980). Effect of oxidative processes. Is there any evidence that hydro­ proteolytic digestion of milk fat globule me m­ lysis of the membrane protein by natural milk pr otea ~e s brane proteins on stability of fat globules. or psychrotrophic milk proteases gives rise to higher Mi l chwi ssenschaft 35, 9- 12. 100 . Juren BJ, Gordin S, Rosenthal I. Laufer A. (1981) levels of free fatty acids? Author: The effect of hydrolysis of t he milk fat globule Chang:es in refrigerated milk caused by Enterobac­ membrane p r·oteins by microbial and milk proteases was t eriaceae. J. Dairy Sci. 64, 1781 - 1784. studied by several authors (28, 99, 100). Disruption of 101 . Darling DG, Butcher r:M'. (1978). Milk fat globule the fat globule membrane by proteases exposes the fat membrane .in homogenized cream. J. Dairy Res. 1.§, globules to the a ction of 1 ipase, particularly at h i gh 197- 208. counts of psychrotr ophic bacteria. Thus, the increase in 102. Miller RG. (1966). Simultaneous Statistical Infer­ t he free fatty acid concen tratio n is the resuJ t of ence. McGraw-Hi 11 Book Co .. Toronto, On tario. lipolytic action on fat globul es destabilized by prote­ Canada. 81 ases. To prevent this from happening, it is important to 103. SUber M, Dirksen G. (1982). Das I.ipomobilisations ­ keep the psychrotrophic bacteria counts in mi lk a s l ow syndrom (Verfettungssyndrom). Prakt. Tierarzt 63, Colloquium Veterinarium, 79- 88. - as possible.

275