Czech Journal of

FOOD SCIENCES

Czech Academy of Agricultural Sciences

1

VOLUME 31 Prague 2013 ISSN 1212-1800

Czech Journal of  FOOD SCIENCES An international peer-reviewed journal published by the Czech Academy of Agricultural Sciences and financed by the Ministry of Agriculture of the Czech Republic The journal is cited by: • Science Citation Index Expanded® • ISI Alerting Services® • Current Contents®/Agriculture, Biology and Environmental Sciences® • Cambridge Scientific Abstract and abstracted by: • Agrindex of AGRIS/FAO database • CAB Abstracts • Czech Agricultural and Food Bibliography • Elsevier’s Bibliographic Databases • Food Science and Technology Abstracts • Dairy Science Abstracts • Chemical Abstracts • FROSTI • PASCAL (INIST) • SCOPUS

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Czech Journal of F ood S ciences is published by the Czech Academy of Agricultural Sciences, in a yearly volume of six issues. The journal welcomes the contribution of original research papers, preliminary reports, short communications and reviews related to all aspects of food science and technology. Papers are published in English.

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Editorial Office Czech Journal of Food Sciences, RNDr. Marcela Braunová, Executive Editor, Czech Academy of Agricultural Sciences, Slezská 7, 120 00 Praha 2, Czech Republic, tel.: + 420 227 010 233, fax: + 420 227 010 116, e-mail: [email protected].

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MK ČR E 6696

Czech Journal of FOOD SCIENCES (continuation of the journal Potravinářské vědy)

Volume 31

2013

Editorial Board Jan Velíšek (Praha, Czech Republic) – Editor-in-Chief Marcela Braunová (Praha, Czech Republic) – Executive Editor

Jennifer Ames Newcastle-upon-Tyne, UK

Jiří Blahovec Praha, Czech Republic

Jiří Davídek Praha, Czech Republic

Ibrahim Elmadfa Wien, Austria

José A. Empis Lisboa, Portugal

Vladimír Filip Praha, Czech Republic

Vincenzo Foglino Portici Napoli, Italy

Elisabeth Guichard Dijon Cedex, France

Anna Halász Budapest, Hungary

Colin Hamlet High Wycombe, UK

Thomas Henle Dresden, Germany

Francisco J. Hidalgo Sevila, Spain

Marie Holasová Praha, Czech Republic

Pavel Jelen Edmonton, Canada

Pavel Kalač České Budějovice, Czech Republic

Norbert de Kimpe Gent, Belgium

Bořivoj Klejdus Brno, Czech Republic

Radomir Lásztity Budapest, Hungary

Paul Nesvadba Aberdeen, UK

Jacek Nowak Poznan, Poland

Musa Özcan Konya, Turkey

Werner Pfannhauser Graz, Austria

Vieno I. Pironen Helsinky, Finland

Mariusz K. Piskula Olsztyn, Poland

Milada Plocková Praha, Czech Republic

Mojmír Rychtera Praha, Czech Republic

Ján Šajbidor Bratislava, Slovak Republic

Peter Schieberle Garching, Germany

Štefan Schmidt Bratislava, Slovak Republic

Peter Šimko Bratislava, Slovak Republic

Zeno Šimůnek Praha, Czech Republic

Leif H. Skibsted Frederikberg C, Denmark

Richard Stadler Orbe, Switzerland

Ingrid Steiner Wien, Austria

Berhard Tauscher Karlsruhe, Germany

Bohumil Turek Praha, Czech Republic

Žaneta Ugarčič-Hardi Osijek, Croatiac

Michal Voldřich Praha, Czech Republic

Lenka Vorlová Brno, Czech Republic

Wang Jun Hangzhou, P.R. China

Weibiao Zhou Singapore

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Czech Journal of

Volume 31, 2013, No. 1

FOOD SCIENCES



Contents Original scientific paper Wang w., Li Z., Liu J.-Z., Wang Y.-J., Liu S.-H., Sun M.: Comparison between thermal hydrolysis and enzymatic proteolysis processes for the preparation of tilapia skin collagen hydrolysates ........................ 1 Marinova E., Georgiev L., Totseva I., Seizova K., Milkova T.: Antioxidant activity and mechanism of action of some synthesised phenolic acid amides of aromatic amines ................................ 5 Yurdakul N.E., Erginkaya Z., Ünal E.: Antibiotic resistance of enterococci, coagulase negative staphylococci and Staphylococcus aureus isolated from chicken meat ................................................................ 14 Toušová R., Stádník L., Ducháček J.: Effects of season and time of milking on spontaneous and induced lipolysis in bovine milk fat ................................................................................................................ 20 Dušková M., Karpíšková R.: Antimicrobial resistance of lactobacilli isolated from food ................................ 27 Kowalski S., Lukasiewicz M., Juszczak L., Kutyła-Kupidura E.M.: Dynamics of 5-hydroxymethylfurfural formation in shortbreads during thermal processing ............................................ 33 Zdjelar G., Nikolić Z., Vasiljević I., Bajić B., Jovičić D., Ignjatov M., Milošević D.: Detection of genetically modified soya, maize, and rice in vegetarian and healthy food products in Serbia .............. 43 Václavíková E., Kvasnička F.: Isotachophoretic determination of glucosamine and chondroitin sulphate in dietary supplements ............................................................................................................................. 49 Pankiewicz U., Jamroz J.: Evaluation of physicochemical and sensory properties of ethanol blended with pear nectar ......................................................................................................................................................... 55 Nogales-Delgado S., Fernández-León A.M., Delgado-Adámez J., Hernández-Méndez Bohoyo-Gil M.T.: Effects of several sanitisers for improving quality attributes of minimally processed Fragaria vesca strawberry ..................................................................................................................... 66 Engmann N.F., Ma Y.-K., Ying X., Qing Y.: Investigating the effect of high hydrostatic pressure processing on anthocyanins composition of mulberry (Morus moraceae) juice ............................................ 72 Čížková H., Rajchl A., Šnebergrová J., Voldřich M.: Filbertone as a marker for the assessment of hazelnut spread quality ........................................................................................................................................ 81 Wang W., Zhang M., Fang J., Zhang L., Zou X., Wang X.: Improved detection of Ochratoxin A by marine bioluminescent bacteria V. harveyi BA ............................................................................................... 88 Kučerová Z., Kýhos K., Aulický R., Stejskal V.: Low-pressure treatment to control food-infesting pests (Tribolium castaneum, Sitophilus granarius) using a vacuum packing machine ................................ 94 List of Reviewers – 2012 .................................................................................................................................................... I

CZECH ACADEMY OF AGRICULTURAL SCIENCES Těšnov 17, 117 05 Prague 1, Czech Republic workplace: Slezská 7, 120 00 Prague 2, Czech Republic e-mail: [email protected] Tel.: + 420 227 010 427, Fax: + 420 227 010 116 Account No. 86634011/0100 KB IBAN CZ41 0100 0000 0000 8663 4011; SWIFT KOMBCZPPXXX The Czech Academy of Agricultural Sciences publishes scientific journals dealing with the problems of agriculture, forestry and food sciences and technology. The periodicals are published in English.

Journal

Number Yearly subscription of issues per year in USD

Plant, Soil and Environment

12

720

Czech Journal of Animal Science

12

720

Agricultural Economics (Zemědělská ekonomika)

12

680

Journal of Forest Science

12

580

Veterinární medicína (Veterinary Medicine – Czech)

12

790

Czech Journal of Food Sciences

6

620

Plant Protection Science

4

175

Czech Journal of Genetics and Plant Breeding

4

175

Horticultural Science

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175

Research in Agricultural Engineering

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155

Soil and Water Research

4

175

Subscription to these journals be sent to the above-mentioned address.

Vol. 31, 2013, No. 1: 20–26

Czech J. Food Sci.

Effects of Season and Time of Milking on Spontaneous and Induced Lipolysis in Bovine Milk Fat Renáta Toušová, Luděk Stádník and Jaromír Ducháček Department of Animal Husbandry, Faculty of Agrobiology, Food and Natural Sources, Czech University of Life Sciences Prague, Prague-Suchdol, Czech Republic Abstract Toušová R., Stádník L., Ducháček J. (2013): Effects of season and time of milking on spontaneous and induced lipolysis in bovine milk fat. Czech J. Food Sci., 31: 20–26. The effects were evaluated of different factors on the level of spontaneous (SPO) and induced (IND) lipolysis as defined by the content of free fatty acids (FFA) in milk. Milk samples were collected at monthly intervals throughout the year from both morning and evening milkings either individually in a milking parlour (SPO; n = 10) or from the bulk tank (IND; n = 10). The data were analysed using SAS 9.1. More intensive SPO was observed from March to May with higher FFA contents (+0.034 to +0.523 mmol/100 g of fat; P < 0.05–0.01), and also from September to November (+0.077 to +0.292 mmol/100 g of fat; P < 0.05). More intensive SPO was also detected in the evening milk than in that coming from morning milking (+0.062 to +0.556 mmol/100 g of fat; P < 0.05–0.01). SPO measured immediately after milking was affected by the season and time of milking. The content of FFA characterising IND in bulk milk (0.33–1.10 mmol/100 g of fat) was higher (P < 0.05–0.001) than that due to SPO in individual samples (0.21–0.86 mmol/100 g of fat), especially in those from evening milking compared to morning milking (+0.10 to +0.47 vs. +0.12 to +0.22 mmol/100 g of fat; P < 0.05–0.001). Keywords: dairy cow; free fatty acid; lipolysis; milking; processing

Milk fat is one of the principal milk solids, and its content considerably changes throughout the entire lactation period and also during a single day (Poláková et al. 2010). Milk fat consists of triacylglycerol, phospholipids, non-esterified fatty acids, and glycerol. In fresh milk, 99% of fatty acids are esterified to triacylglycerol, and their composition influences the nutritive and technological properties of milk and milk fat (Hanuš et al. 2010). A certain level of lipolytic activity caused by lipoprotein lipase occurs in each bovine milk sample. It results in the formation of free fatty acids, diacylglycerols, monoacylglycerols, and glycerol (Deeth 2006). Lipolysis of triacylglycer-

ols to glycerol and free fatty acids (FFA) may lead to undesirable modifications in milk and dairy products. High quality raw milk, even after 24 h of storage including cooling and stirring, should not contain more than 1 mmol FFA per 100 g of fat. The amount of FFA depends on the extent of the damage to the fat globule membrane, and the value of 1.5 mmol/l of milk is considered as critical (Deeth 2006). Three different types of fat lipolysis may occur in milk depending on different factors: spontaneous, induced (Forman 1984), and microbial (Cempírková & Mikulová 2009). Spontaneous lipolysis is caused by the activity of milk lipases, and its intensity as well as milk fatty

Supported by the Ministry of Education, Youth and Sports of the Czech Republic, Project MSM 6046070901, S Grant of MSMT CR, and by the Ministry of Agriculture of the Czech Republic, Project No. QH91270.

20

Czech J. Food Sci. acid composition is influenced by the stage of lactation (Gonzáles-Martín et al. 2009), diet type and composition (Cieslak et al. 2010; Kalač & Samková 2010), and energy status (Hanuš et al. 2010). Induced lipolysis is the result of mechanical damage to the fat globule membranes arising during milking, milk transport, storage, and processing, and is followed by the contact of free fat with milk lipases (Quattar et al. 2004). The level of microbial lipolysis depends on the incidence of lipolytic bacteria. Especially psychrotrophic microorganisms are considered dangerous, as they are able to reproduce even at storage temperatures (Cempírková & Mikulová 2009). Individual differences exist in the susceptibility to spontaneous lipolysis (Miller & Puhan 1985). Most lipolytic changes in chilled milk occur during the first 24 hours. It was reported that milk with a content of FFA higher than 1.5 mmol/l is not acceptable for human consumption (IDF 1987). Negative energy balance is another factor increasing the content of FFA. High milk yields and a limited ability of feed intake in early lactation trigger the process of lipomobilisation and the release of energy from the body fat reserves (Gonzáles et al. 2011). As a result, the contents of fat and FFA increase both in blood and milk (Kulig et al. 2010). Therefore, the content of FFA may indicate the health status of dairy cows (Hanuš et al. 2004). Under negative energy balance or low concentrations of insulin, the secretion of hormone-sensitive lipase is stimulated, triggering lipolysis with the subsequent release of fatty acids in their nonesterified forms (NEFA, resp. FFA) into the bloodstream (Nelson & Cox 2000). Thus, the concentration of NEFA may reach a value detrimental to the health status of cows both prepartum (Poláková et al. 2010) and postpartum (Herdt 2007). A wide range of dairy cows’ production diseases are treated using antibiotics which affect the final quality of raw milk as well (Navrátilová et al. 2011). Based on the facts mentioned above, we assume that differences in FFA contents can be detected among animals as well as among bulk tank samples collected in different seasons and milking times. It can also be assumed that differences exist in total FFA content depending on the intensity of spontaneous lipolysis in milk samples collected in a milking parlour, and that the FFA content will increase as a result of induced lipolysis due to mechanical stress imposed on milk during pumping, storage, cooling, and stirring in a tank. Little information is available

Vol. 31, 2013, No. 1: 20–26 on the content of FFA as affected by the season. In addition, sufficient data describing the lipolysis intensity in milk obtained at different milking times are entirely lacking. Therefore, the objective of this study was to determine the effects of season and the time of milking on the extent of spontaneous and induced lipolysis based on the contents of FFA in milk samples collected either from individual animals or from a bulk tank. Material and methods Milk samples were collected from Holstein cows at monthly intervals throughout the year. The cows were kept in a loose-housing system on a slatted floor, and the manure was removed using a v-shaped scraper. The winter season diet consisted of 23 kg of maize silage, 6.5 kg of clover/grass silage, 6.2 kg bean-clover pellets, 1 kg of peas GPS, 1 kg of beans GPS, 2 kg of wheat straw, and the concentrate mixture digestible nitrogen substances (DOPS 121 g/kg, NEL 611.82 MJ/kg, fibre 58 g/kg, Ca 4.6 g/kg, and P 7.2 g/kg). The summer diet consisted of 35 kg of clover/grass mixture, 10 kg of maize silage, 2.5 kg of hay, 2 kg of wheat straw, and the concentrate mixture mentioned above. The transition periods for gradual diet changes were March to April and October to November. A carousel parlour was used for milking, and milk was stored in a 5000 l tank. The milk samples were collected from ten cows having calved in January. The parity of these cows was similar to that of the entire herd, 3 cows in the 1 st lactation, 4 cows in the 2 nd lactation, and 3 cows in the 3rd and subsequent lactations. Milk of all cows was checked by NK test and no symptoms of mastitis or high level of somatic cells were determined during the observation. Daily milk yield of the evaluated cows was in the range from 6.4 kg to 39.5 kg with the average value 18.57 kg and standard deviation 6.72. Fat content in the individual milk samples ranged from 2.85% (s d = 0.610) to 4.24% (s d = 0.367) in the morning milk and from 3.06% (s d = 0.387) to 4.36% (s d = 0.339) in the evening milk during the whole period observed. Milks from morning and evening milkings were sampled directly, in the parlour with the aim of determining the intensity of spontaneous lipolysis caused by the action of milk lipases. In addition, bulk milk samples (n = 10) were also collected from tanks 1 h after milking to measure the level of induced lipolysis, which 21

Vol. 31, 2013, No. 1: 20–26

Czech J. Food Sci.

results from mechanical damage to fat globule membranes, thus making milk fat more accessible to lipases. The evening milk samples were stored in refrigerator at 6°C during the night and analysed together with the morning samples collected next day. The length of the period between the collection and analyses was 12 h with the evening samples and 2 h with the morning samples. The only one difference was due to the storage of the evening samples, however, the methodology of sampling, manipulation, transportation, and analyses was completely the same for both the morning and evening samples. The milk samples met all the microbiological requirements given by the quality standard, and significant differences were detected neither in total bacteria nor in psychrotrophic bacteria counts. Similar milking conditions were secured during the experimental period as each cow evaluated always entered the same parlour stall equipped with the same milking machine. The content of FFA was analysed using the Milcoscan FT 6000 apparatus (Foss, Hillerød, Denmark) based on infrared spectrophotometry. The following statistics were used to evaluate the magnitude and significance of differences between the dependent variables: arithmetic mean, standard deviation, and P value of statistical significance. The pair t-test was used to compare the differences at P < 0.01 and P < 0.05 levels of statistical significance. The calculations were performed using SAS 9.1 (SAS 2004).

Results and discussion The content of FFA was determined in a total of 220 milk samples. Table 1 shows the development of spontaneous lipolysis demonstrated on the basis of average FFA contents from morning and evening milkings in different months of the experimental period. However, lipolysis may sometimes occur already during the process of milking due to rising and frothing of milk in milk lines and therefore, it is not always possible to distinguish between spontaneous and induced lipolysis (Evers et al. 2001). The milk from certain cows is particularly susceptible to spontaneous lipolysis, and the content of FFA may reach as much as 10 mmol/l (Deeth & Fitz-Gerald 1995). Such high levels were not, however, observed in our study. The milk from some other cows can be partially resistant to spontaneous lipolysis with the level of FFA less than 0.5 mmol/l. The average contents of FFA range from 0.24 to 1.16 mmol/100 g of fat depending on the diet, breed, and individual cows (Abeni et al. 2005). The levels of spontaneous lipolysis observed in our study (0.10–1.10 mmol/100 g of fat) were in agreement with those reported by other authors. Compared to other months, higher FFA contents in morning milking samples were observed in May (+0.072 to +0.453 mmol/100 g of fat; P < 0.05–0.01), compared to evening milking samples in March and April (+0.034 to +0.523 mmol/100 g of fat; P < 0.05) (Table 1). Also, FFA contents in milks

Table 1. Mean free fatty acid contents (mmol/100 g of fat) in morning and evening milk samples of 10 dairy cows (spontaneous lipolysis of milk fat) Month

Morning

Evening

0.400 ± 0.18

DjK

0.327 ± 0.16

Egjk

III (C)

0.306 ± 0.11

dEgjk

IV (D)

0.197 ± 0.08 EFGhIJK

I (A) II (B)

0.650 ± 0.26

fH

VI (F)

0.394 ± 0.09

k

VII (G)

V (E)

P

0.527 ± 0.16

Cgh

*

0.445 ± 0.13

Cd

N

0.862 ± 0.34

efGHIjK

**

0.665 ± 0.26 fGH

**

0.491 ± 0.22

N gh

N

0.479 ± 0.16 H

0.339 ± 0.10 iJk

N

0.307 ± 0.08

jk

0.369 ± 0.07

iJk

*

IX (I)

0.442 ± 0.18

jk

0.578 ± 0.24

j

*

X (J)

0.578 ± 0.24

0.631 ± 0.22

N

XI (K)

0.506 ± 0.15

0.544 ± 0.19

N

VIII (H)

0.467 ± 0.11

month – month of lactation/calendar month; upperscript letters means significant difference among rows – a, b, c, d, e , f, g, h, i, j, k = P < 0.05; A, B, C, D, E, F, G, H, I, J, K = P < 0.01; stars means significant difference between columns – *P < 0.05, **P < 0.01, N = P > 0.05

22

Czech J. Food Sci.

Vol. 31, 2013, No. 1: 20–26

coming from both times of milking were higher in October and November than in the summer months (+0.077 to +0.292 mmol/100 g of fat; P < 0.05). These results are in agreement with those of Hanuš et al. (2008), who reported that higher FFA contents in milk, were frequently caused by metabolic disorders of cows. In our study, such disorders were due to the deteriorated feed quality at the end of both winter and summer periods, and due to the problems in the transition periods from winter to summer and from summer to winter diets. Significant differences in morning FFA contents were observed between April and most other months (–0.109 to –0.453 mmol/100 g of fat; P < 0.05–0.01). Significant differences were also detected between May and February, March, and April (P < 0.01). Morning concentrations of FFA observed in October and November differed from those found in January, February, March, April, August, and September (P < 0.05–0.01). Compared to the other months, the highest evening FFA content was observed in March (P < 0.05–0.01). The evening FFA contents were lower (P < 0.05–0.01) in July and August compared to those in January, March, April, June, September, October, and November. On the contrary, higher FFA contents in milk were previously detected during the pasture season compared to the rest of the year (Frelich et al. 2009). However, the effect of the time of milking was not tested in that study. Our results confirm the seasonal character of FFA contents, with the

most distinct changes observed in March and April, thus in the transition period from winter to summer diets. The contents of FFA in both morning and evening milk samples were higher from September to November. Milk fat composition is mainly affected by the diet (Samková et al. 2009; Dai et al. 2011). Our results are also in agreement with the study by Kon and Saito (1997), who reported that particularly cows in late lactation may be endangered by spontaneous lipolysis due to low milk yields and less intensive diet. It was suggested that the increased milk content of FFA in late lactation is associated with a poor energy intake at the end of the pasture season (September to November). Body fat deposits are mobilised, and FFA as a source of energy are released into the blood and transported into milk (Kulig et al. 2010). The fat content and the fat/protein ratio in milk therefore belong among the most important indicators of energy balance in animals (Sojková et al. 2010; Ducháček et al. 2012). The results concerning the energy status of animals also confirm the conclusions by Hanuš et al. (2008). The differences in FFA contents indicating the level of spontaneous lipolysis were tested between the milk samples from morning and evening milkings of 10 cows (Table 1). Significantly higher FFA contents in milk from evening milkings (P < 0.05–0.01) were detected only in January, March, April, August, and September (+0.062 to +0.556 mmol/100 g of fat). In most other months,

Table 2. Mean free fatty acid contents (mmol/100 g of fat) in morning and evening milk samples from selected dairy cows (n = 10; spontaneous lipolysis – SPO) and from the bulk tank (n = 10; induced lipolysis – IND) Month

Morning

Evening

SPO

IND

SPO

IND

I

0.400 ± 0.18

0.33 ± 0.02

0.527 ± 0.16

0.65 ± 0.07A

II

0.327 ± 0.16

0.48 ± 0.03A

0.445 ± 0.13

0.70 ± 0.07C

0.306 ± 0.11

0.49 ± 0.04

C

0.862 ± 0.34

0.64 ± 0.11

B

0.665 ± 0.26

0.77 ± 0.09

III IV

0.197 ± 0.08

0.31 ± 0.03

V

0.650 ± 0.26

0.72 ± 0.06

0.491 ± 0.22

0.66 ± 0.05A

VI

0.394 ± 0.09

0.44 ± 0.03

0.467 ± 0.11

0.61 ± 0.03B

VII

0.479 ± 0.16

0.55 ± 0.04

0.339 ± 0.10

0.44 ± 0.02B

VIII

0.307 ± 0.08

0.43 ± 0.03C

0.369 ± 0.07

0.49 ± 0.02C

IX

0.442 ± 0.18

0.49 ± 0.05

0.578 ± 0.24

0.77 ± 0.06A

X

0.578 ± 0.24

0.80 ± 0.08A

0.631 ± 0.22

1.10 ± 0.13C

XI

0.506 ± 0.15

0.52 ± 0.05

0.544 ± 0.19

0.71 ± 0.05A

month – month of lactation/calendar month; A = P < 0.05, B = P < 0.01, C = P < 0.001 between columns



23

Vol. 31, 2013, No. 1: 20–26 0.9

Czech J. Food Sci.

SPO

y = -0.0004x4 + 0.011x3 – 0.0952x2 + 0.3352x + 0.0812 R² = 0.2754

IND

0.8

Polynomial (SPO)

0.7

Polynomial (IND)

0.6 0.5

Figure 1. Development of mean free fatty acid contents (mmol/100 g of fat) in the morning milk from selected dairy cows (n = 10; spontaneous lipolysis – SPO) and from the bulk tank (n = 10; induced lipolysis – IND)

0.4 0.3

1.0 0.9

ct

r em

ob

be

er

r

N

ov

O

pt Se

SPO IND Polynomial (SPO) Polynomial (IND)

1.1

em

ug A

except for March and April, whereas morning FFA contents differed in February, March, April, August, and October. October contents of FFA in bulk milk exceeded 1.0 mmol/100 g of fat thus indicating its deteriorated quality, however, they were below the critical value of 1.5 mmol/l of milk (Deeth 2006). As the time interval between the end of milking and the analyses performed was always the same, it is evident that the higher FFA contents in bulk milk were due to induced lipolysis as a result of milk fat globule disruption and exposure of the lipid substrate to the action of lipase. This occurred during the process of pumping and transport of milk to the bulk tank, which was followed by its stirring, cooling, and storage (Quattar et al. 2004; Evers 2004). A similar FFA content increase from 0.68 to 1.21 mmol/100 g of fat corresponding to our results was reported earlier (Wiking et al. 2006). However, the differences

FFA contents were also higher in the evening milk, but the differences lacked statistical significance (P > 0.05). Previous studies were mostly directed at the effects of the lactation stage or season on different types of lipolysis in bulk milk, and the information on differences between morning and evening milkings is thus not available. FFA contents in morning and evening milks from 10 cows as spontaneous lipolysis indicators were compared to those determined in bulk milk considered to be the indicators of induced lipolysis (Table 2). The average FFA content in bulk milk (0.33–1.10 mmol/100 g of fat) is higher than that in the samples coming from individual cows (0.21–0.86 mmol/100 g of fat), particularly in the evening compared to morning milk (+0.10 to +0.47 vs. +0.12 to 0.22 mmol/100 g of fat; P < 0.05–0.001). Significant differences in evening FFA contents were detected between all the months 1.2

be

us

t

ly Ju

ne Ju

ay M

il pr A

ar M

ry ua br

Fe

Ja

nu

ar

y

0.2

ch

y = 0.0005x4 – 0.0128x3 + 0.1056x2 – 0.3151x + 0.6176 R² = 0.2999

y = –0.0013x4 + 0.0312x3 – 0.2532x2 + 0.7394x + 0.077 R² = 0.4717

0.8 0.7 0.6 0.5 0.4

24

er

N

ov

em

b

er ct

O

be em

pt Se

ob

r

t us ug A

ly Ju

ne Ju

ay M

pr li A

ch ar

ry ua br

Fe

Ja

nu

ar

y

0.2

y = –0.0011x4 + 0.0293x3 – 0.2572x2 + 0.8209x – 0.1364 R² = 0.5612 M

0.3

Figure 2. Development of mean free fatty acid contents (mmol/100 g of fat) in the evening milk from selected dairy cows (n = 10; spontaneous lipolysis – SPO) and from the bulk tank (n = 10; induced lipolysis – IND)

Czech J. Food Sci. between the morning and evening FFA contents were not accounted for in previous studies. Figures 1 and 2 show the development of FFA contents in the morning and evening milks as well as polynomial regression equations including reliability values. The reliability of the trend function was higher with the evening milking, which may have been related to the elevated contents of solid milk components, especially milk fat, in both individual and bulk samples (+0.04 to +0.41 g/1 and +0.14 to 0.44 g/1, respectively). However, this fact was not confirmed by Pearson correlation coefficients calculated between the fat and FFA contents. Also, the pattern of the trend functions was similar with the individual and bulk samples collected during evening milking. The same pattern of the trend functions and the higher reliabilities (R 2 higher by +0.1963 to +0.2613) confirm the higher informative value of higher FFA contents in both individual and bulk samples of the milk collected during evening milking. Conclusions It was confirmed that the content of FFA and thus the level of spontaneous lipolysis was affected by the individuality of the cow. Induced lipolysis characterised by increased contents of FFA in bulk milk samples occurred due to the damage to milk fat globules during milk processing (transport, cooling, stirring, and storage) already at the farm level. FFA content differences existed between bulk milk and individual milk samples collected from 10 cows, and, in addition, they were also affected by the calendar month and diet intensity. Higher FFA contents resulting from both spontaneous and induced lipolysis were detected in evening milk samples. The results of this study indicate the need for further investigation of milk lipolysis with regard to its relationship to negative energy balance, as this is considered the main cause of fertility and health problems in dairy cows. The FFA content in milk was higher than 1.0 mmol/100 g of fat in several months even before the transport of milk from the farm and therefore, the result of this study may raise the necessity of determining the FFA content as an indicator of milk quality at both farm and dairy plant levels. Acknowledgements. We thank Mrs. Lois Russell for her editorial help with the manuscript.

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Corresponding author Ing. Renáta Toušová, CSc., Česká zemědělská univerzita, Fakulta agrobiologie, potravinových a přírodních zdrojů, Kateda speciální zootechniky, Kamýcká 129, 165 21 Praha 6-Suchdol, Česká republika; E-mail: [email protected]

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