Protein quality of Spanish Murciano-Granadina goat milk during lactation

Small R u m i n a n t Research ELSEVIER

Small Ruminant Research 14 (1994) 67 72

Protein quality of Spanish Murciano-Granadina goat milk during lactation A. Quiles ~'*, C. Gonzalo b, Y. Barcina c, F. Fuentes a, M. H e v i a ~ ~'Departamento de ProduccitJn Animal, Facultad de Veterinaria, 30100-Espinardo, Murcia, Spain hDepartamento de Producci6n Animal, Facultad de Veterinaria, 24071-Le6n, Spain "Unive rsidad P~blica de Na varra, 31006- Pamplona, Spain Accepted 3 September 1993

Abstract

The evolution of contents of total protein, caseins ( o~,/3,K) and whey proteins ( o~-lactalbumin,/3-1actoglobulinand 'remaining' whey proteins) in the milk of 44 Spanish goats (Murciano-Granadina breed) was studied during part of the lactation ( 70 to 210 d after kidding) using polyacrylamide gel electrophoresis-SDS. Mean values of protein groups (g/l) and their fractions were: total protein (40.9), total casein (32.1), whey proteins (8.7), o~-casein(8.5),/3-casein (21.0), K-casein (2.5),/3-1actoglobulin (5.8), o~-lactalbumin (1.5) and 'remaining' whey protein (1.4). All proteins groups and fractions increased significantly (P <0.01) during the lactation except for 'remaining' whey proteins which decreased (P<0.001). Stepwise discriminant analysis showed that or-casein and/3-1actalbumin differed significantly between sample dates (P < 0.001 ), with more variation than the other proteins ( F = 48.0 and F = 17.3, respectively, P < 0.001 ). Keywords: Lactation; Electrophoresis; Goat: Protein

1. Introduction

The chemical composition of goat milk varies considerably due to stage of lactation, feeding, breeding, individual animal differences, climate, etc. (Devendra, 1972; Mba et al., 1975; Akinsoyinu and Akinyele, 1979; Faulkner et al., 1982). Gross composition of goat milk from different breeds and countries has been reviewed (Jenness, 1980). Interest in the use of goat milk has recently increased. In order to manufacture new products, or to optimize the manufacturing procedure of existing products, more information is required concerning the chemical *Corresponding author. 0921-4488/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI092 I - 4 4 8 8 ( 9 3 ) E 0 I 0 6 - 3

composition of goat milk and its techonological properties. Protein quality of goat milk is of special importance because: (a) A better knowledge of the raw material in relation to the final processed product is necessary. Protein quality is important for a rational payment system for milk, since it has direct relationship with cheesemaking properties (rennet-coagulation time) (Ricordeau and Mocquot, 1967; Ambrosoli et al., 1988). (b) There is a potential benefit of incorporating a better knowledge of milk protein composition into existing schemes of selection and of goats and different breeds. The aim of the present paper was to determine the concentration of the different protein fractions of goat

68

A. Quiles et al. / Small Ruminant Research 14 (1994) 67-72

milk by polyacrylamide gel electrophoresis and to study the variation in protein composition using milk collected throughout one lactation period (70-210 d after kidding).

2. Material and methods

Forty-four goats of the Murciano-Granadina breed from the herd of the Department of Agriculture of the Autonomous Community of Murcia (Spain) located at E1 Palmar were used in this study. Distribution of goats according to number of laction was: 9, 16, 11 and 8 of first, second, third and fourth lactation, respectively. Kidding took place in autumn (from 14 October to 4 November). The average milk yield was 579.7 kg in 210 d of lactation. None of the animals had clinical mastitis. The specific density of Murciano-Granadina milk was about 1.030 g/ml. Milking was carried out mechanically once a day (8:00 a.m.) from weaning (70 d after kidding to drying-off 210 d after kidding). Fifty ml milk was taken from each animal on d 85,100, 130, 160, 190 and 210 after kidding. Samples were carried refrigerated to the laboratory and kept frozen ( - 3 0 ° C ) until analysed. Analysis was always made between 7 and 10 d after milking. Milk samples were centrifuged to remove milk fat (3500 x g for 30 min at 5°C). Preparation of the samples for electrophoretic analysis was carried out according to Assenat (1967), extraction of precipitated proteins at pH 4.6. Once the complete desiccation of caseins was made, hydrolysis was carried out according to Ng-Kwai-Hang and Krocker (1984), dissolved in 6 M urea containing bromophenol blue as a tracking dye. Electrophoretic fractionation of whey proteins and caseins was made by polyacrylamide-SDS gel electrophoresis (Weber and Osborn, 1969 ) at pH 7 continuous buffer system: sample buffer - 0.01 M sodium phosphate, 1% sodium dodecyl sulfate-SDS, 5%/3-mercaptoethanol, pH 7.0; electrophoresis buffer - 0.05 M sodium phosphate, 0.1% sodium dodecyl sulfate-SDS, pH 7.0; gel buffer - 0.1 M sodium phosphate, 0.2% sodium dodecyl sulfate-SDS, pH 7.0. Electrophoresis was carried out in vertical gel tubes measuring 75 mm long X 8 mm wide (7 mA per gel). Total running time was 5 h. Gels were stained for 4 h with 0.1% (w/v) Coomassie brilliant blue R-250 in methanol/acetic acid/water (50:7:43 v/v). The gels were destained

with a solution containing methanol/acetic acid/water (40:10:50 v/v). Gels were automatically scanned and quantified with a Profil Ecran Densitometer (SEBIA, Paris, France). Densitometric peak areas were converted to concentrations of as-caseins (as = as~ + a~2), /3-casein and Kcasein using total casein concentration. Likewise, concentration of total whey proteins was used to calculate concentration of/3-1actoglobulin, a-lactalbumin and 'remaining' whey proteins (immunoglobulins, seroalbumin and minor proteins). Parallel to protein electrophoretic analyses the total protein in raw milk and whey protein of each sample were determined. Casein content was obtained by difference. These analyses were carried out in a MilkoScan automatic Mod 104 (N. Foss Electric, Denmark) analyser, previously checked by the Kjeldahl method.

Statistical analysis The individual protein concentration matrix was subjected to multivariant analysis (stepwise discriminant analysis) of the BMDP statistical package of the University of California (Dixon, 1983). This allowed for the identification of variables that differentiate the groups (days) under consideration. It also provided a number of canonical functions which were a linear combination of those variables showing discriminant power. Furthermore, the analysis gave a classification function which could be used later in order to classify new cases into first groups.

3. Results and discussion

Mean concentrations of total proteins, caseins, whey proteins and fractions of the latter two categories are given in Table 1. Stage of lactation had significant (P < 0.001 ) effects on all proteins constituents. During the milking period (85-210 d after kidding) the concentrations of total proteins, caseins, whey proteins and each fraction significantly increased (P < 0.001 ) with the excepction of 'remaining' whey proteins that decreased. A similar trend was observed by Mba et al. (1975) and Mahieu et al. (1977). Other workers have reported that protein concentration decreased during the first 4 months of lactation, and then increased until the end of lactation (Anifantakis and Kandarakis, 1980; Brendehaug and Abrahamsen, 1986). Singh and Singh

A. Quiles et al. / Small Ruminant Research 14 (1994) 67-72

69

Table 1 Average values (g/1 ) a n d standard deviations o f protein groups and fractions during different days o f lactation in Spanish M u r c i a n o - G r a n a d i n a goats Protein

S a m p l i n g date ( d a y s after kidding) 85

100

130

160

190

210

F(5.258)

Total protein

37.00"

40.07 h

40.33 °

41.00 °

42.97 c

43.96 c

20.69***

SD Total casein

4.01 28.55"

4.10 31.47 b

3.50 31.67 °

2.67 32.36 b

3.11 33.85 c

3.77 34.68 ~

20.63"**

4.46 8.32 a 0.80 7.44 b

3.18 8.65 ° 0.92 8.17 ~

2.27 8.63 ° 0.88 8.66 d

2.42 9.12 c 1.03 9.69 ~

3.12 9.29 ~ 0.98 10.37 f

48.09 * * *

1.22 21.47 b

1.26 20.70 "°

1.21 21.28"

1.56 21.31 o

1.71 21.42 °

2.48" *

2.39 2.52 ° 0.80 5.70 °

2.63 2.55 ° 0.78 5.76 h

1.99 2.7 l° 0.86 6.17 c

2.45 2.76 ° 0.83 6.28 ~

0.96 1.53 ° 0.35 1.442 ° 0.65 44

0.86 1.60 ° 0.36 1.26 ~ 0.66 44

0.92 1.78 ~ 0.41 1.17 c 0.67 44

0.9 l 1.77 ~ 0.45 1.22 ~ 0.63 44

SD W h e y protein SD a-Casei n SD /3-Casein SD K-Casein SD /3-Lactoglobulin SD a-Lactoalbumin SD ' R e m a i n i n g ' w h e y protein SD n

3.36 8.44 "° 1.04 6.48" I. 15 19.90" 2.72 2.25 ~ 0.72 5.40" 0.84 1.23" 0.31 1.79 a 0.60 44

3.10 2.48 "° 0.76 5.32 a 0.85 1.29 a 0.27 1.69 ~ 0.61 44

7.12 * * *

2.33"* 8.28* * * 17.39*** 7.10"**

~' ~Means in the s a m e r o w with different superscript letters are significantly different ( P < 0.05 ). F ( 5 . 2 5 8 ) = F i s h e r - S n e d e c o r between the different s a m p l i n g days (degree freedom). n = No. of observations.

(1980a) reported mean values between middle and end of lactation from 34.0 to 38.2 g/l for total protein, from 8.2 to 9.5 g/1 for whey proteins and 26.0 to 28.7 g/1 for caseins in four goat breeds (Jamnapari, Beetal, Barbari and Black Bengal). These authors also indicated the existence of breed differences in the concentrations of protein groups, which explains slight differences with our results. Average protein content (40.8 g/l) found was higher than values reported by Devendra (1972) for British Alpine goats; Ranawana and Kellaway (1977), Chang and Kin (1978), Middleton and Fitz-Gerald ( t981 ) for Saanen; Castagnetti et al. (1984), Ghionna et al. (1984), E1-Zayat et al. (1984) and Voutsinas et al. (1990) for Alpine; but lower than values reported by Mba et al. (1975), Sawaya et al. (1984) and Merin et al. (1988). Casein content of milk followed the same variation pattern (from 28.5 to 34.6 g/l) of protein in agreement with Mahieu et al. (1977) and Singh and Singh (1980a). Average casein content was close to that for

Saanen goats in Greece (Anifantakis and Kandarakis, 1980) but higher than reported by Grappin et al. ( 1981 ), and lower than values of Qureshi et al. ( 1981 ) and Veinoglou et al. (1982). Average a-, /3- and Kcasein contents of milk were 8.5, 21.0 and 2.5 g/l, respectively. Concentrations of a-, /3- and K-casein showed an increasing trend as the lactation advanced in agreement with the results by Singh and Singh (1980b). In this Murciano-Granadina goat study the ratio of casein × 100/total (78.5%) was similar to reports by Singh and Singh (1980a) for the four Indian breeds, but higher than observed by Morand-Fehr et al. (1986). This ratio slightly increased throughout the milking period from 77.2% to 78.9%. Average whey protein content of milk (8.74 g/l) was close to that reported by Singh et al. (1972), Grappin et al. (1979) and Csapo et al. (1984), but higher than results of Devendra (1972) and Castagnetti et al. (1984) for British Alpine and Alpine goats, respectively. The concentration of/3-1actoglobulin and c~-lac-

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A. Quiles et al. / Small Ruminant Research 14 (1994) 67-72

Table 2 Correlation matrix between proteingroups and fractionsof goat milk duringthe lactation

Total protein Total casein Whey protein s-Casein /3-Casein K-Casein /3-Lactoglobulin a-Lactalbumin 'Remaining' whey proteins

1

2

3

4

5

6

7

8

0.96*** 0.67*** 0.72*** 0.70*** 0.43*** 0.55*** 0.53*** -0.10

0.49*** 0.71"** 0.70*** 0.42*** 0.41"** 0.44*** -0.12

0.43*** 0.40*** 0.29** 0.78*** 0.60*** -0.00

0.30** 0.38*** 0.39*** 0.46*** -0.20

0.07 0.24** 0.17" 0.67

0.26** 0.25** -0.09

0.47*** -0.54***

-0.38***

*P< 0.05; **P<0.01; ***P <0.001. Table 3 Classificationfunctionresultingfrom stepwise discriminantanalysis Protein

Samplingdate (days after kidding) 85

a-Casein ot-Lactalbumin Constant

100

130

160

190

210

30.88 67.14

35.96 68.02

39.00 83.05

41.43 86.56

46.44 95.80

50.27 92.14

- 15.94

- 19.59

- 24.08

- 16.68

- 32.84

- 36.03

Table 4 F Matrix (2.257)" between each pair of groups (days after kidding), taking only variables with discriminantpower (a-casein and ~lactoaibumin) Day

100 130 160 190 210

Day 85

100

130

160

190

5.43** 20.23*** 33.13"** 72.05*** 97.49***

6.30** 13.57"** 40.63*** 58.50***

1.60 15.94"** 29.65***

7.47*** 17.62"**

2.90

**P< 0.01; ***P<0.001. "Fisher-Snedecor matrix ( degree freedom).

talbumin increased thoughout lactation. This trend is consistent with findings ofBrochet (1980) in ewe milk. With respect to 'remaining' whey proteins, their concentration decreased ( P < 0.001 ) as the lactation proceeded. However, Poutrel et al. (1982) detected significant increases of bovine seroalbumin content in milk between 150 and 270 d of lactation. Should this have occurred in our goats, there would probably have

been a decrease of inmunoglobulins, as these proteins represent between 15.1 and 11.1% of the whey protein content (Stupintskii and II'Chenko, 1967; Lin et al., 1984). Mean contents of ~-lactoglobulin (5.8 g / i ) and ~-lactalbumin ( 1.5 g / l ) in this study differed from 2.4 and 2.3 g/l, respectively, obtained by Johke et al., (1964). The immunoassay technique used by these authors may have included new variation.

A. Quiles et al. / Small Ruminant Research I4 (1994) 67-72

High correlation coefficients between total protein, caseins and whey proteins (Table 2) confirm relations between them when results of different authors or different stages of lactation are compared (Mahieu et al., 1977; Castagnetti et al., 1984) because lower/higher values of total protein correspond to lower/higher concentrations of whey and casein proteins. The rest of correlation coefficients were lower than reported by Quiles et al. ( 1991 ) in the first 4 d after kidding for the same breed (r = 0.33 to 0.94). Sharp decreases in all protein fractions in the beginning of lactation explain such differences. Low corrrelation coefficients between 'remaining' whey proteins and other proteins or fractions were probably due to different variations of these proteins during lactation. Discriminatory analysis (Tables 3 and 4) carried out between successive milking dates permitted classification of different individuals or corresponding sampling days as a function of a-casein and a-lactalbumin concentrations (the only variables with discriminatory power), which were showing a sharper evolution during lactation (Table 1). The a-casein increased 60.0% during lactation showed higher linear correlations among the caseins. According to Storry et al. (1983) and Morand-Fehr ct al. (1986), the a-casein and a//3casein ratio play an important role in rennet clotting time and in stabilization of clotting by pressure. The Kcasein showed a lower relationship with the rest of caseins, agreeing with results of Quiles et al. ( 1991 ). Table 4 shows Fisher-Snedecor 'F' data, that were obtained from comparison between different groups (85, 100, 130, 16(/, 190 and 210 d after kidding) as a function of discriminant power variables ( a-casein and a-lactalbumin). Statistically significant differences between these groups were recorded with the exception of samples 130-160 and 190-210 d after kidding. It is concluded that stage of lactation had significant effects on variation in protein fractionation of goat milk, which was particularly evident at the beginning and end of the lactation period. This was important l¥om zootechnical and technological points of view because of contribution of the proteins in milk to cheese yield and quality of final processed product (Portmann et al., 1968; Loewenstein et al., 1980; Storry et al., 1983).

71

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Quiles, A.J., Gonzalo, C., Fuentes, F., Hevia, M. and Sanchez, J.M., 1991. Protein composition and vadation of caprine colostrum (Murciano-Granadina breed) by means of polyacrylamide-SDS gel electrophoresis. Anim. Prod., 52:311-316. Qureshi, H.A., Deshpande, K.S. and Bonde, H.S.. 1981. Studies on chemical composition of goat milk. Indian Vet. J., 58:212-214. Ranawana, S.E. and Kellaway, R.C. 1977., Responses to postruminal infusions of graded levels of caseins in lactating goats. Br. J. Nutr., 37: 67-79. Ricordeau, G. and Mocquot, G., 1967. Influence des variations saisonni~res de la composition du lait de ch~vre sur le rendement en formage. Cons6quences pratiques pour la s61ection. (Influence of seasonal variations in goats milk composition on cheese yield. Practical consequences for selection). Ann. Zootech., 16: 165181. Sawaya, W.N., Sail, W.J., AI-Shalhat, A.F. and AI-Mohammad, M.M. 1984. Chemical composition and nutritive value of goat milk. J. Dairy Sci., 67: 1655-1659. Singh, N.P., Sachdeva, K.K. and Sengar, O.P.S., 1972. A study on the nitrogen distribution of goats' milk. Milchwissenschafi, 27: 165-167. Singh, V.B. and Singh, S.N., 1980a. Total protein, whey proteins and casein content of milk of four Indian goat breeds during lactation, Int. Goat Sheep Res., 1(2): 118-124. Singh, V.B. and Singh, S.N., 1980b. Milk casein: Electrophoretic Alpha, Beta and Gamma fractions from four Indian goat breeds during lactation. Int. Goat Sheep Res., I (2): 125-131. Storry, J.E., Grandison, A.S., Millard, D., Owen, A.J. and Ford, G.D., 1983. Chemical composition and coagulating properties of renneted milks from different breeds and species of ruminant. J. Dairy Sci., 50: 215-229. Stupintskii, R.M. and II'Chenko, M.D., 1967. Electrophoresis of goat's milk. Fiziol. Biokhim. Sel'khoz. Zhivot. Respub. Mezkved. Temat. Nauch. sb. (5): 62 (Dairy Sci. Abstr., 30: 3240, 1968). Veinoglou, B., Baltadjieve, M., Anifantakis, E. and Edearyan, M., 1982. Composition of goats' milk in the Plovdir region of Bulgada and in Ioannina in Greece. Le Lait, 62: 55-66. Voutsinas, L., Pappas, C. and Katsiad, M., 1990. The composition of Alpine goat's milk during lactation in Greece. J. Dairy Res., 57: 41-51. Weber, K. and Osboru, H., 1969. The reliability of molecular weight determination by dodecyl sulfate-polyacrylamide gel electrophoresis. J. Biol. Chem., 244: 4406--4412.

Resumen Quiles, A., Gonzalo, C., Barcina, Y., Fuentes, F. and Hevia, M., 1994. Protein quality of Spanish Murciano-Granadina goat milk during lactation. Small Rumin. Res., 14: 67-72. Se ha estudiado la evoluci6n del contenido total de prote/nas, caseinas (ct,/3, K) y proteinas s6dcas (ot-lactalbtlmina, fl-lactoglobulina y 'otras' protefnas del lactosuero) en 44 cabras de raza Murciano-Granadina, durante el periodo de la curva de lactaci6n comprendido entre el dia 70 y el 210 post-parto, utilizando para ello la t6cnica electrofor6tica poliacrilamida-SDS. Los valores medios de los grupos protefcos (g/l) y sus fracciones fueron los siguientes: Prote/nas totales (40.9), caseinas totales ( 32.1 ), protefnas s6dcas ( 8.7 ), a-casefna ( 8.5 ),/3-caseina (21.0 ), K-caseina (2.5), /3-1actoglobulina (5.8), ot-lactalbtimina (1.5) y 'otras' protefnas del lactosuero (1.4). Todos los grupos protefcos y sus fracciones aumentaron de forma significativa (P < 0.01 ) a lo largo de la lactaci6n, excepto 'otras' protefnas del lactosuero que disminuy6 (P < 0.001 ). El an~isis discriminante paso a paso muestra que la a-caseina y la ot-lactalbtimina tienen poder discriminante entre los diferentes dias de muestreo (P < 0.001 ), mostrando mayor variaci6n que el resto de la protefnas (F = 48.0 y F = 17.3, respectivamente, P < 0.001 ).