Composition of raspberry pomace and its nutritive value for monogastric animals

Animal Feed Science and Technology, 45 (1994) 139-148

139

0377-8401/94/$07.00 © 1994 - Elsevier Science B.V. All rights reserved SSDI0377-8401 (93)00520-6

Composition of raspberry pomace and its nutritive value for monogastric animals N. Ruth McDougall 1, R.M. Beames* Department of Animal Science, Universityof British Columbia, Vancouver,B.C. V6T 1Z4, Canada (Received 5 May 1993; accepted 8 July 1993)

Abstract

Raspberry pomace, consisting of seeds, pulp and added rice hulls, is the residue from the pressing of raspberries for juice production. The pomace was evaluated as a feedstuff for pigs by means of chemical analyses, a balance trial with pigs, and balance and growth trials with rats. On average, the pomace contained (dry matter (DM) basis) 1I. 1% crude fat, 10.0% crude protein, 59.5% total dietary fibre, 46.0% acid detergent fibre, 11.7% lignin, 6.0% cutin, 2.2% acid detergent ash, 26.9% cellulose and 25.13 MJ kg -1 gross energy. Digestibility measurements ( n = 4 ) with male castrate pigs of 35-55 kg body weight, using diets of 60% complete basal and 40% test material produced the following apparent digestibility values (%) for unmilled and hammer-milled (1. 6 mm screen) pomace respectively: DM 10.7 and 20.8 (SEM 1.30); protein 10.6 and 14.7 (SEM 4.83); fat 24.1 and 79.7 (SEM 3.47); energy 7.9 and 28.5 (SEM 1.80). Dry matter digestibility determined with rats showed close agreement with results obtained with pigs. Protein quality was evaluated in tests with rats to measure true protein digestibility (TD) and biological value (BV) for coarse milled ( 1 mm screen) and fine milled (ball-milled) pomace, either freeze dried or dried at 100°C. Average TD was 33.3% with only small treatment differences. The BV (average 79.3%) was significantly higher for the freezedried, coarse milled pomace (91.0%) than for the pomace subjected to the other three treatments. In a rat growth trial, where pomace replaced barley incrementally, growth rate was not affected at a replacement level of 20%, but it declined consistently thereafter as the level of inclusion increased. Although raspberry pomace has a low content of digestible energy (6.26 MJ kg-1 ) and digestible protein (1.5%), the results with rats suggest that an inclusion level of up to 20% in a balanced diet would not markedly affect the growth rate of growing finishing pigs.

Introduction

The Fraser Valley of British Columbia, Canada, is ideally suited for raspberry production. During 1989, only 5% of the crop was sold as fresh product, with the remainder being processed. Raspberry juice, which is one of the main products, is extracted by heating the berries to 40-55 °C for 1-2 h, followed by the addition of pectinase to increase the extraction rate and rice hulls at a level of approximately 12% of the dry matter to act as a press-aid. The residue *Corresponding author. ~Present address: B.C. Hog Marketing Commission, Abbotsford, B.C. V2S 6X8, Canada.

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is pomace, which consists of seeds, pulp, trash and rice hulls. Pomace has a low dry matter (DM) (44%), and is highly perishable. Although the oil from the seed is currently being extracted and used as a flavouring agent (E. MacIntyre, personal communication, 1987), such an outlet may not always be available. Consequently, information on its value as a feedstuff for animals would be desirable. Bucldey ( 1985 ) reported a rumen in vitro DM digestibility of 28% for pomace which had been dried at 50°C and hammer-milled through a 1 m m screen. In spite of this low figure, the high gross energy content (22.59 MJ kg- l ) and a lysine, methionine and threonine content which had been reported to be higher than that of average Canadian feed grade barley (Papke, 1983 ) suggested a possible role as a dietary component of growing-finishing pig diets. The following experiments were designed to estimate the feeding value of raspberry pomace for monogastric animals. Materials and methods

To obtain a measure of the variability in composition, 1 kg samples of raspberry pomace were collected over 10 days of juice production. Samples were frozen immediately after collection and stored at - 20 ° C. For chemical analyses, the samples were then thawed, ball milled in the wet form for 18 h, lyophilised and stored at - 20 ° C until required. For the balance and growth trials, two 200 1 drums of wet raspberry pomace which had been previously frozen at - 20 ° C were thawed, subdivided into 51 bags and stored again at - 20 ° C. The contents of each bag were then dried at 55-60°C for 24 h and stored at ambient temperature. There were three experiments.

Experiment 1: Digestibility in pigs Digestibility of dry matter, fat, energy and protein by pigs was determined by the difference method using complete faecal collection. Four YorkshireLandrace crossbred barrows (25-30 kg body weight at the start of the experiment) were used in a randomised 4 × 4 Latin square design. The four diets were: (1) basal (B) hammer-milled through a 1.6 m m screen; (2) 60°/0 B + 40% barley hammer-milled through a 1.6 m m screen; (3) 60% B + 40% pomace hammer-milled through a 1.6 m m screen; (4) 60% B + 40% unmilled pomace. Formulation of the basal diet is presented in Table 1, together with measured crude protein, crude fat and gross energy content. The pigs were kept individually in digestibility crates in a controlled atmosphere room at a temperature of 23 ° C. Each pig had free access to a nipple waterer. They were fed

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Table 1 Formulation and content of crude protein, crude fat and gross energy of diets used for pig digestibility measurements (Experiment 1 ) Diet Basal

Basal 60 + barley 40%

Basal 60% +ground pomace 40%

Basal 60% + unground pomace 40%

88.18

48.18

48.18

10.08 0.42 0.72 0.30 0.30

40.00 10.08 0.42 0.72 0.30 0.30

40.00 10.08 0.42 0.72 0.30 0.30

17.7

14.9

14.8

15.1

1.8

1.9

6.4

6.2

17.78

18.12

19.48

19.41

Dietary component (g per I00 g DM) Barley 80.30 Raspberry pomace ground unground Soya-bean meal 16.80 Dicalcium phosphate 0.70 Limestone 1.20 TM-Vitamin mix ~ 0.50 Iodized salt 0.50 Composition 2 (DM basis) Crude protein (gper 100g) Crude fat (g per 100 g) Gross energy (MJkg -~)

~TM-Vitamin mix (kg-~ ): vitamin A, 825000 IU; vitamin D, 55000 IU; vitamin E, 2700 IU; vitamin K, 0.49 g; thiamin, 0.1 g; riboflavin, 0.8 g; niacin, 4.0 g; Ca-pantothenate (45%), 6.0 g; vitamin B~2, 2.5 mg; choline, 50.0 g; copper sulphate (5H20), 3 g; zinc sulphate, 25 g; manganese sulphate, 7.0 g; sodium selenite, 15.7 mg. 2By analysis.

1.5 kg of air-dry feed daily in two equal feedings, at 09:30 and 16:00 h. To minimise wastage, feed was mixed with water in a 1:1 ratio before it was fed. There was a 5 day preliminary period and a 5 day collection period for each measurement.

Experiment 2: Growth of rats and dry matter digestibility measurement Thirty male Wistar rats weighing between 80 and 90 g were housed in stainless steel metabolism cages for 3 weeks in a controlled atmosphere room at 23 °C and 60% humidity and were randomly allocated to six diets (Table 2 ), with five rats per diet. The basal diet consisted of barley plus minerals and vitamins, with the other five diets containing pomace at levels of 19.4, 38.6, 58.0, 77.2 and 96.4%, with the pomace replacing the barley. All diets were balanced for mineral and vitamin content. Body weight was measured weekly. Diet digestibility was measured by the chromic oxide marker technique.

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Table 2 Formulation of diets (g per 100 g D M ) used in dry matter digestibility measurements with rats (Experiment 2) Diet

Barley Pomace ~ Dicalcium phosphate Calcium carbonate Iodized salt TM-Vitamin mix 2 Chromic oxide

1

2

3

4

5

6

96.9 0 0.4 1.2 0.5 0.75 0.25

77.4 19.4 0.7 1.0 0.5 0.75 0.25

58.0 38.6 1.0 0.9 0.5 0.75 0.25

38,6 58.0 1.2 0.7 0.5 0.75 0.25

19.3 77.2 1.4 0.6 0.5 0.75 0.25

0 96.5 1.6 0.4 0.5 0.75 0.25

~See Table 3 for composition, 2See Table 1 for composition,

Experiment 3." Nitrogen balance measurements in rats A nitrogen balance trial was undertaken with rats to determine the effect of heating and fineness of grinding on the true digestibility (TD), biological value (BV), and net utilisation ( N P U ) of the protein in raspberry pomace. The experimental procedure has been described by Eggum ( 1973 ). Twenty male Wistar weanling rats of 65-70 g body weight were used in a 2 × 2 factorial design with five rats per treatment. There were two degrees of grinding, ball milled (very fine) and hammer-milled through a 1 mm screen, and two heating treatments, freeze-drying and heating at 100 °C for 2 h in a forced draft oven the material that had been dried previously at 60 ° C. The original intention had been to include another heat treatment (heating to 150°C of the material which had been previously dried at 60 ° C), but in preliminary feeding tests, voluntary feed intake of this material was extremely low.

Chemical and statistical analyses In both feed and faeces, nitrogen was analysed by the method of Wall and Gehrke ( 1975 ). Amino acids were determined with a Beckman 6300 amino acid analyser (Beckman Instruments, Palo Alto, CA) after acid hydrolysis in 3 N hydrochloric acid for 24 h. To define the composition of pomace, lipid was determined by ether extraction (Association of Official Analytical Chemists, 1984) but for the estimation of digestibility of lipid, a prior acid hydrolysis was employed using a Biichi 810 Soxhlet fat extraction apparatus, according to the method described by Thorbek and Henckel (1977). Combustible energy was measured in a Gallenkamp adiabatic bomb calorimeter, and chromic oxide by the method of Williams et al. (1962). The raspberry pomace (which included the press-aid of rice hulls), was analysed for total

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dietary fibre (TDF) after ether extraction by the method of Prosky et al. (1984), incorporating the modification of Asp et al. (1983) to separate soluble and insoluble fibre components. The method of Goering and Van Soest (1970) was employed to determine acid detergent fibre (ADF) and neutral detergent fibre (NDF), cellulose, lignin, tannin and cutin, while water-soluble carbohydrates were measured with the anthrone reagent (Ministry of Agriculture, Fisheries and Food, 1973 ). All results were subjected to analysis of variance using software of the Statistical Analysis Systems Institute (SAS, 1985 ) and means were tested using the Newman-Keuls test (Keuls, 1952). Results and discussion

Composition of pomace The raspberry pomace contained approximately 12% rice hulls (DM basis ) and 88% seeds, pulp and trash (Table 3). It was reported by Buckley ( 1985 ) that the proportion of seeds in the pomace itself ranges from 57 to 76%, with the higher percentage being found in the pulp of fruit which had been previously frozen. The water-soluble carbohydrate content was 7.4% (DM basis), which is understandably lower than the value of 17.3% (DM basis) for whole fruit reported by Englyst ( 1981 ). On average, the water-soluble carbohydrate consists of 34.6% fructose, 31.3% glucose and 33.6% sucrose (Wrolstad and Schallenberger, 1981 ). The TDF content (not including indigestible protein and ash) was approximately 60%, with the remaining 40% consisting of lipid, protein, starch, watersoluble components and ash. Using the TDF method of analysis, there was approximately 5.2% insoluble (indigestible) crude protein, which corroborates the poor nitrogen digestibility values obtained with both pigs and rats. The water-soluble fibre content of 2.3% was understandably lower than the 7.5% reported by Englyst ( 1981 ) for whole raspberries. Analysis by the detergent method showed the NDF content to be 54%, and the ADF content to be 46% with the latter being composed of 26.9% cellulose, 11.7% lignin, 6% cutin and 2% acid-detergent-insoluble ash. The lignin content of 11.7% would have included approximately 1.3% from the rice hulls (National Research Council, 1972 ) leaving 10.4% contributed by the pomace. The crude protein content of pomace varied considerably, from 9.1 to 12.3%, with an average of 10%. The lysine level of 0.57 g per 100 g was less than the expected value of 1.0 g per 100 g reported by Papke ( 1983 ), which was part of the background information which stimulated the initiation of this work. Another reason for our interest in the pomace was the relatively high level of lipid which averaged 11.1 g per 100 g DM in the present study. With the resultant high gross energy content of 21.8 MJ kg-1, this would be of some

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Table 3 Composition of raspberry pomace plus rice hulls

Physical composition (N = 5) (%) Dry matter (DM) Raspberry seeds, pulp and trash (in DM) Rice hulls (in DM )

Mean

Range

SEM l

Sample for animal trials

44.4

43.3 -45.8

0.52

44.5

87.8 12.2

85.8 -89.9 10.1 - 14.2

0.63 0.63

85.8 14.2

8.6 -12.6 21.46-21.96 3.2 -5.2 5.2 -9.0

0.37 0.14 0.21 0.39

12.6 21.96 3.4 6.2

51.6 -64.6 49.6 -62.1 1.6 -3.4 9.1 -12.3 4.4 -6.8 48.8 -56.4 43.3 -47.2 9.6 -15.4 3.2 -9.1 1.4 -3.1 24.5 -33.3 0.61-0.67 0.26-0.32 0.42-0.50 0.70-0.80 0.49-0.59 0.12-0.14 0.39-0.45 0.34-0.40 0.23-0.28 0.43-0.54

1.17 1.20 0.17 0.27 0.23 0.64 0.41 0.56 0.55 0.19 0.80 0.009 0.009 0.011 0.015 0.014 0.002 0.008 0.008 0.007 0.015

61.4 58.4 3.1 10.3 4.4 53.4 46.6 12.6 5.5 1.8 26.8 0.67 0.32 0.48 0.79 0.58 0.14 0.44 0.38 0.25 0.50

Chemical composition (N = 10) (DM basis) Crude fat (%) 11.1 Gross energy (MJ kg- ' ) 21.84 Ash (%) 4.1 Water-soluble carbohydrates (%) 7.4 Dietary fibre (%) Total 59.5 Insoluble 57.2 Soluble 2.3 Crude protein (%)2 10.0 Insoluble crude protein (%)2 5.2 Neutral detergent fibre (%) 54.1 Acid detergent fibre (%) 46.0 Lignin (%) 11.7 Cutin (%) 6.0 Acid detergent ash (%) 2.2 Cellulose (%) 26.9 Arginine (%)3 0.64 Histidine (%) 0.29 Isoleucine (%) 0.47 Leucine (%) 0.77 Lysine (%) 0.57 Methionine (%) 0.13 Phenylalanine (%) 0.44 Threonine (%) 0.37 Tyrosine (%) 0.26 Valine (%) 0.50

~Standard error of mean.

2N X 6.25. 3For amino acids, N= 6. Values expressed as residues.

nutritional advantage if the lipid were reasonably well digested and would partly offset the adverse effect of high fibre on the digestible energy value.

Digestibility measurements in pigs The results of digestibility measurements in pigs are given in Table 4. Mea-

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Table 4 Digestibility by growing pigs in E x p e r i m e n t 1 o f dry m a t t e r , protein, fat a n d energy N u t r i e n t source

Basal diet ~ Barley Milled p o m a c e 2 Unmilled pomace S t a n d a r d error o f m e a n

Apparent

digestibility (%)

Dry matter

Protein

Fat

Energy

81.8 a 79.9 a 20.8 b 10.7 c 1.30

78.3 c 75.0 a 14.7 b 10.6 b 4.83

28.7 c 42.4 b 79.7a 24.1 c 3.47

81.1 a 78.6 a 28.5 b 7.9 c 1.80

IFor c o m p o s i t i o n , see Table 1. 2 H a m m e r - m i U e d t h r o u g h 1.6 m m screen. M e a n s w i t h i n c o l u m n s with different superscripts are significantly different ( P < 0.05).

surements on barley were included for comparative purposes. Only in the digestibility of fat when the pomace was milled (79.7%) was the pomace superior to barley. Even with this greater digestibility, the energy digestibility of the milled pomace was only 28.5%. Milling resulted in a marked improvement in the digestibility of all constituents of the pomace, except for protein. The high digestibility by the pigs of the lipids in the pomace, which contain mostly unsaturated fatty acids (Pourrat and Carnat, 1981 ), agrees with the normally high digestibility of these fatty acids (Gurr, 1983 ). It is obvious that for pomace to be of any nutritional value, the seed must be ruptured. It is possible that such rupturing may be able to be achieved by pelleting, as was found by the authors with rapeseed screenings, which contain predominately small whole seeds (Beames et al., 1986), where dry matter digestibility was increased from 27.2 to 78.8% with pelleting (McKinnon, 1988 ). Digestibility and growth measurements in rats

For this experiment, all the dietary components were finely milled ( 1 mm screen), so fineness of milling was not a factor as in the pig digestibility measurements. The dry matter digestibility of 20.9% (Table 5 ), when the entire diet consisted of raspberry pomace (except for minerals and vitamins), was essentially the same as that obtained with the pigs (20.8%) using the method of difference. Using this value to calculate digestibility for the various levels of inclusion by interpolation gave values which agreed closely with the measured values, except for the diet which contained 38.6% barley and 58.0% pomace. No reason can be advanced for this anomaly. This close agreement between digestibility values in pigs and rats is in agreement with published data (Eggum and Beames, 1986).

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Table 5 G r o w t h o f rats a n d digestibility o f d r y m a t t e r in E x p e r i m e n t 2 Diet 1

2

3

4

5

6

SEM

96.9 0 3.1

77.4 19.4 3.2

58.0 38.6 3.4

38.6 58.0 3.4

19.3 77.2 3.5

0 96.4 3.6

80.8 a 19.2 a 4.7 a

71.5 b 68.8 19.8 a 4.5 a

59.3 c 56.8 21.6 a 3.9 b

54.5 d

44.9 21.2 a 3.2 c

30.7 e 32.9 19.9 a 2.3 d

20.9 f 16.5 b 1.0 e

1.14 0.65 0.14

4.3 ~

4.8 a

6.2 b

7.4 c

9.6 ~

26.1 e

1.19

Composition (g per I00 g DM) Barley ~ Pomace Minerals, v i t a m i n s 2

Rat utilisation D M digestibility (%) Measured By interpolation 3 Feed intake (g D M day -~ ) Weight gain ( g d a y - l ) Feed c o n v e r s i o n ratio (kg D M feed k g - ~ weight g a i n )

~Barley a n d p o m a c e h a m m e r - m i l l e d t h r o u g h a 1.0 m m screen. 2Trace m i n e r a l s a n d v i t a m i n s (see Table 1 ) a d d e d at 0.5% level. C a l c i u m a n d p h o s p h o r u s supplem e n t s a d d e d to equalise c a l c i u m a n d p h o s p h o r u s levels (see Table 2 ). 3Calculated f r o m m e a n digestibilities o f Diets 1 a n d 6. M e a n s within rows with different superscripts are significantly different ( P < 0.05 ).

Table 6 T r u e digestibility ( T D ) , biological value ( B V ) , a n d net utilisation ( N P U ) o f the protein o f raspberry p o m a c e m e a s u r e d with weanling m a l e rats in E x p e r i m e n t 3 Treatment

TD

BV

NPU

(%)

(%)

(%)

35.7 a 30.9 b 0.47

82.0" 76.5 a 2.44

29.3 a 23.8 b 0.81

33.8 a 32.8 a 0.47

83.1 a 75.& 2.44

28.2 ~ 25.0 b 0.81

36.0 a 31.5b 35.4 ~ 30.2 b 0.66

91.0 a 75.2 b 73. lb 78.1 b 3.46

32.7 a 23.7 ~ 25.9b 24.0 b 1.15

Fineness o f grind Coarse ( h a m m e r milled, 1 m m ) Fine (ball-milled) SEM

Drying temperature Low (freeze-drying) High ( 1 0 0 ° C ) SEM

Interaction Coarse × low t e m p . Fine × low t e m p . Coarse×high temp. Fine × high temp. SEM

M e a n s within groups within c o l u m n s with different superscripts are significantly different ( P < 0.05 ).

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Nitrogen balance measurements with rats Results for the measurements of TD, BV and N P U are presented in Table 6. Very fine milling (ball milling), rather than improving the digestibility of nitrogen, actually significantly reduced TD from 35.7 to 30.9%. This effect was independent of the m e t h o d of drying. An effect of method of drying on BV was apparent only with the coarsely milled pomace, where low temperature drying improved BV from 73.1 to 91.0%. With the finely milled pomace, the average BV was 76.5% and did not show any effect of drying temperature. The significant reduction in TD and N P U as a result of the very fine particle size achieved with ball milling may have occurred as a result of tannins being released. These tannins, which are bound in the outer shell of the raspberry seed, may have formed indigestible complexes with proteins and amino acids in the gastrointestinal tract (Hagerman and Klucher, 1986).

Conclusion On the basis of chemical analyses and the measurements in pigs and rats, the nutritive value of raspberry pomace for monogastric animals was found to be very low. In spite of the hammer-milled pomace containing 10.0% apparent digestible fat, the high level of fibre (53.4% N D F ) resulted in a low digestibility of dry matter (20.8%) and energy (28.5%). The digestible energy content of milled pomace, as assessed in pigs, was thus only 6.26 MJ kg-1. The digestible energy content of unmilled pomace was much lower ( 1.74 MJ kg- 1). Although the BV of the protein in the milled unheated pomace was high (91%), the poor TD of the protein (36%, as determined in rats), made its protein value extremely low.

Acknowledgements We wish to thank Tracey Innes and Christa Wallace for their technical assistance. Also, we wish to acknowledge the financial support of the Science Council of British Columbia and the East Chilliwack Agricultural Co-op.

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