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J.Sci. Fd Agric. 1974,25, 1063-1070 Batch Dry Rendering : Influence of Processing Conditions on Meat Meal Quality L. S. Herbert,a J. F. DillonYb M. W. MacDonald" and G. R. Skurrayd CSIRO Division of Food Research, Meat Research Laboratory, Cannon Hill, Queensland Poultry Research Station, Department of Agriculture, Seven Hills, New South Wales ' Department of Poultry Technology, Queensland Agricultural College, Gatton, Queensland Department of Biochemistry and Nutrition, University of New England Armidale, New South Wales, Australia (Manuscript received 23 February 1973 and accepted I April 1974) A series of meat-and-bone meal samples was prepared during batch cycles in a commercial dry-rendering plant, in which offal was cooked to the usual end-point, then the cooker contents were held at high temperatures for prolonged periods. The expected decrease in nutritive value was not detected by chick assays even for meals that had been heated at 145 "C for 2 h after end-point. An apparent increase in nutritive value was detected in meals heated at 115 "C for up to 80 min after end-point. Since chick assays were carried out using diets similar to industrial formulations, it is concluded that the experimental processing conditions had no detrimental effect on the meals as feed additives. Available lysine values showed no trends with processing conditions and tended to confirm that the biological value of the meal protein had not suffered. Results of chemical analyses showed some variability, attributable mainly to sampling errors that are hard to avoid when obtaining a small sample representative of the 5 to 10-kg portions of meal used in chick assays. 1. Introduction The use of meat- or meat-and-bone meals as protein supplements in chicken rations has been a common practice for several years. These meals contain up to 55 % crude protein (as estimated by Kjeldahl nitrogen analysis) and since they are byproducts of the meat industry, they are in continuous supply at prices competitive with alternative sources of protein. Stock feed mills, however, require protein concentrates of uniform quality. While these can be obtained readily from vegetable or fish sources, with meat meals it is difficult to guarantee the constancy of the protein content both within and between batches. The wide variations in quality which occur cannot be detected and remedied with sufficient speed to permit quality control. Thus, meatworks as suppliers and poultry and pig producers as users have become increasingly interested in research aimed at defining the factors determining meat-meal quality with a view to optimising its use as a feed supplement. Meat-and-bone meals are generally considered to be low-quality sources of animal protein for reasons given by Atkinson and Carpenrer.' It is typical of work in this field I 38 1063

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Page 1: Batch dry rendering: Influence of processing conditions on meat meal quality

J.Sci. Fd Agric. 1974,25, 1063-1070

Batch Dry Rendering : Influence of Processing Conditions on Meat Meal Quality

L. S. Herbert,a J. F. DillonYb M. W. MacDonald" and G. R. Skurrayd

CSIRO Division of Food Research, Meat Research Laboratory, Cannon Hill, Queensland Poultry Research Station, Department of Agriculture, Seven Hills, New South Wales ' Department of Poultry Technology, Queensland Agricultural College, Gatton, Queensland

Department of Biochemistry and Nutrition, University of New England Armidale, New South Wales, Australia (Manuscript received 23 February 1973 and accepted I April 1974)

A series of meat-and-bone meal samples was prepared during batch cycles in a commercial dry-rendering plant, in which offal was cooked to the usual end-point, then the cooker contents were held at high temperatures for prolonged periods. The expected decrease in nutritive value was not detected by chick assays even for meals that had been heated at 145 "C for 2 h after end-point. An apparent increase in nutritive value was detected in meals heated at 115 "C for up to 80 min after end-point. Since chick assays were carried out using diets similar to industrial formulations, it is concluded that the experimental processing conditions had no detrimental effect on the meals as feed additives. Available lysine values showed no trends with processing conditions and tended to confirm that the biological value of the meal protein had not suffered. Results of chemical analyses showed some variability, attributable mainly to sampling errors that are hard to avoid when obtaining a small sample representative of the 5 to 10-kg portions of meal used in chick assays.

1. Introduction

The use of meat- or meat-and-bone meals as protein supplements in chicken rations has been a common practice for several years. These meals contain up to 55 % crude protein (as estimated by Kjeldahl nitrogen analysis) and since they are byproducts of the meat industry, they are in continuous supply at prices competitive with alternative sources of protein. Stock feed mills, however, require protein concentrates of uniform quality. While these can be obtained readily from vegetable or fish sources, with meat meals it is difficult to guarantee the constancy of the protein content both within and between batches. The wide variations in quality which occur cannot be detected and remedied with sufficient speed to permit quality control. Thus, meatworks as suppliers and poultry and pig producers as users have become increasingly interested in research aimed at defining the factors determining meat-meal quality with a view to optimising its use as a feed supplement.

Meat-and-bone meals are generally considered to be low-quality sources of animal protein for reasons given by Atkinson and Carpenrer.' It is typical of work in this field

I 38 1063

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1064 L. S . Herbert et af.

that little attention has been given to the methods of production of the commercial meat meals used in nutritive value assays. Although Atkinson and Carpenter1 and Kondos and McClymont2 reported in more than usual detail on the sources of their meals, there is, in general, little appreciation of the wide variations in methods and practices used in abattoirs.

In a process as primitive as rendering it cannot be assumed that. any standard pro- cedure, either as regards input materials or processing conditions, is, or indeed can be, carried out from batch to batch. It is believed that an incomplete knowledge of such factors is one of the main causes of difficulty in interpreting and correlating results of studies on the nutritive value of meat meals.’

In the course of investigations into heat and mass transfer in a batch dry rendering plant,3 a commercial cooker was extensively instrumented and a detailed knowledge of processing conditions was obtained in a series of experiments. Meat-and-bone meal samples were prepared during the course of three batch cycles in the cooker, so that accurate details were known of charge weight and type, rendering time and temperature and other processing conditions. The present report describes a collaborative study aimed at establishing the relationship between processing conditions and nutritive value of these samples.

2. Experimental

2.1. Sample preparation Three batch rendering cycles were conducted on days when the nominal works kill was 500 cattle and 7000 sheep. Soft offal (washed and hashed gut material) and hard offal (crushed heads, feet and boning room bones) were weighed into the unheated cooker to give initial charge compositions detailed in Table 1 .

TABLE 1. Charge details

Charge composition

Soft offal Hard offal Batch , - . I -. Water content

no. Wet wt (kg) % of charge Wet wt (kg) % of charge ( %)

1 1532 46.3 1780 53.7 57 2 1655 45.9 1951 54.1 55 3 1620 48.4 1725 51.6 46

The water contents were calculated from mass balances, as described by Herbert and N ~ r g a t e . ~ Rendering was carried out under “open vent”, so that at no time were the cooker contents subjected to pressures higher than 2.7 x lo4 N m-’. The tempera- ture of the contents remained in the range 105 to 110 “C for about 2 h, after which a rapid increase in temperature occurred, indicating that practically all the water had been evaporated. The usual “end-point’’ of the batch corresponded to a temperature of the contents of around 115 “C and the cycle would normally be terminated at that

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Effect of processing conditions on-meat meal 1065

150 I 1 I I I I

Time in cooker (mid

Figure 1. Processing conditions for experimental batches.

point, with the contents discharged from the cooker for further processing. For the three experimental batches, heating was continued beyond the usual end-point, with the temperatures of the contents rising to values given in Table 2 and Figure I , which also show the times at which samples were taken.

TABLE 2. Sampling details

Temperature at time Time from start Batch no. Sample no. of sampling ("C) of cycle (min)

1 1 2 3 4

2 1 2 3 4

3 1 2 3 4

111 118" 130 130 115" 143 145 145 111 115" 116 115

104 119 152 212 126 156 186 246 86

106 126 186

a Usual "end-point'' as judged subjectively by plant operator.

Each meal sample was obtained by briefly opening the cooker discharge door to allow 100 kg of contents to fall into the percolator, where some of the tallow drained away. The tallow-wet meals were stored at ambient temperature for not more than three days before being reheated to about 80 "C so as to facilitate removal of most of the remaining tallow in a small batch centrifuge. They were then comminuted in a hammer mill, having grate apertures of 4-mm diam, thoroughly mixed and subdivided

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1066 L. S. Herbert et ul.

into 5 to 10-kg portions for despatch to the following laboratories: Poultry Research Station, Seven Hills, NSW; Dept of Poultry Technology, Queensland Agricultural College (Q.A.C.), Gatton; and Dept. of Biochemistry and Nutrition, University of New England, (U.N.E.), Armidale, N.S.W.

3. Analytical procedures Proximate analyses were carried out substantially in accordance with the methods of the A.0.A.C.4 except for crude protein at U.N.E., which was determined by the method of Clare and Stevenson5 with a Technicon Auto-analyzer. Available lysine values were estimated by the method of Carpenter.'j

Chick assays were carried out on each sample according to the usual practice of the participating laboratories, as detailed in Table 3. In each case, average weight gain per chick was used as the criterion of relative nutritional value.

TABLE 3. Details of chick-assay procedures

Seven Hills U.N.E. Q.A.C.

Stock Broiler chicks WL x BA Cockerels WL x A 0 Cockerels assay period 11-21 days of age 7-14 days of age 7-21 days of age

No. of chicks per 20 cockerels and 20 40 cockerels in two 8 cockerels individu- treatment pullets in four groups groups ally caged

Amount of protein in 20" 20" Approx. 20b assay diet (%)

Amount of meat meal 5" 10" Approx. 5b protein in assay diet ( %)

phorus and energy level of assay diet

assays, including diets obtainable from

Protein, calcium, phos- Equalised Equalised Not equalised

Full details of chick Reference 9 References 10 and 11 Reference 9

Isonitrogenous diets determined by crude-protein analysis. Meat meal (assumed 50% crude protein) added at 10% by weight of diet.

4. Results and calculations 4.1. Chick assays Results of chick assays are given in Table 4, the standard error of means being calcu- lated separately for each laboratory.

The calculations of analysis of variation that were made on the weight-gain data of Table 4 are presented in Table 5.

4.2. Chemical analysis Proximate analysis results, given in Table 6, are expressed as percentages of the air-dried samples and ALV as g lysine/l6 g nitrogen in the air-dried sample.

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Effect of processing conditions on meat meal

Table 4. Results of Chick Assays

1067

~~ ~ ~~ ~ ~

Mean weight gain/chick/day (g) Significantly

Batch no. Sample no. Seven Hills U.N.E. Q.A.C. Average treatments' , different

1 1 15.6 4.7 9.2

9.9 2 15.4 5.5 8.5 3 15.6 5.2 8.9 4 15.1 7.0 9.2

2 1 15.5 6.1 9.9 10.5 2 15.0 5.3 9.3 3 15.1 5.6 10.0 4 15.9 5.0 9.7

2 14.7 5.5 9.2 9.8 abb 3 15.4 6.0 9.7 10.4 bcb 4 15.8 6.2 10.9 11.0 Cb

10.4 E 1 N*S.

10.2 l::; I N.S. 3 1 15.1 4.8 7.4 9.1 ab

S.E. 0.49 S.E. 0.49 S.E. 0.49

a L.S.D. at 5 % level is 0.815 g. Average values labelled with the same letter are not significantly different.

TABLE 5. Analysis of variance

Source of variation d.f. Mean square Fratio and comments

*** Laboratories 2 293.9441 Samples 11 0.6969 F = 2.40 P > 0.05 Batches 2 0.0656 N.S. Samples in batches 9 0.9336 F = 3.21 P> 0.05 Labs. x samples 22 0.2907 N.S. Error (pooled within assay) 35 0.2401 S.E. of sample mean = 0.2941 g. L.S.D. of sample mean = 0.815 g.

TABLE 6. Results of chemical analyses

Seven Hills U.N.E.

Crude protein Tallow Calcium Crude protein ALV Batch no. Sample no. (%) ( %) ( %) (%) (g/16gN)

1 1 39.8 14.7 14.3 45.7 3.5 2 41.9 17.9 12.7 50.5 5.3 3 50.5 17.6 9.5 54.4 5.0 4 49.0 17.1 10.7 45.7 5.0

Average 45.3 16.8 11.8 49.1 4.7 2 1 48.0 15.1 10.7 48.5 5.8

2 44.2 12.8 13.4 47.0 4.4 3 48.4 14.3 10.7 51.0 4.2 4 47.3 16.7 11.8 44.5 4.9

Average 47.0 14.7 11.7 47.8 4.8 3 1 41.2 10.7 13.0 45.6 4.8

2 39.4 10.7 14.4 46.5 5.5 3 44.2 13.0 12.8 49.5 5.1 4 51 .o 12.4 9.6 - 5.2

Average 44.0 11.7 12.5 47.2 5.2

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1068 L. S. Herbert et ul.

5. Discussion 5.1. Chick assays The Q.A.C. and Seven Hills chick-assay procedures were designed to determine meat meal protein quality differences when the meat meals were incorporated into commer- cial-type diets. The amount of meat meal was set, as in industry, by the need to limit the calcium content of the diet to a practical level. Grain and other proteins were added at the levels required to meet the total protein and energy needs and accepted amino-acid requirements. As with commercial diets, methionine was the only acceptable amino-acid supplement.

The U.N.E. procedure allowed for approximately half the protein in the diets to be supplied by the meat meals, so that their diets were closer to those commonly used in protein quality tests by stock feeders and meat-meal producers. Such diets had pre- viously been used by Kondos and McClym~nt ,~ who were able to determine small differences in protein quality of dry-rendered meat meals.

The conversion of chick assay results from the three laboratories to a common basis of wt gain/chick/day eliminated much of the apparent heterogeneity of the data originally reported as wt gain/chick. Homogeneity of the converted data is confirmed by the absence of a significant lab. x sample interaction (Table 5). No significant differences are noted between batches, but significant differences are noted between samples and between samples in batches. Differences between average weight gains of samples in Batches 1 and 2 are not significant but in Batch 3, significant differences in samples are noted as indicated in the last column of Table 4. Thus on the evidence of chick assays carried out in three different laboratories, no differences in nutritive value could be detected between commercial-type diets containing meat meals dry rendered to the usual end-point (I 15 "C) and those held at temperatures up to 145 "C for 2 h after the usual end-point. In the samples from Batch 3, a significant increase in nutritive value is noted for meals held at 115 "C for up to 80 min after usual end- point. The results do not preclude the possibility that the more heat-sensitive essential amino acids were affected; minor changes could be masked by the presence of the affected amino acids in other constituents of the diets.

Kondos and McClymont2 reported that nutritive values of meat meals processed in a continuous dry-rendering cooker at discharge compartment temperatures of 121.5 "C and 127.5 "C were greater than meal processed at 116 "C, where the processing time for each temperature was ca 40 min. It appears therefore that an increase in nutritive value results either from increasing cooking time or increasing temperature in the range 11 6 to 127 "C. The same workers noted a significant decrease in nutritive value only in meals processed above 138 "C, whereas in the present work such decrease was not apparent in meals processed at 145 "C for 2 h. Wilder,7 reporting on work on a pilot batch dry-rendering plant, also noted that "the destruction of amino acids in the protein, so often noted when other types of protein materials are heated in the dry stage, is not found in meat scrap heated under normal cooking conditions".

5.2. Chemical analysis In two of the laboratories chemical analyses were carried out in order to assist with chick-diet formulation. It can be seen from Table 6 that batch average crude protein

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Effect of processing conditions on meat meal 1069

contents and ALVs were in the ranges expected for meat-and-bone meals. ALVs showed no trends with processing time and temperature and thus tend to confirm that the biological value of the meal protein had not suffered. The average tallow content was variable and higher than usual for commercial meals, probably because of the experimental procedure adopted to separate tallow from meal by using a small batch centrifuge. There are insufficient data to establish any significant trends in the analytical results.

Some variability is evident in the results: for example, different protein contents were obtained for different samples from the same batch, analysed in one laboratory (Seven Hills 1-1, 1-2, 1-3 and 1-4). Similarly the protein contents of portions of the same sample sent to different laboratories varied considerably (U.N.E. 1-2 and Seven Hills 1-2).

These variations may result from analytical error or from real differences in material presented for analysis. In the light of the long experience of both laboratories in the established methods of analysis analytical error is considered to account for errors of around k0.5 %. When considering the possibility of differences in the material presented, it is worthwhile describing the steps followed when presenting a subsample of the meals for analysis. Step 1: 100 kg of cooker contents were discharged, when about 1600 kg of almost dry material remained in the cooker-a reduction ratio of 16. Step 2: after centrifuging, 550 kg samples of meal were comminuted, well mixed and divided in 5 to 10 kg portions-a reduction ratio of up to 10. Step 3: 2-g subsamples were withdrawn from the portions for chemical analysis-a reduction ratio of 5500.

Even after comminution, meat-and-bone meals are heterogeneous mixtures of particles of diverse sizes and densities, so that the sampling procedure in step 3, nvolving a high reduction ratio and small subsample weight, is the step at which sampling error is most likely to occur.

Sampling is recognised as a potential source of error in the analysis of mixtures of particles, and Allen and Kahns recently reported on the effects of sampling method on analytical error. The methods used in the present study for step 3 were variations of the scoop or coning and quartering methods, which are reported by Allen and Kahn to give high variability. These sampling methods continue to be used, however, since alternatives are complicated and time consuming. The results in Table 6 are therefore considered to reflect sampling errors, in particular those involved in preparing sub- samples for chemical analysis, and are not considered to represent real differences in the portions as received by different laboratories.

Acknowledgements

The financial support of the Australian Meat Research Committee for this investigation is gratefully acknowledged, as is the co-operation of management and staff at the Altona abattoir of R. J. Gilbertson Pty. Ltd. Staff of CSIRO Division of Chemical Engineering supervised the plant runs and subsequent preparation of meat-meal samples.

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1070 L. S . Herbert et al.

References 1. Atkinson, J.; Carpenter, K. J. J. Sci. Fd Agric. 1970, 21, 360. 2. Kondos, A. C.; McClymont, G. L. Aust. J . agric. Res. 1972,23, 913. 3. Herbert, L. S.; Norgate, T. W. J. Fd Sci. 1971,36, 294. 4. Oficial Methods of Analysis, A.O.A.C., Washington. 1960,9th ed. 5. Clare, N. T.; Stevenson, A. E. N.Z. J. agric. Res. 1963,7,198. 6. Carpenter, K. J. Biochem. J. 1960,77, 604. 7. Wilder, 0. H. M. Am. Meat. fnst. Foundation 1952, Circ. No. 4. 8. Allen, T.; Kahn, A. A. Chem. Engr, Lond. 1970, CE108. 9. McDonald, M. W. ; Solvyns, A. ; Dillon, J. F. Proc. Australasian Poult. Sci. Conoention Surfers

Paradise, 1967, pp. 85-93. 10. Sathe, B. S . ; McClymont, G. L. Aust. J. agric. Res. 1964,15,200. 11. Sathe, B. S . ; McClymont, G. L. Aust. J. agric. Res. 1965,16, 243.