Transactions and Proceedings of the New Zealand Institute, 1920 [electronic resource]

Art. IV.—The Food Values of New Zealand Fish: Part I.

By (Mrs.)Dorothy E. Johnson, B.Sc. in Home Science.

Communicated by Professor J. Malcolm.

[Read before the Otago Institute, 9th December, 1919; received by Editor, 31st December, 1919; issued separately, 4th June, 1920.]

In all countries where procurable, fish should be made an easily accessible article of diet—i.e., it should be both plentiful in quantity and reasonable in cost; but, so far, the greatest possible use has not been made of the bountiful supply in New Zealand waters. Beyond the investigation of the composition of frost-fish and oysters by Malcolm ^* no attempt has been made to estimate the food values of New Zealand fish.

Recognizing the necessity for the prosecution of research in the Dominion, the New Zealand Government placed funds at the disposal of the New Zealand Institute, which enabled that body to make a grant to Professor J. Malcolm for the investigation of the chemistry and food values of the New Zealand fish. This paper outlines the work done in that connection. The aim has been to ascertain—

(a.)	The percentage composition of the edible portion of the fish investigated.
(b.)	The caloric value of the fish (by calculation).
(c.)	The percentage of waste in the fish as bought.
(d.)	From the point of view of cost, to arrive at some conclusion as to the comparative values of the fish as an article of diet.

Methods.

The fish were obtained from Dunedin retail fish-dealers, with the exception of one “baby” groper, which was sent from the Portobello Fish-hatcheries, and a sample each of mullet and snapper, which were sent from Auckland by boat. With the larger fish, from ½ lb. to 1 lb. was purchased, as would be done for home consumption. Wherever possible three samples, bought at different times, were analysed, but this was not always possible.

In a few instances there is some doubt as to the exact variety of fish bearing a commonly known name: e.g., “sea-bream” is applied to two or three different varieties of fish,^† and exact identification would have been difficult owing to the fish being for the most part obtained in slices. It is likely, however, that in such instances the differences in composition would not be very marked—probably less than the difference between individuals of the same variety.

(I.) Percentage of Edible Material and Percentage of Waste.

Skin, bones, &c., were separated from the muscle, and the two portions, edible and non-edible, weighed. The flesh was finely minced and well

[Footnote] * Trans. N.Z. Inst., vol. 44, pp. 265–69, 1912.

[Footnote] † Private information from the Hon. G. M. Thomson.

mixed. Then, after a portion had been set aside for the estimation of the water and protein percentage, the rest was spread in thin layers on glass plates and dried, either over a low-temperature water-bath or in an oven maintained at 52° C. Some oxidation of the fat was unavoidable in this process. The dried material was minced again, passed through a fine sieve, and the larger pieces ground in a coffee-mill. The whole powder was carefully sifted and stored in a bottle. In the case of tarakihi 1 and mullet 1 further oxidation of the fat was noticeable in that part exposed to the light.

(II.) Percentage of Water and Solids.

This was carried out in a hot-air oven at 65°–70° C., the average of three estimations per sample being taken.

(III.) Percentage of Protein.

The total nitrogen was estimated on fresh material by the Kjeldahl method, 0.2 N solutions of acid and alkali being used. The protein was calculated as total nitrogen multiplied by 6.25, and the average of two estimations per sample taken.^*

(IV.) Percentage of Fat.

The dried powder from (I) was extracted with sulphuric ether in a Soxhlet extractor. After twelve hours' extraction the solvent was evaporated somewhat, the mixture filtered, the remainder of the ether carefully evaporated, and the oil finally dried for three hours or more at 52° C. The figure in the tables is the average of two estimations. (The water percentage of the powder was estimated, to obtain the amount of fresh material represented.)

(V.) Percentage of Ash.

This was carried out in the usual way with the dried material from (II) in a Davy's crucible furnace. The longer method of extracting the chlorides with distilled water after the first charring, and adding the residue after evaporation to the ash, was used at first but discontinued, as the results from the shorter method were found to vary but little from those of the longer method, and the greater accuracy seemed unnecessary, as the protein and fat estimations could only be approximate.

(VI.) Calculations.

From these results the following figures were calculated:—

(1.)	Calories per cent., using the factors 4.1 large calories per gramme of protein and 9.3 large calories per gramme of fat.
(2.)	The cost of 1,000 calories, and of 100 grammes of protein.
(3.)	For purposes of comparison the composition of milk, meat, and eggs was taken as given in Hutchison's Food and Dietetics

Results.

The results are shown in the following tables (I-VI).

[Footnote] * The use of this figure (6.25) is not quite satisfactory, as the proper factor to use with fish proteins requires investigation.

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Table L—General Table showing Percentage Composition of Fish analysed.
Common Name of Fish.	Specimen.	Scientific Name.	Date received.	Water.	Solids, by difference.	Fat.	Protein.	Ash.	Total.
Groper (hapuku)	1	Oligorus gigas	16/7/19	70.50	29.50		20.50	1.12
"	2	"	30/7/19	76.00	24.00	1.90	19.20	1.27	98.40
"	3	"	11/8/19	76.10	23.90	3.40	19.34	1.08	99.90
Baby groper (hapuku)	1	"	28/8/19	77.03	22.97	2.93	18.42	1.08	99.50
"	2	"	11/9/19	76.41	23.59	2.32	19.75	1.10	99.58
Sea-bream (warehou)	1	(?)	26/8/19	73.37	26.63	4.25	19.51	1.18	98.30
Crayfish	1^*		5/9/19	73.13*	26.87	0.72	22.90	1.54	98.30
"	2		8/9/19	77.45	22.55	0.52	19.78	1.55	99.30
"	3*		13/10/19	74.23*	25.77	1.30	22.35	1.40	99.28
Snapper (tamure)	1	Pagrus unicolor	8/10/19	76.92	23.08	0.60	20.68	1.23	99.43
"	2	"	27/11/19	78.67	21.33	0.42	18.93
Mullet (kanae)	1	Mugil perusii	8/10/19	69.43	30.57	10.09	19.29	1.04	99.85
Tarakihi	1	Chilodactylus macropterus	13/10/19	69.23	30.77	10.30	19.71	1.07	100.31
"	2	"	22/11/19	76.00	24.00	3.05	20.31
Blue cod (pakirikiri)	1	Percis colias	16/10/19	79.70	20.30	0.90	18.79	1.05	100.44
Kingfish (haku)	1	Seriola lalandii	3/11/19	75.65	24.35	4.32	18.72	0.93	99.62
"	2	"	11/11/19	74.37	25.63	4.10	19.84	1.14	99.45
Trumpeter (kohikohi)	1	Lafris hecateia	28/10/19	75.86	24.14	3.31	19.37	1.01	99.55
Moki	1	Latris ciliaris	28/10/19	78.00	22.00	1.63	19.12	0.93	99.69
"	2		10/11/19	76.41	23.59	3.21	18.32	1.09	99.03

[Footnote] * Boiled specimen.

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Table II.
Name of Fish, &c.	Kind of Sample.	Price.(Pence.)	Weight. (Grammes.)	Edible. (Percentage.)	Waste. (Percentage.)
Groper 1	Slice	4	322	82 92	17.08
" 2	"	6	316	94 62	5 38
" 3	"	6	271	97 05	2.95
Baby groper 1	"	9	283 5	87 32	12.68
" 2	Whole		3,742	39 31	60 69
Sea-bream 1	Slice	15	553	87 05	12 95
Crayfish 1	Tail	2	228.5	33.20	66.80
" 2	"	3	83	79 50	20.50
" 3	Whole	6	680	31.18	68 82
Snapper 1	"	17.5	1,544	44.37	55.63
" 2	"	30	2,735	39.56	60 44
Mullet 1	"	18	1,240	63.31	36 69
Tarakihi 1	"	30	1,895	51.44	48 56
" 2	"	9	520	53 46	46.54
Blue cod 1	Slice	21	744	47.44	52 56
Kingfish 1	"	12	498	73.30	26.70
" 2	"	15	561	78 25	21.75
Trumpeter 1	Whole	18	909	50 82	49.18
Moki 1	"	18	1,159	50.12	49.88
" 2	Slice	15	572	78 32	21 68
Egg	One	2	50	88 00	12 00
Beef	Steak	12	454	100 00
Milk	Pint	3	586	100 00

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Table III.
Name of Fish.	Calories per 100 Grammes of Undried Edible Material.	Cost of 100 Grammes Protein (Pence.)	Cost of 1,000 Calories. (Pence.)
Groper 1		7.3
" 2	96 39	10.5	20.8
" 3	110 92	11.8	20 6
Baby groper 1	102.78	19.8	34.4
" 2	102.56
Sea bream 1	119.51	160	25 9
Crayfish 1	100 59	11.5	26 1
" 2	85 96	22.9	52 9
" 3	103.73	12.7	27.1
Snapper 1^*	90.38	12 4	28 3
" 2	81.51	14 6	23.8
Mullet 1*	172 89	9.0	13.3
Tarakihi 1	167 45	15 6	17.4
" 2	111.64	16 0	29 0
Blue cod 1	85 40	31.7	69.7
Kingfish 1	116 93	17 6	28 1
" 2	119 47	17.2	28 6
Trumpeter 1	110 20	20.1	35 3
Moki 1	93.56	16.2	33.1
" 2	104 96	18.3	31.9
Eggs at 2s. per dozen	158 33	32.9	29 5
Beef at 1s. per pound	137.25	12.6	19 1
Milk at 3d. per pint	70 00	14 6	7.3

[Footnote] * Auckland prices.

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Table IV.—Showing Fish in Order of Fat Content.
	Per Cent.
Tarakihi 1	10.30
Mullet	1 10 09
Kingfish 1	4 32
" 2	4.10
Sea-bream 1	4 25
Groper 3	3 40
Trumpeter 1	3 31
Moki 2	3 21
Tarakihi 2	3 05
Groper 4	2 93
Baby groper	2.32
Groper 2	1 90
Crayfish 3	1 30
Moki 1	1 63
Blue cod 1	0.90
Crayfish 1	0 72
Snapper 1	0 60
Crayfish 2	0 52
Snapper 2	0 42
Egg	10 50
Meat (beef)	5.50
Milk	4 00

Table V.—Showing Fish in Order of Caloric Values.
(Total calories per 100 grammes fresh material.)
	Per Cent.
Mullet 1	172 89
Tarakihi 1	167 45
Sea-bream 1	119 51
Kingfish 2	119.47
" 1	116 93
Tarakihi 2	111 64
Groper 3	110 92
Trumpeter 1	110 20
Moki 2	104 96
Crayfish 3	103 73
Groper 4	102 78
Baby groper	102 56
Crayfish 1	100 59
Groper 3	96 39
Moki 1	93 56
Snapper 1	90 38
Crayfish 2	85 96
Snapper 2	81 51
Blue cod 1	85 40
Egg	158 33
Beef	137 25
Milk	70 00

Table VI.—Showing Fish in Order of Cost of 100 Grammes Protein.
	Pence.
Groper 1	7 31
Mullet 1	8 96
Groper 2	10 45
" 3	11 80
Crayfish 1	11 49
" 3	12 66
Snapper 1	12 35
" 2	14 64
Tarakihi 1	15 61
" 2	15 95
Sea-bream 1	15 99
Moki 1	16 21
Kingfish 1	17 22
" 2	17 56
Moki 2	18 27
Groper 4	19 78
Trumpeter 1	20 11
Crayfish 2	22 98
Blue cod 1	31 66
Beef	12 60
Milk	14 62
Eggs	32 94

Discussion.

The following points are noticeable:—

1. The percentage of water and of solids shows much the same variation that similar analyses ^* of American and European food fishes have shown. Further, the analyses exhibit the fact that a high fat value goes with a low water percentage, the protein percentage fluctuating but little from the mean of 19.69. In the process of fattening, therefore, the water,

[Footnote] * R. Hutchison, Food and the Principles of Dietetics, Clark and Almy, Journal of Biological Chemistry, vol. 33, p. 483, 1918.

not the protein, is replaced by fat. In a fatty fish there is an absolute gain in nutritive value though a decrease in digestibility. For example,—

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Fish	Water Percentage.	Fat Percentage.	Protein Percentage.
Blue cod	79.70	0.90	18.79
Kingfish	75.65	4.32	18.72
Groper	76.10	3.40	19.34
Mullet	69.43	10.09	19.29
Snapper	69.23	10.30	19.71

2. Table IV shows the fish in order of fat content, which is the usual order of classification for dietetic purposes. There is considerable variation from tarakihi (sample 1) with 10.30 per cent. to snapper (sample 2) with 0.42 per cent. One noticeable fact, however, is the difference between two samples of the same variety of fish, even when bought at short intervals from each other. For example,—

Fish.	Date of Purchase.	Fat Percentage.
Tarakihi 1	13th October, 1919	10.30
" 2	22nd November, 1919	3.05
Moki 1	28th October, 1919	1.63
" 2	10th November, 1919	3.21

This question needs to be investigated further before definite comparison can be made of the fat content of various fish. It may be a question, say, of metabolism or of seasonal variation.

3. Table V shows the caloric values. The figures represent the total calories per 100 grammes of edible material. The presence to any great extent of fat increases the caloric value considerably, as will be seen by comparing Tables IV and V. Mullet 1, tarakihi 1, kingfish 1 and 2, seabream 1, groper 3, and trumpeter 1 occupy almost the same positions a the head of each table, and compare quite favourably with egg, beef, and milk.

4. The cost of the fish, as shown in Tables II and VI, is the price actually paid as for home consumption. For comparative purposes the cost of 100 grammes of protein has been calculated. It will be noticed that there is considerable variation in price for the same variety of fish; fish being a perishable commodity, and the supply being erratic owing to weather conditions, the fluctuations of the market are considerable.

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Fish.	Date of Purchase.	Price.
			s. d.
Groper	16th July, 1919	0 8 per pound
"	30th July, 1919	1 0 "
"	28th August, 1919	1 6 "

The price, therefore, is not necessarily indicative of the food value. This is also apparent from the fact that 100 grammes of protein can be obtained from groper at 7½d., mullet at 9d., kingfish at 1s. 6d., but from blue cod the cost is 2s. 8d. Hence the popularity of the last-named fish has little

to do with its food value, but probably has considerable influence on its price. Also, a chemical analysis does not take into account such qualities as delicacy of flavour and texture, which, appealing to a buyer, exert an influence in increasing the amount he is willing to pay.

5. Table II also points out that in dealing with fish the element of waste must be considered in comparing the cost. When bought in slices the average waste is one-sixth of the total weight, but with whole fish as much as one-half tends to be lost. There is also a further loss on cooking, but that has not been dealt with in this investigation.

6. The methods used in ascertaining the percentage of protein give the maximum figure, since part of the total nitrogen will be contained in extractives and gelatin substances. As a source of protein, therefore, a fish containing 19 per cent protein has really not the same value as meat or egg with 19 per cent protein. But, without considering this factor, with beef at Is. per pound the corresponding prices for fish should not be greater than the following:—

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	Per 1b.	Per 1b.	Average price paid.
Groper	8½d.	instead of 1s. 2d.
Kingfish	7½d.	" 1s. 1½d.
Tarakihi	5½d. to 7½d.	" 7½d.
Blue cod	3½d.	" 1s. Od.
Sea-bream	9d.	" 1s. 3d.
Snapper	3d.	" 5½d.
Mullet	10d.	" 6d.

These figures point to the high prices prevailing for a food that is naturally plentiful, and seem to indicate a state of artificial scarcity in the market. Another point which is very apparent in making these calculations is that the amount of waste (from a food point of view) is an important determinant in comparing prices: e.g., compare groper and kingfish. From the analyses (calories per cent.) the edible portion of kingfish is superior to that of groper in the proportion of 118 to 105; but the waste is 24 per cent. with kingfish, and only 7 per cent. with groper (slices). Therefore (compared with beefsteak at 1s. per pound) the housewife can afford to pay 8½d. per pound for groper, but only 7½d. per pound for kingfish.

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Name.	Calories (Percentage).	Waste (Percentage).	Maximum Price per Pound.
Kingfish	118	24	7½d.
Groper	105	7	8½d.

It is necessary to point out, however, that these deductions are based on twenty samples (eleven kinds), and more complete investigation may make modifications necessary; but it is noticeable that in many salient features the results concur with those of wider investigations carried out in other countries.

Besides acknowledging, with thanks, the constant help I have received from Professor J. Malcolm—to whom, indeed, the initiation of this research is due—I have also to thank the Council of the University of Otago for the use of their laboratories and apparatus.

All the expenses incurred have been defrayed by a grant from the New Zealand Government, through the New Zealand Institute.