Showing papers in "Journal of the Science of Food and Agriculture in 1953"

The enzymic degradation of pectin and other polysaccharides. II—Application of the ‘Cup-plate’ assay to the estimation of enzymes

Abstract: The agar ‘cup-plate’ diffusion technique has been applied to the quantitative determination of enzyme activity, principally to amylase, polygalacturonase, cellulase, protease and pectin-esterase. With all enzymes so far examined, the relationship between diameter of zone and log(amount of enzyme) is linear over a wide range, and may be used for the quantitative estimation of the enzymes. The cup-plate assay of polygalacturonase, like viscometric methods, measures the initial destruction of the colloidal properties of pectic acid, and, owing to the complex nature of polygalacturonase, bears no simple relationship to the assay of polygalacturonase by the estimation of glycosidic hydrolysis.

The development of a numerical scoring system for the sensory assessment of the spoilage of wet white fish stored in ice

Abstract: An attempt is made to classify the sensorily perceptible quality-factors of cod fish, stored in ice, throughout the spoilage chain from absolute freshness to putridity. The classification is given numerical form to ease the handling and interpretation of the resulting data. A panel has been trained to agree in assessing any one sample, and its internal consistency is descussed on the basis of some experimental data. The importance of the method would seem to be that those factors are classified which would give rise to opinions of preference in the ordinary consumer, were the food presented to him. In practice the accuracy obtained by the panel was such that samples could be clearly differentiated, in terms of periods of storage in ice under certain standard conditions, to within a day or two.

The water‐soluble carbohydrates of grasses. I.—Changes occurring during the normal life‐cycle

Abstract: The water-soluble carbohydrates [glucose and fructose (reported together as total hexoses), sucrose and fructosan] in the leaf, stem and head portions of four grasses have been determined at regular intervals throughout their growth cycle during two successive years. Hexoses were at all times present in only small amounts. The concentration of sucrose varied with the stage of growth, rising to a peak in May-June, and the effect of the stage of growth on the amount of sucrose was similar in both leaf and stem. Fructosan was present in a much higher concentration in the stem than in the leaf, and stage of growth had a marked effect on the amount present. A relationship is suggested between these fluctuations in fructosan content and morphological changes, first in the development of the growing point from a vegetative to a floral state, and later in seed formation.

Animal fats: Recent researches in the fats research laboratory, D.S.I.R., New Zealand

Abstract: The views recorded in the first section of this survey dealing with the relationship between the dietary and depot fats are in some cases based on the results of other investigators. In the second section the work of this Laboratory on the fatty-acid composition of butter fat has been examined in the light of the recent British discoveries on the synthetic activity of the mammary gland. Finally, the work of the Fats Research Laboratory on the isolation from animal fats of trace constituents, particularly the branched-chain fatty acids, is reviewed.

Studies on egg shells. II.—A method for marking and counting pores

Abstract: A method has been developed for marking the pores in egg shells by immersing them in concentrated nitric acid for very short periods of time. This makes the pores easily visible under the microscope, and counting can then be done by a statistical method. Not only is the total number of pores determined, but also a frequency distribution is obtained which indicates that the pores are not distributed at random.

Determination of nitrogen in soil and plant materials: Use of boric acid in the micro-kjeldahl method

Abstract: The use of boric acid for trapping ammonia in the micro-Kjeldahl determination is examined. A suitable procedure, together with a modified type of micro-distillation apparatus, is described. The buffer capacity of boric acid solutions was examined in relation to the sensitivity in the titration of ammonia dissolved in them. Two grades of boric acid, ‘pure’ (technical) and AnalaR, were compared; the former showed appreciable buffering on the acid side. The pH values of solutions of both grades decreased with increasing concentration. The sensitivity of the three indicators examined for the titration of ammonia diminished with increasing concentration of boric acid as a result of the increased buffering. With concentrated boric acid, all three indicators showed wide transitional periods at the end-point, but in solutions of concentration up to 1-0% of AnalaR grade the end-points shown by all three indicators were sharp. The methylene blue-methyl red indicator, however, was generally preferable. The ammonia-fixing capacity of boric acid was studied in air-bubbling tests and by recovery of a known amount of ammonia by distillation. A volume of 10 ml. of 1-0% boric acid fixed 5 mg. of nitrogen as ammonia sufficiently firmly to afford accurate analyses. For macro-determinations, 100 ml. of 2-0% boric acid held firmly up to 90 mg. of nitrogen.

The tocopherol content of farm feeding‐stuffs

Abstract: The amounts of the individual tocopherols in some common farm feeding-stuffs have been determined and the presumable vitamin-E potencies of the feeding-stuffs calculated from them. Grass, clover and Iucerne contained 10-40 mg. of tocopherol/100 g. of dry matter, and it has been shown that the concentration in grass fell to a low level as the plant matured. Only minute amounts of tocopherols were present in root crops. Barley, maize, oats and wheat contained 1-7 mg. of tocopherols/100 g., but the vitamin-E activity of these crops was lower than the total tocopherol-content might suggest, because of the presence of appreciable amounts of the less active β- and γ-compounds. The bearing of the results on naturally-occurring muscular dystrophy in farm animals is discussed.

Manuring of grassland. I.—Some effects of heavy dressings of nitrogen on the mineral composition of grassland herbage†

Abstract: Results are given for the effects of heavy dressings of nitrogen, in the presence and absence of phosphorus and potassium supplements, on: dry-matter yield; botanical composition of herbage; contents of crude protein, phosphorus, potassium, calcium, magnesium, sodium and manganese. Brief reference is also made to the effects of the various experimental treatments on the uptake of certain other trace-constituents. The results indicate that high yields of pasture herbage having high protein and normal mineral contents can be maintained over a period of years by the use of fertilizer nitrogen, provided adequate fertilizer dressings of other major nutrients are given. Attention is drawn to various ion-antagonism effects that may influence the mineral composition of the herbage.

Sodium as a plant nutrient

Abstract: 1. The present paper gives a critical re-examination of different data and conceptions on the action of sodium in relation to deficiency symptoms and yield response. 2. The importance of sodium for different agricultural crops is discussed in relation to the replacement of potassium and independent sodium effects. 3. The results of pot experiments on oats, reported in the literature, indicate that sodium has an independent function other than that of replacing potassium. Both the nitrate and chloride of sodium appeared to be suitable for oats. 4. Field experiments testing sodium for early potatoes in Holland showed little effect on yield of tubers, but there were effects on the tops. Even at high levels of potassium there were responses in yields of main-crop tubers from dressings of sodium. The effect of sodium was studied by comparing sodium nitrate with calcium nitrate. When sodium chloride was applied to potatoes, either as common salt or with 20-40% muriate of potash, there were decreases in yield and starch contents of the tubers. 5. Results are given of recent Dutch experiments with fodder beet, testing sodium as nitrate of soda. The influence of soil type and addition of farmyard manure is discussed.

Studies on egg shells. I.—The determination of membrane‐, pore‐ and matrix‐protein

Abstract: The protein in egg shells consists of the matrix-protein closely associated with the mineral matter, the protein in the pores and a thin cuticle on the outside. In addition, the shell membranes are usually considered under the same heading although, strictly speaking, they are not part of the shell. A method has been devised by which the shell-plus membrane-protein can be divided into three distinct entities, by making use of the different rates at which these entities dissolve on boiling with sodium hydroxide solution. The method is arbitrary, and thus not absolutely accurate, but it appears to give a measure of entities which probably represent (1) membrane- and cuticle- (2) pore- and (3) matrix-protein.

Analytical studies on the carbohydrates of grasses and clovers. III.—Carbohydrate breakdown during wilting and ensilage†

Abstract: Considerable enzymic breakdown of sucrose and fructosan has been found to occur during wilting and laboratory ensilage of grass. The implications of this are discussed with respect to the collection of grass samples for analysis and the preparation of grass silage.

The composition of bracken some major- and trace-element constituents.

Abstract: Periodic samples of bracken taken during the growing season have shown that the concentration of major elements (except calcium and sodium) decreases with age in fronds, and remains relatively constant in rhizomes, whereas trace-element concentration varies widely. Soil type has little effect on the mineral composition of fronds. Examination of three rhizome types revealed no wide differences in the content of major elements; pinnules generally contained higher concentrations of major and trace elements than fronds. Comparison of results with those published elsewhere for moorland plants grown under similar conditions indicates that bracken contains rather more potassium and less molybdenum.

The chemical estimation of vitamin‐E activity in cereal products. I.—The tocopherol pattern of wheat‐germ oil

Abstract: Details are given of a method for determining the individual tocopherols and associated unidentified substances in oil extracted from cereal products. The technique depends ultimately on separating the tocopherols by paper chromatography by means of liquid paraffin B.P. and 75% aqueous ethanol as the stationary and mobile phases respectively. Typical results obtained with wheat-germ oil are quoted: they indicate that the tocopherol pattern of this oil consists of α-tocopherol, β-tocopherol and two unidentified substances, one of them possibly an unreported tocopherol.

The water‐soluble carbohydrates of grasses. II. —Grasses cut at grazing height several times during the growing season

Abstract: Four perennial grasses were cut with a motor mower each time they reached a height of about 8-10in. during the growing seasons of 1951 and 1952. The water-soluble carbohydrates, glucose and fructose (reported together as free hexoses), sucrose and fructosan were determined in each cut. Grasses in which the growing point had recently changed to a floral development (in May or June) contained more carbohydrate than grass grown and cut later in the season. The primary reason for this was that the later grasses were more leafy, and, secondly, that their stems contained much less fructosan than those of the earlier cuts.

Estimation of sterilizing values of processes as applied to canned foods. II.—Packs heating by conduction: Complex processing conditions and value of coming‐up time of retort

Abstract: A method is presented for estimating the Fc value, for conduction packs, of a heating process of any degree of complexity. As a corollary, the value of the coming-up time of the retort may be estimated in terms of time at retort temperature.

Studies on egg shells. III.—Some physical and chemical characteristics of the egg shells of domestic hens

Abstract: Fifty eggs have been examined and a number of physical and chemical characteristics determined. These include shell thickness, porosity coefficients, pore counts, membrane-, pore- and matrix-protein, calcium, carbonate, magnesium, phosphorus and citric acid. Apart from calcium, carbonate and magnesium, the characteristics all show pronounced bird differences. Certain relationships such as shell thickness: weight per unit area, shell weight: calcium content, calcium content: carbonate content and pore count: porosity coefficient have also been developed, and some may prove to be of value in eliminating laborious work such as shell-thickness measurements and calcium and carbonate determinations.

Some typical analyses of red seaweeds

Abstract: The seaweeds with which this paper is concerned all belong to the group Rhodophyceae, the best known of which are Gelidium spp. and other genera, from which agar is obtained, and Gigartina spp. and Chondrus spp., collectively known as Irish moss. This work was carried out under the auspices of the Institute of Seaweed Research with a view to obtaining a comparative survey of the general analytical characteristics of the group as a whole, although particular attention has been devoted to the distribution of the various sugars present (as shown in Table II).

Connective tissue of meat. II.—Determination of Hydroxyproline

Abstract: The density of colour produced in Neuman & Logan's method for the estimation of hydroxyproline was measured in a Hilger Spekker absorptiometer. On any one occasion satisfactory duplication was obtained with aliquots of the same solution of hydroxyproline, and a smooth curve resulted when concentration was plotted against colour density. However, from time to time the level of the curve fluctuated slightly, and therefore the colour should be developed in standard solutions when any ‘unknowns’ are being estimated, as recommended by Neuman & Logan. The density of the colour was depressed to some extent by amino-acids present in the solution (e.g. in the form of protein hydrolysate) when the ratio of amino-acid to hydroxyproline was about 50 to 1 or greater.

The estimation of vitamin-E activity by paper chromatography.

Abstract: Paper chromatography has recently been applied to the separation and estimation of the individual tocopherols. The present communication draws attention to errors that are likely to arise if a solution of ‘Vaseline’ petroleum jelly in ethyl ether is used to impregnate the filter paper in order to achieve phase-reversal. The use of liquid paraffin B.P., dissolved in light petroleum, not only overcomes these objections, but enables the elution after chromatography to be simplified. Losses of tocopherols are minimized by chromatography in an inert atmosphere. The modified technique, which is described in detail, has consistently given recovery figures of 95%, or better, when tested with mixtures of synthetic tocopherols.

The objective approach to sensory tests of food

Abstract: The use of a technique, previously described, for assessing the quality factors of iced white fish is discussed Results are given to show that the explicit training of a panel of assessors to agree is a chief factor in achieving accuracy The validity of comparing results from different investigations is then examined, with reference to such factors as the internal consistency of the panel, the use of control samples or standards and of certain physicochemical criteria

Amino-acids in New Zealand cheddar cheese:Their possible contribution to flavour

Abstract: 1. Paper partition chromatographic analysis of four maturing New Zealand Cheddar cheeses showed them to contain the following ninhydrin-reacting compounds: glutamic acid, lysine and/or arginine, leucine and iso, leucine, valine, phenylalanine, alanine, aspartic acid, glycine, glutamine, asparagine, threonine, methionine, a peptide, and sometimes tyrosine, serine and proline, in the water-soluble nitrogenous fraction. 2. All the amino-acids increased steadily in amount as the cheeses matured, except for tyrosine, the concentration of which fluctuated in the different cheeses, probably as a result of the decarboxylating activity of some of the lactobacilli present in the cheeses. 3. Comparison of the times of appearance of the individual amino-acids with flavour development indicated no correlation between a particular acid or acids and the development of Cheddar cheese flavour. 4. The individual amino-acids and their corresponding amines, as well as mixtures of the amino-acids as found in mature cheese, did not possess any aroma or taste which might suggest that they contributed to the typical flavour of Cheddar cheese.

The free amino-acids and peptides of plant tissues

Abstract: Free amino-acids were extracted from pasture plants with 80% alcohol, and the residue was extracted with water to remove bound amino-acids (peptide fraction). The alcohol extracts and the hydrolysed water-extracts were assayed microbiologically for 17 amino-acids. Total amino-nitrogen was also estimated in these extracts by Van Slyke's nitrous acid method. Most of the free amino-nitrogen was due to relatively few amino-acids, chiefly the dicarboxylic acids (and their amides), alanine and serine. A larger number of amino-acids contributed significantly to the peptide fraction. Treatment of the grasses with different nitrogenous fertilizers resulted in some differences in the amino-acid patterns. Larger differences were noted between young and more mature tissues. Of the total amino-nitrogen measured by Van Slyke's method about 70% in the free amino-acid fraction and about 95% in the peptide fraction were accounted for by assay of individual amino-acids.

The nitrogenous extractives from fresh fish muscle. II—Comparison of several gadoid and elasmobranch species

Abstract: The fractionation of the aqueous-alcoholic extracts of the muscle of several species of marine gadoids and elasmobranchs by displacement chromatography by means of ion-exchange resins, has shown the presence of 13 amino-acids in addition to creatine, creatinine, trimethylamine oxide and possibly glutathione in all species examined. Betaine and sarcosine appear to be confined to the elasmobranchs, and anserine and methylhistidine to the gadoids.

The mechanism of the interaction of sulphur dioxide with certain sugars

Abstract: In the course of certain studies on the behaviour of sulphur dioxide in concentrated citrus juices and other sulphited food products it has been suggested that sulphur dioxide may yield an addition product only with the aldehydic open-chain form of certain sugars. Experimental results are presented here to show that the sulphonate is an open-chain compound, namely elementary analyses coupled with the state of hydration of the product, the measurement of its infra-red absorption spectrum which indicates the absence of a C—O—C bond, and the determination of its optical rotation. Pure crystalline ‘sodium glucose sulphonate’ was prepared after the optimum conditions had been studied. ‘Sodium arabinose sulphonate’ was also prepared, but attempts to combine fructose with sulphur dioxide at ordinary temperatures were unsuccessful. It is considered that this phenomenon is due to the mutarotation of fructose proceeding along quite different lines from that of glucose.

The effect of aggregation on diffusion of gases and vapours through soils

Abstract: The effect of aggregate size upon the relationship between diffusion coefficient of gases through porous media and the porosity has been investigated. Over the range of aggregate sizes used, no differences were found. The presence of moisture in the soil was found to exert an influence directly related to the amount of water present, irrespective of the degree of aggregation of the soil. When the reduction in porosity due to the presence of water is calculated, the observations made fit the curve for air-dry soils with fairly good agreement.

Changes in the pH and buffering capacity of fish during spoilage

Abstract: Claims have recently been made once again for a test for freshness of fish based on a decrease in buffering capacity with increasing staleness. This decrease has been shown to be due chiefly to the bacterial reduction of trimethylamine oxide. However, under commercial conditions the results appear to be too irregular for such a test to be reliable. The buffering capacity of fish flesh in various ranges of pH and its variation with degree of spoilage have been almost completely accounted for by the contributions of proteins and water-soluble constituents. The pH changes in fresh and spoiling fish, which depend in large measure on buffering capacity, are also too irregular to be satisfactorily correlated with freshness.

Chemical aspects of thermal damage to the nutritive value of vegetable oils. II.—The possible formation of cyclized or branched monomeric acyl radicals

Abstract: Distillation of the ethyl esters of heat-polymerized linseed oil at low pressures gives a monomeric distillate, but approximately one-fifth of this distillate is incapable of forming urea adducts. Acetyl-value determinations indicate that this fraction does not represent hydroxy-acids. Estimations of terminal methyl groups support the tentative conclusion that branched acyl chains are absent. Data are presented for the ultra-violet absorption of the non-adduct-forming distillate fraction before and after alkali-isomerization. Some tentative views on the possible presence of cyclic acids are advanced.

Behaviour of fumigants during vacuum fumigation. I. — Penetration of methyl bromide into boxes of dates

Abstract: The penetration of fumigants into packages during treatment by various methods employing reduced pressures, as well as at atmospheric pressure, can be studied by measuring gas concentrations. A ‘penetration factor’ is defined, which allows comparison of the effectiveness of penetration in different methods of treatment. Preliminary laboratory tests with methyl bromide have been carried out, mainly on boxes containing tightly compressed dates. The ‘sustained-vacuum’ method, as normally used, gave higher penetration factors at the centres of boxes of dates in three hours than the method in which an air-fumigant mixture is introduced to the evacuated chamber. Very low penetration factors were obtained in this period in tests at atmospheric pressure. It was found that, after a period of fumigation at reduced pressure, release of the vacuum produced very high concentrations at the centres of boxes. It is suggested that utilization of this effect in a modified vacuum-fumigation procedure should result in increased efficiency. The ‘air-washing’ technique for the removal of fumigant at the end of a treatment has also been examined.

The reduction of nitrate in mixtures of minced grass and water.

Abstract: Nitrate is partially reduced in grass/water slurries to nitrite, which, in the presence of the lactic acid produced in simultaneous fermentation, is partially converted into nitric oxide. The initial reduction is brought about by strains of Escherichia coli (Bact. coli) and it has been further noted that ascorbic acid, normally undergoing 60% decomposition, is destroyed more rapidly and to a greater extent if nitrate is present in the fermenting mixture.

The bleaching of carotene by a lipoxidase-linoleate system.

Abstract: A system for studying the coupled oxidation of carotene by lipoxidase and similar fatty acid oxidases is described. The experimental characteristics of the system are illustrated, and particular attention is paid to the effect of pH on the observed reaction velocities. The system presents certain advantages over previous systems of a similar nature.