K.D.Anthony Taylor

The improved whitening of minced cod flesh using dispersed titanium dioxide

A simple effective method of whitening fish mince using titanium dioxide has been developed. The whitener comprised a dispersed titanium dioxide (TiO 2 ) suspension stabilised with xanthan gum (20 g TiO 2 /1 g xanthan gum/79 ml water) which produced significant whitening of fish mince derived from cod waste. The whitener was incorporated during the mixing stage of conventional fish mince manufacture, and achieved an even spread of coloration. The whitened fish mince was found to be stable to high temperature cooking systems, such as frying. Taste and texture of the fish mince were not affected by the level of xanthan gum and TiO 2 used. Xanthan gum and TiO 2 were sufficiently heat stable and inert with respect to taste, odour and chemical reactivity, to be suitable for use for such a purpose, unlike other compounds investigated and conventional dispersed fat/oil whiteners. A level of 1 g kg -1 of TiO 2 in the fish mince was found to give optimal level.

Methods of extraction composition and stability of vitamin A and other components in dogfish (Squalus acanthias) liver oil

Oil was extracted from dog fish (Squalus acanthias) livers by the Bligh and Dyer, Soxhlet and steaming extraction methods. Oil yields using the steaming method (22% ww) were lower than from the solvent extraction methods (68% ww). The vitamin A content of the oil produced by steaming was 54 mg retinol/100 g oil, and slightly higher (62–68 mg/100 g) contents were recorded in the solvent extracted oils. The Bligh and Dyer extraction produced an oil containing 12% phospholipid, much higher than the 4% via the Soxhlet and 1 % in the steaming extractions. The level of squalene (40 mg/100 g) in the oil produced by steaming was higher than in the other oils (28 and 32 mg). Concentrations of vitamin E and cholesterol were similar in all three oils at approximately 25 mg tocopherol/100 g and 1.1 g cholesterol/100 g, respectively. Oils were stored under air at room temperature in half filled dark coloured bottles. Although highest PVs were observed in the stored Bligh and Dyer-extracted oils, the highest apparent loss of vitamin A (30% in 3 weeks) occurred in the oil extracted by steaming.

The improved whitening of cod and haddock flaps using hydrogen peroxide

Fish mince, derived from cod or haddock flaps, was successfully whitened by pre-treating flaps prior to separation with an aqueous solution (5–8 gl−1) of hydrogen peroxide. Soaking in H2O2 reduced the superficial blood discoloration of flaps and subsequently improved the colour of recovered mince after separation. Objective textural analysis (texture profile analysis) using a texture analyser, did not reveal any additional damage to the texture of the mince derived from treated flaps. Sensory evaluation of control and whitened fish mince showed no difference in taste or odour, immediately after treatment or after 8 months cold storage. No residual H2O2 was detected in the samples after treatment, using a membrane oxygen electrode determination method (detection limit 3 µg g−1). Treatment of flaps with 8 gl−1 aqueous solution of hydrogen peroxide for 90 min also reduced significantly the total viable count of bacteria (mesophilic aerobes).

Assessment of quality of cod roes and relationship between quality and maturity stage

Cod roe landings are subject to great variability regarding their quality and subsequent price for the food industry. A scheme was developed for the classification of cod roe into four quality grades (A, B, C and D) based on appearance and texture attributes as described by cod roe traders. Evaluation of the maturity stage of 80 commercial cod ovaries through the frequency distribution of oocyte diameter and the percentage presence of empty follicular sacks revealed that cod ovaries with commercial value are at stage 4 (ripe or vitellogenic), stage 5 (spawning) and stage 6 (spent) of development. The designated maturity stages were found to be closely related to the described quality grades. This relationship implied that vitellogenic ovaries (stages 4a, 4b and 4c) were of A quality, early spawning ovaries (stage 5a) were most often classed as B quality, advanced and late spawning ovaries (stage 5b and 5c) were of C quality, whilst spent ovaries (stage 6) were of the lowest quality grade (D). Several physicochemical characteristics recorded (eg pH, membrane features) were also found to be related to the quality and the maturity stage of the ovaries. There is a significant relationship between roe quality and moisture content, with roes of higher quality having a lower moisture content.

Extraction and purification of hyaluronoglucosidase (EC 3.2.1.35) from Norway lobster (Nephrops norvegicus)

Abstract The waste of Norway lobster (Nephrops norvegicus also known as Dublin Bay prawn and scampi) constitutes 75–80% of the whole animal by weight. This includes the hepatopancreas which is a good source of hyaluronoglucosidase (EC 3.2.1.35), commonly referred to as hyaluronidase. This enzyme was partially purified by acetone fractionation, ion-exchange column chromatography on a Type-I polystyrene-based anion-exchange resin, Amberlite™ IRA 420 and subsequently by gel filtration on Sephadex™ G-200. The anion-exchange step of the purification was optimised by including a wash with 10 mM sodium acetate buffer containing 12.5 mM NaCl after loading the column with the enzyme preparation. This was followed by gradient elution with 12.5–500 mM NaCl in 500 ml of the same buffer. The gel filtration step was optimised using Sephacryl™ S-200-HR gel filtration medium. As a result of these modifications to the purification process a 763-fold purification was achieved, with 32% of the enzyme from the original crude extract in 0.25 M sucrose solution being recovered. A loss of 41% of the enzyme activity was recorded during acetone fractionation and 34% during gel filtration. However, recovery from the anion-exchange step using Amberlite™ IRA 420 was as high as 81%. A sample of the purified extract was subjected to native polyacrylamide gel electrophoresis with PhastGel™ Gradient 10-15 using PhastGel Native Buffer Strips which indicated the presence of three proteins.

Studies on the roles and identification of the small molecule factors on phenolase activation in Norway lobster (Nephrops norvegiens)

The direct effect of small molecule factor(s) on the activation of phenolase in the suggested multiple component process of blackspot development in Norway lobster (Nephrops norvegicus) was studied. When acetone-precipitated phenolase was treated with the small molecule filtrate, the phenolase activation profile was lower compared to the control, particularly at pH 6.7. However, when purified form I phenolase was treated with small molecule filtrate no activation was observed, the assayed phenolase activity being constant but lower than the control. A similar effect was observed when form I phenolase was treated with 1.5 mM dihydroxyphenylalanine (DOPA) (approximately the concentration found in the small molecule filtrate), indicating that this lower pattern resulted from the competition of the phenolase substrates (catechol, DOPA, and possibly tyrosine) in the small molecule filtrate. When the activity of the three proteases in the acetone-precipitated phenolase was studied, it was found that there was a high recovery of proteases I and II in the precipitate but little protease III. This also confirms that the effect of the small molecule filtrate on phenolase activity in acetone-precipitated phenolase was due to its indirect effect on the proteases present. The modification of the compounds that absorb at 270 nm was studied by a high-performance liquid chromatographic (HPLC) separation method and the quantitative analysis of tyrosine and DOPA in the small molecule filtrate was achieved. Some of the small molecules were identified, by an HPLC method, as tyrosine, DOPA, oxidised DOPA, vitamin C in oxidised form or breakdown product of vitamin C. Oxidised DOPA, DOPA, tyrosine and N-acetyldopamine inhibit the proteases to varying degrees. Vitamin C also inhibits all three proteases at pH 6.4; however, at pH 8.2 it markedly activates protease III and slightly activates the two thiol proteases (I and II).

Studies on the influence of small molecule factor(s) on protease activities in Norway lobster (Nephrops norvegicus)

The interactions of small molecule(s) and proteases in the suggested multiple component process of phenolase activation in Norway lobster (Nephrops norvegicus) were studied. It was observed that protease I is mainly a visceral protease, whilst proteases II and III exist in approximately equal amounts in viscera and flesh, respectively. It was found that the small molecule factor(s) (molecular weight less than 10 000) inhibited proteases I, II and III at pH 6.7 and 8.2, except when it was freshly prepared and then it activated only protease III and only at pH 8.2. This indicates that the small molecule(s) may be modified on storage. It was found that the small molecule factor(s) is primarily water-soluble and heat-stable, with heating resulting in a similar change to storage in its effect on proteases. Treatment of the small molecule filtrate with a cation-exchanger also increased the inhibition effect on proteases. However, whilst treatment with an anion-exchanger at pH 8.2 reduced inhibition, treatment at pH 4.0 restored activation of protease III. These results also infer that the small molecule factor(s) is modified on storage or exists in two forms.