Hake Muscle Altered by Frozen Storage as Affected by Added Ingredients

The effect of three ingredients (triphosphate, lecithin and sucrose ester) on functionality and extractability of hake muscle proteins that had been intensely aggregated by frozen storage was investigated. Muscle proteins were extracted in 0.6M NaCl, 2% sodium dodecyl sulfate (SDS) and 2% SDS+5% (β-mercaptoethanol (ME). Treatment with the added ingredients increased the amount of protein extracted when secondary interactions were broken with SDS. The same effect, although less pronounced, was found in the lots treated with triphosphate and sucrose ester when electrostatic bonds were broken with NaCl. The amphipathic ingredients (lecithin and sucrose ester) increased the amount of protein linked by nondisulfide covalent bonds.     

Influence of ultrasound on mass transport during cheese brining

 The effect of ultrasound on mass transfer during cheese brining has been investigated. The rate of water removal and NaCl gain increased when ultrasound was applied in comparison with brining performed under static or dynamic conditions, suggesting that ultrasound improves both external and internal mass transfer. A simple diffusional model was developed to simulate mass transport during acoustic brining. Model parameters were estimated using experimental data from acoustic brining experiments carried out on cheese cylinders of 1.7×10^–2m radius and 3×10^–2 m height at different temperatures (5, 15 and 20  °C). Effective water (D _W) and NaCl (D _S) diffusivities estimated using the proposed model ranged from 5.0×10^–10m²/s and 8.0×10^–10 m²/s at 5  °C to 1.3×10^–9m²/s and 1.2×10^–9 m²/s at 20  °C. Both D _W and D _S varied with temperature according to the Arrhenius equation. Through the proposed model, water losses and NaCl gains of the experiments used in the parameter identification were accurately simulated (average %var=98.2%) and also of two additional acoustic experiments carried out under different conditions of temperature (10  °C) and sample size and geometry [parallelepiped of (6×2.5×1.25)×10^–2 m] to those used in the parameter identification (average %var=98.4%). Received: 22 September 1998 / Revised version: 20 November 1998     

Effect of curing and pre-storage dip treatments on the control of storage mould of kola nuts

 The effect of curing kola nuts at 30  °C was evaluated at the Cocoa Research Institute of Nigeria, Ibadan, to determine the effect of curing time and delay between inoculation and initiation of curing on storage rot. For nuts inoculated 24 h prior to curing, 48–72 h curing at 30  °C gave optimal disease control. The incidence of rot was higher when the treatment was delayed for 48 h after inoculation. When artificially wounded and inoculated kola nuts were dipped in a solution of 1.0 g l^–1 of sodium bicarbonate for 2 mins, disease development was significantly reduced compared to the 0.5% sodium hypochorite treatment. Sodium metabisulphite also reduced disease development but the level of disease control achieved was not significantly different from that of the water-dipped controls. The in vivo results were consistent with the in vitro results. Received: 15 April 1998     

Effect of curing and pre-storage dip treatments on the control of storage mould of kola nuts

 The effect of curing kola nuts at 30  °C was evaluated at the Cocoa Research Institute of Nigeria, Ibadan, to determine the effect of curing time and delay between inoculation and initiation of curing on storage rot. For nuts inoculated 24 h prior to curing, 48–72 h curing at 30  °C gave optimal disease control. The incidence of rot was higher when the treatment was delayed for 48 h after inoculation. When artificially wounded and inoculated kola nuts were dipped in a solution of 1.0 g l^–1 of sodium bicarbonate for 2 mins, disease development was significantly reduced compared to the 0.5% sodium hypochorite treatment. Sodium metabisulphite also reduced disease development but the level of disease control achieved was not significantly different from that of the water-dipped controls. The in vivo results were consistent with the in vitro results.     

Quality of cauliflower as influenced by film wrapping during shipment

 Throughout the season, 'Siria' cauliflower heads from three harvesting periods were film-wrapped and stored for 1 week at 1.5  °C to simulate a maximum period of commercial shipment. After cold storage, the heads were kept for 2.5 days at 20  °C to simulate a retail sale period. Different polymeric films – polyvinyl chloride (PVC) of 14 μm thickness, low-density polyethylene (LDPE) of 11, 15 and 20 μm thicknesses and a special LDPE of 11 μm thickness adapted for microwave ovenuse – were used for wrapping. Soluble solid content, pH, titratable acidity, weight loss, physiological disorders, fungal attacks, visual quality and gas composition within packages were monitored. After the shelf life simulation, among the LDPE films studied, the best results were obtained by using 11 μm LDPE. Gas composition (about 16% O₂ and 2% CO₂ during cold storage, and about 11% O₂ and 3.5% CO₂ during retail sale simulation), overall quality, yellowing and browning of the head, and Alternaria spp. development were at similar levels among the films studied. However, weight loss was considerably lower for all LDPE films than for PVC film. For commercial purposes 11 μm LDPE could be a good alternative to PVC for wrapping cauliflower. Received: 30 October 1998 / Revised version: 18 January 1999     

Effect of dietary levels of fat, α-tocopherol and astaxanthin on colour and lipid oxidation during storage of frozen rainbow trout (Oncorhynchus mykiss) and during chill storage of smoked trout

 Female rainbow trout (Oncorhynchus mykiss) with an initial weight of 0.8–0.9 kg were raised in two experiments including a total of 2550 fish divided into 17 groups. The fish were raised for 6 months on 13 different feeds (four fish groups were replicates) varying in dietary levels of fat (27% or 32%), astaxanthin (40, 70 or 100 mg astaxanthin/kg feed) and vitamin E (α-tocopherol; 100, 300 or 600 mg all-rac-α-tocopheryl acetate/kg feed). The levels of fat, astaxanthin and α-tocopherol in the fillets all increased with increasing dietary levels of each feed component. Furthermore, astaxanthin deposition was found to be significantly improved by increasing the dietary fat level from 27% to 32%, but was not affected by dietary levels of α-tocopherol. The highest deposition of α-tocopherol was found in fish fed the lowest level of astaxanthin (40 mg/kg), whereas α-tocopherol deposition was unaffected by the dietary fat level. Frozen storage (–28  °C) of gutted, cleaned and glazed raw fish for 18 months significantly reduced astaxanthin and α-tocopherol levels, while lipid oxidation, measured as thiobarbituric acid reactive substances (TBARS) was limited. In the first experiment, the highest TBARS levels were found during frozen storage in fish fed the lowest level of astaxanthin (40 mg/kg versus 70 mg/kg or 100 mg/kg); unaffected by dietary levels of α-tocopherol (100 mg/kg versus 600 mg/kg), whereas the dietary astaxanthin level (70 mg/kg versus 100 mg/kg) did not influence lipid oxidation in frozen fish in the second experiment. After brine injection, fillets of fish were smoked and a vacuum-packed (95%), sliced product in a transparent laminate was produced. The quality (pigmentation and lipid oxidation) during 3 weeks of illuminated, chill storage (3  °C) was compared for smoked products produced from fresh fish and from fish stored at –28  °C for 12 months and 18 months. Smoked fillets from fish fed 32% fat were found to be less red than those from fish fed 27% fat, and the astaxanthin content and surface redness of the smoked product decreased during chill storage. Lipid oxidation was pronounced in smoked trout, but a high level of α-tocopherol in the fillet significantly reduced lipid oxidation during chill storage of the smoked product. Lipid oxidation in smoked fillets from fish fed 32% fat was more pronounced than in fish fed 27% fat, but increasing the dietary α-tocopherol level from 300 mg/kg feed to 600 mg/kg feed effectively counteracted the negative effect of the high-fat diet on lipid oxidation in the smoked product. Astaxanthin did not affect lipid oxidation in the chill-stored smoked product, in contrast to the frozen, raw fish. Astaxanthin seems to protect against the very early stages of lipid oxidation, while α-tocopherol is more important as an antioxidant at more advanced stages of lipid oxidation. Received: 8 January 1998 / Revised version: 23 March 1998     

The effects of fermentation on the thermostability of the yellow-orange pigments extracted from cactus pear (Opuntia ficus-indica)

 Cactus pear (Opuntia ficus-indica) juice with a total soluble solids content of 15.94 °Brix was fermented using the wine yeast Saccharomyces cerevisiae. A 94.54% conversion of fermentable sugar was achieved with an ethanol production of 55.3 ml/l. The pigment degradation was found to be 17% at the end of the time allowed for fermentation. However, the fermentation had actually ceased due to depletion of fermentable sugars after 12 h, a point at which only 9.4% pigment degradation was observed and there was no further total soluble solids degradation. The thermal stability of the yellow-orange pigment of the fermented juice was determined as a function of temperature at pH 5.0. The kinetic experiments were carried out at three different temperatures, 50, 70 and 90  °C. For a pseudo-first order thermal degradation rate the reaction rate constants were determined to be 0.0066, 0.0206 and 0.1244 min^–1 for temperatures of 50, 75 and 90  °C, respectively. The activation energy was calculated as 15.71 kcal mole^–1. The fermentation process did not affect the thermostability of the pigment extract. Received: 10 January 2000 / Revised version: 31 March 2000     

Fatty acids of a salami-type sausage made of Baltic herring fillets, pork and lard

 The fatty acid composition of "fish wurst", a fermented salami-type sausage made of pork, lard and Baltic herring fillets (Clupea harengus var. membras) was investigated. Changes in the proportions of the 35 most abundant fatty acids were examined throughout the 1-month ripening period followed by a 4-month storage period. The fat composition of the product was stable (32–35%) and retained the characteristics of the main ingredients: oleic acid (37.4%, mean of three production batches) palmitic acid (23.7%) and linoleic acid (10.7%) from lard and fish, stearic acid (11.7%) mainly from lard, and palmitoleic acid (3.0%) and long-chain (C20–C24), polyunsaturated fatty acids (c.a. 6%) mainly from fish. During the 4-week ripening period a statistically significant increase (P≤0.05) was detected in the proportions of minor fatty acids only, i.e. eicosenoic acid (20 : 1n-9), eicosadienoic acid (20 : 2n-6), docosadienoic acid (22 : 2n-6) and docosatrienoic acid (22 : 3n-3). During the 4-month storage of the ripe sausage, the fatty acid composition stabilized. Only the proportion of stearic acid increased significantly during storage, from 11.7% to 12.5%. Received: 23 January 1998 / Revised version: 1 April 1998     

Multielement analysis of Chinese tea (Camellia sinensis) by total-reflection X-ray fluorescence

 Total-reflection X–ray fluorescence (TXRF) was used for the simultaneous determination of 15 elements in tea samples which were produced either by acid digestion or acidified infusion of tea leaves (Camellia sinensis). The accuracy and precision of the method were checked by its application to a certified reference material (GBW 08505 : tea). A variety of 39 tea samples of different kinds and/or qualities produced in different regions of China were analysed. The range and mean of the concentrations of elements in the tea leaves (0.1–30.000 μg g^–1) and their solubility in infusions (0.5–85%) were determined and the influence of the origin, type and quality of the tea samples was studied. In some tea leaves produced in a Se-rich region, the content of Se was found to be very high (up to 7.5 μg g^–1), in contrast to a concentration of only about 0.1 μg g^–1 Se in most of the tea leaves examined. Received: 27 January 1998     

Lipid oxidation in high-pressure processed chicken breast muscle during chill storage: critical working pressure in relation to oxidation mechanism

 The oxidative stability of chicken breast muscle subjected to high-pressure treatment at 300, 400, 500, 600, 700 or 800 MPa for 5 min or 10 min, or to heat treatment (80  °C for 10 min) and subsequent storage at 5  °C was evaluated over a 2-week period. Lipid oxidation in pressure-treated chicken breast muscle monitored as formation of thiobarbituric acid reactive substances depended to a high degree on the working pressure and less on the pressurizing time. The pressure treatment at 800 MPa for 10 min was found to enhance lipid oxidation to the same extent as the heat treatment. Pressure treatment at 600 MPa and 700 MPa resulted in less oxidation. Chicken breast muscle exposed to pressure at or below 500 MPa showed no indication of rancidity, similar to what was found for untreated meat during chill storage; accordingly 500 MPa is a critical pressure for pressure treatment of chicken breast muscle. Analysis of non-heme iron in pressure-treated chicken breast muscle revealed that the notable increase in lipid oxidation caused by high pressure above 500 MPa did not result from the release of iron ions during high-pressure treatment. Furthermore, no influence of high-pressure treatment on the catalytic activity of metmyoglobin on lipid oxidation was observed in a model system, and it is concluded that increased lipid oxidation is probably related to membrane damage. Received: 23 August 1999     

Fatty acids of a salami-type sausage made of Baltic herring fillets, pork and lard

 The fatty acid composition of "fish wurst", a fermented salami-type sausage made of pork, lard and Baltic herring fillets (Clupea harengus var. membras) was investigated. Changes in the proportions of the 35 most abundant fatty acids were examined throughout the 1-month ripening period followed by a 4-month storage period. The fat composition of the product was stable (32–35%) and retained the characteristics of the main ingredients: oleic acid (37.4%, mean of three production batches) palmitic acid (23.7%) and linoleic acid (10.7%) from lard and fish, stearic acid (11.7%) mainly from lard, and palmitoleic acid (3.0%) and long-chain (C20–C24), polyunsaturated fatty acids (c.a. 6%) mainly from fish. During the 4-week ripening period a statistically significant increase (P≤0.05) was detected in the proportions of minor fatty acids only, i.e. eicosenoic acid (20 : 1n-9), eicosadienoic acid (20 : 2n-6), docosadienoic acid (22 : 2n-6) and docosatrienoic acid (22 : 3n-3). During the 4-month storage of the ripe sausage, the fatty acid composition stabilized. Only the proportion of stearic acid increased significantly during storage, from 11.7% to 12.5%. Received: 23 January 1998 / Revised version: 1 April 1998     

Use of β-hydroxyacyl-CoA-dehydrogenase (HADH) activity to differentiate frozen from unfrozen fish and shellfish

 Further work on an enzymic method to differentiate frozen from unfrozen fish and shellfish is reported. The method is based on the release of the β-hydroxyacyl-CoA-dehydrogenase (HADH) from mitochondria during freezing. Enzymic activity was evaluated in fresh and frozen thawed samples from sole (Solea solea), sea bream (Pagellus centrodontus), hake (Merluccius merluccius), gilt headed bream (Sparus aurata), sea bass (Dicentrarchus labrax), salmon (Salmo salar), prawn (Penaeus japonicus) and Norwegian lobster (Nephrops norvegicus). Changes in the HADH activity of fresh and frozen thawed samples were compared after freezing at –196  °C for 15 min. Two values were obtained: U (by dividing: HADH activity of samples frozen at –196  °C, then thawed/HADH activity of unfrozen samples) and F (by dividing: HADH activity of samples frozen at –18  °C, thawed, then frozen at –196  °C /HADH activity of samples frozen at –18  °C, then thawed). Statistical analysis showed significant differences (P≤0.05) between both quotients for gilt headed bream, salmon, sea bream, sole and prawn, and an arbitrary limit was set at 2 to differentiate frozen thawed from unfrozen samples. The application of this limit made it possible to discriminate the unfrozen from the frozen thawed state of around 90% of the total samples analysed. Best results were obtained for prawn (100% of samples differentiated). In the present paper, a laboratory routine is proposed based on the comparison of the HADH activity of a sample analysed straight away and that of a sample frozen at –196  °C and then thawed. The reported method is simple and fast. The entire laboratory procedure can be performed in 45 min. Received: 20 July 1998 / Revised version: 2 November 1998     

Optimization of stepwise blanching of frozen-thawed potato tissues (cv. Monalisa)

 Response surface methodology was used to compare the effect of temperature and time of the first step of blanching on compression, shear, tension and stress-relaxation parameters of frozen-thawed potato tissues. A central, composite rotatable design was used to study the effects of variation in levels of temperature (52.93–67.07  °C) and time (15.86–44.14 min) on rheological parameters. Blanching temperature was the most important factor affecting the mechanical properties tested. The models fitted for the apparent modulus of elasticity in compression, maximum tension force, and relaxed force in the first cycle (F _r1); all had R ²>0.85 (P≤0.01) and were used for doing predictions. Optimum conditions were with in the ranges of temperature (60–65  °C) and time (25–35 min) used for each factor. In the experimental verification of the models at 65  °C during 30 min, the lowest percentage residual between experimental and predicted values was obtained for F _r1 (0.644), which was therefore the most appropiate parameter for detecting the firming effect that the pectinesterase activity produced on frozen potato tissues as a consequence of stepwise blanching under these conditions. Received: 3 February 1999 / Revised version: 12 April 1999     

Freeze- and bake-stable glazing for confectionery products characterized by differential scanning calorimetry

 A freeze- and bake-stable glazing for pastry has been developed based on an optimization procedure in which starches and carrageenans as thickening agents were combined with sugar alcohols and sodium tripolyphosphate. Instrumental gloss measurement on test biscuits showed that glazing consisting of 3% ι-carrageenan and 15% sorbitol (w/w) had maximal gloss. This was confirmed on pastry products. In contrast to glazing based on mannitol, no crystallization problems were encountered for this glazing, for which differential scanning calorimetry showed that some water freezes at –3  °C followed by freezing of supercooled encapsulated water at –20  °C and by a glass transition at –61  °C. During normal frozen storage of preglazed, nonbaked pastry, the glazing is thus in a nonstable rubbery state with a limited resistance to water migration and ice crystal formation, which can be substantially improved by storage at temperatures below –61  °C. Received: 1 March 1999 / Revised version: 19 April 1999     

Kinetics of green asparagus ascorbic acid heated in a high-temperature thermoresistometer

 Thermal degradation of green asparagus ascorbic acid in high-temperature short-time conditions was studied by heating in a five-channel computer-controlled thermoresistometer. Ascorbic acid was heated to between 110  °C and 140  °C and the degradation kinetics were analyzed assuming that two different inactivation mechanisms were occurring, one aerobic and the other anaerobic. The two reactions followed first-order kinetics, with E _a=12.3(2.0) kcal/mol and k _125  °C=47.0(3.0)×10^–3 s^–1 for the aerobic oxidation, and E _a=6.1(1.4) kcal/mol and k _125  °C=4.1(0.2)×10^–3 s^–1 for the anaerobic degradation. Received: 30 January 1998 / Revised version: 11 June 1998     

Effect of Treating of Squid with Sodium Chloride in Combination with Oxidising Agent on Bleaching,Physical and Chemical Changes During Frozen Storage

Pink discolouration is a problem faced in the squid processing industry, and some treatments have been implemented to tackle such a problem. The study aimed to elucidate the impact of NaCl in combination with oxidising agents on the quality changes of squid during frozen storage. The effects of treatment of pink squid using 3% (w/v) NaCl solution containing oxidising agents (0.05–0.5% (w/v) H₂O₂ or 0–10 ppm NaOCl) on colour and chemical and physical changes of squid during frozen storage were investigated. The lowest decreases in a*, b* values, ∆E* and ∆C* of squid were obtained with the treatment using 3% NaCl solution containing 0.5% H₂O₂. Nevertheless, NaOCl (0–10 ppm) had no impact on a* and b* values. During frozen storage at −18 °C for 10 weeks, fresh squid, pink squid samples without and with treatments with 3% NaCl solution containing 0.5% H₂O₂ had no changes in a* and b* values during frozen storage. Nevertheless, thiobarbituric acid reactive substances value, disulphide bond content, thaw drip and shear force were more pronounced in treated pink squid, compared with pink squid without treatment (control) and fresh squid, respectively, during the extended storage (p < 0.05). Higher denaturation and aggregation of muscle proteins during frozen storage were observed in treated pink squid than that without treatment and fresh squid, respectively. Therefore, pink squid treated with oxidising agent was prone to protein aggregation and denaturation during the extended frozen storage, though it could lower the pink colour. Therefore, fresh squid without treatment using oxidising agent is recommended for production of frozen squid with negligible loss in quality during extended storage.     

Photodegradation kinetics of acesulfame-K solutions under UV light: effect of pH

 The objective of this research was to study the effect of pH on the photodegradation of aqueous solutions of 5×10^–5 M acesulfame-K (λ_max, 226 nm;ε, 11 400 mol^–1 L cm^–1). Photodegradation followed first-order kinetics and was found to be pH-dependent. The degradation rate constant was calculated to be 6.7×10^–2 min^–1, 4.5×10^–2 min^–1, 3.4×10^–2 min^–1 and 17.4×10^–2 min^–1, respectively, at pH 3, pH 9 and pH 12. Received: 21 April 1998 / Revised version: 9 June 1998     

Response surfaces for solubility of crude soylecithin lipid in super critical carbon dioxide

 The solubility of soy lecithin lipids in supercritical CO₂ was measured at pressures of 120, 200 and 280 bar and at temperatures of 40, 50 and 60  °C. The effects of temperature and pressure on the solubility of total lipids were studied by response surface methodology. The response surface equation to predict the solubility of total lipids in the above range of pressure and temperature is: Y=–3.237+0.0431* P–7.3×10^–5 P ²–0.00011 P*T where Y is the total lipid solubility in g/kg CO₂, P is the pressure in bar and T is the temperature in   °C. The total lipids solubility increased with pressure at constant temperature, but decreased with increasing temperature. The total lipids consisted of a very small phospholipid content compared to neutral lipids and glycolipids at all the pressures and temperatures studied. Optimum search indicated a maximum solubility of total lipids of 1.829 g/kg CO₂ at 263 bar and 40  °C. Received: 1 April 1999     

Bound sulphadimidine residues in raw fermented sausage: release under acidic conditions and bioavailability in rats

 Sulphadimidine (SDM), a drug frequently administered to pigs, is partially converted into other compounds by processing meat to produce raw, fermented sausage. With the aid of ¹⁴C-labelled SDM, evidence was obtained that part of the radioactive matter was covalently bound to the matrix. Part of these bound residues could be released in vitro by 4 M HCl at 21  °C or by 0.024 M HCl at 37  °C. Female rats were also able to release bound SDM residues and to excrete these in their urine, in amounts approaching those obtained by treatment with 4 M HCl. Both the parent compound and its main metabolite, N ⁴-acetyl-SDM, were observed in the urine of rats. Received: 29 December 1997 / Revised version: 20 February 1998     

Applicability of lactic acid and nisin to improve the microbiological quality of cold-smoked rainbow trout

 The effect of lactic acid and nisin whey permeate on the microbiological and sensory quality of cold-smoked rainbow trout was studied. Lactic acid and whey permeate were mixed with salt solution and injected into fish fillets in concentrations of up to 2.5 g/kg lactic acid, 30 g/kg whey permeate and 20 g/kg sodium chloride. After smoking at 28  °C for 6 h the fillets were sliced, vacuum packed and stored at 3  °C. The aerobic and anaerobic/facultative anaerobic counts were measured after 1, 8, 15, 22 and 29 days of storage. The influence of the treatment on the sensory characteristics was analysed after 8 and 22 days by sensory profiling. A triangle test was used in order to ascertain at which stage the sensory quality of the samples changed during storage. Bacterial counts of smoked fish stored for 29 days were lowest in those samples containing a combination of lactic acid, sodium chloride and nisin whey permeate. Lactic acid alone did not affect the odour or flavour characteristics of the fish but did affect their texture as determined by sensory evaluation making it less elastic when stored at +3  °C for 8 days. A combination of lactic acid and nisin whey permeate enhanced the characteristic fishy flavour of the product. Differences between treatments in elasticity and fishy flavour were not detected after 22 days of storage. According to the triangle test, the samples from all treatments remained unchanged over the first 15 days. Received: 23 March 1998 / Revised version: 19 June 1998