Comparative study of physical and sensory properties of pre-treated potato slices during vacuum and atmospheric frying

The objective of this research was to study the effect of different processing conditions on physical and sensory properties of potato chips. Potato slices of Desirée and Panda varieties (diameter: 30 mm; thickness: 3 mm) were pre-treated in the following ways: (i) control or unblanched slices without pre-drying; (ii) blanched slices in hot water at 85 °C for 3.5 min and air-dried at 60 °C until a final moisture content of ∼0.6 kg water/kg dry solid; (iii) control slices soaked in a 3.5 kg/m³ sodium metabisulphite solution at 20 °C for 3 min and pH adjusted to 3. Pre-treated slices were fried at 120 and 140 °C under vacuum conditions (5.37 kPa, absolute pressure) and under atmospheric pressure until they reached a final moisture content of ∼1.8 kg water/100 kg (wet basis). An experimental design (3 × 2³) was used to analyze the effect of pre-treatment, potato variety, type of frying and frying temperature over the following responses: oil content, instrumental color and texture and sensory evaluation. Vacuum frying increased significantly (p < 0.05) oil content and decreased instrumental color and textural parameters. Sensory attributes, flavor quality and overall quality, were significantly improved using vacuum frying. The higher frying temperature (140 °C) increased ΔE, maximum breaking force, hardness and crispness and decreased L^* and b^* values. On the other hand, Panda potato variety improved the color of the product. A great improvement on color parameters was obtained using sulphited potato slices instead of the other pre-treatments. Although, the better flavor was obtained for control potato chips, no significant differences were found for overall quality between control and sulphited potato chips. Significant correlations (p < 0.01) between sensory and instrumental responses were found.     

Heating condition effects on thermal resistance of fifth-instar Amyelois transitella (Walker) (Lepidoptera: Pyralidae)

Successful development of a thermal treatment protocol depends on reliable information on fundamental thermal death kinetics of targeted insects under different heating conditions. The effects of heating rates (1, 10, and 15 °C min⁻¹), pre-treatment conditioning (30 °C+6 h), and the difference between long-term laboratory cultures and recently isolated cultures on thermal mortality of fifth-instar navel orangeworm, Amyelois transitella (Walker), were studied using a heating block system. There was no significant difference in insect mortality resulting from heating rates of 10 and 15 °C min⁻¹. Temperature control at 1 °C min⁻¹ was more uniform than for the other heating rates, resulting in reduced variability for insect mortality. The mean mortality at the heating rate of 1 °C min⁻¹ was significantly lower than for the two faster heating rates only at 48 °C+30 min. The pre-treatment conditioning of fifth-instar Amyelois transitella enhanced their thermotolerance only at certain temperature-time combinations. Fifth-instars from long-term laboratory and recently isolated cultures were equally susceptible to elevated temperatures. Therefore, thermal death kinetic information obtained from the long-term laboratory cultures can be used to develop thermal protocols against field pests.     

Attachment and biofilm formation by Escherichia coli O157:H7 at different temperatures, on various food-contact surfaces encountered in beef processing

Escherichia coli O157:H7 attached to beef-contact surfaces found in beef fabrication facilities may serve as a source of cross-contamination. This study evaluated E. coli O157:H7 attachment, survival and growth on food-contact surfaces under simulated beef processing conditions. Stainless steel and high-density polyethylene surfaces (2 × 5 cm) were individually suspended into each of three substrates inoculated (6 log CFU/ml or g) with E. coli O157:H7 (rifampicin-resistant, six-strain composite) and then incubated (168 h) statically at 4 or 15 °C. The three tested soiling substrates included sterile tryptic soy broth (TSB), unsterilized beef fat-lean tissue (1:1 [wt/wt]) homogenate (10% [wt/wt] with sterile distilled water) and unsterilized ground beef. Initial adherence/attachment of E. coli O157:H7 (0.9 to 2.9 log CFU/cm²) on stainless steel and high-density polyethylene was not affected by the type of food-contact surface but was greater (p < 0.05) through ground beef. Adherent and suspended E. coli O157:H7 counts increased during storage at 15 °C (168 h) by 2.2 to 5.4 log CFU/cm² and 1.0 to 2.8 log CFU/ml or g, respectively. At 4 °C (168 h), although pathogen levels decreased slightly in the substrates, numbers of adherent cells remained constant on coupons in ground beef (2.4 to 2.5 log CFU/cm²) and increased on coupons in TSB and fat-lean tissue homogenate by 0.9 to 1.0 and 1.7 to 2.0 log CFU/cm², respectively, suggesting further cell attachment. The results of this study indicate that E. coli O157:H7 attachment to beef-contact surfaces was influenced by the type of soiling substrate and temperature. Notably, attachment occurred not only at a temperature representative of beef fabrication areas during non-production hours (15 °C), but also during cold storage (4 °C) temperatures, thus, rendering the design of more effective sanitation programs necessary.     

Kinetics of oil uptake during frying of potato slices:: Effect of pre-treatments

Oil uptake in fresh, blanched and, blanched and dried potato slices was studied during frying. Potato slices blanched in hot water (85 °C, 3.5 min) and potato slices blanched (85 °C, 3.5 min) and then dried until to a moisture content of ∼60 g/100 g (wet basis) were deep fried in sunflower oil at 120, 150 and 180 °C. A control treatment consisted of unblanched potato slices without the pre-drying treatment (fresh samples). It was studied applying two empirical kinetic models in order to fit the oil uptake during frying: (i) a first order model; (ii) a proposed model, with a linear time behavior for short times, while time independent for long times. Oil uptake was high even for short frying times at the different temperatures tested suggesting that oil wetting is an important mechanism of oil uptake during frying. For control slices, oil uptake increased approximately by 32% as the frying temperature decreased from 180 to 120 °C at moisture contents ?1 g water/g dry solid. No apparent effect of frying temperature in oil uptake was observed at moisture contents ?0.5 g water/g dry solid in fried slices previously blanched and dried. The two kinetic models studied fitted properly the values of oil uptake during frying, with similar correlation coefficient r².     

Effects of light,temperature and water activity on the kinetics of lipoxidation in almond-based products

Lipoxidation in almond-derived products was investigated using the chemiluminescence (CL) and thiobarbituric acid-reactive substances (TBARS) methods to detect the first and later reaction products, respectively. The effects of light during storage at 5 °C, 22 °C and 40 °C were studied, as well as the effects of combined heat/water activity treatments in the 60–120 °C and 0.38–0.72 range. During storage, light was found to enhance the CL and TBARS values, and specific responses were observed in almond paste and the final Calisson product. During the heating of almond paste, as the initial water activity (a_w) increased, the CL rate constants increased during heating to 60 °C and 80 °C, but interestingly, these values decreased during further heating to 120 °C, whereas the maximum TBARS rate constants occurred at a_w 0.57 at all the heating temperatures tested. The activation energies, based on the CL and TBARS values, decreased specifically when the a_w increased from 0.38 to 0.72, giving overall values ranging from110 kJ mol⁻¹ to 60 kJ mol⁻¹. Likewise, in the same water activity range, the temperature-dependent rate constant enhancing factor (Q₁₀) decreased from 3.3 to 1.6.     

Influence of sugar composition on water sorption isotherms and on glass transition in apricots

Desorption isotherms of fresh and osmotically treated (70%, 30 °C) apricots have been measured at 30, 45 and 60 °C by the static gravimetric method. A differential scanning calorimeter was used to determine the T_g of samples equilibrated with several water activities. The osmotic pretreatment affected the shape of the desorption isotherms because of biopolymer binding at low activities values and dissolution of sucrose at high activities values. At 45 °C, isotherms of fresh and sucrose impregnated apricots are identical. At 60 °C, sucrose impregnation depressed water activity, while at 30 °C the opposite effect is observed. Evolution of moisture content at the first saturation layer expresses these effects of sucrose impregnation and temperature. Peleg model fitted the best experimental desorption isotherms of the fresh and osmotically treated apricots (0.990 ? r² ? 0.999, 0.005 ? S ? 0.045). A strong plasticizing effect of water on the T_g was found, with a great reduction in this value with increase in water activity.     

Thermal inactivation of Yersinia enterocolitica in pork slaughter plant scald tank water

The objective of this study was to establish the time–temperature combinations required to ensure the thermal inactivation of Yersinia enterocolitica during scalding of pork carcasses. A 2 strain cocktail of Y. enterocolitica (bioserotypes 2/O:5,27 and 1A/O:6,30) was heat treated at 50, 55 and 60 °C in samples of scald tank water obtained from a commercial pork slaughter plant. Samples were removed at regular intervals and surviving cells enumerated using (i) Cefsulodin–Irgasan–Novobiocin Agar (CIN) supplemented with ampicillin and arabinose and (ii) Tryptone Soya Agar (TSA), overlaid with CIN agar with ampicillin and arabinose. The data generated was used to estimate D- and z-values and the formula D_x = log^− 1(log D₆₀ − ((t₂ − t₁)/z)) was applied to calculate thermal death time–temperature combinations from 55 to 65 °C. D₅₀, D₅₅ and D₆₀-values of 45.9, 10.6 and 2.7 min were calculated from the cell counts obtained on CIN agar, respectively. The corresponding D-values calculated from the TSA/CIN counts were 45.1, 11 and 2.5 min, respectively. The z-value was 7.8. It was concluded that a time–temperature combination of 2.7 min at 60 °C is required to achieve a 1 log reduction in Y. enterocolitica in pork scald tank water. The predicted equivalent at 65 °C was 0.6 min. This study provides data and a model to enable pork processors to identify and apply parameters to limit the risk of carcass cross-contamination with Y. enterocolitica in pork carcass scald tanks.     

Valorisation of grape pomace by the extraction of phenolic antioxidants: Application of high voltage electrical discharges

The aim of this study was to optimise the electrically assisted extraction in order to obtain grape pomace extracts with high polyphenols content, which would be potentially interesting for applications as natural antioxidants. High voltage electrical discharges (HVED) were applied for intensification of the extraction. The effects of the energy input, the electrodes distance gap and the liquid-to-solid ratio were studied. Diffusion was then carried out in different mixtures of water and ethanol for one hour at 20, 30, 40 and 60 °C. The most efficient extraction was (i) an HVED pre-treatment at 80 kJ/kg with an electrodes distance of 5 mm in a liquid-to-solid ratio of 5 followed by (ii) a diffusion with 30% ethanol in water at 60 °C for 30 min. The highest total polyphenols content reached 2.8 ± 0.4 gGAE/100gDM with a corresponding antioxidant activity of 66.8 ± 3.1 gTEAC/kgDM. The polyphenols extraction rate increased with temperature in accordance to an Arrhenius type of relationship: activation energy of 21.5 ± 1.1 kJ/mol for HVED treated systems against 0.5 ± 0.2 kJ/mol for untreated ones.     

Extraction and quantification of major carotenoids in processed foods and supplements by liquid chromatography

A simple, fast and robust method with minimum steps, small sample size and amounts of solvents was developed to determine major carotenoids contents in processed foods, tablets and gel capsules. The method involves dispersion of the sample in hot water (60 °C) with added butylated hydroxytoluene (BHT) in ethanol to minimize oxidation, followed by extraction with chloroform and analysis by liquid chromatography. Chromatographic parameters were: a C30 column protected with a C18 guard cartridge; gradient elution at the rate of 1.0 mL/min starting with 100% methanol (A) and ending with 40:60 (v/v) methanol/isopropanol (B); detection set at 450 nm for carotenoids, and 325 nm for retinol, retinyl acetate and retinol palmitate. The method exhibited: (i) high degree of repeatability (%rsd); (ii) linear calibration curves (r² ? 0.9998); (iii) low detection; and quantification limits. The method was validated with standard reference material 2383 for trans-β-carotene; and tested for α-, and β-carotenes, lutein, zeaxanthin, cryptoxanthin, trans-retinol in processed foods, tablets and gel supplements.     

Effects of cooking methods and chemical tenderizers on survival of Escherichia coli O157:H7 in ground beef patties

This study evaluated chemical tenderizers and cooking methods to inactivate Escherichia coli O157:H7 in ground beef patties (model system for non-intact beef). Ground beef was inoculated with E. coli O157:H7 and mixed with (i) nothing (control), (ii) calcium chloride (CC) and flavoring agents (FA), (iii) CC, FA, and acetic acid (AA), (iv) sodium chloride (SC), sodium tripolyphosphate (ST), and potassium lactate (PL), and (v) the combination of SC, ST, PL, and AA. Patties were stored in aerobic or vacuum bags at − 20, 4, and 12 °C. Samples were grilled, broiled, or pan-fried to 60 or 65 °C. Total bacterial and E. coli O157:H7 populations remained unchanged during storage. Broiling was more effective in reducing E. coli O157:H7 than grilling and pan-frying, and acidified tenderizers reduced E. coli O157:H7 more than non-acidified tenderizers in broiling. Higher reductions were observed at 65 °C than 60 °C in broiled and grilled samples. These results indicate that acidified tenderizers and broiling may be useful in non-intact beef safety.     

Optimisation of ethanol modified supercritical carbon dioxide on the extract yield and antioxidant activity from Garcinia mangostana L.

Xanthones are an important class of secondary metabolites present in mangosteen fruit pericarp. Herein we have used supercritical fluid technology to extract the active constituents from mangosteen pericarp. Ethanol was added (5% w/w) as a co-solvent to increase the polarity of the CO₂, thus favouring the extraction of xanthones. The maximum extraction yield of 15 wt.% was achieved at a pressure of 280 bar, temperature of 50 °C and a time of 8 h, while without co-solvent the yield was 7.5 wt.%. Conditions for antioxidant activity as measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging assay was 280 bar at 50 °C and 5 h. Box–Behnken design was used to study the efficiency of extraction pressure (180, 280, and 380 bar), temperature (40, 50, and 60 °C) and time (2–8 h) on the total extraction yields and their radical scavenging activity. Experimental results of the total extract yield and radical scavenging activity were close to the predicted values calculated from the polynomial response surface models equations (R² = 0.99 and 0.98).     

Thermophysical properties and thermal behavior of leafy vegetables packaged in clamshells

Little is known about the thermophysical properties of fresh-cut lettuce other than heat of respiration. Empirical correlations based on food composition remain the only way to estimate the thermophysical properties of fresh-cut lettuce. The objectives of this study were (i) to determine the thermophysical properties of several baby-leaf lettuce and brassica greens and (ii) to verify the measured thermophysical properties by using them in a heat transfer model and comparing the predicted product temperatures with measured product temperatures in a simulated interruption of a cold chain. Density, leaf thickness, thermal conductivity, specific heat and water activity from nine varieties of baby-leaf lettuce and brassica greens were measured. A broken cold chain was simulated in a low temperature incubator set at 10 °C for a length of time before readjustment at 2 °C. Results showed that density (1078–1112 kg m⁻³), leaf thickness (0.18–0.54 mm), thermal conductivity (0.55–0.70 W (m °C)⁻¹) and specific heat (3.1–4.3 kJ (kg °C)⁻¹) varied significantly (P < 0.05) between varieties. However, no significant differences were observed for water activity (0.959 ± 0.006). Using thermophysical properties as input in the heat transfer model, experimental and calculated temperatures were well correlated (R² = 0.98) with a root mean square error of 0.57 °C over the 10–40 mg CO₂ (kg h)⁻¹ range of respiration rate. The measured thermophysical properties adequately predicted the temperature of the baby-leaf greens during simulated broken cold chains. A sensitivity analysis performed with the heat transfer model showed that the thermal conductivity, the specific heat and the density were relatively more important on the thermal behaviour of the baby-leaf greens than the heat of respiration.     

Strategy to inactivate Clostridium perfringens spores in meat products

The current study aimed to develop an inactivation strategy for Clostridium perfringens spores in meat through a combination of spore activation at low pressure (100–200 MPa, 7 min) and elevated temperature (80 °C, 10 min); spore germination at high temperatures (55, 60 or 65 °C); and inactivation of germinated spores with elevated temperatures (80 and 90 °C, 10 and 20 min) and high pressure (586 MPa, at 23 and 73 °C, 10 min). Low pressures (100–200 MPa) were insufficient to efficiently activate C. perfringens spores for germination. However, C. perfringens spores were efficiently activated with elevated temperature (80 °C, 10 min), and germinated at temperatures lethal for vegetative cells (≥55 °C) when incubated for 60 min with a mixture of l-asparagine and KCl (AK) in phosphate buffer (pH 7) and in poultry meat. Inactivation of spores (∼4 decimal reduction) in meat by elevated temperatures (80–90 °C for 20 min) required a long germination period (55 °C for 60 min). However, similar inactivation level was reached with shorter germination period (55 °C for 15 min) when spore contaminated-meat was treated with pressure-assisted thermal processing (568 MPa, 73 °C, 10 min). Therefore, the most efficient strategy to inactivate C. perfringens spores in poultry meat containing 50 mM AK consisted: (i) a primary heat treatment (80 °C, 10 min) to pasteurize and denature the meat proteins and to activate C. perfringens spores for germination; (ii) cooling of the product to 55 °C in about 20 min and further incubation at 55 °C for about 15 min for spore germination; and (iii) inactivation of germinated spores by pressure-assisted thermal processing (586 MPa at 73 °C for 10 min). Collectively, this study demonstrates the feasibility of an alternative and novel strategy to inactivate C. perfringens spores in meat products formulated with germinants specific for C. perfringens.     

Isolation of Alicyclobacillus and the influence of different growth parameters

Alicyclobacillus species are thermo-acidophilic, endospore-forming bacteria that are able to survive pasteurisation and have been implicated in a number of spoilage incidents involving acidic foods and beverages. The aim of this study was to compare three isolation methods used for the detection of Alicyclobacillus acidoterrestris and to investigate the influence of incubation temperature on the growth of A. acidoterrestris and A. acidocaldarius. Peach juice samples inoculated with A. acidoterrestris K47 were analysed using either the International Federation of Fruit Juice Producers (IFU) Method No. 12 (Method A), which involved spread plating onto Bacillus acidoterrestris (BAT) agar at pH 4.0; Method B, which involved pour plating using potato dextrose agar (PDA) at pH 3.7; or Method C, which made use of membrane filtration followed by incubation on K agar at pH 3.7. The performance of the three methods differed significantly, with the IFU Method No. 12 recovering the highest percentage of cells at 75.97%, followed by Method B at 66.79% and Method C at 3.43%. These findings strengthen the proposal of the IFU for the use of the IFU Method No. 12 as a standard international method for the detection of Alicyclobacillus. To investigate the effect on growth of different incubation temperatures A. acidoterrestris (three strains) and A. acidocaldarius (two strains) were incubated at either 45 °C or 25 °C. Growth at 25 °C was slower and maximum cell concentrations were lower (1 × 10⁵-10⁶ cfu/mL compared to 1 × 10⁷-10⁸ cfu/mL) than at 45 °C for A. acidoterrestris. A. acidocaldarius was unable to grow at 25 °C and cell concentrations decreased by 1-2 logs. Since a growth temperature of 25 °C could not inhibit growth of A. acidoterrestris, cooling to room temperature (20°-25 °C) is not an effective control measure for A. acidoterrestris inhibition.     

Modeling water loss and oil uptake during vacuum frying of pre-treated potato slices

The objective of this research was to determine the kinetics of water loss and oil uptake during frying of pre-treated potato slices under vacuum and atmospheric pressure. Potato slices (diameter: 30 mm; width: 3 mm) were pre-treated in the following ways: (i) raw potato slices “control”; (ii) control slices were blanched in hot water at 85 °C for 3.5 min; (iii) blanched slices were dried in hot air until reaching a moisture content of ∼0.6 g water/g dry basis. The slices were fried under vacuum (5.37 kPa, absolute pressure, at 120, 130 and 140 °C) and atmospheric conditions (at 180 °C). Two models based on the Fick's law were used to describe water loss: (i) with a constant effective diffusive coefficient; and (ii) with a variable effective diffusive coefficient. Oil uptake data were fitted to an empirical model, with a linear behavior for short times whereas the model was time independent for long times. The variable diffusivity model better fitted experimental water loss, giving values of effective diffusivity between 4.73 × 10⁻⁹ and 1.80 × 10⁻⁸ m²/s. The proposed model for the study of the kinetics of oil uptake fitted the experimental data properly. Control and blanched vacuum fried potato chips increased their final oil contents to 57.1% and 75.4% respectively, when compared with those fried at atmospheric pressure. However, the oil absorption of dried vacuum fried potato chips diminished by ∼30%.     

Effect of processing methods on the concentrations of bioactive components of ginseng (Panax ginseng C.A. Meyer) adventitious roots

Adventitious roots of Korean mountain ginseng (Panax ginseng C.A. Meyer) were processed by using forced air drying methodology at 30, 50 and 70 °C for 1, 3, 5, 10 and 20 h with objective of developing suitable processing/drying technique. Drying of adventitious roots at 50 °C for 10 h was found suitable as desirable moisture content (3.13 g water/dry matter i.e. 10%) could be reached with dried roots. Roots which were dried by such treatment were also possessing higher amount of ginsenosides (1.5 mg g⁻¹ DW triols, 15.9 mg g⁻¹ DW diols and 17.4 mg g⁻¹ DW of total ginsenosides) and phenolics. Adventitious roots were also processed by using far infrared and freeze drying methods and results revealed that forced air drying method is superior to far infrared and freeze drying methods.     

Optimisation of the aqueous extraction conditions of phenols from meadowsweet (Filipendula ulmaria L.) for incorporation into beverages

Meadowsweet was extracted in water at a range of temperatures (60–100 °C), and the total phenols, tannins, quercetin, salicylic acid content and colour were analysed. The extraction of total phenols followed pseudo first-order kinetics, the rate constant (k) increased from 0.09 ± 0.02 min⁻¹ to 0.44 ± 0.09 min⁻¹, as the temperature increased from 60 to 100 °C. An increase in temperature from 60 to 100 °C increased the concentration of total phenols extracted from 39 ± 2 to 63 ± 3 mg g⁻¹ gallic acid equivalents, although it did not significantly affect the proportion of tannin and non-tannin fractions. The extraction of quercetin and salicyclic acid from meadowsweet also followed pseudo first-order kinetics, the rate constant of both compounds increasing with an increase in temperature up until 90 °C. Therefore, the aqueous extraction of meadowsweet at temperatures at or above 90 °C for 15 min yields extracts high in phenols, which may be added to beverages.     

Modelling the effect of water immersion thermal processing on polyacetylene levels and instrumental colour of carrot disks

C₁₇ polyacetylenes are a group of bioactive compounds present in carrots which have recently gained scientific attention due to their cytotoxicity against cancer cells. In common with many bioactive compounds, their levels may be influenced by thermal processes, such as boiling or water immersion. This study investigated the effect of a number of water immersion time/temperature combinations on concentrations of these compounds and attempted to model the changes. Carrot samples were thermally treated by heating in water at temperatures from 50–100 °C and holding times of 2–60 min. Following heating, levels of falcarinol (FaOH), falcarindiol (FaDOH), falcarindiol-3-acetate (FaDOAc) and Hunter colour parameters (L^∗, a^∗, b^∗) were determined. FaOH, FaDOH, FaDOAc levels were significantly reduced at lower temperatures (50–60 °C). In contrast, samples heated at temperatures from 70–100 °C exhibited higher levels of polyacetylenes (p < 0.05) than did raw unprocessed samples. Regression modelling was used to model the effects of temperature and holding time on the levels of the variables measured. Temperature treatment and holding time were found to significantly affect the polyacetylene content of carrot disks. Predicted models were found to be significant (p < 0.05) with high coefficients of determination (R²).     

Scaled-up production of zero-trans margarine fat using pine nut oil and palm stearin

An interesterified structured lipid was produced with a lipid mixture (600 g) of pine nut oil (PN) and palm stearin (PS) at two weight ratios (PN:PS 40:60 and 30:70) using lipase (Lipozyme TL IM, 30 wt.%) as a catalyst at 65 ^°C for 24 h. Major fatty acids in the interesterified products were palmitic (35.1–40.4%), oleic (29.5%), and pinolenic acid (cis-5, cis-9, cis-12 18:3; 4.2–5.9%). α-Tocopherol (1.1–1.3 mg/100 g) and γ-tocopherol (0.3–0.4 mg/100 g) were detected in the interesterified products. Total phytosterols (campesterol, stigmasterol, and β-sitosterol) in the interesterified products (PN:PS 40:60 and 30:70) were 63.2 and 49.6 mg/100 g, respectively. Solid fat contents at 25 ^°C were 23.6% (PN:PS 40:60) and 36.2% (PN:PS 30:70). Mostly β′ crystal form was found in the interesterified products. Zero-trans margarine fat stock with desirable properties could be successfully produced from pine nut oil and palm stearin.     

Segregative interactions and competitive binding of Ca in gelling mixtures of whey protein isolate with Naκ-carrageenan

Gelling mixtures of Na⁺κ-carrageenan with whey protein isolate (WPI) at pH 7.0 have been studied rheologically and by differential scanning calorimetry (DSC), with comparative measurements for the individual constituents of the mixtures. The concentration of WPI was held fixed at 10.0 wt% and carrageenan concentration was varied in the range 0.05–3.0 wt%. Ca²⁺ cations, which have been shown previously to be particularly effective in inducing gelation of κ-carrageenan, were introduced as CaCl₂. The concentration of CaCl₂ used in most of the experiments was 8 mM, but other concentrations were also studied. Mixtures were prepared in the solution state at 45 °C, and showed no evidence of either phase separation or complex formation. Rheological changes were monitored by low-amplitude oscillatory measurements of storage modulus, G′, during (i) cooling (1 °C/min) and holding at 5 °C, to induce gelation of the carrageenan in the presence of non-gelled WPI; (ii) heating and holding at 80 °C to dissociate the carrageenan network and induce gelation of WPI; (iii) cooling and holding again at 5 °C, to give composite networks with both components gelled; and (iv) re-heating to 80 °C to dissociate the carrageenan network. Gel structure was characterised further by creep–recovery measurements at the end of each holding period, and by torsion measurements at 5 °C, before and after thermal gelation of WPI.