Chemical and quality traits of ‘Olinda’ and ‘Campbell’ oranges after heat treatment at 44 or 46 °C for fruit fly disinfestation

The chemical and quality characteristics of ‘Olinda’ and ‘Campbell’ oranges (nucellar budlines from Valencia late cultivar) were evaluated after exposure to a fruit core temperature of 44 °C and held at 44 °C for 100 min or 46 °C and held at 46 °C for 50 min, subsequent storage at 6 °C for 2 weeks and an additional week of simulated marketing period (SMP) at 20 °C. Exposure to either heat treatment caused neither visible damage nor fruit softening. Fruit weight loss rate in ‘Olinda’ oranges was unaffected by treatment but was higher than control fruit in heat exposed ‘Campbell’ oranges after storage, though at the end of SMP differences between treated and untreated fruit were non-significant. While neither heat treatment affected decay incidence in ‘Olinda’ oranges, significantly less decay was found in heat treated ‘Campbell’ fruit compared to control fruit both during storage and SMP.The chemical analyses of flavedo tissue of ‘Olinda’ oranges revealed that there were no treatment differences in neutral sugars, soluble and insoluble pectins and calcium bound to insoluble pectin fraction. The calcium content bound to soluble pectin fractions increased following heat treatments. At the end of SMP there was a significant decrease of soluble pectin and a significant increase of calcium bound to insoluble pectins in flavedo from oranges of the 46 and 44 °C treatments.Following treatment at 46 °C ‘Olinda’ fruit had a significantly lower content of soluble solids concentration. However, differences in soluble solids concentration between treated and control fruit after storage and SMP were not significant.Post-treatment levels of ethanol in both cultivars were significantly higher than in non-treated fruit. During storage and SMP, significant increases of ethanol were detected in control fruits with respect to their initial levels, whereas a reverse trend occurred in fruit subjected to heat treatment. Upon termination of the heat treatment at 44 or 46 °C, mean taste scores of ‘Olinda’ oranges were lower than those of untreated fruit, while the taste of ‘Campbell’ oranges was adversely affected only by the 46 °C treatment. After storage and SMP, taste differences between treated and control fruit were not significant. Flavour scores were unaffected by the treatment at 44 °C. Following treatment at 46 °C flavour rating in ‘Olinda’ fruit was significantly lower than control fruit while after storage and SMP the differences in flavour scores between treated and untreated fruit were non significant. Heat treatment to a fruit core temperature of 44 °C for 100 min or 46 °C for 50 min can thus have important commercial applications as an alternative to toxic chemical fumigants or to longer and more expensive disinfestation treatments such as cold quarantine.     

Effects of postharvest hot air treatments on the quality and antioxidant levels in tomato fruit

‘Rhapsody’ tomatoes heated for 24 h in air at 34 or 38 °C were compared to fruit heated in 5% O₂ at 38 °C in order to determine if heat treatment applied in reduced O₂ pressure might reduce stress-related oxidative changes that sometimes accompany heat injury. Fruit were subsequently stored at 4 or 10 °C for up to 30 d. Unheated fruit and those heated in air at 34 °C for 24 h developed the best colour during storage at 10 °C. Storage at 4 °C inhibited carotenoid development in all treatments. Fruit heated in air or in 5% O₂ lost the most ascorbic acid and isoascorbic acid. Glutathione reductase activity at the end of storage was similar in all fruit, while glutathione S-transferase activity was higher in fruit that had initially been heated in 5% O₂. Heating of ‘Rhapsody’ tomato fruit in air at 34 °C for 24 h prior to storage at 10 °C for up to 30 d resulted in the least losses in antioxidant content, and fruit colour developed adequately. Reduced O₂ neither improved the efficacy of the heat treatment in reducing chilling injury nor protected tomato fruit from the negative effects of heat treatment.     

Thermal and dielectric properties of shucked oysters

Thermal conductivity, thermal diffusivity and specific heat were measured for shucked oysters. Thermal conductivity increased from 0.577 to 0.677 W/m °C as temperature increased from 0 to 50 °C measured by a line heat source thermal conductivity probe. Specific heat was measured using a differential scanning calorimeter. It increased from 3.795 to 4.047 kJ/kg °C when temperature was raised from 10 to 50 °C. Thermal diffusivity of oysters was calculated from thermal conductivity, specific heat and density values. Dielectric properties of oysters were determined by an open-ended coaxial cable connected to a network analyser between 300 MHz and 3 GHz. At microwave frequencies of 915 and 2450 MHz, it was observed that the dielectric constant decreased (64.02–50.89 at 915 MHz and 59.10–47.67 at 2450 MHz), while the loss factor increased (13.84–20.14) at 915 MHz as temperature increased from 1 to 55 °C. Models were developed to describe the temperature effects on thermal and dielectric properties of shucked oysters.     

Screening for and characterization of Lactococcus lactis bacteriophages with high thermal resistance

Fifty-six Lactococcus lactis phage isolates collected from different German dairies and obtained from a starter culture manufacturer were tested for their heat resistance. About 40% of these isolates resisted treatment at 80 °C for 5 min when they were heated in milk. The most resistant phage isolate, P1532, was collected from sour cream. Plaque-formation was still detectable even after heating at 97 °C for 5 min. The second heat-resistant one, P680, showed some plaque-forming ability after heating at 95 °C for 5 min. Kinetic parameters for the thermal inactivation of these two resistant phages were determined for temperatures ranging from 70 to 97 °C. The inactivation of phage P1532 in skim milk and in buffer medium were found to follow first-order kinetics and did not exhibit tailing, whereas in the inactivation curves of phage P680 tailing was observed. The D-value of P1532 at pasteurization temperature of 72 °C was calculated as 112 min.     

Effect of heat treatment and casein to whey protein ratio of skim milk on graininess and roughness of stirred yoghurt

The aim of this work was to study how heat treatment and casein (CN) to whey protein (WP) ratio of skim milk affect physical characteristics of stirred yoghurt. Different heat treatments (95 °C/256 s, 110 °C/180 s and 130 °C/80 s) were applied to the yoghurt milk with the CN to WP ratios of 1.5:1, 2:1, 3:1 and 4:1. Physical properties, including graininess and roughness, of stirred yoghurt were determined during storage at 4 °C for 15 days. Visual roughness, number of grains, perimeter of grains, storage modulus, and yield stress decreased, when heating temperature or CN to WP ratio increased.     

Influence of protein heat treatment on the continuous production of food foams

The influence of WPI heat treatment on the continuous production of food foams was investigated using a model food including xanthan. The temperature of heat treatment was increased up to 90 °C using a plate heat exchanger; a rotor–stator unit was used for aeration purpose. The aim was to determine the interplay between heat-induced protein denaturation and aggregation, and the process parameters of aeration operation: namely, rotation speed, residence time and operating pressure. Microstructure, texture and stability of 200% overrun foams were analysed. Experimental results demonstrated that foam microstructure, namely overrun and bubble size distribution, was governed by the process parameters of aeration and depended only slightly on thermal treatment. Conversely, foam stability was strongly improved by heat treatment. These trends agreed roughly with results obtained in a batch kitchen mixer, but batch methods remained unable to predict quantitatively the behaviours observed in continuous aeration operation.     

Effect of chilling applied to suckling lamb carcasses on hygienic,physicochemical and sensory meat quality

The effect of post mortem temperature treatment on suckling lamb carcass and meat quality was study. Conventional (2 °C for 24 h), ultra-rapid (− 20 °C for 3.5 h, 2 °C until 24 h) and slow chillings (12 °C for 7 h, 2 °C until 24 h) were compared. Total viable counts (TVC), weight losses, and pH and temperature falls were recorded on carcasses. Meat colour, water holding capacity (WHC), Warner-Bratzler shear force, sarcomere length and sensory analysis were evaluated in M. longissimus. Ultra-rapid treatment reduced TVC and weight losses. The pH decline was faster in slow chilled carcasses than in faster chilled carcasses. No significant differences were found for colour and WHC. Slow treatment carcasses showed significantly lower shear force and higher sarcomere length. In the sensory analysis, tasters also rated the early post mortem slow-treated meat as more tender, less fibrous and chewy. Therefore, delay chilling in suckling lamb carcasses made it possible to obtain meat with better organoleptic characteristics, without affecting weight loss or hygienic quality.     

Cheese made from instant infusion pasteurized milk: Rennet coagulation,cheese composition,texture and ripening

Milk subjected to instant infusion pasteurization (IIP) at 72 °C, 100 °C and 120 °C (holding time 0.2 s) exhibited increased rennet coagulation time and decreased curd firming rate for increasing heat treatment temperature, when compared with raw or high temperature short time pasteurized (HTST) milk. However, addition of 4.5 mm or 9.0 mm of calcium restored the impaired rennet coagulation ability. Open texture cheeses produced from IIP milk (100 °C and 120 °C) contained significantly more moisture, had lower pH and shorter texture than similar cheese from IIP at 72 °C and HTST pasteurized milk. Cheese ripening was also affected by heat treatment, and different patterns of casein breakdown and peptide formation resulted from cheeses made from milk treated to IIP at 100 °C and 120 °C compared with cheeses made using IIP at 72 °C or HTST.     

Aqueous fractionation yields chemically stable lupin protein isolates

The chemical stability of lupin protein isolates (LPIs) obtained through aqueous fractionation (AF, i.e. fractionation without the use of an organic solvent) at 4 °C or 20 °C was assessed. AF of lupin seeds results in LPIs containing 2 wt.% oil. This oil is composed of mono- and poly-unsaturated fatty acids and the isolate may thus be prone to lipid and protein oxidation. Lipid and protein oxidation marker values of LPIs obtained at 4 °C and at 20 °C were below the acceptability limit for edible vegetable oils and meat tissue protein; the level of lipid oxidation markers was lower at 20 °C than at 4 °C. The fibre-rich pellet and the protein-rich supernatant obtained after AF also had lower levels of oxidation markers at 20 °C than at 4 °C. This is probably the result of a higher solubility of oxygen in water at lower temperature, which could promote lipid oxidation. The differences between fractions can be explained by the differences in their composition; the fibre-rich pellet contains polysaccharides that potentially have an anti-oxidative effect, while the protein-rich supernatant is rich in sulphur-rich proteins that may scavenge metal ions and free radicals from the aqueous phase. Additionally, the differences in solubility of metal ions and metal-chelating properties of protein at pH 4.5 and pH 7.0 explain the higher level of oxidation in the LPI at pH 4.5 compared with the LPI at pH 7.0. The application of a heat treatment to reduce oxidation decreased the protein and oil recovery values, and increased oxidation values above the acceptability limit. Therefore, AF at 20 °C is the most suitable process to obtain chemically stable LPIs.     

Effect of pH and heat treatment of cheese whey on solubility and emulsifying properties of whey protein concentrate produced by ultrafiltration

The effects of pH and heat treatment of cheese whey on protein solubility (PS) at pH 4.6 and on emulsifying properties of whey protein concentrate (WPC) were studied by response surface methodology (RSM). PS followed a quadratic relationship with pH and a linear relationship with heat treatment. Highest values for PS were found between pH 6.0 and 6.6 with heat treatment at 68 °C for 2 min, and maximum solubility was reached at pH 6.3. Heat treatment strongly decreased protein solubility throughout the entire pH range. The emulsifying properties were notably benefited by raising the pH from 6 to 7, best values being shown at pH 7 with a heat treatment of 70 °C for 2 min. The effect of heat treatment on the emulsifying properties was dependent on the pH level. At about pH 7, the heat treatment adversely affected the emulsifying properties, probably due to excessive protein denaturation.     

Structural and rheological properties of amaranth protein concentrate gels obtained by different processes

The heat-induced gelation of amaranth protein concentrates (APCs) by three processes was studied. The first was the conventional process for isolating protein (standard process-st), the second included an acid washing step prior to protein extraction (acid washing process-aw) and the third included heating (50 °C) during the alkaline extraction step (heat process-ht). The dispersions (12%, w/v) were heated to 55–90 °C and assessed by rheological measurements made under small deformations, whereas the gels obtained by heating at 70, 80 or 90 °C/30 min were subjected to uniaxial compression measurements (TPA and mechanical properties). The rheological parameters associated with the network structure, elasticity modulus (E) and storage modulus (G′), increased with increasing gelation temperature. For the APCst and APCht gels, protein aggregation occurred in two steps, whereas for APCaw, gelation occurred in a single step. The APCht gels showed the highest fracturability, hardness and adhesiveness, followed by the APCst and APCaw gels (p < 0.05). Similar results were obtained for the mechanical properties at fracture. Increasing the heat treatment temperature from 80 to 90 °C resulted in a more structured matrix with greater water-holding capacity as compared to gels obtained at 70 °C, and these properties were influenced by the extraction processes used to obtain the APCs. Heat extraction (APCht) improved the gelation and water-holding properties, whereas the acid treatment had the opposite effect.     

Survival of Lactobacillus delbrueckii UFV H2b20 in ice cream produced with different fat levels and after submission to stress acid and bile salts

The survival of Lactobacillus delbrueckii UFV H2b20 in three ice cream formulations (low fat, fat free and high fat) was evaluated after the processing and storage at ?16 °C. The survival of L. delbrueckii UFV H2b20 was not significantly affected (P > 0.05) in three ice cream formulations after processing. The same result was observed during storage for 40 days at ?16 °C. Cells of L. delbrueckii UFV H2b20 incorporated in three ice cream formulation survived when exposed to acid stress and bile salts. The results demonstrate that L. delbrueckii UFV H2b20 has potential for being used in ice cream and capacity to resist acid stress and to grow in the presence of bile salts. This demonstrates that reduction of fat in ice cream does not compromise the viability of L. delbrueckii UFV H2B20.     

Graininess and roughness of stirred yoghurt as influenced by processing

The aim of this work was to study how heat treatment, the type of starter culture, incubation temperature, and storage time can affect the physicochemical characteristics of stirred yoghurt. A four-factor experimental design was used for data analysis. Yoghurt milk was heated at 95 °C for 5 min or 130 °C for 80 s. Yoghurts were produced with three different starter cultures that had been incubated at 37, 42 or 45 °C and stored at 4 °C for 15 days. Visual roughness, number of grains, perimeter of grains, storage modulus, and yield stress all decreased when heating temperature was increased, when an exopolysaccharide-producing starter culture was used, or when incubation temperature was decreased. Storage time did not affect any of the physicochemical properties of yoghurt, except for the pH.     

Optimization of Soaking Duration and Temperature for Two Nigerian Rice Cultivars

Optimization of soaking duration and temperature for two Nigerian rice cultivars were evaluated. Temperatures of 50°C, 70°C and 90°C were used for both long and short grain rice paddy. Each treatment had three replicates of 12, 18 and 24 h of soaking durations. The physical analysis of the long/short rice paddies were 1000 kernel volume 24.3/22.3 cm³, 1000 kernel weight 24.2/24.3 g, density 1.3/1.1 gcm³, length, 9.9/8.2 mm, width, 2.95/3.3 mm, water absorption rate of 34/11% and moisture content of 14/11% respectively. Sensory evaluation of the long/short grain rice yield based on colour and general acceptability showed that significant differences existed among the samples with colour 8.05/7.85, general acceptability 8.10/7.80 respectively. The long/short grain percentage breakages were 2.7/1.2% and total yield 70/67%, respectively. At 70°C long grain rice yield increased as soaking duration increased, and at 90°C, short grain rice yield increased as soaking duration increased. The best quality was achieved by soaking the long grain at 70°C for 24 h and short grain at 90°C for 24 h.     

Heat transfer modeling of chicken cooking in hot water

To calculate the slowest heating point and optimum cooking time of whole chicken cooking in hot water, a 2-dimensional heat transfer model was developed to predict temperature profile and history of the chicken cooked in hot water at 85, 90 and 95 °C. Chickens were divided into 12 sections and the heat transfer model was applied to each cross section. These models were solved with an I-DEAS program. Specific heat and thermal conductivity were measured at temperatures ranging from 25 to 95 °C. The temperature of chicken did not significantly affect the thermal properties. The average values of specific heat of white and dark meats were 3.521 and 3.654 kJ/(kg K), respectively, and the average thermal conductivity values were 0.5093 and 0.4930 W/(m K), respectively. The model was validated against experimental results, and provided an average root mean square error of 2.8 °C. Temperature distributions showed that the slowest heating point was deep in the breast part of the second cross section (3.6 cm far from shoulder) at the symmetric line of the chicken, around 2.1–2.5 cm deep from breast skin. For food safety consideration, the recommended cooking times, for whole chickens in weight range of 2.3–3.2 kg with different initial temperatures (5–30 °C), were around 74–84, 64–74 and 57–67 min for cooking temperatures of 85, 90, and 95 °C, respectively.     

Properties of low-fat stirred yoghurts made from high-pressure-processed skim milk

Physical properties of stirred yoghurt made from reconstituted skim milk that was high-pressure (HP)-treated at 100, 250 or 400 MPa, at 25, 70 or 90 °C, for 10 min, prior to inoculation with yoghurt cultures, were studied; portions of milk HP-treated at 25 °C were also heat-treated at 90 °C for 10 min before or after pressure treatment. Control yoghurts were made from skim milk given a heat treatment at 90 °C for 10 min. Fermentation time was not affected by treatment applied to the milk. HP treatment of skim milk at 25 °C, before or after heat treatment, gave stirred yoghurts of similar viscosities to that made from conventionally heat-treated milk. Lower viscosities were obtained when stirred yoghurts were made with milk HP-treated at elevated temperatures. A model is proposed to correlate properties of yoghurt with HP/heat-induced changes in interactions and structures of protein in the milk samples.Industrial relevanceTo meet end user expectations, the dairy industry needs to diversify its product range by tailoring specific functionalities. To meet these expectations, new processing methods such as high-pressure processing are of interest for their potential to achieve specific and/or novel functionalities and/or improve efficiencies, including reduced chemical and water use. In this paper, an investigation of the use simultaneous pressurization and heating of milk before the manufacture of stirred yoghurt is presented.     

Mechanical and thermal characteristics of amaranth starch isolated by acid wet-milling procedure

Effects of soaking conditions during acid wet-milling of amaranth grain on mechanical and thermal properties of amaranth starch were investigated. A factorial design based on temperature (40–60 °C) and SO₂ concentration (0.1–1.0 g/L) was used. Dynamic oscillatory tests involved heating and cooling cycles (25–90 °C) with tempering at 90 °C followed by a frequency sweep (0.1–20 Hz) at constant temperature. Thermal properties of starch suspensions were based on DSC tests. Viscoelastic modulus and thermal properties were affected by both factors, being significant the interaction effect. Maximum values of viscoelastic modulus at the end of heating and cooling steps were determined for samples corresponding to soaking conditions of 50 °C and 1.0 g/L SO₂. Based on Ross-Murphy index from frequency sweep analysis it was found that paste behavior occurs at 60 °C and 0.1 g/L, while at 47.4 °C and 0.72 g/L starch suspension gave a strong gel. Onset (61.7 °C) and peak (66.2 °C) temperatures showed a minimum at 50 °C and 1.0 g/L. As SO₂ concentration decreased, the end of gelatinization took place at lower temperature. Maximum gelatinization enthalpy (12.7 J/g) was found at 40 °C and 0.1 g/L SO₂.     

High-pressure homogenisation of raw bovine milk. Effects on fat globule size distribution and microbial inactivation

Whole raw milk was processed using a 15 L h⁻¹ homogeniser with a high-pressure (HP) valve immediately followed by a cooling heat exchanger. The influence of homogenisation pressure (100–300 MPa) and milk inlet temperature T_in (4°C, 14°C or 24°C) on milk temperature T₂ at the HP valve outlet, on fat globule size distribution and on the reduction of the endogenous flora were investigated. The T_in values of 4–24°C led to milk temperatures of 14–33°C before the HP valve, mainly because of compression heating. High T_in and/or homogenisation pressure decreased the fat globule size. At 200 MPa, the d_4.3 diameter of fat globules decreased from 3.8±0.2 (control milk) to 0.80±0.08 μm, 0.65±0.10 or 0.37±0.07 μm at T_in=4, 14°C or 24°C, respectively. A second homogenisation pass at 200 MPa (T_in=4°C, 14°C or 24°C) further decreased d_4.3 diameters to about 0.2 μm and narrowed the size distribution. At all T_in tested, an homogenisation pressure of 300 MPa induced clusters of fat globules, easily dissociated with SDS, and probably formed by sharing protein constituents adsorbed at the fat globule surface. The total endogenous flora of raw milk was reduced by more than 1 log cycle, provided homogenisation pressure was ⩾200 MPa at T_in=24°C (T₂∼60°C), 250 MPa at T_in=14°C (T₂∼62°C), or 300 MPa at T_in=4°C (T₂∼65°C). At all T_in tested, a second pass through the HP valve (200 MPa) doubled the inactivation ratio of the total flora. Microbial patterns of raw milk were also affected; Gram-negative bacteria were less resistant than Gram-positive bacteria.     

Influence of lupin-based milk alternative heat treatment and exopolysaccharide-producing lactic acid bacteria on the physical characteristics of lupin-based yogurt alternatives

In the present study we investigated the influence of heat treatment of lupin-based (LB) milk alternatives and different exopolysaccharide (EPS)-producing lactic acid bacteria on the physical characteristics of set-type LB yogurt alternatives. LB milk alternatives, obtained from protein isolate of Lupinus angustifolius cv. Boregine, were either pasteurized at 80 °C for 60 s or ultra-high temperature (UHT) heated at 140 °C for 10 s and was fermented with Lactobacillus plantarum TMW 1.460 and 1.1468, Pediococcus pentosaceus BGT B34 and Lactobacillus brevis BGT L150. Fermentation duration was strongly affected by heat treatment: different strains needed between 25 to 35 h in UHT LB milk alternative to reach a pH of 4.5 compared to 14 to 24 h in pasteurized LB milk alternative. EPS extraction revealed slightly higher amounts of EPS for UHT LB yogurt alternatives (~ 0.5–0.9 g/l; pasteurized: ~ 0.4–0.7 g/l). The more intensive heat treatment (UHT) resulted also in better rheological (apparent viscosity, hysteresis loop area, flow point, elastic, viscous and complex modulus) and textural properties (firmness, consistency, cohesiveness and index of viscosity) of the investigated LB yogurt alternatives. Furthermore, LB yogurt alternatives out of UHT milk alternative revealed a lower tendency to syneresis, measured with siphon and centrifugation method. This work contributes to the fundamental knowledge of the textural properties of LB yogurt alternatives.     

Acidified sodium caseinate emulsion foams containing liquid fat: A comparison with whipped cream

Aeration properties of acidified casein-stabilized emulsions containing liquid oil droplets have been compared to the whipping of dairy cream. The foam systems were characterized in terms of overrun, microstructure, drainage stability, and rheology. With acidification using glucono-δ-lactone, the casein-stabilized emulsions could be aerated to give foams of far higher overrun (>600%) than whipped cream (∼120%). The development of foam volume, stability and rheology in the aerated casein-stabilized emulsion systems was found to be strongly dependent on the pH and the concentration of added calcium ions. Whereas whipped cream is stabilized by partially coalesced fat globules, the casein emulsion foams are stabilized by aggregation (gelation) of the protein coat surrounding the oil droplets. Casein emulsion foams formed at low pH were found to be more stable than whipped cream, whilst those formed at high pH were predominantly liquid-like and unstable. Instability arose in the acidified casein emulsion foams mainly through gel syneresis. We conclude that there are substantial textural differences between whipped cream and acidified casein emulsion foams, especially in terms of the small-deformation rheology and the extent of the linear viscoelastic regime.