Showing papers in "Lwt - Food Science and Technology in 1995"

Use of a Free Radical Method to Evaluate Antioxidant Activity

Abstract: The antiradical activities of various antioxidants were determined using the free radical, 2,2-Diphenyl-1-picrylhydrazyl (DPPH*). In its radical form. DPPH* has an absorption band at 515 nm which dissappears upon reduction by an antiradical compound. Twenty compounds were reacted with the DPPH* and shown to follow one of three possible reaction kinetic types. Ascorbic acid, isoascorbic acid and isoeugenol reacted quickly with the DPPH* reaching a steady state immediately. Rosmarinic acid and δ-tocopherol reacted a little slower and reached a steady state within 30 min. The remaining compounds reacted more progressively with the DPPH* reaching a steady state from 1 to 6 h. Caffeic acid, gentisic acid and gallic acid showed the highest antiradical activities with a stoichiometry of 4 to 6 reduced DPPH* molecules per molecule of antioxidant. Vanillin, phenol, γ-resorcylic acid and vanillic acid were found to be poor antiradical compounds. The stoichiometry for the other 13 phenolic compounds varied from one to three reduced DPPH* molecules per molecule of antioxidant. Possible mechanisms are proposed to explain the experimental results.

Changes in Colour and Myoglobin of Minced Beef Meat Due to High Pressure Processing

Abstract: Minced beef meat was packaged under vacuum, air or oxygen, and pressurized at 10°C for 10 min. L* colour values increased significantly in the range 200–350 MPa, the meat becoming pink, while a* values decreased at 400–500 MPa, the meat becoming grey-brown. Simultaneously, total extractible myoglobin decreased in the range 200–500 MPa, while the proportion of metmyoglobin increased at the expense of oxymyoglobin at 400–500 MPa. Pressurization did not significantly increase the extractibility of heme iron by an acid solution. Packaging of meat under vacuum with an oxygen scavenger partly protected meat colour, since samples processed at 400 MPa became pink, without any change in a* value or metmyoglobin content. Blending chilled minced meat with NaNo 2 (and NaCl) 18 h before processing at 350–500 MPa afforded a similar protection. Cysteine, ascorbic acid, nicotinamide or nicotinic acid had no protective effects. Meat discoloration through pressure processing may result from (1) a whitening effect in the range 200–350 MPa, due to globin denaturation and/or to heme displacement or release, and (2) oxidation of ferrous myoglobin to ferric metmyoglobin, at or above 400 MPa. Only the latter phenomenon is prevented by total oxygen removal or prior formation of nitrosomyoglobin.

Microbial contamination of spices and herbs: A review

Abstract: The popularity of highly spiced cuisine and consumer demand for more flavorful foods which are also low in sodium and fat have resulted in a continuing interest in the use of spices and herbs in food products. Although such condiments are generally used for the aesthetic properties they contribute to food products, spices and herbs can often be a major source of microbial contamination. Studies investigating bacterial and/or fungal contamination of spices and herbs are reviewed. The high levels of microbial contamination in spices and herbs reported by many of the studies reviewed suggests a need for better control in all aspects of the production, processing and usage of these products to prevent potential food spoilage and food-borne illnesses due to contaminated spices and herbs.

Analysis of roasted coffee powders and brews by gas chromatography-olfactometry of headspace samples

Abstract: The highly volatile, potent odorants of coffee samples were evaluated by gas chromatography-olfactometry of decreasing headspace samples (GCO-H) 2,3-Butanedione, 2,3-pentanedione, 3-methyl-2-butenthiol (I), methional, 2-furfurylthiol (II) and 3-mercapto-3-methylbutylformate (III) were the key odorants of both, the powders of Arabica and Robusta coffees 2-Methyl-3-furanthiol (IV), 2,3-diethyl-5-methylpyrazine and an unknown compound were additional key odorants of the latter An increase in the odour potencies of acetaldehyde, propanal, methylpropanal, 3-methylbutanal and dimethyltrisulphide as well as a decrease in the odour potencies of the thiols I to IV in the brews were the major differences with regard to the powders

Development of an Objective Method for Dough Stickiness

Abstract: An objective method was developed to measure dough stickiness. The texture analyser provided the required compression force and measured the tension. A cell was designed and built that caused the dough to separate from the probe surface under tensile stress. This is critical for the measurement of dough surface stickiness. The procedure was highly reproducible and appeared to correlate well with subjective measurements of dough stickiness. A number of factors that affected dough stickiness were studied by the developed procedure. Although many factors were shown to affect dough stickiness, none appeared to explain the increased stickiness found with certain flours.

Mass and heat transfer during deep-fat frying of potato slices —I. Rate of drying and oil uptake

Abstract: The influence of oil temperature, dry matter content of potato tubers and thickness of slices on drying and oil uptake during deep-fat frying of potato chips (British: potato crisps) was investigated. Experiments were carried out on a laboratory scale at strictly isothermal frying conditions, and by using uniform slices cut from potato tubers of known weight (size) and specific gravity (dry matter content). An exponential model and a multiple linear regression model was applied successfully to describe dehydration and oil uptake, respectively. Drying may be accelerated by increasing oil temperature. A higher initial dry matter content abbreviates drying time due to the start of the process at lower moisture content. As oil uptake calculated on the weight of potato chips is controlled primarily by residence time in the frying unit, final fat content is lower at higher oil temperatures and initial dry moisture contents. Oil uptake calculated on the constant basis of wet weight of raw potato slices is correlated positively to the oil temperature, to the initial dry matter content and to the inverse of the slice thickness. This indicates that oil is deposited on the surface and does not penetrate into the centre of slices to a large extent.

Structural changes of starch during cooking of durum wheat pasta

Abstract: Textural quality of Durum wheat pasta is influenced by the properties and transformation of the protein and starch fraction. The aim of this study was to evaluate changes in the structure of dried pasta during cooking in relation to surface and internal structure of Durum wheat spaghetti. Light microscopy with two specific staining procedures for protein and starch, respectively, and scanning electron microscopy were used. Cooking in excessive water resulted in a disintegration of the starch granules with a substantial leakage of amylose in the outer layer of the strand, and in the formation of domains containing high amounts of starch in the protein matrix. In the centre of pasta, starch granules retained their shape due to a limited water diffusion, and the protein network remained dense. On the surface of dry spaghetti, numerous loosely attached starch granules were visible. With increasing cooking time, the surface of the spaghetti became rough, and parts of gelatinized starch granules were well recognizable. It is likely that both the state of starch and the surface structure contribute to the development of the elastic texture and in particular to the stickiness of pasta.

Modelling of browning kinetics of bread crust during baking

Abstract: A mathematical model was set up to predict browning kinetics of bread crust during baking. A bread dough was placed into a cylindrical steel mould and baked in a pilot forced-convection oven at 200 and 250°C. The sample surface temperature was measured using both a type J thermocouple and an infrared thermometer. Surface browning (ΔE) of bread crust during baking was measured by a tristimulus colorimeter. The kinetic model for bread crust browning was obtained by instant heating of dried crumb on contact with a refractory plate at 140, 150, 165, 185, 210, 235 and 250°C. At all temperatures ΔE tended asymptotically to ΔE∞ = 52, which corresponded to the burnt sample. The colour difference varies as a function of first-order kinetics. The rate constant k depends on temperature according to the Arrhenius equation (ko = 42,000 s−1; Ea = 64,151 J/mol). Kinetics was validated under dynamic temperature conditions: the experimental results were compared with those obtained from a mathematical model for heat and mass transfer during baking connected to the kinetic model for browning.

Nonthermal inactivation of Saccharomyces cerevisiae in apple juice using pulsed electric fields

Abstract: High intensity pulsed electric fields were utilized in a continuous system for inactivation of Saccharomyces cerevisiae in apple juice. The applied electric energy inactivated microorganisms in apple juice and, because the pulse duration was only 2.5μs, energy remaining to heat the apple juice was minimized. The microbial inactivation was defined in terms of applied field intensity and treatment time. Less than 10% of the electrical energy for HTST was needed for achieving 6 log reduction in inactivation of S. cerevisiae in apple juice. The PEF-treated apple juice, at both 4°C and 25°C storage, had a shelf-life of more than 3 weeks.

Pressure-induced aggregation of β-lactoglobulin in ph 7.0 buffers

Abstract: Solutions of a β-lactoglobulin isolate in water, in potassium phosphate buffer (20 or 50 mmol/L), and in pressure-resistant buffers, at a protein concentration of 25 g/kg and at pH 7.0, were processed at 150, 250, 350 or 450 MPa and 25 °C, for 15 min, then stored at 4 °C, usually for 24 h, before analysis. Bis-Tris (20 or 50 mmol/L) and bis-Tris-propane (10, 20 or 50 mmol/L) were selected as pressure-resistant buffers, while the pH of water or phosphate buffer is known to decrease reversibly by 0.2–0.3 pH unit per 100 MPa. After pressurization, nitrogen solubility at pH 4.7 and 7.0, and aggregation patterns by polyacrylamide gel electrophoresis were determined. Both indicated that aggregation of β-lactoglobulin was more extensive in pressure-resistant buffers than in phosphate buffer or in water. Electrophoretic patterns also revealed the progressive formation of dimers to hexamers and of higher polymers of β-lactoglobulin as a function of the type and molarity of buffer and of the pressure level. All high molecular weight aggregates and most oligomers disappeared when pressurized solutions were treated with β-mercaptoethanol (15 mL/L) prior to electrophoresis. Thus pressure induced the formation of intermolecular S-S bonds, especially when the pH was maintained close to neutral. Previous studies with thermally-induced β-lactoglobulin gels had shown that SH/ S-S interchange reactions were enhanced at or above neutrality.

Impact of food processing on the environment—an overview

Abstract: Each step in the food industry system — food production, processing, transportation, storage, distribution and marketing — has some impact on the environment and there is much concern about environmental pollution. Due to the highly diversified nature of the food industry, various food processing, handling and packaging operations create wastes of different quality and quantity, which, if not treated, could lead to increasing disposal problems and severe pollution problems. Additionally, they represent a loss of valuable biomass and nutrients if not recovered by appropriate methods and technologies for upgrading, bioconversion or reutilization. Research should be intensified to improve efficiency in waste treatment, and to minimize waste in food processing and manufacturing operations through advanced manufacturing practices, and constructive utilization of what is unavoidable by bioconversion of by-products and waste into edible food, feed or industrial chemicals in order to decrease environmental loadings as a consequence of better integrated waste management. This review deals with the general characteristics and treatment operations of by-products, wastes and effluents from different categories of the food processing industry and their impact on the environment.

Volatile organic compounds produced by thermophilic and mesophilic single strain dairy starter cultures

Abstract: The potential of different commercially used starter cultures to form volatile organic compounds were determined. Special interest was laid on the so-called minor constituents compounds that are present in the low μg/kg-range in the end-product aroma of the investigated starter cultures. The variability of the tested single strain cultures was very wide within the investigated species. It was not possible to group the strains according to the species by applying statistical procedures such as principal component analysis or cluster analysis on the GC-MS-data of the samples. Applying the concept of odour unit values to all cultures tested, it was possible to estimate the impact of each volatile organic compound investigated on the resulting aroma of the end product. Of 32 quantified compounds only 2,3-butanedione (odour unit values between 6 and 362), 2,3-pentanedione (between 0 and 363), and to a lesser extent demethyl sulfide (between 6 and 12), and benzaldehyde (between 0 and 3) are supposed to have such an impact. Mixed cultures were formed, using three strains of Lb. delbruckii ssp. bulgaricus and S. salivarius ssp. thermophilus , respectively, to produce yogurt. The most interesting finding was that 2,3-pentanedione is produced by all mixed strain cultures in three to five times the amount of the sum produced by the respective single strains.

HPLC Quantitation of Major Carotenoids of Fresh and Processed Guava, Mango and Papaya

Abstract: The major carotenoids in 52 samples of guava, mango, papaya and some of their processed products were quantitated by HPLC, using both external standardisation and standard addition calibration techniques. The results, submitted to theFandttests, demonstrated that the precision and the means obtained by the two calibration procedures were not significantly different. The concentrations of β-carotene and lycopene in guava, β-carotene in mango and β-carotene, β-cryptoxanthin and lycopene in papaya samples were coherent with those obtained previously with open column chromatography. The major problem in the HPLC quantitation of carotenoids is still obtaining and maintaining pure standards.

High pressure-induced gel formation of a whey protein and haemoglobin protein concentrate

Abstract: High pressure-induced gel formation of whey protein concentrate (WPC), egg white concentrate (EWC), blood plasma concentrate (BPC), and haemoglobin protein concentrate (HPC), was studied at operating pressures up to 4 kbar without additional supply of heat to the pressure vessel. High pressure (4 kbar: 30 min) generated weaker gel networks for WPC and HPC compared to heat set gels (80°C: 30 min) at a given protein concentration of 90 to 180 g/L for WPC, and 80 to 140 g/L for HPC. A minimum operating pressure of 2 kbar for WPC and 3 kbar for HPC, combined with a minimum protein concentration of 160 and 120 g/L respectively, were necessary for network formation to occur. Longer durations generated stronger gel networks, while the effects of repeated compression remained limited. For WPC, only strong high pressure-induced gels were formed in the alkaline pH region. Pressure-sensitive buffer salts (e.g. phosphate) reduced the strength of high pressure-induced WPC gels, presumably caused by lowering the pH under pressure. For BPC and EWC, which easily form heat set gels, no visual gel formation occurred after a pressure treatment of 30 min at 4 kbar.

Influence of Protein and Fat Content and Cooking Temperature on Texture and Sensory Evaluation of Bologna Sausage

Abstract: Considering the possibility of adjusting the properties of low-fat products in the light of how these properties are influenced by both composition and a number of processing factors, the purpose of this research was to assess the effects of protein content (P, ranging from 100 to 160 g/kg), fat level (F, ranging from 101 to 220 g/kg) and cooking temperature (CT, ranging from 77°C to 105°C) on the instrumental textures and sensory evaluation of Bologna sausages. Response Surface Methodology (RSM) was used to study simultaneously the effect of two composition variables and one processing variable. Significant models of regression were established for hardness, chewiness, penetration force, work of penetration and the sensory parameters texture and overall acceptability. These models indicate that protein content was the variable which most influenced the characteristics of the product; cooking conditions, on the other hand, had scarcely any effect at all on sausage texture and sensory evaluation. Both fat and protein percentages generally had a significant direct linear effect on instrumental textural parameters.

Rheological properties of food gums as related to their water binding capacity and to soy protein interaction

Abstract: Water binding capacity and hydration time of several food gums were measured by the Baumann method. Xanthan gum was by far the best water binder (232 mL/g) followed by guar gum (40 mL/g) and sodium alginate (25 mL/g). Propylene glycol alginate and locust bean gum (LBG) were the poorest water binders (15 and 11.6 mUg). Hydration time ranged from 50 min for sodium alginate to 3500 min for guar gum. A good correlation was obtained between the consistency coefficient of gum dispersion and the imbibed water fraction calculated from Baumann measurements. Soy protein (20 g/kg) showed synergism with xanthan and guar gum (1.5 or 3 g/kg) as shown by the increase of the consistency coefficients of mixed systems over the expected values from 81 to 139%. For the xanthan gum and soy protein systems, yield stress was greatly enhanced too. The interaction between locust bean gum and soy protein changed from antagonism at 20 g/kg soy protein and 1 g/kg LBG to synergism for 1.5 and 3 g/kg gum concentration. When soy protein interacted with a blend (1:1) of xanthan and guar, the synergistic increase in the consistency coefficient and yield stress was also apparent. However, soy protein showed an antagonistic interaction with the blend xanthan/LBG (2 g/kg) as it decreased gel properties of the system.

Large scale isolation of water-soluble and water-insoluble pentosans from wheat flour

Abstract: A procedure has been developed which allows the isolation of enriched pentosan fractions from wheat flour. The procedure is based on mixing flour and water (50 kg/150L). After centrifugation the supernatant is heat-treated and then concentrated by cross-flow ultrafiltration to give water-soluble pentosans, whereas the insoluble residue is treated with Alcalase and then Termamyl to give water-insoluble pentosans. Starting from 50 kg of flour from three different varieties (Soissons, Thesee, Apollo), water-soluble and water-insoluble pentosans containing respectively 100–200 g of water-soluble and 250–350 g of water-insoluble arabinoxylans, were prepared within 2 d. Water-soluble pentosans are constituted of approx. 40% arabinoxylans and are contaminated by proteins, whereas water-insoluble pentosans are composed of arabinoxylans (ca. 30%) and are contaminated by residual starch (ca 40%). Enrichment factors in arabinoxylans ranged from 98 to 66 for water-soluble and 27 to 19 for water-insoluble pentosans as compared with initial flour.

Baking and nutritional qualities of a spelt wheat sample

Abstract: Flours from a sample of hard red winter (HRW) wheat and spelt wheat were evaluated for milling, baking and nutritional qualities, Milling flour yield from the spelt wheat sample was consistently lower than from the corresponding HRW wheat sample: pup loaves made with spelt flour also showed lower volume and total scores. Both wheat grains tested positive for gluten and, thus, would be unsuitable for gluten-intolerant individuals. With one exception (higher zinc content), spelt wheat grain did not differ significantly from HRW wheat in the contents of nutritionally important components—protein, fiber, minerals and vitamis. Expressed on g/100g protein basis, all amino acids, except tyrosine, aspartic acid and methionine, were lower (lysine by 28%) in spelt wheat as compared to HRW wheat. The protein efficiency ratios of spelt and HRW wheat grain measured 1.3 and 1.4 (casein, 2.5) and protein digestibilities 80.1% and 78.9% (casein, 91.6%), respectively. Thus, the superior nutritional content and other claims that have been suggested for spelt wheat may be unfounded.

Liquid-holding capacity and structural changes in comminuted salmon (Salmo salar) muscle as influenced by pH, salt and temperature

Abstract: The loss of liquid in salmon muscle comminuted with salt was studied as a function of pH and heating temperature. A factorial experiment was designed to compare the effects of; the raw material, NaCl concentration, pH, degree of comminution and heating temperature in order to evaluate both main effects and interaction effects. The liquid-holding capacity was measured by a low speed centrifugation net test. The changes in microstructure in the samples were investigated by light microscopy using fat- and protein-staining techniques. The heating temperature, pH, NaCl concentration, variation of raw material and degree of comminution influenced liquid loss according to a second-order interaction linear model. The interaction effect between low pH, low salt concentration and high temperature was strongest. Addition of salt extracted the myofibrillar proteins and resulted in a homogeneous protein matrix with few intact fibres and uniformly dispersed fat droplets. Liquid loss was closely related to the microstructure of the comminutions. When heated above 30 °C, enlarged pores and gaps, some of them forming channels, occurred in the protein matrix. In comminutions prepared with a low salt concentration and/or a low pH the more frequent presence of pores and gaps enhanced the liquid loss.

Vitamin C Destruction During the Cooking of a Potato Dish

Abstract: The kinetics of vitamin C destruction during the cooking of a potato dish were measured. Five domestic cooking apparatuses, including a superheated steam oven, a free convection oven, a forced convection oven, a microwave oven and a pressure cooker, were compared. Whatever the cooking condition, when the residence time was equal to the cooking time, the reduced quantity of vitamin C remaining in the potato dish was approximately 0.7. A model considering the thermal and the enzymatic destruction of vitamin C and the thermal deactivation of enzymes was proposed. The parameters of the model were identified using the results of the cooking experiments and isothermal kinetics of vitamin C destruction in potato extracts. The simulations showed that the loss of vitamin C at the cooking time was mainly due to the enzymatic destruction. A prolonging of the residence time resulted in additional losses by thermal destruction. A low water content and the presence of air in the cooking atmosphere further increased the destruction rate.

Production and purification of a sugar syrup from carob pods

Abstract: Carob pods contain about 200–500 g/kg of total sugars, a higher content of sugar than is present in beet or cane, which is below 200 g/kg. In the present paper a sugar syrup (concentrate solution of several sugars) from carob pods has been obtained with a concentration of sugars near 580 g/kg, 62° Brix and 93% of purity. Extraction and purification techniques were performed. From the results of the extraction researches it can be concluded that a 10 column system connected in series is the most advantageous for efficiency and automation of the sugar extraction reaching a yield of at least 90%. In the purification technique a discontinuous treatment followed by purification in several types of columns connected in series have been studied in order to obtain a transparent and colourless extract.

Capillary Electrophoresis of Wheat Gliadin: Initial Studies and Application to Varietal Identification

Abstract: Wheat gluten proteins have important functional properties, and are reliable indicators of genotype. They are also very heterogeneous, demanding use of powerful analytical techniques. Gel electrophoresis methods are widely used for gluten analysis, but they are labor-intensive, and their data are not easily quantified. Methods of capillary electrophoresis (CE) are now available that promise to overcome these disadvantages. We here report successful application and optimization of two CE procedures for gliadin analysis. The first procedure used 0.06 mol/L sodium borate buffer, pH 9.0, containing 200 mL/L acetonitrile + 10 g/L sodium dodecyl sulfate; separations were excellent, but reproducibility was difficult to maintain. The second buffer, 0.1 mol/L phosphate, pH 2.5, containing a linear hydrophilic polymer, overcame this problem, providing separations of gliadins that are rapid, high-resolution, automatic, and easily quantified. CE analyses of gliadin also reliably differentiate varieties of all U.S. wheat classes. CE is thus a valuable technique for gliadin analysis, complementary to other methods of electrophoresis and chromatography. CE has much potential to become a routine tool for wheat varietal identification and classification, and for prediction of quality.

Effects of calcium level on the structure of pre-heated whey protein isolate gels

Abstract: The effects of Ca level (10–360 mmol/L) on the gelation, at room temperature, of pre-heated whey protein isolate (100 g/L, pH 7.0) were investigated. At a low Ca concentration a clear gel was formed. Scanning and transmission electron micrographs (SEM, TEM) revealed the formation of a fine protein strand microstructure. As the Ca level increased, larger and thicker strands were formed. This was associated with a progressive reduction in the gel's clarity as was measured objectively with a colour meter. At 180 mmol/L Ca, TEM micrographs showed large aggregate formation which was associated with a significant reduction in water-holding capacity. Using 360 mmol/L Ca resulted in a gel similar to the 180 mmol/L treatment. Shear stress at fracture increased as the Ca level increased up to 180 mmol/L Ca and then levelled off. Shear strain decreased with the increase in Ca. The same was observed for water-holding capacity, indicating that the fine strand microstructure could hold moisture better than the aggregated structure. In a heat-induced gel (produced for comparison purposes) low Ca concentration (10 mmol/L) formed a typical opaque, aggregated gel. The water-holding capacity and shear stress values of the cold set gels were significantly higher than that of the heat-induced gels.

Relationship between aflatoxin production and mold growth as measured by ergosterol and plate count

Abstract: Samples of sterile long grain white rice were inoculated with different inoculum levels of Aspergillus flavus subsp parasiticus spores and incubated at 25°C. Ergosterol content, mold count and aflatoxin production were determined. Ergosterol was determined using a method that consisted of methanol-hexane extraction, saponification and quantification using HPLC with UV-detection. At low inoculum levels mold spores and ergosterol were not detected until the third day of incubation. Generally aflatoxin B1 followed the same trend as ergosterol. At high inoculum levels ergosterol and mold spore counts were detectable before aflatoxin B1. There was no clear pattern between aflatoxin G1 production and ergosterol content. Ergosterol appears to be a sensitive early indicator of low levels of fungal activity and aflatoxin production in rice.

Sucrose hydrolysis in a glassy starch matrix

Abstract: The purpose of present work was to investigate whether the glassy state may prevent sucrose inversion in an acid-containing amorphous starch powder (native or pre-gelatinized). It was found that sucrose hydrolysis occurred to a significant extent in the glassy state (in both native and gelatinized starch). Moisture content of the system affected the extent of sucrose hydrolysis but its effect was not attributable to the plasticizing effect of water. Little reaction occurred at moisture contents below the so-called B.E.T. monolayer. Temperature was a critical factor controlling sucrose inversion.

Applications of fractal analysis to food structure

Abstract: Fractal analysis has been recently applied to the study of food structure. Fractal techniques can be particularly useful tools for characterizing food morphology because the highly irregular structures of many food materials elude precise quantification by conventional means. Measured fractal dimensions also have been related to product functionality, processing history, or storage conditions. This paper explains the principle of fractal analysis and reviews the application of different fractal analysis methods to images, surfaces and networks of food materials.

Modelling of starch gelatinization kinetics of bread crumb during baking

Abstract: A mathematical model was set up to predict the extent of gelatinization of starch in bread crumb during baking. A bread dough was placed into a cylindrical steel mould and baked in a pilot forced-convection electric oven at 250 °C. A type J thermocouple was placed into the bread crumb (i.e. at a depth of 22 mm in axial position) in order to measure the temperature. Samples were extracted at different final baking temperatures (60, 65, 70, 75, 77, 80, 85, 90, 95, 98°C) and the determination of starch gelatinization kinetics was carried out on differential scanning calorimetric traces. It was shown that the extent of starch gelatinization follows first-order kinetics, where the rate constant varies with temperature according to the Arrhenius equation ( K o = 2.8 10 18 s −1 ; E a = 138 kJ/mol). Kinetics were validated under dynamic temperature conditions: the experimental results were compared with those obtained from a mathematical model for heat and mass transfer during baking connected to the kinetic model for gelatinization.

Fluid-to-particle heat transfer coefficients in cans during end-over-end processing

Abstract: Convective heat transfer coefficients were measured during end-over-end (EOE) processing of canned Newtonian fluids (oil and water) with a suspended thermocouple equipped polypropylene spherical particle (diameter = 19 mm). Particle transient temperatures were measured at the center using a flexible fine wire (0.0762 mm diameter) thermocouple, allowing for particle movement inside the can during the EOE rotation. Three retort temperatures (110 to 130°C) and four rotational speeds (0 to 20 rpm) were employed as variables in a water immersion rotary retort (Stock PR-900) employed for processing. The fluid-to-particle heat transfer coefficient, hfp, varied from 65 to 120 W/(m2·K) (between water and particle) and 20 to 85 W/(m2·K) (between oil and particle) overall heat transfer coefficient. U. varried from 480 to 880 W/(m2·K) for water and 115 to 165W/m2·K) for oil depending on processing conditions. A dimensionless correlation was developed in terms of Nusselt number (Nu), Reynolds number (Re), Prandtl number (Pr) and dimensionless temperature (φ), to predict the U: N u = 115 + 18 R e 0.33 P r 0.16 φ 3.61 The characteristic dimension in Nu and Re was the diameter of rotation. This correlation, with R2 = 0.88 is valid for Re: 240–48,000; Pr: 7.0–1175 and φ: 0.82–0.85.

Determination of the Solubility Parameter of Soybean Oil by Inverse Gas Chromatography

Abstract: The solubility parameter of soybean oil, σ 2 , has been determined by the technique of inverse gas chromatography (IGC). Using soybean oil as the stationary phase, solute retention volumes were precisely determined as a function of temperature using 22 solute probes of varying solubility parameter (σ 1 ). Solvent (oil)-solute interaction parameters, χ, were also calculated from the solute retention data and indicate complete miscibility of the solute probes with the soybean oil at conditions of infinite dilution. The χ values and their dependence on temperature were used to compute σ 2 at 59, 79, 101, and 123°C. Over this temperature interval, the σ 2 decreased from 7.9 to 6.9 cal 1/2 /cm 3/2 with decreasing temperature, a trend consistent with the loss of cohesional energy density in the liquid soybean oil.

Flavour, chemical and textural profile changes in accelerated ripened Gouda cheese

Abstract: This investigation was carried out to study the flavour, chemical and textural changes during the accelerated ripening of buffalo milk Gouda cheese. Gouda cheese was manufactured using heat-shocked cells of Lactobacillus helveticus and Flavorage enzymic preparation. Cheese was analysed for different attributes at pre-determined intervals. The study revealed that the flavour and body and texture developments were more rapid in the experimental cheeses. The pH, soluble protein and FFA values were higher in experimental cheeses than in the controls. Synergistic action of Lactobacillus helveticus and Flavorage resulted in the fastest changes in cheese. The Instron textural studies revealed that hardness, springiness, gumminess and chewiness decreased during ripening, whereas cohesiveness increased. All textural attributes, except cohesiveness, were lower in experimental cheese as compared to control.