Kinetics of colour and texture changes in Gulabjamun balls during deep-fat frying

Gulabjamun, a popular Indian milk sweet, is prepared by deep-fat frying of balls of dough made of khoa, wheat flour and baking powder, and subsequent dipping in sugar syrup. Kinetics of colour and texture changes in gulabjamun balls were investigated with regard to frying temperature (120, 130, 140 °C). Crust colour was evaluated in terms of CIELAB parameters L*, a*, b*, and ΔE, and rheological properties in terms of hardness, stiffness and firmness. Frying-induced surface browning was reflected in a decreasing lightness value L* as well as the ratio of yellow hue index b* and red hue index a* and total colour expressed in terms of ΔE, L* following a zero-order change whereas the other parameters, a first-order change. Increase in the texture parameters hardness and firmness followed zero-order reaction kinetics whereas stiffness rise followed a first-order reaction. The temperature dependence of reaction constants could be explained by the Arrhenius equation. Activation energy was also obtained for both the colour and texture changes, which were in the range of 24.5-77.6 kJ/mol. High correlations between colour and texture parameters were observed and it was concluded that L* alone could be used to predict the firmness of deep-fat fried gulabjamun balls.     

Color degradation kinetics of pineapple puree during thermal processing

Improvement of color, as a quality attribute of processed pineapple puree, has been made possible by the increase in knowledge of kinetic of color change. The kinetics of color degradation of pineapple puree were investigated during heat treatment at 70-110 °C in order to cover the temperature range that used in preheat and sterilization of commercial aseptic pineapple puree. Color changes associated with heat-treated puree were monitored using Hunter colorimeter (L, a, b, total color difference—ΔE) and Browning index (A₄₂₀). The changes in L and b values fitted well to the first-order kinetic model while ΔE, a value, and Browning index followed the zero-order kinetic. The dependence of the rate constant on temperature was represented by an Arrhenius equation. The results suggested that ΔE and lightness, based on activation energy, were the most sensitive measures of color change at temperature range 70-90 and 95-110 °C, respectively.     

Heat Curing of Soy Protein Films at Selected Temperatures and Pressures

Vacuum and temperature effects on moisture content, water vapor permeability (WVP), color (L, a, b, and ΔE), tensile strength (TS), elongation (E), and total soluble matter (TSM) of soy protein isolate (SPI) films were examined. SPI films were cured at 60, 72.5, or 85 °C and at 101.3, 81.32, or 61.32 kPa for 24 h. As a result of heat-curing moisture content, WVP, E, and TSM decreased, and total color difference and TS increased. Pressure, individually and interactively with temperature, significantly affected film moisture content, TS, and TSM.     

Changes in color parameters of corn kernels during roasting

Changes in color parameters (L*, a*, b*, ΔE*, h°, and C* values) of corn during roasting were investigated and subsequently described using mathematical models. Corn kernels were roasted for 50 min at 160, 180, 200, 220, and 240°C. The L*, b*, h°, and C* values tended to decrease more rapidly as the roasting temperature and time increased up to 220°C and 50 min, whereas a* and ΔE* values tended to increase. Variation of L* and ΔE* values was found to be proportional to the roasting temperature and time. Variation of L* value during roasting above 180°C was adequately described by a first-order model. Cubic model satisfactorily described changes in all of color parameters over the temperature range. Activation energies of L* and ΔE* values were determined as 34.04 and 79.16 kJ/mol, respectively. Results suggest that L* and ΔE* values may be used as color control indicators during roasting of corn kernels.     

Advances in the study of the kinetics of color and fluorescence development in concentrated milk systems

The kinetics of color and fluorescence development in systems containing whole milk powder (WMP), sucrose (S) and water were studied; the influence of three design variables: pH (6, 7 and 8), temperature (105, 122.5 and 140 °C) and WMP/S ratio (R = 0.3, 0.68 and 1.06) being particularly investigated. The Kubelka-Munk index (K/S), luminance or lightness (L), optical density (OD) and fluorescence (F), were measured at different reaction times. Reaction pseudo-order (n) varied between 0 and 1 and reaction rate constants for the development of fluorescence and the color parameters were found to be more dependent on temperature than on R at all measured pH values. Temperature dependence of CP was analyzed through the activation energy (E_a) values. The variables F and OD, which are related to the molecular aspects of the systems, showed the extreme values of E_a, while than K/S and 100/L, related to the macroscopic appearance or reflectance, showed intermediate E_a values and lower dependence with R and pH. When compared to the variables related to brown pigment development, fluorescence development showed a higher relative change, which shows its higher sensitivity as a reaction marker. The variables that most affected color and F development were temperature and protein concentration, respectively.     

Effects of brine concentration and temperature on color of vacuum pulse osmotically dehydrated sardine sheets

The effects of brine concentration (0.15-0.27 g NaCl/g) and temperature (30-38 °C) on the color parameters (L, a, b, ΔE) of vacuum pulse osmotically dehydrated sardine sheets were investigated. The results showed that osmotic dehydration has a significant effect on color of sardine sheets. Redness (a-value) and yellowness (b-value) decreased through dehydration time while lightness (L-value) and total color difference (ΔE) increased. The decreases in redness and yellowness were lesser with increasing temperature and brine concentration while increases in lightness and ΔE were higher. These changes would be predicted by simple models as a function of the temperature, brine concentration, and dehydration time.     

Peeling,drying temperatures,and sulphite-treatment affect physicochemical properties and nutritional quality of sweet potato flour

The effects of peeling, drying temperature (55–65 °C) and pretreatment on the physicochemical properties and nutritional quality of sweet potato flour were investigated. The flours were prepared from peeled and unpeeled sweet potatoes dipped in 0.5% sodium hydrogen sulphite (NaHSO₃). There were significant differences (p < 0.05) in ΔE values and browning index between flours from peeled and unpeeled sweet potatoes without sulphite-treatment (PF and UF). On the other hand, flours from peeled and unpeeled sweet potatoes with sulphite-treatment (PSF and USF) had higher L∗, a∗, and b∗ values, swelling capacity, ascorbic acid, and total phenolics than PF and UF. However, USF and UF had higher β-carotene content than PSF and PF. β-Carotene and ascorbic acid contents decreased with increasing drying temperature for all flours, whereas total phenolics increased for PSF and USF. Therefore, the best quality product was obtained when samples were pretreated with sulphite before drying at any temperature.     

A Fraction Conversion Kinetic Model for Thermal Degradation of Color in Red Chilli Puree and Paste

The kinetics of degradation of color was evaluated using a fraction conversion model during thermal treatment of red chilli puree at 60, 70, 80 and 90°C (up to 20 min) and storage of red chilli paste at 5, 25 and 37°C (up to 6 mo). Red chilli puree was subjected to heat treatment at different temperatures in a well-stirred water bath. Test samples were removed from the bath at selected time intervals (0-20 min after come-up), cooled immediately and analysed for color using a Hunterlab colorimeter. Chilli paste was prepared by a standard formulation by adding common salt (8%) and the required volume of citric acid to bring the pH to 4.0. The paste was thermally processed at 85°C for 15 min, filled into glass bottles and stored at selected temperatures for 6 mo. Red chilli color was expressed as a tristimulus combination value (L·a·b) as well as the total color difference (ΔE). The fraction conversion model adequately described the kinetic changes in both color values during thermal treatment of puree and storage of puree. The process activation energies were 24.2 and 24.8 kJ/mol, respectively, for ΔE and L·a·b during the thermal treatment, and during the storage the respective values were 24.1 and 25.0 18;kJ/mol. Up to the end of the 6-mo storage, the paste was microbiologically stable with no major changes in other physico-chemical characteristics.     

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.     

Stability of nutritionally important compounds and shelf life prediction of tomato ketchup

Ketchup is an important source of tomato antioxidants in human nutrition, this ambient stable product is processed using several relatively important heat treatments and can be stored for one or more years at ambient temperature. Model storage experiments were carried out with two sets of commercial ketchup produced according to the Czech recipe: (a) hot-filled without subsequent pasteurization and (b) filled and pasteurized in the jar. The samples were stored at 25, 50, 75 and 90 °C, during the storage the content of total lycopene and ascorbic acid was observed as well as the colour parameters (a*, ΔE). The obtained data were processed using the pseudo first order (total lycopene, ascorbic acid and a*) and zero order kinetics (ΔE). The obtained results corresponded with the published data, but were not consistent between the both sets of the samples. The total lycopene and ascorbic acid degradation is more dependent on the conditions in the product, mainly on the previous history of heat treatment. The colour parameters, especially ΔE seemed to be more robust criterion, which could be used for the shelf life prediction estimation. The empirically set up shelf life by the producer was confirmed.     

KINETICS of QUALITY CHANGE DURING COOKING and FRYING of POTATOES: PART II. COLOR

Color, as a quality attribute of cooked and fried potatoes, is affected by the extent and nature of heat during thermal processing. Improvement of color parameters has been made possible by the increase in knowledge of kinetics of color change. Analysis of kinetic data allows processors to minimize undesirable changes and optimize color retention. the objective of this study was to evaluate kinetics of color change during cooking and frying of potatoes. Potatoes were cut into cylinders (diameter × height: 20 mm × 20 mm for cooking and 10 mm × 20 mm for frying) and cooked in a temperature controlled water bath at 80–100C or fried in a commercial fryer at 160–190C for selected times. Color changes associated with cooked and fried potatoes were evaluated using a tristiumulus colorimeter in the L, a, b mode. For cooked potatoes, L and b values decreased while ΔE and a values increased with time at each cooking temperature. For fried potatoes, L value decreased while a, b and ΔE values increased as frying time increased. A modified first order model was used to characterize color change kinetics of both cooked and fried potatoes based on changes occurring between the initial and a maximum or minimum value. Temperature sensitivity of rate constants was adequately described by the Arrhenius and z‐value models.     

Evaluation of transglutaminase and caseinate for a novel formulation of beef patties enriched in healthier lipid and dietary fiber

The food intake in developed countries is characterized by a deficient consumption of n-3 fatty acids and fiber. In this study, modified beef patties enriched with polyunsaturated n-3 fatty acids and fiber were developed. The texture profile was compared to traditional beef patties, showing lower values for all parameters except springiness. To improve its texture, pretreatments using transglutaminase (TG) and sodium caseinate (C) were assayed by response surface methodology. Mathematical models were obtained and used to determine the effect of TG, C, temperature and time of pretreatment on the texture of beef patties. The overall optimization indicated that a pretreatment with 0.1 U/g of TG at 40 °C for 17 min allowed to have a traditional texture for beef patties enriched in n-3 PUFAs and fiber. The models showed that the addition of caseinate was not needed. Minimal effects of pretreatment were observed on composition, color and cooking loss of the product.     

Application of computer vision technique for on-line monitoring of shrimp color changes during drying

The effects of drying temperature and drying medium velocity on color change kinetics of shrimp viz. lightness (L^∗), redness (a^∗), yellowness (b^∗), total color difference (ΔE), chroma (CH), hue angle (H°), and browning index (BI) were on-lineally investigated. Drying experiments were carried out on dryer equipped with computer vision systems using hot air drying (HAD) temperatures of 50–90 °C and superheated steam drying (SSD) temperatures of 110–120 °C at drying medium velocities of 1–2 m/s. Zero-, first-order, and fractional conversion models were utilized to describe the color changes of shrimps and the fractional conversion model successfully tracked the experimental data. The results showed that the color parameters were significantly influenced by the studied parameters. Lightness of the samples decreased, while other color parameters increased as drying proceeded. Generally, increasing drying medium temperature decreased L^∗ and H°, whereas increased other color parameters. The color characteristic of the SSD finished products were acceptable than the HAD processed samples. Finally, dimensionless moisture content of shrimps during drying was accurately correlated to the color parameters and drying time using a quadratic regression model. Moisture ratio had strong relationship with the lightness change compared with the redness and yellowness variations.     

Extraction, thermal stability and kinetic behavior of pectinmethylesterase from hawthorn (Crataegus pubescens) fruit

Pectinmethylesterase (PME) extracted from hawthorn (Crataegus pubescens) fruit was evaluated for its thermal stability and kinetic behavior. The enzyme extraction process was established after studying different NaCl concentrations (0.5-3.0 moles/L). A maximum PME extraction of 51.61 units/mg protein was obtained using 2 moles/L NaCl. Kinetic parameters (K_m and V_max) were determined using a commercial citrus pectin and C. pubescens pectin as substrates. The effects of NaCl concentration, pH and temperature on PME activity were investigated. PME showed higher affinity for C. pubescens pectin (K_m and V_max of 2.84 mg/mL protein, and 64.10 units/mg protein, respectively) than for citrus pectin. C. pubescens PME extract showed maximum activity at 0.4 moles/L NaCl, pH 7.5, and 55 °C. The E_a and Q₁₀ for thermal activation were 36.27 kJ/mol and 2.01 (20-30 °C), respectively. About 50% of the activity still remained after heating for 25 min at 60 °C, and it was completely inactivated by incubation at 80 °C for 10 min. The Q₁₀ and E_a values for thermal inactivation reaction were 20.06 (70-80 °C) and 146.16 kJ/mol, respectively. These results provide useful information about the factors that affect the activity of C. pubescens PME, and might be used as a starting point for texture control during post-harvest handling and processing of this fruit.     

Effects of nitrite levels,endpoint temperature and storage on pink color development in turkey rolls

The objective of this research was to determine the relationship between minimum nitrite level, endpoint temperature and storage period on pink discoloration of turkey rolls. Rolls were prepared with 0, 3 or 5 parts per million (ppm) NO₂^–, cooked to an endpoint temperature of 75 °C or 85 °C and stored at 4 °C. During the 13-day storage period, on the 0th, 4th, 8th and 13th days cured pigment, total pigment, residual nitrite and color parameters were measured and sensory color was evaluated. At each endpoint temperature, addition of 3 ppm or 5 ppm NO₂^– significantly increased cured pigment and total pigment levels. Cured pigment levels of turkey rolls cooked to 75 °C were higher than rolls cooked to 85 °C, regardless of the NO₂^– level. There was a significant decrease in cured pigment levels at the end of the storage period (13th day). Analysis of residual NO₂^– in all treatment groups showed no detectable amounts. Endpoint temperature and addition of NO₂^– affected L* values: rolls cooked to the 75 °C endpoint had higher L* values. The additon of nitrite with the 75 °C endpoint temperature resulted in higher a* values. a* values also increased during the storage. The higher endpoint temperature (85 °C) resulted in lower a* values. Yellowness was not affected by final cooking temperature. Both the addition of NO₂^– and storage decreased b* values. The panel found no differences in pinkness intensity between the two levels of added nitrite (3 and 5 ppm). Sensory pinkness intensity in nitrite-added samples increased with increasing storage.     

Thermal Kinetics of Colour Degradation of Yellow Sweet Pepper (Capsicum Annum L.) Undergoing Microwave Assisted Convective Drying

Experiments were conducted to study the kinetics of colour change of yellow sweet pepper during microwave-assisted convective drying at power levels of 280, 210, 140, and 70 W; temperatures of 60, 45, and 30°C; and a constant air velocity of 1.5 m/s. Colour change kinetics were determined using Hunter’s primary L, a, b values, chroma, hue, total colour change (ΔE), and browning index (BI) values. The results indicated that the degradation of a, ΔE, and hue followed zero order kinetics and L, b, chroma, and browning index followed first order kinetics. The rate constant was assumed to have Arrhenius-type dependence on temperature. Again, based on activation energy, b and hue parameters proved to be the most sensitive measures of color change, which could be taken into account during thermal processing of capsicum for getting a quality product.     

Kinetic Modeling of Texture and Color Changes During Thermal Treatment of Chicken Breast Meat

Heat treatment is commonly applied as a primary method for ensuring the microbial safety of poultry meat and to enhance its palatability. Although texture and color of cooked chicken breast meat are important quality parameters for the consumers that need to be controlled during thermal processing, studies assessing the temperature-time-dependent quality changes during thermal treatment are lacking. This work aims to investigate the texture and color changes of chicken breast meat during thermal processing and to develop kinetic models that describe these changes. We studied the storage modulus changes of chicken breast meat as function of temperature. The storage modulus increases from 55 °C until leveling off in an equilibrium value above 80 °C, which was attributed to microstructure changes and described with a sigmoidal function. The changes in the texture (TPA) and color (CIE L ^* a ^* b ^* ) of chicken breast meat were measured as function of temperature and time. The texture and color parameters show a rise with heating time until reaching an equilibrium value, while the rate of change increased with temperature. Kinetic models that take the non-zero equilibrium into account were developed to describe the color (lightness) and texture (hardness, gumminess, and chewiness) changes with heating time and temperature. The kinetic models provide a deeper insight into the mechanisms of texture and color changes during thermal treatment. They can be used to predict the texture and color development of chicken breast meat during thermal processing and, thus, help to optimize the process.     

Sensory,physical and chemical characteristics of cooked ham manufactured from rapidly chilled and earlier deboned M. semimembranosus

Effects of rapid chilling of carcasses (at − 31 °C in the first 3 h of chilling, and then at 2–4 °C) and earlier deboning (8 h post-mortem), compared to rapid (till 24 h post-mortem) and conventional chilling (at 2–4 °C, till 24 h post-mortem), on quality characteristics of pork M. semimebranosus and cooked ham were investigated. Quality measurements included pH value, colour (CIEL*a*b* values) and total aerobic count of M. semimebranosus, as well as sensory (colour, juiciness, texture, and flavour), physical (pH value, colour – CIEL*a*b* values and texture – Warner–Bratzler shear and penetration forces) and chemical (protein, total fat, and moisture content) characteristics of cooked ham. The cooked ham was manufactured from pieces of M. semimebranosus with ultimate lightness (CIEL* value) lower than 50. Rapid chilling and earlier deboning significantly increased quantity of M. semimebranosus desirable for cooked ham manufacturing. Earlier start of pork fabrication did not affect important quality characteristics of cooked ham.     

Comparison of free/bi-axial,fixed axial,end-over-end and static thermal processing effects on process lethality and quality changes in canned potatoes

Thermal processing as the most prevalent food preservation technique has been extensively studied and used for years. Different modes of agitation that can be employed in the canning process are characterized by relatively different, heat impacts and their associated quality changes. Hence, the main objective of this study was to evaluate the impact of different retort conditions on lethality (F_o), color and textural changes in potato cubes. Process variables employed were: retort temperature: 115, 120, 125 ºC; agitation orientations: vertical (end-over-end) and horizontal (fixed and bi-axial); agitation speed: 0 (static), 10, 20 rpm. A water immersion single basket rotary retort was retrofitted to simultaneously accommodate agitating modes of rotation. Accumulated process lethality values were calculated for each experimental run. Color quality in terms of parameters such as, yellowness (b-value), total color difference (ΔE values) and textural quality in terms of hardness values were compared for the particles processed under each condition. All process variables had a significant (p < 0.05) influence on F_o, color and texture parameters of potato particles. The quality changes were found to correlate well with the accumulated F_o values achieved during processing. As can be expected, the quality loss increased with an increase in F_o and vice versa.