Effect of temperature on the drying characteristics,colour, antioxidant and beta‐carotene contents of two apricot varieties

In this study, the drying characteristics, colour, oxygen reactive antioxidant capacity (ORAC) and beta‐carotene contents of two apricot varieties dried at different temperatures were compared. The hot air drying of apricot slices for both varieties consisted of a constant rate period (CRP) and two of falling rate periods (FRP). The CRP drying rate and the first and second FRP drying coefficients increased with drying temperature for both apricot varieties. The first and second FRP of both apricot varieties gave activation energies of 23.5–28.7 and 25.6–29.3 kJ mole^?1, respectively. The colour values (L*, a* and b*) of both dried apricot varieties decreased with increasing temperature, while the total colour change of both dried apricot varieties increased with temperature. The chroma, hue angle and browning index values of both dried apricot varieties decreased with increasing temperature, and the hydrophilic ORAC and beta‐carotene contents increased with drying temperature.     

Effect of non‐isothermal processing and moisture content on the anthocyanin degradation and colour kinetics of cherry pomace

Anthocyanins (ACY) and colour changes in cherry pomace under non‐isothermal processing were investigated. Pomace at moisture levels of 70% (MC‐70), 41% (MC‐41) and 25% (MC‐25) was heated at 126.7 °C in a retort for 25, 40 and 60 min. Total ACY, Hunter colour values, total colour difference (ΔE), chroma, hue angle (h°) and browning index (BI) were analysed. Thermal degradation kinetics for colour parameters were determined using zero‐ and first‐order models. ACY degradation increased with heating time and ranged from 34 to 68% for 25 and 60 min heating, respectively. The half‐life of ACY was 38, 33 and 27 min for MC‐70, MC‐41 and MC‐25 pomace, respectively. The ΔE increased with increasing heating time, whereas BI exhibited an inverse trend. Except for ?E for MC‐70, the zero‐order kinetic model showed better fit (R² = 0.85–0.97) to experimental data than the first‐order kinetic model for Hunter colour b values and ?E.     

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.     

Effect of blanching and drying treatments on quality of bamboo shoot slices

The enzymes activity, texture, pectin, microstructure and colour change in bamboo shoots (Dendrocalamus latiflorus) were examined to evaluate the effect of blanching and drying treatments on quality of bamboo shoot slices (BSS). Peroxidase (POD), phenylalanine ammonia‐lyase and polyphenol oxidase in BSS will become completely inactive at 95 °C for 6‐, 9‐ and 12‐min blanching treatments, respectively. The hardness and protopectin (PP) content decreased after the blanching treatment. Meanwhile, the content of water‐soluble pectin increased initially and then decreased gradually during the blanching. After the blanching treatment, the L* and a* of BSS decreased, while b* increased, ΔE > 2. The hardness of rehydrated BSS decreased by 43.57% after freeze drying (FD), which, however, decreased more after hot air drying (HAD). The pectin of rehydrated BSS was also determined to explain the hardness change in BSS. The BSS acquired similar microstructure of fresh samples after FD, while microstructure of BSS was severely damaged after HAD. The colour of BSS changes significantly after drying treatment. However, FD can maintain better colour of BSS than HAD. The results may provide a reference for industrial production of BSS.     

Degradation Kinetics of Colour and Total Carotenoids in Jackfruit (Artocarpus heterophyllus) Bulb Slices During Hot Air Drying

The kinetics of colour and carotenoids degradation in jackfruit bulb slices was evaluated during hot air drying at 50, 60 and 70 °C. Visual colour as well as total carotenoids (TC) content was found to be influenced by the drying process. Tri-stimulus colour parameters such as Hunter L and b values decreased and a value increased during drying. The combination of Hunter L × b value was found to represent the colour change adequately. Degradation of TC and visual colour in terms of Hunter L × b value followed first-order reaction kinetics; however, zero-order reaction kinetics was found adequate to describe changes in total colour difference (TCD) and non-enzymatic browning (NEB). Dependence of the rate constant followed the Arrhenius relationship. The process activation energies (E _a) for Hunter L × b value, TCD, NEB and TC were 29.96, 27.21, 27.48 and 55.61 kJ/mol, respectively. Higher E _a for TC content indicated greater temperature sensitivity as compared with other colour parameters. Relationship of TC content and Hunter L × b value was found to be more consistent through regression analysis with R ² ≥ 0.979.     

The use of bulgur as a meat replacement: bulgur‐sucuk (a vegetarian dry‐fermented sausage)

In this study, bulgur was used to produce a new sucuk (Turkish dry‐fermented sausage) as a vegetarian product. Yellow and black/brown bulgurs were mixed into the sucuk dough as fat and meat imitations respectively. Instead of animal fat, olive oil was used for lubrication. Nitrite and nitrate were not added to the recipe. The bulgur‐sucuk was ripened at 60–95% relative humidity and 18–25 °C over 15 days. During ripening, pH, moisture content and textural (hardness, adhesiveness, springiness, cohesiveness, gumminess, chewiness and resilience), sensory (flavour, colour, cutting and overall scores) and colour (Hunter L, a, b, yellowing index (YI), total colour difference, hue angle, chroma and browning index values) attributes were monitored. The pH and moisture content of the bulgur‐sucuk were 5.81 and 493 g kg^?1 respectively before ripening and decreased to 4.14 and 280 g kg^?1 during ripening. The colour values L, a, b and YI decreased significantly (P < 0.05) to 33.03, 7.67, 11.63 and 80.70 respectively during ripening. Some of these decreases in colour values were expected owing to the lack of nitrite and nitrate. All instrumentally measured textural properties of the bulgur‐sucuk increased significantly (P < 0.05) during ripening. From the results of the parameter measurements and sensory evaluations, bulgur appears to be suitable as a meat replacement when used in a dry‐fermented formulation. Copyright © 2006 Society of Chemical Industry     

A colorimetric study of oenin copigmented by procyanidins

A colorimetric method was used to analyse the influence of procyanidin structure on colour changes of malvidin 3‐O‐glucoside (oenin) solution resulting from copigmentation. The study was performed in hydroalcoholic citrate/phosphate buffer solution (120 g L^?1) at pH 3.6 and ionic strength 0.2 mol L^?1. Chromatic L*, a* and b* coordinates (CIELAB, D65/10° illuminant/observer condition) obtained from spectral curves recorded between 360 and 830 nm allowed the calculation of lightness L*, chroma C* and hue angle h_ab. In general, addition of copigment induced colour enhancement (loss of lightness and increased chroma). The prevailing parameters affecting colour changes were lightness and chroma for monomers and lightness and hue for procyanidins B5 and B8 (C4–C6 dimers). A small blueing effect was observed only for catechin monomer‐copigmented solutions. For procyanidin copigments, as the structural complexity of the copigment increased, the hue angle moved to yellower values. The ester gallate of dimer B2 produced the strongest modification of colour attributes of oenin solution. Copyright © 2006 Society of Chemical Industry     

Influence of particle characteristics and E/Z‐isomer ratio on the colour of concentrated β‐carotene dispersions

The influence of particle concentrations (0.02–0.40%), mean particle sizes (0.45–1.5 μm) and all‐E‐isomer ratios (95–30%) on the CIELAB colour coordinates (L*, a*, b*) of concentrated β‐carotene dispersions was investigated. Particle concentration between 0.06% and 0.40% had a slight impact on the colour parameters. However, with decreasing the mean particle size from 1.50 to 0.45 μm, there were increases in ΔL* = 8.0, in Δa* = 2.26 and in Δb* = 13.1. And with decreasing the all‐E‐isomers ratio from 95% to 30%, there were increases in ΔL* = 8.66, in Δb* = 17.51 but decrease in Δa* = 7.42. The experimental results were explained in terms of the scattering and absorption of light by dispersions. These findings have important implications for food industry as they offer a means to control and optimise the colour of food dispersions.     

Influence of microwave,the combined microwave/hot air and only hot air roasting on the formation of heat-induced contaminants of carob powders

ABSTRACT

This study aims to investigate the effects of microwave, combined microwave/hot air treatment and hot air-only roasting on the formation of heat-induced contaminants of carob powders. Moisture content, water activity and pH values of the product decreased with the increasing roasting time and microwave power, while browning index (BI) and ultraviolet absorbance (UV-A) values were increased. While L and b values of carob powders decreased with increasing the roasting time and microwave power, a and ΔE values were increased. Varying roasting conditions also significantly affected the content of Maillard reaction products (MRPs): 5-hydroxymethylfurfural (HMF) (0.69–28.32 mg/kg dry matter), furfural (<LOD-10.44 mg/kg dm), furan (6.65–10.26 mg/kg dm) and acrylamide (78.69–122.87 µg/kg dm). MRPs contents increased with increasing the roasting time and microwave power. The highest MRPs were found in the samples roasted at 140°C for 20 min by hot air. Significant correlations between the amount of MRPs and colour values were found, especially with a and b values.     

Carotenoid contents of extruded and non-extruded sweetpotato flours from Papua New Guinea and Australia

Carotenoid contents of extruded and non-extruded flours of Papua New Guinean and Australian sweetpotato cultivars were studied, using spectrophotometry and high performance liquid chromatography (HPLC). The cultivars differed (p < 0.05) in their total carotenoid and β-carotene contents, and the Original Beauregard cultivar had the highest total carotenoid and β-carotene contents among the cultivars. The spectrophotometry (84–1720 μg/g solids) method generally over-estimated the total carotenoid content compared to the more specific HPLC (23–355 μg/g solids) method. Extrusion significantly (p < 0.05) decreased the ΔL^∗ Hunter colour values, while the Δa^∗, Δb^∗, total colour change (ΔE), chroma (CR), and browning indices (BI) increased. With the extruder and screw configuration used, extrusion at 40% moisture and 300 rpm screw speed retained carotenoid maximally at more than 80%. This study reports, for the first time, carotenoids of flours from south Pacific sweetpotato cultivars, and carotenoid retention during extrusion.     

Determination of optimum processing conditions for hot‐air roasting of hulled sesame seeds using response surface methodology

Sesame paste (tahin) is produced by milling hulled, roasted, sesame seeds. In this study, a hot‐air roasting process for the production of sesame paste was optimised by response surface methodology (RSM) over a range of air temperatures (120–180 °C) for various times (30–60 min). The colour parameters (L, a and b values), browning index (BI), hardness, fracturability and moisture content of the seeds were used as response parameters to develop predictive models and optimise the roasting process. Increases in roasting temperature and time caused increases in the a and b values and in the BI. The hardness and fracturability of seeds also decreased with increasing roasting temperature and time. The quadratic and linear models developed by RSM adequately described the changes in the colour values and textural parameters, respectively. The result of RSM analysis showed that all colour parameters and textural parameters should be used to monitor the roasting of sesame seeds in a hot‐air roaster. To obtain the desired colour and texture, the optimum roasting range for production of sesame paste was determined as 155–170 °C for 40–60 min. Copyright © 2006 Society of Chemical Industry     

Changes in pigment profile and surface colour of fig (Ficus carica L.) during drying

In this study, anthocyanins in three fresh fig varieties (Ficus carica L.) cultivated in Turkey were characterised and quantified by HPLC/DAD and HPLC/MS. In addition, the carotenoid composition of Sar?lop and Sar?zeybek, yellow fig varieties, was determined, and then the ripening‐ and drying‐related changes in carotenoids and surface colour of figs were monitored during conventional sun‐drying. Four different anthocyanins, cyanidin‐3‐glucoside, cyanidin‐3,5‐diglucoside, cyanidin‐3‐rutinoside (major anthocyanin) and pelargonidin‐3‐glucoside, were identified in samples. Lutein, zeaxanthin, β‐cryptoxanthin and β‐carotene were carotenoids in yellow fig varieties. Approximately 80% of carotenoid compounds in yellow fig varieties degraded at the end of drying (i.e. seventh day). L (lightness), a (redness and greenness) and b (yellowness and blueness) colour parameters were measured by Hunter Lab system. Great changes in carotenoid composition and surface colour were observed at ripening stage on tree. A significant reduction in L and b values that refers to browning in figs was made in the first 3 days of drying process.     

Changes in browning‐related components of apple slices during different stages of instant controlled pressure drop‐assisted hot air drying (AD‐DIC)

The effect of instant controlled pressure drop‐assisted hot air drying (AD‐DIC) on browning‐related components in apple slices was studied. Results showed the AD temperature had no significant effect on colour index of final apple slices. The aspartic acid, glutamic acid, lysine, histidine, arginine, sucrose and dehydroascorbic acid (DHAA) in apple slices increased firstly during the AD process and then decreased during DIC process. The fructose, glucose, reduced ascorbic acid and major phenolic compounds reduced with the abrupt increase of 5‐hydroxymethylfurfural (5‐HMF) during AD‐DIC. There were significant correlations (P < 0.05) among moisture content (w.b.), water activity (a_w), water state, reduced ascorbic acid, DHAA, chlorogenic acid, procyanidin B₁, (+)‐catechin, (?)‐epicatechin and phlorizin during AD‐DIC. The colour difference showed that the major browning reaction of apple slices during the predrying process was enzymatic browning, while nonenzymatic browning played a crucial role on green‐red value (CIE a* value) during DIC.     

Physical,functional and pasting properties of different maize (Zea mays) cultivars as modified by an increase in γ‐irradiation doses

Physical, functional and pasting properties of six maize (Zea mays) cultivars as modified by an increase in γ‐irradiation doses were investigated. From the L*, a* and b* measured, deltachroma, colour intensity and hue angle were calculated. Functional and physicochemical properties of maize flours were determined using standard methods and Rapid Visco Analyser, respectively. Often, the effect of γ‐irradiation on L*, a* and b* values within each cultivar was almost never significant but pronounced between the yellow and white cultivars. Generally, deltachroma, colour intensity and hue angle decreased with increased γ‐irradiation dose. Mean seed bulk density and 100 kernel weight varied from 0.73–0.77 g cm^?3 and 23.13–35.42 g, respectively. Loose and packed bulk densities, and water (WAC) and oil absorption capacities of the maize flours were not significantly affected by γ‐irradiation. WAC of nonirradiated and γ‐irradiated maize flours ranged from 1.54–1.62 and 1.09–1.70 g g^?1, respectively. Peak, trough, breakdown, final and setback viscosities decreased significantly (P < 0.05) with increased γ‐irradiation dose.     

Steam blanching effect on polyphenoloxidase,peroxidase and colour of mango (Mangifera indica L.) slices

The heat stability of peroxidase (POD) and polyphenoloxidase (PPO) was investigated in mango (Mangifera indica L.) slices, and the relative colour was studied after different steam blanching times. There was complete inactivation after 5 min for POD and 7 min for PPO. Steam blanching of 3 min gave residual activity of 2.85% and 8.33% for PPO and POD, respectively, and when compared with samples blanched for 5 min had no effect on colour over 20 days of storage. Correlation was found between activities of PPO, POD and colour change over 20 days. After 7 min steam blanching the browning index was stable but less than at 3 and 5 min because non-enzymic browning had occurred. This research suggests that yellowness (b) and lightness (L) values contribute positively to the browning index (BI), compared to redness (a).     

Browning reactions during storage of low-moisture Australian sultanas: Evidence for arginine-mediated Maillard reactions

Browning during storage of low‐moisture dried Vitis Vinifera L. cv. Sultana (Thompson Seedless) grapes was examined in a multifactorial treatment and storage trial. Grapevines were subjected to two different levels of sun exposure, harvested fruit was dipped and subjected to different drying treatments to obtain a range of initial moisture contents (a_w= 0.419–0.558). The storage effects of temperature (10^oC and 30^oC), and the presence of oxygen on colour change (CIE L*a*b* tristimulus values, hue‐angle (h_ab*)) and chroma (C_ab*) over a fourteen‐month period were observed. The most significant changes in colour were measured for samples stored at 30^oC, both aerobically and anaerobically, although the largest changes occurred in the presence of oxygen. Initial a_w had a strong effect on colour changes; higher a_w non‐sunfinished samples underwent more significant browning compared to lower a_w sunfinished controls regardless of their oxygen status. Changes in the concentration of the free‐arginine and free‐proline, the most abundant free amino acids in sultanas, were monitored throughout the storage period. Free arginine decreased significantly at 30^oC in both the absence and presence of oxygen, whereas free proline increased (at both 10^oC and 30^oC), implying that free proline did not play a role in browning reactions at those temperatures. In addition to the decreases in free arginine, the concentration of 5‐hydroxymethyl furfural (5‐HMF), a marker of Maillard browning reactions, increased significantly in samples stored at 30^oC. Significant differences in the concentrations of 5‐HMF under the two oxygen conditions indicated sultana Maillard reactions, and possibly other non‐enzymatic browning processes, were oxygen sensitive.     

苹果片热风薄层干燥过程中颜色变化的动力学模型

为了研究苹果片在热风薄层干燥过程中的颜色变化规律,分别在60、70、80、90、100℃下对苹果片进行热风薄层干燥处理,以亮度值(L*)、红绿值(a*)、黄蓝值(b*)、总色差(ΔE)、饱和度、褐变指数(BI)等为指标描述苹果片的颜色变化,并分别应用零级和一级反应动力学方程进行数学模型的拟合分析。结果表明,热风薄层干燥过程中,苹果片的L*值随着干燥时间的延长而逐渐降低,而a*值、b*值、ΔE、饱和度、BI值则逐渐升高,且反应速率常数k随着干燥温度的升高而呈现出一定的规律性变化。根据拟合决定系数R2的比较结果,零级反应动力学模型能更好的描述和预测苹果片在热风薄层干燥过程中的L*、a*、b*、ΔE值变化,而饱和度和BI值的变化则更符合一级反应动力学模型。该模型可以对苹果片在热风薄层干燥中的颜色变化进行预测,为优化干燥工艺提供参考。      

Colour of post-harvest ripened and vine ripened tomatoes (Lycopersicon esculentum Mill.) as related to total antioxidant capacity and chemical composition

Greenhouse grown tomatoes (cvs ‘Durinta’, ‘Favorita’ and ‘Liberto’) were harvested green and vine ripe. Colour measurements and chemical analyses were performed on green, post‐harvest red and vine‐ripe fruits. Partial least square (PLS) regression was applied to predict the ferric reducing ability of plasma (FRAP) by means of colour measurements (L*, a* and b*). The PLS showed that 78% of the variation in colour were able to predict 74% of the variation in FRAP value. Chemical variables and colour variables together were able to predict 88% of the variation in FRAP by means of PLS regression. Linear regression showed a high negative correlation between high values of L*, b* and FRAP, and a high positive correlation between titratable acidity, a*, hue, a*/b*, soluble solids, vitamin C, dry matter and FRAP values. Thus, colour measurements of intact tomatoes can be used as a non‐destructive method to assess total antioxidant capacity of tomatoes.     

Effect of ripeness and postharvest storage on the evolution of colour and anthocyanins in cherries (Prunus avium L.)

The relationship between colour parameters and anthocyanins of four sweet cherry cultivars, Burlat, Saco, Summit and Van was studied. The colour (L^∗, a^∗, b^∗, chroma and hue angle parameters) and anthocyanins were analysed during two different years at two different ripening stages (partially ripe, and ripe, respectively). The cherries were analysed at harvest and after storage at 1.5 ± 0.5 °C and 15 ± 5 °C for 30 and 6 days, respectively. The colour was measured by tristimulus colourimetry (CIELAB system) directly on the fruits, while anthocyanins were quantified by HPLC-DAD analysis on methanolic extracts of freeze-dried samples of the fresh cherries and on the differently stored cherries. L^∗, chroma, and hue angle values were always lower for the ripe than for the partially ripe cherries. All of the cultivars were found to contain cyanidin-3-rutinoside and cyanidin-3-glucoside as the major anthocyanins. The total anthocyanin content in fruits of the different cultivars varied in the order Burlat > Saco > Van > Summit. The concentration of anthocyanins increased at both temperatures of storage in both ripe and partially ripe cherries, but the extent of increase varied among cultivars. Cherries stored at 15 ± 5 °C showed higher reduction of L^∗, chroma and hue angle than fruits stored at 1.5 ± 0.5 °C. L^∗, a^∗, b^∗, chroma and hue angle correlated negatively (P < 0.001) with the total anthocyanins levels, but not with the total phenols. These results show that chromatic functions of chroma and hue correlate closely with the evolution of colour and anthocyanins levels during storage of sweet cherries and indicate that colour measurements can be used to monitor pigment evolution and anthocyanin contents of cherries (and vice versa).