CHLORINATED WATER TREATMENTS AFFECTS POSTHARVEST QUALITY OF GREEN BELL PEPPERS

Green bell peppers (cv. Bell boy) were dipped in 0, 50, 100, 150 and 200 μg/mL chlorine solutions for 20, 30 and 45 min to study the effect of chlorine on pepper quality characteristics. Chlorinated water treatments as well as dipping time had no major effect on external color or total sugar content of green peppers. However, total chlorophyll soluble solids content and ascorbic acid content decreased with increasing time of dipping and chlorine concentration. A 20 min dipping time in 50 to 100 μg/mL chlorinated solutions can be used without reducing the overall quality of green bell pepper.     

OPTIMIZING THE DEHYDRATION CONDITIONS OF GREEN BELL PEPPERS (CAPSICUM ANNUUM L.): QUALITY CRITERIA

Green bett pepper (Capsicum annuumL.) dices were dehydrated at different dry bulb air temperatures (55, 60, 65, 70 and 75C) and relative humidities (15, 20, 25, 30, 35 and 40%). Color, L-ascorbic acid and sugar retention were adversely affected by temperature and RH during dehydration. Loss of color and reduction in L-ascorbic acid and sugar were more prominent at the higher temperatures (70 and 75C) used. Sugar retention was negatively affected by drying, in that levels decreased, but no distinguishable pattern existed between the drying conditions and sugar retention. Optimum quality (maximum retention of color and L-ascorbic acid) green peppers were attained at drying conditions of 55 and 60C (15–40% RH) as well as at 65 and 70C (15% RH).     

A COMPARISON OF LIPID AND LIPID/HYDROCOLLOID BASED COATINGS TO EVALUATE THEIR EFFECT ON POSTHARVEST QUALITY OF GREEN BELL PEPPERS

Maintaining quality of harvested fruit and vegetables is a challenge. The study investigated the effects of two lipid and lipid/hydrocolloid based coatings on maintaining post harvest quality of green bell peppers. Quality characteristics measured during the 4‐week storage period included: respiratory rate, moisture content (weight loss), chlorophyll content, puncture force, ascorbic acid (AA) and dehydroascorbic acid (DHA) contents. No significant differences (P>0.05) between uncoated and coated peppers were noted for respiration rate, puncture force, chlorophyll content, and AA. Significant differences (P<0.05) were found in moisture content and DHA content in the uncoated and coated peppers. Continued research is needed in creating more sophisticated bilayer coatings to enhance product shelf‐life.     

EFFECT OF STORAGE CONDITIONS, PACKAGING MATERIAL AND METABISULPHITE TREATMENT ON THE COLOR OF DEHYDRATED GREEN BELL PEPPERS (CAPSICUM ANNUUM L.)

Green bell pepper dices were dipped in two metabisulphite solutions, 2400 and 3600 mg. kg‐¹, respectively, and dehydrated. The dehydrated peppers were sealed in laminated pouches of different oxygen and moisture transmission rates, and stored in the dark at 0, 10 and 20C for 12 weeks. Color was evaluated by objective color measurement and a sensory panel during storage. The different packaging materials did not significantly influence color retention, while the SO₂ treatments showed only limited differences in their effect, but storage temperatures significantly affected visual and objective color. The best correlation between visual color evaluation and the objective color measurements, was obtained for the a* (greenness) measurements. Panelists could discriminate between samples stored at 0 and 10C in contrast to a* measurements which did not differ significantly. Calculated hue angles exhibited the highest discriminatory ability of any of the objective color parameters.     

STORAGE QUALITY OF BELL PEPPERS PRETREATED WITH HOT WATER AND POLYETHYLENE PACKAGING

Treatments of bell peppers (Capsicum annuum, L) with hot water at 45Cfor 15 min or SSC for 4 min prior to storage at 8C markedly reduced the incidence of fungal infections. However, the hot water treatment induced shriveling during storage. When hot water treated pepper fruits were subsequently placed in low density polyethylene bags, storage quality of these peppers improved tremendously including retention of firmness, reduction of water loss, retardation of color change, and alleviation of chilling injury. Total soluble solids, titratable acidity, and pH values in the pepper fruit were generally not affected by these treatment. A 4 min dip at 53C followed by packaging with 0.065 mm low density polyethylene film was very effective in maintaining pepper quality. This treatment inhibited respiration rate, reduced decay, retained turgidity and green color, and maintained excellent overall quality after 28 days of storage at 8C. Hot water treatment combined with polyethylene film packaging is a promising technique for improving the storage quality of bell peppers.     

REHYDRATION KINETICS OF MICROWAVE-DRIED OKRAS AS AFFECTED BY DRYING CONDITIONS

The aim of the present work was to understand the effect of drying conditions (microwave output powers and sample amounts) and rehydration temperature on rehydration kinetics of microwave-dried okras. Four different models, Peleg's, Weibull, first order and exponential association, were applied to experimental data, and the corresponding parameters of the models were obtained. In addition, the kinetic parameters of the models were correlated with the ratio of microwave output power to sample amount and temperature. Although all the models applied provided a good agreement with the experimental data with high values of the coefficient of determination of R ², the first-order kinetic model was chosen as the appropriate model because of its simplicity. By using the kinetic parameters of this model, the activation energy for rehydration kinetics was estimated as 1.15 kJ/mol.

PRACTICAL APPLICATIONS

Drying, in general, is a means of removal of water from the material. The purpose of drying food products is to allow longer periods of storage with minimized packaging requirements, reduce shipping weights, and preserve seasonal plants and make them available to consumers during the whole year. Besides these advantages, some important changes take place, as structural and physicochemical modifications, which affect the final product quality during dehydration. Rehydration is a complex process aimed at the restoration of raw material properties when dried material contacted with water, and can be considered as a measure of the injury to the material caused by drying. The objective of rehydration study is to attain as many products in their original characteristics as fast as possible. An improved knowledge of rehydration kinetics would significantly enhance the feasibility of this process.     

DISPLAY LIGHT AND ACCEPTABILITY OF GREEN, RED AND YELLOW PEPPERS

The effects of incandescent (INC), fluorescent (FL), and metal halide (MH) light sources on the appearance of red, green, and yellow sweet bell peppers were investigated. The color of the red pepper was significantly preferred when presented under INC than under FL and MH lights. The term used by the panelists to describe the color of peppers under INC light was mainly bright red, but dark red under FL and MH. Relative luminance data, collected with a fiber optic probe connected to a photo diode array, demonstrated the reason to be the low red light output from the FL and MH sources, which resulted in a low visible red color. The color of the green pepper was more acceptable under INC than under MH. For the yellow pepper, there was no significant effect of the light source because all three light bulbs emit a strong yellow component.     

FIRMNESS AND COLOR RETENTION IN BLANCHED GREEN BEANS AND GREEN BELL PEPPER

A comparative study of the effects of single-stage conventional high temperature – short time (HTST) blanching, two-stage low temperature – long time followed by high temperature – short time (LTLT/HTST) blanching, and vacuum infiltration of calcium followed by HTST-blanching on the firmness and color of green beans and green bell pepper was carried out. The two-stage blanching procedure significantly improved the firmness of the blanched vegetables, but resulted in the development of an olive green/brown color in sharp contrast to the dark green color of vegetables subjected to HTST-blanching alone. On the other hand, vacuum infiltration of calcium into the vegetable tissues resulted in blanched materials which were nearly or equally as firm as those subjected to LTLT/HTST-blanching and which were equally as green as, if not greener than, the corresponding single-stage HTST- blanched samples.     

MODELING THERMAL SOFTENING KINETICS OF POTATOES USING FRACTIONAL CONVERSION OF RHEOLOGICAL PARAMETERS

Texture degradation in potatoes was investigated during heating of cylindrical test samples, 15 mm diameter and 30 mm long, in water at 60, 70, 80 and 90C by mechanical testing. The rheological parameters obtained from the axial and radial compression, creep and stress relaxation tests decreased exponentially with an increase in heating duration and temperature approaching steady levels corresponding to the remaining texture after prolonged heating. A single first-order kinetic model described the changes in various rheological parameters due to thermal softening of potatoes using fractional conversion technique indicating very high values of the coefficient of determination (R² > 0.97). In general, the visco-elastic test parameters were relatively more sensitive to texture degradation in potatoes in comparison with the quasi-static test parameters. Overall comparison showed that elasticity and viscosity parameters in Kelvin component of the 4-element model (E₂ and η₂) from creep tests and elasticity moduli from axial and radial compression tests (E_a and E_r) best presented the texture degradation kinetics in potatoes with R² ranging from 0.98 to 0.99.     

PROLONGING THE SHELF-LIFE OF FRESH GREEN CHILE PEPPERS THROUGH MODIFIED ATMOSPHERE PACKAGING AND LOW TEMPERATURE STORAGE

The postharvest quality of green chile fruit was compared after storage in 3 types of packages at 2 temperatures (24C and 8C). Package types were corrugated cardboard boxes, pressed cardboard trays overwrapped with VF-71 polyethylene, or low-density polyethylene (LDPE) bags. Fruit packaged in boxes or overwrapped trays had 24.8% and 10.1% weight loss, respectively, after 1 week of storage at 24C. Fruit packaged in polyethylene bags lost 0.3% weight and remained green. After 1 week at 8C, the weight losses were 3.8%, 1.8% and 0% for the boxed, overwrapped and bagged treatments, respectively. Postharvest quality was maintained up to 4 weeks when fruit were packaged in LDPE bags and stored at 8C. In a second study, steady state O₂ and CO₂ levels were determined inside the LDPE packages as fruit weight and temperature were varied. Storage temperatures were 24C, 16C and 8C. At 8C, steady state O₂ levels ranged from 12.0 kPa to 0.9 kPa, and CO₂ levels ranged from 2.0 kPa to 4.6 kPa as fruit weight was increased from 120 to 480 g. At 24C and 16C, fruit packaged in 480 g units had slower ripening rates than fruit packaged in smaller units; however, fruit stored at 8C remained green the longest, regardless of fruit weight.     

SHELF-LIFE MODELING OF SWEETENED CONDENSED MILK BASED ON KINETICS OF MAILLARD BROWNING

Nonenzymatic browning and related changes were monitored in commercial sweetened condensed milk stored at 7, 15, 30, 45 and 55C. Darkening of the color measured in terms of absorbance (100 - reflectance percent) followed zero-order kinetics, the apparent activation energy (E_a) being 45.2 kJ/mol at 7–30C and 139.9 kJ/mol at > 30–55C. Hydroxy-methyl-furfural (HMF) showed a first-order increase, the associated E_a values being smaller than those for absorbance. The pH exhibited a linear decline after a small initial rise at 30C and below. As browning progressed, the coffee whitening ability of the product decreased along zero-order kinetics. The Q₁₀ values for these variables ranged from 1.21 to 1.84 for temperatures up to 30C and were nearly 2–3 times higher above 30C. The sensory color score was negatively correlated with absorbance. The linear regression of color score on absorbance and the temperature dependence of the latter as expressed by Arrhenius relationship were combined into a mathematical model which could be useful in predicting the product's shelf-life.     

CLEANING KINETICS MODELING OF HOLDING TUBES FOULED DURING MILK PASTEURIZATION1

In the present study, 25 cm tubes fouled during pilot plant scale pasteurization of raw whole milk were cleaned with sodium hydroxide. The pasteurization conditions resembled those of the dairy industry. An optical sensor sensitive to the turbidity of suspended deposits removed by the cleaning solution was placed successively at the outlet of each fouled tube. Use of this sensor combined with a nonrecycled cleaning solution process enabled us to measure the cleaning rate on line. In these conditions it was observed that, at zero time, the cleaning rate was null. Based on the above observations a kinetic model of cleaning was established. It consists of two steps in series. The adhesive deposit passes through an intermediate state before being washed away by the cleaning solution. Each step is a first order reaction related to the mass of the adhesive deposit and the mass of the intermediate compound, respectively. Among the many physico-chemical parameters affecting the cleaning process, three major ones were studied; temperature, concentration and circulation rate of the soda solution. An empirical model of the rate constant was set up which takes into account those three parameters and the initial weight of deposit to be cleaned. A 1% increase in the amount of NaOH caused the same increase in the constant rate as 8°C or 0.5 m/s.