Drying kinetics and quality changes during drying of red pepper

Effects of post-drying methods on pomelo fruit peels

Changes in physicochemical properties of moisture, ash, and fat contents, and color, due to freeze and oven post-drying treatments on flavedo, albedo, and lamella pomelo fruit peels were investigated. Physicochemical properties influence consumer acceptability and only a few studies are known. Pomelo peels were subjected to freeze drying and conventional drying at 60°C. Fresh pomelo peel was used as a control. Post-drying treatment changes in moisture, ash, and fat contents were observed, compared to controls. Minimal color changes were observed for freeze drying, compared with oven drying for flavedo, albedo, and lamella. Useful information for evaluation of drying treatments that can be used on pomelo peels is provided.

A comparative study of the capsaicinoid and phenolic contents and in vitro antioxidant activities of the peppers of the genus Capsicum: an application of chemometrics

This paper presents a comparison of the contents of capsaicin, dihydrocapsaicin and total phenolics as well as of the antioxidant activities of six types of peppers of the genus Capsicum. The varieties were analyzed in terms of their in vitro antioxidant activity using ferric reducing antioxidant powder (FRAP), 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azinobis 3-ethylbenzothiazoline 6-sulfonate (ABTS(●+)) assays. The contents of phenolics and capsainoids as well as the antioxidant activities were higher in seeds than in pulps. The correlations (ρ < 0.01) between the phenolic composition and the capsaicinoids levels were high (r = 0.98). Similarly high were also the correlations between the antioxidant activities and the contents of total phenolics and capsaicinoids. Data were analyzed using principal component analysis (PCA), hierarchical cluster analysis (HCA) and multiple linear regression (MLR). PCA explained 97.77 % of the total variance of the data, and their separation into three groups in a scatter plot was divised. Using HCA, three clusters were suggested. Cluster one, formed by pulps (bell pepper, orange habanero, cayenne, dedo de moça and red habanero), showed the lowest levels of the compounds quantified. Most seed samples were grouped in cluster two (bell pepper, cayenne, dedo de moça and malagueta) together with malagueta pulp. Cluster three was formed by orange and red habanero seeds, which showed the highest levels of all compounds analyzed. The MRL revealed that the values of capsaicinoids and total phenols are more adequate to predict the antioxidant activity measured by the FRAP assay.

Effect of far-infrared radiation assisted microwave-vacuum drying on drying characteristics and quality of red chilli

Fresh red chilli (Capsicum frutescens L.) was dried using microwave-vacuum drying (MVD) and the far-infrared radiation assisted microwave-vacuum drying (FIR-MVD) method. The MVD was operated using the microwave power of 100, 200 and 300 W under absolute pressure of 21.33, 28.00 and 34.66 kPa. In terms of FIR-MVD, far-infrared power was applied at 100, 200 and 300 W. The effect of drying conditions, i.e., microwave power, absolute pressure and FIR power, on drying characteristics and qualities of dried product were investigated. It was observed that an increase in microwave power and FIR power with a decrease in absolute pressure could accelerate the drying rate. It was also found that FIR-MVD method required shorter drying time than MVD. Moreover, qualities, i.e., color changes, texture, rehydration ability and shrinkage, of FIR-MVD chilli were found to be better than those of MVD. Consequently, the optimum drying condition of FIR-MVD within this study was microwave power of 300 W under absolute pressure of 21.33 kPa with FIR power of 300 W.

Convective Drying of Apples: Kinetic Study, Evaluation of Mass Transfer Properties and Data Analysis using Artificial Neural Networks

In the present work, the effect of drying was evaluated on some chemical and physical properties of apples, and the functions were modelled using feed-forward artificial neural networks. The drying kinetics and the mass transfer properties were also studied. The results indicated that acidity and sugars were significantly reduced by drying. Regarding colour lightness decreases, whereas redness and yellowness increased. As for texture, the dried samples were softer and less cohesive as compared to the fresh ones. Mass diffusivity increased with temperature, from 4.4×10−10 m2/s at 30°C to 1.4×10−9 m2/s at 60°C, and so did the mass transfer coefficient, increasing from 3.7×10−10 m/s at 30°C to 7.4×10−9 m/s at 60°C. As to the activation energy, it was found to be 34 kJ/mol. Neural network modelling showed that all properties can be correctly predicted by feed-forward neural networks. The analysis of the networks’ behaviours input layer weight values also shows which properties are more affected by dehydration or more dependent on variety.

Effects of Different Cooking Methods on the Antioxidant Properties of Red Pepper (Capsicum annuum L.)

We investigated the effect of various cooking methods (boiling, steaming, stir-frying, and roasting) and three cooking times (5, 10, and 15 min) on the antioxidant properties of red pepper. Raw and cooked peppers were measured for proximate composition, ascorbic acid (AsA) content, total carotenoid content (TCC), total polyphenol content (TP), and 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical scavenging activities. Results showed that the proximate composition, AsA content, TCC, TP, and antioxidant activities were significantly (p<0.05) affected by the cooking procedure; the loss rate varied among individual compounds. Boiling and steaming significantly reduced AsA content (24.3~66.5%), TP (13.9~ 54.9%), and antioxidant activity (21.7~60.5%) in red pepper, while stir-frying and roasting slightly reduced AsA content (2.7~25.9%), TP (1.8~4.9%), and antioxidant activity (4.9~17.9%). The highest loss was observed after boiling, followed by steaming, roasting, and stir-frying. Stir-frying and roasting better preserved AsA content, TCC, TP, and antioxidant activity. In conclusion, dry-heat cooking methods such as stir-frying and roasting may be preferred to retain the nutrient compositions and antioxidant properties of red pepper.

Evolution of antioxidants in dietary fiber powder produced from white cabbage outer leaves: effects of blanching and drying methods

White cabbage outer leaves, which are usually discarded both during industrial processing and selling in a consumer market, have proven to be a good source of dietary fiber (DF) as well as antioxidants and can be effectively transformed into functional DF powder. In the past, however, only hot air drying was used to prepare DF powder from cabbage outer leaves although it is well recognized that this drying technique could lead to much quality degradation of a dried product. This work was therefore aimed at studying the evolution of selected important antioxidants, e.g., phenolic compounds and vitamin C, in white cabbage outer leaves during vacuum drying at 60, 70 and 80 °C. The effect of pretreatment viz. steam blanching was also evaluated. The results showed that there were losses of antioxidants during steam blanching; vacuum dried blanched leaves nevertheless contained higher antioxidant contents and activity than dried unblanched leaves. Losses of antioxidants during vacuum drying were also noted to be less than those during hot air drying. Overall, the results showed that there were no differences in the antioxidants retention among all the tested conditions performed in this study. Therefore, the most suitable condition for the production of antioxidant DF powder from cabbage outer leaves is vacuum drying at 80 °C as this condition requires the minimum specific energy consumption.

Influence of process temperature on drying kinetics, physicochemical properties and antioxidant capacity of the olive-waste cake

The objective of this study was to determine the effect of drying temperature on the drying kinetics, proximal analysis, energy consumption and the antioxidant capacity of the olive-waste cake "Picual" variety from 40 to 90°C. Evaluation of proximal analysis evidenced the influence of temperature on the waste parameters. Values of effective moisture coefficients were in the range of 1.97-6.05 × 10(-9)m(2)s(-1) under the studied conditions. Activation energy was found to be 28.24 kJ mol(-1). The Weibull model was successfully applied (r(2)>0.973). Specific energy consumption decreased as temperature increased, showing the effect of drying times over temperature. Although dehydrated samples decreased the initial total phenolic content, significant differences were not detected. Effects of drying temperatures did not present significant differences on antioxidant capacity (ORAC and DPPH) when compared to fresh samples. The oleic acid (main fatty acid in fresh samples) presented a maximum increased at 90°C.

Degradation of carotenoids in apricot (Prunus armeniaca L.) during drying process

Carotenoids are natural compounds whose nutritional importance comes from the provitamin A activity of some of them and their protection against several serious human disorders. The degradation of carotenoids was investigated during apricot drying by microwave and convective hot-air at 60 and 70 °C. Seven carotenoids were identified: antheraxanthin, lutein, zeaxanthin, β-cryptoxanthin, 13-cis-β-carotene, all-trans-β-carotene and 9-cis-β-carotene; among these, all-trans-β-carotene was found to be about 50 % of total carotenoids. First-order kinetic models were found to better describe all-trans-β-carotene reduction during drying, with a degradation rate constant (k1) that increased two folds when temperatures increased by 10 °C, in both methods. No differences were found in k1 between apricots dried by hot air at 70 °C (k1 = 0.0340 h(-1)) and by microwave at 60 °C. The evolution of total carotenoids (117.1 mg/kg on dry basis) during drying highlighted a wider decrease (about 50%) when microwave heating was employed, for both set temperatures. Antheraxantin was found to be the carotenoid most susceptible to heat, disappearing at 6 h during both trials with microwave as well as during convective hot-air at 70 °C. For this reason, antheraxanthin could be a useful marker for the evaluation of thermal damage due to the drying process. Also the degree of isomerization of all-trans-β-carotene could be a useful marker for the evaluation of the drying process.

Effects of hot air and freeze drying methods on antioxidant activity, colour and some nutritional characteristics of strawberry tree (Arbutus unedo L) fruit

Antioxidant activity, colour and some nutritional properties of hot air and freeze-dried strawberry tree ( Arbutus unedo L.) fruits were investigated. Additionally, the effects of two pre-treatments, namely ethyl oleate and water blanching, were compared in terms of drying characteristics. For determination of antioxidant activities in ethanol extracts, two different analytical methods were used: 1,1-diphenyl-2-picrylhydrazyl scavenging activity and β-carotene bleaching activity. As a result, the ethyl oleate pre-treatment shortened the drying time by hot air method and gave a higher 1,1-diphenyl-2-picrylhydrazyl scavenging activity (82.16 ± 0.34%), total phenolic content (7.62 ± 1.09 µg GAE/g extract), ascorbic acid content (236.93 ± 20.14 mg/100 g), besides hydromethylfurfural was not observed. Freeze-dried fruits exhibited higher ascorbic acid content (368.63 ± 17.16 mg/100 g) than those fresh fruits (231.33 ± 19.51 mg/100 g) and nearly 1,1-diphenyl-2-picrylhydrazyl activity (93.52 ± 0.41 %) to fresh fruits (94.03 ± 1.18%). Colour characteristics, sugar content and mineral contents of fruits were significantly affected by pre-treatments and drying methods ( p < 0.05). It is concluded that the drying of strawberry tree fruits should bring a valuable and attractive foodstuff to food industry due to the rich nutritional components, antioxidant activity and colour. Another conclusion from this study is that the freeze-drying is the best drying method to keep the nutritional value, antioxidant activity and sensory properties of fruits.