Effect of Chemical Pretreatments on the Physical Properties of Kiwi

In this work the effect of pre-treatments on the physical properties of fresh kiwi was studied. For that, a set of tests using chemical pretreatments was used, in which the samples were subjected to aqueous solutions of ascorbic acid and potassium metabisulfite at concentrations of 0.25% and 1% (w/v) for periods of 30 and 60 minutes, in order to understand the implications of the treatments in the color and texture of the kiwi as compared to its original properties. The results showed that the kiwi treated with ascorbic acid changed its color very intensively when compared to the fresh product, and this trend was intensified after storage. Contrarily, when potassium metabisulfite was used, the changes in color were quite negligible right after the treatment and even lower after the storage period of 6 days under refrigeration. After the treatments with both solutions, the kiwi texture was drastically changed, diminishing hardness considerably and increasing elasticity for all treatments. The same could be observed after six days of refrigeration.

Evaluation of thermo-physical properties and drying kinetics of carrots in a convective hot air drying system

This paper presents an experimental study on the evolution of carrot properties along convective drying by hot air at different temperatures (50ºC, 60ºC and 70ºC). The thermo-physical properties calculated were: specific heat, thermal conductivity, diffusivity, enthalpy, heat and mass transfer coefficients. Furthermore, the data of drying kinetics were treated and adjusted according to the three empirical models: Page, Henderson & Pabis and Logarithmic. The sorption isotherms were also determined and fitted using the GAB model. The results showed that, generally, the thermo-physical properties presented a decline during the drying process, and the decrease was faster for the temperature of 70ºC. It was possible to verify that the Page model presented the best prediction ability for the representation of kinetics of the drying process. The GAB model used to fit the sorption isotherms showed a good prediction capacity and, at a given water activity, despite some variations, the amount of water sorbed increased with the decrease of drying temperature.

Some factors that may affect the physical-chemical properties of blueberries

The aim of the present study was to investigate the effect of different production and conservation factors on some properties of blueberries. Among the production factors considered were cultivar (Duke, Bluecrop and Ozarkblue) and production mode (organic or conventional). Regarding the conservation factors were evaluated temperature (ambient or refrigeration) and storage time (0, 7 and 14 days). The properties under study belong to three categories: physical properties (color and texture); chemical properties (moisture content, sugars and acidity) and phenolic and antioxidant properties (total phenols, anthocyanins, tannins, ABTS antioxidant activity, DPPH antioxidant activity). The results revealed that moisture content was only influenced by cultivar and that both acidity and sugar contents varied according to the production mode used. Also it was evidenced that the antioxidant activity was not statistically different between cultivars, production modes or conservation conditions. Regarding the phenolic compounds, the tannins were significantly higher for the blueberries produced in organic agriculture. Regarding color significant differences were also encountered and the most intense blue was found in blueberries from cv. Duke, produced in organic farming and stored under refrigeration. Textural attributes were also very significantly influenced by all factors at study: cultivar, production mode and conservation, and the berries from cv. Duke stored under refrigeration showed the highest firmness.

Variação da composição nutricional e propriedades de cenouras durante a secagem

Este trabalho teve como objetivo a determinação das propriedades da cenoura (Daucus carota L.), da variedade Nantes, antes, durante e após a secagem por convecção a três temperaturas diferentes (50, 60 e 70 ºC).De forma a verificar as alterações ao nível de diferentes propriedades, tais como: propriedades químicas (humidade, proteínas, fibras, cinzas, açúcares e 'aw') propriedades físicas (textura, cor, porosidade e densidade) e propriedades termofísicas (calor específico, condutividade térmica, difusividade e entalpia). Dos resultados obtidos foi possível concluir que a temperatura de secagem de 70 º C foi a que mais afetou as propriedades químicas analisadas, tais como a humidade, proteínas e açúcares redutores, onde estes sofreram uma diminuição ao longo das secagens. A 'aw' também apresentou uma diminuição ao longo das secagens, onde apresentou um menor valor na secagem a 70 ºC, tendo passado de 0,97 para 0,69, enquanto as temperaturas de 50 ºC e 60 ºC apresentaram um valor final igual, de 0,74. No que diz respeito às propriedades físicas, verificou-se que em relação à textura registaram-se evoluções semelhantes em termos de dureza, mastigabilidade e gomosidade, na medida em que sofreram uma acentuada diminuição nas primeiras horas de secagem, e a temperatura de 70 ºC foi a que mais afetou estas propriedades. No caso da cor a temperatura de 60 ºC foi a que provocou uma maior diferença de cor, a qual ao longo da secagem esta foi aumentando. A porosidade sofreu um aumento com as secagens devido à diminuição da humidade, no entanto a temperatura de 70 ºC foi a que obteve uma menor porosidade, e as temperaturas de 50 ºC e 60 ºC apresentaram valores de porosidade semelhantes. As propriedades termofísicas registaram uma diminuição ao longo da secagem, onde o calor específico sofreu uma maior diminuição com a temperatura de 70 ºC, passando de 3,90 kJ/kg.K para 1,99 kJ/kg.K. A condutividade térmica também sofreu uma maior diminuição com a temperatura de 70 ºC, diminuindo de 0,5243 W/m.K para 0,2782 W/m.K. A difusividade foi de igual forma afetada pela temperatura de 70 ºC, tendo diminuído de 1,50×10-7 m2/s para 1,06×10-7 m2/s. No caso da entalpia, esta sofreu uma maior diminuição com a temperatura de 50 ºC, passando de 233 J/kg para 96,7 J/kg. As isotérmicas de sorção foram ajustadas ao modelo de GAB, onde se verificou que apesar de algumas oscilações a quantidade de água sorvida a uma determinada aw, aumentou com a diminuição da temperatura.Os dados da cinética de secagem foram tratados e ajustados de acordo com três modelos: Page, Henderson & Pabis e Logarítmico, tendo-se verificado que o modelo de Page foi o que mostrou melhor descrever os processos em estudo, enquanto o pior modelo para descrever a cinética de secagem foi o Logarítmico.

Effect of drying on the physical, chemical and sensorial properties of kiwi

Kiwi fruit is a highly nutritional fruit due to the high level of vitamin C and its strong antioxidant capacity due to a wide number of phytonutrients including carotenoids, lutein, phenolics, flavonoids and chlorophyll [1]. Drying consists of a complex process in which simultaneous heat and mass transfer occur. Several alterations occur during the drying of foods at many levels (physical, chemical, nutritional or sensorial) which are influenced by a number of factors, including processing conditions [2]. Temperature is particularly important because of the effects it produces at the chemical and also at the physical level, particularly colour and texture [3]. In the present work were evaluated the changes in sliced kiwi when exposed to air drying at different temperatures (50, 60, 70, 80 ºC), namely in terms of some chemical properties like ascorbic acid or phenolic compounds, physical characteristics like colour and texture and also at the sensorial level. All experiments followed standard established procedures and several replicates were done to assess each property. The results obtained indicated that moisture was reduced with drying by 74 to 87%, depending on the temperature. Also ascorbic acid decreased with drying, being 7% for 50 ºC and increasing up to 28% for the highest temperature (80 ºC). The phenolic compounds and antioxidant activity were also very much affected by the drying temperature. The water activity of the dried samples varied from 0.658 to 0.753, being compatible with a good preservation. Regarding colour, the total colour difference between the dried samples and the fresh sample was found to vary in the range 9.45 – 17.17. The textural parameters were also much affected by drying, namely hardness which decreased by 45 to 72 %, and all other parameters increased: cohesiveness (approximately doubled), springiness (increased 2 to 3 times) and chewiness which increased up to 2.5 times that off the fresh sample. Adhesiveness, which was observed for the fresh samples (-4.02 N.s) disappeared in all the dried samples. The sensorial analysis made to the dried samples allowed establishing the sensorial profiles as shown in Figure 1.

Effect of Chemical Pretreatments on the Physical Properties of Kiwi

In this work the effect of pre-treatments on the physical properties of fresh kiwi was studied. For that, a set of tests using chemical pretreatments was used, in which the samples were subjected to aqueous solutions of ascorbic acid and potassium metabisulfite at concentrations of 0.25% and 1% (w/v) for periods of 30 and 60 minutes, in order to understand the implications of the treatments in the color and texture of the kiwi as compared to its original properties. The results showed that the kiwi treated with ascorbic acid changed its color very intensively when compared to the fresh product, and this trend was intensified after storage. Contrarily, when potassium metabisulfite was used, the changes in color were quite negligible right after the treatment and even lower after the storage period of 6 days under refrigeration. After the treatments with both solutions, the kiwi texture was drastically changed, diminishing hardness considerably and increasing elasticity for all treatments. The same could be observed after six days of refrigeration.

Chemical Composition and Bioactive Compounds in Bananas and Postharvest Alterations

Bananas arise as one of the most popular fruits consumed all around the world. Banana belongs to the genus Musa from the family Musaceae. It is original from tropical regions and presents a strong ability to protect itself from the oxidative stress caused by extreme climatic conditions such as intense sunshine and high temperature. For this protection, bananas increase the production of bioactive compounds with antioxidant activity, which protect the fruit from the oxidative damage. Scientific studies have demonstrated that bananas (both in the pulp and peel) contain different antioxidant compounds, like vitamins (A, B, C and E), β-carotene and phenolic compounds (catechin, epicatechin, lignin, tannins, anthocyanins). Furthermore, banana is also notably rich in minerals, like potassium and phosphorus. The knowledge about the chemical composition and the contents in compounds with biological activity is of high interest given the importance of bananas as a valuable food all over the world. However, because bananas are perishable due to some factors like chemical reactions, including those that result in the production of ethylene, their postharvest conservation in pivotal for the commercialization. The effects of postharvest treatments and storage conditions on the composition of bananas are, therefore, essential. In this way, the present chapter focus on the composition of bananas, including macronutrients, micronutrients and bioactive compounds, as well as the effect of postharvest treatments and storage conditions in the quality of bananas.