Dimitrios Argyropoulos

Effect of Air Temperature and Pre-treatment on Color Changes and Texture of Dried Boletus edulis Mushroom

In the present work, the effects of drying air temperature and pre-treatment on color changes and texture of Boletus edulis (Bull.: Fr.) mushrooms were investigated during convective drying. The drying experiments were conducted in a laboratory hot-air dryer at temperatures of 50, 60, and 70 °C under thermal (water or steam blanching) and chemical (solution of potassium metabisulfite or citric acid) treatments. Changes in color were evaluated by the CIELAB color system and the experimental color parameters (L* a* b*) were fitted to a first order kinetic model. Values of total color difference (ΔE*), hue angle (h*), and chroma (C*) were also calculated. The texture of dried mushrooms was measured by an Instron texture analyzer and expressed as hardness. The model fitted the experimental a* and b* values sufficiently. The results showed that during convective drying, lightness decreased slightly while yellowness and redness increased. Chemical pre-treatments did not influence the color of mushrooms positively while blanching caused intensive color deterioration. Moreover, the ΔE* value could contribute to the assessment of color change effectively. Hardness increased as drying proceeded and was found to be greater at higher temperatures. Mushrooms subjected to water or steam blanching were harder in texture. A temperature limit of 60°C is imposed for the dehydration of B. edulis mushrooms. Thermal treatment prior to drying is not recommended for B. edulis mushrooms when color and texture are desirable quality criteria.

Compositional and functional dynamics of dried papaya as affected by storage time and packaging material.

Papaya has been identified as a valuable source of nutrients and antioxidants, which are beneficial for human health. To preserve the nutritional properties after drying, appropriate storage specifications should be considered. This study aimed to investigate the quality and stability of air-dried papaya in terms of quality dynamics and behavior of bio-active compounds during storage for up to 9 months in two packaging materials: aluminum laminated polyethylene and polyamide/polyethylene. Samples with moisture content (MC) of 0.1328 g g(-1) and water activity (aw) of 0.5 were stored at 30 °C and relative humidity (RH) of 40-50%. The MC, aw, degree of browning (DB) and 5-hydroxymethylfurfural (HMF) content were found to notably increase as storage progressed. On the contrary, there was a significant decrease in antioxidant capacity (DPPH, FRAP and ABTS), total phenolic (TP) and ascorbic acid (AA) contents. Packaging in aluminum laminated polyethylene under ambient conditions was found to better preserve bio-active compounds and retard increases in MC, aw and DB, when compared to polyamide/polyethylene.

Safety of Foods Based on Mushrooms

Abstract Throughout the long period of human history, mushrooms played a very important role in some societies, where they were used as a highly appreciated food and medicine and as a psychoactive substances in some religious rites. As extremely healthy and nutritious foodstuffs, low in calories, fats, and essential fatty acids, and on the other hand high in vegetable proteins, vitamins, and minerals, mushrooms are recommended and desirable in our daily diet. Most people prefer to eat them fresh due to much more attractive flavor and texture, which rarely can be compared to that of processed mushrooms. However, mushrooms are highly perishable foods, subject to extremely rapid microbiologic and biochemical changes. In an effort to extend their shelf life and thus make them available to more people, over a longer period, several preserving methods have been developed.

Temperature stability of vitamin D2 and color changes during drying of UVB-treated mushrooms

ABSTRACT The study investigates the effect of drying temperature on vitamin D2 content and color changes of UVB-treated shiitake (Lentinula edodes), oyster (Pleurotus ostreatus), and white and brown button mushrooms (Agaricus bisporus). Fresh samples were UVB treated up to 1.5 J/cm2 for 20 min at 25°C and either dried in a high precision dryer (temperatures: 40, 60, 80°C, specific humidity: 10 g/kg, air velocity: 0.6 m/s) or frozen at −25°C, and then freeze-dried (pressure: 0.28 mbar). Vitamin D2 content was not negatively affected by the increased temperatures of the drying air. The highest content of vitamin D2 was detected in freeze-dried (171.84 µg/g) and hot-air dried shiitake at 60°C (169 µg/g), followed by oyster (121.96 µg/g), whereas the lowest amount was observed in brown button mushrooms at 40°C (34.65 µg/g). Although vitamin D2 indicated a remarkable stability even at 80°C, the dried samples were characterized by intensive tissue darkening.

An innovative laser-based optical technology to predict moisture content and color of Bell pepper (Capsicum annuum L.) during drying

Bell pepper (Capsicum Annuum L.) is a fruit rich in pigments such as chlorophylls, anthocyanins and carotenoids which is dried to produce spices. The aim of this research was to test the feasibility of laser light for predicting moisture content changes during drying. Green (532 nm) and red light (635 nm) were applied to the pepper tissue at different drying conditions. Detection of discoloration during the drying process using a CCD camera was also investigated by comparing of the RGB color values with CIE L*, a*, b* color coordinates measured by a Minolta Colorimeter. Cross validation analysis showed the highest correlation between laser light at wavelengths of 532 and 635 nm for yellow pepper (R=0.93). On the contrary, the behavior of green and red light in samples with corresponding colors raises questions for the ability to predict moisture content changes. Additional studies are still required to determine the suitability of digital images as an alternative method to the colorimeter for the evaluation of color change during drying of bell pepper. The described optical technology may represent a basis for future in-line quality monitoring of drying processes.

Potential for Automated Systems to Monitor Drying of Agricultural Products Using Optical Scattering

Drying of agricultural products is a critical and energy-intensive processing step in the production of many foodstuffs. During convective drying, products are highly susceptible to thermal damage. In recent years, novel techniques have been established based on optical scattering due to the interaction of light with organic materials. The presented research investigated this approach using vis/NIR wavelengths to observe changes of quality parameters during drying of foodstuffs. The method was proven useful to monitor changes in moisture, color, and texture in a variety of products such as apple, mango, papaya, litchi, and bell pepper. Although many applications have been confirmed, additional hardware and software aspects still need to be refined. Optical scattering shows strong potential for implementation as a non-destructive method for in-line control of product qualities during industrial drying processes. A robotic prototype should be developed that is capable of automated measurement of agricultural products during drying. Optimization of product quality and prevention of energy waste by over-drying are among the potential impacts of the developed technology.