Drying of tomato slices: changes in drying kinetics, mineral contents, antioxidant activity and color parameters Secado de rodajas de tomate: cambios en cinéticos del secado, contenido en minerales, actividad antioxidante y parámetros de color

Effects of microwave drying on physicochemical characteristics, microstructure, and antioxidant properties of propolis extract

BACKGROUND

The heat sensitivity of phenolics and flavonoids leads to considerable losses of these compounds during conventional drying. Microwave drying has the advantage of shorter drying time and rigorous process control, minimizing damage to heat-sensitive compounds. Microwave drying kinetics and the impacts of microwave drying on physicochemical characteristics, morphological structure, antioxidant properties, total phenolics, and flavonoid content of propolis extract were investigated.

RESULTS

Increasing the microwave power output from 180 to 900 W resulted in a 67% reduction in drying time. Morphological changes were more noticeable at higher microwave power levels as shown in scanning electron microscopy images. Water activity values of microwave dried propolis extracts were below 0.4, which satisfied the requirement for shelf-stable dry products. The solubility of microwave dried propolis extract increased with increasing microwave power level, and the highest solubility was achieved for the propolis extract microwave dried at 900 W. Microwave dried propolis extracts exhibited lower total phenolic content levels than fresh propolis extract. The microwave power level did not affect the total flavonoid content but it affected 2,2-diphenyl-1-picrylhydrazyl (DPPH) free-radical scavenging activity of microwave dried propolis extracts. The DPPH free-radical scavenging activity closest to the fresh propolis extract was obtained for the microwave dried propolis extract at 900 W. This also showed the highest 6-hydroxy-2,5,7,8-tetramethyl-2-carboxylic acid (Trolox) equivalent antioxidant capacity.

CONCLUSION

Microwave drying of propolis extract at 900 W was found to be the most efficient drying condition because it yielded the shortest drying time, the highest effective moisture diffusivity, and phenolic and flavonoid content levels that were very similar to those in fresh propolis extract. © 2023 Society of Chemical Industry.

Drying kinetics and economic analysis of bitter gourd flakes drying inside hybrid greenhouse dryer

In this study, a heat storage-based hybrid greenhouse dryer has been developed and analysed for drying bitter gourd flakes under the climatic condition of Ranchi, India. Proposed heat storage-based hybrid greenhouse dryer consists of a solar air heater with a 2.12-m² area, greenhouse dryer and DC fan to induce and force the air. The significant objective of the present study is to analyse the drying efficiency, drying kinetics, property analysis, economic analysis, embodied energy and CO₂ mitigation of the hybrid greenhouse dryer for drying of bitter gourd flakes. An experiment was performed simultaneously on proposed system and open sun drying for the proper comparative analysis. Moisture contents reduced from 88.14 to 10.14% in 6 h in proposed dryer and 88.14 to 11.01% in 15 h for open system. Thus, significant drying time is reduced in proposed system by 8 h as compared to open system. Environmental impact analysis shows that the energy payback time was found to be 0.4907 years only. Cost of the proposed system dryer is 22664.30 INR. The total embodied energy is found 1591.07 kWh and earned carbon credit ranges from 16844.76 to 67379.05 INR, while CO₂ mitigation was 46.28 tonnes for 35 years of expected lifetime. Seven standard mathematical models for drying of bitter gourd flakes were studied. Ahmad and Prakash model was found to be the best as compared to other models. The metal contents of dried bitter gourd flakes were also examined. Bitter gourd dried in proposed dryers possesses superior metal content as compared to open systems. Impact analysis demonstrates that the hybrid greenhouse dryer is more suitable for reducing post-harvest loss with environmental sustainability.

Influence of Dehydration Temperature and Time on Physicochemical Properties of Tomato (Solanum lycopersicum L.) Powder

The purpose of this research was to determine the optimum dehydration temperature and time length for a better physicochemical quality of tomato powders. The treatments consisted of 70, 80 and 90°C dehydration temperatures and 9, 11, and 13 h time durations arranged in a completely randomized design (CRD) with triplicates. The inlet and outlet air temperatures of the hot air oven dryer were about 24 and 60°C respectively with an air velocity of about 2.9 m/s. Fresh tomatoes were used as a control. It has been observed that the major quality parameters of tomato powders were significantly increased with increasing dehydration temperature and time up to 80°C and 11 h respectively. When the dehydration temperature and time length went beyond 80°C and 11 h respectively, the quality of tomato powders declined. The maximum TSS content (7.433 °Brix), titratable acidity (0.4967), rehydration ratio (3.437), lycopene content (0.4512 mg/100 g) and lower pH value (4.433) were obtained at 80°C temperature and 11 h dehydration time. Moisture content was reduced to 11% at the same dehydration temperature and time length without considerable physiochemical quality loss. Inversely, vitamin C was reduced as dehydration temperature and time increased. Generally, the results of this study showed that dehydration of tomatoes with 80°C and 11 h temperature and time length respectively, provides better physicochemical quality of tomato powders. Future research is suggested on consumers' acceptance of dehydrated tomato powders.

Shelf-Life Evaluation of "San Marzano" Dried Tomato Slices Preserved in Extra Virgin Olive Oil

Since ancient times, vegetables have been preserved in oil, to be consumed throughout the year, and not just during the period in which they were harvested. Dried tomato slices in Extra Virgin Olive Oil (EVOO) are one of the most famous Italian preserves. This is the first study which aimed to investigate the shelf-life parameters of this preserve during the 12 months of storage in both light and dark conditions. For this purpose, quality and CIELab color parameters were analysed in EVOO alone and as preserving liquid; total phenols and carotenoids content as well as β-carotene and lycopene content, a fatty acids profile, and antioxidant activities were examined. Results showed that samples stored in the dark are protected against degradative processes. Moreover, after 6 months of storage, the EVOO used as preserving liquid is enriched by the phytochemicals contained in dried tomato slices. This enrichment of EVOO by tomato bioactive compounds is reflected in the increase in the antioxidant activity of the oil independently by the presence of light during storage.

The Potential of Exploiting Economical Solar Dryer in Food Preservation: Storability, Physicochemical Properties, and Antioxidant Capacity of Solar-Dried Tomato (Solanum lycopersicum) Fruits

This study investigated the effect of solar drying on storability and physiochemical and antioxidant capacities of dried tomatoes. Sliced fruit was dried at 45 ± 2 °C for 24 h under a solar tunnel dryer and stored at ambient temperature for 90 and 180 days. Solar drying treatments significantly (p < 0.05) reduced the bacterial and mold load, and eliminated Staphylococcus aureus, S. saprophyticus, and Escherichia coli in all samples. Solar drying treatment reduced the water activity of the dried tomato's to 0.31 that remained at the same level during storage period 180 days. Storage of dried tomato slices resulted in the decrease of both color and vitamin C content while it increased the total carotenoid, lycopene, phenolic compound content, and antioxidant activity. Furthermore, the principle component analysis (PCA) revealed that solar drying of tomato slices enhanced its physicochemical properties, antioxidant capacity particularly after storage for 90 and 180 days. Interestingly, the solar drying process enhanced tomato slices storage and physicochemical characteristics, that resulted in extending the shelf life by up to 6 months, indicating the great potential application of low-tech solar in food industry and could become an emerging effective post-harvest preservative method for seasonal perishable vegetable and fruit, particularly in developing countries.

Microwave flow and conventional heating effects on the physicochemical properties, bioactive compounds and enzymatic activity of tomato puree

BACKGROUND

Thermal processing causes a number of undesirable changes in physicochemical and bioactive properties of tomato products. Microwave (MW) technology is an emergent thermal industrial process that offers a rapid and uniform heating, high energy efficiency and high overall quality of the final product. The main quality changes of tomato puree after pasteurization at 96 ± 2 °C for 35 s, provided by a semi-industrial continuous microwave oven (MWP) under different doses (low power/long time to high power/short time) or by conventional method (CP) were studied.

RESULTS

All heat treatments reduced colour quality, total antioxidant capacity and vitamin C, with a greater reduction in CP than in MWP. On the other hand, use of an MWP, in particular high power/short time (1900 W/180 s, 2700 W/160 s and 3150 W/150 s) enhanced the viscosity and lycopene extraction and decreased the enzyme residual activity better than with CP samples. For tomato puree, polygalacturonase was the more thermo-resistant enzyme, and could be used as an indicator of pasteurization efficiency.

CONCLUSION

MWP was an excellent pasteurization technique that provided tomato puree with improved nutritional quality, reducing process times compared to the standard pasteurization process. © 2016 Society of Chemical Industry.

Soil compost amendment enhances tomato (Solanum lycopersicum L.) quality

BACKGROUND

Tomato (Solanum lycopersicum L.) is one of the most important crops in the world and represents a key crop in southern Italy. With the aim to evaluate the nutritional characteristics of tomato fruits in relation to NPK and compost fertilisation, the concentrations of the main nutrients, toxic elements, primary metabolites and total phenols were determined in two varieties (Lido and San Marzano). Each variety was cultivated in a different experimental field, subjected to different agronomic techniques.

RESULTS

Concentrations of toxic elements (Cd and Pb) were below the limits indicated by the EU Regulation (2011) in all the fruits analysed. Moreover, fruits obtained from San Marzano plants grown on organic amended soils showed a better overall quality than those obtained on mineral fertilised soil, being characterised by lower N (attributed to lower nitrate and nitrite concentrations), lower Cd, and higher soluble sugar concentrations. Higher concentrations of soluble sugars in fruits from organic amended soils were also observed in the Lido variety.

CONCLUSIONS

The agricultural use of quality compost represents an effective strategy to obtain high quality products in an economically and environmentally sustainable way. © 2016 Society of Chemical Industry.