Effect of temperature and moisture contents on dielectric properties at 2.45 GHz of fruit and vegetable processing by-products.

Microwave heating is a part of several food processing unit-operations, while also emerging as a processing technology for by-products. Process efficiency depends on dielectric properties; however, data of these by-products are scarce in literature. The present study is focused on the effect of temperature and moisture content (M) on the dielectric constant (ε') and loss (ε'') of carrot waste, apple pomace, pineapple peel and spent coffee grounds at 2.45 GHz. Results on ε' showed moisture-dependent temperature effect with an inflection point at M = 50.3%. The ε'' increased with increasing M up to 60% and decreased at higher moisture levels. Results at different temperatures were significantly affected by the composition of the studied materials and thus the calculated power penetration depth. Although fresh food dielectric properties are available in literature, the data is not always suitable to estimate food waste properties as processing may cause compositional changes. The obtained results support microwave process optimization in the field of food-waste valorization.

Correction: Effect of temperature and moisture contents on dielectric properties at 2.45 GHz of fruit and vegetable processing by-products.

[This corrects the article DOI: 10.1039/C9RA10639A.].

Predation on rose galls: parasitoids and predators determine gall size through directional selection.

Both predators and parasitoids can have significant effects on species' life history traits, such as longevity or clutch size. In the case of gall inducers, sporadically there is evidence to suggest that both vertebrate predation and insect parasitoid attack may shape the optimal gall size. While the effects of parasitoids have been studied in detail, the influence of vertebrate predation is less well-investigated. To better understand this aspect of gall size evolution, we studied vertebrate predation on galls of Diplolepis rosae on rose (Rosa canina) shrubs. We measured predation frequency, predation incidence, and predation rate in a large-scale observational field study, as well as an experimental field study. Our combined results suggest that, similarly to parasitoids, vertebrate predation makes a considerable contribution to mortality of gall inducer larvae. On the other hand, its influence on gall size is in direct contrast to the effect of parasitoids, as frequency of vertebrate predation increases with gall size. This suggests that the balance between predation and parasitoid attack shapes the optimal size of D. rosae galls.

Thermal degradation of grape marc polyphenols.

Bioactive compounds of wine making by-products are of interest in food, cosmetics and pharmaceutical industries. Extraction of antioxidants under mild conditions is time-consuming, giving ground to the development of intensification processes where the operation at high temperature may deteriorate extract quality. This study examined thermal degradation of grape marc and its filtered extract (80, 100 and 150°C). The decrease in anthocyanin content was modelled under non-isothermal conditions by first order kinetics, using the Arrhenius equation. Simulated degradation under isothermal heating showed that the grape marc is more sensitive by one order of magnitude to heat than the filtered extract. This tendency was also confirmed by analyses of the total phenolic content and antioxidant activity. It is suggested that an optimal combination of temperature, treatment time and also raw material environment could be found in process intensification.

The influence of the energy absorbed from microwave pretreatment on biogas production from secondary wastewater sludge.

In this study, microwave treatment is analyzed as a way to accelerate the hydrolysis in anaerobic digestion of municipal wastewater sludge. The influence of the absorbed energy, power and athermal microwave effect on organic matter solubilization and biogas production has been studied. In addition, a novel method that considers the absorbed energy in the microwave system is proposed, in order to obtain comparable experimental results. The absorbed energy is calculated from an energy balance. The highest solubilization was achieved using 0.54 kJ/ml at 1000 W, where an increment of 7.1% was observed in methane production, compared to the untreated sample. Using a higher energy value (0.83 kJ/ml), methane production further increased (to 15.4%), but solubilization decreased. No power influence was found when 0.54 kJ/ml was applied at 1000, 600 and 440 W. Microwave heating was compared to conventional heating in two different experimental setups, providing similar methane yields in all cases.