The influence of compositional changes in reconstituted potato flakes on thermal and dielectric properties and temperatures following microwave heating

Effects of the sludge physical-chemical properties on its microwave drying performance

Thermal drying is an effective sludge treatment method for dealing with large volumes of sludge. Microwave (MW) technology has been proposed as an effective and efficient technology for sludge drying. The physical-chemical properties of the sludge depend both on the origin of the sludge, as well as on the treatment process at which the sludge has been exposed. The physical-chemical properties of the sludge affect the performance and the subsequent valorisation and management of the sludge. This study evaluated the effect of certain physical-chemical properties of the sludge (moisture content, organic content, calorific value, porosity, hydrophobicity, and water-sludge molecular interaction, among others) on the MW sludge drying and energy performance. Four different types of sludge were evaluated collected from municipal wastewater treatment plants and septic tanks. The performance of the MW system was assessed by evaluating the sludge drying rates, exposure times, energy efficiencies and power input consumed by the MW system and linking the MW drying performance to the sludge physical-chemical properties. The results confirmed that MW drying substantially extends the constant drying period associated with unbound water evaporation, irrespective of the sludge sample evaluated. However, the duration and intensity were determined to depend on the dielectric properties of the sludge, particularly on the distribution of bound and free water. Sludge samples with a higher amount of free and loosely bound water absorbed and converted MW energy into heat more efficiently than sludge samples with a lower amount of free water. As a result, the sludge drying rates increased and the constant drying rate period prolonged; hence, leading to an increase in MW drying energy efficiency. The availability of free and loosely bound water molecules was favoured when hydrophobic compounds, e.g., oils and fats, were present in the sludge.

Influence of fat content and water activity on the heating pattern of model systems submitted to microwave heating

This research analyzed the influence of fat content (1%, 3%, 5%, and 10%, w.b.) and of water activity (0.85, 0.90, 0.95, and 0.99) on the effectiveness of microwave heating within model systems (agar gel). Findings indicate that an increased fat content promotes more uniform heating in the model systems and results in longer heating times to reach the target temperature of 50°C. In the model systems with different a_w values, the warming of the central model zone was slower while in the corners, heating was accelerated. Additionally, in these models, heating times increased as the a_w was decreased. PRACTICAL APPLICATION: The study of model systems allows for a detailed assessment of food when subjected to microwaves; and how heating is influenced by food properties such as a_w and fat content. Findings indicate that changes in product formulation could improve the heating of ready-to-eat foods, either by increasing the fat content (better uniformity) or having high a_w (shorter heating time).

Detection of Artificially Water-Injected Frozen Octopus minor (Sasaki) Using Dielectric Properties

A few importers of marine products have practiced the fraud of artificially injecting water into Octopus minor for increasing their weights prior to the freezing process. These rampant practices have recently become a serious social issue and threaten public health. Therefore, it is necessary to develop the detection method for artificially water-injected frozen Octopus minor. This study was conducted to develop the nondestructive method for verifying adulterated Octopus minor by measuring dielectric properties using the coaxial probe method. Regardless of weight and measurement locations, a significant difference between ε values from normal octopuses was not observed. The ε values of Octopus minor were decreased in the microwave frequency range between 500 and 3000 MHz. The ε values of water-injected octopuses also showed similar trend with normal octopuses; however, the dielectric loss factor (ε″) values of adulterated octopuses were much lower than normal octopuses. After thawing normal, adulterated, and imported frozen Octopus minor, the ε values measured at the trunk part from these octopuses were compared and statistically analyzed. The ε″ values from normal frozen octopus were significantly different from adulterated and imported frozen octopuses. In addition, the ε″ values from the adulterated frozen octopus group that weight gain rate was less than 20% was significantly different from other adulterated octopus groups with higher weight gain rate than 20%. The ε″ values from adulterated frozen octopus groups with the range of weight gain rate between 20 and 30% were quite similar to imported frozen octopuses. Therefore, it was found that the measurement of ε″ values from Octopus minor has a great possibility to distinguish normal frozen octopuses and artificially water-injected frozen octopuses.

Modeling of Dielectric and Thermal Properties of Protein-Enriched Instant Noodles as a Function of Food Chemical Composition

Dielectric property measurement instruments are expensive and not readily available. Hence, models of the dielectric and thermal properties of protein-enriched instant noodles (PEIN) were developed as a function of the product moisture, protein, ash, fat, carbohydrate, and crude fiber contents. The chicken meat, egg yolk, and seaweed in PEIN varied from 0 to 30, 0 to 15, and 0 to 6 g/100 g flour, respectively. Results revealed that protein, fat, and ash contents of PEIN increased by chicken meat, egg yolk, and seaweed supplementation. Regression equations indicated that the moisture and protein contents significantly (P ≤ 0.05) increased, while the fat content decreased the dielectric and thermal properties. The R2 values of the dielectric constant and loss factor, thermal conductivity, and specific heat equations were 0.75, 0.87, 0.78, and 0.98, respectively. Finally, no significant differences (P > 0.05) between the properties values predicted from the model equations and the experimental data (not included in the development of model equations) was observed which indicated a good model fit.

Effect of Microwave Irradiation on the Physicochemical and Digestive Properties of Lotus Seed Starch

The objective of this study is to investigate the effect of microwave irradiation on the physicochemical and digestive properties of lotus seed starch. The physicochemical properties of lotus seed starch were characterized by light microscopy, (1)H NMR, FT-IR spectroscopy, and HPSEC-MALLS-RI. The starch-water interaction and crystalline region increased due to the changed water distribution of starch granules and the increase of the double-helix structure. The swelling power, amylose leaching, molecular properties, and radius of gyration reduced with the increasing microwave power, which further affected the sensitivity of lotus seed starch to enzymatic degradation. Furthermore, the resistant starch and slowly digestible starch increased with the increasing microwave irradiation, which further resulted in their decreasing hydrolysis index and glycemic index. The digestive properties of lotus seed starch were mainly influenced by the reduced branching degree of amylopectin and the strong amylose-amylose interaction.