Effects of microwave-assisted hot water treatments designed against Mexican fruit fly (Anastrepha ludens) on grapefruit (Citrus paradisi) quality

Effects of inside-out heat-shock via microwave on the fruit softening and quality of persimmon during postharvest storage

Rapid postharvest softening largely limits the shelf-life of persimmon (Diospyros kaki L.) fruit. Microwave is a new environmental-friendly inside-out heat-shock approach, whose effect on the fruit softening and quality has not yet been investigated. The current study applied two kinds of microwave treatments (low-power long-time, LPLT, or high-power short-time, HPST) to persimmon fruit with comparison to the hot water (HW) treatments. The results showed both microwave treatments maintained firmness, facilitated the deastringency, and increased soluble solid contents (SSC) and sugar-acid ratio of persimmon fruit. The microwave treatments reduced the cellulose and pectin degradation, and inhibited the cellulase activity, resulting in a significantly higher firmness than HW treatment and control after 2 and 4 days of storage. Moreover, application of HPST treatment down-regulated gene expression of DkPG1, DkPE2 and DkEGase1 compared with untreated fruits. These results indicated that microwave treatment is a promising soft-delaying method for the preservation of persimmon fruit.

Reduction of Aflatoxin B1 in Corn by Water-Assisted Microwaves Treatment and Its Effects on Corn Quality

Aflatoxin B₁ (AFB₁) is one of the most commonly found mycotoxin in corn, which is highly toxic, carcinogenic, teratogenic, and mutagenic for the health of humans and animals. In order to reduce the AFB₁ in corn, corn kernels were processed with Water-assisted Microwaves Treatment (WMT) and the feasibility of WMT processing on AFB₁ reduction and its effects on corn quality were analyzed. Increasing the treatment time and microwave power could increase the reduction of AFB₁, and the maximum reduction rate could reach 58.6% and 56.8%, respectively. There was no significant correlation between the initial concentration of AFB₁ and the reduction rate of AFB₁. During WMT, the main toxigenic molds were sterilized completely, and the moisture content of corn climbed up and then declined to the initial level. WMT could obviously increase the fatty acid value and pasting temperature of corn and reduce the all paste viscosity of corn. However, it had little effect on the color of corn. The results indicated that WMT could reduce AFB₁ effectively and avoid the vast appearance of heat-damaged kernels simultaneously. Undoubtedly, water played an important role in WMT. This result provides a new idea for the reduction of AFB₁ by microwave.

Postharvest heat treatments to inhibit Penicillium digitatum growth and maintain quality of Mandarin (Citrus reticulata blanco)

Use of fungicides is a common practice as a postharvest treatment to control fruit decay. Nowadays, environment friendly technologies, such as heat treatments, are viable replacements. This study evaluated the effects of post-harvest heat treatments (traditional and microwave-assisted) on mandarins intentionally inoculated with Penicillium digitatum. For the studied heat treatments, the target temperature was 50 °C, which was held for 2.5 min. After heating, mandarins were cooled and stored at 25 °C for 13 days. MW treatments effectively prevented mold growth during storage, while HW only delayed it. Control mandarins (without treatment) showed the highest significant weight loss. Neither thermal treatment nor storage affected fruit juice pH (p > 0.05). Treated mandarins had a significantly lower vitamin C content than control fruits throughout storage, and all mandarins lost firmness by the 13^th day (p < 0.05). Control and MW-treated mandarins had lower citric acid content; however, they retained color, total soluble solids (TSS) and had a higher maturity index. While HW mandarins did not have changes in citric acid content, they had higher TSS, and lower maturity index. MW-assisted treatments were effective at inactivating molds and helped retain some nutritional and physical-chemical characteristics of mandarins. However, juice of MW-treated mandarins was not preferred by judges in the sensory tests, the juice was rated lower than that obtained from the other treatment. Postharvest heat treatments may constitute a helpful application to control mandarin’ fungal decay.

Agricultural and Forest Residues towards Renewable Chemicals and Materials Using Microwave Liquefaction

Microwave-assisted liquefaction is regarded as a promising thermochemical approach to produce renewable and sustainable chemicals and materials from lignocellulosic biomass. Agricultural and forest residues as sources of lignocellulosic biomass have great potential in this regard. With process optimizations, several biomass types have been subjected to liquefaction in different solvents with various catalysts. The products from recent microwave liquefaction with and without further fractionation have been thoroughly analyzed and used for the synthesis of biomaterials. Renewable chemicals, polyurethane foams with partial use of renewable raw materials, and phenolic resins have been the main products from microwave-liquefied products. Further research on microwave liquefaction mechanisms and scalable production should be enhanced to fully evaluate the economic and environmental benefits. This work presents an overview on achievements using liquefaction in combination with microwave energy to convert lignocellulosic biomass into value-added products and chemicals.