Temperature and moisture dependent dielectric properties of legume flour associated with dielectric heating

Dielectric properties data are important in developing thermal treatments using radio frequency (RF) and microwave (MW) energy and are essential in estimating heating uniformity in electromagnetic fields. Dielectric properties of flour samples from four legumes (chickpea, green pea, lentil, and soybean) at four different moisture contents were measured with an open-ended coaxial probe and impedance analyzer at frequencies of 10-1800 MHz and temperatures of 20-90 °C. The dielectric constant and loss factor of the legume samples decreased with increasing frequency but increased with increasing temperature and moisture content. At low frequencies and high temperatures and moisture contents, negative linear correlations were observed between the loss factor and frequency on a log-log plot, which was mainly caused by the ionic conductance. At 1800 MHz, the dielectric properties data could be used to estimate the legume sample density judging from high linear correlations. Loss factors for the four legume samples were similar at 27 MHz, 20 °C and low moisture contents (e.g. <15 g/100 g). At the highest moisture content (e.g. 20 g/100 g) soybean had the highest loss factor at 27 MHz and 20 °C, followed by lentil, green pea, and chickpea. The difference in loss factor among the four legumes did not show clear patterns at 915 MHz. Deep penetration depths at 27 MHz could help in developing large-scale industrial RF treatments for postharvest insect control or other applications that require bulk heating in legumes with acceptable heating uniformity and throughputs.     

Metabolic response to combined mild heat pre-treatments and modified atmosphere packaging on fresh-cut peach

The combined influence of mild heat pre-treatments (MHPT) and two types of modified atmosphere packaging conditions on metabolic response of fresh-cut peach was monitored during a 8-day long storage under refrigeration (4^C). The quality-affecting parameters were evaluated by physical and chemical methods (solute leakage, weight loss, firmness, colour, pH and soluble solid content) and by the evaluation of physiological aspects (respiration rate, PPO and PME activity) as well as vitamins, organic acids and sugars. Regarding main acid compounds, lower levels of malic acid are evident in heat-treated samples. Succinic and citric acids did not seem to be affected by the treatments. Provitamin A (β-carotene) was not affected by MHPT. The decrease in ascorbic acid content observed along the storage period was similar for both treated and untreated samples. Significant firmness improvements were obvious after MHPT due to the activation of PME (≈25%) and the ensuing production of calcium pectates. Efficiency of the passive modified atmosphere was enough to preserve the quality attributes of fresh-cut peaches subjected to MHPT.     

乙醛熏蒸处理对草莓贮藏品质的影响

研究了不同水平的乙醛熏蒸处理对草莓贮藏品质的影响,结果表明,草莓果实采收后立即用0.5％乙醛蒸汽处理1h,可以降低果实的腐烂率、减少失重、提高糖酸比、改善风味、增进着色、诱导香味和延缓采后软化;0.15％乙醛处理4h效果不明显;0.5％乙醛处理4h反而促进果实腐烂。     

鲜食葡萄采后SO2熏蒸及检测方法的评述

概述了鲜食葡萄贮运中，目前国际通用的最有效的保鲜方法－ＳＯ２熏蒸处理法和ＳＯ２检测方法的研究成果。     

不同温度贮藏对欧李采后生理和品质的影响

研究了不同温度条件下贮藏对欧李采后生理和品质指标的影响。结果表明,低温可显著降低欧李的呼吸强度,降低MDA含量,保持较高的SOD活性,提高贮藏品质,1℃贮藏保鲜效果最好。     

Cumulative oxygen consumption during development of two postharvest insect pests: Callosobruchus maculatus Fabricius and Plodia interpunctella Hübner

Insect pests such as Callosobruchus maculatus Fabricius and Plodia interpunctella Hübner cause substantial losses to grain during postharvest storage. In the last few years, hermetic storage technologies have been successfully used by smallholder farmers in Africa and Asia to protect their harvested grain against insect pests. Hermetic technologies owe much of their effectiveness to restricting oxygen availability to insects confined in the containers. There is a need to better understand the biology of specific storage insect pests and their responses to hypoxia. We employed a novel and non-invasive analytical technology, the OxySense 5250i, to measure oxygen levels in closed containers, and evaluated its effectiveness in measuring the total oxygen consumption of two insect pests during their development: C. maculatus and P. interpunctella. The total amount of oxygen consumed by C. maculatus during its larval development period determined with the OxySense apparatus was not different from that previously recorded using another instrument, the Mocon Pac Check 325 gas analyzer. Using the OxySense 5250i, we found that P. interpunctella consumes nearly three times as much oxygen per insect over its larval-to-adult developmental period compared to C. maculatus. Information on the lifetime oxygen consumption of insects provides relevant information to the effectiveness and ability of hermetic technologies to protect stored products against insect pests.     

Bioactive components and antioxidant capacity of Chinese bayberry (<Emphasis Type="Italic">Myrica rubra</Emphasis> Sieb. and Zucc.) fruit in relation to fruit maturity and postharvest storage

Total phenolics, flavonoids, anthocyanins, cyanidin-3-O-glucoside (Cy-3-glu) and antioxidant capacity of Chinese bayberry fruit (Myrica rubra Sieb. and Zucc.) differed among the four cultivars “Baizhong” (white), “Fenhong” (pink), “Wuzhong” (red) and “Biqi” (dark red). Antioxidant capacity determined by both the ferric reducing antioxidant power (FRAP) assay and 2,2-diphenyl-2-picrylhydrazyl (DPPH^.) radical scavenging capacity was significantly correlated with the antioxidant components in the fruit, and directly related to fruit color. Cy-3-glu accounted for at least 82, 38, and 12% of the total antioxidant capacity in “Biqi”, “Wuzhong” and “Fenhong” fruits, respectively. No detectable Cy-3-glu was found in “Baizhong” fruit. Greater fruit maturity was associated with higher levels of all the bioactive components and antioxidant capacity. Significant increases were also found during postharvest storage of “Biqi” fruit held at either 20 °C for 2 days or 0 °C for 5 days. However, these levels decreased during a 2-day shelf-life at 20 °C after 5 days at 0 °C. These results show that storage and shelf-life conditions are important if health-based bioactive components of bayberry fruit are to be maintained after harvest.     

Microwave Finish Drying of Osmotically Dehydrated Cranberries

Abstract

Combined microwave and hot-air drying characteristics was studied for the drying of cranberries that had been previously partially dehydrated by osmosis in a high fructose corn syrup (76°Brix). A 750 W 2450 MHz microwave oven was used to dry cranberry samples from 57% to 15% moisture content using three different power densities (0.75, 1.0, 1.25 W/g of initial cranberries) and two different power cycles (30 s On/30 s Off and 30 s On/60 s Off). All combinations of these variables were tested in triplicate. Quality of the cranberries was measured using a universal testing machine, chromameter, and with the use of a taste test panel. Drying times ranged from 2.2 to 5.0 h. Power times and power cycles affected the drying time and the quality of the dried cranberries. Lower power densities resulted in cranberries with higher quality. High power densities (125 W/g) resulted in the burning of some cranberries.