Growth of Escherichia coli,Salmonella enterica and Listeria spp., and their inactivation using ultraviolet energy and electrolyzed water,on ‘Rocha’ fresh-cut pears

The present study aimed at evaluating the growth of Escherichia coli, Salmonella enterica, and Listeria spp. and studying the efficacy of Ultraviolet-C (UV-C) irradiation, acidic electrolyzed (AEW) and neutral electrolyzed (NEW) waters in the reduction of these bacteria on ‘Rocha’ pear. Fresh-cut pieces were inoculated and incubated at 4–20 °C for 8 days. Inoculated pears were treated with UV-C (2.5–10 kJ/m²), AEW, NEW and sodium hypochlorite (SH) and microbiological and quality parameters were evaluated. The three bacteria, inoculated at 6.1–6.2 log cfu/g, grew on the pear at high growth rates at 12 and 20 °C reaching populations of 8.1–8.6 log cfu/g, in 24 h. At 8 °C the microorganisms increased their populations by at least 1 log cfu/g in three days. At 4 °C adaptation phases of less than 24 h for Listeria spp. were measured before exponential growth occurred and the enterobacteria did not grow despite having survived for 8 days. AEW and NEW caused microbial reductions similar to SH, of approximately 1 log cfu/g, while the best UV-C dose (7.5 kJ/m²) of at least 2.4 log cfu/g. Fresh-cut pears were a good substrate for foodborne bacteria emphasizing the importance of preventing contaminations and cross contaminations. The UV-C was more effective than the chemical decontaminations, as it provided superior microbial reductions without greatly affecting the quality of pears.     

Stabilization of anthocyanins on thermally processed red D'Anjou pears through complexation and polymerization

Stabilization of red anthocyanins on the surface of thermally processed red pears (D'Anjou) through complexation with metallic ions and polymerization was investigated. Pears were treated briefly in an aqueous solution containing stannous (Sn) ion, hydrochloric acid, formaldehyde, and tannic acid prior to steaming and canning processes. Polymerization capacity of the treatment solutions was investigated by monitoring the haze formation of the solutions. Aqueous acetone extracts of the peels from fresh and treated pears at major processing steps (pre-treatment, steam-heating, and canning) were subjected to HPLC qualitative analysis on anthocyanins. The total phenolics (TP) and anthocyanin content (ACN) of the peels were measured by Folin-Ciocalteu assay and pH-differential method, respectively. Polymerization capacity of the solution was influenced by the composition, setting-time, and the time of Sn addition into the formulated solutions. The pre-treatment along with steam-heating resulted in stable red pigments on the peels of canned pears. The new pigments are believed to be the complexes of stannous and phenolics, including anthocyanins. No major newly formed anthocyanins or small phenolics were detected in treated pears. Although developed treatment formula did not represent a commercial application yet, this study revealed an effective approach of retaining red anthocyanins on thermally processed fruits.     

Effects of chitosan coating on oxidative stress in bruised Yali pears (Pyrus bretschneideri Rehd.)

The protective effects of chitosan on oxidative stress in bruised Yali pears (Pyrus bretschneideri Rehd.) were investigated. The fruit were treated with 1.5% chitosan before or after damage, respectively, and then stored at 16 °C and 90% relative humidity. Postharvest quality, reactive oxygen species (ROS) and antioxidant enzymes were analysed. Results showed that bruise induced the accumulation of H₂O₂ and O^2?. However, chitosan treatments reduced the levels of ROS and delayed the decease of glutathione (GSH) content in bruised fruit. Meanwhile, activities of antioxidant enzymes, including catalase, peroxidases, superoxide dismutase, ascorbate peroxidase or GSH reductase was 40.7%, 98.1%, 62.3%, 127.8% or 23.8% higher in chitosan‐bruised fruit and 41.1%, 80.8%, 18.5%, 102.9% or 45.2%, respectively, higher in bruised‐chitosan fruit than untreated bruised fruit on the 15th day.     

使用自动顶空进样器测定梨中代森锰锌残留量的电子捕获气相色谱法

建立了一种测定梨中代森锰锌残留量的气相色谱顶空-电子捕获法。通过添加助剂,采用代森锰锌工作曲线法进行测定并计算,消除了代森锰锌转化不很确定所带来的困难。该方法测定准确度较高,最低检测浓度0.05mg/kg,可应用于梨中代森锰锌残留测定。     

Loss of ascorbic acid during storage of Conference pears in relation to the appearance of brown heart

To investigate the causes of brown heart (BH) in Conference pears, the contents of ascorbic acid (AA) and dehydroascorbic acid (DHAA) in fruits were studied during the first period of storage. AA was studied in 1999 and 2000, DHAA in 1999 only. Pears from normal and very late harvest stored immediately or after a delay in a controlled atmosphere with 2% O₂ and low (0.7%) or high (5%) CO₂ were compared. DHAA content did not change during storage in any treatment. AA decreased in storage according to an exponential model. The rate of AA loss was different in the two years and was higher in late‐harvest fruits and in those stored in 5% CO₂. BH appeared in different treatments when AA decreased below a threshold, which was about 2 mg kg^?1 fresh weight, corresponding to 5% of the AA content at harvest. The frequency and severity of symptoms depended linearly on the time spent by fruits in low‐ascorbate conditions. Advanced maturity at harvest and storage in high CO₂ determine the appearance of BH and increase the rate of AA loss, probably through a reduction in the turnover of antioxidants. © 2002 Society of Chemical Industry     

Influence of Maturity at Processing on Quality Attributes of Fresh-cut Conference Pears

ABSTRACT: Influence of ripeness state of Conference pears on the respiration and quality changes of the minimally processed fruit was studied. The fruits processed at partially ripe maturity were the most suitable to obtain fresh-cut products. Slightly under-ripe pears exhibited less browning and firmness degradation. Treatments consisting of dips in 10 g/L ascorbic acid and 5 g/L calcium chloride and packaging in 15 cm^-2× m^-2× 24 day^-1× bar^-1 preserved the initial appearance of pear cubes for at least 14 d. Because of a significant inhibition of ethylene production, 0 kPa O₂ initial atmosphere was effective in preventing quality changes. Presence of ethanol, as a result of fermentative anaerobic processes, increased with ripeness, especially beyond the 1st 21 d of storage at 4 °C. On the contrary, acetaldehyde was less affected than ethanol by processing and storage conditions.     

海藻酸钠处理对鲜切雪花梨生理生化的影响

目的研究海藻酸钠涂膜对鲜切雪花梨外观,质地及营养成分的影响。方法以鲜切雪花梨为材料,采用海藻酸钠(1%海藻酸钠+0.15%半胱氨酸+0.3%VC+0.6%醋酸)进行涂膜处理鲜切梨,测定经涂膜处理后的鲜切雪花梨的生理生化指标。结果雪花梨经过鲜切后在4℃和10℃贮藏期间,海藻酸钠涂膜处理明显减轻了鲜切雪花梨的褐变程度,抑制了多酚氧化酶和过氧化物酶的活性,保持较高的硬度、可滴定酸和VC含量,延缓了水分散失。结论海藻酸钠处理较好地保持了贮藏期间鲜切雪花梨的外观和质地。     

气相色谱法测定梨和土壤中戊唑醇的残留消解动态

[目的]对戊唑醇在梨和土壤中的残留分析方法进行了探讨并测定了其残留消解动态.[方法]采用乙腈提取、Flolisil小柱净化、GC-μECD进行检测.[结果]梨添加标准品0.01、0.05、0.5、1 mg/kg,回收率分别为110.3％、77.8％、81.5％、74.5％;土壤中添加标准品0.01、0.05、0.5、1 mg/kg,回收率分别为110.5％、97.1％、88.4％、82.8％.通过田间试验样品检测得到的戊唑醇的消解动态方程,其在梨上半衰期为8.6 d,在土壤中半衰期为7.2 d.[结论]方法灵敏度、准确度、精密度高,仪器耗材普遍易得,能为大规模监测戊唑醇的残留情况提供参考.