Consumer acceptance of fresh-cut iceberg lettuce treated with 2% hydrogen peroxide and mild heat

An antibacterial treatment consisting of 2% hydrogen peroxide at 50 degrees C for 60 s was evaluated for its effects on the sensory quality of fresh-cut iceberg lettuce. Treated lettuce was packaged in polyethylene film by a protocol used in the fresh-cut produce industry and then stored along with untreated controls for 3, 10, and 15 days at 5 degrees C. Gas chromatographic analysis confirmed that the desired initial volume (approximately 6 liters) and oxygen gas content (approximately 10%) were maintained during storage. Consumers from the local community who were the primary shoppers for their households and who purchased and ate lettuce regularly evaluated the appearance, color, aroma, flavor, and texture of the lettuce and their overall liking of the lettuce. Forty consumers were recruited to evaluate processing replication 1 on 26 April, and another 40 were chosen to evaluate processing replication 2 on 3 May. Because replication differences were observed in instrumental color measurements and in mean sensory ratings, replications were not pooled for the two test dates. Lettuce purchased for processing replication 2 was considerably greener than that used in replication 1. Overall, the antibacterial treatment was more effective than the control treatment in maintaining sensory quality over 15 days of storage, provided that the lettuce was initially intensely green. Three-fourths of the participants indicated that they would be willing to buy precut packaged lettuce that had already been treated at the packinghouse or processing plant with an antibacterial solution, and of these participants, 62.5% indicated that they would be willing to pay 5 to 10 cents more per bag.     

NO处理对鲜切牛蒡品质和褐变的影响

为控制鲜切牛蒡褐变,延长其货架期,文中研究了NO处理对鲜切牛蒡贮藏期间品质和褐变的影响。结果表明:未经处理的对照样品2 d就明显褐变,NO处理的牛蒡贮藏13 d仍具有较好的色泽,且感官品质明显好于对照。NO处理抑制了多酚氧化酶(PPO)和苯丙氨酸解氨酶(PAL)的活性,降低了总酚含量和呼吸速率;同时降低了电导率及丙二醛(MDA)的含量。说明NO处理抑制褐变可能与抑制呼吸代谢和酚类物质的合成,及保持膜的稳定性相关,从而达到延长鲜切牛蒡货架期的目的。     

Hot air treatment delays senescence and maintains quality of fresh-cut broccoli florets during refrigerated storage

A postharvest treatment with hot air (48 °C during 3 h) was applied to fresh-cut broccoli to investigate its effect on quality and senescence during storage at 0 °C. The treatment delayed yellowing as evidenced by lower decrease of Hue values during storage. After 21 days of storage, treated broccoli had chlorophyll content approximately 40% higher than controls. The treatment did not affect either weight loss or respiratory activity but induced lower electrolyte leakage, indicating that treated samples conserved higher tissue integrity. Heating reduced phenolic content and antioxidant capacity during the first two weeks, but the samples recovered after 3 weeks reaching values similar to controls. Finally, after 3 weeks of storage, treated samples had higher levels of total sugars, and total and soluble proteins. The results suggest that a short postharvest heat treatment may reduce senescence, tissue damage and contribute to maintain a better quality of the product during storage at 0 °C.     

草酸与柠檬酸抑制鲜切香蕉酶褐变的比较研究

对草酸和柠檬酸抑制鲜切香蕉片酶褐变的效果进行了研究。鲜切香蕉片分别用0、5、10、20、40、60、80、100mmol/L的草酸和柠檬酸溶液浸泡5min,然后置于白纸上常温存放8h,每2h抽样测定香蕉片的L*值;鲜切香蕉片分别用60mmol/L草酸、60mmol/L柠檬酸、60mmol/L草酸+0.5%异抗坏血酸钠和60mmol/L柠檬酸+0.5%异抗坏血酸钠溶液浸泡5min,然后装在塑料托盘里,用PE保鲜膜包扎,在10℃下贮藏5d,每天抽样测定香蕉片的L*值。结果表明,无论常温还是低温下,草酸和柠檬酸均可有效抑制鲜切香蕉褐变,而且草酸抑制鲜切香蕉褐变的效果均好于柠檬酸。     

Identification of the miRNAs and their target genes involved in fresh-cut potato browning inhibition by nitrogen

Browning decreases the quality and shortens the shelf life of fresh-cut potato, causing enormous economic losses. This study indicated that nitrogen treatment could inhibit this browning process. However, whether microRNAs (miRNAs) are involved in inhibiting the fresh-cut potato browning by nitrogen remains unclear. Therefore, nine small RNA libraries were constructed and performed high-throughput sequencing using fresh-cut potatoes from control and nitrogen-treated for 1 h groups at 25 °C to identify the miRNAs and their target genes involved in fresh-cut potato browning inhibition by nitrogen. The results revealed that four common differentially expressed miRNAs (DEmiRNAs) were identified as associated with browning. The correlation analysis indicated that fresh-cut potato browning was closely related to the expression of DEmiRNAs and their potential target genes. The miR172d targeting APETALA2/ethylene response factor and phospholipase D, miR482e targeting ATPase GET3-like, and PC-3p-17015_391 targeting stachyose synthase are vital in the nitrogen inhibited fresh-cut potato browning by regulating the ethylene signalling pathway, membrane lipid metabolic process, ATPase activity, and carbohydrate metabolic process. This study provides new insights into fresh-cut potato browning inhibition and helps to improve the quality of fresh-cut potato using nitrogen.     

Effect of whey protein concentrate on phenolic profile and browning of fresh-cut lettuce (Lactuca Sativa)

The in vitro kinetics of lettuce PPO with respect to dissolved oxygen using catechin, chlorogenic acid, caffeic acid and gallic acid has been examined. In-vitro lettuce polyphenol oxidase (PPO) activity was determined by measuring the consumption of oxygen during the oxidation reaction. The effect of whey protein concentrate (WPC) was tested on the inhibition of lettuce PPO comparing with ascorbic acid (AA) and cysteine. A competitive model that considered inhibitors was the most appropriate model to explain reaction kinetics. Browning of lettuce was also monitored during storage for 24 h. Addition of WPC prevented loss of lightness in lettuce. Loss of identified phenolic compounds in lettuce was measured during the enzymatic browning process by high-performance liquid chromatography. Degradation of identified phenolic compounds followed first order kinetics during storage. Combination of WPC with cysteine was proposed for the protection of phenolics compounds against PPO-catalysed oxidation.     

Dual effectiveness of sodium chlorite for enzymatic browning inhibition and microbial inactivation on fresh-cut apples

The dual effectiveness of sodium chlorite for browning inhibition and microbial inactivation on fresh-cut apples was investigated and compared to other anti-browning and antimicrobial agents. Results indicate that sodium chlorite significantly (P < 0.001) inhibited the browning reaction of fresh-cut Red Delicious apples stored at 5 °C for 14 days. This treatment also significantly reduced polyphenol oxidase activities. Treatments with acidified sodium chlorite, calcium chloride, or calcium ascorbate exhibited strong inhibition on apple browning during the early storage, these treatment effects diminished after 7 days in storage. Combining calcium chloride with sodium chlorite further significantly (P < 0.001) improved the firmness of apple slices, and browning inhibition during storage. Additionally, treatments with acidified sodium chlorite, sodium chlorite, or the combination of sodium chlorite and calcium chloride significantly (P < 0.001) reduced Escherichia coli populations on fresh-cut apples by 3.0, 3.6, and 3.9 log cfu g⁻¹ over the water control. The dual effectiveness of sodium chlorite to inhibit enzymatic browning and inactivate E. coli may allow this compound to achieve a prominent role in improving the quality and safety of products in the fresh-cut apple and other food industries.     

鲜切莴苣生理生化变化及其保鲜技术的研究进展

该文基于近几年国内外有关鲜切莴苣的研究,分析莴苣加工后的品质变化,并总结了鲜切莴苣物理、化学和生物保鲜技术的研究现状,旨在为鲜切莴苣尤其是鲜切蔬菜保鲜技术的研究提供理论参考。     

鲜切果蔬酶促褐变关键酶的研究进展

新鲜果蔬经过切割处理后,产生的机械伤害会刺激诱导表面组织发生酶促褐变反应,而使鲜切产品的感官品质下降、货架期显著缩短。鲜切果蔬的外观色泽变化主要是由酶促褐变引起的,起主要作用的关键酶有:多酚氧化酶(PPO),过氧化物酶(POD)、苯丙氨酸解氨酶(PAL)、脂氧合酶(LOX)、抗坏血酸过氧化物酶(APX)、超氧化物歧化酶(SOD)和过氧化氢酶(CAT)等。本文就近几年有关鲜切果蔬酶促褐变发生中一些关键酶的作用机理进行了综述,为鲜切果蔬酶促褐变的控制和质量保持提供理论参考。      

Effect of calcium lactate and heat-shock on texture in fresh-cut lettuce during storage

Textural and microstructural changes in fresh-cut lettuce were analysed over 12 days storage. The vegetable was treated with 120 ppm chlorine and with 15 g/L calcium lactate at room temperature (∼18–20 °C) and at 50 °C (heat-shock). Texturometer analysis showed that samples washed with calcium lactate had significantly (p > 0.05) higher crispness values than samples washed with chlorine. However the use of 50 °C treatment (heat-shock) gave better textural properties at the end of storage and significantly retarded the softening process, being in agreement with the sensorial results. Cryo-SEM micrographs showed a loss of turgor (shrinkage) of the tissue cells in the samples washed with chlorine, effect not so evident in calcium lactate treated samples. The use of heat-shock in combination with calcium lactate reduced this phenomenon better than the other two treatments. Pectin methyl esterase (PME), enzyme related to textural changes, showed higher activity in samples treated with calcium lactate at 50 °C. The combination of calcium lactate and 50 °C washing temperature maintained objective and sensorial textural properties of fresh-cut lettuce better than the calcium lactate or chlorine washing treatments at room temperature.     

Effect of hydrogen peroxide treatment on microbial quality and appearance of whole and fresh-cut melons contaminated with Salmonella spp

The efficacy of hydrogen peroxide treatment on the inactivation of Salmonella spp. inoculated on the external surface of cantaloupe and honeydew melon was investigated. Salmonella was inoculated onto whole cantaloupe and honeydew melon to a final concentration of 4.65 log(10) CFU/cm(2) and 3.13 log(10) CFU/g, respectively. Inoculated whole melons stored at 5 degrees C for up to 7 days were washed with water, 2.5% and 5% hydrogen peroxide at day 0 and 5. Hydrogen peroxide (2.5% and 5%) treatments of whole melon for 5 min caused a 3 log(10) CFU/cm(2) reduction of the indigenous surface microflora and a 3.0 log(10) CFU/cm(2) reduction in Salmonella spp. on all melon surfaces. The efficacy of the hydrogen peroxide treatments was less when the interval between inoculation and treatment of cantaloupe exceeded 24 h. Unlike cantaloupe fresh-cut pieces, Salmonella was not recovered from fresh-cut pieces prepared from treated whole honeydew melon. Growth of Salmonella occurred in cantaloupe fresh-cut pieces stored at 10 or 20 degrees C, and by 2 weeks, levels reached approximately 1 log CFU/g. A rapid decline in appearance and overall acceptability was observed in fresh-cut pieces prepared from untreated whole cantaloupe. While Salmonella was recovered from fresh-cut pieces from and whole treated cantaloupe, sanitizing the surface of contaminated whole melons with hydrogen peroxide before and after cutting and storage of the fresh-cut pieces at 5 degrees C can enhance the microbial safety and acceptability rating for about 2 weeks after processing.     

Sensorial and chemical quality of gamma-irradiated fresh-cut iceberg lettuce in modified atmosphere packages

A study was conducted to investigate the effects of various doses of irradiation on the quality of fresh-cut iceberg lettuce and to determine a suitable maximum dose. Fresh-cut iceberg lettuce packaged in film bags was exposed to 0, 1, 2, 3, and 4 kGy of gamma radiation and stored at 3 degrees C for 14 days. CO2 levels were higher and O2 levels were lower in packages containing irradiated lettuce than in those containing nonirradiated lettuce for most of the storage period. Comparison with nonirradiated lettuce indicated that total ascorbic acid (ascorbic acid plus dehydroascorbic acid) content and firmness were not significantly influenced by irradiation at 1 or 2 kGy. The overall visual appearance was best for lettuce irradiated at 1 or 2 kGy. This improved quality may be related to the high CO2 and low O2 levels observed for the irradiated samples. Electrolyte leakage for lettuce increased with higher radiation doses and was correlated (R2 = 0.99) with a soggy appearance. The leakage for lettuce irradiated at > or = 2 kGy was significantly more extensive than that for nonirradiated lettuce. The irradiation of fresh-cut lettuce in modified atmosphere packages at doses of 1 kGy and perhaps 2 kGy for safety enhancement and quality improvement is feasible.     

Effect of hot water and hydrogen peroxide treatments on survival of salmonella and microbial quality of whole and fresh-cut cantaloupe

Cantaloupe melon has been associated with outbreaks of salmonellosis. Contamination might be introduced into the flesh from the rind by cutting or by contact of cut pieces with contaminated rinds. Our objectives were to investigate the efficacy of hot water or hot 5% hydrogen peroxide treatments in reducing the population of native microflora and inoculated Salmonella on cantaloupe rind and transfer to fresh-cut tissue during cutting. Whole cantaloupes, inoculated with a cocktail of Salmonella serovars to give 4.6 log CFU/cm2 and stored at 5 or 20 degrees C for up to 5 days, were treated with hot water (70 or 97 degrees C) or 5% hydrogen peroxide (70 degrees C) for 1 min at 0, 1, 3, or 5 days postinoculation. Aerobic mesophilic bacteria and yeast and mold on treated whole melon and fresh-cut pieces were significantly (P < 0.05) reduced by all three treatments. Treatments with hot water (70 and 97 degrees C) caused a 2.0- and 3.4-log CFU/cm2 reduction of Salmonella on whole cantaloupe surfaces irrespective of days of postinoculation storage prior to treatment up to 5 days at 5 or 20 degrees C, respectively. Treatment with 5% hydrogen peroxide (70 degrees C) caused a 3.8-log CFU/cm2 reduction of Salmonella. Fresh-cut pieces prepared from untreated inoculated melons and those treated with 70 degrees C hot water were positive for Salmonella. However, fresh-cut pieces prepared from inoculated whole melon dipped in water (97 degrees C) or hydrogen peroxide (70 degrees C) for 60 s were negative for Salmonella, as determined by dilution plating onto agar medium, but were positive after enrichment at days 3 and 5 of storage at 5 degrees C. The ability to detect Salmonella in fresh-cut pieces was dependent on the initial level of inoculation. The results of this study indicate that the use of hot water (97 degrees C) or heated hydrogen peroxide to reduce the population of Salmonella on contaminated whole cantaloupes will enhance the microbial safety of the fresh-cut product.     

Inactivation of MS2 F(+) coliphage on lettuce by a combination of UV light and hydrogen peroxide

The efficacy of a produce decontamination method based on a combination of UV light (254 nm) and hydrogen peroxide (H2O2) to inactivate the MS2 F(+) coliphage inoculated onto iceberg lettuce was evaluated. Lettuce inoculated with 6.57 log PFU of MS2 was reduced by 0.5 to 1.0 log unit when illuminated with UV light alone for 20 to 60 s (12.64 to 18.96 mJ/cm2). In contrast, a 3-log reduction in MS2 was achieved with 2% (vol/vol) H2O2 spray delivered at 50 degrees C. No significant increase in log count reduction (LCR) was observed when H2O2 and UV light were applied simultaneously. However, H2O2 sprayed onto lettuce samples for 10 s, followed by a further 20-s UV illumination, resulted in an LCR of 4.12 that compares with the 1.67 obtained with 200 ppm of calcium hypochlorite wash. No further increase in MS2 inactivation was achieved by the use of either longer H2O2 spray or UV illumination times. The extent of MS2 reduction was significantly (P < 0.05) decreased when the H2O2 spray was delivered at 10 or 25 degrees C compared with 50 degrees C. In the course of aerobic storage at 4 degrees C, lettuce treated with UV light and H2O2 (10 or 25 degrees C) developed discoloration (polyphenol accumulation) within 6 days. In contrast, lettuce treated with UV light and H2O2 at 50 degrees C developed less discoloration within this time period and was comparable to untreated controls. This study demonstrated that the combination of UV light and H2O2 represents an alternative to hypochlorite-based washes to reduce the carriage of viruses on fresh produce.     

偕胺肟纤维负载氧化铁制备及过氧化氢催化分解

通过配位沉淀法制备偕胺肟纤维负载氧化铁的复合物,用于过氧化氢催化分解。研究了制备工艺条件(铁源浓度、水浴反应时间、水浴反应温度、烘干温度等)对偕胺肟纤维负载氧化铁的过氧化氢催化分解性能影响。采用扫面电镜(SEM)、能谱分析(EDS)研究了催化剂结构,考察了催化剂的重复使用和再生性能。结果表明:在铁源浓度0.20 mol/L、水浴温度80℃、水浴加热时间2 h、烘干温度140℃的条件下,制备的偕胺肟纤维负载氧化铁催化剂表现出较好的过氧化氢催化分解性能和重复使用与再生性能。     

Nitric oxide fumigation stimulates flavonoid and phenolic accumulation and enhances antioxidant activity of mushroom

The effects of nitric oxide (NO) on antioxidant activity and contents of phenolics and flavonoids in mushroom Russula griseocarnosa were investigated. Freshly harvested mushrooms were fumigated with 0, 10, 20 and 30μLL(-1) NO at 20°C for 2h and then taken to examine the antioxidant activities using assays of reducing power, chelating effect on ferrous ions, scavenging effect on hydroxyl free radicals, and 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity. The results showed that the antioxidant activities of the mushrooms fumigated with NO were significantly increased when compared to the controls. Moreover, NO fumigation significantly enhanced phenolic and flavonoid contents and stimulated the activities of phenylalanine ammonia-lyase and chalcone synthase. The results indicated that NO fumigation might have potential application for enhancing the bioactive compounds and improving antioxidant activities in the mushrooms. Furthermore, the data suggested that the NO-induced phenolic and flavonoid accumulation was due to the activation of the biosynthetic pathways in the mushrooms.     

Phenolic profiling reveals the metabolite basis of flesh colour and fresh-cut browning in apple fruit

Flesh colour, which is affected by cultivars and browning, can largely impact consumer acceptance in fresh-cut apples. The study profiled phenolic metabolites from apple flesh of twenty-three cultivars by widely targeted metabolomics. Comparison among white- and yellow-fleshed cultivars showed fifteen phenolics, mainly quercetin 3-O-glucoside, hyperoside, hesperetin 5-O-glucoside and cymaroside, in white-fleshed apples were significantly higher than those in yellow-fleshed apples. It may indicate a metabolite basis of yellow and white flesh colour, and better potential nutrition in white-fleshed apples. In addition, ten phenolic metabolites including five cyanidin glycosides showed significant differences between the highest and the lowest browning groups, indicating them may be crucial in browning of fresh-cut apple. This work elucidates the differences of phenolic profiles among apple cultivars with different flesh colour and provides useful data to evaluate the suitability of apple for fresh-cut processing.     

外源乙烯处理对鲜切莴苣和甘蓝苯丙烷代谢的影响

为阐明外源乙烯对鲜切叶菜类蔬菜苯丙烷代谢的影响,本实验以莴苣和甘蓝为材料,经清洗与切割后,采用外源乙烯处理鲜切莴苣和鲜切甘蓝,研究了乙烯对苯丙烷代谢过程中关键酶—苯丙氨酸解氨酶(PAL)活性的影响,同时,还分析了主要次生代谢物质,总酚、类黄酮和木质素的含量变化。结果表明:外源乙烯处理对鲜切莴苣和鲜切甘蓝组织中PAL活性具有明显抑制作用,降低了总酚和类黄酮含量,促进了木质素合成而使含量有所上升,鲜切莴苣对乙烯作用的敏感性显著大于鲜切甘蓝(p<0.05)。