不同清洗消毒方法对鲜切生菜贮藏过程中微生物影响

以鲜切生菜为试验材料,研究电解水、次氯酸钠和紫外线照射方法对鲜切生菜贮藏中微生物的控制效果.结果表明,pH值12.5的电解水、质量分数为0.1 g/kg的次氯酸钠溶液、紫外线处理30 min均能显著控制鲜切产品菌落数.0.1 g/kg的次氯酸钠溶液可使鲜切生菜保藏6d,仍具有商业价值.     

赖氨酸和精氨酸复配处理对鲜切苹果褐变的影响

以红富士苹果为原料,研究了两种碱性氨基酸复配结合对鲜切苹果的褐变控制技术。通过单因素及正交试验筛选确定赖氨酸和精氨酸复配的最佳条件,初步探讨了其对鲜切苹果浆液 pH及多酚氧化酶（PPO）活性的影响。结果表明,赖氨酸和精氨酸复配的最佳工艺条件为：2.0%赖氨酸+1.0%精氨酸,20 ℃下浸泡处理10 min。鲜切苹果经处理后在2~4 ℃的低温条件下贮藏,可保持初始感官品质达4 d;赖氨酸和精氨酸复配可显著提高鲜切苹果浆液pH,且对于抑制PPO活性有很好的效果,进而显著抑制褐变的发生。     

Thinking of the Architectural Language and Concept

通过对鲜切甘蓝的切分、前处理、蒸烫、添加剂溶液浸泡、离心脱水、包装、贮藏等工艺点的调控,研究其对鲜切甘蓝品质的影响,并通过测定呼吸强度、多酚氧化酶（ppo）活力、褐变度等指标观察鲜切甘蓝质量变化,以确定最佳保鲜工艺条件。试验结果表明,经优化工艺处理的鲜切甘蓝保鲜期可达到10天以上。     

复合涂膜液的筛选及其对鲜切苹果保鲜效果的影响

以不同浓度的壳聚糖、氯化钙、甘氨酸为复合涂膜液材料,以鲜切苹果的丙二醛含量为考察指标,采用正交试验方法筛选最优复合涂膜保鲜液,并以去离子水为对照,研究该复合涂膜保鲜液对贮藏在28、4℃条件下的鲜切苹果相关品质指标的影响。结果表明:1.0%壳聚糖、1.5%氯化钙和1.0%甘氨酸的复合涂膜液对鲜切苹果具有良好的保鲜效果,且在4℃时保鲜效果更佳。     

鲜切芹菜自发气调包装的筛选

为延长鲜切芹菜货架期,采用不同透气率和不同面积的气调窗与包装袋相结合进行试验,分别筛选和优化出鲜切芹菜最适宜的气调包装。结果表明,鲜切芹菜适宜选用O_2和CO_2透过速率分别为4×10~5,1.6×10~6cm~3/m~2·d·atm,透气比为1∶4的气调窗,需要气调窗的面积为0.5～1.0 cm~2/kg,在4℃条件下至少可延长货架期6 d;综合计算气调窗和薄膜的透气量可知,适于鲜切芹菜包装袋O_2和CO_2的透过量应分别为0.92×10~3～1.04×10~3,1.13×10~3～1.59×10~3cm~3/kg·d·atm。研制的自发气调包装袋可使鲜切芹菜处于适宜的气体状态,可以很好地解决包装袋内由于无氧呼吸产生的异味问题,延长其货架期,为鲜切企业提供有力的技术支持。     

可食性复合膜在鲜切苹果块保鲜中的应用研究

利用保鲜剂对鲜切苹果块进行涂膜处理,研究了涂膜保鲜对鲜切苹果块的保鲜效果.以硬度、失重率为主要指标,结合感官评定,研究了羧甲基纤维素钠、柠檬酸、氯化钙、山梨酸钾添加量对鲜切苹果保鲜效果的影响,并通过正交试验进行配方优化,得出可食性涂膜对鲜切苹果块品质影响的最佳工艺参数.结果表明,可食性复合膜的最佳工艺配方为:羧甲基纤维素钠3.0％,柠檬酸0.6％,氯化钙0.25％,山梨酸钾0.5％,该条件下涂膜处理能够获得表面光亮、无褐变、无斑点、无腐烂、清脆爽口的鲜切苹果块,在50 h内不发生褐变和变质,保持一定的硬度,无明显失重,色泽、口感良好.试验结果显示,可食性涂膜可以有效延长鲜切苹果块的保鲜时间,且能保持较好状态,并可用于其他水果的保鲜.     

贮藏温度对鲜切金艳猕猴桃片货架品质的影响

以鲜切金艳(Actinidia chinensis×Actinidia eriantha,黄肉型品种)猕猴桃片为试材,研究了4种贮藏温度(1、5、10、20℃)对包装后猕猴桃片货架期内贮藏品质的影响。结果表明,在本试验条件下,贮藏温度对鲜切金艳猕猴桃片包装袋内气体成分、色差L*和b*值、组织相对电导率、可溶性固形物含量、总体感官、菌落总数、霉菌和酵母数量具有显著影响(P0.05)。1、5、10、20℃条件下,鲜切猕猴桃片的货架期分别为13、10、3、1 d;其中,1℃和5℃条件下贮藏10 d内鲜切金艳猕猴桃片外观和营养品质指标保持良好,各测定指标间差异不显著。     

一氧化氮对冷藏鲜切桃贮藏品质的影响

为探究适宜的鲜切桃冷藏条件下抑制褐变的方法,将鲜切"蒙阴"桃分别在清水(对照)、5、10、15μmol/L一氧化氮(NO)溶液中浸泡5 min,并于5℃下贮藏10 d,研究NO对鲜切桃贮藏期间品质的影响。结果表明,与对照相比,NO处理有效延缓了鲜切桃片褐变度的升高以及硬度、L^*值、可溶性固形物含量的下降,从而使鲜切桃在贮藏期间保持了较好的外观品质;同时NO处理减低了多酚氧化酶(PPO)和过氧化物酶(POD)活性高峰值,从而降低了褐变程度,提高了鲜切桃超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性,抑制了丙二醛(MDA)、活性氧(ROS)和总酚含量的上升,提高了鲜切桃片的贮藏品质,其中以10μmol/L NO保鲜效果最好。由此表明,10μmol/L NO处理是一种较好的抑制鲜切桃褐变的加工方法。     

鲜切茭白护色技术的研究

研究不同温度条件下护色液的种类和浓度对鲜切茭白护色效果的影响。实验表明,采用质量分数为0.1%的NaCl先护色10min,再用质量分数为0.1%的L-半胱氨酸护色20min,在4℃状态下贮藏,护色效果最好且能较好地保持鲜切茭白的原有质地。     

纳他霉素处理对鲜切白萝卜品质的影响

研究了纳他霉素处理对鲜切白萝卜品质的影响。首先,将鲜切白萝卜在浓度分别为0.05、0.08、0.10 g/L的纳他霉素溶液中分别浸泡3 min和5 min,定期测定其霉菌及酵母菌总数,筛选出最适浸泡浓度及时间。其次,采用喷雾和浸泡两种方式处理鲜切白萝卜,并定期对其失重率、硬度、VC含量、可溶性固形物含量、过氧化物酶(POD)活性、霉菌及酵母菌总数进行测定。试验结果表明:鲜切白萝卜采用0.10 g/L的纳他霉素溶液浸泡3 min是最佳的处理方式,与对照(不做处理)组相比,该处理的白萝卜失重率降低了18.9%,VC含量、可溶性固形物含量和硬度分别提高了50%、14.28%和9.2%,并能够抑制霉菌及酵母菌的生长繁殖及POD活性。适宜的纳他霉素处理可以延缓白萝卜组织衰老,有利于保持鲜切白萝卜贮藏期间的品质。     

不同处理对鲜切莴苣褐变及贮藏品质的影响

以莴苣为研究材料,以10 g/L L-抗坏血酸、5 g/L柠檬酸、0.2 g/L水杨酸和0.2 g/L阿魏酸处理鲜切莴苣,去离子水浸泡为对照组,通过测定褐变度、总酚、类黄酮、多酚氧化酶(PPO)活性、过氧化物酶(POD)活性及苯丙氨酸解氨酶(PAL)活性,探讨不同抗褐变剂对鲜切莴苣褐变的影响。结果表明,4种抗褐变剂处理均能够有效抑制酶促褐变有关酶活性的升高,减少多酚物质的含量,降低褐变度,有效地保证了鲜切莴苣的贮藏品质,其中0.2 g/L阿魏酸处理的效果最好。     

不同保鲜剂处理对切割生菜品质影响的研究

研究了5种保鲜剂（1mmol／L苯甲酸、0．5％氯化钙、1．0％过氧化氢、1．0％维生素C、1．0％柠檬酸）处理对新鲜切割生菜（10～15mm切割度）在3℃贮藏期间品质变化及贮藏效果的影响。结果表明,在3℃贮藏条件下,5种处理中,1mmol／L苯甲酸和0．5％氯化钙显著延缓切割生菜的叶绿素、总酸、VC以及可溶性固形物含量的下降,保持了较好感官品质,贮藏到第12天仍有商品价值;1,0％过氧化氢和1,0％VC处理对保持切割生菜的品质有一定的作用,但处理效果略次于苯甲酸和氯化钙,商品贮藏期仅为8天：1．0％柠檬酸的处理效果不明显,商品贮藏期仅为6天左右。     

Preharvest and postharvest factors related to off-odours of fresh-cut iceberg lettuce

The influence of different preharvest and postharvest factors affecting off-odour development of fresh-cut iceberg lettuce in low-O₂ modified atmospheres (MA) was investigated. Fresh-cut iceberg lettuce developed undesirable off-odours under low O₂ and elevated CO₂ atmospheres. A strong relationship between CO₂ concentration and off-odour development was observed. Significant differences in off-odour development existed among different cultivars in two harvests in consecutive years. The influence of maturity stage was evaluated, comparing fresh-cut product from immature and over-mature heads with commercial ones. Higher CO₂ concentrations and higher accumulation of ethanol and acetaldehyde were detected in the headspace of MA-packed lettuce from immature heads. Differences in respiration rate of the fresh-cut product from heads cultivated during the winter–spring seasons were around 30%. Respiration rate of fresh-cut iceberg lettuce increased when medium temperature during cultivation increased. Changes in the product weight generated different CO₂ levels which correlated with the production of ethanol and acetaldehyde and other off-odour metabolites related with the lipoxygenase (LOX) pathway such as hexanal, 1-hexanol, and cis-3-hexen-1-ol. Volatile compounds such as cis-3-hexen-1-ol, β-elemene, ethyl acetate and dimethyl sulphide increased their content more than 10 times compared with other volatiles. Moreover, differences in the initial flushed gas-mixture with or without CO₂ showed higher CO₂ concentrations and the development of stronger off-odours when samples were flushed with an enriched CO₂ gas-mixture. In summary, visual quality of fresh-cut iceberg lettuce is important but so are odour and flavour. MAP currently used for fresh-cut lettuce may need some modification to inhibit off-odours and achieve better aroma and flavour qualities for preserving “freshness” of the cut product. Screening for cultivars with low browning potential and fermentation, harvested at optimum maturity stage and with an adequate package design are recommended.     

Effect of new sanitizing formulations on quality of fresh-cut iceberg lettuce

In the present study, three recently patented decontamination agents: peroxyacetic acid combined with lactic acid, and two different combinations of hydrogen peroxide with citric acid (with and without propylene glycol), were compared with sodium hypochlorite and tap water washing regarding their effect on equilibrium modified atmosphere packaged (EMAP) fresh-cut iceberg lettuce. Effects of these sanitizers on respiration rate, electrolyte leakage, microbial levels, and sensory quality of the product after decontamination and during storage (3 d at 4 °C followed by 4 d at 7 °C) were elucidated. Hydrogen peroxide based sanitizers provoked a significant increase in the respiration rate and the electrolyte leakage of fresh-cut iceberg lettuce compared with tap water washing. Peroxyacetic acid combined with lactic acid resulted in similar results to those of tap water washing for all the parameters analyzed. However, other aspects of the combination of peroxyacetic and lactic acids (e.g. efficacy for cross-contamination avoidance) should be assessed in the future in order to determine its suitability for fresh-cut iceberg lettuce processing.     

Sensory quality,bioactive constituents and microbiological quality of green and red fresh-cut lettuces (Lactuca sativa L.) are influenced by soil and soilless agricultural production systems

Quality characteristics and shelf-life of fresh-cut lettuce cultivated in soil, as the traditional production system, and soilless, as an innovative production system, were investigated. Three lettuce genotypes, lollo rosso and red oak leaf as red-leafed genotypes, and butterhead as a green-leafed genotype, were studied. Lettuces from both production systems were grown in the same open field and at the same time in the winter season. A longer growing period was needed, to obtain the same maturity stage, in the soil than in the soilless (102 and 63 d after planting, respectively). After harvest, the visual quality of the fresh-cut produce from red-leafed lettuce cultivated in soilless was better than those in soil. In the case of green-leafed genotype, the soilless system gave a lower visual quality of the fresh-cut product. Lollo rosso cultivated in the soilless system had a higher content of phytochemicals, including vitamin C and individual and total phenolics, than that cultivated in soil. At the end of storage, fresh-cut lollo rosso and red oak leaf grown in the soilless system showed significantly higher content of vitamin C than those in soil. This high content of antioxidants was linked to a better maintenance of visual quality and the control of browning when compared with the fresh-cut product from lettuces cultivated in soil. The soilless system was more effective in controlling microbial contamination as lettuce cultivated in the soilless system had a lower initial microbial load and slower microbial growth during storage. At the end of shelf-life, differences in microbial counts between soil and soilless lettuce were 3 and 1.5 log units higher for lactic acid bacteria and total coliforms, respectively, in soil. This study shows that higher quality and microbiologically safer raw product can be provided by the soilless system as a new growing system although it depends on the genotype and the season.     

Changes in respiration of fresh-cut butterhead lettuce under controlled atmospheres using low and superatmospheric oxygen conditions with different carbon dioxide levels

The effect of different O₂ levels from 0 to 100 kPa in combination with 0, 10 and 20 kPa CO₂ on the respiration metabolism of greenhouse grown fresh-cut butter lettuce was studied. Controlled atmospheres of 20 or 75 kPa O₂ with 0 or 10 kPa CO₂ showed a constant respiration rate during the first 2–4 days at different temperatures (1, 5 and 9 °C). Therefore, constant respiration rates during a short period of 2–4 days could be considered as valid for a large part of the commercial life of, for instance, a modified atmosphere package development. The fresh-cut lettuce exposed to low O₂ levels (2–10 kPa) combined with moderate to high CO₂ levels (10 and 20 kPa) had a higher respiration rate than when 20–100 kPa O₂ were used. Moderate CO₂ levels (10 kPa) reduced the respiration rates of fresh-cut lettuce 20–40% at 9 °C. This effect was less noticed at lower temperatures. Gas composition with high CO₂ levels (20 kPa) probably caused a metabolic disorder increasing the respiration rate of fresh-cut butter lettuce. It was concluded that 80 kPa O₂ must be used in modified atmosphere packaging (MAP) to avoid fermentation of fresh-cut butter lettuce in combination with 10–20 kPa CO₂ for reducing their respiration rate.     

鲜切生菜伤害信号的初步研究

本文用简易的方法对鲜切Romaine生菜中伤害信号进行了研究。实验结果表明,切割后在其切割位点产生伤害信号物质,它能在很短的时间内传导至邻近未受伤组织中,并诱导一系列的生理反应,例如PAL（苯丙氨酸解氨酶）的合成,酚类物质的合成和累积,切割面的褐变等。己醇能显著的抑制伤害信号的传导,植物组织提取液对其抑制作用具有抵消作用。同时研究发现,伤害信号能通过溶液进行传导。生菜的伤害信号可能不是蛋白类物质。     

Suitability of aqueous chlorine dioxide versus sodium hypochlorite as an effective sanitizer for preserving quality of fresh-cut lettuce while avoiding by-product formation

Aqueous chlorine dioxide (ClO₂) has been postulated as an alternative to sodium hypochlorite (NaClO) for fresh-cut produce sanitization with the advantage of avoiding the risks associated with chlorination by-products. However, little is known about its influence on preserving quality and the potential formation of trihalomethanes (THMs) under typical processing conditions. The suitability of aqueous chlorine dioxide (3 mg L⁻¹) as an effective sanitizer of fresh-cut iceberg lettuce stored under active modified atmosphere packaging (MAP) at refrigerated conditions was determined and compared with sodium hypochlorite (100 mg L⁻¹). Fresh-cut lettuce washed with tap water was used as a control. The epiphytic microbiota were characterized by the evaluation of the major relevant microbial groups such as mesophiles, psychrophiles, Pseudomonas spp., Enterobacteriaceae, lactic acid bacteria, yeasts and moulds. Additionally, gas composition, sensory quality, vitamin C and individual and total phenolics were monitored after washing and during storage for 3 d at 4 °C followed by 7 d at 8 °C. In general, the natural microbiota of fresh-cut lettuce after washing and storage was equally affected by the different washing solutions, with the exception of yeasts which showed the highest growth after 10 d storage in samples washed with chlorine dioxide. None of the tested washings negatively affected sensory quality, which was acceptable after 10 d storage. Additionally, the content of bioactive compounds was not significantly affected either by washing solution or by storage time. The potential formation of THMs was evaluated by the analysis of lettuce washed in water with a chemical oxygen demand (COD) of 700 mg L⁻¹ treated for 30 min with sodium hypochlorite (100 mg L⁻¹) or chlorine dioxide (3.7 mg L⁻¹). Trihalomethane formation was only detected in the process water in which sodium hypochlorite was applied (217 ± 38 μg L⁻¹). However, THMs formation in fresh-cut lettuce was negligible despite the sanitation procedure. The formation of THMs was only detected in fresh-cut lettuce when sodium hypochlorite was used under very extreme conditions where lettuce was washed in water with a high level of organic matter (COD = 1800 mg L⁻¹), high sodium hypochlorite concentration (700 mg L⁻¹) and long contact time (60 min). Our data suggest that aqueous chlorine dioxide is as suitable as sodium hypochlorite for fresh-cut lettuce sanitation with the advantage of preventing the formation of THMs.     

Baby-leaf and multi-leaf of green and red lettuces are suitable raw materials for the fresh-cut industry

Consumer demand for softer leaves with variation in taste, shape and colours has encouraged the development of new lettuce products of baby-sized leaves. The objective of this study was the comparison of whole-head lettuce, as the most common raw material for fresh-cut, with baby-leaf and multi-leaf as the newest baby-sized lettuce leaves. Lettuces (Lactuca sativa L.) of the types Green Leaf, Red Leaf and Lollo Rosso were cultivated in the same field with different plant densities, under commercial conditions. Although baby-leaf was subjected to far less wound damage than the shredded lettuce from the whole-head, leaf age could play an important role in increasing respiration rate and determining postharvest quality. After 9-11 d of storage, minimally processed products from the three types of raw material showed good visual quality without differences among them. However, over the 12-d storage period, quality decreased to the limit of marketability mainly due to browning of the cut edge surface of the fresh-cut product from whole-heads and decay due to the soft tissue in the case of baby-leaves. Additionally, with the processing of whole-heads, the increase in cut-damage surfaces and availability of cell nutrients provided conditions that favoured the growth of lactic acid bacteria (LAB) and total coliforms compared to uncut surfaces of baby-sized leaves. The ratio between the oxidized and reduced forms of ascorbate (DHA/AA) increased 2-4 times after 9-11 d of storage. Furthermore, baby-sized leaves had higher phenolic contents than the shredded product from the whole-head which probably contributed to reaching a shelf-life of 11 d. In conclusion, the new green and red baby-sized leaves both at immature and mature stages provided high quality lettuce for the fresh-cut market, meeting specific requirements regarding visual quality, microbial load and high content of phytochemicals.     

Role of commercial sanitizers and washing systems on epiphytic microorganisms and sensory quality of fresh-cut escarole and lettuce

Increasing concerns about the possible formation of carcinogenic compounds and the emergence of new, more tolerant pathogens, have raised questions on the use of chlorine in fresh-cut produce. There is a growing need to investigate the efficacy of new commercial sanitizing and other alternative technologies. In the present study, the effectiveness of chlorine and other commercial sanitizer agents (Sanova, Sanoxol 20, Tsunami 100, Purac FCC 80, Citrox 14W and Catallix) was evaluated on epiphytic microorganisms and their influence on the sensory quality of fresh-cut escarole and lettuce. Different sanitizer concentrations (manufacturer's recommended dose and half of this dose) and application systems (submersion and spray) were also compared. The antimicrobial efficacy of the treatments was evaluated, initially after washing, and after 8 days of storage simulating a commercial shelf-life (3 days at 4 °C + 5 days at 8 °C). All the tested washing solutions were more effective in reducing the microbial load than water washes, particularly in fresh-cut escarole. However, the microbial load of fresh-cut escarole and lettuce after 8 days of storage was very similar for most of the treatments despite the different application systems and concentrations of the sanitizers. Clearly epiphytic microorganisms of fresh-cut escarole and lettuce were able to grow rapidly during storage under low temperature, reaching similar or higher values than the unwashed fresh-cut produce at the day of production. The overall visual quality of fresh-cut salad leaves was scored as good or very good (≥6) after 8 days of storage, except for the product washed with Purac. Thus, despite the high number of mesophilic bacteria present in the product, between 6 and 8 log cfu g⁻¹, it was not associated with a detrimental quality. Therefore, the determination of the initial epiphytic reductions of fresh-cut products after washing with different sanitizing agents provides little information about the microbial or sensory quality of the product at the time of consumption.