Effect of wounding on phenolic enzymes in six minimally processed lettuce cultivars upon storage

The effect of wounding on polyphenol oxidase (PPO), peroxidase (POD), and phenylalanine ammonia-lyase (PAL) was studied in six minimally processed lettuce (Lactuca sativa L.) cultivars upon storage for 7 days at 5 degrees C (Iceberg Mikonos (IM), I. Green Queen (IGQ), I. Asdrúbal (IA), Little Gem Sandra (LGS), Romaine Cazorla (RC), and R. Modelo (RM)). Wounding of lettuce tissue midribs (because of minimal processing) caused an exponential increase in PPO activity due to the activation process from latent to fully active PPO by following first order kinetics in the time range from 3.7 days (LGS) to 6.3 days (RC). However, total PPO activity (active plus latent) remained constant. Isoform pattern of PPO changed upon storage probably because of posttranslational processes. POD activity linearly increased with induction of new POD isoenzymes. PAL activity presented a typical bell-shaped induction pattern in four cultivars. Only IM and IGQ showed a second induction response which has not been previously described in the literature. IM was the cultivar most susceptible to browning and RC was the cultivar least susceptible. However, no clear correlation was observed between browning and any of the biochemical and physiological attributes investigated (PPO, PAL, and POD activities, total and individual phenols accumulation, and ascorbic acid content).     

Effect of different washing procedures on phenolic metabolism of shredded, packaged iceberg lettuce during storage

Different washing treatments applying chlorinated, ozonated, and tap water were examined for their effect on the phenolic metabolism of minimally processed iceberg lettuce (Lactuca sativa L.) during storage in consumer-sized bags at 4 degrees C for up to 9 days. To eliminate problems associated with raw material inhomogeneity, processing was conducted on a pilot-plant scale under operating conditions of industrial practice. Inherent product heterogeneity caused by diverse lettuce leaf tissues was compensated for by pooling large-sized samples, and frequent sampling ensured significant data about the activities of phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), and peroxidase (POD), as well as the contents of caffeic acid derivatives over storage time. In the homogeneous lettuce samples, specific responses caused by different washing procedures were detectable. PAL activity in the samples increased for up to 5-8 days of storage. Compared to tap and ozonated water, the use of chlorinated water (100-200 mg/L free chlorine) for washing trimmed heads or shredded lettuce significantly reduced PAL activity and the concomitant rise of 3,5-di-O-caffeoylquinic acid (isochlorogenic acid isomer) concentrations. The phenolic acids O-caffeoyltartaric (caftaric acid), di-O-caffeoyltartaric (chicoric acid), 5-O-caffeoylquinic (chlorogenic acid isomer), and O-caffeoylmalic were less influenced by different washing treatments. Individual contents either were constant or decreased during storage. Additionally, the novel finding of a further caffeic acid isomer, tentatively identified as meso-di-O-caffeoyltartaric acid, is reported. PPO and POD activities were less affected by different washing treatments and thus were less suitable physiological indicators of stress reactions triggered by alternative processing.     

Phenolic compounds and related enzymes are not rate-limiting in browning development of fresh-cut potatoes

The effect of minimal processing on polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia-lyase (PAL), and phenolic compounds was studied in five potato cultivars (Agria, Cara, Liseta, Monalisa, and Spunta). Minimal processing caused an overall increase in PPO, POD, and PAL activities. The isoform pattern of PPO was the same for all of the cultivars before and after processing. No latent PPO was detected. The isoperoxidase pattern was approximately the same among cultivars. An increase in POD activity was related to the specific induction of an acidic isoperoxidase. PAL showed an induction pattern characterized by the presence of a maximum peak of activity after 4 days of processing for all of the cultivars. The sequence of browning susceptibility of potato cultivars was as follows: Monalisa > Spunta > Liseta > Cara > Agria. Browning development was only partially correlated to PAL activity (only during the first 4 days after wounding). However, this correlation could not explain the above sequence of browning susceptibility. Minimal processing caused an increase of chlorogenic acid, whereas tyrosine content remained unchanged. In summary, no significant correlation was found between either rate or degree of browning and any other biochemical and physiological attribute investigated (PPO, POD, hydrogen peroxide, ascorbic acid content, and initial phenolics content as well as total and individual phenolics accumulation).     

Characterization and role of polyphenol oxidase and peroxidase in browning of fresh-cut melon

Polyphenol oxidase (PPO) and peroxidase (POD) were extracted from two different varieties of melon ( Cucumis melo L. cantalupensis cv. Charentais and C. melo L. inodorus cv. Amarillo) and characterized using reliable spectrophotometric methods. In both cases the enzymes followed Michaelis-Menten kinetics, showing different values of kinetics parameters between the two cultivars: K m = 7.18 +/- 0.70 mM ('Charentais') and 6.66 +/- 0.20 mM ('Amarillo') mM; V max = 7.93 +/- 0.35 units/min ('Charentais') and 13.82 +/- 0.37 units/min ('Amarillo'), relative to PPO; K m = 24.0 +/- 2.10 mM ('Charentais') and 5.05 +/- 0.19 mM ('Amarillo') mM; V max = 344.83 +/- 10.32 units/min ('Charentais') and 80.64 +/- 2.01 units/min ('Amarillo'), relative to POD. Optimum pH for PPO was 7.0 for 'Charentais' and 7.5 for 'Amarillo, whereas it was 4.5 for both cultivars relative to POD. Melon PPO had maximum activity at 60 degrees C in both 'Charentais' and 'Amarillo' cultivars, whereas POD maximum activity was found at 45 degrees C in 'Charentais' and at 25 degrees C in 'Amarillo'. POD from both cultivars showed higher thermolability compared with PPO, losing >90% of relative activity after only 5 min of incubation at 70 degrees C. POD's activation energy was much higher than that of PPO (Delta E (#) = 86.3 and 160.6 kJ mol (-1) for 'Charentais' and 'Amarillo', respectively). PPO and POD activities from both cultivars showed a decreasing pattern as sugar concentration in the assay medium increased, except in POD extract from 'Charentais', which maintained its activity in the presence of high d-glucose concentration (up to 5 M). Changes in L*, a*, b*, chroma, and hue angle values were chosen to describe the browning development in the samples during storage at 5 degrees C. A slight decrease in L* value and a more marked reduction of a* value were noted in both cultivars above all at the end of storage period. POD activity during storage at 5 degrees C was highly correlated with changes of parameters a*, b*, chroma, and hue angle ( r (2) from 0.82 to 0.97) for cultivar 'Charentais'. According to these results, only POD activity seemed to be involved in browning of minimally processed melon.     

Biochemical study of leaf browning in minimally processed leaves of lettuce (Lactuca sativa L. var. acephala)

A series of biochemical parameters, including the concentration of total ascorbic acid (ASA(tot)) and the activities of phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), and peroxidases (PODs), was investigated during cold storage (72 h at 4 degrees C in the dark) in fresh-cut (minimally processed) leaves of two lettuce (Lactuca sativa L. var. acephala) cultivars differing in the susceptibility to tissue browning: Green Salade Bowl (GSB), susceptible, and Red Salade Bowl (RSB), resistant. The two cultivars showed differences also at the biochemical level. The content in ASA(tot) increased in RSB, as a consequence of increased DHA concentration; conversely, ASA(tot) diminished in GSB, in which ASA was not detectable after 72 h of storage, thus suggesting a disappearance of ascorbate (both ASA and DHA) into nonactive forms. The antioxidant capacity (as determined by using FRAP analysis) decreased significantly during storage in RSB, while a strong increase was observed in GSB. PAL activity increased soon after processing reaching a maximum by 3 h, then it declined to a relatively constant value in RSB, while in GSB it showed a tendency to decrease in the first few hours from harvest and processing. POD activity, at least for chlorogenic acid, increased significantly during storage only in GSB.     

Effect of natamycin in combination with pure oxygen treatment on postharvest quality and selected enzyme activities of button mushroom (Agaricus bisporus)

The combined effects of natamycin (NA) and pure oxygen (PO) treatment on microbial and physicochemical characteristics of button mushroom ( Agaricus bisporus ) stored at 4 ± 1 °C for 16 days was investigated. Mushroom respiration rate, weight loss, firmness, color, percent open caps, total soluble solids, microbial and activities of polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), and peroxidase (POD) were measured. The results indicate that treatment with natamycin + pure oxygen (NAPO) maintained tissue firmness, inhibited increase of respiration rate, delayed browning and cap opening, and reduced microorganism counts of yeasts and molds compared to control treatment. The efficiency was better than that of NA or PO treatment. Furthermore, NAPO inhibited the activities of PPO, PAL, and POD throughout the storage period. Our study suggests that NAPO treatment has the potential to improve the quality of button mushroom and extend the shelf life.     

减压贮藏对去壳黄甜竹笋的保鲜效果及其生理和分子机制

为了探讨减压贮藏延缓采后去壳黄甜竹笋木质化和褐变的效果及其作用机制,本试验以黄甜竹笋为试验材料,笋剥壳后于温度6 ±1℃、相对湿度80％～85％、55 kPa减压环境下贮藏10 d,测定其品质指标、竹笋木质化和褐变关键酶的活性和相关基因的相对表达量.结果表明,减压贮藏(中后期)显著抑制了黄甜竹笋基部切面的褐变(P＜0....     

Warm water treatment in combination with modified atmosphere packaging reduces undesirable effects of irradiation on the quality of fresh-cut iceberg lettuce

Fresh-cut iceberg lettuce dipped in either 5 or 47 degrees C water for 2 min was packaged in modified atmosphere film bags and then exposed to 0, 0.5, 1, or 2 kGy gamma-radiation. Dipping cut lettuce in 47 degrees C water for 2 min prior to irradiation reduced antioxidant and phenolic accumulations induced by irradiation. Irradiation at 2 kGy increased cellular leakage and sogginess of cut lettuce dipped in both temperatures. Samples irradiated at 0.5 and 1 kGy had similar firmness and vitamin C and antioxidant contents as the controls after 14 and 21 days of storage except 1 kGy samples dipped at 47 degrees C had lower antioxidant contents than controls at 14 days of storage. Lettuce dipped at 47 degrees C and irradiated at 0.5 and 1 kGy had better overall visual quality and less tissue browning than corresponding irradiated samples dipped at 5 degrees C. These results suggest lettuce treated with warm water and irradiated at 0.5 or 1 kGy had the best sensory quality without significant loss in texture, vitamin C, or total antioxidants.     

石榴果实发育期果皮褐变及相关酶活性变化

为探明石榴果实发育期果皮褐变及其相关酶活性、总酚和抗氧化能力的变化规律及相互关系,以泰山红和泰山三白甜石榴为试材,研究各发育期果皮褐变度、多酚氧化酶(PPO)活性、过氧化物酶(POD)活性、苯丙氨酸解氨酶(PAL)活性、总酚含量和DPPH自由基清除率的变化。结果表明,2个品种果皮褐变度、PPO活性、POD活性、总酚含量和DPPH自由基清除率随着发育天数的增加逐渐降低,均在7月15日达到最高。2个品种果实发育期果皮PAL活性呈先降低后升高再降低的变化趋势,分别在7月15日和9月13日出现峰值。泰山红抗褐变能力高于泰山三白甜,二者分别在9月23日和9月13日采收能减轻褐变的发生。相关性分析表明,PAL、PPO、POD、总酚和DPPH自由基清除率均与石榴果实酶促褐变密切相关,石榴果实酚类物质含量高低与其抗氧化能力极显著正相关。本研究结果为深入揭示石榴果实褐变机理提供了理论依据。     

Characterization of polyphenol oxidase and peroxidase and influence on browning of cold stored strawberry fruit

Polyphenol oxidase and peroxidase were extracted from two different varieties of strawberry fruit (Fragaria x ananassa D, cv. 'Elsanta' and Fragaria vesca L, cv. 'Madame Moutot') and characterized using reliable spectrophotometric methods. In all cases, the enzymes followed Michaelis-Menten kinetics, showing different values of peroxidase kinetics parameters between the two cultivars: Km = 50.68 +/- 2.42 mM ('Elsanta') and 18.18 +/- 8.79 mM ('Madame Moutot') mM and Vmax = 0.14 +/- 0.03 U/g ('Elsanta') and 0.05 +/- 0.01 U/g ('Madame Moutot'). The physiological pH of fruit at the red ripe stage negatively affected the expression of both oxidases, except polyphenol oxidase from 'Madame Moutot' that showed the highest residual activity (68% of the maximum). Peroxidase from both cultivars was much more thermolable as compared with PPO, losing over 60% of relative activity already after 60 min of incubation at 40 degrees C. The POD activation energy was much lower than the PPO activation energy (DeltaE = 97.5 and 57.8 kJ mol-1 for 'Elsanta' and 'Madame Moutot', respectively). Results obtained from d-glucose and d-fructose inhibition tests evidenced a decreasing course of PPO and POD activities from both cultivars as the sugar concentration in the assay medium increased. Changes in CIE L*, a*, b*, chroma, and hue angle values were taken as a browning index of the samples during storage at 4 degrees C. A decrease in L* was evident in both cultivars but more marked in 'Elsanta'. PPO and POD activities from cv. 'Elsanta' were very well-correlated with the parameter L* (r2=0.86 and 0.89, respectively) and hue angle (r2=0.85 and 0.93, respectively). According to these results, the browning of the fruit seemed to be in relation to both oxidase activities.     

短波紫外线处理对采后香菇褐变的影响

为了控制采后香菇在贮藏过程中的褐变并提高其贮藏品质,本试验采用不同剂量(2、4、6和8 kJ·m^-2) 短波紫外线(UV-C)对新鲜香菇进行预处理,研究不同剂量UV-C处理对香菇色泽、总酚含量、多酚氧化酶(PPO)活性、过氧化物酶(POD)活性、超氧化物歧化酶(SOD)活性、过氧化氢酶(CAT)活性、苯丙氨酸解氨酶(PAL)活性、可溶性蛋白含量、还原糖含量、游离氨基酸含量以及香菇表面微生物的影响。结果表明,UV-C处理延缓了香菇色泽的下降,保持了较高的总酚含量,并且有利于POD、SOD、CAT和PAL活性维持在较高水平,抑制了PPO活性,同时可以保持较高的还原糖和可溶性蛋白含量,在一定程度上延缓了蛋白质的降解,而且可以有效抑制微生物的生长,其中4 kJ·m^-2 UV-C处理效果最佳。综上所述,UV-C处理可以有效地抑制香菇褐变,延长其贮藏期。本研究结果为香菇的贮藏保鲜提供了理论依据。     

减压贮藏对冷藏枇杷果实品质和木质化败坏的影响

为阐明低温减压贮藏对枇杷果实品质和木质化败坏的影响,该研究应用40～50 kPa压力于(0±0.5)℃下贮藏果实49 d,并每隔7 d测定果实的营养品质、出汁率、硬度、褐变指数、呼吸速率、乙烯产生速率、过氧化物酶(POD)和苯丙氨酸解氨酶(PAL)等木质化相关酶活性及木质素含量的变化.结果表明,减压处理可明显抑制冷藏枇杷果实的呼吸强度、乙烯产生和果实褐变,并保持较高的果实可溶性固形物、可滴定酸度和维生素C含量,抑制贮藏21 d后果实硬度的增加,减轻出汁率的下降,降低POD和PAL酶活性的上升趋势,抑制木质素含量的增加.另外,减压贮藏减轻冷藏枇杷果实的木质化败坏,可能与抑制POD和PAL酶活性有关.低温减压贮藏可有效保持果实食用品质,延长贮藏期,是适合枇杷果实贮藏的有效方法.     

Ozonated water extends the shelf life of fresh-cut lettuce

The use of ozonated water as a sanitizer to extend the shelf life of fresh-cut lettuce and the effect on the antioxidant constituents (polyphenols and vitamin C) were investigated. Fresh-cut iceberg lettuce (Lactuca sativa L.) was washed at 4 degrees C using three different ozonated water dips [10, 20, and 10 activated by ultraviolet C (UV-C) light mg L(-1) min total ozone dose], and the dips were compared with water and chlorine rinses. Treated lettuce was packaged in air or active modified atmosphere packaging (MAP) (4 kPa of O2 + 12 kPa of CO2 balanced with N2) and stored for 13 days at 4 degrees C. Despite its strong oxidizing activity, ozonated water did not stimulate the respiratory activity of fresh-cut lettuce. Moreover, ozonated water maintained the initial visual appearance of fresh-cut lettuce and controlled browning during storage in air. Initially, ozonated water and chlorine reduced the total mesophilic population by 1.6 and 2.1 log, respectively, when compared with water. Active MAP was effective in controlling total microbial growth, achieving 2.0 log reduction in relation to samples stored in air at the end of storage. On the other hand, active MAP caused a 2.0-3.5 reduction of coliforms on sanitized samples compared with water-washed samples. The most efficient treatments were ozone 20 and ozone 10 activated by UV-C, which were as effective as chlorine. Changes in individual phenolic compounds were independent of the washing treatments. In air, chlorogenic and isochlorogenic acid contents increased noticeably after 13 days while monocaffeoyltartaric and dicaffeoyltartaric acids remained unchanged. MAP effectively suppressed accumulation of caffeoylquinic derivatives, whereas caffeoyltartaric derivatives decreased during MAP storage to reach similar levels. The content of vitamin C (ascorbic acid and dehydroascorbic acid) decreased during storage, particularly under MAP. Ozonated water could be an alternative sanitizer to chlorine for fresh-cut lettuce due to good retention of sensorial quality and browning control with no detrimental reduction in the antioxidant constituents.     

莲藕膨大过程中褐变酶活性的变化

本实验以3个熟性不同的莲藕品种为材料,研究了莲藕膨大过程中褐变酶活性的变化。实验表明:随着膨大节数的增加,过氧化物酶(POD)、多酚氧化酶(PPO)的活性增加;第4节藕体随着采收时间的推迟,褐变酶活性增加,且熟性不同品种之间有明显差异。并探讨了品种熟性、藕体大小和环境条件对莲藕褐变酶的影响。     

纳他霉素处理对采后甜樱桃生理代谢及品质的影响

为了研究纳他霉素与维生素C（Vc）复配处理对采后甜樱桃果实生理代谢与品质的影响及其作用机理,该试验采用10 mg/L纳他霉素溶液、100 mg/L Vc溶液以及10 mg/L纳他霉素+100 mg/L Vc溶液中浸泡处理甜樱桃10 min,然后将果实置于5℃下贮藏,在贮藏期间,分析测定了呼吸速率以及与抗病性有关的多酚氧化酶（PPO）、过氧化物酶（POD）、苯丙氨酸解氨酶（PAL）等酶活性,同时,测定了果实颜色、硬度、Vc含量、酚类物质含量以及腐烂率等品质指标。结果表明,单独的纳他霉素处理或与Vc复配处理均可有效延长贮藏期达10 d以上,尤其是复配处理还可显著提高PPO、POD、PAL酶活性并使酚类物质含量增加,降低果实呼吸速率与腐烂率,保持较高的Vc含量和硬度,单独的纳他霉素处理也具有一定的调节生理代谢与防腐作用,而单独的Vc处理作用不明显。研究结果认为纳他霉素与Vc复配溶液可作为天然保鲜剂在采后甜樱桃果实的实际贮运中应用。     

涂膜和热处理对葡萄能量和贮藏生理及品质的影响

研究不同处理对欧亚种"维多利亚"葡萄组织能量水平和生理品质的影响。采后葡萄经钙联合涂膜和热处理,即在质量分数为0.2%Ca Cl2和1%壳聚糖中浸泡20 min,45℃的0.2%Ca Cl2溶液中浸泡20 min,晾干后(4±0.5)℃贮藏,每10d测定果实的呼吸强度、褐变指数(browning index,BI)、腐烂率、硬度、丙二醛(malondialdehyde,MDA)含量、三磷酸腺苷(adenosine triphosphate,ATP)、二磷酸腺苷(adenosine diphosphate,ADP)、单磷酸腺苷(adenosine monophosphate,AMP)的含量,多酚氧化酶(polyphenol oxidase,PPO)、过氧化物酶(peroxidase,POD)、脂氧合酶(lipoxygenase,LOX)和超氧化物歧化酶(soperoxide dismutase,SOD)活性变化,以未处理为对照。结果显示对照组葡萄组织中能量物质处于亏损状态,呼吸强度减弱,细胞膜氧化增加,膜透性、BI、腐烂率增加,PPO、POD和LOX活性增加,SOD降低,果实软化。钙联合热和涂膜处理较好维持了果实的能量水平和生理品质,且涂膜优于热处理。ATP与硬度、SOD显著正相关(r=0.938,0.930,P0.01),与MDA、膜透性、LOX显著负相关(r=-0.896,-0.932,-0.940,P0.01);能荷(energy charge,EC)值与膜透性、LOX负相关(P0.05),与呼吸强度和SOD活性正相关(P0.05)。随贮藏时间的延长,葡萄组织的能量水平处于亏损状态,能量水平显著影响生理品质。经适当的采后处理可延缓能量亏损,涂膜优于热处理。     

草酸对冷藏去壳马蹄笋的保鲜效果及机制研究

为探讨外源草酸延缓采后去壳马蹄笋木质化和褐变的效果及其作用机制,本试验以马蹄笋为试验材料,笋去壳后于水和5 mmol·L^-1草酸溶液中浸泡10 min,而后晾干并于温度6 ±1℃,相对湿度80%~85%条件下贮藏10 d,测定其品质指标以及与木质化、褐变、抗氧化相关酶的活性和基因表达量。结果表明,草酸处理抑制了去壳马蹄笋切面的褐变(P<0.05),延缓了笋肉木质化(P<0.05);草酸处理抑制了呼吸速率、相对电导率、超氧阴离子自由基($O_2^{·-}$)产生速率以及丙二醛(MDA)、过氧化氢(H₂O₂)含量的上升,抑制了苯丙氨酸解氨酶(PAL)、过氧化物酶(POD)、肉桂醇脱氢酶(CAD)、多酚氧化酶(PPO)的活性及其编码基因的相对表达量(P<0.05),提高了超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性及其编码基因的相对表达量。综上,草酸处理能够有效抑制采后去壳马蹄笋的木质纤维化和褐变,延缓品质劣变。本研究结果为草酸在马蹄笋采后保鲜的应用提供了理论依据。     

Pineapple juice and its fractions in enzymatic browning inhibition of banana [Musa (AAA group) Gros Michel

The effectiveness of pineapple juice in enzymatic browning inhibition was evaluated on the cut surface of banana slices. After storage of banana slices at 15 degrees C for 3 days, pineapple juice showed browning inhibition to a similar extent as 8 mM ascorbic acid but less than 4 mM sodium metabisulfite. Fractionation of pineapple juice by a solid-phase C18 cartridge revealed that the directly eluted fraction (DE fraction) inhibited banana polyphenol oxidase (PPO) about 100% when compared to the control. The DE fraction also showed more inhibitory effect than 8 mM ascorbic acid in enzymatic browning inhibition of banana puree during storage at 5 degrees C for 24 h. Further identification of the DE fraction by fractionation with ion exchange chromatography and confirmation using model systems indicated that malic acid and citric acid play an important role in the enzymatic browning inhibition of banana PPO.     

Etiology of UV-C-induced browning in var. Superior white table grapes

White table grapes, var. Superior, were treated with UV-C light after harvest to increase stilbenes concentration, especially trans-resveratrol (RES), because this may be of relevance to the health-promoting properties assigned to these compounds. However, irradiated grapes also developed some browning on the surface on the third day of storage at 22 degrees C, with the subsequent detriment in the sensorial quality of the fruit. Possible causes for browning development during storage were investigated. The phenolic-related oxidative enzymes, polyphenol oxidase (PPO) and peroxidase (POD), were not specifically activated, and no new isoforms appeared upon UV-C treatment. UV-treated grapes had lower content of chlorophyll b than control grapes on the fourth day of storage, concomitant with the increase of pheophytins (chlorophyll degradation derived compounds). Microscopy data showed lower fluorescence emission in chloroplasts from the UV-treated samples, which may explain the decrease of chlorophylls content in the corresponding grape berries extracts. In addition, microscopy images showed cell wall thickening in the skin tissue of UV-treated grapes which could be considered as a general wound response in plant tissues. These results suggest that the development of browning in Superior white grapes after UV-C treatment is not closely related with the evolution of oxidative enzymes during storage and may be mainly due to the decrease of chlorophylls content.     

Cinnamaldehyde inhibits enzymatic browning of cut lettuce by repressing the induction of phenylalanine ammonia-lyase without promotion of microbial growth

Cinnamaldehyde treatment inhibited the browning of cut lettuce during cold storage. In this study, to clarify the mechanism of inhibitory action of cinnamaldehyde against the browning and to show its microbiological merit, its effect on the browning of cut lettuce was compared to that of mild heat treatment. Both cinnamaldehyde and mild heat treatments inhibited the induction of phenylalanine ammonia-lyase (PAL) activity because of cutting. As a result, the biosynthesis of polyphenols, which are substrates of polyphenol oxidase, was inhibited. This reduction of polyphenol synthesis caused the inhibition of the browning. Cinnamaldehyde treatment repressed the induction of PAL mRNA, while mild heat treatment did not repress its induction. The increase in microbes in cut lettuce treated with cinnamaldehyde was less than that treated with mild heat after 12 days.