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.     

聚乙烯袋包装和0℃冷藏对结球生菜品质的影响

研究0.02 mm和0.06 mm聚乙烯袋包装、(0±0.5)℃条件下冷藏18d对结球生菜品质的影响。结果表明,随着冷藏时间延长,失重率逐渐增高,VC、可溶性糖、可溶性蛋白等营养成分含量逐渐降低。0.06mm聚乙烯袋包装的结球生菜冷藏效果好于0.02mm聚乙烯袋包装的结球生菜,冷藏18d后0.06mm聚乙烯袋包装的结球生菜感官评价为3.4,失重率为2.15%,VC含量为25.9mg/100g,可溶性糖含量为1.22%,可溶性蛋白为53mg/100g。     

Effects of gas atmosphere, antimicrobial dip and temperature on the fate of Listeria innocua and Listeria monocytogenes on minimally processed lettuce

The growth and survival of inoculated strains of Listeria innocua and L. monocytogenes on minimally processed lettuce were studied. The effects of package atmospheres (lettuce sealed within packages after flushing with 100% N₂ or without flushing with N₂, lettuce sealed within perforated packages), antimicrobial dips (100 p.p.m. chlorine solution for 5 min, 1% citric acid solution for 5 min) and storage temperatures (3°C and 8°C) were investigated. Populations of L. innocua and L. monocytogenes on undipped lettuce stored at 3°C gradually decreased (by 1–1.5 log cycles) during a 14 day storage period. By contrast counts on lettuce stored at 8°C did not change significantly ( P > 0.05). Flushing packages of lettuce with 100% N₂ followed by storage at 8°C resulted in a significant increase ( P < 0.05, by 2–3 log cycles) in L. innocua and L. monocytogenes counts during storage. L. innocua , strain NCTC 11288, behaviour was similar to that of L. monocytogenes (strains ATCC, 19114 and NCTC 11994) under these storage temperatures and atmospheres. Using L. innocua as a model for L. monocytogenes , it was found that dipping lettuce in a chlorine or citric acid solution followed by storage at 8°C resulted in a significant increase ( P < 0.05, by 2 log cycles) in L. innocua populations compared with undipped samples. It is concluded that N₂ flushing or use of antimicrobial dips combined with storage at 8°C, both enhanced the survival and growth of Listeria populations on shredded lettuce.     

Glycine Betaine-Mediated Protection of Peas (Pisum sativum L.) During Blanching and Frozen Storage

We used glycine betaine (5–20% w/v) for blanching green peas (100°C, 60 s), and their subsequent freezing and storage (–20°C, 90 days). Blanching after the addition of glycine betaine at ≥10% (w/v) followed by a 90 day storage period which resulted in the most desirable outcome: higher vitamin C levels, a superior green color, enhanced organoleptic quality and texture, and improved retention of peroxidase and lipoxygenase activity relative to control peas (no glycine betaine added). Microscopic characterizations of control and treated peas revealed that glycine betaine acts as a cryoprotectant which maintains cellular integrity. Glycine betaine (10% w/v) could be used commercially for production of frozen peas with better quality attributes.     

有机酸及茶多酚对保鲜鸭肉品质特性的影响

新鲜鸭肉经不同浓度的有机酸及茶多酚液处理后真空包装,鸭肉在贮藏过程中,ＴＶＢＮ值与贮藏时间呈极显著正相关（Ｐ＜０．０１）,ｐＨ值在一定的范围内波动;０．１％茶多酚对鸭脂具有最强的抗氧化作用,若茶多酚浓度过高,会发生助氧化作用。低温、真空包装、有机酸和茶多酚处理均能延长鲜鸭肉的保鲜期,而且以１％山梨酸钾处理后的鲜鸭肉感观品质最好。     

Effect of Calcium Lactate, 4-Hexyl Resorcinol and Vacuum Packing on Physico-chemical, Sensory and Microbiological Qualities of Minimally Processed Litchi (Litchi chinensis Sonn.)

Litchi (Litchi chinensis Sonn.) fruits are very susceptible to pericarp browning which adversely affects consumer acceptability even though the aril portion remains in excellent condition. Litchi arils (litchis) were treated with a solution containing 0–2% (w/v) calcium lactate (CL), 0–0.02% (w/v) 4‐hexyl resorcinol (4‐HR) and 1% potassium sorbate. The pH of solution was adjusted to 4.0 with citric acid. Treated litchis were packed in polystyrene trays, over‐wrapped with polypropylene film, vacuum‐packed (0, 47409.3, 94831.9 Pa) and stored at 4 ± 2 °C. Drip losses, pH, total soluble solids (TSS), sensory attributes and microbiological quality of stored samples were estimated. A four‐factor, three‐level experimental design (D₆ Hokes design) with 19 experiments was chosen. Mathematical models were developed to analyse and predict the effect of CL, 4‐HR, in‐package vacuum and storage time on the responses. TSS, pH and sensory scores decreased significantly (P 0.01), whereas drip losses and microbial count increased significantly (P 0.01) with time. Drip loss was significantly (P 0.1) reduced by addition of CL. 4‐HR prevented browning and changes in colour score during storage were significantly less. Vacuum in packages exerted significant (P 0.01) effect over pH, TSS, sensory and microbiological qualities of minimally processed litchis.     

EFFECTS OF DIETARY GLYCINE BETAINE ON BLOOD CHARACTERISTICS AND PORK QUALITY

This study was conducted to determine the effects of dietary glycine betaine on pork quality and blood characteristics. A total of 80 female pigs (Landrace  ×  Yorkshire  ×  Duroc) were randomly allotted into one of four experimental diet groups. Each group of pigs fed with a commercial diet (control) added with 0.2 g glycine betaine (T1), 0.4 g glycine betaine (T2) and 0.6 g glycine betaine (T3)/kg diet during 40 days. Glycine betaine concentrations in plasma and loin muscle were significantly increased by dietary glycine betaine; however, triglyceride concentration in serum was decreased by dietary glycine betaine. Creatine phosphokinase concentrations in plasma had no significant difference among the dietary groups. Redness ( a* ) was significantly higher in T2 and T3; however, at the first and seventh days of storage, redness ( a* ) was not significantly different between dietary groups. Shear force was significantly higher in dietary glycine betaine groups at the first day of storage. Cholesterol content was significantly lower in T2 and T3, whereas T1 was not significantly different compared with the control group. In fatty acid composition, the ratio of saturated fatty acids was increased, whereas unsaturated fatty acids were decreased by dietary glycine betaine.

PRACTICAL APPLICATIONS

Glycine betaine is an amino acid (trimethylglycine) present in most organisms, and is an obligatory intermediate in the catabolism of choline. Glycine betaine has been reported to affect some aspects of pork qualities. As a result of this study, dietary glycine betaine should improve meat redness and reduce cholesterol. However, dietary glycine betaine did not influence creatine phosphokinase levels in plasma. These results will be helpful to the pork industry and meat scientists for improving meat qaulity.     

抗褐变剂处理及MAP技术保鲜莴苣效果的研究

研究了抗褐变剂处理和MAP技术保鲜莴苣的效果及莴苣贮藏过程中常见病害的抑制情况。研究表明 :质量分数 0 .5 %的抗坏血酸 +质量分数 0 .5 %的抗柠檬酸能够较好地抑制莴苣的酶促褐变 ;MAP技术中以 φO2 +φCO2 +φN2 =1% +2 % +97%保鲜莴苣的效果较好 ;在莴苣低温贮藏的 6d内 ,O2 及CO2 的体积分数基本达到动态平衡 ,并且分别维持在 9%及 2 6%左右 ;10 0mg/kgH2 O2 +MAP(φO2 +φCO2 +φN2 =1% +2 % +97% ) +低温 (4℃ )能够很好地抑制莴苣贮藏过程中的常见病害     

Cross-contamination of lettuce with Escherichia coli O157:H7

Contamination of produce by bacterial pathogens is an increasingly recognized problem. In March 1999, 72 patrons of a Nebraska restaurant were infected with enterohemorrhagic Escherichia coli (EHEC) O157:H7, and shredded iceberg lettuce was implicated as the food source. We simulated the restaurant's lettuce preparation procedure to determine the extent of possible EHEC cross-contamination and growth during handling. EHEC inoculation experiments were conducted to simulate the restaurant's cutting procedure and the subsequent storage of shredded lettuce in water in the refrigerator. All lettuce pieces were contaminated after 24 h of storage in inoculated water (2 x 10(9) CFU of EHEC per 3 liters of water) at room temperature or at 4 degrees C; EHEC levels associated with lettuce increased by > 1.5 logs on the second day of storage at 4 degrees C. All lettuce pieces were contaminated after 24 h of storage in water containing one inoculated lettuce piece (approximately 10(5) CFU of EHEC per lettuce piece) at both temperatures. The mixing of one inoculated dry lettuce piece with a large volume of dry lettuce, followed by storage at 4 degrees C or 25 degrees C for 20 h resulted in 100% contamination of the leaves tested. Microcolonies were observed on lettuce stored at 25 degrees C, while only single cells were seen on leaves stored at 4 degrees C, suggesting that bacterial growth had occurred at room temperature. Three water washes did not significantly decrease the number of contaminated leaves. Washing with 2,000 mg of calcium hypochlorite per liter significantly reduced the number of contaminated pieces but did not eliminate contamination on large numbers of leaves. Temperature abuse during storage at 25 degrees C for 20 h decreased the effectiveness of the calcium hypochlorite treatment, most likely because of bacterial growth during the storage period. These data indicate that storage of cut lettuce in water is not advisable and that strict attention must be paid to temperature control during the storage of cut lettuce.     

含钙离子壳聚糖涂膜对鲜切莴苣的保鲜性研究

制备氯化钙(CaCl2)质量浓度分别为0、2 g/100 mL、4 g/100 mL、6 g/100 mL的壳聚糖/CaCl2溶液,将其对鲜切莴苣进行涂膜处理,考察该膜对鲜切莴苣的保鲜性。结果发现,随着贮藏期延长,壳聚糖/CaCl2涂膜能一定程度的保持鲜切莴苣的感官品质、抑制色度,失重率、硬度和VC含量下降,从而延长鲜切莴苣的货架寿命。结果表明,CaCl2质量浓度为4 g/100 mL的壳聚糖涂液处理的鲜切莴苣的各项指标最好,使鲜切莴苣的保质期延长到2 d。     

Residues of the quinone outside inhibitor fungicide trifloxystrobin after postharvest dip treatments to control Penicillium spp. on citrus fruit

The effectiveness of postharvest dip treatment with trifloxystrobin (TFX) or imazalil (IMZ) was compared for controlling green and blue mold (caused by Penicillium digitatum and Penicillium italicum, respectively) of citrus fruit. Residues retained by fruit were determined as a function of treatment time, dip temperature, and storage conditions. Trials on 'Avana apireno' mandarin oranges artificially inoculated with P. digitatum or P. italicum revealed that treatments with 200 to 600 mg/liter active ingredient TFX at 20 degrees C were less effective than 100 mg/liter TFX at 500C for controlling P. digitatum but equally effective for controlling P. italicum. IMZ treatments with 200 mg/liter IMZ at 20 degrees C or 25 mg/liter IMZ at 50 degrees C resulted in more than 98% reduction of P. digitatum and ca. 93% reduction of P. italicum compared with untreated fruit. Total suppression of pathogens was achieved when higher IMZ doses were applied. Studies on artificially wounded lemons, oranges, clementines, and mandarins revealed that treatment with 100 mg/liter TFX at 50 degrees C effectively controlled decay development (mainly due to P. digitatum) after 7 days of storage at 20 degrees C. These results were confirmed on nonwounded oranges of cv. Tarocco and on grapefruits of cvs. Marsh Seedless and Star Ruby during 3 weeks of simulated quarantine at 1 degrees C, storage (5 weeks at 8 degrees C for oranges and 8 weeks at 11degrees C for grapefruits), and an additional 1 week of simulated marketing conditions at 20 degrees C. IMZ at 50 degrees C was highly effective for controlling decay during storage and the simulated marketing period. TFX treatment at 50 degrees C was as effective as IMZ for controlling decay in most samples. After treatment with 100 mg/liter TFX at 20 degrees C, fungicide residues in 'Tarocco' oranges doubled from 0.15 mg/kg to 0.30 mg/kg when dip time increased from 0.5 to 3 min, whereas when treatments were performed at 50 degrees C TFX residues were not related to dipping time. Residues of TFX were significantly correlated with dip temperature. A 3-min dip treatment at 50 degrees C resulted in a deposition of TFX that was approximately twofold higher than that obtained when treatments were carried out at 20 degrees C.     

ASSESSMENT OF A WASH TREATMENT WITH WARM CHLORINATED WATER TO EXTEND THE SHELF–LIFE OF READY–TO–USE LETTUCE

Abstract The influence of a warm chlorine wash on the microbiological quality and shelf–life of ready–to–use (RTU) shredded iceberg lettuce was examined using the electronic nose (EN) and culture methods. There was a significant difference in psychrotrophic counts (P<0.0001) of warm chlorine (100 ppm) washed lettuce at 47 ± 2C for 30 s, 60 s, and 180 s exposure from days 1 to 10 of storage at 4C compared with cold chlorine (100 ppm) washed lettuce at 4 ± 1C for 30 s. There were no significant differences in psychrotrophic counts between wash treatments of 30 s and 60 s during 17 days storage (P < 0.05). The EN detected initially high levels of volatiles in this group compared with cold treatment. Lettuce samples treated with cold or warm chlorine wash water showed no differences in the presence/absence or levels of Listeria monocytogenes. The warm chlorine washed lettuce samples were rated acceptable upon sensory evaluation up to day 14.     

Freezing Rate and Frozen Storage Effects on Color and Sensory Characteristics of Pineapple Fruit Slices

This study was carried out to evaluate the influence of freezing process (cold room –18°C and air-blast freezer –50°C) and frozen storage (–18°C for 0 to 12 mo) on color and sensory quality of pineapple fruit slices (Smooth Cayenne and Red Spanish cultivars). L, –a and +b color parameters showed differences (P ≦ 0.05) with cultivar, but not with freezing rate. No differences (P ≥ 0.05) were found in sensory analysis (color and appearance) between the cultivars, frozen at different rates, compared to fresh product, or after 1 yr frozen storage. The two cultivars are suitable for freezing.     

CO2高传导保鲜膜处理对雪青梨贮藏品质及生理的影响

以雪青梨果实为试材,研究CO2高传导保鲜膜在低温贮藏条件下对雪青梨果实采后贮藏品质及生理特性的影响。结果表明：CO2高传导保鲜膜处理可推迟雪青梨呼吸高峰的出现,抑制PPO活性的升高,降低MDA含量,从而减缓果实的衰老;处理组可明显延缓雪青梨果实硬度、可滴定酸和VC含量的下降,抑制可溶性固形物含量的升高,从而较好地保持果实在贮藏期间的品质和风味。     

Effects of sodium acetate dip treatment and vacuum-packaging on chemical,microbiological, textural and sensory changes of Pearlspot (Etroplus suratensis) during chill storage

The effects of sodium acetate dip treatment, followed by vacuum-packaging, on the shelf life of beheaded, scaled and gutted Pearlspot (Etroplus suratensis) during chill storage were examined. Sodium acetate (2%, w/v) solution was used for the dip treatment. Pouches (size: 15 × 22 cm) made of 12μ-polyester laminated with 300 gauge low-density polyethylene were used for packing fish. After packing, all the packs were iced with flake ice in the ratio (1:1) fish: ice in an insulated box and were kept in a cold room maintained at 0–2 °C. The control and the treated packs were analysed periodically for chemical (pH, TBA, TMA, TVB-N), microbiological (total viable count), textural and sensory characteristics. Changes in Staphylococcus aureus, Enterobacteriacea and Feacal streptococci were determined for fresh fish and for fish samples at the time of sensory rejection. Air packed samples were found to have a shelf life of about 8 days; vacuum-packed samples were found to be acceptable up to 10 days, whereas sodium acetate-treated vacuum packed samples were found to be acceptable up to 15 days. Thus, vacuum-packaging, in combination with sodium acetate, was found to delay the spoilage, thereby significantly extending the shelf life of Pearlspot at refrigeration temperatures.     

不同包装方式对捻转贮藏过程中品质变化的影响

为研究不同包装方式对捻转贮藏过程中品质变化的影响,以捻转为研究对象,采取PE普通包装、真空包装和气调包装(70% N₂+30% CO₂)3种不同包装方式处理,在4℃下贮藏,并隔天测定感官、水分、pH、色泽、菌落总数、质构等指标。结果表明:不同包装方式对捻转品质变化的影响存在显著性差异(p<0.05),其中气调包装贮藏效果最佳;PE普通包装和真空包装的样品在贮藏6 d后感官评分就明显下降,而气调包装的样品在贮藏10 d后仍有较高的评分;同时气调包装能抑制微生物繁殖,延缓样品pH、水分下降速率,硬度、咀嚼性也低于另两种包装方式,弹性、内聚性则差异不显著(p>0.05)。综合比较分析,PE普通包装、真空包装、气调包装样品的货架期分别为4、6和10 d。因此,将气调包装应用于捻转,能较好维持样品的色泽和风味,保证产品品质,延长其货架期。     

Inhibition of Listeria monocytogenes on the surface of individually packaged hot dogs with a packaging film coating containing nisin

The objective of this study was to determine the effectiveness of packaging films coated with a methylcellulose/hydroxypropyl methylcellulose-based solution containing 10,000, 7,500, 2,500, or 156.3 IU/ml nisin for controlling Listeria monocytogenes on the surfaces of vacuum-packaged hot dogs. Barrier film coated with a methylcellulose/hydroxypropyl methylcellulose-based solution containing nisin or no nisin (control) was heat sealed to form individual pouches. Hot dogs were placed in control and nisin-containing pouches and inoculated with a five-strain L. monocytogenes cocktail (approximately 5 log CFU per package), vacuum sealed, and stored for intervals of 2 h and 7, 15, 21, 28, and 60 d at 4 degrees C. After storage, hot dogs and packages were rinsed with 0.1% peptone water. Diluent was spiral plated on modified oxford agar and tryptic soy agar and incubated to obtain counts (CFU per package). L. monocytogenes counts on hot dogs packaged in films coated with 156.3 IU/ml nisin decreased slightly (approximately 0.5-log reduction) through day 15 of refrigerated storage but was statistically the same (P > 0.05) as hot dogs packaged in films without nisin after 60 d of storage. Packaging films coated with a cellulose-based solution containing 10,000 and 7,500 IU/ml nisin significantly decreased (P < 0.05) L. monocytogenes populations on the surface of hot dogs by greater than 2 log CFU per package throughout the 60-d study. Similar results were observed for hot dogs packaged in films coated with 2,500 IU/ml nisin; however, L. monocytogenes populations were observed to be approximately 4 log CFU per package after 60 d of refrigerated storage from plate counts on tryptic soy and modified oxford agars.     

Effect of gamma irradiation on microbial growth and sensory quality of fresh-cut lettuce

Fresh-cut lettuce was irradiated and microbiological and sensory quality was examined during storage at 4 degrees C. Experimental results showed that the number of aerobic mesophilic bacteria on fresh-cut lettuce irradiated with 1.0 kGy was reduced by 2.35 logs and sensory quality was maintained best during storage for 8 days at 4 degrees C. It was indicated that Gompertz model could predict the bacterial number on fresh-cut lettuce if the initial level was known.     

INFLUENCE OF TEMPERATURE ON SHELF LIFE OF BUTTERHEAD LETTUCE LEAVES UNDER PASSIVE MODIFIED ATMOSPHERE PACKAGING

The aim of the present work was to study the influence of temperature on sensory and microbiological qualities, and on shelf life of butterhead lettuce leaves in passive modified atmosphere packages. Butterhead lettuce was washed and placed under ambient air in 30  ×  40 cm polypropylene bags, and stored at 5, 10 and 15C. A first-order equation was obtained for the development of the evaluated appearance sensory attributes as a function of storage time. For all the evaluated storage temperatures, microbiological shelf lives (14, 17 and 42 days at 5, 10 and 15C) were higher than estimated sensory shelf lives (8, 14 and 26 days at 5, 10 and 15C), showing that shelf life of lettuce in passive modified atmosphere packages was limited by sensory properties and not by microbial growth.

PRACTICAL APPLICATIONS

Sensory shelf life of lettuce in passive modified atmosphere packages was estimated using consumer data, which are an improvement of a more arbitrary criteria presented in most studies. Moreover, if failure criteria used in other studies were applied, consumer rejection at the end of shelf life would be higher, suggesting that more conservative criteria are necessary to assure the product's quality at the end of its shelf life.     

Nucleotide degradation of sodium acetate and potassium sorbate dip treated and vacuum packed Black Pomfret (Parastromateus niger) and Pearlspot (Etroplus suratensis) during chill storage

Quality changes of vacuum packed Black Pomfret (Parastromateus niger) and Pearlspot (Etroplus suratensis) treated with sodium acetate and potassium sorbate, respectively, and subsequently stored in vacuum packs in ice during chill storage were evaluated by measuring the volatile base nitrogen values, K-values and sensory parameters. The effects of sodium acetate (2% w/v) and potassium sorbate (2% w/v) dip treatments on vacuum packed Black Pomfret and Pearlspot were also examined. Total volatile base nitrogen values were found to increase slowly with time, whereas the K-values were found to increase linearly with time in samples of both the species and exceeded the acceptability limit on the day of sensory rejection. The K-values, representing the ratio between the sum of inosine and hypoxanthine to the sum of all other ATP breakdown products, was found to be a more reliable method for estimation of the quality of fresh/preserved fish. Sodium acetate/potassium sorbate dip treated and vacuum packed Black Pomfret and Pearlspot exhibited lower K-values compared to untreated samples. Treated vacuum packed samples of Black Pomfret were found to be in good and acceptable condition up to 16 days whereas treated vacuum packed samples of pearlspot remained in good condition up to 15 days compared to vacuum packed and air packed samples which were acceptable only up to 10 and 8 days, respectively. The sensory characteristics correlated well with the K-values for both the species.