MICROBIAL QUALITY OF FRESH‐CUT ICEBERG LETTUCE WASHED IN WARM OR COLD WATER AND IRRADIATED IN A MODIFIED ATMOSPHERE PACKAGE*

ABSTRACT

The microbial keeping quality of fresh‐cut iceberg lettuce was determined after being washed in either cold water (5C) for 3 min or warm water (47C) for 2 min followed by a cold water rinse (5C) and packaged in a modified atmosphere film bag. The lettuce samples were treated with gamma radiation to 0, 1 or 2 kGy while maintaining a refrigerated temperature (4C). The samples were analyzed for total aerobic, total coliform and Enterobacteriaceae counts after refrigerated storage up to 12 days. No difference in aerobic counts was observed between the hot‐ and cold‐washed samples immediately after washing. The coliform and Enterobacteriaceae counts were reduced by 2 log after the warm water wash and no difference for the cold water‐washed sample. The irradiation treatment at 1 kGy reduced the aerobic, coliform and Enterobacteriaceae counts by 2 log for the warm‐washed samples. At the 2‐kGy treatment level, the aerobic and coliform counts were reduced by 3 log for the cold‐washed lettuce, whereas the Enterobacteriaceae counts were reduced by only 2 log. The observed log reductions in bacterial counts after irradiation were maintained for 12 days when stored at 4C. The combination of a cold water wash and irradiation to 2 kGy had the best microbial keeping quality.

PRACTICAL APPLICATIONS

Fresh‐cut lettuce, when washed in either cold or warm water, shows neither an appreciable removal of the microbial load nor a significant increase in the keeping quality when compared with unwashed fresh‐cut controls. Placing the washed lettuce into modified atmosphere packaging (MAP) did not lessen the overall bacteriologic load, and after 12 days of storage at 4C, the microbial counts increased. However, gamma irradiation of the washed, MAP‐stored lettuce to a dose of 2 kGy significantly reduces the overall microbe count, thereby increasing both the shelf life and the safety of the produce. A 2‐kGy dose of gamma irradiation provides a pathogen‐free, long shelf life, fresh‐cut lettuce that is bacteriologically safer and sensorially indistinguishable from bagged, nonirradiated, fresh‐cut lettuce.     

A Survey of Nitrate and Nitrite Concentrations in Conventional and Organic‐Labeled Raw Vegetables at Retail

A national survey of the nitrate () and nitrite ( ) concentrations in raw and highly consumed vegetables available at retail in the United States was conducted. A total of 194 samples of fresh broccoli, cabbage, celery, lettuce, and spinach categorized as conventional or organic by label were collected from 5 major cities in different geographic regions of the United States and analyzed to determine and concentrations. There were no differences in the mean values of conventional compared with organic vegetables taken from the 5 metropolitan areas. However, significant differences in mean pairwise comparisons between some conventional and organic vegetables for content were observed. The mean concentration of both conventional and organic vegetables ranged between 0.1 and 1.2 mg/kg of fresh weight (FW) with the exception of conventional spinach that contained 8.0 mg/kg FW. Mean contents of conventional broccoli, cabbage, celery, lettuce, and spinach were 394, 418, 1496, 851, and 2797 mg/kg FW, respectively, while their organic‐labeled counterparts averaged 204, 552, 912, 844, and 1318 mg/kg FW. In most cases, organic vegetables were numerically lower in content than their conventional counterparts. Based on survey results, the finding that low levels were observed in some organic vegetables in different cities may warrant further study to determine if true differences exist, due to production practices, seasonal differences, and the magnitudes of those differences. Furthermore, the geographic differences in content of vegetables may flaw estimates of daily and exposure.     

Antioxidant Activity of Selenium‐Enriched Peptides from the Protein Hydrolysate of Cardamine violifolia

Cardamine violifolia is a selenium (Se)‐enriched plant found in China. In this study, the Se‐enriched peptides of C. violifolia (CP) were isolated using a 1 kDa ultrafiltration membrane after enzymatic hydrolysis by alkaline and neutral proteases. The peptides were separated by DEAE‐Sepharose FF anion‐exchange chromatography and purified using preparative high‐performance liquid chromatography (prep‐HPLC). The component with the highest antioxidant activity, CPR13, was identified by comparing the 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH?), hydroxyl (?OH), 2,2′‐azino‐bis (3‐ethylbenzothiazoline‐6‐sulfonic acid) (ABTS⁺?), and superoxide () radical scavenging ability of each fraction. At a concentration of 0.1 mg/mL, the DPPH?, ?OH, , and ABTS⁺? scavenging activities of CPR13 were 89.2%, 26.3%, 40.6%, and 42.9%, respectively. Amino acid sequences were obtained by liquid chromatography combined with mass spectrometry as follows: GRVGSSSC, GRAGGSYM, GHPNFKLNCSGG, GTKSCKA, ASSNARDMI, TAGGCYIPI, and KNCALQ. The seleno‐amino acids were identified as selenomethionine, methylselenocysteine, and selenocysteine. Correlation analysis among organic Se content, peptide content, and antioxidant activity revealed that organic Se plays a greater role in free radical scavenging than peptides, and that the organic Se content of the Se‐enriched peptides was positively correlated with their antioxidant ability (P < 0.05). It indicated that CP has a great potential as natural functional materials for dietary supplement.     

Efficacy of slightly acidic electrolyzed water in killing or reducing Escherichia coli O157:H7 on iceberg lettuce and tomatoes under simulated food service operation conditions

Abstract: The objective of this study was to evaluate the efficacy of slightly acidic electrolyzed (SAEO) water in killing or removing Escherichia coli O157:H7 on iceberg lettuce and tomatoes by washing and chilling treatment simulating protocols used in food service kitchens. Whole lettuce leaves and tomatoes were spot‐inoculated with 100 μL of a mixture of 5 strains of E. coli O157:H7. Washing lettuce with SAEO water for 15 s reduced the pathogen by 1.4 to 1.6 log CFU/leaf, but the treatments did not completely inactivate the pathogen in the wash solution. Increasing the washing time to 30 s increased the reductions to 1.7 to 2.3 log CFU/leaf. Sequential washing in SAEO water for 15 s and then chilling in SAEO water for 15 min also increased the reductions to 2.0 to 2.4 log CFU/leaf, and no cell survived in chilling solution after treatment. Washing tomatoes with SAEO water for 8 s reduced E. coli O157:H7 by 5.4 to 6.3 log CFU/tomato. The reductions were increased to 6.6 to 7.6 log CFU/tomato by increasing the washing time to 15 s. Results suggested that application of SAEO water to wash and chill lettuce and tomatoes in food service kitchens could minimize cross‐contamination and reduce the risk of E. coli O157:H7 present on the produce. Practical Application: SAEO water is equally or slightly better than acidic electrolyzed (AEO) water for inactivation of bacteria on lettuce and tomato surfaces. In addition, SAEO water may have the advantages over AEO water on its stability, no chlorine smell, and low corrosiveness. Therefore, SAEO water may have potential for produce wash to enhance food safety.     

Efficacy of Slightly Acidic Electrolyzed Water and UV‐Ozonated Water Combination for Inactivating Escherichia Coli O157:H7 on Romaine and Iceberg Lettuce during Spray Washing Process

Spray washing is a common sanitizing method for the fresh produce industry. The purpose of this research was to investigate the antimicrobial effect of spraying slightly acidic electrolyzed water (SAEW) and a combination of ozonated water with ultraviolet (UV) in reducing Escherichia coli O157:H7 on romaine and iceberg lettuces. Both romaine and iceberg lettuces were spot inoculated with 100 μL of a 3 strain mixture of E. coli O157:H7 to achieve an inoculum of 6 log CFU/g on lettuce. A strong antimicrobial effect was observed for the UV‐ozonated water combination, which reduced the population of E. coli by 5 log CFU/g of E. coli O157:H7 on both lettuces. SAEW achieved about 5 log CFU/g reductions in the bacterial counts on romaine lettuce. However, less than 2.5 log CFU/g in the population of E. coli O157:H7 was reduced on iceberg lettuce. The difference may be due to bacteria aggregation near and within stomata for iceberg lettuce but not for romaine lettuce. The UV light treatment may stimulate the opening of the stomata for the UV‐ozonated water treatment and hence achieve better bacterial inactivation than the SAEW treatment for iceberg lettuce. Our results demonstrated that the combined treatment of SAEW and UV‐ozonated water in the spray washing process could more effectively reduce E. coli O157:H7 on lettuce, which in turn may help reduce incidences of E. coli O157:H7 outbreaks.     

A pilot plant scale evaluation of a new process aid for enhancing chlorine efficacy against pathogen survival and cross-contamination during produce wash

Developing food safety intervention technology that can be readily adopted by the industry often requires test conditions that match as closely as possible to those of commercial food processing operations; yet biosafety risks inherent in pathogen studies constrain most experiments to laboratory settings. In this study, we report the first semi-commercial pilot-scale evaluation of a new process aid, T128, for its impact on enhancing the antimicrobial efficacy of chlorinated wash water against pathogen survival and cross-contamination. A non-pathogenic, BSL-1, strain of Escherichia coli O157:H7 was inoculated onto freshly harvested baby spinach leaves and washed with large amounts of freshly cut un-inoculated iceberg lettuce shreds in wash water with free chlorine periodically replenished, in the presence or absence of T128. Changes in water quality and pathogen survival and cross-contamination were monitored at every 2min intervals for up to 36min for each treatment during the wash operation. Results indicated that the use of T128 did not significantly (P>0.05) influence the rate of wash water deterioration, nor the pathogen populations remaining on the inoculated spinach leaves. However, in the absence of T128 (control), survival of E. coli O157:H7 in wash water and cross-contamination of un-inoculated lettuce frequently occurred when free chlorine in solution dropped below 1mg/l during the wash process. In contrast, the use of T128 significantly reduced the occurrence of E. coli O157:H7 surviving in wash water and of cross-contamination to un-inoculated shredded iceberg lettuce under the same operational conditions, suggesting that the application of T128 in a chlorine-based fresh produce sanitization system could increase the safety margin of process control on fresh-cut operations.     

Challenges in Model Development for Meat Composition Using Multipoint NIR Spectroscopy from At‐Line to In‐Line Monitoring

This study evaluates the efficiency of multipoint near‐infrared spectroscopy (NIRS) to predict the fat and moisture content of minced beef samples both in at‐line and on‐line modes. Additionally, it aims at identifying the obstacles that can be encountered in the path of performing in‐line monitoring. Near‐infrared (NIR) reflectance spectra of minced beef samples were collected using an NIR spectrophotometer, employing a Fabry‐Perot interferometer. Partial least squares regression (PLSR) models based on reference values from proximate analysis yielded calibration coefficients of determination of 0.96 for both fat and moisture. For an independent batch of samples, fat was estimated with a prediction coefficient of determination of 0.87 and 0.82 for the samples in at‐line and on‐line modes, respectively. All the models were found to have good prediction accuracy; however, a higher bias was observed for predictions under on‐line mode. Overall results from this study illustrate that multipoint NIR systems combined with multivariate analysis has potential as a process analytical technology (PAT) tool for monitoring process parameters such as fat and moisture in the meat industry, providing real‐time spectral and spatial information.     

Application of host‐specific source‐tracking tools for rapid identification of fecal contamination in fresh produce by humans and livestock

BACKGROUND: Fecal contamination in fresh produce is a public health concern because it may contain human pathogens. We introduced host‐specific quantitative real‐time polymerase chain reaction (qPCR) assays for the rapid detection and identification of fecal contamination sources from humans and farm animals (cow, pig, chicken) in fresh produce. Each composite fecal sample was spiked on lettuce at two contamination levels (0.2 mg or 2 mg feces g^?1), followed by qPCR assays for detecting each host‐specific genetic marker: BoBac (cow); PF163 (pig); CP3‐49 (chicken); and HF183 and gyrB (human). Two commercial DNA extraction kits were compared to evaluate DNA recovery yields and removal of PCR inhibition. Sketa2 assay was conducted to assess the presence of PCR inhibition in the contaminated lettuce. RESULTS: All the qPCR assays yielded reliable detection from contaminated lettuce (2 mg feces g^?1), where their target gene numbers were 1.5–5.0 × 10³ (HF183), 0.8–2.2 × 10³ (gyrB), 0.6–1.6 × 10³ (BoBac), 1.6–3.0 × 10³ (CP3‐49) and 1.1–2.2 × 10³ (PF163) copies g^?1 of lettuce. Among the two extraction kits, QIAamp DNA Stool Kit resulted in 2–3 times higher sensitivity and 20% less PCR inhibition than the PowerFood^? kit. CONCLUSION: This study provides information on the optimized host‐specific qPCR assay in identifying sources of fecal contamination in fresh produce and is useful for tracking the contamination source and improving agricultural practice. © 2012 Society of Chemical Industry     

Chlorine stabilizer T-128 enhances efficacy of chlorine against cross-contamination by E. coli O157:H7 and Salmonella in fresh-cut lettuce processing

During fresh-cut produce processing, organic materials released from cut tissues can rapidly react with free chlorine in the wash solution, leading to the potential survival of foodborne bacterial pathogens, and cross-contamination when the free chlorine is depleted. A reported chlorine stabilizer, T-128, has been developed to address this problem. In this study, we evaluated the ability of T-128 to stabilize free chlorine in wash solutions in the presence of high organic loads generated by the addition of lettuce extract or soil. Under conditions used in this study, T-128 significantly (P<0.001) decreased the rate of free chlorine depletion at the presence of soil. T-128 also slightly decreased the rate of free chlorine depletion caused by the addition of lettuce extract in wash solution. Application of T-128 significantly reduced the survival of bacterial pathogens in wash solutions with high organic loads and significantly reduced the potential of cross-contamination, when contaminated and uncontaminated produce were washed together. However, T-128 did not enhance the efficacy of chlorinated wash solutions for microbial reduction on contaminated iceberg lettuce. Evaluation of several produce quality parameters, including overall visual appearance, package headspace O2 and CO2 composition, and lettuce electrolyte leakage, during 15 d of storage indicated that iceberg lettuce quality and shelf life were not negatively impacted by washing fresh-cut lettuce in chlorine solutions containing 0.1% T-128. PRACTICAL APPLICATION: Reported chlorine stabilizer is shown to enhance chlorine efficacy against potential bacterial cross-contamination in the presence of high organic loads without compromising product quality and shelf life.     

A Comparative Study of Natural Antimicrobial Delivery Systems for Microbial Safety and Quality of Fresh‐Cut Lettuce

Nanoencapsulation can provide a means to effectively deliver antimicrobial compounds and enhance the safety of fresh produce. However, to date there are no studies which directly compares how different nanoencapsulation systems affect fresh produce safety and quality. This study compared the effects on quality and safety of fresh‐cut lettuce treated with free and nanoencapsulated natural antimicrobial, cinnamon bark extract (CBE). A challenge study compared antimicrobial efficacy of 3 different nanoencapsulated CBE systems. The most effective antimicrobial treatment against Listeria monocytogenes was chitosan‐co‐poly‐N‐isopropylacrylamide (chitosan‐PNIPAAM) encapsulated CBE, with a reduction on bacterial load up to 2 log₁₀ CFU/g (P < 0.05) compared to the other encapsulation systems when fresh‐cut lettuce was stored at 5 °C and 10 °C for 15 d. Subsequently, chitosan‐PNIPAAM‐CBE nanoparticles (20, 40, and 80 mg/mL) were compared to a control and free CBE (400, 800, and 1600 μg/mL) for its effects on fresh‐cut lettuce quality over 15 d at 5 °C. By the 10th day, the most effective antimicrobial concentration was 80 mg/mL for chitosan‐PNIPAAM‐CBE, up to 2 log₁₀ CFU/g reduction (P < 0.05), compared with the other treatments. There was no significant difference between control and treated samples up to day 10 for the quality attributes evaluated. Chitosan‐PNIPAAM‐CBE nanoparticles effectively inhibited spoilage microorganisms’ growth and extended fresh‐cut lettuce shelf‐life. Overall, nanoencapsulation provided a method to effectively deliver essential oil and enhanced produce safety, while creating little to no detrimental quality changes on the fresh‐cut lettuce.     

Microbial and chemical characterization of commercial washing lines of fresh produce highlights the need for process water control

Process wash water and washed products from three different fresh produce processing lines were characterized at commercial scale. Different physicochemical and microbiological characteristics of wash water were measured. Great variability between processing lines on the physicochemical quality of process wash water was observed, caused in part by the type of produce washed. The relationship between lower aerobic mesophilic bacteria and higher free chlorine (FC) concentrations in wash water was detected (Pearson's correlation coefficient (PCC) = −0.53). Independently of the FC concentration, most of the water samples (>80%) showed presence of cultivable (limit of detection 1 CFU/100 mL), probably caused by the uncontrolled pH conditions. Higher values of FC and oxidation-reduction potential (ORP) in wash water were related to lower microbial load in washed produce (PCC = −0.82, and − 0.79, respectively). Higher concentration of chlorine was linked to a higher presence of disinfection by-products (DBPs) in the wash water, and washing in chlorinated water led to a significant increase in the concentration of DBPs in produce. However, the accumulation of trihalomethanes (THMs) in process wash water was not correlated with higher concentrations of these DBPs in produce.Industrial relevanceThe washing step of fresh produce processing lines is a critical process. The dose of disinfectants needs to be adequately optimized to avoid microbial contamination without generating the accumulation of disinfection by-products (DBPs). In this study, critical parameters that influence the efficacy of water disinfection and the occurrence of DBPs in fresh produce processing lines were identified under commercial conditions. The results evidenced that monitoring and control of pH play a critical role by maximizing the concentration of the most active form of chlorine in the water. The parameter UV254 measured on-line in the washing tank, can be suggested as a suitable indicator of the presence of organic matter in fresh produce wash water.     

SENSORY QUALITY OF READY‐TO‐EAT LETTUCE WASHED IN WARM,CHLORINATED WATER1

Three prepackaging treatments were evaluated for ready‐to‐eat (RTE) lettuce. Fresh iceberg lettuce pieces were dipped for 3 min in cold water (4C) with 100 ppm total chlorine, warm (47C) water with 100 ppm chlorine and tap water at room temperature. The lettuce was dewatered by centrifugation, packed in breathable film bags (OTR: 1600‐2000 cc/m²/24 h) and stored for 11 days at 1C. Sensory evaluation revealed that the texture and visual appearance of stored RTE lettuce were improved by the warm water treatment. However, heat processing induced changes in the flavor of the lettuce, and a chlorinaceous off‐odor was detected by some panelists.     

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.     

Use of ozone in a lettuce‐washing process: an industrial trial

Bacteria such as Escherichia coli and Salmonella spp. may cause serious problems for the quality maintenance of pre‐packaged lettuces. The aim of this study was to evaluate the bactericidal effect of ozonated water in the washing of iceberg lettuce. For this purpose an ozone generator was integrated into a commercial lettuce‐washing facility. Lettuce samples were removed from this process and analysed for mesophilic total viable count (TVC), E. coli, Salmonella spp., vitamin C and sugar content. The analyses were carried out either directly after washing or at the end of best‐before date (BBD), in which lettuces were stored at 4 °C for 6 days. Water samples were analysed for total organic carbon (TOC) content and pH. Through the addition of ozone to the wash water the quality of lettuce during storage time was unaffected while there was only a limited observed decrease in populations of microorganisms. Copyright © 2007 Society of Chemical Industry     

Comparison of calcium lactate with chlorine as a washing treatment for fresh‐cut lettuce and carrots: quality and nutritional parameters

The efficacies of calcium lactate and chlorine washing treatments of fresh‐cut lettuce and carrots were compared during storage at 4 °C over 10 days. The gas composition of packages, colour, enzyme activity, texture, sensory attributes, microflora and levels of ascorbic acid and carotenoids were evaluated at 1, 3, 7 and 10 days. Calcium lactate treatment was not significantly different to chlorine treatment (p < 0.05) in terms of maintaining colour, texture and acceptability of fresh‐cut lettuce and carrots during the entire storage period. The washing treatments did not affect levels of ascorbic acid of fresh‐cut lettuce or carrots. Carotenoid levels were higher in calcium lactate‐treated carrots than chlorine‐treated samples at the end of storage. Mesophilic, psychrotrophic and lactic acid bacteria counts were not significantly different between treatments for both vegetables. Copyright © 2005 Society of Chemical Industry     

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.     

Fate of Foodborne Viruses in the “Farm to Fork” Chain of Fresh Produce

Norovirus (NoV) and hepatitis A virus (HAV) are the most important foodborne viruses. Fresh produce has been identified as an important vehicle for their transmission. In order to supply a basis to identify possible prevention and control strategies, this review intends to demonstrate the fate of foodborne viruses in the farm to fork chain of fresh produce, which include the introduction routes (contamination sources), the viral survival abilities at different stages, and the reactions of foodborne viruses towards the treatments used in food processing of fresh produce. In general, the preharvest contamination comes mainly from soli fertilizer or irrigation water, while the harvest and postharvest contaminations come mainly from food handlers, which can be both symptomatic and asymptomatic. Foodborne viruses show high stabilities in all the stages of fresh produce production and processing. Low‐temperature storage and other currently used preservation techniques, as well as washing by water have shown limited added value for reducing the virus load on fresh produce. Chemical sanitizers, although with limitations, are strongly recommended to be applied in the wash water in order to minimize cross‐contamination. Alternatively, radiation strategies have shown promising inactivating effects on foodborne viruses. For high‐pressure processing and thermal treatment, efforts have to be made on setting up treatment parameters to induce sufficient viral inactivation within a food matrix and to protect the sensory and nutritional qualities of fresh produce to the largest extent.     

Adhesion,Cohesion, and Friction Estimated from Combining Cutting and Peeling Test Results for Thin Noodle Sheets

The aim of this study was to estimate the adhesive and cohesive fracture energies, and frictional characteristics of 7 types of cooked starch and flour sheets and combine these into a model framework for textural analysis. Cutting tests with wires of diameter 0.30 to 0.89 mm were performed with and without lubrication. Plots of the work done, normalized to the area cut by the wire, showed that this to be linearly related to wire diameter irrespective of lubrication. The oil had little impact on the intercept of these plots, giving cohesive fracture energy (G_c) ranges for these foods between 6.8 and 32.5 J/m². However, lubrication had a strong influence on the slope of the plots. From a comparison of the slopes for lubricated versus unlubricated tests, the kinetic coefficient of friction could be calculated. Values for between 0.007 and 0.521 for different foods were obtained. Peeling tests were performed by lifting sheets vertically away from a fresh mica surface. The adhesive fracture energy G_a, varied from 2.5 to 4.8 J/m². The results can be modeled by plotting the ratio of cohesive to adhesive fracture energy against the coefficient of friction. Thresholds in both axes suggest a physical basis for distinguishing textural perceptions. However, sensory testing with 12 subjects using the 7 food types could not establish whether this framework, however well‐established physically, would apply to oral sensations. A much larger test would be required.     

Ultrasound decontamination of minimally processed fruits and vegetables

The effectiveness of power ultrasound for the microbial decontamination of minimally processed fruits and vegetables was studied. Reductions in Salmonella typhimurium attached to iceberg lettuce obtained by cleaning with water, chlorinated water, ultrasound with water and ultrasound with chlorinated water were 0.7, 1.7, 1.5 and 2.7 logs, respectively, for small-scale (2 L) trials. The cleaning action of cavitation appears to remove cells attached to the surface of fresh produce, rendering the pathogens more susceptible to the sanitizer. For large-scale (40 L) trials, the addition of chlorine to water in the tank gave a systematic difference in Escherichia coli decontamination efficiency. However, the frequency of ultrasound treatment (25, 32–40, 62–70 kHz) had no significant effect on decontamination efficiency ( P  > 0.69). With the potentially high capital expenditure together with the expensive process of optimization and water treatment, it is unlikely that the fresh produce industry would be willing to take up this technology. Furthermore, the additional one log reduction achieved by applying ultrasound to a chlorinated water wash does not completely eliminate the risk of pathogens on fresh produce.