John C. Beaulieu

Rapid Detection of Viable Salmonellae in Produce by Coupling Propidium Monoazide with Loop-Mediated Isothermal Amplification

ABSTRACT Recent outbreaks linked to Salmonella-contaminated produce heightened the need to develop simple, rapid, and accurate detection methods, particularly those capable of determining cell viability. In this study, we examined a novel strategy for the rapid detection and quantification of viable salmonellae in produce by coupling a simple propidium monoazide sample treatment with loop-mediated isothermal amplification (PMA-LAMP). We first designed and optimized a LAMP assay targeting Salmonella. Second, the performance of PMA-LAMP for detecting and quantifying viable salmonellae was determined. Finally, the assay was evaluated in experimentally contaminated produce items (cantaloupe, spinach, and tomato). Under the optimized condition, PMA-LAMP consistently gave negative results for heat-killed Salmonella cells with concentrations up to 108 CFU/ml (or CFU/g in produce). The detection limits of PMA-LAMP were 3.4 to 34 viable Salmonella cells in pure culture and 6.1 × 103 to 6.1 × 104 CFU/g in spiked produce samples. In comparison, PMA-PCR was up to 100-fold less sensitive. The correlation between LAMP time threshold (TT ) values and viable Salmonella cell numbers was high (R 2 = 0.949 to 0.993), with a quantification range (102 to 105 CFU/reaction in pure culture and 104 to 107 CFU/g in produce) comparable to that of PMA in combination with quantitative real-time PCR (PMA-qPCR). The complete PMA-LAMP assay took about 3 h to complete when testing produce samples. In conclusion, this rapid, accurate, and simple method to detect and quantify viable Salmonella cells in produce may present a useful tool for the produce industry to better control potential microbial hazards in produce.

Volatile and quality changes in fresh-cut mangos prepared from firm-ripe and soft-ripe fruit, stored in clamshell containers and passive MAP

A study was performed to assess volatile and quality changes in stored fresh-cut mangos prepared from ‘‘firm-ripe’’ (FR) and ‘‘soft-ripe’’ (SR) fruit, and to assess what effect passive modified atmosphere packaging (MAP) may hav eo n cut fruit physiology, overall quality and volatile retention or loss. Florida-grown ‘Keitt’ and ‘Palmer’ mangos were used, without heat-treatment. Subjective appraisals of fresh-cut mangos based on aroma and cut edge or tissue damage indicated that most SR cubes were unmarketable by day 7 at 4 8C. Both varieties stored in MAP at 4 8C had almost identical O2 consumption, which was independent of ripeness. Percent CO2 and O2 data for cubes stored in passive MAP indicates that the system was inadequate to prevent potential anaerobic respiration after 7 days storage. A significant three-way interaction (container/ripeness/day) was observed for L* (lightness) between stored cubes prepared from FR versus SR fruit of both varieties. There was a linear L* decrease for SR ‘Keitt’ cubes stored in clamshell containers. d-3-Carene was the dominant terpene in both varieties in all treatments throughout most of the study, and FR cubes had statistically higher levels of seven terpenes compared with the respective SR treatments. Most terpenes in FR and SR cubes stored in both package types displayed a transient increase, occurring on day 4 or 7, followed by a decline. Published by Elsevier B.V.

Effect of Hot Water Surface Pasteurization of Whole Fruit on Shelf Life and Quality of Fresh-Cut Cantaloupe

Cantaloupes are associated with recent outbreaks of foodborne illnesses and recalls. Therefore, new approaches are needed for sanitization of whole and cut fruit. In the present study, whole cantaloupes were submerged into water in the following 3 conditions: 10 degrees C water for 20 min (control), 20 ppm chlorine at 10 degrees C for 20 min, and 76 degrees C water for 3 min. Populations of microflora were measured on the rinds of the whole cantaloupes. Quality and microbial populations of fresh-cut cantaloupes prepared from whole fruit were analyzed after 1, 6, 8, 10, 13, 16, and 20 d of storage at 4 degrees C. The hot water significantly reduced both total plate count (TPC) and yeast and mold count on rind of whole fruits while chlorine or cold water wash did not result in a significant reduction of microbial population. Fresh-cut pieces prepared from hot water-treated cantaloupes had lower TPC than the other 2 treatments in the later storage periods (days 13 to 20) in 2 of 3 trials. The hot water treatment of whole fruits was inconsistent in reducing yeast and mold count of fresh-cut pieces. Soluble solids content, ascorbic acid content, fluid loss, and aroma and appearance scores were not consistently affected by either hot water or chlorine treatment. Our results suggested that hot water pasteurization of whole cantaloupes frequently resulted in lower TPCs of fresh-cut fruit during storage and did not negatively affect quality of fresh-cut cantaloupes.

Physicochemical properties and aroma volatile profiles in a diverse collection of California-grown pomegranate (Punica granatum L.) germplasm

Colorful antioxidant-rich fruits often convey astringency and sourness that juice consumers may not appreciate. We assessed properties in juices from a collection of California-grown pomegranate from the National Clonal Germplasm Repository. The goal was to evaluate overall differences in germplasm with quality traits classified as sweet, sweet-sour and sour. Previous relationships noted in sweet and sour cultivar attributes were observed. Wonderful generally clustered with sweet-sour and sour cultivars. Sweet low acid cultivars occasionally clustered closely with Wonderful which is hard to rationalize. The dominant compounds were 3-hexenol and 1-hexanol which allowed separation of Kara Gul, Haku-botan and Wonderful. Aldehyde and terpene content can be used to characterize cultivars. The study represents the first data on variation in juice qualities in different sweet, sweet-sour and sour cultivars, grown in California, compared with Wonderful. Data may help the juice industry better select raw juice materials in order to ultimately satisfy consumers.

Physiological, Volatile, and SEM Surface Effects Resulting from Cutting and Dipping Treatments in Cantaloupe

UNLABELLED Previous research examined sanitation treatments on cut cantaloupe tissue to deliver germicidal and food safety effects. However, an apparent compromise between volatile loss and treatment/sampling efficacy appeared. Subsequently, a physiological and volatile reassessment of thinly sliced tissue against cubes was performed in cantaloupe tissue. Thin sliced cantaloupe L* decreased 27.5%, 40.5%, and 52.9% in 3, 2, and 1 mm thickness, respectively, compared with cut cubes after 3 d. Overall color (C) decreased in freshly prepared cubes (2.4%) and slices (14.4%) that were washed in cold water. Surface area per unit volume (SA: vol) in slices was 4.1 times greater than typical cubes, as reflected by substantial water loss (20.4%, 9.5%, and 6.7% in 1, 2 and 3-mm slices, respectively) after 1 d at 5 °C. Rinsing cubes and thin-slices with 5 °C deionized water resulted in roughly 15% soluble solids loss. SEM indicated 65.4% reduced cell size in 1-d old thin slices, evidenced by excessive cell damage and desiccation compared with stored fresh-cut cubes. In thin-sliced tissue exposed 15 min to an open atmosphere (mimic sanitation treatments), total esters decreased 92.8% and 95.8%, respectively, after 1 and 3 d storage at 5 °C. Washing tissue provided a boundary layer that reduced short-term ester losses in slices and cubes. Excessive cutting, sanitation treatment regimes, and storage can radically alter the desirable volatile profile of cut cantaloupe. Reduction of tissue size to maximize food-safety sanitation efficacy or delivering items to a niche market will need substantial work to engineer equipment and develop protocols to insure that product quality and volatiles are not compromised. PRACTICAL APPLICATION We have demonstrated that cutting method and sampling protocol are critically important when using volatiles as a means by which to assess or interpret stress response and ascribe fresh-cut quality. Reduction of tissue size to maximize food-safety sanitation efficacy (for example, thin slices) will need substantial work to engineer equipment and design protocols to insure product quality and volatile profiles are not compromised.

Effect of hot water dips on the quality of fresh-cut Ryan Sun peaches

Los productos cortados enfresco son una importante categoria en desarrollo dentro de la industria de alimentos y como respuesta a los estilos de vida actuales se han popularizado debido a su conveniencia, frescura y calidad nutricional. Sin embargo, los productos cortados en fresco tienen una limitada vida util debido a que su elaboracion dana fisicamente el tejido, produciendo una respuesta fisiologica, fisica y quimica (aumento de la tasa de respiracion y produccion de etileno, perdida de sabor, decoloracion de la superficie de corte, pardeamiento, perdida de color, pudriciones, incremento de la tasa de perdida de vitaminas, ablandamiento acelerado, marchitez y reduccion de la vida de almacenamiento), lo que influye en la aceptacion por parte del consumidor. El objetivo de este trabajo consistio en analizar el efecto de las inmersiones en agua caliente sobre la calidad de los duraznos Ryan Sun cortados en fresco, aplicadas antes o despues del procesamiento. Los duraznos Ryan Sun cortados en fresco se envasaron y se almacenaron 6 dias a 5 °C. Durante el periodo de almacenamiento se analizaron la tasa de respiracion,firmeza, acidez titulable, contenido de compuestosfenolicos totales, actividad antioxidante y calidad sensorial. Los resultados demostraron que las inmersiones en agua caliente a 50 °C durante 3 min, previo al procesamiento en fresco, son eficientes para mantener la firmeza, la luminosidad y el tono de la pulpa de los duraznos Ryan Sun cortados en fresco, debido a la inactivacion de las enzimas relacionadas con el pardeamiento y el ablandamiento. Ademas, este tratamiento permitio mantener una alta acidez titulable, la que influye positivamente en el sabor del producto y por ende en la aceptabilidad por parte del consumidor.