Impact of postharvest UV-C and ozone treatments on microbiological properties of white asparagus (Asparagus officinalis L.)

To meet the increasing demand for safe and high quality fresh white asparagus and the recent food safety regulations, optimization of postharvest handling, processing and storage is essential. Modern sanitation techniques relying on physical methods and/or Generally Recognized As Safe (GRAS) compounds are desired for reducing microbiological spoilage. To evaluate the effects of aqueous ozone and UV-C on the microbial load of spears, samples were UV-C irradiated (254 nm, 1 kJ m-2) and/or washed with ozonated water (approx. 3 ppm or 4.5 ppm at 10 °C), and analyzed at three times during a four day storage. Also, the potential effects of initial natural microbial loads, and precondition of the spears in terms of water and sugar contents on the responsiveness of asparagus to these treatments were determined in detail over four growing seasons. The initial microbial loads (mould and yeasts, and aerobic mesophilic total bacterial counts) of white asparagus spears varied considerably during the different harvest seasons of this four-year study. This variability could not be explained by the variance of climatic conditions nor by the respective water and sugar content. Furthermore, there was never a clear cut relation of the initial microbial load and the growth of pathogens during four-day storage at 20 °C in nearly water vapour saturated atmosphere. Neither washing the spears with ozonated water (3 or 4.5 ppm) nor treating them with UV-C radiation (1 kJ m-2) systematically and significantly affected their microbial loads during storage. In addition, the assumption that a combination of both treatments could synergistically improve the effect of each treatment could not be verified during this long-term study. In conclusion, microbial load and pathogen development in asparagus spears are highly persistent and, thus, to meet hygienic requirements further investigations will be necessary

Effects of Pre-Processing Hot-Water Treatment on Aroma Relevant VOCs of Fresh-Cut Apple Slices Stored in Sugar Syrup

In practice, fresh-cut fruit and fruit salads are currently stored submerged in sugar syrup (approx. 20%) to prevent browning, to slow down physiological processes and to extend shelf life. To minimize browning and microbial spoilage, slices may also be dipped in a citric acid/ascorbic acid solution for 5 min before storage in sugar syrup. To prevent the use of chemicals in organic production, short-term (30 s) hot-water treatment (sHWT) may be an alternative for gentle sanitation. Currently, profound knowledge on the impact of both sugar solution and sHWT on aroma and physiological properties of immersed fresh-cuts is lacking. Aroma is a very important aspect of fruit quality and generated by a great variety of volatile organic compounds (VOCs). Thus, potential interactive effects of sHWT and sugar syrup storage on quality of fresh-cut apple slices were evaluated, focusing on processing-induced changes in VOCs profiles. Intact ’Braeburn’ apples were sHW-treated at 55 °C and 65 °C for 30 s, sliced, partially treated with a commercial ascorbic/citric acid solution and slices stored in sugar syrup at 4 °C up to 13 days. Volatile emission, respiration and ethylene release were measured on storage days 5, 10 and 13. The impact of sHWT on VOCs was low while immersion and storage in sugar syrup had a much higher influence on aroma. sHWT did not negatively affect aroma quality of products and may replace acid dipping

Effects of Pre-Processing Short-Term Hot-Water Treatments on Quality and Shelf Life of Fresh-Cut Apple Slices

Processing, especially cutting, reduces the shelf life of fruits. In practice, fresh-cut fruit salads are, therefore, often sold immersed in sugar syrups to increase shelf life. Pre-processing short-term hot-water treatments (sHWT) may further extend the shelf life of fresh-cuts by effectively reducing microbial contaminations before cutting. In this study, fresh-cut ‘Braeburn’ apples, a major component of fruit salads, were short-term (30 s) hot water-treated (55 °C or 65 °C), partially treated with a commercial anti-browning solution (ascorbic/citric acid) after cutting and, thereafter, stored immersed in sugar syrup. To, for the first time, comprehensively and comparatively evaluate the currently unexplored positive or negative effects of these treatments on fruit quality and shelf life, relevant parameters were analyzed at defined intervals during storage at 4 °C for up to 13 days. Compared to acid pre-treated controls, sHWT significantly reduced the microbial loads of apple slices but did not affect their quality during the 5 day-standard shelf life period of fresh-cuts. Yeasts were most critical for shelf life of fresh-cut apples immersed in sugar syrup. The combination of sHWT and post-processing acid treatment did not further improve quality or extend shelf life. Although sHWT could not extend potential maximum shelf life beyond 10 d, results highlighted the potentials of this technique to replace pre-processing chemical treatments and, thus, to save valuable resources

Chlordioxid zur Reduktion von humanpathogenen Mikroorganismen bei der Salatwäsche

Der Markt für abgepackte verzehrfertige Frischsalate ist in den vergangenen Jahren stark gewachsen. Für die Herstellung von mikrobiologisch unbedenklichen Produkten wurde der Zusatz von Chlordioxid (ClO2) zum Waschwasser auf sein Potenzial zur Minimierung relevanter humanpathogener Mikroorganismen getestet. Dabei wurden auch wichtige Parameter der Produktqualität, wie z. B. Farbe und Inhaltsstoffe, berücksichtigt. Eine ClO2-Behandlung ermöglicht es, die Konzentration von Mikroorganismen im Waschwasser um 5 bis 6 log-Einheiten zu reduzieren, abhängig vom chemischen Sauerstoffbedarf (CSB-Wert). Farbe und Vitamin-C-Gehalt der Salatblätter werden von der Behandlung nicht beeinflusst. Demnach ist ClO2 zur Hygienisierung von Salatwaschwasser geeignet.During recent years, the consumption of prepackaged readyto- eat salads has strongly increased. To facilitate the production of microbiological safe fresh-cut products, the potential of chlorine dioxide for decontamination of iceberg lettuce during washing and its effects on external and internal quality parameters of the produce were investigated. ClO2 application results in 5 to 6 log reduction of microorganisms in the washing water, depending on its chemical oxygen demand (COD). Colour parameters and vitamin C content of leaves were not affected by chlorine dioxide washing. Therefore, chlorine dioxide is an appropriate sanitizer to minimize human pathogens in lettuce washing water

Influence of Washing Method on the Quality of Prepacked Iceberg Lettuce

Rosana G. Moreira, Editor-in-Chief; Texas A&M UniversityThis is a paper from International Commission of Agricultural Engineering (CIGR, Commission Internationale du Genie Rural) E-Journal Volume 7 (2005): Influence of Washing Method on the Quality of Prepacked Iceberg Lettuce by Karin Hassenberg and Christine Idle