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Byline: Marisol Castaner (1), Maria I. Gil (1), M. Victoria Ruiz (1), F. Artes (1) Keywords: Key wordsaMinimally processed lettuce; Enzymatic browning; Phenolics; Phenylalanine ammonia lyase; Polyphenol oxidase Abstract: aThis study was conducted to determine the effects of cultivar, tissue susceptibility and storage temperature on the keeping quality of minimally processed Baby and Romaine lettuces. Midrib and photosynthetic tissues were lightly processed and stored for up to 7days at 5aadegC and 13aadegC. Changes in L .sup.* and a .sup.* values and absorbance at 430nm were compared. The relationship between polyphenols, phenylalanine ammonia lyase (PAL) and polyphenol oxidase (PPO) activities and browning was examined. Measurements of L .sup.* and a .sup.* values on midribs showed that browning discoloration was the same for Baby as for Romaine lettuces and there was no relationship for temperature. In addition, L .sup.* and a .sup.* values in photosynthetic tissue indicated a decrease in green pigmentation during storage, especially at 13aadegC. For both kinds of tissue at the end of cold storage an increase in soluble brown polymers was detected. In midribs, total phenolics increased significantly throughout the storage period because of the tissue-wounding response. The photosynthetic tissue had a higher phenolic content than the midrib one. For both kinds of tissue an increase in PPO activity occurred throughout cold storage. On the other hand, PAL activity in midrib tissue only increased initially, followed by a slow decline to reach normal levels. Browning potential estimated by L .sup.* values correlated significantly (P&gt 95%) with PPO activity and with absorbance at 430nm for Romaine lettuce. Based on colour and browning potential no differences between Romaine and Baby lettuce cultivars were observed. However, photosynthetic tissue was the most suitable tissue for the preparation of minimally processed salad mixes because of its high phenolic content. Author Affiliation: (1) Postharvest and Refrigeration Laboratory, Food Science and Technology Department, CEBAS-CSIC, P.O. Box 4195, E-30080 Murcia, Spain e-mail: fr.artes@natura.cebas.csic.es, ES Article note: Received: 28 September 1998

A study focuses on microbiological stability and safety in fresh vegetables by examining the microbiology of a butter head lettuce cultivated and harvested in mulch and on bare soil and then comparing it to potential changes during storage. Mulch grown lettuce had lower microbiological decay whereas some growth was seen in lettuce grown on bare soil thus concluding that different growing conditions result in different responses to low temperatures.

An investigation to compare the potential of sodium hypochlorite washes and irradiation to remove leaf internalized Escherichia coli O157:H7 cells and to find the impact of lettuce variety on the effectiveness of the process, is given. It is demonstrated that irradiation efficiently minimizes viable E.coli O157:H7 cells internalized in lettuce and also that the type of lettuce affects the specific reaction.

The analysis of 100 bagged lettuce and spinach samples have indicated mean total bacterial counts of 7.0 [log.sub.10] CFU/g and a broad range of =11,000/g coliforms are found in 55 samples and generic Escherichia coli bacteria is detected in 16 samples, but no Escherichia coli count has exceeded 10 MPN/g.

A study is conducted to evaluate the water status, chlorophyll content (C) and overall visual quality (OVQ) of fresh butter lettuce (Lactuca sativa var. Lores). The observations of this study made in the external, middle, and internal zones of lettuce heads are presented.

The chemical and physical properties of 'Waldmann's' dark green leaf lettuce during cold storage were examined after application of ascorbic acid by two hydrocooling methods. The total ascorbate content increased up to 7 d due to hydrocooling of leaf lettuce by immersion or spraying using 1 percent ascorbic acid solution.