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Freshly made Mexican white cheese, "Queso Chihuahua," obtained in Chihuahua and Hermosillo, Mexico, was analyzed. An initial representative sample was taken to determine microbial quality, chemical composition and amine content. The remainder was cut into portions and randomized for storage at 5 or 25°C. Representative samples were taken at 4, 8 and 12 days for analysis. Chihuahua cheese contained 43.7% fat, 49.2% protein, 2.7% salt, and 45% moisture. Water activity was 0.95 and pH 5.25. No pathogens were isolated. However, aerophilic plate count and coliforms exceeded permissible levels. Initially, amines were low, but increased during storage as proteolysis occurred. PH, salt and protein had the greatest influence on amine production.

In the first part of this study, samples were collected from farms, cheese processing plants (CPPs), and retail markets located in various geographical areas of Sonora, Mexico, over a 12-month period during the summer of 2004 and winter of 2005. Four (all Queso Fresco [QF] from retail markets) of 349 total samples tested positive for Listeria monocytogenes (Lm). Of these four positive samples, three were collected in the northern region and one in the southern region of Sonora. Additionally, two were collected during the winter months, and two were collected during the summer months. For the second part of the study, a total of 39 samples from a farm, a CPP, and retail markets were collected and processed according to a combination of the Norma Oficial Mexicana NOM-143-SSA1-1995.10 method (NOM) and the U.S. Food and Drug Administration (FDA) Bacteriological Analytical Manual method, and 27 samples from these same locations were collected and processed according to the U.S. Department of Agriculture Food Safety and Inspection Service method (USDA-FSIS). The NOM-FDA method recovered the pathogen from 6 (15%) of 39 samples (one cheese and five product contact surfaces), while the USDA-FSIS method recovered the pathogen from 5 (18.5%) of 27 samples (all product contact surfaces). In addition, the 40 isolates recovered from the 15 total samples that tested positive for Lm grouped into five distinct pulsotypes that were ca. 60% related, as determined by pulsed-field gel electrophoresis analysis. The results of this study confirmed a 3.4% prevalence of Lm in QF collected from retail markets located in Sonora and no appreciable difference in the effectiveness of either the NOM-FDA or USDA-FSIS method to recover the pathogen from cheese or environmental samples.

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Jumbo squid (Dosidicus gigas), an abundant species in the Gulf of California, can have a great potential for production of gelled-emulsified type products. Thus, formulation, processing and physicochemical characteristics of frankfurter-type product from jumbo squid mantle muscle (JSF) was achieved. JSF were vacuum-packed and stored at 2-4°C. Samples were analysed for physicochemical (colour, texture, TBARS, peroxide value, folding test, pH, and water content and holding capacity) and microbial changes at regular intervals during storage for up to 27 days. The sensory quality of the product was also evaluated. Shear force, cohesiveness and colour (hue angle and total colour difference) were the most affected (P < 0.05) parameters at day 27, changes most probably because of microbial growth as total aerobic counts increased to >2.7 · 10 5 CFU g )1 (day 21). Product showed acceptability. Results suggest a stable gelled-emulsified type product can be developed from jumbo squid mantle muscle opening a range of possibilities for product development.