Citrus juice impedes microbes in ceviche.

Ceviche is a traditional fish dish served in Latin America. Enormously popular in the western countries of South America as well as Mexico, the Caribbean and other parts of Latin America, it has many variations, but it is basically a simple blending of fish and citrus juice, with the addition of vegetables and spices. The chemical process that occurs when the acid of the citrus comes in contact with the fish is similar to what happens when the fish is cooked, and the flesh becomes opaque and firm. The ceviche is relying on citrus juice acids to denature its muscle tissue and inactivate microbes.

The safety of ceviche is a concern due to the potential for microbial contamination of the fresh fish and variations in preparation methods. There are conflicting data in the literature concerning the effectiveness of citrus juices in reducing the microbial load of a product. But scientists at Brigham Young University found that citrus juice treatments impeded bacterial survival in ceviche. They also determined the buffering capacity of the fish tissue. It appears that the volume of juice added to ceviche preparations influences the level of microbial inactivation.

Fresh tilapia (Oreochromis spp.) fillets were purchased from a local vendor, cubed and prepared according to a traditional Ecuadorian ceviche recipe using salt, onions and citrus juice. The amount of citrus juice added varied up to 1.5 mL per g of tissue, in 0.25 mL per g increments. The scientists refrigerated the fillets for 2.5 hours. The pH of the marinades and the internal pH of the tissue were measured before and after refrigeration.

After refrigeration, the researchers diluted and homogenized representative samples from each treatment. The homogenates were then plated in duplicate to obtain total and coliform plate counts.

Microbial log reductions ranged from 0 to 3.3 for total counts and from 0 to 3.4 for coliform counts. The extent of reduction increased as the product was treated with more juice. Coliforms were eliminated in all juice treatments that were greater than 0.25 mL per g. During the refrigeration period, the changes in tissue pH and solution pH ranged from -0.24 pH to 0.13 pH and from -0.14 pH to 0.46 pH, respectively. Buffering of the solution pH was minimal.

Further information. Frost Steele, Department of Nutrition, Dietetics and Food Science, Brigham Young University, S-221 ESC, Provo, UT 84602; phone: [phone]; fax: [phone]; email: [e-mail].