Behavior of Listeria monocytogenes in Avocado Pulp and Processed Guacamole

Abstract

The potential ability of Listeria monocytogenes to grow or survive in avocado pulp (AP) and processed guacamole (PG) stored at 22, 4 to 7, and -18 degrees C was studied. Both products were obtained from a factory in Michoacan, Mexico. PG consisted of AP mixed with dehydrated vegetables, antioxidants, and preservatives. Populations of L monocytogenes in AP stored at 22 degrees C increased from 2 to 6 and 9 log CFU/g after 24 and 48 h, respectively. At 4 to 7 degrees C, the growth rate of L monocytogenes in AP was greatly decreased; generation time was 8.2 h, in contrast with 1.35 h observed at 22 degrees C. L. monocytogenes populations did not increase in PG either at 22 degrees C for 48 h or at 4 to 7 degrees C for 15 days. The bacteriostatic effect in PG may have resulted from the presence of added substances, especially citric acid and disodium dihydrogen pyrophosphate. Aerobic plate counts and coliforms increased in AP and PG stored at ambient temperature and under refrigeration. However, these increments did not affect the growth of the pathogen. L. monocytogenes (50,000 most probable number [MPN]/g) survived at least 58 weeks in both products stored frozen at -18 degrees C; the final population was 335 MPN/g in AP and 23 MPN/g in PG. Although the composition of avocado fruit differs significantly (high content of lipids and scarcity of simple carbohydrates) from that typical of most fruits, these results underline AP as a potential vehicle of human listeriosis and indicate that freezing should not be used as the sole mechanism to control this pathogen.

Microbial Safety of Tropical Fruits

“…The majority of tropical fruits come to the U.S. following production in other regions of the world where no uniform food safety standards exist for production and postharvest practices, thus the safety of these products remains a concern. Outbreak surveillance systems and pathogen detection capabilities in many of these countries do not exist or are so poor that many outbreaks related to tropical fruit may Iturriaga et al, 2002. e Lund and Snowdon, 2000. f Souza, 1998. g Che Man, et al, 1996. h Bassett and McClure, 2008. i Ergun et al, 2005. j Melo, et al, 2000 adults are typically self-limiting without the need for hospitalization.…”

“…The U.S. is the leading importer of avocados accounting for 30% of the total import share (FAO, 2003). Avocados imported to the U.S. are mainly used in the production of guacamole, a mixture of fleshly diced cilantro, tomato, chili, lime juice, and salt (Iturriaga et al, 2002). Avocados are susceptible to foodborne pathogens due to their high water activity (0.98) and pH (6.5) (Iturriaga et al, 2002).…”

“…Avocados imported to the U.S. are mainly used in the production of guacamole, a mixture of fleshly diced cilantro, tomato, chili, lime juice, and salt (Iturriaga et al, 2002). Avocados are susceptible to foodborne pathogens due to their high water activity (0.98) and pH (6.5) (Iturriaga et al, 2002). A survey of guacamole from street vendors and restaurants in Mexico found S. aureus, E. coli, Salmonella, and L. monocytogenes in samples.…”

“…Although growth S. aureus in avocado pulp was slower than Salmonella and E. coli O157:H7, the potential for S. aureus contamination from food handlers is high, thus avocado pulp should be considered a potential vector of S. aureus (Arvizu-Medrano et al, 2001). Listeria monocytogenes grew in avocado pulp stored at ambient temperatures over a 48 h storage period, with the majority of growth seen in the first 24 hours (Iturriaga et al, 2002). The lag time for L. monocytogenes in avocado pulp was found to be 3 hours at ambient temperature conditions, highlighting the importance of temperature control.…”

Evaluation of composition and performance of composts derived from guacamole production residues

“…Clostridium botulinum (Dorantes-Alvarez et al, 2012;Iturriaga et al, 2002). Food industries take the necessary measures to prevent microbial contamination but these measures apply only to the main food product and not to production residues.…”