Shellfish Microbial Food Safety

Shellfish are deeply loved by people because of their tender meat, delicious taste and rich nutrients. In recent years, shellfishery in our country has made great progress. Shellfish production accounts for 75% of mariculture production, and its industrial scale and output rank first in the world. Main economic shellfish include oysters, clams, mussels, razor clams, scapharca subcrenata, sea cucumber, etc. Therefore, how to monitor and control foodborne pathogenic microorganism in shellfish is of great significance to guarantee the food safety.

Let’s take oysters as an example. Oysters, commonly known as HAO, also known as LI HUANG, HAI LI ZI, are rich in protein, with low fat and delicious taste, thus become one of favourite seafood for people. Oysters also contain a variety of active substances as characters of marine organisms, among which bezoar acid can strengthen the body immunity, promote the neonatal brain development, and enhance intelligence. According to the statistics from yearbook, China’s main economic shellfish oysters output reached 3.76 million tons in 2011. Oysters are filter feeders, thus have strong ability of filter-feeding (an oyster with a weight of 20 g can filter 8-22 litres of seawater per hour; some even can reach 31-34 litres per hour). This life habit makes them absorb many poisonous and harmful substances (foodborne pathogenic microorganisms in the water, etc.) into their body while filter-feeding. Therefore, oysters and other economic shellfishes have become the main carrier for the spread of foodborne pathogenic microorganisms. Common foodborne pathogenic microorganism include: Vibrio parahaemolyticus, Vibrio vulnificus, Salmonella, Noroviruses, Rotaviruses and Hepatitis A virus, etc.

According to our study, oyster gill, coat film, digestive gland and other organs of oysters are enriched with foodborne pathogens. However, in order to guarantee the delicious taste of them, people usually eat them under raw or half-cooked conditions, with their entrails not be removed. According to our monitoring on the deputy hemolytic vibrio contamination condition in shellfish for sales in Shanghai in recent 3 years, the bacteria contamination rate was equal to that in developed countries, and the positive rate of bacterial pathogens showed a downward trend year by year, which reflects that shellfish for sales are in good condition. Yet it is suggested for people (especially young children and the elderly) to eat shellfish fully cooked. When people eat raw or half-cooked shellfish, they should mix them with vinegar, ginger and garlic juice. In case of any food poisoning caused by eating shellfish, try to take antibiotics. If taking antibiotics does not work, do not be panic; most of food poisoning caused by pathogenic microorganisms is self-limiting, generally the patient will recover within 1-3 days; yet during this period, pay attention to ensure no dehydration. In addition, the person with food poisoning should not engage in any activity of preparing meals, in order to avoid infection of others caused by food contamination.

It is suggested to: buy fresh shellfish; cook for immediate consumption (not to eat overnight shellfish dishes); clean the containers for processing shellfish in time to avoid cross contamination. For guarantee purposes, food-grade chlorine dioxide solution may be used to soak them for 20 to 30 minutes.

Tips: How to select fresh shellfish?

Appearance inspection: Don’t select shellfish with broken shells. For shellfish fed in the water, select those whose meat is out of shells, and if you touch the meat it will go back to the shell; for shellfish not fed in the water, select those with their shells closed completely. After boiled, those with their shells partially or completely open are fresh shellfish.

Smell inspection: No foreign smell.

Copyright © | Bor S. Luh Food Safety Research Center  of Shanghai Jiao Tong University 2015