Scientists have found a combination that could be an effective sanitizer to process fresh organic vegetables.

A research team led by Professor Hongshun Yang from the Food Science and Technology program at the Department of Chemistry, National University of Singapore found a combination of organic acid (lactic acid, 2 percent volume concentration) and food grade sodium hypochlorite (4 milligrams per liter) is an effective sanitizer for organic food products.

Yang said the findings provide valuable references for the organic food processing industry, especially for organic fresh-cut vegetables which are widely used for making salads. The study was published in the International Journal of Food Microbiology.

Researchers tested the sanitization ability of different combinations of electrolyzed water, sodium hypochlorite and organic acids on organic broccoli sprouts containing Listeria innocua. Listeria innocua is a non-pathogenic bacterial species that has similar characteristics to the pathogenic species Listeria monocytogenes, which causes foodborne infections.

They found the sanitization treatment did not have any observable adverse effects on the sensory quality (color, texture and smell) of the organic broccoli sprouts over a storage period of six days.

Sanitizers for organic products

Sanitizers are commonly used in the food industry to help kill bacteria and other microorganisms that can cause foodborne illness. Although they are commercially available, regulations for organic food products limit the type of sanitizers that can be used to process organic vegetables.

Washing sanitizers such as chlorine solutions (sodium hypochlorite, 50 to 200 mg/L) are commercially used to disinfect freshly cut produce but they may not meet the regulatory requirements for processing organic produce under the United States’ National Organic Program (NOP).

The approach by the team from Singapore uses sanitizers approved by the NOP and is able to achieve a sanitizing effect comparable to those used for freshly cut produce. In experiments, the research team found the approach can reduce the bacterial population by about 1.8 log colony forming units per gram (cfu/g) on organic broccoli sprouts after washing treatment for two minutes.

Antimicrobial effects on organic broccoli sprouts showed the combined treatment resulted in reductions of 0.82, 1.51, and 1.77 log cfu/gram fresh weight for aerobic bacteria, yeasts and molds, and inoculated Listeria innocua at day zero.

The lactic acid disrupted the cell membrane of Listeria innocua within a short time. This eventually led to cell rupture. Addition of food grade sodium hypochlorite could induce oxidative damage to the bacterial cell, making the cell walls more permeable to the lactic acid, which results in better sanitizing performance.

Atomic force microscopy images showed morphological changes in the combination treated cells, which presented lower width and height and increased roughness.

“The selected washing sanitizers are Generally Recognized as Safe (GRAS) and approved by the United States NOP. They are convenient, effective and relatively low cost for consumers, which makes them suitable for the food processing industry,” said Lin Chen, a Ph.D. student working on the project.

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