Survival of Listeria monocytogenes inoculated in retail soymilk products

Growth, persistence and toxin production of pathogenic bacteria in plant-based drinking milk alternatives

The present study investigated the microbiological safety of the increasingly popular plant-based milk alternatives. No (10/27) or only very low microbial counts (17/27) were detected in the tested products. These were mainly identified as spore formers via MALDI-ToF-MS. Three products contained Bacillus cereus group isolates, which were able to form considerable amounts of enterotoxins and exhibited cytotoxicity towards CaCo-2 cells. Preliminary tests showed good growth of B. cereus, Listeria monocytogenes, and Salmonella enterica in all tested products (maximum bacterial counts: 5 × 1012 cfu/mL). These experiments also revealed strain-, time-, and temperature-, but especially product-specific enterotoxin production of B. cereus. In propagation and persistence tests according to DIN EN ISO 20976-1:2019-09, rapid bacterial proliferation was also detected in all products. B. cereus generally showed lower bacterial counts (106-107 cfu/mL) compared to L. monocytogenes and S. enterica (108-109 cfu/mL), but was detectable in a larger number of products over the test period of 6 weeks. pH values decreased (20/27) over time and visual and/or olfactory alterations (24/27) were observed. The present study provides information on the occurrence, growth and persistence of pathogenic bacteria in plant-based drinking milk alternatives. It also points out that the accompanying changes in pH, odor, and appearance are not necessarily recognizable to the consumer. PRACTICAL APPLICATION: The present study contributes to the understanding of the microbial risk related to plant-based drinking milk alternatives. It is crucial that the manufacturer ensures that particularly spore formers have been effectively eliminated from the products. Among them, especially toxin-producing bacteria can pose a risk to the consumer, as these products promote proliferation and persistence of the bacteria.

Soy, Rice and Oat Drinks: Investigating Chemical and Biological Safety in Plant-Based Milk Alternatives

During the last decades, plant-based milk has become very appreciated by consumers, becoming a staple ingredient, especially for alternative breakfasts. Milk contains lactose, which is a sugar hydrolysed by the lactase enzyme. Lactose intolerance and lactose malabsorption are very common food intolerances among individuals. However, a lot of consumers consider themselves as lactose intolerant on the basis of self-reported intolerance and start to avoid dairy products, ignoring that plant-based milk alternatives are not nutritionally comparable to animal milk, especially in terms of protein intake. The aim of this study is to grow folder knowledge of the security of plant-based drinks, helping competent authorities to issue a risk assessment and to apply national plans about consumer safety. Results show that proper sanitary practices, such as pasteurization, are necessary in plant-based milk alternatives as well as in dairy milk. Chemical analysis has highlighted that there are no pesticide risks for consumers.

In situ production of pediocin PA-1 like bacteriocin by different genera of lactic acid bacteria in soymilk fermentation and evaluation of sensory properties of the fermented soy curd

The lactic acid bacteria (LAB) are found to produce bacteriocins with enhanced nutritive properties in the fermented foods. In the present study, the ability of LAB cultures (Pediococcus acidilactici NCIM 5424, Enterococcus faecium NCIM 5423 and Lactobacillus plantarum Acr2) to produce pediocin PA-1 like bacteriocin was evaluated during soymilk fermentation. The isolates E. faecium NCIM 5423 and Lb. plantarum Acr2 were able to produce bacteriocin as well as ferment soymilk within 6 h of incubation. Upon plating the cultures E. faecium NCIM 5423 and Lb. plantarum Acr2 in soymilk were found to be viable even after 15 days of storage at 4 °C. No significant variation was observed in the viable counts of E. faecium NCIM 5423 and Lb. plantarum Acr2 (P>0.05). The effect of crude bacteriocin on Listeria cells was evidenced through scanning electron microscope (SEM) photographs wherein cell membrane damage was observed. On co-cultivation of E. faecium NCIM 5423 and Lb. plantarum Acr2 individually with Listeria monocytogenes ScottA a decrease in the Listeria count was observed within 24 h of incubation. However, during co-cultivation of ScottA with P. acidilactici NCIM 5424, no significant difference was observed in the viable counts (P>0.05). The pH, titratable acidity, pediocin activity, anti-oxidant property and sensory attributes for E. faecium NCIM 5423 were studied. It was observed that E. faecium NCIM 5423 fermented soymilk had an acceptable sensory score during storage period. Hence, such culture can be an ideal starter for development of functional foods with longer shelf life.