Study Highlights Prevalence of Spore-Forming Microbes in Plant-Based Dairy Ingredients

A recent research initiative, conducted by scientists from NZIO Food Research and Wageningen University and Research (WUR), has shed light on the levels and varieties of microbial contaminants present in 88 distinct plant-based ingredients utilized in the production of dairy alternatives. The study uncovered substantial variations in microbial loads among different ingredients and noted a significant prevalence of spore-forming microbes in various samples.

In essence, the research findings underscore the fact that the starting concentrations and types of microbial contaminants found in plant-based ingredients, even within the same category, can be influenced by numerous factors that are often beyond control.

The primary aim of this study was to enhance our comprehension of the microorganisms present in various plant-based ingredients. This knowledge, in turn, can inform microbial risk assessments and strategies to mitigate microbial hazards and spoilage risks throughout the production of plant-based foods. The researchers focused their attention on spore-forming bacteria, specifically Bacillus and Clostridium, due to the challenge they pose in removal and the fact that Bacillus is commonly found in plant-based foods.

While the plant-based ingredients analyzed in this study are not new, reformulating traditional products with new plant ingredients or altering processing conditions for existing ingredients necessitates a thorough evaluation of microbiological safety and recipe stability. In dealing with contamination by spore-forming microbes, food manufacturers employ various inactivation and food preservation methods. However, treatments such as heat application to eliminate spores or fermentation to prevent spoilage organism growth may not be suitable for plant-based dairy alternatives. Given that most plant protein-based dairy alternatives undergo pasteurization, knowledge of the types and levels of spore-forming microorganisms in raw materials is crucial.

The study analyzed samples of commercially available ingredients provided by producers of plant-based dairy alternatives. These ingredients included pulses (e.g., pea, faba bean, chickpea, and mung bean), cereals/pseudocereals (e.g., oat, rice, amaranth, and quinoa), and drupes (e.g., coconut, almond, and cashew). Depending on the ingredient type, samples were sourced from 4 to 12 different suppliers, originating from various geographical locations, including Europe, the Americas, and Asia.

The analysis involved assessing microbial total viable count (TVC), total aerobic mesophilic spore count (TMS), heat-resistant aerobic thermophilic spore count (HRTS), anaerobic sulfite-reducing Clostridium spore count (SRCS), and Bacillus cereus spore count (BCES).

Notably, numerous ingredients exhibited a substantial proportion of spores within their total aerobic mesophilic counts. In 63 percent of the samples, the difference between TVC and TMS counts was 1 Log10 unit or less, particularly among pea isolates and concentrates, faba bean isolates, oat kernels and flakes, and, for the most part, chickpea isolate, almond, amaranth, rice, quinoa, and coconut flours. Concentrations of TVC ranged from less than 1 to 5.3 Log10 colony forming units per gram (CFU/g) across different samples, while TMS varied between less than 1 and 4.1 Log10 CFU/g. Levels of HTRS, BCES, and SRCS were generally low, frequently falling around or below the limit of detection at 1 Log10 CFU/g.

The analysis identified a total of 845 individual bacterial colonies, spanning 33 different genera. Bacillus licheniformis and B. cereus group strains were the most commonly found among Bacillus isolates, mainly originating from pea and oat samples. Geobacillus stearothermophilus was the dominant species within HRTS. Among Clostridium isolates, Clostridium sporogenes/tepidum were the prevailing species, primarily discovered in pea and almond samples.

Strains with the potential to induce foodborne infection or intoxication were genetically typed using PCR-based methods to detect toxin genes. In the B. cereus group, 9 percent of isolates contained the ces gene, 28 percent harbored hbl, 42 percent possessed cytK, and 69 percent tested positive for the nhe gene. For all isolated C. sporogenes/tepidum strains, the absence of the boNT-A and -B genes was confirmed. An overwhelming majority (98 percent) of B. licheniformis isolates were positive for the lchAA gene.

Collectively, individual samples of the same ingredient type demonstrated significant disparities in concentrations of TVC, TMS, HRTS, SRCS, and BCES. These disparities likely stem from the fact that ingredient contamination can occur at various stages of production, including crop cultivation, influenced by factors such as geographical location, climate, and the utilization of biological pesticides. Furthermore, the methods employed to create different ingredient forms can influence the types and levels of microorganisms encountered. The analysis indicated a broad spectrum of microorganisms present in plant-based samples as part of the TVC isolates, with the greatest diversity of non-spore formers observed in pulses.