Metataxonomic Sequencing to Assess Microbial Safety of Buffalo Yogurts in Amasra Region

Introduction

Considering the economic importance and increasing demand for buffalo milk products, the aim of this study is to investigate whether there are potentially pathogenic microbial taxa in yogurts marketed in local markets that are declared to be made from buffalo milk.

Methods

Five yogurt samples (MY1–MY5) fermented with their natural yeasts by artisan and local producers were taken from the local markets of the Amasra district of Bartın province in Turkey. Each sample was collected from a different vendor. Genomic DNA isolation was performed shotgun metagenomics, by Quick-DNA™ Fecal/Soil Microbe Miniprep Kit, Cat. No. D6010 (Kürekci et al., 2016). The Kraken metagenomic system was used to characterize sequences (Wood and Salzberg, 2014).

Results and Discussion

Salmonella enterica was found in all yogurts (3.17–1.2%). The highest percentage of bacteria was found in MY4 with 6.32%. Pathogenic strains of Salmonella are common causes of foodborne illness. A possible transmission route of S. enterica to milk is feces, and hygiene measures should be increased to prevent it (Karns et al., 2005). According to Savran and Halkman (2017), S. enterica can survive at low abundance, very low incubation temperature, and high pH (pH >4.5), which can pose an important public health problem. For this reason, it is important to prevent its transmission.

Klebsiella pneumoniae was found to be 1.12% and 5.15% in MY2 and MY3 yogurts (Fig. 1). K. pneumoniae is a bacteria that can cause a wide variety of infections, including septicemia, pneumonia, urinary tract infections, and surgery and catheter-related infections (Gonzalez-Ferrer et al., 2021). It is an important cause of mastitis in dairy cows, it can be thought that it is transmitted to yogurts from the animal udder in which it is found. Generally, the highest prevalence of mastitis is found in countries where the dairy industry is underdeveloped and there is no udder hygiene (Osman et al., 2014).

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FIG. 1.

Relative abundance of the species found in buffalo yogurts.

Staphylococcus aureus was found at 3.17% only in MY2. S. aureus's ability to survive in yogurt poses a food safety problem. The presence of S. aureus in yogurt samples indicates that adequate hygienic precautions are not taken during production and that there may be contamination from personnel, especially (Oyeleke, 2009).

Homemade yogurts are considered to be healthier than commercial yogurts (Demirci and Ocak, 2020). But in this study, it is seen that all of the samples taken from the buffalo yogurts that are traditionally produced and offered for sale in public markets do not comply with the standards. Considering how unwanted bacteria are transmitted in yogurt, it can be said that raw milk can be an important source.

It is a correct assumption that the microflora of the milk changes due to bacterial contamination of raw milk during animal husbandry, storage or processing of the product, and, therefore, these bacteria can be found in yogurt (Addis et al., 2016). According to all these results, yogurts are hygienically weak and have very worrying results in terms of health.

The lack of a standard hygiene protocol and the high risk of contamination may cause low microbiological quality in yogurts. From this point of view, it is important to determine the microbiological quality of buffalo yogurts produced in family-type enterprises. The data obtained as a result of this study revealed that strict hygienic measures should be taken during the production, processing, and distribution of the product in question, and that the products offered for sale in public markets and that carry a risk of contamination should be periodically controlled by the relevant authorities. In addition, keeping milk and dairy products in the cold chain at refrigerator temperatures until consumption is another important issue that needs attention.