Bacterial spores isolated from ingredients, intermediate and final products obtained from dairies: thermal resistance in milk

Abstract

The ingredients used for the development and production of milk-based products pose the risk of the introduction of new, emerging spore-formers producing highly thermoresistant spores. Therefore, the aim of this study was to examine the heat resistance of spores isolated from dehydrated ingredients, intermediate and final products. Furthermore, the influence of the heating medium (milk or phosphate buffer) on the heat resistance was determined in order to assess which medium is best to use in the context of dairy processing. Sixteen spore-forming strains from seven different species (Bacillus amyloliquefaciens, Bacillus flexus, Bacillus subtilis, Bacillus thermoamylovorans, Bacillus smithii, Geobacillus pallidus, Geobacillus stearothermophilus) producing thermoresistant spores were selected after their isolation from diverse food products obtained from local dairies such as cocoa powder, milk powder, spices, and dessert products. Spores produced from the chosen strains were tested regarding their heat resistance at 110, 120, and 125°C for 30 min. Highly thermoresistant spores surviving a heat treatment for 30 min at 125°C in milk were produced by B. amyloliquefaciens and G. stearothermophilus. The inactivation of the spores was higher in milk than in phosphate buffer. This study highlights that not only raw milk but also dehydrated ingredients are important sources of thermoresistant spores in dairy processing. Since

Microbiological evaluation of infant foods quality and molecular detection of Bacillus cereus toxins relating genes

“…Also, B. cereus, B. circulans and B. pumilus were isolated with percentage of 16.7, 13.3 and 20% in infant milk formulae, respectively [ 31 ]. B. smithii was isolated from diverse food products obtained from local dairies such as cocoa powder, milk powder and dessert products [ 80 ].

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Probiotic characterization of Bacillus smithii: Research advances, concerns, and prospective trends

“…However, Margosch et al (2004) found that the fermentation media can severely affect the heat resistance of the bacteria. Stoeckel et al (2016) also found that the heat tolerance of B. smithii spores in milk is different from that of spores in phosphate buffer salts, with spores in phosphate buffer being more heat resistant, and that the media can greatly influence the physiological characteristics of the bacteria, all of which could be taken into account for subsequent consideration in culture optimization.…”

Sources, transmission, and tracking of sporeforming bacterial contaminants in dairy systems

“…Beyond the contribution of raw milk itself, another important source of spores is ingredients used in the manufacture of processed dairy products ( Stoeckel et al, 2016 ). For example, cocoa powder mixes (typically composed of cocoa powder, sucrose [or other sugar], starches, gums, flavorings, and so on) have been shown to contribute high levels of spores to chocolate milk and other chocolate-flavored dairy products (e.g., chocolate ice cream mix; Douglas et al, 2000 ; Cadirci et al, 2018 ).…”

“…While raw milk is still an important source of spores in milk and whey powders, thermophilic spores may also originate from biofilms in processing equipment (e.g., separators, heat exchangers, and evaporators) that are not adequately cleaned and sanitized ( Flint et al, 2020 ) as the conditions inside dairy powder processing equipment is ideally suited to select for thermophiles ( Seale et al, 2015 ). The use of dried dairy ingredients in reconstituted and heat-treated beverages (e.g., sports beverages, nutritional beverages, and so on) is of particular importance because obligate thermophiles represent a major proportion of the spore contaminants in many dairy powders ( Yuan et al, 2012 ; Miller et al, 2015 ) and spores of these organisms exhibit much higher heat resistance than other groups of spores ( Stoeckel et al, 2016 ), potentially leading to spore survival during UHT processing in end product applications. Additionally, nondairy ingredients including spices, dried herbs, vanillin, stabilizers, egg products, and so on have all been shown to be important potential sources of spores in processed dairy products ( Lücking et al, 2013 ).…”