Endospores of Thermophilic Bacteria in Ingredient Milk Powders and Their Significance to the Manufacture of Sterilized Milk Products: An Industrial Perspective

Abstract

Milk powder is one of the most widely traded dairy products globally-with a large amount being used to manufacture commercially sterilized products. Milk powder invariably contains endospores of thermophilic bacteria-the dominant strains grow and produce spores in manufacturing steps operating in their temperature growth range. Although they produce proteolytic and lipolytic enzymes in vitro, and the spores have the potential to survive sterilizations, their presence in ingredient powders does not mean that spoilage of sterilized products is inevitable-treatment severity, low spore numbers in ingredient powders, variability in spore resistance, and in-market temperatures usually ensure commercial sterility.

The heat resistance and spoilage potential of aerobic mesophilic and thermophilic spore forming bacteria isolated from Chinese milk powders

“…Biofilms, in additions, serve as important niches where bacteria can grow and produce thermally stable enzymes (Teh et al, 2012) and spores (Flint et al, 2001). These spores survive all the subsequent stages of milk powder manufacture process such as concentrate heating and spraying draying (Hill and Smythe 2012). Most of the enzymes are also thermally stable and can survive pasteurization (Shamsuzzaman et al, 1986) as well as the UHT process (Koka and Weimer 2001;Griffiths et al, 1981;Chen et al, 2004) and result in functional and flavor defects, instability problems and reduced shelf life of dairy products during storage (Cogan 1977).…”

Preconditioning with Cations Increases the Attachment of Anoxybacillus flavithermus and Geobacillus Species to Stainless Steel

“…Geobacillus and A. flavithermus attach to and form biofilms on stainless steel product contact surfaces in milk powder manufacturing plants and are the predominant bacteria that contaminate milk powder (17,18). Unprocessed milk typically has total (sum of bound and free) Na ϩ , K ϩ , Ca 2ϩ , and Mg 2ϩ concentrations of 22, 37, 30, and 5 mM, respectively (19); however, these concentrations can be manipulated during processing.…”

Changes in Sodium, Calcium, and Magnesium Ion Concentrations That Inhibit Geobacillus Biofilms Have No Effect on Anoxybacillus flavithermus Biofilms

“…and Anoxybacillus flavithermus groups are the predominant spoilage bacteria that may contaminate milk during its manufacture into milk powder (1,2). The number of thermophilic bacilli in milk powder is of major importance because it is a measure of its quality and determines its market selling price (1,2). Geobacillus spp.…”

“…Geobacillus spp. and A. flavithermus grow as biofilms on product contact surfaces in regions of milk powder manufacturing plants, such as in plate heat exchangers and evaporators, that are held at high temperatures (up to 70°C) (1,2). It is postulated that these biofilms act as a reservoir of cells that slough off and disperse into milk as it transits through the plant (1,2).…”

“…It is postulated that these biofilms act as a reservoir of cells that slough off and disperse into milk as it transits through the plant (1,2). The majority of thermophilic bacilli that appear in milk powder originate from biofilms on product contact surfaces (2).…”