Fundamental Food Microbiology, Third Edition - Fuad Fathir

282 FUNDAMENTAL FOOD MICROBIOLOGY
IX. LIQUID SWEETENERS AND CONFECTIONERIES
Liquid sweeteners include honey, sugar syrups, maple syrups, corn syrups, and
molasses. Confectionery products include soft-centered fondant, cream, jellies, chocolate,
and Turkish delight. Most of these products have an A w of 0.8 or below, and
are normally not susceptible to bacterial spoilage. Under aerobic conditions, some
xerophilic molds can produce visible spoilage. However, osmophilic yeasts from
genera Zygosaccharomyces (Zygosaccharomyces rouxii), Saccharomyces (Saccharomyces
cerevisiae), Torulopsis (Torulopsis holmii), and Candida (Candida valida)
can ferment these products. To prevent growth of yeasts in some of these products
with slightly higher A w (such as in maple syrup), chemical preservatives are added.
X. MAYONNAISE, SALAD DRESSINGS, AND CONDIMENTS
These products normally contain some molds, yeasts, spores of Bacillus and
Clostridium, and aciduric bacteria such as Lactobacillus and related species. Because
of low pH, acid-sensitive bacteria may not survive long. Mayonnaise, with 65% or
more edible oil and ca. 0.5% acetic acid, has an A w of ca. 0.92 and a pH of 3.6 to
4.0. Salad dressings generally contain 30% or more edible oil, 0.9 to 1.2% acetic
acid, an A w of 0.92, and a pH of 3.2 to 3.9. The major factors controlling microbial
growth are undissociated acetic acid, low pH, and relatively low A w. However, some
aciduric microorganisms can grow to cause spoilage. Molds can grow only on the
surface exposed to air. Some microaerophilic and facultative anaerobic yeasts and
heterolactic Lactobacillus spp. (especially those that can grow at an A w of 0.92) can
also multiply to produce CO 2. Lab. fructivorans hydrolyzes sucrose present in the
products and produces gas (CO 2), especially from rapid metabolism of fructose that
is released from sucrose. Strains of Sac. bailii have also been implicated in gas
spoilage (CO 2 and alcohol) of these products. Lab. fructivorans cells usually die
rapidly after multiplication and are difficult to isolate unless specific methods are
used. This can lead to a wrong assumption regarding the microorganisms that cause
spoilage of these products.
Low-calorie salad dressing, in which oil and acetic acid are added in much lower
concentrations, has high pH and A w values. Many microorganisms can grow in these
products. To enhance their shelf life (and safety), refrigerated storage is recommended.
Yeasts, Lactobacillus spp., and Leuconostoc spp. can also cause gassy spoilage
of catsup, salsa, sauces, and prepared mustard. Some Bacillus spp. have also been
implicated in gassy spoilage of mustard preparations. To control growth of spoilage
microorganisms, additional preservation methods, especially chemical preservatives,
are used. 1,2,9
XI. FERMENTED FOODS
Desirable microorganisms are used directly or indirectly to produce many types of
fermented foods and beverages from meat, fish, milk, vegetables, fruits, cereal grains,