Fundamental Food Microbiology, Third Edition - Fuad Fathir

468 FUNDAMENTAL FOOD MICROBIOLOGY
was used on ships and trains in Europe to transport meat and fish from other
countries. Linde, in Germany, developed the first domestic refrigerator ca. 1874 and
started commercial production before 1890. The popularity of domestic refrigerators
was initially slow in the U.S.; in 1930, 2 to 3% of the households had the units. In
the U.S., methods to freeze fruits and vegetables were developed and commercially
used around the 1930s. During this time, retail stores also started using cabinets to
display frozen foods.
During World War II (1941 to1944), consumer interest in refrigerated and frozen
foods increased dramatically, which helped develop the technology necessary for
processing, transporting, retailing, and home storage of refrigerated and frozen foods
in the U.S. The popularity of refrigerated and frozen foods has increased steadily
since then. In the 1960s, 1970s, and early 1980s, frozen food consumption increased
sharply, mainly because of the long shelf life. Since the mid-1980s, there has been
increased interest in refrigerated and chilled foods, which consumers view as natural
and healthy. The major drawback of many refrigerated foods is their relatively short
shelf life, ca. 1 to 2 weeks. But in recent years, several technological improvements,
such as oxygen-impermeable packaging materials, good vacuum-packaging equipment,
innovative packaging systems, low-temperature refrigeration units (£–1�C),
and use of the hurdle concept to preserve food (Chapter 40) have helped increase
the shelf life of many refrigerated foods to 60 d, and for some products, more than
90 d. At present, of the total foods consumed, low-temperature preserved foods
constitute more than 65%, and the trend shows a steady increase in the future. To
suit the taste of consumers, many new products are being developed that are low in
fat (caloric), high in fiber, phosphates, and other additives, and have low amounts
or no preservatives. To achieve the long shelf life and to make these products safe,
extra precautions are being introduced for microbiological control. This has helped
many new or emerging pathogenic and spoilage bacteria, in the absence of competition
from associated microorganisms, to become predominant (Chapter 28). New
designs of processing equipment for high-production efficiency, centralized production
of large volumes of products, transportation of products for long distances in
regional storage facilities, retailing conditions, and consumers’ handling of the
products have facilitated these so-called new pathogenic and spoilage bacteria in
gaining prominence (Chapter 20). Unless some effective intervention strategies are
developed, new pathogenic and spoilage microorganisms will continue to surface in
refrigerated foods stored for a long time. 1–3
II. OBJECTIVES
The main microbiological objective in low-temperature preservation of food is to
prevent or reduce growth of microorganisms. Low temperature also reduces or
prevents catalytic activity of microbial enzymes, especially heat-stable proteinases
and lipases. Germination of spores is also reduced. Low-temperature storage, especially
freezing (and thawing), is also lethal to microbial cells, and, under specific
conditions, 90% or more of the population can die during low-temperature preservation.
However, the death rate of microorganisms at low temperature, as compared