Effect of varied storage temperatures on microorganisms in frozen concentrated orange juice.

Extensive studies on the effects of conditions that may be encountered in commercial handling on quality of frozen foods have been under way at the Western Utilization Research and Development Division of the U. S. Department of Agriculture during recent years. The commodities investigated have included frozen concentrated orange juice. Chemical and physical changes in this commodity under varied conditions of time and temperature have been reported by McColloch et al. (1957). The present paper deals with microbiological changes in 5 of the 9 lots of concentrate studied by McColloch and co-workers. Although extensive research has been done on certain phases of the microbiology of citrus products, that published on the effect of varying storage temperatures on microorganisms in frozen concentrate is very limited. Faville et al. (1951) noted that bacteria were the predominating type of microbial flora in frozen concentrated orange juice and that these decreased rapidly in number when the product was stored at 17 C. They also observed that various microorganisms inoculated into orange concentrate were destroyed more rapidly at 40 C than at 30 or 3 C. The latter observations, however, were based on observations of periods from 1 to 7 hr and do not necessarily reflect what would happen in subfreezing storage for several months. The phenomenon of storage temperature effect on other frozen foods has been observed by other workers. Berry (1932, 1933, 1936) observed repeatedly that greater destruction occurred in berry packs stored at 15 F (-9 C) than in those stored at -15 F (-26 C). Similar observations were made by Prescott et al. (1932), who found that in certain foods higher storage temperatures resulted in more rapid microbial destruction.