Nuts, Seeds, and Cereals

The culinary definition of nuts is very broad and includes botanically defined nuts (e.g.,acorn, chestnut, and filbert), seeds (e.g.,Brazil nut, cashew, pignoli or pine nut, and pumpkin, sesame, and sunflower seeds), legumes (e.g.,peanut), and drupes (e.g.,almond, coconut, macadamia nut, pecan, pistachio, and walnut). This chapter presents an overview of the behavior of microorganisms on nuts, cereals, and products produced from them, with particular emphasis on describing conditions that permit or inhibit growth and treatments that can be used for microbial control or elimination. Worldwide, the production, harvesting, and processing techniques for nuts range from highly mechanized to labor intensive, and methods vary significantly among various types of nuts. The initial microbiota of peanuts, which develop beneath the soil surface, originates from the soil. The aspergilli, especially Aspergillus flavus, are ubiquitous invaders of nuts and can produce the mycotoxin aflatoxin. Processing steps that involve a thermal treatment often play a dual role of altering the texture and appearance of nuts and reducing microbial contamination. Microbiological contamination of cereal grains occurs while the grains are growing in the field. These contaminants can increase in number while the grains are actively growing and after harvesting. Milled cereal grains are produced by a dry-milling process. The resulting flours can be further wet processed, or “hydroprocessed,” in order to separate the gluten and starch components.