Chemical Effects in Food Stored at Room Temperature Marcus Karel Department of Nutrition and Food Science, Massachusetts Institute of Technology. Cambridge, MA 02139 T h e strateav of food nreservation is based on elimination of microhial & w h since microorganisms are the major cause of d~teriorationof foods. When microbial mowth is nrevented. the remaining causes of deterioration of foods stored a t room temperature are physical changes and chemical reactions occurring in the food. Table 1 outlines organoleptic and nutritional changes which may be produced by reactions occurring in the absence of microbial growth in food and provides an overview of the role of environmental factors in the rate and extent of these chemical reactions. Table 2 summarizes how environmental factors which affect the major deteriorative reactions may be controlled. Below we discuss the behavior of two important chemical deteriorative mechanisms: non-enzymatic hrowningand lipid oxidation. Non-mzymatir browning is the major cause of darkenine of concentrated and dehvdrated stored foods and is also the cause of various cooked and stale flavors in foods ( 1 ). Lipid oxidation is the major cause of rancidity in foods
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Non-Enzymatic Browning Non-enzymatic browning is one of the major chemical reactions occurrine in foods. The overall nature of this reaction and of the reactants and products is shown in Figure 1.This reaction has been studied extensivelv. .. and several recent reviews have been published ( 1 , 3 , 4 ) . The most sensitive stored products are dry and concentrated foods. T h e major concern in processing is in heating,
drying, and concentrating, but here we rue concerned with changes occurring in stored foods. The manifestations of browning which are of particular importance to the technologist are the development in storage of undesirable dark color, loss of available lysine in milk and cereal products, and especially the development of stale flavors ( 1 , 5 ) .The same reaction, when carried out a t very. h i. ~ temperatures, h such as roasting, can have much more drastic t.tTt.cts, including production of mutagens ( 6 , 7 ) ,but these effects arc i~robablvnot of c o n ~ e q u e n cin~ the milder conditions &curring in storage. The tests which can be used effectively to follow the course of browning include the following: 11 measurrment oiloss ut free aminogrwps ( R I (Fiz. 21, formarim of inrermrdiatei leg., furmme and p.ymd
