There are three broad types of browning re- 

 actions recognized in foods. The first is car- 

 amelization which occurs when polyhydroxy- 

 carbonyl compounds are heated to relatively 

 high temperatures in the absence of amino 

 acids. The second is a group of oxidative re- 

 actions which convert ascorbic acid and poly- 

 phenols into di- or polycarbonyl compounds. 

 The third type, which is the most common, in- 

 volves the reactions of aldehydes, ketones, and 

 reducing sugars with amines, amino acids, pep- 

 tides, and proteins and is known as the Maillard 

 reaction. 



Liston et al. (1963) state that the free amino 

 groups of fish proteins are available for re- 

 actions with reducing sugars or with some of 

 the products of oxidation of lipid material. 

 The end result of a complicated series of re- 

 actions is the formation of brown colors as 

 well as changes in flavor. 



According to Von Tigerstrom and Tarr 

 (1965), the browning which occurs in muscles 

 of many species of fish post mortem is due to 

 the Maillard reaction. Von Tigerstrom and 

 Tarr (1965) also brought out the importance 

 of D-ribose as playing a significant role in the 

 Maillard reaction. Other researchers have 

 also indicated that ribose is one of the reducing 

 sugars which is a main contributor to the 

 Maillard reaction (Tarr and Gadd. 1965; Pom- 

 eranz et al,, 1962; Gilka, 1963; and Jones, 

 1962). 



Most browning inhibitors have been shown 

 to be carbonyl reagents such as cyanide (Barnes 

 and Kaufman, 1947), hydroxylamine (Burton, 

 1945) , hydrazine (Barnes and Kaufman, 1947) , 

 mercaptans (Guss, 1952; Song and Chichester, 

 1967), bisulfite (Olcott, 1953), and glutathione 

 (Joslyn and Ponting, 1951). Most of these 

 chemicals, however, have undesirable side 

 effects in meat and fish. Other methods used 

 in inhibiting the flesh browning are (1) low 

 storage temperatures and (2) lowering the 

 moisture content in dehydrated foods. 



In spite of the commercial importance of 

 good skin color of red snapper, there has been 

 very little work done on preventing skin color 

 fading. According to Tsukuda and Amano 

 (1966) , storage temperatures as low as —30° C 

 did not prevent skin discoloration in Lepido- 

 trigla giintheri, Lusk et at, (1964) reported 

 the changes in the amount of astacene pigment 



in freeze-dried shrimp during freeze dehydra- 

 tion and subsequent storage both in air atmos- 

 phere and a nitrogen atmosphere. The pigment 

 in shrimp stored in the air atmosphere was 

 essentially all bleached after one week whereas 

 shrimp stored in a nitrogen atmosphere re- 

 tained their pigment color over the same period. 

 Yamaga and Morioka (1962) described the 

 effectiveness of certain antioxidants used to 

 prevent the skin color fading in certain red 

 fishes. 



The purposes of this paper are to describe 

 an experiment designed to show (1) the in- 

 hibitory effects that certain chemicals have on 

 the browning of the flesh of frozen snapper 

 fillets and (2) the effect vacuum packaging has 

 on preventing the skin discoloration of frozen 

 snapper fillets. 



MATERIALS AND METHODS 

 Preparation of Samples 



Yelloweye snapper (Luijanus vivanus). — 



Fifty-two fresh, iced, eviscerated, heads-on 

 snapper were obtained from a local fishery. 

 These fish were scaled and headed. Their 

 weights averaged approximately 3 lb. 



Chemicals. — All chemicals were either food 

 grade or reagent grade quality. The chemicals 

 used in this study were 3,3'-thiodipropionic acid 

 (TDP), glutathione (Glu), disodium ethylene- 

 diaminetetraacetate dihydrate (Na 2 EDTA) in 

 combination with propyl gallate (PG), and 

 monotertiary butylhydroquinone (TBHQ). 



Method of chemical application. — -The 

 technique involved using a hypodermic syringe 

 to iniect a scaled eviscerated snapper prior to 

 filleting with an aqueous solution of the desired 

 chemical. Each side of the fish was injected 

 with two 2-ml shots evenly spaced down the 

 lateral line. The solutions of TDP and gluta- 

 thione were injected in the amount necessary 

 to produce a residual concentration of the chem- 

 icals equivalent to 0.02 r '< of the snapper oil 

 content. TBHQ was injected in an amount to 

 produce a 50 ppm residual. A combination of 

 Na 2 EDTA and PG was injected in the amount 

 to produce a 50 ppm residual of the combina- 



