highest score (2.7) at the end of 12 months of 

 frozen storage while the Na 2 EDTA + PG 

 treated fillets were given the lowest score for 

 appearance (1.8) over the same storage period. 



Visual observations of the progression of 

 browning are supported by changes in free and 

 total ribose content of snapper flesh over a 12- 

 month frozen storage period. The greatest de- 

 crease in free ribose content of snapper fillets 

 between 1 and 12 months of frozen storage was 

 exhibited by fillets treated with TBHQ, NA 2 - 

 EDTA + PG, and by the control (Table 3). 

 The fillets treated with TDP and glutathione 

 showed the least differences in free ribose con- 

 tent over the same period. The fillets that 

 showed the largest decreases in total ribose 

 content over the 12-month storage period were 

 the control, those treated with Na 2 EDTA + 

 PG, and those treated with TBHQ. The least 

 change in total ribose content over the 12-month 

 storage period was observed for the TDP and 

 glutathione treated fillets. 



By the end of 3 months of frozen storage, 

 the flesh of the control, the Na 2 EDTA + PG, 

 and the TBHQ treated fillets were noticeably 

 turning brown. By the end of 6 months of 

 storage, these fillets had turned even browner, 

 approaching the color of a brown pasteboard 

 box. The flesh of the TDP and glutathione 

 treated fillets, however, was nearly as white as 

 that of a freshly filleted snapper. The TDP 

 treated fillets received the highest organoleptic 

 score for appearance throughout the storage 

 period. Between 9 and 12 months of frozen 

 storage, the texture of all the fillets became 

 woody or slightly tough. 



The skin color deterioration problem was 

 successfully met by packaging the fillets in vac- 

 uum-sealed Cryovac bags. None of the samples 

 deteriorated appreciably with regard to skin 

 color over the 12-month frozen storage period. 

 There was no difference noted in skin color 

 between the control fillets or the fillets treated 

 with the chemicals used in this experiment. 



DISCUSSION 



The organoleptic scores for both TDP and 

 TBHQ treated fillets at the 1- and 3-month 

 draws were not obtained since both of these 

 chemicals were still considered experimental. 



Subsequently, we learned that both chemicals 

 were approved for use in foods by the Food 

 and Drug Administration (FDA) and organ- 

 oleptic studies were initiated on the fillets 

 treated with these chemicals. 



Bound ribose is present in fish flesh in the 

 form of nucleic acids such as RNA, nucleotides 

 such as IMP, and nucleosides such as inosine, 

 to name a few. The majority of the free ribose 

 present in fish flesh is produced by the post 

 mortem degradation of one or more of the gen- 

 eral classes of compounds mentioned above. 

 Several researchers (Von Tigerstrom and Tarr, 

 1965; Tarr and Gadd, 1965; and Pomeranz 

 et al., 1962) have indicated that it is the free 

 ribose which is involved in the Maillard reaction 

 in post mortem browning of fish muscle. 



The test pack of red snapper was stored in 

 a —10° F (—23.3° C) freezer. At the slightly 

 warmer storage temperature of — 18° C, the 

 nucleotide IMP (inosine monophosphate) in 

 frozen swordfish steaks is degraded at the rate 

 of only 0.(129 /^moles per gram per week. IMP 

 degrades at the rate of 0.24 /umoles per gram 

 per week at —8° C (Dyer and Hiltz, 1969). 

 This type of degradation results in a change 

 in the free and bound ribose content of fish 

 flesh. According to Dyer et al. (1966) , no sig- 

 nificant change in content of IMP, inosine, and 

 hypoxanthine in the ordinary muscle of fast- 

 frozen swordfish steaks occurs during freezing 

 and frozen storage at — 26° C for a period of 

 from 4 to 5 months. Therefore, at the tem- 

 perature at which this pack was stored (ap- 

 proximately — 26° C), no changes in free and 

 bound ribose due to enzymatic degradation of 

 nucleotides and nucleosides should have oc- 

 curred. Consequently, the progress of brown- 

 ing in the frozen snapper flesh can be followed 

 by analyzing the flesh for free and total ribose. 



As browning progresses in frozen snapper 

 flesh, the amount of free ribose decreases due 

 to a reaction between ribose and a free amino 

 acid or the amino group of a protein; this re- 

 action is the first of a series of complicated 

 reactions which occur in the browning process. 



The greatest decrease in free ribose content 

 occurred in the control fillets and those which 

 had been treated with TBHQ and Na 2 EDTA 

 + PG. The least amount of decrease in free 

 ribose content occurred in those fillets which 

 had been treated with TDP and glutathione. 



