230 Chilled foods 4 Chill storage time(days) Fig. 9.3. Effect of cooking and storage atmospheres on woF development in chicken breasts(O-O) cooked and stored in air; (x-x)cooked in nitrogen, stored in air; )cooked in air, stored in nitrogen,([A]-[AD cooked and stored in nitrogen. atmosphere reduced the TBa values and sensory scores for WOF intensity as compared with those cooked in air and stored in either nitrogen or air(Fig. 9.3) Autooxidation or oxidative rancidity is by no means confined to meat and meat products. Dairy products and fatty fish are also highly susceptible. Migration of copper into cream on churning can initiate the oxidative sequence of reactions causing rapid flavour impairment. Buttermilk has a high proportion of unsaturated phospholipids, particularly phosphatidylethanolamine, that can bind metal ions in a prooxidative fashion, and the presence of a metal-phospholipid complex 1-water interface facilitates lipid hydroperoxide formation. Fish fats contain a high proportion of n-3 polyunsaturated fatty acids, which are vulnerable to oxidation by atmospheric oxygen leading to deteriorative changes. Despite this, rancid flavours only appear to affect the acceptability fattier species such as trout, sardine, herring and mackerel; and even then, trout and gutted mackerel oxidize at temperatures above 0oC whereas herring remains relatively unaffected. Castell(1971)has suggested that in fish, oxidized lipids become bound in lipid-protein complexes rather than forming carbonyl compounds associated with rancid flavours. The lipid-protein complexes also ontribute to the toughened texture of poorly stored fish. Competing demands for vailable oxygen from microorganisms and enzymes, which differ between species, may also influence whether oxygen is available for autooxidation. In trout, reports of lipoxygenase activity in the skin tissue have suggested theatmosphere reduced the TBA values and sensory scores for WOF intensity as compared with those cooked in air and stored in either nitrogen or air (Fig. 9.3). Autooxidation or oxidative rancidity is by no means confined to meat and meat products. Dairy products and fatty fish are also highly susceptible. Migration of copper into cream on churning can initiate the oxidative sequence of reactions causing rapid flavour impairment. Buttermilk has a high proportion of unsaturated phospholipids, particularly phosphatidylethanolamine, that can bind metal ions in a prooxidative fashion, and the presence of a metal–phospholipid complex at an oil-water interface facilitates lipid hydroperoxide formation. Fish fats contain a high proportion of n
3 polyunsaturated fatty acids, which are vulnerable to oxidation by atmospheric oxygen leading to deteriorative changes. Despite this, rancid flavours only appear to affect the acceptability of fattier species such as trout, sardine, herring and mackerel; and even then, trout and gutted mackerel oxidize at temperatures above 0ºC whereas herring remains relatively unaffected. Castell (1971) has suggested that in fish, oxidized lipids become bound in lipid-protein complexes rather than forming carbonyl compounds associated with rancid flavours. The lipid–protein complexes also contribute to the toughened texture of poorly stored fish. Competing demands for available oxygen from microorganisms and enzymes, which differ between species, may also influence whether oxygen is available for autooxidation. In trout, reports of lipoxygenase activity in the skin tissue have suggested the Fig. 9.3. Effect of cooking and storage atmospheres on WOF development in chicken breasts. (❍—❍) cooked and stored in air; ( —) cooked in nitrogen, stored in air; (■— ■) cooked in air, stored in nitrogen; ([]—[]) cooked and stored in nitrogen. 230 Chilled foods