Abstract:The main chemical changes occurring during biscuit cooking result from two complex reactions involving reducing sugars: the Maillard reaction and caramelisation, both of them being responsible for non enzymatic browning. These reactions were assessed by determinations of furosine (Fu), hydroxymethylfurfural (HMF), and colour at different times (each 2 min) of the cooking process (10 min). The surface colour of biscuits was carried out with L* a* b* parameters, and the global browning development was measured by the reflectance of the whole biscuit in powder. Simultaneous formation of HMF, Fu and browning were investigated to evaluate the correlation between parameters during cooking and identify the best indicators of the biscuit quality. Fu was almost stable during the first 4 min before decreasing in the last 6 min. In contrast, HMF exponentially increased after 4 min, when the water activity reached 0.6. Reflectance was linearly correlated to cooking time and was well correlated to HMF. We conclude that HMF could be a useful indicator for controlling the cooking process of biscuits.
Abstract:The oxidation rate of vegetable oils strongly depends on the content of polyunsaturated fatty acids, natural antioxidants and prooxidants. The resistance of oil against oxidation thus depends very much on the linoleic acid content. Virginia peanut oil (a traditional cultivar, containing 30% linoleic acid) was compared with SunOleic peanut cultivar (containing only 3% linoleic acid). The tocopherol content was rather similar in the two oil samples. Emulsions were prepared using soybean lecithin as an emulsifying agent. The formation of conjugated hydroperoxides was measured at 234 nm. The induction period differred very much in bulk oil, but only moderately in emulsions containing copper ions as prooxidants. The effect of copper ions on the rate of oxidation was lower in SunOleic oil emulsion, compared with the Virginia oil emulsion. Similarly, the effect of sage extracts on the resistance against autoxidation was higher in SunOleic oil emulsions than in Virginia oil emulsions.
P������ J., P���������� L., R������ Z., T�������� L., S������ H., U������ T., M������� M., Y��� T. (2003): Changes on storage of peanut oils containing high levels of tocopherols and β-carotene. Czech J. Food Sci., 21: 19-27.We compared changes of tocopherols and β-carotene in a traditional peanut oil (cultivar Virginia, 30.5% linoleic acid) with a modified high-oleic peanut oil (cultivar SunOleic, 2.7% linoleic acid), developed in Florida, USA. The initial contents of tocopherols and trace lipid oxidation products, including hydroperoxides, were of the same order in both oils. The stability against oxidation was tested under the conditions of the Schaal Oven Test at 40 and 60°C, in emulsion, using AOM, Rancimat, and the apparatus Oxipres at 100°C. Tocopherols were determined using HPLC with an electrochemical detection (without previous saponification). The high-oleic peanut oil SunOleic was about 4-8 times more stable against oxidation than the traditional peanut oil Virginia. The contents of total tocopherols were 303 mg/kg in Virginia oil and 426 mg/kg in SunOleic oil, respectively. Ratios of α-:γ-:δ-tocopherols were rather similar in both oils. Thus, the observed differences in the oxidative stabilities cannot be due to tocopherols only. The decomposition of tocopherols in peanut oils, containing an addition of 500 mg/kg γ-tocopherol, on storage was substantially slower in high-oleic SunOleic peanut oil than in Virginia peanut oil. Very similar results were observed in the case of the additions of 50 mg/kg β-carotene to peanut oil. The vitamin value was much better preserved in high-oleic peanut oil than in traditional peanut oil.
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