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Peroxidase (POD) and lipoxygenase (LOX) inactivation temperature and time were investigated on broccoli florets at different blanching treatments. In addition, retention of nutritional components,which reduced POD and LOX activities, was compared. LOX inactivation required 14 min at 70 °C, 6 min at 80 °C, 11/2 min at 90 °C, 1 min at 100 °C water blanching and 1 min for steam blanching, 2 min in microwave without water and 6 min with microwave and water. The highest nutritional content of broccoli was evaluated in microwave blanching without water by comparison to all treatments. The decline of nitrate and nitrite value of broccoli was higher under longer time blanching than under higher temperature blanching.
To estimate the quality deterioration caused by lipid peroxidation in stored ground poppy-seed samples, the kinetic behaviour of different biochemical parameters characteristic of lipid peroxidation was studied and compared with flavour deterioration. It was found that the probability of rapid deterioration of samples is low when the change in AC values (the ratio of the values at the time of measurement and at the beginning of investigation) for peroxide values is a linear function of storage time and when lipoxygenase activity is low. When the kinetics is immediately non-linear and high activity of lipoxygenases is detected, the possibility of rapid quality deterioration can be anticipated.
Alteration of physical and chemical qualities of pressurized and heat treated Nam Prig Nhum (Thai-green-chili paste) was thoroughly assessed upon storage for eight weeks. During storage, colour L, –a*, and b* parameters of pressurized Nam Prig Nhum displayed comparatively low changes. The enzyme activities of peroxidase, lipoxygenase, and polyphenol-oxidase nearly fell by half during storage. Peroxidase was the most resistant to pressure followed by lipoxygenase and polyphenol-oxidase. For pungent components, all capsaicinoids in Nam Prig Nhum underwent alteration by the thermal processes as well as by acidic and oxidative degradation during storage. However, higher amount of capsaicinoids were retained in pressurized than in heat treated products.
Blanching of vegetables before freezing has some advantages as well as a number of disadvantages. Process optimization involves measuring the rate of enzyme destruction, such that the blanching time is just long enough to destroy the indicator enzyme. Eventually, peroxidases were almost universally the enzymes of choice, as they are usually the most heat-stable enzymes found in vegetables and fruits, so by the time they are inactivated no other enzymes or micro-organisms remain. But there is no evidence that peroxidases are involved in deteriorative reactions in the food. The aim of this work was to improve blanching technology in Hungarian frozen food industry with special emphasis on broccoli treatment. Instead of peroxidases, lipoxygenases were chosen to determine the adequate blanching parameters. Usually, lipoxygenases accompany lipases, so lipase activity is measured, too. On the basis of model blanching experiments, the conclusion is that lipoxygenase could be used as indicator enzyme. Being less heat stable than peroxidase, this enzyme requires shorter heat treatment, hence its inactivation should result in minimum quality deterioration and economic loss.
In the microflora of sunflower seeds stored in domestic stores the, Alternaria species dominate, while those of Penicillium, Trichoderma, Stemphylium and Absidia spp. are present in lower numbers. During model tests (cca 20% seed moisture content, 25 °C, 4 weeks storage) the Alternaria species were almost completely eliminated and on the seeds mainly Aspergillus species, characteristic of stores, propagated. The moulds significantly deteriorated the quality of the seed and that of the produced oil and meal (reproductive ability, germinating power, oil content, lipoxygenase enzyme activity, acid value, peroxide value, fatty acid composition, UV absorbance, colour, sensorial properties, as well as the protein content, amino acid composition, colour and the smell of the meal), but no aflatoxin production occurred. The findings offer a comprehensive picture on the multiple destructive effects of incorrect storage.
Davies, C.S., Nielsen, S.S., Nielsen, N.C. (1987) Flavor improvement of soybean preparations by genetic removal of lipoxygenase-2. JAOCS , 64(10): 1428–1433. Nielsen N.C. Flavor
