Browsing by Author "Mustonen, Otto"

Tiivistelmä/Referat – Abstract In food matrices usage of legumes is challenging due to formation of volatile compounds during storage and processing. These volatile compounds form beany flavors, which cause sensory problems in food matrices. Because the formation of volatile compounds in legume matrices is quite quick, it is supposed that enzymatic oxidation is significant when lipids are oxidized in legume matrices. The literature review of this thesis focused on the mechanisms of lipid oxidation in plants, enzymes and formation of volatile compounds in food matrices. The aim of the experimental part was to investigate how volatile compounds are formed from different faba bean and lupine cultivars by endogenic enzymes using different lipid substrates. The activity of lipoxygenase and incubation conditions were optimized at first and those conditions were used to analyse the actual samples. The main legume matrix in this study was faba bean (4 cultivars) and two lupine cultivars were also investigated. The selected legumes were pretreated by grinding the dried pods of legumes in certain particle size. Legume flours were mixed with water to prepare slurries to extract the endogenic enzymes of legume matrices. Due to lipoxygenase’s significant role in enzymatic oxidation of lipids the optimum pH-level of lipoxygenase was determined by using UV/VIS-spectrophotometer. The optimum pH-level for lipoxygenase was found at the pH 6. Optimization and formation of volatile compounds was determined by using HS-SPME-GC-MS-method. In addition, the activity of lipase and product specificity of lipoxygenase (formation of hydroperoxides) were determined. In both legume matrices the pH-optimum of lipoxygenase was at 6 and all the actual samples were measured at that pH. Quantitatively and qualitatively the widest spectrum of volatile compounds was formed when using linoleic acid as a substrate. The spectrum of volatile compounds included different alcohols, ketones, aldehydes and furans. The amounts of hexanal were at the highest when using linoleic acid as a substrate and the lowest when using α-linolenic acid as a substrate. When using trilinolein and rapeseed oil as substrates aldehydes and ketones were the only volatile compounds which were formed. Saponification of rapeseed oil improved the formation of the volatile compounds. In addition, from the saponified rapeseed oil a wider spectrum of volatile compounds were formed when compared to untreated rapeseed oil. The lipoxygenases of faba bean and lupine were shown to form different types of hydroperoxides from linoleic acid: the faba bean produced more 13-hydroperoxides than 9-hydroperoxides and lupine produced only 13-hydroperoxides. Used method when measuring the formation of free fatty acids of legume matrices did not revealed the activity of lipase. On the other hand, this result only tells that lipase activity couldn’t be measured by using this particular method and other methods could reveal lipase activity on those legume matrices. Both of the legume matrices formed different kinds of volatile compounds from different lipid substrates in certain reaction conditions. When those volatile compounds are formed in foods containing legume matrices they lower the sensory value of those foods. The formation volatile compounds in food matrices containing legumes is very plausible due to food matrices pH-level (many of them are at neutral) and usage of suitable lipid substrates and reaction conditions. Inactivation of enzymes can be obtained for example by heating, which could at the same time lower the nutritional value of foods.