Soaking and fermentation of Lupin seeds to improve their nutritional properties
Abstract: Lupin seeds contain like many other grains and legumes the mineral inhibitor phytate. The presence of this anti-nutrient decreases the bioavailability of minerals such as zinc and iron. Especially people that live in areas where grains and legumes are the staple food source, as well as vegan and vegetarian groups, may be more vulnerable to mineral deficiencies. The presence of phenolic compounds in food can prevent cellular damage and act as an antioxidant. During this study, different methods were investigated to reduce the phytate content alongside an increase of total phenolic content, thereby increasing its nutritional profile. By dehulling, soaking, and fermenting the Lupin seeds the possible reduction of phytate and increase in total phenolic content were analyzed. The seeds of the Lupin angustifolius plant have, with their low carbohydrate (<2%), high protein (36%) and fiber (35%) content, a strong nutritional profile that is comparable to other legumes like soybean and lentils. Not only the nutritional profile but also the ability to grown at many geographic locations, and the ability to convert atmospheric nitrogen into more usable forms that improve the soil quality make it an excellent growing crop with many benefits. The Lupin seeds were bought from a local farmer in Skåne and divided into three batches. The seeds in method 1 were dehulled and submerged for 24-hour in water with a ratio of 1:3 (w/v) containing 0.5% NaCO3, followed by a 24-hour fermentation (37°C) with Lactobacillus plantarum 299v (1%). The seeds in method 2 ware dehulled and subjected to a 24-hour fermentation (37°C) with Lactobacillus plantarum 299v (1%). Where in method 3 whole lupin seeds were subjected to a 24-hour soaking period (ratio 1:3 w/v, 0.5% NaCO3) and 24-hour fermentation (37°C) with Lactobacillus plantarum 299v (1%). During the fermentation, the pH, TTA (titratable acidity), protein, phytate, and total phenolic content were determined every 3 hours until 12 hours, and 24 hours after the initial start of the fermentation. Neither of the 3 methods was able to reduce the phytate content significantly (p=>0.05). Where results from ANOVA showed that only a combination of dehulling and soaking reduced the phytate content significant (p=<0.05) with 19%. On the other hand, the initial total phenolic content increased on average 3 fold, all the 3 methods showed to be significant (p=<0.05). The seeds that were dehulled, soaked and fermented (method 1) showed with 24% the biggest increase of phenolic compounds, the seeds that underwent only the dehulling and fermentation process (method 2) showed the smallest increase of 21%. According to this study, a combination of dehulling, soaking, and fermentation does not significantly reduce the phytate content. Whereas a 3 fold increase is measured of total phenolic content after a 24-hour fermentation period. For further research, it is possible to use a different Lactobacillus species and soak the seeds at a temperature that is more in line with the optimum temperature for phytase activation. Further, the phytase activity can be measured throughout the entire process to follow its changes.
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