Characterization of puffed and freeze-dried lupin seeds

Australia is a major producer of lupin. Lupin is high in protein and fiber, gluten-free, low glycaemic index and contains many compounds with documented health benefits. These have led to great interest to use lupin as an ingredient in food. However, lupin has not been fully utilized in food due to a number of technical drawbacks in the processing of lupin. Therefore, new approaches for lupin processing is required to increase its usage in food systems. This study investigated the use of puffing and freeze drying to modify lupin seed texture. Lupin seed moisture content before puffing (MCBP) was adjusted to 10, 15, 20, 25% while moisture content before freeze drying (MCBF) was adjusted to 15, 30, 45, 63%. All puffed samples were thicker than raw sample although no significant changes in seed depth, width and density were observed. High MCBP resulted in thicker puffed samples. Freeze dried samples were significantly bigger than raw samples. High MCBF resulted in bigger freeze-dried sample with lower density. Water absorption capacity of most freeze-dried samples was higher than the raw and puffed samples. This is consistent with scanning electron microscopic study which showed less densely packed cell structure of freeze-dried samples compared to puffed samples. Freeze-dried sample with lower MCBF was found to have significantly tougher texture. Lower MCBP however, did not translate to tougher texture of puffed samples. All puffed samples were darker and more yellow compared to raw and freeze-dried samples. This study demonstrates the possibility of using food processing method to modify physical properties of lupin seeds.