ABSTRACT
In this study lupin-based milk alternative (LBMA), obtained from protein isolate of Lupinus angustifolius cv. Boregine, was homogenized and was subjected to different heat treatments (unheated; pasteurized: 80°C, 60s; ultra-high temperature heating (UHT): 140°C, 10s). Upon thermal treatment, lupin proteins, namely ß-conglutin and α-conglutin, were stepwise denatured, which was accompanied by the exposure of masked sulfhydryl groups, the decrease of free sulfhydryl groups and reoxidation to disulfide bridges. Moreover, quaternary structure of lupin proteins was influenced upon heat treatment displayed with molecular weight distribution (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Further, particle size distribution showed that heat treatment promoted the formation of smaller particles. Differently heated LBMA were additionally fermented to lupin-based yogurt alternatives (LBYA) with different lactic acid bacteria (Lactobacillus plantarum TMW 1.460 and 1.1468, Pediococcus pentosaceus BGT B34 and Lactobacillus brevis BGT L150) and microstructural observations (Confocal Laser Scanning Microscopy, cryo-Scanning Electron Microscopy) were performed. Micrographs showed that harsher thermal treatments of LBMA (UHT heating) led to more close-meshed microstructures of respective LBYA. Further, the choice of microorganisms seemed to play a decisive role in microstructural appearance of respective LBYA as the composition of the networks were fundamental different.
ABSTRACT
AIMS: The main objectives were to determine the influence of secondary plant metabolites and antinutritives in lupin seeds on the fermentation performance of lactic acid bacteria and to study their ability to degrade these substances. The suitability of lupin raw materials as fermentation substrates was examined. METHODS AND RESULTS: To evaluate the fermentation performance, microbial growth, metabolite formation and substrate uptake in three different lupin substrates was monitored. On the one hand, a lupin protein isolate, which contained only trace amounts of phytochemicals was used in the study. On the other hand, the flour of Lupinus angustifolius cv. Boregine and the flour of the alkaloid rich lupin Lupinus angustifolius cv. Azuro were inoculated with Bifidobacterium animalis subsp. lactis, Pediococcus pentosaceus, Lactobacillus plantarum and Lactococcus lactis subsp. lactis. The micro-organisms showed no significant differences in the fermentation performance on the different lupin flours. Similarly, the growth of most strains on lupin protein isolate was comparable to that on the lupin flours. The fermentation with Bifidobacterium animalis subsp. lactis led to a significant decrease in flatulence causing oligosaccharides. During fermentation with Lactobacillus plantarum the phytic acid content was partially degraded. CONCLUSIONS: Neither the secondary plant metabolites nor the antinutritives of lupin flour inhibited the growth or metabolic activity of the tested micro-organisms. Therefore, lupin flour is suitable for lactic fermentation. Some strains showed the ability to degrade oligosaccharides or phytic acid. SIGNIFICANCE AND IMPACT OF THE STUDY: This work contributes to the fundamental knowledge of the metabolism of lactic acid bacteria during fermentation of lupin substrates. Fermentation of lupin raw materials could be used to improve the nutritional value of the substrates due to the reduction of antinutritives.
