Journal
INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY
Volume 235, Issue -, Pages 1-9Publisher
ELSEVIER
DOI: 10.1016/j.ijfoodmicro.2016.06.039
Keywords
Okara; Soybean residue; Yarrowia lipolytica; Fermentation; Flavour; Yeast
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Okara, or soybean residue, is a soy food processing by-product from the manufacture of soymilk and soybean curd (tofu). In this study, solid-state fermentation of okara was conducted over 5 days using yeast Yarrowia lipolytica, and the changes in proximate composition, antioxidant capacity, non-volatiles and volatiles were investigated. Yeast metabolism of okara significantly increased the amounts of lipid, succinate and free amino acids and enhanced the antioxidant capacity. In particular, there was a marked increase in important umami tastants after fermentation, with 3-fold increase in succinate and a 20-fold increase in glutamate. The final fermented okara contained 337 g succinate and 335 mg glutamate/100 g dry matter. Aldehydes and their derived acids in the fresh okara were catabolised by Y. lipolytica mainly to methyl ketones, leading to a reduced grassy off odour and a slightly pungent, musty and cheese-like odour in the fermented okara. Amino acid-derived volatiles, such as 3-methylbutanal and 2-phenylethanol, were also produced. Overall, the okara fermented by Y. lipolytica had a greater amount of umami-tasting substances, a cheese-like odour, improved digestibility and enhanced antioxidant capacity. These changes highlight the potential of Yarrowia-fermented okara as a more nutritious, savoury food product or ingredient. Y. lipolytica was thus demonstrated to be suitable for the biovalorisation of this soy food processing by-product. (C) 2016 Elsevier B.V. All rights reserved.
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