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Received: September 8, 2016
Accepted: May 4, 2017
Summary
Flaxseed oil cake was subjected to fermentation with Rhizopus oligosporus (DSM 1964 and ATCC 64063), and the phytate (InsP6) content, myo-inositol phosphate profile and in vitro bioavailability of essential minerals were studied. Flaxseed oil cake had a phytate mass fraction of 13.9 mg/g. A 96-hour fermentation of flaxseed oil cake by R. oligosporus DSM 1964 and R. oligosporus ATCC 64063 decreased the InsP6 content by 48 and 33 %, respectively. The strains had different phytate-degrading activities: fermentation of flaxseed oil cake with R. oligosporus DSM 1964 was more advantageous, yielding InsP3_5 as a pre-dominating myo-inositol compound, while fermentation with R. oligosporus ATCC 64603 produced predominantly InsP5-6. Solid-state fermentation of flaxseed oil cake enhanced in vitro bioavailability of calcium by 14, magnesium by 3.3 and phosphorus by 2-4 %.
Key words: flaxseed oil cake, solid-state fermentation, phytates, myo-inositol phosphates, mineral availability
Introduction
Flaxseed oil cake is the solid remaining after pressing the flaxseeds to extract the oil. It is often used as a feed component due to its high nutritional value (1). However, flaxseed oil cake, especially after cold pressing, is high in soluble fibre, high-quality protein, plant lignans, minerals and polyunsaturated fatty acids and may offer benefits when used as a food additive (2). Protein isolates obtained from fl axseed oil cake have functional value (3) and pro-health and therapeutic properties (4). Flaxseed oil cake has also been used as a component of a food product obtained through solid-state fermentation (SSF) (5), as well as a valuable component of dough in baking bread (6,7).
Despite these advantages, flaxseed by-products also contain antinutrients. Depending on the variety and growth conditions of plants, flaxseed meal contains 2.3-3.3 % of phytic acid (myo-inositol-(1,2,3,4,5,6)-hexakisphosphate) (S). Phytates are the main storage forms of phosphorus in plants. A highly charged phytic acid molecule electrostatically binds minerals and proteins in complexes, decreasing their bioavailability (9,10). Phytate dephosphorylation may be performed by means of thermal hydrolysis, e.g. during cooking, or be the result of the action of phytases. Phytases are produced endogenously in plant seeds during soaking and sprouting (11), and are also secreted by various bacteria (12) and filamentous fungi (13). Feed supplementation with phytases is a commonly used practice in the...