Effect of alkali on the refunctionalization of soy protein by hydrothermal cooking

Abstract

The effects of hydrothermal cooking (HTC) at alkaline conditions on refunctionalization of heat-denatured protein of extruded-expelled (EE) soy meals and on preparation of soy protein isolate (SPI) from EE soy meal were determined. Two HTC setups, flashing-out HTC (without holding period) and HTC with holding for 42 s at 154°C, were evaluated. Alkali (NaOH) addition dramatically enhanced the refunctionalization of EE meal having an initial protein dispersibility index of 35. The more alkali added, the more refunctionalization occurred. Extensive refunctionalization was achieved at 0.6 mmol alkali/g EE meal, and additional improvement was small with more alkali. For both HTC setups, the solids and protein yields of SPI from alkali-HTCtreated EE meals were significantly higher than those from HTC without alkali addition. The yield of protein as SPI increased from 40 to 82% after HTC treatment at 0.6 mmol alkali/g EE meal compared with no alkali addition. The emulsification capacities of SPI after alkali-HTC were similar to those from HTC without alkali. SPI from holding-tube HTC-treated EE meals had higher emulsification capacities than those prepared by flashing-out HTC.Paper no. J11081 in JAOCS 82, 451-456 (June 2005).The use of soy protein ingredients by the food industry is increasing rapidly owing to health benefits, low cost, and versatile functionalities. Most soy protein products are manufactured from highly soluble (flash-desolventized) hexane-defatted soybean meal. Solvent extraction is capital intensive and unsuitable for processing small amounts of identity-preserved soybeans. Extrusion-expelling (EE) is a promising technique that presses the oil from the whole or cracked seeds and is suitable for processing small lots of identity-preserved seeds (1,2). EE differs from traditional screw pressing in that a dry extruder replaces steam-heated stack cookers or rotary dryers. Compared with solvent-extracted white flakes, EE protein meals that are processed into EE soy flour have much more heat exposure and protein denaturation [15-60 vs. 80-90 protein dispersibility index (PDI)], contain significantly more residual oil (6-12 vs. 1%), have lower levels of heat-sensitive antinutritional factors (trypsin inhibitors) and enzymes (such as lipoxygenase), and possess a pleasant nutty flavor. Typical EE meal contains 50% protein and 6% oil, and 90% of its trypsin inhibitors are inactivated (1). The use of protein ingredients prepared from EE meal in foods, however, is limited by their poor functional properties and low yields of soy protein isolate (SPI), a direct consequence of heat denaturation of the protein.Our previous work showed that SPI could be prepared from EE meals; however, the yields were low (the SPI and protein yields were only 25 and 40%, respectively) (6). Inspired by the work of Johnson (3) and Wang and Johnson (4), we demonstrated that hydrothermal cooking (HTC) could be used to refunctionalize heat-denatured proteins of EE meals (5). We also demonstrated the feasibility of using HTC as a pretreat...

The net contribution of dairy production to human food supply: The case of Austrian dairy farms

“…Basis for estimating the human-edible fraction References Wheat Milling grade depending on type of flour (fine flour -whole grain flour) a Vetrimani et al, 2005;Zwingelberg, 2004 Barley Milling grade depending on type of flour (pearls -dehulled grain flour) a Bhatty, 1986;Kling and Wöhlbier, 1983;Ullrich, 2011 Maize Possible nutrient extraction rates b,c or milling grade a Eckhoff et al, 1999;Lee et al, 2007;Mestres et al, 1991;Stolp, 2004 Triticale Similar nutrient composition and qualities as wheat = > calculated in wheat equivalents a Peña, 2004;Peña and Amaya, 1992;Serna-Saldivar et al, 2004 Rye Milling grade depending on type of flour (fine flour -whole grain flour) a Glitso and Knudsen, 1999;Zwingelberg, 2004 Wheat bran High fibre content of wheat bran increases faecal energy losses, thus amounts for human consumption are limited a Stevenson et al, 2012 Peas Possible protein and starch extraction b or dehulled whole peas a Boye et al, 2010;Hoover et al, 2010;Pelgrom et al, 2013;Vose, 1980 Soybeans Possible protein and fat extraction (concentrates/isolates) c or dehulled whole beans a Fischer et al, 2001;Shallo et al, 2001;Wang et al, 2005 Soybean/sunflower/rapeseed cake and expeller…”

Mechanism for refunctionalizing heat‐denatured soy protein by alkaline hydrothermal cooking

“…The slurry was then released into the flash chamber. The cooking temperature was adjusted by a control valve located between the holding tube and the flash chamber; the temperature was monitored by a thermocouple (1). All HTC-treated SPI were cooled to ambient temperature, neutralized to pH 7, and stored at 5°C until analyzed.…”

“…The density difference in Stokes' law is defined as the mean density of particles (dispersed phase) minus the density of the continuous phase (we used the density of the supernatant after centrifugation at 15,000 × g for 15 min as the estimate for the density of the continuous phase) at ambient conditions. Because settling particles can precipitate under centrifugation, the mean density of the settling particles at different centrifugal speeds (rpm) were calculated by using the following formula, assuming the sum of the volume of precipitate and supernatant after centrifugation equals the volume before centrifugation: [1] The density difference between dispersed particles and continuous phase is centrifugation speed-specific when using this formula. An approach was needed to derive the density difference under gravity alone.…”

“…Our previous work showed that hydrothermal cooking (HTC), especially when the protein was dispersed in alkali (0.2-0.8 mmol/g meal) prior to HTC, improved the functional properties, such as solids dispersibility, emulsification capacity, and foaming properties, of extruded-expelled (EE) soybean protein meals (1,2). The protein yield of soy protein isolate (SPI) after alkali dispersion with HTC (alkaline HTC) of EE soybean meal was improved by twofold (from 40 to 81%) compared with the original meal, whereas the protein yield after water dispersion with HTC (HTC without alkali) was 53%.…”

Gelation enhancement of soy protein isolate by sequential low‐ and ultrahigh‐temperature two‐stage preheating treatments

“…UHT treatment, also known as hydrothermal cooking, is another alternative technique employed to modify protein structure by which to improve the functional properties of protein, such as solubility (Hua et al ., ; Wang & Johnson, ; Wang et al ., ; Zheng et al ., ) and gelling capacity (Nagano et al ., ). According to the protein gelation theory proposed by Ferry (), a protein gel with a strong viscoelasticity is formed only when the initial heating favours slow unfolding (exposures of reactive amino acid side chain groups) to allow an ordered protein–protein interaction that follows.…”