Targeted inactivation of soybean proteinase inhibitors using zinc.

In this study the potential targeted use of zinc to inactivate proteinase inhibitors (PI) has been investigated as an alternative to the widely applied heat treatment used industrially for inactivation of PI. Zinc was utilized for the reduction of disulfide bonds leading to the structural changes in proteins, thus affecting the decreased affinity between PI and proteinases. The protein disulfide bond reduction mechanism was studied using a newly developed micellar electrokinetic capillary chromatography (MECC) with the glutathione redox reaction with dithiothreitol (DTT) as model system. This model proved efficient in monitoring the reduction of disulfide bonds in the Kunitz trypsin inhibitor (KTI) and Bowman-Birk inhibitor (BBI). The use of zinc as a reductant resulted in a significant reduction of trypsin inhibitor activity (TIA) of 72% for KTI and 85% for BBI, highlighting zinc as a promising potential agent to reduce the activity of PI as an alternative to heat treatment.

Piglet performance and physiological effects linked to reduced glucosinolate transformations in feed products based on rapeseed pressed cakes.

The nutritional quality of rapeseed press cakes (RPCs) in piglet feed is closely linked to its digestibility and the content of glucosinolates. This study investigates the significance of intact glucosinolate (glc) levels and degree of glc transformations on piglets performance. Four different RPCs were made from a low glc (11 µmol/g seed DM) containing B. napus L. seed variety Lioness (RPC-LW, RPC-LXW, RPC-LC, RPC-LCD). RPC made from the variety Excalibur containing the upper level of glc (24 µmol/g seed DM) of double rapeseed and produced at higher and prolonged temperature (RPC-UXW) served as negative control, while soya bean protein concentrate served as positive control. Piglets (8 kg) were fed ad libitum diets balanced for RPC protein content, with RPC inclusion of 84-98 g/kg (day 0-14) and 151-178 g/kg (day 15-50). Glc transformation was reduced from 42% to 24% (7.3-4.2 µmol/g RPC) when the temperature input was lowered in the warm pressing of oil, while the glc loss was less pronounced (17%) when cold pressing was applied. The following feed pelleting process further reduced Glc concentration from 11% to 40% in warm-pressed RPCs and 54 to 85% in cold-pressed RPCs. The RPC products replaced soya bean protein without any negative effects on performance, except for piglets served cold-pressed RPC, which had a reduction in average daily weight gain (ADG) (5%-7%, p < 0.05, Day 15-50). RPC in the feed led to increased liver weight in all piglets (p = 0.026). This may point at long-term effects from feeding with RPC. Intestinal absorption of intact glcs was proven by their detection in urine. In conclusion, warm-pressed RPC can be used as feed for piglet, while the presence of active myrosinase may have a negative effect on performance and cakes should either be included in lower amounts than used in the present study (18%) or include myrosinase inactivation before use.

The impact of newly produced protein and dietary fiber rich fractions of yellow pea (Pisum sativum L.) on the structure and mechanical properties of pasta-like sheets.

Two fractions from pea (Pisum sativum L.), protein isolate (PPI) and dietary fiber (PF), were newly produced by extraction-fractionation method and characterized in terms of particle size distribution and structural morphology using SEM. The newly produced PPI and PF fractions were processed into pasta-like sheets with varying protein to fiber ratios (100/0, 90/10, 80/20, 70/30 and 50/50, respectively) using high temperature compression molding. We studied protein polymerization, molecular structure and protein-fiber interactions, as well as mechanical performance and cooking characteristics of processed PPI-PF blends. Bi-modal particle size distribution and chemical composition of the PPI and PF fractions influenced significantly the physicochemical properties of the pasta-like sheets. Polymerization was most pronounced for the 100 PPI, 90/10 and 80/20 PPI-PF samples as studied by SE-HPLC, and polymerization decreased with addition of the PF fraction. The mechanical properties, as strength and extensibility, were likewise the highest for the 100 PPI and 90/10 PPI-PF blends, while the E-modulus was similar for all the studied blends (around 38 MPa). The extensibility decreased with the increasing amount of PF in the blend. The highest amounts of ß-sheets were found in the pasta-like sheets with high amounts of PPI (100, 90 and 80%), by FT-IR. An increase in PF fraction in the blend, resulted into the high amounts of unordered structures as observed by FT-IR, as well as in an increase in the molecular scattering distances observed by SAXS. The water uptake increased and cooking loss decreased with increased proportions of the PF fraction, and the consistency of 10 min cooked pasta-like sheets were alike al dente texture. The new knowledge obtained in this study on the use of extraction-fractionation method to produce novel PPI and PF fractions for developing innovative high nutritious food can be of a great importance. The obtained knowledge on the pea protein and fiber processing behaviour could greatly contribute to a better control of functional properties of various temperature-processed products from yellow pea.

In Vitro Digestibility of Rapeseed and Bovine Whey Protein Mixtures.

Partial replacement of animal protein sources with plant proteins is highly relevant for the food industry, but potential effects on protein digestibility need to be established. In this study, the in vitro protein digestibility (IVPD) of four protein sources and their mixtures (50:50 w/w ratio) was investigated using a transient pepsin hydrolysis (1 h) followed by pancreatin (1 h). The protein sources consisted of napin-rich rapeseed (Brassica napus L.) protein concentrates (RPCs; RP1, RP2) prepared in pilot scale and major bovine whey proteins (WPs; α-LA, alpha-lactalbumin; ß-LG, beta-lactoglobulin). IVPD of individual protein sources was higher for WPs compared to RPCs. The RP2/ß-LG mixture resulted in an unexpected high IVPD equivalent to ß-LG protein alone. Protein mixtures containing RP1 showed a new IVPD response type due to the negative influence of a high trypsin inhibitor activity (TIA) level. Improved IVPD of RP1 alone and in protein mixtures was obtained by lowering the TIA level using dithiothreitol (DTT). These results showed that napin-rich protein products prepared by appropriate processing can be combined with specific WPs in mixtures to improve the IVPD.